If you feel like you’re constantly in battle with your body, you're not alone. Many runners get fixated on reaching a certain “ideal weight” that doesn’t necessarily match—and may even be at odds—with your physiology. The better way to go: work with what you have to enjoy every run and nail some personal bests.

Too many runners allow a number on the scale to define them, and that number is often grounded in nothing more than a notion of what they think they should weigh. But it’s time to break that mentality.

You Are More Than a Number

“My first bit of advice is to step off the scale for at least a month,” says Stacy Sims, Ph.D., author of ROAR, How to Match Your Food and Fitness to Your Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life.

“I would also encourage you to identify your somatotype, which is your natural shape and size,” says Sims. (Though she specializes in women’s physiology, Sims makes these recommendations for men as well as women.)

Most of us can slot our overall build into one of three general categories, recognizing that there are a wide variety of shapes and sizes even within these three categories, and you can be a combination of two, rather than just a single “type.”

  • Ectomorph: You tend to be long limbed and not particularly muscular; can be smaller in size without necessarily having lean body composition.
  • Mesomorph: You find it relatively easy to build muscle mass, are medium boned, and generally proportionally built.
  • Endomorph: You tend to have larger bone structure, have a curvier build, and generally store fat relatively easily.

The Science of Somatotypes

The concept of somatotypes dates back thousands of years to Ancient Greece and Hippocrates. In the 1940s, William Sheldon, M.D., Ph.D., came up with the three somatotypes that we know today.

At the time, Sheldon, who was a psychologist as well as a physician, assigned specific personality and psychological characteristics to them as well, positing that mesomorphs were assertive; endomorphs were easy-going, and ectomorphs were introverted, for instance. Those ideas have largely been debunked, but the fundamental physical characteristics have endured with research finding relationships between somatotypes and specific types of sports performance.

On the power and strength end of the spectrum, a 2018 study published in the journal PLoS One found that, among active men, those with mesomorph and ectomorph builds performed better in lower body strength exercises like the back squat and a 30-second max sprint test on a stationary bike. Mesomorphs performed better in upper body strength tests like the bench press.

Overall, the researchers found that about one-third of strength performance could be predicted by the exerciser’s somatotype.

On the cardio endurance side, a study published in the British Journal of Sports Medicine found that, among active men, those who had mesomorph and blended mesomorph-ectomorph builds showed the greatest improvements in aerobic capacity (measured by VO2max) after performing 12 weeks of twice-weekly track interval training sessions compared with other somatotypes.

That doesn't mean people with endomorph builds can’t be fast runners, Sims says. “Being an endomorph does not automatically mean you’re ‘overweight,’” she says. “You can be strong and muscular and fast.”

Many things influence your somatotype, including your genes and ethnicity. Research shows that diet and exercise can influence your somatotype, bringing you closer to one build or another, but there may be a limit to how dramatically you can change your build (especially without a lot of focused effort).

Former Olympic marathoner Ryan Hall, now 37, is a prime example. During the heyday of his running career, at 5-feet, 10-inches, he weighed 127 pounds, but maintaining that weight came with a price of chronically low testosterone and extreme fatigue.

After he retired in early 2016, he ran less, lifted more and put on 38 pounds of muscle in a matter of months, which is a strong indication that he’s naturally more meso than ectomorph. Today, he can deadlift an impressive 455 pounds and though he only runs a little here and there, he could still bang out three miles at a 5:40 pace weighing nearly 40 pounds above his “race weight.”

Ultimately, that’s the goal. To identify your body type and to work with it rather than against it for the healthiest, happiest, and naturally fittest you. Here’s what Sims recommends.

Ectomorph Body Type

You tend to be long limbed and not particularly muscular; can be smaller in size without necessarily having lean body composition.

Ectomorphs are the body type that is the most resistant to weight and muscle gain because of a fast metabolism. People with this body type have little observable body fat, are only lightly muscled, and have a small frame and joints. Long-distance runners often have ectomorph builds because they have less weight to move over the many miles. Your goal might be to optimize your body composition by maintaining healthy muscle tissue to protect your joints and produce power.

»Eating as an ectomorph: Ectomorphs are sometimes more lax about healthy eating because they don’t gain weight easily. But not having visible body fat does not mean you’re healthy or well-fueled. Eat high-quality fats and aim to get 25 to 30 grams of muscle-making protein with every meal, along with good-quality, whole-food carbohydrates to fuel your runs.

»Training as an ectomorph: Your slighter build can leave you susceptible to injuries. With less muscle, you may also lack power to sprint for the finish. When training, focus on power and resistance training to build strength and protective muscle tissue as well as to build bone health.

Mesomorph Body Type

You find it relatively easy to build muscle mass, are medium boned, and generally proportionally built.

Mesomorphs generally lose and gain weight easily and are able to build muscle quickly. This body type tends to have a long torso and shorter limbs. Mesomorphs excel in explosive sports—that is, sports calling for power and speed. The reason for this lies in the type of muscle mesomorphs possess. Mesomorphs have a higher percentage of fast-twitch fibers and will gain muscle mass more quickly than any other body type. It’s common to see triathletes with this build. Your goal is to manage your muscle, so you have what you need to produce power without more than you need weighing you down.

»Eating as a mesomorph: Mesomorphs generally can maintain a healthy body composition by balancing their macronutrients, taking in fairly even amounts of fat, protein, and complex carbohydrates. You can adjust your intake according to training days, taking in more carbohydrates on long endurance days and fewer on shorter and/or easier days.

»Training as a mesomorph: For training, focus on moderate endurance training, high-intensity interval training (HIIT), and plyometrics. If you’re focusing on longer distances like marathons, you can rely on bodyweight training like Pilates to add strength without unwanted muscle.

Endomorph Body Type

You tend to have larger bone structure, have a stockier and/or curvier build, and generally store fat relatively easily.

Endomorphs naturally tend to have curvy, fuller figures. This body type may have a hard time keeping body fat in check and may put on weight easily. You may need to pay attention to details like body glide to avoid chafing and finding supportive, but not constricting attire for maximum comfort on your runs.

»Eating as an endomorph: Because you can put on weight easily, you’ll be better able to optimize your body type by eating fewer carbohydrates outside of training to help control insulin and blood sugar, and focusing on good quality fats and protein. Aim to have breakfast within 45 minutes of waking up to bring down cortisol (which can encourage fat storage). Be careful, too, not to under-eat, which some endomorphs do to try to lose weight—that generally backfires. Instead, focus on fueling your runs with carbs as needed and then focusing on high-quality fats and proteins and getting more of your carbohydrates from vegetables outside of exercise.

»Training as an endomorph: You may find it easier to change your body composition—increasing muscle and decreasing fat—rather than strictly losing weight. Training-wise, along with your regular running, high-intensity activities such as HIIT- and CrossFit-style training are great for fat loss and muscle maintenance. Incorporating more general activity and less sitting time into your day can also boost your generally slower metabolism.


This article has been adapted from ROAR, How to Match Your Food and Fitness to Your Female Physiology for Optimum Performance, Great Health, and a Strong, Lean Body for Life.

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Selene Yeager
“The Fit Chick”
Selene Yeager is a top-selling professional health and fitness writer who lives what she writes as a NASM certified personal trainer, USA Cycling certified coach, Pn1 certified nutrition coach, pro licensed off road racer, and All-American Ironman triathlete.