Ever wonder if different body types respond differently to exercise training?
In simplistic terms, humans come in 3 basic body types: Endomorphs (round types with higher body fat, less muscle), Mesomorphs (square body types typically with lots of muscle), and ectomorphs (skinny body types who have little muscle or fat).
And it turns out that body type can predict the response to exercise training. Van Etten, Verstappen and Westerterp  reported significant increases in fat-free mass for a mesomorphic group after 12 weeks of resistance training, whereas an ectomorphic (skinny) group recorded no significant differences having followed an identical training routine.
Therefore, it appears that those who are naturally lean and muscular to start with, can gain strength and size to a much greater degree than naturally ‘skinny’ individuals.
This is important because persons such as weightlifting or bodybuilding champions with impressive strength or size most likely have the very good genetic pre- disposition for building muscle. And these genetically gifted often work as coaches and personal trainers, and often rely on their experiences that yielded positive results for them, personally. However, anyone with less suitable genetics will almost certainly not attain the same levels of muscular strength or size regardless of training program.
What this means is that we must take body type into consideration when designing and exercise program, and have realistic expectations of just how our body will respond to training.
 Van Etten LMLA, Verstappen FTJ, Westerterp KR. Effect of body build on weight-training-induced adaptations in body composition and muscular strength. Med Sci Sports Exerc 1994; 26: 515-21.