Your Body Type Should Not Determine How You Work Out

Knowing your body type is supposed to tell you what sort of training and diet program you should adopt. ("If you look like this, then your body type is this, and here’s how you should eat and train.")

Somatotyping—the system of classification of body types—works fine as a way of describing the way someone looks. If you’re thin and tall, you’re an ectomorph. If you’re short and fat, you’re an endomorph. Athletic and muscular, and you’re a mesomorph.

However, the system falls apart when it tries to predict how well your body will respond to training, or prescribe how you should train and eat.

Let’s start out with the first assumption—namely, that knowing your body type can predict how your body will respond to training. If you start out as a tall and skinny ectomorph, for example, you’re supposed to have a hard time building muscle. But is this claim accurate?

It’s true that some people build muscle very quickly when they start lifting weights. Others tend to progress a lot more slowly. In one study, a group of guys lifted weights for 12 weeks, and had their body composition measured at the start and end of the study.

When the researchers looked at the results of the men who built the most muscle (dubbed the "high responders") and those who built the least muscle (the "low responders"), they found roughly four times greater gains in muscle in the high versus the low responders.

To put it another way, you and a friend could follow the same training program and diet for the next three months. But individual variations in the rate of muscular growth mean that he might gain 10 pounds of muscle. You, on the other hand, might gain just half that amount.

In other words, some people respond extremely well to strength training. Some will get “good but not great” results. Others will make progress a lot more slowly.

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However, it’s extremely difficult to tell just by looking at someone how well their muscles will respond to training. That is, the fact that you’re currently skinny doesn’t automatically mean you’ll have a hard time gaining muscle when you start lifting weights.

Some evidence for this comes from a 2018 study published by researchers at Auburn University. A group of men who’d never lifted weights embarked on a training program that involved working out three times a week for 12 weeks. Muscle thickness was measured at the start of the study, and once again at the end.

When the researchers analyzed the results, individuals who started out with less muscle posted the biggest gains in muscle size after 12 weeks of training. In other words, the guys who began the study with the least amount of muscle were the ones who made the fastest progress.

There are people with a low baseline level of muscle mass, but with the potential for rapid growth. Likewise, there are also people with a high baseline level of muscle mass who won’t see the same level of growth when they start lifting weights.

Starting out with an ectomorph body type—tall and skinny—doesn’t automatically mean that you have less potential for growth than other people. In fact, there’s no solid evidence to show that somatotyping has any proven value when it comes to predicting who will be the fast and slow responders to resistance training.

You may well come across various “train right for your body type” articles, which claim to be able to tell you how the three different body types should train. However, there are a couple of problems with the concept of basing your training program on your somatotype.

First, let’s take the example of a guy who looks like a typical endomorph—fat and chunky. He starts lifting weights and goes on a diet. Over a period of time, he loses 30 pounds of fat and gains 15 pounds of muscle.

As a result, he now looks lean, muscular and athletic. So what is he now? A mesomorph? Or is he still an endomorph? Should he change what he’s doing in the gym, and start taking advice geared towards mesomorphs? Or should he carry on training like an endomorph?

Second, you’ll find very little scientific evidence to support any of the common recommendations about how the various body types should train. There is a very good reason for that. And that reason is simple: There isn’t any. Much of the advice is like astrology, in the sense that it’s so generic that it could apply to anyone.

In one article I came across, endomorphs are advised to “combine an intense cardio regime along with a moderate weight-training program,” while mesomorphs are told to “aim for a balanced diet that focuses on lean protein and vegetables.” That sort of advice is interchangeable and can apply to anyone, irrespective of their body type.

There’s no convincing research to show that somatotyping can be used to estimate how quickly you can gain muscle, or has any value when it comes to deciding what your diet and training program should look like.

Are there people who burn lots of calories and have to eat constantly in order to put on weight? Yes. Are there individuals who find it easy to gain weight? Absolutely. Are there people who are naturally strong and muscular? Most definitely. But those facts alone don’t validate the use of somatotyping as a way to predict how an individual will respond to training, or to prescribe how that same individual should train and eat.

You’re far better off dropping the labels, experimenting with different approaches to diet and exercise, and adjusting what you do based on how your body responds.

Christian Finn is a UK-based personal trainer who holds a masters degree in exercise science. He writes frequently about fitness and weight loss on MuscleEvo.

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