Only form of stretching I get is doing very light weight on the exercise I'm performing...but then I'm reading on articles on doggcrapp training and fs7 and they keep mentioning this deep type of stretch is crucial in muscle growth, one in dc training had me confused said to hold 90 pound dumbbells above chest with lungs full of air and lower to the point it hurts for 50 seconds? Wasn't sure anyone do this type of stretching?