Other than Olympic race walkers, people generally find it more comfortable to run than walk when they start moving at around 2 meters per second about 4.5 miles per hour.
North Carolina State University biomedical engineers Dr. Gregory Sawicki and Dr. Dominic Farris have discovered why: At 2 meters per second, running makes better use of an important calf muscle than walking, and therefore is a much more efficient use of the muscle's and the body's energy.
Published online this week in Proceedings of the National Academy of Sciences, the results stem from a first-of-its-kind study combining ultrasound imaging, high-speed motion-capture techniques and a force-measuring treadmill to examine a key calf muscle and how it behaves when people walk and run.
The study used ultrasound imaging in a unique way: A small ultrasound probe fastened to the back of the leg showed in real time the adjustments made by the muscle as study subjects walked and ran at various speeds.
The high-speed images revealed that the medial gastrocnemius muscle, a major calf muscle that attaches to the Achilles tendon, can be likened to a "clutch" that engages early in the stride, holding one end of the tendon while the body's energy is transferred to stretch it. Later, the Achilles the long, elastic tendon that runs down the back of the lower leg springs into action by releasing the stored energy in a rapid recoil to help move you.
The study showed that the muscle "speeds up," or changes its length more and more rapidly as people walk faster and faster, but in doing so provides less and less power. Working harder and providing less power means less overall muscle efficiency.
When people break into a run at about 2 meters per second, however, the study showed that the muscle "slows down," or changes its length more slowly, providing more power while working less rigorously, thereby increa
|Contact: Mick Kulikowski|
North Carolina State University