Discovery News: Why walking is harder for smaller people

A Nov. 15 article on Discovery News cites the research of SMU physiologist and biomechanist Peter Weyand in which he and other scientists found that everyone uses about the same amount of energy when they walk, but short people use more energy over a given distance. The reason: people with shorter legs take more steps to cover the same distance as people with longer legs.

Weyand says the study has clinical applications and weight balance applications. In addition, the military is interested too because metabolic rates influence the physiological status of soldiers in the field, he said.

Read the full story.

Also covering the research is MSNBC with the story Take that, Stretch! Short people burn more calories walking, and UPI, with its story Equation calculates energy cost of walking.

Weyand is an SMU associate professor of applied physiology and biomechanics in the Annette Caldwell Simmons School of Education & Human Development. He led a team of experts in biomechanics and physiology that conducted experiments on Oscar Pistorius, a South African bilateral amputee track athlete. Pistorius has made headlines trying to qualify for races against runners with intact limbs, including the Olympics.

Excerpt:

By Liz Day
Discovery News

Why do children tire more quickly than adults when out for a walk?

Like most people who have had to carry a tired child home after a long walk, Peter Weyand of Southern Methodist University asked himself that same question. Scientists had long recognized that smaller people use more energy per kilogram body mass than larger individuals when walking.

He wanted to know why.

The reason smaller people use more energy is not due to a different gait or a less efficient metabolic rate per stride. The key was something simpler: their height.

Smaller people tire faster because they take more steps to cover the same distance or travel the same steps as taller people. Their strides are shorter.

Weyand teamed up with three other researchers to study the issue. Their findings are published in the Journal of Experimental Biology.

To test the cost of walking, the team measured the metabolic rates of children and adults. Participants ranged from 5 to 32 years old, from 35 to 195 lbs and from 3’6 to a little over 6 feet tall.

The volunteers were filmed walking on treadmills. Their oxygen consumption and carbon dioxide production were measured to gauge their metabolic rate.

The team compared their walks too — measuring their strides, the way they walked, stride durations and the proportion of each stride spent in contact with the ground.

Results showed everyone moved in the exact same way, no matter if they were 4 feet or 6 feet tall. Analysis also found that everyone used the same amount of energy per stride, regardless of height. So, the energy discrepancy was not due to the style of walking.

Finally, the researchers plotted walkers’ heights against their minimum energy expenditure. The results excited them. The walkers’ energy costs were almost perfectly inversely proportional to their heights. Ergo, tall people walk more economically because they have longer strides and take fewer steps to cover the same distance.

Read the full story.

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