The Physiological Differences Between Male and Female Runners

Running like a girl should mean training like one. Though seemingly an obvious statement, science is just now appreciating the differences between the sexes and the importance of tailoring nutrition, training and recovery to the needs of female athletes. And determining the special considerations of female athletes is becoming increasingly important since, according to Running USA, female runners now form the majority of participants in U.S. road races.

Before we discuss the differences, let’s focus on an important similarity. For both men and women, the foundation of endurance performance remains the same—aerobic capacity or VO2max, running economy and lactate threshold. Improvements in any or all of these three components are responsible for reaching new PRs or feeling stronger on group runs with speedy friends.

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But for all the strides that women have made over the last several decades—and all their potential to continue to run faster and longer—the reality is that there are physiological differences between male and female runners. In order to improve performance, it’s important to identify them in order to determine an optimal training strategy for female runners.

“Here’s the basic landscape: If a woman follows a general training program designed for a dude (or rather a program not designed to take a woman’s physiology into account), she will most likely end up overtrained, slow, and have extra body fat,” says Dr. Stacy Sims, physiologist and co-founder of Osmo Nutrition.

Recent research may explain some of the biological reasons behind those differences.

According to researchers from the University of Texas, Southwestern, a variation in the way female endurance athletes adapt to exercise may significantly influence running performance. In the 2015 study, presented in the Journal of Applied Physiology, researchers investigated whether males and females would respond similarly to an equivalent training stimulus over a 1-year period. The goal of the training was to prepare the 12 subjects (five men, seven women) of the study for either a marathon, triathlon or long distance cycling event. By the end of the training year, individuals were training up to 9 hours per week.

The study found that the training response in females was markedly attenuated, that after an initial improvement in heart size and aerobic fitness, gains plateaued for the remainder of the study. “The development of ventricular hypertrophy and increase in VO2max in females is markedly blunted compared with males,” the researchers state. What it means is that the size of the heart muscle, which is one of the cardiovascular adaptations that allows more blood and oxygen to be pumped to working muscles, didn’t grow as much in the female athletes. That in turn limited gains in aerobic capacity.

In the study’s male subjects, the training response was much greater. Both heart size and aerobic fitness steadily increased in response to an increase in training intensity and duration.

Other studies investigating changes in heart structure after exercise training have established similar levels of adaptation. A 2014 article in the Scandinavian Cardiovascular Journal found that the heart atria of female runners did not change in size after training as markedly as that of male runners. Though that does limit cardiac output and aerobic capacity in female athletes, the study’s authors emphasize that this may not be all negative, as it also lowers the chance of developing the cardiac arrhythmias associated with exercise induced changes in heart size.

But female runners also have performance adaptations that are superior to that of male runners. Studies of distance runners suggest that men are more likely than women to slow their pace in a marathon. Recent research, presented in the May 2015 edition of Medicine and Science in Sports and Exercise, used the results of 2,929 runners from 14 marathons in 2011. Male runners slowed an average 16 percent from the first half of a marathon to the second while females only dropped their pace by 12 percent.

RELATED: Study: Women are Better at Marathon Pacing Than Men

A variety of factors might contribute to this sex difference in marathon pacing. For example, men are more susceptible to muscle glycogen depletion, which can contribute to the “hitting the wall” sensation. Men may also be more vulnerable to slowing because, during endurance exercise, women generally use proportionately more fat and less carbohydrate at a given intensity of exercise.

Another possibility is that men might be more susceptible to over-heating, which is believed to be another frequent contributor to marathon slowing.

So what does this mean for female runners looking to continue to improve performance? Far from indicating that female runners can’t get faster, the research merely proves the value of tailoring training to their specific needs. After all, aerobic capacity is only one of the three determinants of performance; improvements can come from maximizing adaptation in running economy and lactate threshold.

Dr. Erin Howden, the lead researcher from the University of Texas, Southwestern study, advises female runners, “While your absolute capacity may not increase with greater increases in training, your ability to hold a higher percentage of your maximum should improve with training.”

To boost performance, changing the other two determinants of endurance performance may be the key for female runners. For example running economy, or the amount of energy it takes to run a consistent pace, is improved in male and female runners after resistance training. Like the fuel economy of your car, improved running economy helps you run faster for longer.

Lactate threshold training, which trains your body to be able to neutralize lactate, is another way to improve the ability to run a higher percentage of maximal pace. Interval training at lactate-threshold pace—about 10 to 15 seconds per mile slower than 5K race pace—will spur improvements in lactate threshold.

Andrew Kastor, head coach of the ASICS Mammoth Track Club, believes that training the individual is the key to success. “I feel it’s important to treat and prescribe workouts to each athlete as an individual and not by gender. On our team, the women typically run 10 to 15 percent lower volume than some of our men—not because they are women, it’s just what their training warrants.”

Howden also believes that adaptation relies on not just the type of training you do, but also what you don’t do, saying, “We know that recovery is also important to allow adaptation to occur, so ensuring hard sessions are followed by active recovery sessions or cross-training is important.”

Also, as the researchers found that female athletes tended to not take in adequate energy to sustain muscle growth, nutrition may be an important part of continued improvements in performance. Muscle growth and adaptation needs to be fueled.

“Research on the differences in physiology don’t suggest that female runners can’t improve performance, it merely emphasizes that female athletes can’t train like males,” says Sims.

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