Prefer Jogging to Walking Fast

Prefer Jogging to Walking Fast
Walking fast tends to get uncomfortable beyond a speed – about 4.5 miles per hour, or 2mt per second - prompting us to break into a jog. Now scientist have an explanation for it.

North Carolina State University biomedical engineers Dr. Gregory Sawicki and Dr. Dominic Farris have discovered that 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 study combined 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 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 increasing its efficiency.

The finding sheds light on why speed walking is generally confined to the Olympics: muscles must work too inefficiently to speed walk, so the body turns to running in order to increase efficiency and comfort, and to conserve energy.

The research could help inform the best ways of building assistive or prosthetic devices for humans, or help strength and conditioning professionals assist people who have had spinal-cord injury or a stroke, Sawicki and Farris say.

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