To measure effectiveness of resistance training
See how it affects muscle soreness. If you are sore you did enough. If not sore, you did not do enough. Even if you didn't feel sore, can measure blood to see mudcle damage. Creatine kinase, when in blood stream, muscle cells have been damaged. Meausre conc. of CK to measure muscle damage. Troponin I which is part of sarcomeare in muscle also can be tested to see if damage.