Your muscles adapt over time to imposed stresses. This muscular adaptation is specific to the way your muscles are trained; if you target strength or flexibility you will experience gains in these particular areas. There are three types of muscle in the body: Smooth, cardiac and skeletal. Unlike your smooth and cardiac muscles, skeletal muscles are voluntary, and control their contractions. Skeletal muscles are often the focus of muscular adaptation exercise programs because they can be strengthened and shaped through training. Through accurate exercise programming you can elicit specific muscular adaptations.
Strength training using external resistance, like dumbbells, overloads muscles increasing their strength and size in an adaptation called hypertrophy. Hypertrophy occurs when muscles are adequately stressed by the amount of weight lifted or repetitions performed. Training for hypertrophy is typically characterized by lifting heavy weights at low repetitions. To induce hypertrophy work all major muscle groups while lifting a resistance heavy enough to fatigue your muscles in eight to 12 repetitions.
Your ability to perform high repetitions on a sub-maximal load is an adaptation called muscular endurance. Strength training using body weight or light external resistance, like exercise bands, are ways to improve muscular endurance. Muscular endurance can be static or dynamic. Static endurance involves a muscle remaining contracted for an extended time period, such as holding a wall squat. Dynamic endurance involves repeatedly contracting and relaxing a muscle like abdominal crunches. To improve the body's muscular endurance train all major muscle groups in the nine to 25 repetition range.
Muscular power is the product of force and velocity. Power is often associated with sports performance because this adaptation combines strength and speed, such as when throwing a shot put or executing a high jump. Training for muscular power adaptations often involves explosive exercises like plyometrics and might also involve a load to mimic sport conditions. Muscular power should be increased slowly with a training prescription appropriate for your level and goal. The training should be specific to the power systems you are looking to improve, such as deep knee bend jumps to increase your vertical leap.
Muscular flexibility is measured by your capacity to move a joint through its full range of motion. Adaptations in muscular flexibility help maintain healthy joint motion and may also improve sports performance and decrease injury risk. Muscular flexibility training requires stretching all major muscle groups following a sufficient warm-up. Flexibility training should help create balance in your range of motion so that both sides of the body are equally flexible. Stretches should be held for at least 30 seconds at the point of pain-free tension.