Women and strength training don’t mix? Wrong!

For a few years now, strong has been establishing itself as the new sexy. More and more women are heading to the weight room. Why? As it turns out, strength training isn’t just for men, but also for women. Before puberty, the reproductive organs are the only significant sex-specific difference between boys and girls. This changes with the onset of puberty. Due to hormonal changes, these distinguishing characteristics become more pronounced.

The influence of hormones

In men, testosterone levels at rest are between 10 and 40 times higher [1,2] than in women. Testosterone has the anabolic potential to regulate muscle mass by either increasing muscle protein synthesis [3] or decreasing muscle protein breakdown [4]. In women, oestrogen is believed to regulate muscle mass. Like testosterone, this hormone can reduce the breakdown of muscle protein [5]. Receptors for oestrogen have been found in muscles, ligaments, and tendons and are thought to regulate muscle proteins and increase sensitivity to anabolic stimuli [6].

Oestrogen decreases in women with age. This has a detrimental effect on the body, namely it’s accompanied by a large decrease in muscle mass and strength [159]. This loss of muscle mass and strength can be mitigated with hormone therapy in postmenopausal women, suggesting oestrogen plays a role in the regulation of muscle [7].

All this points to both men and women being able to build muscle mass and strength. However, women have less muscle mass to begin with. Because of this, any relative changes are more significant.

Differing study results

Many studies have addressed sex differences in strength training between men and women. Roth et al. [8] investigated the influence of age and sex on muscle volume following a strength training intervention. Six young women, eight young men, ten older women, and nine older men participated in a six-month strength training programme in which all major muscle groups of the upper and lower body were trained three times per week. The volume of the thigh muscle and quadriceps were measured by MRI before and after the intervention. Strength training resulted in a significant increase (P < 0.001) in muscle volume in all age and sex groups. There was no statistically significant difference between the groups; neither age nor sex influenced the increase in muscle volume due to strength training.

In another study [9], which investigated the effect of intensive strength training on muscle volume in young and older subjects, the thigh muscles of the dominant leg were trained three times per week over a period of nine weeks. The absolute increase in muscle volume was significantly greater in men than in women (204 ± 20 vs 101 ± 13 cm3, P < 0.01). Even after adjusting for baseline muscle volume, a sex-specific difference persisted. In addition, after 31 weeks of no exercise, there was a significantly greater loss of absolute muscle volume in men than in women (151 ± 13 vs 88 ± 7 cm3, P < 0.05). The authors concluded that the muscle mass response was influenced by sex, as men increased their muscle volume by about twice as much as women.

Using biopsies, Bamman et al. [10] examined the sex-specific cross-sectional size adaptations induced by strength training in older women (66 ± 1 years, n = 5) and men (69 ± 2 years, n = 9). The study participants exercised their leg muscles three times a week for 26 weeks. Although strength training increased muscle cross-sectional area in all fibre types (i.e. I, IIA, IIX) in both sexes, hypertrophy (P < 0.05) and strength gain (P < 0.05) were greater in men than in women.

Walts et al. [11] examined the influence of sex and ethnicity on the effects of strength training on thigh muscle volume. They recruited 181 inactive healthy women (63 ± 0.9 years, n = 99) and men (63 ± 0.9 years, n = 82) to perform unilateral knee extension of the dominant leg three times a week for ten weeks. The volume of the quadriceps muscle was measured by CT before and after the experiment. The absolute increase in muscle volume was significantly greater in men (P < 0.001) than in women. However, both sex groups significantly increased their muscle volume in response to strength training (P < 0.001).

Hubal et al. [12] studied 342 women and 243 men. Participants completed isometric and dynamic strength training for the biceps brachii of the non-dominant arm. MRI was used to determine muscle cross-section before and after twelve weeks of progressive dynamic strength training. In men, the absolute increase in muscle cross section was 2.5% greater compared to women (P < 0.01). However, despite the absolute increase, the relative increases in strength measures, i.e. the maximum voluntary isometric contraction and single repetition maximum, were greater in women than in men (P < 0.05).

These results are consistent with a study by West et al. [13], who performed a sex-specific comparison of muscle protein synthesis (MPS) after a single bout of high-intensity strength training while fasted in eight men and eight women. Results showed that although serum testosterone levels increased 45-fold in men compared with women, MPS did not differ between men and women when compared 1 to 5 hours after exercise as well as after protein intake 24 hours into recovery. Although testosterone levels are significantly different in men and women in response to a single bout of high-intensity strength training, MPS is significantly elevated in both sexes. Thus, there appears to be no relationship between post-exercise testosterone levels and muscle protein synthesis; it’s also increased in women, though they have low systemic testosterone concentrations.

Conclusion: strength training is beneficial for everyone

Although men and women differ in their basal anabolic hormone levels, women and men show similar changes in muscle mass and strength in response to strength training. However, the absolute increase in muscle mass is greater in men than in women. Even so, MPS is significantly increased in both sexes in response to strength training. Therefore, all men and women are encouraged to do strength training. Strength training is beneficial for everyone.

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