All stretches are either passive or active. With passive stretching, you rely on your body weight, gravity or a prop -- such as a strap or stretching device -- to stretch a muscle. In an active stretch, you stretch a muscle by contracting the muscle that performs the opposite function. For example, you would stretch your hamstrings by contracting your quadriceps. There are two types of active stretches: static and dynamic.
In an active-static stretch, you hold the stretch for a period of time, generally between 10 and 30 seconds. For example, you can sit on the floor with your legs straight. Then, flex your ankles and hold the position. Because the muscles on the front of your lower leg contract to flex your ankles, this is an active stretch for your calf muscles. For an active-static hamstring stretch, lie on the floor with your knees bent. Straighten one leg and lift it as close to your torso as possible. Then, hold the position. Your quadriceps contract to produce the hamstring stretch.
In an active-dynamic stretch, you move your muscle through its entire range of motion, without stopping in any position. For example, you can sit on the floor with your legs straight. Then, repeatedly flex and point your ankles. Here you use muscular contractions to produce the movement and stretch your calf muscles as your ankles move through their entire range of motion. For an active-dynamic hamstring stretch, lie on the floor with one knee bent and one knee straight. Repeatedly raise and lower your extended leg. Your quadriceps and hip flexors contract as you lift your leg and stretch your hamstrings.
A study published in the "Clinical Journal of Sports Medicine" found that active stretching produces greater gains in range of motion when compared with passive stretching. Additionally, subjects who followed a program of active stretches better maintained their range of motion after stopping the stretching program. The benefits of active stretching apply to both sports performance and functional movements. Research published in the "American Journal of Physical Medicine and Rehabilitation" indicates that older individuals can significantly improve their functional mobility by performing active stretches.
While active stretching is generally safe -- because you control the intensity of the stretch solely by the force of your own muscular contractions -- you must be able to figure out if the stretch you are doing is actually an active stretch. Pay attention to the role of gravity throughout the movement. Sometimes, gravity and your own body weight produce the stretch even when you think you are contracting the opposing muscular group. If you have questions about a particular stretch and its suitability for your physical condition and exercise goals, consult a personal trainer or other fitness professional.