Women of all ages have recognized the numerous benefits of resistance exercise and an active lifestyle. Resistance training is a common practice among women, whether for general health and fitness or specific strength and performance goals. In various roles such as fitness enthusiasts, soldiers, police officers, and firefighters, women are integrating resistance exercise into their overall conditioning routines.

This section focuses on addressing a range of topics related to resistance training for women. With only a few exceptions, women can follow resistance training programs nearly identical to those designed for men. This is because there are relatively few significant sex-based differences that impact resistance training program design. Women exhibit similar acute and chronic physiological responses to resistance training as men. Moreover, from a health perspective, resistance training offers several advantages for women, particularly in terms of its positive impact on bone health and the reduction of osteoporosis risk.

While it is evident that there are inherent physiological and performance differences between the sexes, many of these differences are influenced by the fundamental biological distinction between men and women. The role of testosterone in muscle cell development, along with androgenic changes during growth, contributes to variations in physiological responses and performance in relation to strength, power, and muscle hypertrophy. Even in elite weightlifting and powerlifting competitions, where participants are matched by body weight categories, men typically outperform women in terms of lifting strength. However, it is essential to recognize that the impact of resistance training on various aspects of physiology and performance is strikingly similar between men and women. The primary distinction lies in the magnitude of the responses, which varies between the sexes.

It is crucial to acknowledge these documented sex-based differences, which have been studied for many years. Understanding these distinctions is essential when designing effective resistance training programs tailored to women’s specific needs and goals. By doing so, women can maximize the benefits of resistance training while accommodating their unique physiological characteristics and performance potentials.

Physical Activity Participation in Women

Over time, social perceptions, gender stereotypes, and misconceptions about women and exercise have discouraged many women from embracing resistance training as a part of their physical activities. There has been a persistent fear among women of “bulking up,” leading them to avoid heavy lifting, often considering it a pursuit reserved for men. As a result, many women engage in resistance training programs that are less effective than those designed for men. However, it is now well-established that the benefits of resistance training cannot be realized without challenging resistance.

Even today, women tend to be less physically active than men, despite a substantial body of research evidence supporting the advantages of resistance training for women, as discussed in the Training in Women section. Historically, more boys have participated in sports than girls, and men have typically engaged in more intense exercise than women. For instance, data among schoolchildren show that 42% of boys meet the guideline of at least one hour of moderate-intensity physical activity a day, while only 11% of girls meet this standard.

Efforts to promote physical activity, particularly resistance training, among both men and women have made some progress. However, it is not yet clear how much progress has been achieved. Data from the U.S. Centers for Disease Control and Prevention (CDC) indicate that only 17.5% of American women and 20% of university-age women meet the CDC’s recommendations for aerobic and strength training. Men do not fare significantly better, with only 23% of men and 37% of university-aged men reaching the CDC’s fitness and physical activity goals.

These participation statistics also differ based on factors such as sex, ethnicity, marital status, and level of education. Participation in strength training tends to decline in women as they age, though education level plays a role in these percentages. This suggests that while the visibility of strength training may have increased with the proliferation of commercial fitness programs and infomercials, participation could still be much higher. Although progress has been made, fitness and strength and conditioning professionals have more work to do in increasing women’s participation in resistance exercise across all age groups.

Physical activity levels during childhood can have lasting effects on health, neurological development, and performance in later life. More active boys and girls tend to have better metabolic scores, indicating the advantages of childhood activity for both sexes. Even in athletic populations, boys exhibit greater isokinetic strength than girls at a young age. In contrast, girls do not consistently demonstrate strength gains with age; in some cases, 12- and 13-year-old girls may display less strength than 9- and 10-year-olds. This disparity in physical activity levels may contribute to compromised bone density, strength, and physical performance in women compared to men, underscoring the importance of resistance training for women.

The lower levels of exercise participation among women, when compared to men, appear to have substantial consequences for women’s lifelong health. The following section will further explore the distinctions between women and men in various parameters, such as strength, power, and muscle fiber composition. It is important to note that these differences can be influenced by various factors, including activity levels starting from childhood and access to resistance training equipment. Increased physical activity among women, at all ages, may help bridge the performance gap between men and women.

Differences in Muscle Fiber Size, Type, and Composition

To understand the variations in physical performance parameters like strength and power between men and women, it’s essential to examine the underlying differences in muscle fibers. While both men and women possess the same types of muscle fibers, some differences in the profiles of these fibers may exist across individuals. Muscle fiber characteristics can vary from person to person based on factors like total muscle area, fiber cross-sectional area, number, type, and recruitment patterns. Importantly, sex does not seem to influence fiber number or the percentage of type II and type I fibers. However, limited research on this topic makes these findings tentative, contradicting anecdotal observations and embryonic cell development changes.

Some of the differences in muscle fiber characteristics could be attributed to lifestyle factors. For instance, women tend to be less physically active and may not consistently engage in progressive resistance training programs throughout their lives. As a result, characteristics of trained muscle, including total muscle cross-sectional area, muscle fiber size, and type II/type I ratios, are generally lower in women. Recent research shows that the cross-sectional area of type I and type II fibers is approximately 10.4% and 18.7% smaller in women compared to men. Moreover, type II fibers in women generate around 17.8% less force and 19.2% less power than those in men, indicating fundamental differences in muscle function. Overall, women have smaller muscle fiber areas compared to men, which can significantly impact their performance.

The number of muscle fibers in various muscles is not consistently different between men and women, and it may depend on factors like muscle type and the nature of the comparison. Anecdotal data suggest that women tend to have fewer muscle fibers, especially in upper-body muscles. Studies on muscle fiber number have reported mixed findings, with women’s muscle fiber numbers being either less than or equal to those in men, depending on the muscle group being studied and the level of training. It is observed that women’s upper bodies generally have fewer muscle fibers than men’s, contributing to differences in upper-body strength performances between the two sexes.

The proportion of type I to type II muscle fibers does not consistently vary by sex, as men and women have similar distributions of these muscle fiber types. In studies examining muscle fiber types, both men and women typically show similar percentages of fiber types I, Ic, IIc, IIa, IIax, and IIx.

While differences in muscle fiber type percentages are not significant, women do have smaller type II fibers than men. Women’s type I and type II muscle fibers both have smaller cross-sectional areas than men’s fibers. For example, female bodybuilders have been reported to have type I fiber cross-sectional areas that are 64% of those in male bodybuilders, while their type II fiber cross-sectional areas are only 46% of the male values. The relative size of type II fibers in women is smaller than that in men.

Sex Absolute Strength Differences

Absolute strength, often measured as the maximal force or resistance generated in a movement or exercise without adjusting for height, weight, or body composition, is an area where differences between men and women are noticeable. In general, women exhibit lower absolute strength compared to men, and this difference persists even as recent changes have narrowed the gap. On average, women’s whole-body strength typically ranges from 60.0% to 63.5% of men’s (Laubach 1976; Shephard 2000a). More specifically, women’s upper-body strength averages around 55% of men’s, while their lower-body strength averages about 72% of men’s (Bishop, Cureton, and Collins 1987; Knapik et al. 1980; Laubach 1976; Sharp 1994; Wilmore et al. 1978).

A look at strength ranges between normally active men and women further confirms these disparities in upper and lower body strength. These differences are evident in various types of strength tests, including both single-joint (e.g., elbow flexion, shoulder extension, hip extension) and multijoint (e.g., bench press, squat, shoulder press) movements. The choice of strength test type also plays a role in these findings, such as testing methods like 1RM (one-repetition maximum), maximal isometric strength, and isokinetic peak torque at various speeds. In all cases, women’s absolute strength tends to be lower than men’s.

Although resistance training can mitigate some of the disparities in absolute strength, it doesn’t always eliminate them entirely. For example, women’s total-body, lower-body, and upper-body strength has been reported to be 57.4%, 58.6%, and 54.1% of men’s, respectively (Lemmer et al. 2007). After both men and women engaged in a 24-week resistance training program, women’s total-body strength increased to 63.4% of men’s, and lower-body strength increased to 67.3% of men’s (Lemmer et al. 2007). However, intriguingly, upper-body strength in women slightly decreased to 53.1% of men’s. This outcome suggests that the design and progression of the training program may play a role in the disparities in upper-body strength gains between women and men.

These differences in upper-body strength gains may be related to women having fewer muscle fibers. Studies have shown that substantial variations in sex differences in maximal strength persist among young adults even after 24 weeks of weight training. Nevertheless, total-body periodized resistance training programs can lead to significant improvements in upper-body bench press and squat strength and power for women over six months, emphasizing the importance of well-designed training programs. Although training can reduce the absolute gap in strength between men and women, it is crucial to recognize that absolute strength alone does not account for differences in body size. Therefore, other measures of strength may be more suitable for comparing strength between men and women.

Relative Strength Differences

When considering absolute strength measures, it becomes evident that women tend to be at a disadvantage compared to men due to differences in body size, muscle mass, and initial fitness levels. On average, adult women aged 20 and older are shorter in height and lighter in body mass compared to men. Women’s height typically ranges from 162.2 cm to 162.8 cm, whereas men’s height is approximately 176.3 cm. In terms of body mass, women weigh around 74.7 kg, while men weigh approximately 88.3 kg (McDowell 2008).

To address these differences in body size, researchers often use relative strength, a measure that expresses absolute strength concerning total body weight or fat-free mass. This approach helps level the playing field, as it accounts for variations in body size.

Studies conducted over the years have consistently shown that when women’s strength is expressed relative to total body weight or fat-free mass, their strength aligns more closely with that of men. For instance, a classic study demonstrated that women’s 1RM bench press was 37% of men’s when measured in absolute terms. However, when this strength was expressed relative to total body weight and fat-free mass, it increased to 46% and 55%, respectively (Wilmore 1974). Similar trends are observed in other strength tests as well.

Women’s isometric leg press strength was found to be 73% of men’s when measured absolutely. However, when adjusting for body size, this measure increased to 92% and 106% when expressed relative to total body weight and fat-free mass, respectively. Similar findings were observed in other strength tests, indicating that relative measures of strength place women almost on par with men in terms of lower-body strength but not upper-body strength (Hoffman, Stauffer, and Jackson 1979).

The ratio of eccentric to concentric strength also reveals differences between men and women. Women’s eccentric isokinetic peak torque relative to fat-free mass is almost equal to men’s, while their concentric strength isn’t. This ratio may be greater in women than in men and may vary by the type of exercise. It is suggested that women might store elastic energy more effectively or have different motor unit recruitment patterns during eccentric and concentric muscle actions.

Training can help reduce or eliminate relative strength differences between men and women to some extent. For instance, a study compared trained men and women’s relative strength in various exercises both before and after a 12-week nonlinear periodized strength training program. It was observed that men initially had greater relative strength than women in upper-body exercises but not in squat exercises. Following the training program, the differences in relative strength for the bench press exercise disappeared. However, variations still existed in the shoulder press and lateral pull-down exercises.

Differences in training status can complicate the comparison of strength between men and women, even among untrained or recreationally trained individuals. Comparisons within highly trained individuals also illustrate that even in these cases, women’s strength, adjusted for body weight, lags behind men’s.

Strength Relative to Muscle Cross-Sectional Area

One of the fundamental factors contributing to the strength disparity between men and women is the difference in skeletal muscle mass. In general, men have more skeletal muscle mass than women, with the largest regional disparities occurring in the upper body (Janssen et al. 2000; Nindl et al. 2000). This variation in muscle mass distribution plays a significant role in explaining differences in strength between the sexes. Researchers have sought to address these differences by using relative strength measures, such as body mass, fat-free body mass, or muscle size, under the assumption that strength primarily depends on muscle mass.

Numerous studies have consistently demonstrated that normalizing maximal strength using relative equations helps reduce the disparity between men and women, particularly in the lower body (Kanehisa et al. 1994, 1996). When comparing concentric isokinetic knee extension torque at 60 degrees per second, researchers found that expressing strength in absolute terms showed a 54% difference between men and women. However, this difference was gradually reduced when strength was normalized relative to body weight (30% difference), fat-free mass (13% difference), and bone-free lean leg mass (7% difference). Notably, the difference between the sexes only became statistically significant when peak torque was expressed relative to bone-free lean leg mass (Neder et al. 1999).

A similar pattern emerged when examining maximal isometric force in the upper arms (elbow flexors and extensors) and thighs (knee flexors and extensors) among both trained and untrained individuals. Regardless of whether strength was expressed in absolute terms, relative to body weight, relative to fat-free mass, or relative to muscle cross-sectional area, differences were observed between men and women. However, when strength was expressed relative to muscle cross-sectional area, no significant difference was found between the sexes (Miller et al. 1992).

Some studies have identified sex differences in strength despite its expression relative to cross-sectional area. For example, research on young adults and competitive bodybuilders found that men had 6% and 10% more muscle cross-sectional area than women, respectively. Both studies showed a significant relationship between maximal force and muscle size. Nevertheless, the strength disparities between men and women could not be entirely accounted for by muscle cross-sectional area alone. The differences may be associated with lower integrated electromyographic activity during maximal voluntary muscle actions in women, a longer electrical-mechanical delay time, or a combination of these factors (Kanehisa et al. 1994).

It’s important to note that the method used to determine muscle cross-sectional area may affect the results, as some studies have used ultrasound for this purpose. While there’s still some uncertainty, it is unlikely that differences in maximal force relative to muscle size are linked to noncontractile tissue within a muscle, as no significant differences in noncontractile tissue between the sexes have been observed. This area of research still requires further exploration to provide a more comprehensive understanding of the strength differences between men and women.

Sex Differences in Power Output

Sex differences in power output play a significant role in many sports and athletic activities. Power is a crucial factor in Olympic-type lifts, which untrained women typically perform at about 54% of the average untrained man’s capability in the clean high pull. After 24 weeks of weight training, women’s performance in the high pull increases to approximately 66% of the average untrained man’s (Kraemer et al. 2002). In Olympic weightlifting, women’s world records are often expressed as a percentage of men’s records. For example, the women’s world records in the 63 kg weight class are about 79% of men’s records in the clean and jerk and 76% in the snatch. While these percentages show that women are achieving a higher percentage of men’s performances in competitive weightlifting, their absolute performance in Olympic-type lifts remains lower than that of men, both in absolute terms and relative to total body weight.

Power output in jumping tasks, like vertical and standing long jumps, tends to be lower in women compared to men when not corrected for relative fat-free mass. Women have been reported to have approximately 54% to 79% of the maximal vertical jump and 75% of the maximal standing long jump compared to men. Even in highly trained athletes, such as Division I volleyball players, men can have a 48% higher vertical jump than women, indicating a substantial difference in maximal power. However, when corrected for fat-free mass, women’s sprint running and stair-climbing abilities become closer to men’s, at 77% and 84-87%, respectively. Vertical jump ability shows only small differences when expressed relative to fat-free mass.

When assessing lower-body power output using the Wingate cycling test, the results have been mixed in terms of whether men have greater power than women. Cycling short-sprint ability appears to be similar between the sexes when expressed relative to fat-free mass. Still, a significant correlation between power and overall fat-free mass has been observed, indicating that more fat-free mass is associated with enhanced power performance. In a study of 1,585 Division I college athletes, men showed a large difference in relative peak power compared to women. This suggests that men tend to have higher lower-body power output than women in this specific investigation.

Women generally exhibit lower isokinetic power than men when expressed in absolute terms, body weight, fat-free mass, and bone-free lean leg mass. The differences are significant until power is normalized by bone-free lean leg mass, highlighting the role of muscle size in these disparities. The time it takes to reach peak velocity during isokinetic movements may also contribute to these differences. In terms of maximal power output relative to 1RM, there may be variations between men and women, particularly in exercises like the bench press, squat jump, and hang pull. Women tend to produce peak power at a higher percentage of their 1RM, making their power output appear relatively lower compared to men when using a low percentage of 1RM.

The reasons behind these power differences are not always clear, but they are thought to relate to muscle size, muscle fiber composition (type II vs. type I fibers), neural differences affecting muscle fiber recruitment, and possibly reduced activation from childhood physical activity. Normalizing power measures by fat-free mass can sometimes overcorrect for lower-body measures, making it crucial to choose appropriate corrections that closely reflect muscle fiber cross-sectional area. Additionally, factors like the percentage of 1RM used for power tests and the range of motion allowed can have a substantial impact on observed differences in power output. 

Pennation Angle

Muscle fiber pennation angle and length are important factors associated with muscle fiber force and velocity capabilities. Pennation angle refers to the angle at which muscle fibers pull relative to the direction needed to produce joint movement. Larger pennation angles allow for greater muscle fiber packing within a given muscle volume, resulting in more force exerted on a tendon.

Studies using ultrasonography have shown sex differences in muscle pennation angles, though the significance of these differences can vary by muscle group. For example, in the tibialis anterior, lateral gastrocnemius, medial gastrocnemius, and soleus muscles, males tend to have larger pennation angles than females. However, these differences and their significance have not always been explicitly reported. The differences in pennation angles tend to become more prominent during maximal voluntary contractions.

These variations in pennation angles have been suggested to contribute to sex differences in vertical jump performance in volleyball players. Muscle size, particularly the vastus lateralis, has been found to have significant relationships with jump performance. Additionally, there are nonlinear relationships between muscle size parameters and pennation angles. However, more research is needed to fully understand the role of muscle fiber pennation angles in sex-related performance differences.

Regarding muscle fiber length, longer fibers have more sarcomeres arranged in series, allowing for greater muscle excursion and contraction velocity. Some studies have examined the effect of sex on muscle fiber length. For example, females have been reported to have greater average muscle fiber length and greater variation in fiber length in certain muscles, such as the gastrocnemius (medialis and lateralis) and soleus. In contrast, males tend to have greater pennation angles in these same muscles. There have been inconsistencies in the reported data, with some studies showing no significant sex differences in fascicle length in various muscles, while others have reported sex differences.

Muscle thickness, which is significantly greater in men than in women, is thought to contribute to their larger pennation angles. Studies have shown positive correlations between pennation angle and muscle thickness. When muscle size increases due to resistance training, it’s likely that pennation angles will increase as well.

Hypertrophy in Women

The concern that resistance training will cause excessive muscle hypertrophy in women, leading to a less feminine appearance, is not supported by scientific evidence. This fear can discourage women from engaging in heavy resistance training, limiting the potential health and fitness benefits, including improved bone and tendon development, physical function, and performance. It’s essential to include heavy loading in training programs to fully engage the entire motor unit pool.

While hypertrophy of muscle fibers, particularly type I and type II (IIa and IIx) fibers, can occur in women through resistance training, the extent of muscle hypertrophy is generally not excessive. Women experience muscle hypertrophy when participating in properly designed resistance training programs that incorporate moderate to heavy loading (e.g., 10-repetition maximum or lower).

In a study involving untrained women in their 20s, different loading schemes were implemented in a lower-body resistance training program using exercises like leg press, squat, and knee extension. The program included resistance training zones of 6-10RM and 20-30RM, performed two days a week in the first week and three days a week in the following five weeks. It was observed that only the 6-10RM resistance training zone produced muscle fiber hypertrophy. In the early phase of training, heavier resistances resulted in more pronounced changes in muscle fiber hypertrophy, whereas the lighter resistance training group did not experience significant muscle fiber hypertrophy. Unfortunately, the promotion of light weights and high repetitions in fitness often plays on women’s fears of excessive muscle growth, limiting the benefits they can gain from these programs.

In studies investigating muscle size, women often see small yet significant increases in muscle size after several months of weight training. Despite concerns about circumference measurements, the observed increases in body circumferences are quite modest, typically ranging from 0.2 to 0.6 cm (0.08 to 0.2 inches) in different body parts. It’s essential to note that these small increases in body circumferences are often a result of both muscle hypertrophy and a decrease in subcutaneous fat. As muscle tissue is denser than fat tissue, the increase in muscle mass, combined with a decrease in fat mass, may not lead to a significant increase in body circumferences. In essence, women become leaner rather than substantially larger with correctly designed progressive heavy resistance training programs.

Men and women generally experience similar relative changes in muscle hypertrophy with resistance exercise. Resistance training programs focused on moderate to heavy loading lead to significant increases in muscle fiber cross-sectional areas in both men and women. While some differences may exist in the hypertrophy response of muscle fibers between the sexes, such as a potentially greater potential for type II fiber hypertrophy in women, these differences are not typically extreme.

Overall, women should not fear excessive hypertrophy as a result of resistance training. When engaged in well-designed resistance training programs, they can experience substantial benefits, including increased strength, improved muscle tone, and a lean, firm physique. Properly structured training programs using appropriate resistance levels can help women achieve their fitness goals without the fear of excessive muscle growth.

Oxygen Consumption and Body Composition in Women

Oxygen Consumption: Women tend to experience significant improvements in their relative peak oxygen consumption (V̇O2peak) after participating in circuit weight training programs lasting 8 to 20 weeks. On average, their V̇O2peak increases by approximately 8%, which is a higher relative increase compared to men whose average increase is around 5% over the same duration. This implies that women’s cardiorespiratory endurance capabilities tend to improve more than those of men when engaging in circuit weight training. The exact reason for this difference is not entirely clear, but it may be associated with the relatively higher baseline cardiorespiratory fitness level of men before starting such training programs.

Surprisingly, recent research has shown that men exhibit higher acute responses in various measures such as absolute and relative oxygen uptake, systolic blood pressure, and respiratory exchange ratio compared to women during circuit weight training. However, it’s essential to note that these acute responses do not necessarily translate into differences in long-term adaptations. In fact, women can achieve even greater gains in relative peak oxygen consumption when engaging in aerobic circuit weight training programs. These programs combine resistance training exercises with short periods of aerobic training, and when done correctly, they can result in substantial improvements in V̇O2peak. For instance, a program involving five sets of resistance and callisthenic exercises interspersed with short aerobic periods led to a remarkable 22% increase in V̇O2peak in previously untrained women over 12 weeks. However, it’s important not to rely solely on circuit training, as it may have limitations in addressing various neuromuscular training goals, particularly due to the use of lighter weights. Overdoing it or using it excessively without adequate recovery can lead to overreaching syndromes.

Body Composition: Both women and men seek changes in body composition through resistance training, aiming to increase fat-free mass and reduce body fat. Over the short term (8 to 20 weeks), both sexes experience similar significant changes in this regard. Men and women participating in identical weight training programs have shown noteworthy reductions in percent body fat, and there have been no significant differences observed between the sexes.

For instance, a 24-week weight training program demonstrated that both men and women experienced a significant increase in fat-free mass with no change in percent body fat. However, men in this particular study showed a significant reduction in fat mass, suggesting that women may find it somewhat more challenging to lose body fat during resistance training.

Moreover, the changes in body composition in different regions of the body are important to consider for women. After six months of engaging in a periodized weight training program combined with endurance training exercises, women displayed a 31% reduction in fat mass in their arms but no change in lean mass. On the other hand, they exhibited a 5.5% increase in lean mass in their legs with no change in fat mass. This suggests that women may find it more difficult to increase lean mass in their upper bodies compared to their lower bodies.

However, there are contrasting findings that challenge this notion. Untrained women participating in several weight training programs for six months showed substantial increases in muscle cross-sectional areas in the upper arms (approximately 15% to 19%) and thighs (approximately 5% to 9%). This indicates that upper-arm musculature experiences greater hypertrophy than the thighs, which is further supported by another report demonstrating increased lean tissue in the upper but not the lower bodies of women who underwent 14 weeks of resistance training.

These findings imply that women can achieve significant improvements in body composition through resistance training, and the need for such training may be even greater in the upper body to counteract age-related muscle loss.

Women’s Hormonal Responses to Resistance Training

Introduction: Hormonal responses are a crucial factor affecting the anabolic and catabolic environment to which muscle tissue is exposed during resistance training. This holds true for both men and women and partly explains the gains in muscle size and strength achieved through resistance training. It’s important to consider women’s hormonal responses in the context of the menstrual cycle, as hormone concentrations can vary depending on its phase. It’s also essential to understand that even when hormone concentrations are relatively low, they can still play an active role in controlling various bodily functions and processes, including tissue growth.

Testosterone

In a resting state, men typically have 10 to 40 times more testosterone in their bloodstream compared to women. This disparity in testosterone levels contributes to the larger muscle mass observed in men since testosterone influences the developmental cell cycle, acts as an acute signal for protein synthesis, and interacts with various cell-signaling processes that activate satellite cells and neurons. However, as highlighted earlier, the testosterone response to resistance exercise depends on several factors, including the amount of activated muscle mass and the manipulation of exercise variables such as intensity and volume.

While women have significantly lower resting testosterone concentrations compared to men, even small changes in their testosterone levels can affect muscle tissue growth. Some studies have reported that women’s serum testosterone levels can significantly increase after a single session of resistance training. However, these increases are generally smaller and more variable than those observed in men. In certain cases, the testosterone levels in women remained unaffected by the resistance training session, while men consistently experienced an increase in serum testosterone levels after identical sessions.

Although most studies in women have not shown significant increases in testosterone levels in response to resistance exercise, some studies have reported temporary and significant elevations in testosterone following resistance training sessions. This suggests that women’s hormonal responses can vary widely, and further research is needed to understand the factors contributing to these differences in hormonal responses. Despite the smaller response in terms of increased testosterone levels, women’s androgen receptors exhibit similar response patterns and interactions with testosterone as seen in men, indicating an active connection with testosterone signaling.

It’s worth noting that the time of day when resistance training occurs can affect the magnitude of testosterone response. Men tend to experience more significant spikes in testosterone when they train later in the day. This could be attributed to higher resting testosterone concentrations at other times of the day, preventing dramatic spikes in circulating or saliva concentrations. This time-dependent testosterone response may not be as pronounced in women, likely due to their lower resting testosterone concentrations in various body compartments, including blood and saliva.

Importantly, resting serum testosterone concentrations do not show significant differences between untrained women and highly competitive women Olympic weightlifters. This highlights that testosterone acts as a signaling hormone rather than an accumulating entity that tracks gains in strength or tissue mass. Some studies have reported that short-term resistance training does not alter resting serum testosterone concentrations in women, while others have shown significant increases in resting testosterone concentrations. These responses are often interpreted as the body’s effort to establish a higher resting baseline and optimize the acute response to exercise. Moreover, training volume can influence the resting testosterone concentration response, with periodized multiple-set programs leading to small but significantly greater increases compared to non-varied single-set programs.

Lastly, the testosterone response in women has been linked to regional body fat distribution, with women having a higher degree of upper-body fat showing a more pronounced response. The exact mechanisms behind this observation remain speculative and necessitate further investigation.

Cortisol

Cortisol’s Regulatory Roles: Cortisol, a hormone with several regulatory functions in metabolism and known for its catabolic effects on protein metabolism, also plays a role in the context of resistance training. It’s important to understand how women’s serum cortisol concentrations respond to resistance training and how various factors influence these responses.

Effects of Resistance Training on Cortisol: When menstrual cycle phase is controlled, women’s serum cortisol concentrations can increase in response to a resistance training session. This response has been observed even when the menstrual cycle phase is not controlled. Additionally, the volume of training, such as performing one set of exercises versus three, can impact the cortisol response in women. This effect is not exclusive to women, as men also experience cortisol responses that depend in part on training volume.

Influence of Athlete’s Level and Emotional State: An athlete’s level of training can influence the hormonal response resulting from exercise stress, particularly in high-intensity resistance training. Emotional state is another factor that can affect the magnitude of cortisol response, regardless of gender. Significant increases in cortisol levels have been observed in both male and female athletes immediately before a competition and up to one hour post-competition. This anticipatory spike in cortisol is believed to enhance performance by increasing arousal and creating a positive stress response that drives athletic performance.

Resting Cortisol Concentrations and Training: Studies have shown that resting serum cortisol concentrations may not change significantly after periods of resistance training. For example, there were no observed changes in resting cortisol concentrations after eight weeks of resistance training or 16 weeks of power-type resistance training in women when menstrual cycle phase was not controlled. However, it’s important to note that resting cortisol concentrations have also been observed to decrease after eight weeks of resistance training when menstrual cycle phase was not controlled. This decrease could be indicative of a reduction in total stress from a combination of factors. Training volume appears to be a crucial factor in determining whether resting cortisol concentrations will decrease as a response to resistance training.

Glucocorticoid Receptors and Gender Differences: In resistance-trained individuals, the content of glucocorticoid receptors in muscle has been studied in response to acute resistance exercise stress. For example, an acute resistance exercise stress with six sets of a 10-repetition maximum (10RM) squat protocol with two-minute rest periods did not alter the glucocorticoid receptor content in muscle in resistance-trained men and women. However, women displayed a much higher concentration of glucocorticoid receptors than men at all time points. This suggests that cortisol might have a more significant influence on catabolic signaling to muscle cell targets in resistance-trained women compared to men. More research is needed to clarify these observed differences.

Multiple Targets for Hormonal Signaling: The studies emphasize the need to consider multiple targets for hormonal signaling in response to resistance exercise stress. While muscle cells might not be significantly affected by cortisol increases, other cells such as immune cells could be more impacted. Moreover, the type of cells, the time frame when receptors are measured, and differences between sexes can all influence the receptor targets available for cortisol binding.

Growth Hormones in Women’s Resistance Training

Varieties of Growth Hormone (GH): The section begins by acknowledging the different forms of growth hormone (GH), ranging from the original 22 kD 191 amino acid polypeptide found in the anterior pituitary somatotrophs to various combinations of GH and binding proteins. These different molecular weight fractions are essential to understanding the response to resistance training in women.

Response to Resistance Training: Women, much like men, experience an increase in serum human 22 kD GH in response to resistance training sessions. The acute GH response in women, similar to the responses of other hormones such as testosterone and cortisol, is influenced by the manipulation of acute program variables. This includes factors like total volume, with higher-volume sessions eliciting a significantly stronger GH response compared to lower-volume sessions. Short rest periods, around one minute, between sets and exercises enhance the GH response, as it is linked to factors like low pH and high H+ concentrations, as indicated by blood lactate concentrations.

Role of GH in Muscle Tissue Hypertrophy: Notably, the text highlights that growth hormones may play a more significant role in signaling muscle tissue hypertrophy in women compared to men. This implies that GH may be particularly important in promoting muscle growth in women during resistance training.

Effect of Training Status: The training status of women also plays a role in their GH response to resistance training. Women with at least one year of weight training experience exhibit a more prolonged elevation of growth hormone above resting values, leading to a greater GH response compared to those with no regular weight training experience. Despite these acute responses, women’s resting serum human growth hormone concentration does not appear to be significantly altered by resistance training, whether it’s over eight weeks or six months.

Gender Similarities in GH Response: In terms of aggregate bioactive GH, both men and women appear to have similar acute and chronic GH responses to resistance training. The acute response is comparable between the sexes, and the chronic response shows no significant change in resting GH concentrations.

Hormonal Contributions to Adaptation: The text emphasizes that the responses of various hormones to resistance training contribute to creating an anabolic environment for skeletal muscles, bones, and other tissues. These hormonal responses, including GH, play a vital role in enhancing strength and muscle hypertrophy in both men and women following resistance training. The section also hints at the involvement of other hormones, such as IGF-I, luteinizing hormone, follicle-stimulating hormone, and estradiol, in women’s adaptations to resistance training.

Menstrual Cycle and Exercise-Induced Irregularities in Women

Understanding Menstrual Cycle Variations: The section starts by highlighting the importance of understanding the menstrual cycle in women’s health, especially for exercise conditioning professionals. Menstrual cycles vary considerably among women, making it challenging to determine what constitutes a regular cycle. Nevertheless, exercise, including resistance training, can lead to variations in menstrual patterns in some women. These irregularities encompass factors like a shortened luteal phase, lack of ovulation, oligomenorrhea (an irregular cycle), and secondary amenorrhea (absence of menstruation for an extended period).

Underlying Causes: Irregular menstrual cycles related to exercise are often secondary to the primary issue of low energy availability. This means women are not consuming an adequate amount of food or calories. Such menstrual disorders in active women are frequently associated with the female athlete triad, which includes disordered eating, amenorrhea, and osteoporosis. These conditions are more prevalent in sports that emphasize low body mass or subjective scoring systems, such as gymnastics and figure skating.

The Female Athlete Triad: The female athlete triad can be detected using psychological tests for the drive for thinness, where energy deficiency in active women can be predicted. The prevalence of disordered eating patterns in so-called “thin-build sports” is notably higher than in the general population. Primary amenorrhea, which is the absence of menstruation, is more common in sports with subjective judging systems, such as cheerleading, diving, and gymnastics, than in the general population.

Association with Sport Types: Various sports and activities come with different risks of menstrual irregularities. For instance, sports with greater training volume, intensity, frequency, and longer training session durations can increase the likelihood of menstrual irregularities. Competitive bodybuilding, which often emphasizes very low body mass and subjective judging, has a significantly higher incidence of oligomenorrhea or amenorrhea compared to recreational resistance training.

Caloric Intake and Age: The risk of menstrual irregularities is often due to inadequate caloric intake rather than the level of physical activity alone. Amenorrhea is more common in younger women, and late menarche (onset of menstruation) is associated with a greater chance of experiencing amenorrhea. A previous pregnancy is linked to a decreased risk of amenorrhea. Additionally, insufficient caloric intake and psychological stress can lead to hormonal disturbances associated with menstrual irregularities.

Health Consequences and Management: Amenorrhea has serious health consequences. The first step in addressing exercise-induced amenorrhea is restoring energy, emphasizing increased caloric intake. Seeking professional assistance to manage such conditions is encouraged. Screening for eating disorders should be conducted, and psychological treatment should be arranged if needed. In many cases, increasing weight can restore normal menstrual function and alleviate the reduced bone density often seen in this population.

Premenstrual Symptoms, Dysmenorrhea, and Menstrual Cycle Effects on Strength Training in Women

Impact on Premenstrual Symptoms: One of the initial adaptations to an exercise program in women is a decrease in normal premenstrual symptoms. Active, athletic women tend to experience fewer premenstrual symptoms compared to sedentary women. These symptoms include breast enlargement, appetite cravings, bloating, and mood changes. If training is reduced, premenstrual symptoms may increase, especially if this reduction in training coincides with weight gain.

Dysmenorrhea (Painful Menstruation): Dysmenorrhea, characterized by painful menstruation, may accompany premenstrual symptoms. It is attributed to an increased production of the hormone prostaglandin, which is associated with uterine cramping. While dysmenorrhea is reported by 60-70% of adult women, it occurs less frequently and is less severe in athletes compared to the general population.

Reduced Frequency and Severity: The reduced frequency and severity of premenstrual symptoms and dysmenorrhea in athletes could be due to differences in hormonal concentrations or differences in pain tolerance. Physical training appears to decrease the incidence of these symptoms, and some treatment strategies and oral contraceptives have been used to address dysmenorrhea and other premenstrual symptoms.

Menstrual Cycle Phase and Strength Training: There is limited information available on the effect of menstrual cycle phase on maximal strength, as various factors make definitive findings challenging. The rationale for variations in strength or performance during different menstrual cycle phases is often explained by hormonal fluctuations. For example, the hormone progesterone, which has a catabolic effect on muscles, reaches its highest concentrations during the luteal phase, as does cortisol, another catabolic hormone. Testosterone remains relatively constant throughout the menstrual cycle, except for an increase during ovulation.

Hormonal Implications for Training: These hormonal changes have led some to suggest that strength training should vary according to menstrual cycle phases, as different phases offer varying conditions for muscle growth and repair. This idea implies that resistance training intensity or volume should be reduced during the luteal phase and increased during the follicular phase.

Research Findings and Hormonal Correlations: A study conducted menstrual cycle-triggered training, which involved training every second day during the follicular phase and about once a week during the luteal phase, over two consecutive menstrual cycles. The results showed that maximal isometric leg strength increased significantly more with menstrual cycle-triggered training than with normal training. Muscle cross-sectional area increases were equivalent, but maximal strength per muscle cross-sectional area was significantly greater with the menstrual cycle-triggered training. This approach showed significant correlations among hormone levels, strength increases, and muscle cross-sectional area changes.

Need for Further Research: While this approach is promising, not all information supports the rationale of menstrual cycle-triggered training. For example, in untrained women, a higher acute growth hormone response to resistance training is evident in the luteal phase compared to the follicular phase. Therefore, more research is needed to better understand the relationship between menstrual cycle phases and strength training in women.

Performance During the Menstrual Cycle and Menstrual Problems

Effect on Athletic Performance: Studies have shown little to no significant difference in aerobic and anaerobic performance during various times of the menstrual cycle. However, some research indicates performance decrements during the premenstrual or menstrual phase, with the best performances occurring during the immediate postmenstrual period and around the 15th day of the menstrual cycle. These decrements are seen in factors like peak power, anaerobic capacity, and fatigue rate. It’s essential to note that individual variations in the effects of menstrual cycle phases on performance can be substantial, with some athletes even experiencing improved performance during menstruation.

Factors Contributing to Performance Changes: Several factors may contribute to decreased performance during the premenstrual or menstrual phase, including self-expectancies, negative attitudes toward menstruation, and weight gain. The use of oral contraceptives or progesterone injections has been suggested to control premenstrual symptoms and dysmenorrhea and ensure that menstruation does not coincide with major competitions. Some anecdotal and retrospective studies have reported performance increases with the use of these measures.

Individual Variation and Unclear Impact: The impact of the menstrual cycle on athletic performance is not clear and is likely specific to the individual. It’s important to note that some athletes have achieved Olympic medal-winning performances during all phases of the menstrual cycle.

Menstrual Cycle Disturbances and Hormonal Response: Some menstrual cycle disturbances accompanied by low estradiol and progesterone serum concentrations may lead to an attenuated growth hormone response to a resistance training session, potentially affecting long-term adaptations to resistance training.

No Detrimental Effect on Health: Overall, participation in physical training and athletic events during menstruation or any other phase of the menstrual cycle is not detrimental to health and should not be discouraged. While menstrual cycle phases may impact performance, individual variation plays a significant role, and strategies like oral contraceptives can be considered to manage any performance-related concerns. It’s essential to focus on each athlete’s specific needs and responses.

Bone Density

Types of Bone and Influencing Factors: Bone density changes are associated with two primary types of bone: cancellous (trabecular) and cortical bone. Cancellous bone, which has a high turnover rate, is more responsive to hormonal changes than to exercise. In contrast, cortical bone, which has a slower turnover rate, is influenced more by mechanical strain.

Effect of Menstrual Dysfunction: Menstrual dysfunction, particularly amenorrhea, is linked to decreased bone density and an increased risk of osteoporosis. Amenorrheic athletes have been observed to have greater bone density than amenorrheic nonathletes. Women who have never had regular menstrual cycles may experience an average 17% deficit in bone density compared to their normally menstruating counterparts. The most significant loss of bone mass often occurs during the first three to four years of amenorrhea.

Impact of Menarche and Duration of Menstrual Dysfunction: Several factors, including the age at menarche, age at menarche with subsequent amenorrhea, duration of oligomenorrhea, and duration of menstrual dysfunction, have been correlated with reduced bone density. Young amenorrheic women might be losing bone mass during a period when it should typically increase.

Potential for Bone Density Restoration: Athletes who were amenorrheic but later regained menses for 15 months showed an increase in bone density, indicating the potential for some restoration when a normal menstrual cycle resumes. However, the ease and extent of such restoration remain to be determined.

Importance of Adequate Caloric Intake: Highly trained women engaged in activities who do not consume sufficient calories to achieve adequate energy levels are at a greater-than-normal risk for menstrual problems and, consequently, may also be at risk for osteoporosis.

Role of Weight Training: Well-designed weight training programs have shown promise in increasing or at least slowing the loss of bone density in women. These effects are observed not only in young women but also in middle-aged and postmenopausal women.

Effect of Oral Contraceptives: It’s noteworthy that oral contraceptives can have a negative impact on total-body bone mineral content, even when exercise is part of the routine.

Hormonal Mechanisms of Menstrual Cycle Disturbances and Bone Density Loss

The Relationship Between Bone Density and Menstrual Cycle Disturbances: Bone density in women typically increases with physical activity. However, menstrual cycle disturbances are associated with factors that stimulate bone resorption (loss) and formation. These disturbances may arise from various stressors, including physical and psychological stress, inadequate caloric intake, and dietary deficiencies.

The Hormonal Pathway: These stressors trigger the release of corticotropin-releasing hormone from the hypothalamus, leading to a decrease in gonadotropin-releasing hormone and, subsequently, a reduction in pituitary hormones like luteinizing hormone and follicle-stimulating hormone. This hormonal cascade can disrupt the menstrual cycle.

Effect on Ovarian Hormones: Menstrual cycle disturbances result in decreased levels of ovarian hormones, particularly estrogen and progesterone. These hormonal changes, in turn, affect bone cells known as osteoclasts (bone resorption) and osteoblasts (bone formation). Consequently, there’s a net decrease in bone mass or density.

Role of Estrogen: Decreased concentrations of estrogen and progesterone are most commonly associated with osteoporosis and bone loss. Some suggest that estrogen primarily reduces bone resorption with limited impact on bone formation, ultimately leading to a net bone loss.

Receptor Presence in Bone: Receptors for hormones like estrogens, androgens, progesterone, and corticosteroids are found in bone, indicating their direct influence. Hormones may also indirectly impact bone by acting through other hormones.

The Role of Corticotropin and Beta-Endorphin: Corticotropin, which stimulates cortisol release from the adrenal cortex, may lead to bone loss and menstrual cycle disturbances. Increases in beta-endorphin, particularly in response to resistance training with a negative caloric balance, could contribute to menstrual cycle disturbances in active women.

Involvement of Other Hormones: Various other hormones like growth hormone, testosterone, estradiol, progesterone, corticosteroids, insulin, and calcitonin are also likely involved to varying degrees in menstrual cycle disturbances and bone loss in active women.

Local Factors in Bone Health: Local factors play a role in bone resorption and formation. Prostaglandin, which stimulates osteoblasts, is released from bone itself and is implicated in the early response to mechanical loading for bone formation. Insulin-like growth factor I, produced in response to growth hormone, is also released from bone in response to mechanical loading and prostaglandin stimulation, further stimulating bone formation.

Overall Hormonal Responses: Hormonal responses collectively lead to decreased bone mass or density in women experiencing menstrual cycle disturbances.

Knee Injuries in Women: Causes and Mitigation

Higher Knee Injury Rates in Women: In sports that involve jumping and cutting, women face a significantly greater risk of experiencing serious knee injuries compared to their male counterparts, with women being four to six times more likely to suffer from such injuries. This difference in injury rates is influenced by a variety of factors including anatomical, neuromuscular, and hormonal differences between men and women.

Anatomical Factors: One of the anatomical distinctions contributing to the discrepancy in knee injury rates is the Q-angle. The Q-angle is the angle formed between a line connecting the anterior superior iliac crest to the midpoint of the patella and a line connecting the midpoint of the patella to the tibia tubercle. Women tend to have a wider pelvic structure, which results in a greater Q-angle compared to men. However, research results on the association between Q-angle and knee injury incidence are mixed. Additionally, women generally have smaller femoral notch widths relative to the anterior cruciate ligament, but it’s inconclusive whether this accounts for the increased injury rates in women.

Neuromuscular Differences: Neuromuscular differences are another area of focus to explain the elevated knee injury rate among women. This theory suggests that variations in muscle recruitment patterns, longer reaction times, and more extended time required to generate maximum force during activities like cutting and landing predispose women to knee injuries. Some studies have observed differences in muscle recruitment patterns, reaction times, and time to generate maximum force in women compared to men, but not all studies have reported these distinctions.

Hormonal Factors: The menstrual cycle and its hormonal fluctuations have also been considered as potential contributors to knee injuries in women. Hormones like estrogen, progesterone, and relaxin can increase joint laxity, affect muscle relaxation, influence the strength of tendons and ligaments, and impair motor skills. Joint laxity can fluctuate during the menstrual cycle, and increased knee laxity is linked to a higher risk of knee injury. As a result, certain phases of the menstrual cycle might predispose women to knee injuries. However, the connection between menstrual cycle phases and tendon properties remains inconclusive.

Mitigation Through Conditioning Programs: Physical conditioning programs, which may include exercises like plyometrics and weight training, have demonstrated the ability to significantly reduce the knee injury rate in women. For instance, a six-week conditioning program for American high school female athletes led to a knee injury rate that was only 1.3 times higher than a control group of male athletes. In contrast, female athletes who did not participate in the program had a knee injury rate 4.8 times higher than male athletes and 3.6 times higher than their female counterparts who underwent the conditioning program. Additionally, those with the poorest starting scores on clinical movement assessment tools like the Landing Error Score System (LESS) appeared to benefit most from these interventions. Extended interventions have also shown more effective long-term retention of movement improvements.

General Needs Analysis for Women in Strength Training.

A notable consideration in program design for women is the higher incidence of knee injuries. Addressing this issue involves implementing a preseason conditioning program that incorporates lower-body plyometrics and weight training. This conditioning aims to reduce the risk of knee injuries in sports with a high incidence. It’s also advisable to continue in-season conditioning to maintain physiological adaptations that might positively impact knee injury rates throughout the season.

One common observation is that women typically have smaller upper-body muscle mass and reduced upper-body performance compared to men. This can limit their effectiveness in sports or activities that demand upper-body strength and power. Accordingly, the training program for such activities may need to emphasize upper-body exercises to enhance overall upper-body strength and power. This can be achieved in several ways. If the program has a relatively low total training volume, one or two upper-body exercises can be added. However, the most effective approach is to extend the preseason weight training program, providing additional time for physiological adaptations.

The weaker upper-body musculature in women can lead to difficulties in performing structural exercises such as power cleans and squats. In these exercises, women may find it challenging or impossible to support resistances with their upper bodies that their lower bodies can handle. To address this issue, it is essential to prioritize exercises aimed at strengthening the upper-body musculature over time. In this context, proper technique should always be emphasized, and lifters should not compromise their form in attempts to lift slightly heavier weights, as this can result in serious injuries.

Lastly, all women, irrespective of their goals, can benefit from using heavier weights to increase bone density. Incorporating loads exceeding 80% of a person’s one-rep max (1RM) approximately once every one to two weeks is considered suitable for individuals of all ages, including elderly women. Exercises should emphasize loading at the spine, hip, and wrist, including structural exercises such as squats. Utilizing heavy weights with fewer repetitions can stimulate bone growth and contribute to improved performance and overall functional health. It’s also noteworthy that jumping exercises, like plyometrics, may enhance bone density due to the ground reaction forces on the body, thus offering potential benefits for knee injury prevention.