According to MedicineNet, muscles respond to exercise through contraction and resistance, both of which eventually result in increased muscular strength. Neural impulses direct fibers to contract, resulting in voluntary exercise. There are three different types of muscles that are worked during exercise, including skeletal, smooth and cardiac muscle, and each one responds differently to physical exercise.
MedicineNet notes that skeletal muscles respond to exercise through voluntary stimuli, while smooth and cardiac muscle respond to exercise involuntarily at the same time. BuiltLean.com explains that all of the skeletal muscles in the body contract upon receiving electrical signals from motor neurons within the brain. Once these signals are sent, the muscles respond by contracting as they do during a lift or other exercise movement.
These responses occur when the sarcoplasmic reticulum within the cells of skeletal muscles is triggered by the neural impulse. According to MedicineNet, the fiber that make up the muscle tissue shortens once a signal is received from the brain telling it to retract. Over time, the muscles become more adept at reading these signals and contracting, improving their response rate to exercise. BuiltLean.com explains that this process is often referred to as muscle strengthening and increased muscle endurance.