You are more likely to make a mistake. Stomach and back exercises can be done daily because of the nature of the muscles involved, Warner said. Building these requires a routine of sit-ups and crunches for the stomach and back extensions for the lower back. Exercises that build the larger lower-body muscles, the quadriceps and the hamstrings, should be done every three days or so, and by slowly building up resistance. The hamstrings and the quads are the opposing strengths around the knee joint.
Most people overdevelop the quads and ignore the hamstrings.
To start, do 15 to 30 repetitions with light weight to build endurance. The muscles will adjust to the exercises after about two weeks. After the adjustment period, Warner suggests adding dumbells or a weight belt during the exercises to increase strength. After another two weeks, and a noticeable increase in ability, Warner said speeding up the exercises will boost muscle power and recovery ability. Getting into a routine like this early helps people stay in their sport longer.