Why do we move more slowly as we get older?

A new study by engineers from the University of Colorado Boulder helps explain why we tend to move slower as we get older.

This work is among the first studies to empirically explain the reasons why those over 65 do not move as quickly as they used to.

The researchers reported that older people may move slower, at least in part, because it costs them more energy than younger people.

The researchers discovered that older people seem to modify their movements under certain conditions to conserve their limited energy supply.

The findings could one day give doctors new tools to diagnose a range of diseases, including Parkinson's disease, multiple sclerosis, and even depression and schizophrenia, said Alaa Ahmed, a professor in the Paul M. Rady Department of Mechanical Engineering and a co-author of the study.

During the study, the researchers asked participants aged 18 to 35 and 66 to 87 years to complete a deceptively simple task: reach a target on a screen, somewhat similar to a video game on the Nintendo Wii.

The researchers discovered that older people seem to modify their movements under certain conditions to conserve their limited energy supply.

“All of us, whether young or old, are driven by nature to obtain the greatest amount of reward from our environment while minimizing the amount of effort it takes to do so,” said Eric Summerside, co-lead author of the new study who received his doctorate in mechanical engineering from the University of Colorado Boulder in 2018. "With that."

Using geometry to understand the brain

Alaa said that researchers have known for a long time that older people tend to be slower because their movements are less stable and precise. But other factors can also play a role in this essential part of growth.

The study explored two hypotheses about why older people move more slowly. The first suggests that older people's muscles may work less efficiently, burning more calories while completing the same tasks as younger adults. The second is that aging may change the reward circuitry in the human brain, as people produce less dopamine, a brain chemical responsible for providing feelings of satisfaction.

During the experiment, participants used a robotic arm to move a cursor toward a target on a computer screen. If they succeed, they will receive a small reward.

All participants ages 18 to 35, and those ages 66 to 87, reached their goals sooner when they knew they would receive a reward, by about 4% to 5% compared to trials without the reward. But they also achieved this goal in different ways.

Younger adults moved the robotic arms faster toward the reward, while older adults mainly improved their reaction times.

When the researchers added a weight of about 3.5 kilograms to the robotic arm of the younger participants, the differences between the two age groups disappeared, indicating that the brain detects small changes in energy use and adjusts the movements accordingly.

The results indicate that the costs of effort to reach the goal during the experiment appear to be the decisive factor in slowing down the movement of older adults.

While the study cannot completely rule out the brain's reward centers as the cause, Dr. Alaa noted that if researchers can determine where and how these changes appear in the body, they may be able to develop treatments to reduce the effects of aging and related diseases.