Just about every time we post a study on social media we get questions about the subject population and their gender, training level, etc. The first thing worth understanding is that subject populations are usually just the most convenient group of people one can study. So more often than not, they’re mostly untrained males. Unfortunately, we’ll have an extremely trained individual pipe up in the comment section and say that the study findings do not apply to them because the subjects were untrained. The idea of study populations not aligning with exactly who you are is another argument for another time, but it’s worth keeping in mind the idea that even though the study population may be a different type of athlete than you are, they are still the same species. Biological and physiological functions are very similar.
With that out of the way, let’s move on to our specific discussion on potential gender differences related to exercise training, performance, and adaptation. Strict care was kept when uncovering information as it’s very easy to dive down a rabbit hole in this discussion. If a gender-specific difference doesn’t influence exercise training, performance, or adaptation, it won’t be discussed here. For that reason, many of the differing hormones between men and women are not mentioned besides estrogen and testosterone. Including those in this piece would turn what’s going to already be a longer article into a full-on book. Ain’t nobody got time for that.
Science shows that men and women express about 3000 skeletal muscle genes differently (32), so let’s strap in and go through what science says about how men and women differ in responses to exercise and adaptation.
Muscle Fiber Composition, Metabolism, and Exercise Performance
First thing’s first, we’re going to dispel a common myth: men are not more fast twitch muscle fiber-dominant than women – both genders have a similar fiber type composition (25). This myth is probably brought about by the findings that women are more reliant on aerobic metabolism during exercise while men are predisposed to using anaerobic metabolism during exercise (12,28). This may be due to the findings that female muscle fibers typically contain fewer anaerobic enzymes than male fibers (28) which would increase their reliance on aerobic metabolism for energy.
So if men don’t contain more fast twitch fibers than women, why are they (typically) naturally stronger and faster? Several studies have shown that while men don’t have a greater percentage of fast twitch muscle fibers, they have significantly larger muscle fibers – especially fast twitch fibers (11,17,25). Some studies also show that men have slightly more muscle fibers in general (17), especially when considering trained bodybuilders (2). The difference in muscle fiber size and overall muscle mass explains many of the differences in strength between men and women, but that doesn’t always explain performance.
Interestingly enough, studies show that male muscle fibers do not contract more quickly than female muscle fibers (14), however, males typically are able to generate force more quickly (4). Why is this? Greater muscle fiber size. If two fibers are contracting at the same velocity but one is larger than the other, the larger fiber is simply going to produce more force. Studies also show that males can relax during muscle contractions more quickly than females (4). Muscle relaxation during contractions is very important for the rate of force development – the relaxation period is simply the amount of time it takes for the contractile proteins to break a bond and re-bond at another point to continue shortening the muscle fiber. The quicker this relaxation period is, the faster force generation can occur.
While men may perform better at strength and speed sports, women certainly have the biological upper hand in endurance activities. Recall the above in which we mentioned that women are more reliant on aerobic metabolism than men. This allows women to maintain a steady state workload much longer than men (8), resist fatigue better than men (12), and recover more quickly between sets than men (15). I would imagine most guys pay attention to the workouts women do in the gym, for one reason or another..; but I think I speak for all men when I say I could never do some of the workouts I’ve seen women perform. Their natural work capacity and ability to perform insane amounts of volume is just incredible. I get gassed from tying my shoes; meanwhile, my wife is running a 5K while dragging a tire and holding a medicine ball above her head.
Anyways, that covers most of the differences between men and women when considering muscle fibers, muscle metabolism, and exercise performance. Men and women have similar fiber type composition, but men just have larger muscle fibers and are more reliant on anaerobic metabolism. Women are more reliant on aerobic metabolism and burn more fat for fuel which makes them killer endurance athletes compared to men.
Differences in Anabolic Hormones
Like I said in the introduction, we’re not going to go super in-depth into the gender differences of hormones. There’s so many confounding factors here that we’re going to take a pretty narrow-minded approach on these differences to avoid the rabbit holes that are prevalent when considering hormones and exercise. For all intents and purposes, the differences we’ll discuss are limited to young and healthy individuals.
Since we’ve narrowed the topic down to anabolic hormones, we’re just going to cover the two main sex hormones that are incredibly different in men and women: estrogen and testosterone. We know estrogen is the primary female sex hormone (8), but what effect does it have on exercise performance, muscle mass, and exercise adaptations? Estrogen doesn’t appear to affect muscle fiber force production or contraction velocity per se (8) but interestingly enough, estrogen can actually assist in muscle repair after damaging exercise (22,24). We see evidence of this in studies where women recover from muscle damage more quickly than men (19).
Even though estrogen might assist in recovery from exercise when considering muscle damage, it doesn’t have any effect on muscle fiber size. In fact, rats supplemented with estrogen actually decreased muscle fiber size (27). This could be one of the reasons why we typically see females having smaller muscle fibers than males. There’s a few theories as to why this might be the case, but we do know that studies show estrogen to have both antioxidant and anti-inflammatory properties. Antioxidants have been shown to negatively affect protein signaling and resistance training adaptations (20) and inflammation has been shown to be important for growth signals following damaging exercise (13) – so reducing inflammation might also impair muscle growth following training.
Men, on the other hand, have much greater levels of testosterone than women (8). I think we’re all pretty familiar with what testosterone can do for muscle size and performance so we’ll just sum that up and say that testosterone is highly associated with muscle mass and strength (18). Again, however, testosterone itself does not appear to directly increase muscle force production or contraction velocity (8), but the general increase in muscle size due to testosterone will increase overall force production (30). The difference in testosterone between genders is likely a primary culprit responsible for the differences we see in muscle fiber size.
Other hormonal differences between men and women certainly exist and do play a role in exercise adaptations, especially when considering body composition, but this article is long enough without mentioning those, so let’s move on.
Differences in Training Recovery
Here’s where things get really interesting between genders as we have solid data on both sides of the fence. Some studies show that men recovery more quickly from resistance training (7), others show that women recover more quickly (9,10), and others show no difference between the two (15). Why the disparity? Let’s look at the protocols and see if there’s any clues.
Men recovered quicker than women in a protocol that involved performing 5 sets of 5 repetitions on the squat at 85% of their 1RM (7). Both subject groups had been strength-trained for at least two years. The protocols that found women to recover quicker involved trained athletes performing 20×1 @ 100% of their squat 1RM (9) or 10×10 @ 70% of their squat 1RM (10). All subjects in these studies had similar levels of training experience, so the theory that trained individuals recover more quickly here doesn’t really make a difference between any protocols. I think, however, we can all agree that performing 20×1 @ 100% and 10×10 @ 70% are immensely more stressful workouts than 5×5 @ 85%. Is it possible that men recover better from moderate volume and moderate/high intensity while women recover better from both high volume and high intensity? These studies unfortunately don’t offer any conclusions as to why this discrepancy exists.
Another study compared fatiguing sprint protocols between men and women. Subjects performed multiple sprints per day for several days in a row. Women were able to recover more quickly between same day sprint trials, but both men and women recovered similarly between days (15).
I have no doubt that estrogen in women may have played a role in the more intense studies showing that women can recover more quickly. Since we know from the above that estrogen can help in repairing muscle damage, protocols that induce extreme amounts of muscle damage might favor recovery in women. 20×1 @ 100% and 10×10 @ 70% would both induce much greater amounts of muscle damage than 5×5 @ 85% or the repeated sprint protocol. Can we surmise then, that women are more capable of recovering from extremely damaging exercise than men? Possibly. But some studies do show that men recover more quickly from, “normal,” training than women, so it’s really tough to make a claim on either side of the fence here.
One potential explanation is that men usually experience greater muscle damage and a greater inflammation response to exercise than women (26). This is more than likely related to estrogen like we already mentioned. Inflammation can easily lead to increased levels of muscle soreness and pain beyond muscle damage alone which can reduce voluntary muscle activation (31). Since many protocols assess recovery by measuring maximal voluntary contraction (MVC) force compared to the baseline level, men may not produce as much MVC force in the days following exercise as they will probably have more muscle soreness. Additionally, since women inherently rely more on aerobic metabolism than men, they will likely experience less muscle damage as their overall metabolic and oxidative stress load will be lower. Fibers that develop more metabolic and oxidative stress likely experience more damage than aerobic fibers (read here).
Overall, the difference between male and female recovery from exercise isn’t exactly certain. Women may be better off recovering from more extreme training sessions while men might recover better from what we would consider, “normal training.” More research definitely needs to be done in this area as this can have major implications for strength and conditioning program design; however, we simply don’t have enough evidence to base prescriptions off of.
Differences in Training Adaptations
Are you ready for a curveball here? Studies show that untrained men and women make very similar gains in size and strength when beginning a training protocol (1,5,6,16,23). While these gains will eventually diverge, this is an incredibly interesting scenario when considering all of the above we just talked about. Women make the exact same progress as men when beginning a training program. Everyone always thinks that women will make much slower gains and have fewer results than men, but for at least the first 6-months or so of training, both can expect similar results.
So why do men eventually make greater gains while women tend to slow or plateau earlier? If we review the initial adaptations to resistance training, we see that gains in muscle size are essentially the last adaptation and can take months to significantly occur. So studies of 8-12 weeks duration don’t really paint the full picture when considering long term gains. Men will eventually make greater gains in size and strength and that probably has a lot to do with testosterone. Testosterone increases muscle size by ramping up protein synthesis (30). Positive protein balance is necessary for muscle growth to occur, so men are more than likely to be in a greater positive protein balance than women at all times. Men have higher baseline fiber size, so increasing that size to a greater extent compared to a female muscle fiber makes the difference in overall muscle size almost exponentially greater in the long term.
For what it’s worth, I dug through some of my old programs and testing sheets from when I worked as a strength and conditioning coach at Ball State University. I compared a semester’s worth of training between a male and female sports team and what effect said training had on their squat max. Now, keep in mind that these were mostly moderately- to well-trained Division 1 athletes here so we’d expect males to make greater gains, right? Not quite. My female team increased their squat max by an average of 38.95% throughout the semester while the male team increased their squat max by 26.15%. While the female athletes would certainly be considered, “trained,” by scientific standards, the male athletes probably had, on average, at least a year greater of strength training experience than the female athletes. So this comparison isn’t exactly apples-to-apples, but it furthers the discussion that women can make gains similarly to men, even in trained populations.
Ultimately, men and women are not that different when considering fiber composition, initial training adaptations, and training recovery. The major differences between the genders appear in metabolism, muscle fiber size, and anabolic hormones. Does this mean women should train differently than men? Definitely not. Dr. Wilson likes to base his training plans off of muscle fiber composition for each muscle group, and since men and women don’t have a significant difference between muscle fiber compositions, there’d be no reason to design a different protocol.
Now, on the flip side, a long term plan between a male and female will be slightly different when considering progressive overload and periodization. There will be a point when a female no longer progresses as quickly as a male and training alterations may have to be made to continue their progress, albeit at a slower pace. For now, we don’t have enough evidence to say whether or not women or men should train more frequently than one another when considering recovery times. Men might recover more quickly from normal training, but females will experience less muscle damage and less inflammation which enhances their perceived recovery over men.
All-in-all, there’s really not much of a reason to think that men and women should train differently. Yes, some key differences do appear between the genders, but these differences don’t impact the ability to perform certain types of training. Women will be naturally better in endurance situations and men will usually be stronger and faster – that doesn’t mean you can’t train what you’re naturally not good at!
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From being a mediocre athlete, to professional powerlifter and strength coach, and now to researcher and writer, Charlie combines education and experience in the effort to help Bridge the Gap Between Science and Application. Charlie performs double duty by being the Content Manager for The Muscle PhD as well as the Director of Human Performance at the Applied Science and Performance Institute in Tampa, FL. To appease the nerds, Charlie is a PhD candidate in Human Performance with a master’s degree in Kinesiology and a bachelor’s degree in Exercise Science. For more alphabet soup, Charlie is also a Certified Strength and Conditioning Specialist (CSCS), an ACSM-certified Exercise Physiologist (ACSM-EP), and a USA Weightlifting-certified performance coach (USAW).