American Council on Exercise by American Council on Exercise

Last Updated October 20, 2023 (originally published October 3, 2014) 

Humans come in all shapes and sizes, so it’s only natural to think that different eating plans and training regimens would be more appropriate or effective for people with different body types. Unfortunately, that notion has led to the proliferation of countless long-lasting misconceptions in the fitness industry.  

Let’s start at the beginning: Discussions of somatotypes (the scientific term for human body types) are often centered on a notion that all people can be categorized into one of three distinct body typesectomorph, mesomorph and endomorph—and that somatotyping can be used to make generalizations about how a person should exercise, eat, live and perform physical activity. The reality is that a person's somatotype attributes can transform over time and people are often a combination of all three somatotypes.  

To be clear, the three somatotypes described below have been described in scientific literature, but the placement of a person within a specific category is more complex than one might think. Making the jump from somatotyping to exercise recommendations and dietary considerations often leads to the dissemination of misinformation. This leads to myth making.   

Here is a quick description of the three somatotypes: 

  • Ectomorph: Characterized by a slim body frame, small shoulders and hips, long arms and legs, and less muscle mass 

  • Mesomorph: Characterized by a medium build with higher-than-average muscular development, a low body-fat percentage, broad shoulders, and a muscular chest, shoulders and limbs. 

  • Endomorph: Characterized by a larger, rounder body shape, high levels of body fat, a propensity to gain weight, and shorter arms and legs. 

Common Myths about Ectomorphs 

The following are some common myths that you may hear from clients or potential clients or read about in popular media. Your job is to sift through these types of statements and look for the evidence—which, in this case, you will not find. 

  • Only those with an ectomorph body type can easily gain muscle. The truth is that you cannot tell how someone is going to respond to training simply by looking at their present shape and body composition 

  • Individuals who have an ectomorph body type should perform fewer reps with heavier weights. This is based on the assumption that these individuals want—or should want—to gain muscle mass and increase their overall weight. A client’s approach to training reps, intensity and volume ought to be dictated by their goals and their responses to training, not their appearance. 

  • People with an ectomorph body type (and the other body types) should eat certain foods while avoiding others. The best approach to nutrition is to find a healthy eating plan that the client can stick to over the long haul. There are no hard and fast rules. And, the negatively worded guidance to avoid a favorite or preferred food is not likely to lead to success. 

  • People with an ectomorph body type have more self-control than the other body types, particularly endomorphs. Never assume that self-control lies at the heart of a person’s nutrition or physical-activity habits, or their appearance. Everyone’s personal experiences are unique and it’s your role as the professional to unravel that history and empower the client to make the behavioral changes they seek. 

  • A person with an ectomorph body type can, and should be encouraged to, eat as many calories as they want, especially if they exercise. Again, this is based on the assumption that these folks want or need to gain weight. Nutrient density and a balanced diet are important for everyone, no matter their body type. 

  • People with ectomorph body types can train less often because of their biological advantages. Because they are slender and less prone to gaining fat mass, people sometimes believe that ectomorphs don’t “need” exercise as much as others, but there are plenty of benefits to physical activity that have nothing to do with appearance. 

A Controversial History 

The three somatotype classifications were first popularized in the 1940s by Dr. W.H. Sheldon—a psychologist—who wrote about them in his book The Varieties of Human Physique. Dr. Sheldon sought to classify people by how much they conformed to those three body types, and then to connect those body types to things like temperament and criminal tendencies.   

While Dr. Sheldon’s work on constitutional psychology was controversial, it unfortunately has had a lasting impact on physical education and the fitness industry. Categorizing people in this way strips away the concept of personalized coaching and programming that lies at the core of being an effective health coach or exercise professional. Making decisions about a person based only on their body type also lends itself to racial and cultural stereotyping. If a particular race tends to be more endomorphic, and there are traits erroneously attributed to people who have high levels of body fat (e.g., laziness, selfishness and a lack of self-control), then the logical extension is to believe that people of that race naturally have those traits. 

This is a great example of an implicit bias that all health coaches and exercise professionals should work to identify and address in the work that they do. Unfortunately, people do often attribute personality traits to the three body types and tend to hold favorable stereotypes of mesomorphs and ectomorphs and negative stereotypes of endomorphs. 

Final Thoughts 

Somatotyping should not take the place of an individualized and client-centered approach to behavior change, as it will not indicate exactly how a person will respond to diet and exercise, and certainly nothing at all about their personality, temperament or self-control 

A person’s appearance alone should not dictate their balance of macronutrients, how many reps they should perform in a resistance-training set or what their goals should be. Instead, let each client’s goals and values be the driving forces behind your programming and approach to behavior change and long-term adherence. Your goal as a health coach or exercise professional is to offer a personalized plan for each client. Making assumptions about people using broad strokes and a lack of evidence will only stand in the way of that. 

Check out this course to explore how you can identify and address your implicit biases and strengthen your communication skills: Taking Action with ACE: Practicing Equity, Diversity and Inclusion as a Health and Fitness Professional?(worth 0.3 ACE CECs).