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The Mechanics of a Stretch: Researchers Work the Kinks Out
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Posted on: 11/30/1999
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Stretch here, stretch there--it seems like everyone's limbering up. On the track and field, stretching is believed by many to enhance performance and prevent injuries. Stretching is even recommended in the workplace, to relieve the tightness that can come from sitting at a desk all day. But how exactly does stretching work? Why does it help most people feel better?
Researchers have long believed that stretching reduces muscle stiffness. But a recent study found that stretching reduces muscle stiffness only briefly--or not at all. Stretching produces a physical sensation. A forceful stretch initially gives a strong sensation of stretching, which soon eases up. When the stretch feeling begins to decrease during the stretch, is there an actual change in muscle stiffness? Or does the feeling let up because the body adapts to the stretch?
These authors studied the effects of a two-week stretching program for the rectus femoris, a muscle on the front of the thigh. The participants were 29 men at a military base in Sweden. They did two supervised stretching programs. One program was for the thigh. The other was for the calf, to act as a comparison. Participants stretched each leg for 80 seconds, four times a week. The flexibility of their thigh muscles was tested before and after each two-week period. The amount of tension they felt in a stretch was also recorded, from "nothing at all" to "extremely strong."
After stretching the thigh for two weeks, participants noted less of a stretch sensation in the muscle. A stretch that was experienced as "strong" before the two-week program was only "somewhat strong" afterwards. Notably, after stretching only the calf for two weeks, the thigh stretch felt just as strong as it had before.
Participants' flexibility didn't change after two weeks of stretching. The authors suspect that the stretching program was not intense enough to change muscle stiffness and range of movement. Also, participants were tested in the same stretch positions each time. But when participants were told to stretch until the feeling was as intense as it had been before they did the stretching program, range of movement actually increased 15 degrees.
The authors conclude that changes in the way a stretch feels are important to how stretching works. The more you stretch, the less stretch sensation you'll have in a stretch over time. Changes in muscle stiffness may come later. This study raises the question of whether stretching works mainly on sensation in a muscle rather than on the physical structure of the muscle.
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References:
Martin Björklund, PT, et al. Sensory Adaptation After a 2-Week Stretching Regimen of the Rectus Femoris Muscle. In Archives of Physical Medicine and Rehabilitation. September 2001. Vol. 82. No. 9. Pp. 1245-1250.
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