Sex Differences in Strength and Muscle Mass: Do Males and Females Gain the Same?

Is it harder for women to build muscle? Men and women have many things in common, but when it comes to building muscle, there are subtle but important things that separate us.

Many things have a say in how much muscle you can gain, and how fast. Anabolic hormones and enzymes in our muscles are factors that tell your body to flip the switch and start adding muscle mass.

Males and females are quite different in these areas, and many people probably think that the advantage is in the male corner. The weights don’t care about your sex, though. We all benefit from strength training. We get bigger and stronger and healthier.

Is it a myth that females have a harder time gaining muscle mass and strength, or can you expect to gain the same regardless of your sex?

That’s what we are going to find out in this article.

Male and Female Muscle Growth and Muscle Breakdown

Contrary to popular belief, you would be hard pressed to find any differences in muscle protein synthesis rates between men and women. We build muscle at the same rate when we are at rest. The same goes for the post-exercise period after a gym session. Both training and protein-rich feedings stimulate our muscle protein synthesis similarly.1

Our basal muscle protein synthesis is not the only thing determining the rate at which we build muscle over time. Neither are the acute responses to strength training and feeding. Looking at the amount of new muscle tissue created by an intense strength training session, there are no significant sex differences.2 3

A single study deviates from the rest. In that study, the scientists observed higher rates of muscle protein synthesis in women.4 However, those results have not been replicated. You can assume that we respond to strength training similarly, if not identically.

After a strength training session, your muscle protein synthesis rates increase by about 50% compared to your basal levels.5 That’s in the fasted state, without any kind of pre- or post-exercise meal. If you do combine your training with a protein-rich feeding, the muscle-building effect of your workout increases dramatically. There are no sex differences there either, though.6

Men Have More Muscle Mass, But Women Gain Muscle Just As Fast

On average, women have less total muscle mass than men, both in absolute terms and in relation to total body mass. The differences in muscle mass between the sexes appear sometime during puberty and remain all throughout our life-span.

Both men and women experience gains in muscle mass through long-term strength training, regardless of age. 7 Men gain more than twice the total amount of muscle mass from heavy strength training compared to women.8

However, you need to keep in mind that women have less muscle mass to begin with. If you take that into consideration, women gain just as much muscle as men.9 10

A large-scale study with 1,300 subjects, 58% of which were women, did not find any sex differences in relative muscle mass after 12 weeks of biceps curls.11

These findings might sound like either good news or bad news, depending on your training goals. Many women don’t want to become as muscular as a man. Those women do not have to lay sleepless worrying about waking up looking like a bodybuilder. Females can’t develop as large muscles as males. One study found that the biceps of competitive male bodybuilders were twice as large as those of competitive female bodybuilders, after years of equivalent training.12 In addition, the male bodybuilders had a larger number of muscle fibers, meaning more building material to start with. Your muscle fibers increase in size when you engage in long-term strength training, not in numbers. This means that females simply can’t catch up, everything else being equal.

In conclusion:

  • Relative to their initial muscle mass, women respond to strength training just as well as men, and gain just as much muscle.
  • Females have less total muscle mass to begin with. This means that, in absolute terms, men gain more muscle mass from strength training, expressed as kg or lbs of body weight.
  • Testosterone likely explains a large part of any differences in muscle mass gains. Even though the acute effects of a strength training are not dependent on hormones, you will see greater long-term gains in muscle mass with higher levels of testosterone.

And speaking of testosterone…

Hormones and Growth Factors

The size of your muscle mass is, to a large extent, controlled by anabolic and catabolic hormones. The most well-known of these is probably the male sex hormone testosterone. Testosterone helps regulate both muscle protein synthesis and muscle protein breakdown. There is a dose-relationship between testosterone levels and fat-free mass, muscle size, strength, and body fat.13

Typical testosterone levels are 10 times higher in men than in women.14 It’s easy to assume that it is much easier for men to gain muscle mass because of this difference in testosterone levels.

Female sex hormones also have anabolic, muscle-building qualities, just like male.

  • Estrogen induces both anabolic and anti-catabolic effects on human musculature. This has been documented in a number of studies.15
  • Progesterone stimulates muscle protein synthesis just as effectively as testosterone.16

You probably don’t think of female sex hormones in a context of gaining muscle mass. Not in the same way testosterone and muscle growth are intimately entwined in the common consciousness. However, these female sex hormones and the way they interact with strength training and hypertrophy explain, at least in part, why women are able to gain as much muscle mass as men through strength training, even though their testosterone levels are far lower.

You might be able to utilize these hormonal advantages in your training. Females have access to a form of natural “doping” called the menstrual cycle. Throughout the menstrual cycle, your hormone balance shifts dramatically. During the first two weeks, the cycle is dominated by estrogen. Even though a recent meta-analysis found the scientific evidence too weak for any definite conclusions, some studies have found that you can optimize lean mass gains through intense, high-frequency, periodized strength training during the initial two weeks of the menstrual cycle.17 18

In addition to all this, there seems to be a relationship between growth factors like insulin-like growth factor 1 (IGF-1) and strength and muscle mass in females.19 In males, no such relationship is evident. Women also produce up to 80 times more growth hormone than men, depending on the time of measuring.20

Even though testosterone might be the more well-known anabolic hormone, females have a number of other hormonal advantages for building muscle.

Age Differences

When we get older, more tangible sex differences in muscle mass and muscle growth start to appear. Aging in general is associated with a reduction in muscle mass and an impaired anabolic response to dietary protein. Men are at an advantage here, with this deterioration of muscle protein metabolism being more apparent in women.

However, basal muscle protein synthesis rates in elderly females are higher than those in age-matched males. In other words, older women build more muscle tissue 24/7 than older men do. This is likely because males have been exposed to high testosterone levels their entire life. Testosterone might be anabolic per se, but a lifetime of male testosterone levels diminish the anabolic sensitivity to the hormone.

Despite the higher basal muscle protein synthesis rates in women, females do lose significantly more muscle mass than males during the aging process. Several factors influence this difference.

  • An increased rate of muscle protein breakdown.
  • Gene expressions that counteract muscle growth following menopause.
  • A diminished anabolic response to both a protein-rich meal and a strength-training sessions post-menopause.

Each meal stimulates muscle protein synthesis less, and each training session results in less new muscle tissue than before menopause. This impaired anabolic response is the result of lower estrogen levels. Older women are at a double disadvantage here compared to men of the same age. They don’t have the help of higher testosterone levels, and their previous estrogen advantage that helped maintain muscle mass is gone.

This sounds worse than it is! There is a cure to the dilemma, or at least an inhibiting drug. A drug called strength training.

Even though the anabolic effects of a strength training session are not as powerful as they once were, they are still powerful enough to, if not outright stop, at least slow the process of muscle loss. Strength training is supremely important to maintain muscle mass as we age. By engaging in strength training, and keeping most if not all of our muscle mass, we also maintain our mobility and quality of life. Regardless of sex. This means that strength training is even more important for females than for males, once past the age of 60.

Despite this, females are at a disadvantage compared to men when it comes to gaining muscle mass at an advanced age. Here is where sex differences in the capacity to build and maintain muscle mass becomes apparent.21

Strength

Everyone knows that testosterone is important, if not critical, for muscle growth. However, the (in)famous male sex hormone probably plays an even more prominent role if you are training for strength.22 In general, males are stronger than females, in absolute terms. It is easy to imagine this translating into an advantage in the gym when it comes to getting stronger.

Lower Body

Females often possess similar lower body strength as males. Again, not in absolute terms, but if you adjust for total body mass, you often even out any differences. More studies compare lower body strength between the sexes than upper body strength.

When women train the same way as men, their strength increases at a similar rate.23 No significant sex differences there, in other words.

Upper Body

Your upper body muscles might have a larger number of anabolic receptors compared to your lower body. Therefore, it seems logical to assume that men, with their 10-fold higher testosterone levels, might respond better to strength training and gain upper body strength faster.

This does not seem to be the case.

In a large, at least in the strength training field, study, 44 young men and 47 young women performed leg presses, leg curls, chest presses, and lat pulldowns twice a week for 10 weeks.24 Isokinetic dynamometer tests could not find any significant differences between sexes. The men improved by 11.61% on average, while the women improved by 11.76%.

These results match those of an earlier study. That study investigated the time course for strength gains following high-intensity strength training. Seventeen young and 20 middle-aged men and women engaged in strength training 3 days per week for 12 weeks.25 Both the males and the females increased their absolute strength similarly in both the upper and lower body. In relation to their total body mass, the females actually demonstrated a slight advantage in strength gains.

Let’s Take a Look at a Recent Meta-Analysis

More than 60 studies have directly or indirectly investigated and compared the effects of strength training on male and female strength and muscle mass. Up until recently, no meta-analyses or systematic reviews have compiled the results of these studies.

As late as May 2020, this oversight was rectified with the publication of the meta-analysis Sex Differences in Resistance Training: A Systematic Review and Meta-Analysis. For the first time, we got a comprehensive overview of whether young to middle-aged males and females respond differently to strength training in the form of muscle mass and strength gains.26

The results can be broken down into a few highlights:

  • Ten studies with a total of 12 outcomes found no significant difference between males and females in terms of hypertrophy.
  • The analysis of 17 studies and 19 outcomes on upper-body strength showed a slight sex difference, favoring females.
  • When it comes to lower-body strength, analyzing 23 studies did not reveal any sex differences.
  • Males and females respond to strength training just as well in regards to muscle hypertrophy and lower-body strength. Looking at upper-body strength relative to body size, the results favored females.

Untrained females might have a greater potential to gain upper-body strength than untrained males. The available research can’t explain Why this difference isw only apparent in the upper body. Sex differences in muscular, neural, and/or motor learning, maybe? Hopefully, future studies will investigate and reveal more. It might even be that the short duration of the available studies limit the possibility of any reliable conclusions.

The More Muscle Mass You Have, the Harder It Is to Gain Even More

If you have been strength training long enough to have left your beginner’s gains behind, you know that additional gains come slower and slower. Over the years, the flood of gains diminishes to a trickle.

In this regard, there are no apparent differences between men and women. It becomes harder for all of us to keep making progress. In one study, competitive bodybuilders, both male and female, stopped gaining any additional muscle mass after a certain point. Sooner or later, you will likely find yourself refining and adding quality to your physique rather than quantity in the form of kilogram after kilogram of new muscle mass. In the study, the bodybuilders, who already had extensive training experience, did not demonstrate any increases at all in muscle fiber size after 24 weeks of monitored training.27 This lack of results occurred even with the help of anabolic steroids. The capacity for muscle growth definitely decreases the more experienced you get.

In Summary

Contrary to popular belief, females respond just as well as males to high-intensity strength training. Maybe even better during the beginner’s stage. Despite much lower levels of the anabolic hormone testosterone.

Male testosterone levels allow them to attain a larger total amount of muscle mass. However, this does not translate into an easier time gaining muscle and strength through strength training. A number of growth factors, hormones, and genes regulate muscle mass, muscle growth, and strength. In several instances, these favor females.

In absolute terms, men do build more muscle mass. If you take an 80-kilogram male and a 60-kilogram woman, and they both manage to increase their muscle mass by 10%, the man will have gained more muscle tissue. However, compared to their starting point, females gain similar amounts of muscle as males, as a rule.

Women who want to gain as much muscle as a man have to train the same way as men. If you are female and want to gain as much muscle as you can, you have to train to gain. This means high-intensity strength training over the course of years. Plenty of women out there in the gyms train just a hard as any man. At the same time, some women use light weights and don’t challenge themselves when they train. Then they wonder why they don’t see the results they want from all the time they spend in the gym.

Conclusion

Despite the fact that men and women are quite different on a physiological level, from hormones to gene expression, we always have one thing in common. We all get more muscular and stronger by hitting the weights.

References

  1. J Appl Physiol (1985). 2012 Jun;112(11):1803-4. Similar muscle protein synthesis rates in young men and women: men aren’t from Mars and women aren’t from Venus.
  2. Acta Physiol (Oxf). 2010 May;199(1):71-81. Resistance exercise increases leg muscle protein synthesis and mTOR signalling independent of sex.
  3. J Appl Physiol (1985). 2009 Oct;107(4):1308-15. No major sex differences in muscle protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adults.
  4. FASEB J. 2009 Feb;23(2):631-41. Higher muscle protein synthesis in women than men across the lifespan, and failure of androgen administration to amend age-related decrements.
  5. Acta Physiol (Oxf). 2010 May;199(1):71-81. Resistance exercise increases leg muscle protein synthesis and mTOR signalling independent of sex.
  6. J Appl Physiol (1985). 2009 Oct;107(4):1308-15. No major sex differences in muscle protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adults.
  7. J Am Geriatr Soc. 2001 Nov;49(11):1428-33. Muscle size responses to strength training in young and older men and women.
  8. J Gerontol A Biol Sci Med Sci. 2000 Nov;55(11):M641-8. Effects of age, gender, and myostatin genotype on the hypertrophic response to heavy resistance strength training.
  9. European Journal of Applied Physiology, January 2000, Volume 81, Issue 3, pp 174–180. Time course for strength and muscle thickness changes following upper and lower body resistance training in men and women.
  10. J Appl Physiol (1985). 2006 Aug;101(2):531-44. Efficacy of 3 days/wk resistance training on myofiber hypertrophy and myogenic mechanisms in young vs. older adults.
  11. BioMed Research International. Volume 2013, Article ID 643575. Highlights from the Functional Single Nucleotide Polymorphisms Associated with Human Muscle Size and Strength or FAMuSS Study.
  12. J Appl Physiol (1985). 1989 Jul;67(1):24-31. Contrasts in muscle and myofibers of elite male and female bodybuilders.
  13. Am J Physiol Endocrinol Metab. 2001 Dec;281(6):E1172-81. Testosterone dose-response relationships in healthy young men.
  14. Sports Med. 2010 Dec 1;40(12):1037-53. Testosterone physiology in resistance exercise and training: the up-stream regulatory elements.
  15. Integrative Biology of Women’s Health pp 35-51. Estrogen Effects on Skeletal Muscle.
  16. The Journal of Clinical Endocrinology & Metabolism, Volume 99, Issue 1, 1 January 2014, Pages 256–265. Testosterone and Progesterone, But Not Estradiol, Stimulate Muscle Protein Synthesis in Postmenopausal Women.
  17. Journal of Science and Medicine in Sport, 17 May 2020. Journal of Science and Medicine in Sport, 17 May 2020.ariations in Strength-Related Measures During the Menstrual Cycle in Eumenorrheic Women: A Systematic Review and Meta-Analysis.
  18. J Sports Med Phys Fitness. 2017 Jan-Feb;57(1-2):43-52. Effects on power, strength and lean body mass of menstrual/oral contraceptive cycle based resistance training.
  19. Eur J Endocrinol. 2011 Feb;164(2):189-96. Circulating levels of IGF1 are associated with muscle strength in middle-aged- and oldest-old women.
  20. Clin Chem. 1998 Jun;44(6 Pt 1):1289-95. Marked gender differences in ambulatory morning growth hormone values in young adults.
  21. Exercise and Sport Sciences Reviews. 42(4):183–192, October 2014. Influence of Sex and Estrogen on Musculotendinous Protein Turnover at Rest and After Exercise.
  22. Am J Physiol Endocrinol Metab. 2006 Dec;291(6):E1325-32. Suppression of endogenous testosterone production attenuates the response to strength training: a randomized, placebo-controlled, and blinded intervention study.
  23. PeerJ. 2016; 4: e1627. Comparison of upper body strength gains between men and women after 10 weeks of resistance training.
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