We’ve all had that male friend who got really into CrossFit and then got really skinny. CrossFit guys lift weight like crazy, so what’s the deal? It turns out that consistently training so hard that you end each workout in a puddle of sweat (sometimes not your own) is a good way to kill any gains in hypertrophy.
Scientists in Brazil took muscle tissue samples from a group of weight trainers pre- and post-workout. They found that muscle soreness and high levels of creatine kinase (a sign of muscle damage) created an environment where muscles would not grow. Only when the subjects adapted to the exercise and were not plagued by insane soreness, did the strength training begin to stimulate growth again. Sometimes leaving a little bit in the gas tank can take you closer to your goals.