It’s frustrating, but as we hit middle age and beyond, even simple movements feel harder. We often feel sluggish and find ourselves mentally budgeting energy before basic actions, like moving a stool or climbing a few extra stairs.
A team at the University of Colorado Boulder, led by biomedical engineering professor Alaa Ahmed, set out to investigate why. The researchers wanted to understand the neural basis of those changes.
The scientists divided participants into two groups. The first group consisted of individuals aged 18 to 35, while the second group included those aged 66 to 87. The team asked all volunteers to complete a simple task: reach for a specific target on a screen. During the task, the researchers measured each response’s reaction time and the amount of energy expended, or metabolic cost.
The researchers found that older participants required more energy than younger ones to perform the same action.
When the researchers offered a reward, both groups reached the target about 5 percent faster than in unrewarded trials. But they did so in different ways.
Younger participants moved their hands more vigorously and quickly toward the reward, while older participants mainly improved by shortening their reaction times. When the team added weight to the younger volunteers’ arms, those differences disappeared — the younger group stopped moving their hands faster and instead improved their reaction times.
Why Do Scientists Need This Knowledge?
The findings were published in the journal JNeurosci. It’s one of the first experiments to pinpoint why older adults (over 65) move more slowly than younger people.
The researchers quantitatively measured the metabolic energy cost of reaching the target. They found that reaching the target required more metabolic energy for older adults.
Robert Kurter, a co-author of the study, said, “The brain can detect very small changes in how much energy the body is using and adjust our movements accordingly. Even when their arms were weighted, a quicker reaction became a more energy-efficient option for getting the reward, which led younger participants to mimic older adults.”
These results could provide doctors with new tools for diagnosing a range of age-related diseases, Ahmed said.
