Isometrics, muscle lengthening and muscle shortening exercises were studied and compared. While isometrics was the emphasis, the instructions included isotonic, cardio, resiliency and endurance routines. Dynamic Tension exercises are not merely isometrics, since they call for movement. In unweighted isometrics the exerciser uses only themselves for resistance. Maxalding is an exercise system of "muscle control" using a form of isometrics. Flexibility may be increased when isometrics are performed at joint range of motion extremes.