Logan Steele
It is a well-known fact that men are physically stronger than women. But is this because men have denser muscles? Scientific studies have shown that men have more muscle mass, with a man's body being about 40 to 50 percent muscle by weight, compared to 30 to 35 percent for women. Men also have larger muscle fibers, with type I fibers being 19% larger, type-IIA fibers 59% larger, and type-IIX fibers 66% larger than those of women. This results in men having significantly more skeletal muscle mass, with one study finding that men had an average of 12 kilograms more muscle than women.
| Characteristics | Values |
|---|---|
| Muscle mass | Men have more muscle mass than women |
| Muscle composition | Women have 27-35% more type I muscle fibres than men |
| Muscle strength | Men are stronger than women |
| Muscle fatigue | Women's muscles fatigue less easily than men's |
| Muscle endurance | Women have greater endurance than men |
| Muscle recovery | Women recover faster than men |
| Muscle fibres | Men have larger muscle fibres than women |
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What You'll Learn
Men have more muscle mass
Men typically have more muscle mass than women. A study in the Journal of Applied Physiology found that men had an average of 12 kilograms more skeletal muscle mass than women. This difference in muscle mass is often attributed to the higher testosterone levels in men, which fuel large increases in muscle. This is evident during adolescence, when the gender divergence in the bone-muscle relationship becomes particularly noticeable.
The higher muscle mass in men also results in them having greater strength. Women exhibited about 40% less upper-body strength and 33% less lower-body strength, on average, in the aforementioned study. Another study in the European Journal of Applied Physiology found that men's greater strength could be attributed to a larger cross-section in individual muscle fibres. Men had significantly larger type I and type II muscle fibre areas than women.
The difference in muscle mass and strength between genders has implications for weight loss. As muscle burns more calories than fat, men often burn more calories at rest and get leaner faster. This means that men can typically consume more calories while still losing weight compared to women. However, this does not necessarily mean that men lose more weight, as the amount of weight lost is dependent on the amount of effort exerted.
While men generally have more muscle mass, there are exceptions. Individual variations exist, and muscle mass can be influenced by factors such as age, fitness level, and genetics. Additionally, women tend to have about 27% to 35% more type I muscle fibres, which are associated with higher endurance. As a result, women may have better endurance than men, despite having lower muscle mass.
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Women have more type I muscle fibres
While men generally have more muscle mass, and therefore greater strength, there are some compositional differences between male and female muscles. Women tend to have 27 to 35% more type I muscle fibres than men. These are also known as slow-twitch muscle fibres, and they are aerobic muscles rich in blood-carrying myoglobin. Type I fibres are smaller and contain less glycogen than Type II fibres, but they are highly endurance-focused. They are recruited first during strength and speed work and, although they are capable of producing less force, they allow for more repetitions and enable a person to run longer and slower than Type II fibres. Type I fibres are also used to hold the body in an erect position all day.
The fact that women have more type I fibres may explain why women fatigue at a similar rate in both muscles, whereas men fatigue more in the lumbar musculature compared with the biceps femoris. Studies suggest that force generation and relaxation are faster during fatigue in men, whereas endurance is higher and recovery is quicker in women. These differences in muscle performance may be due to the larger numbers of type-I fibres in women, which are characterised by slow oxidative metabolism and, therefore, higher endurance.
Hormones likely play a role in the sex differences in fibre-type composition. The hormonal regulation of skeletal muscle development and contractility is well-documented. For example, testosterone has been found to play a role in muscle fibre-type distribution. In mice, castration produces a decrease in body weight, which is attenuated with testosterone supplementation.
The distribution of type I and type II fibres may also be influenced by body type. A mesomorphic body type is one with well-developed and defined muscles on the trunk and limbs. They have a high muscle-to-fat ratio and may look fit even without exercise. Endomorphic body types, on the other hand, are rounder and softer, with more fat surrounding their gluteals and quadriceps. Their muscles are not as well-defined, and they have a higher fat-to-muscle ratio on their trunks and limbs. Ectomorphic body types are long and rectangular, with flat chests and slender hips, and they have poor muscle development and relatively low body weight.
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Men have larger muscle fibres
While men and women differ in terms of strength and muscle performance, these variations are mostly due to differences in muscle mass. Men's bodies are about 40 to 50 per cent muscle by weight, while women's bodies are about 30 to 35 per cent muscle by weight.
Studies of vastus lateralis biopsies show that men have significantly larger cross-sectional areas (CSA) of muscle fibres than women. Specifically, type-I fibres are 19% larger, type-IIA fibres are 59% larger, and type-IIX fibres are 66% larger in men than in women.
The difference in muscle mass between men and women can be attributed to various factors, including hormones. Testosterone, for example, has been shown to increase fibre size. In one study, testosterone supplementation in postmenopausal women led to a 50% increase in protein synthesis rate, while estrogen treatment had no effect.
Additionally, men tend to have larger muscles in specific areas of the body, such as the biceps brachii and the knee extensors, which can contribute to their overall greater muscle mass.
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Women have better endurance
While men and women differ in terms of muscle strength and performance, this is mostly due to differences in muscle mass and body composition. A woman's body is typically about 30 to 35% muscle by weight, while a man's body is about 40 to 50% muscle by weight. However, women have been found to have better endurance, especially in ultra-endurance sports.
Women have been found to have better endurance than men in ultra-endurance sports like ultra-marathons and long-distance swimming. In the 1990s, the rate of improvement in female sports performance was greater than that of male sports performance, likely due to the increasing involvement of females in high-level sports.
There are several possible reasons for women's superior endurance. Firstly, women have more Type I ('slow-twitch' or oxidative) muscle fibres than men. These fibres are characterised by slow oxidative metabolism and higher endurance. Type I fibres produce less force than Type II fibres but are much more fatigue-resistant and have better oxygen delivery. This results in women having a more even running speed and better pacing in endurance events.
Additionally, women have more of the metabolic machinery required for oxidising fat, along with gene expression that favours this process, partly due to their greater Type I fibre proportion. This benefit is particularly evident in ultra-endurance exercises, where glycogen depletion rates are slower. As a result, women have attenuated caloric requirements and can consume fewer exogenous carbohydrates, which can cause gastrointestinal distress during exercise.
Furthermore, the higher body fat percentage in women may also contribute to their better performance in long-distance swimming as body fat provides buoyancy. Estrogen, the predominant female sex hormone, is also believed to aid in muscle recovery, which is crucial in endurance events.
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Testosterone increases muscle mass
Men typically have denser muscles than women, and this can be attributed to a variety of factors, including hormones, muscle composition, and body composition. One key factor is testosterone, which plays a significant role in muscle development and growth.
Testosterone is a hormone that plays a crucial role in the development and maintenance of muscle mass. During adolescence, increases in testosterone levels in males fuel large increases in muscle mass, resulting in greater muscle strength and endurance. This increase in testosterone-driven muscle growth coincides with and contributes to the larger growth in bone dimensions and strength observed in males during this period.
Studies have shown a positive correlation between testosterone levels and muscle mass in men. Higher testosterone levels are associated with increased muscle mass, while low testosterone levels can lead to a decrease in muscle mass and impaired muscle growth, as seen in hypogonadal male mouse models and boys with low androgen levels, respectively.
The role of testosterone in muscle development is further supported by the observation that castration in male animals, such as guinea pigs and mice, results in muscle atrophy and a decrease in body weight. However, testosterone supplementation can attenuate this weight loss, highlighting the importance of testosterone in maintaining muscle mass.
Additionally, men generally have a larger cross-sectional area of individual muscle fibers, contributing to their greater muscle strength. This is evident in studies comparing muscle fibers in the biceps and vastus lateralis, where men exhibited significantly larger type I and type II fiber areas than women.
In summary, testosterone is a key factor influencing muscle mass and strength in males. Higher testosterone levels during adolescence contribute to the development of larger muscle mass, resulting in greater strength and endurance. This, combined with differences in body composition and muscle fiber types, contributes to the denser muscles typically observed in men compared to women.
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Frequently asked questions
Yes, men have denser muscles. A study in the Journal of Applied Physiology found that men had an average of 26 lbs. (12 kilograms) more skeletal muscle mass than women.
The higher density of muscles in men is caused by higher testosterone levels, which fuel large increases in muscle.
Yes, men are, on average, physically stronger than women. Women exhibited about 40% less upper-body strength and 33% less lower-body strength, according to the study. However, women may have an edge in some physical tasks as they have more body fat and are better at burning fat as energy, leading to better endurance than men.
