1. Time consuming- the stretch reflex will cause the stretched muscle to contract therefore requiring a prolonged hold time to allow for the muscle to habituate and relax before the lengthening can occur. This typically takes 20-30 seconds for 1 repetition.
2. Reduced blood flow- therefore decreased oxygen and nutrients to the stretched muscle during a prolonged hold. This can lead to muscle soreness.
3. No education- the muscle may lengthen, but will progressively lose the length over time. With dynamic stretching, the agonist (contracting) muscle is learning to move through new ROM and the antagonist (stretching) is learning to allow the new ROM. The active component provides the needed education for lasting results. A recent study comparing active stretching and static stretching on hamstring flexibility yielded interesting results. The study used active knee extension ROM to determine hamstring flexibility. After 3 weeks of stretching, the active stretching participants showed improvements that almost doubled the passive participants. By the end of 6 weeks, the passive participants caught up slightly, but were still significantly less. This shows active stretching gains occur more quickly. The most interesting finding was in the maintenance of the ROM. The stretching was stopped and the participants were retested at 4 weeks. The passive group lost almost all the gained ROM while the active group only lost about 25%.
Active Isolated Stretching is one very effective type of active stretching that uses a 2-second hold time allowing for more repetitions, maintenance of blood flow and neuro re-education.