Which muscle group has the largest increase in circumference when contracted? why do you think this occurred?

The muscle group that has the largest size in circumference when it contracts is the quadriceps femoris which is a skeletal muscle. It is compose of 4 parts namely the rectus femoris, vastus lateralis, vastus interomedialis and vastus medialis. It contracts because of the nerve supply from the precentral gyrus which is in the motor area of the brain. The nerve then goes to the quadriceps femoris and then to the rectus femoris then it contracts and extends the knee and flexes the thigh of the hip.