How Women Respond to Strength Training, According to Science

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To keep fit, the Omaha Daily Bee advised back in 1911, women should try “the imaginary motion of lifting a piano” and the real-life challenge of pulling a cork from a bottle. “Hold the bottle between your knees and pull and pull at the tightly driven cork,” the writer advised. Sadly, she didn’t specify how many sets and reps of cork-pulling one should aspire to, but she did promise that it would firm up the abdominal muscles and reduce the hips.

It’s worth keeping this sort of patronizing and nonsensical advice in mind as we contemplate what exercise advice women need these days. After leaving the imaginary-piano period behind, researchers moved on to assuming that men’s and women’s training should be more or less the same, or at least that training for women could be extrapolated from studies conducted almost exclusively on men. More recently, the pendulum has swung back. Women, many experts now believe, need advice that takes into account menstrual cycles, menopause, pregnancy, body composition and hormonal profile, differing hydration needs, and so on. It’s not always clear, though, which differences matter or whether training advice really needs to be changed.

That’s the background for a new systematic review of research on resistance training in healthy young women, published in the Journal of Strength and Conditioning Research by scientists from Brazil, Portugal, Italy, and Australia. Their goal was to figure out how women respond to resistance training, and what training variables are most important for determining whether you gain strength and muscle mass.

In theory, this is a pretty basic and well-studied question. The American College of Sports Medicine, for example, suggests a generic prescription of 1 to 3 sets of 8 to 12 repetitions at 70 to 85 percent of your one-rep max weight for novices hoping to gain strength and muscle. This is based on a huge pile of research: the ACSM position stand cites 280 references. The problem is that the subjects in these studies are mostly men, and where there are female subjects they’re simply mixed in with the male subjects, so it’s impossible to know if there are any systematic differences in response.

The authors of the new review were able to gather the results of 40 different studies including a total of 1,312 women between the ages of 18 and 35. Most of the participants were untrained or sedentary; a quarter of the studies included “physically active” participants, and just one had subjects with prior strength training experience. On average, the studies lasted for ten weeks, typically with two to three workouts per week. The median number of total sets per week was 72, with a typical weight of 80 percent of one-rep max.

The main outcome was that—wait for it—strength training worked. The improvements in both strength and muscle size (measured with a variety of techniques, including MRI, CT scans, ultrasound, and so on) were statistically significant. In order to compare between studies, the results were expressed as “standardized mean differences.” An SMD of 1 means that the average increase in the outcome measure was equal to the standard deviation of values seen in the entire experimental group. Overall, muscle mass increased by 1.2 SMD, which means that the vast majority of subjects saw at least some increase. Strength, on the other hand, only increased by 0.4 SMD, meaning that roughly a third of subjects saw no improvement.

From a practical point of view, studies with more workouts per week produced bigger increases in muscle mass, and studies with a higher total number of weekly sets produced bigger increases in strength. Given that median number of 72 sets per week in the meta-analysis, it’s perhaps mildly surprising that the highest volumes seemed to produce the best results—after all, 72 sets is already a lot! It works out to three sets each of eight different exercises, three times a week, significantly higher than the minimum thresholds for effective strength training. The authors note that prior research has hinted that women have higher fatigue tolerance (that is, their performance at a given relative intensity drops off more slowly) and faster recovery capacity than men. Perhaps that’s why women might benefit from higher volumes of training than men.

Or perhaps not. What’s missing, aside from simply having more data, are direct comparisons of men and women doing the same exercise routines under the same conditions. Only with apples-to-apples comparisons will we be able to determine whether men and women benefit from different strength training approaches. Even the vastly larger literature on men leaves open endless debates about very basic questions like, say, how many sets you should do of each exercise. For now, the new meta-analysis reaffirms that the generic strength training guidance offered up in documents like the ACSM position stand does work for women. Whether there are some subtle tweaks and adjustments that might work even better remains to be seen.

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