As we age, it’s a common observation that our movements become slower. A recent study led by researchers at the University of Colorado Boulder sheds light on this phenomenon, revealing that older adults may move more cautiously due to increased energy costs and altered brain reward responses.
The research, published in The Journal of Neuroscience, is among the first to experimentally investigate the reasons behind the slower movements in older adults. The team discovered that older individuals modify their motions to conserve energy, particularly when faced with challenging tasks.
This finding could potentially aid in diagnosing various conditions, such as Parkinson’s disease, multiple sclerosis, depression, and schizophrenia, according to co-author Alaa Ahmed, a professor in the Paul M. Rady Department of Mechanical Engineering.
Ahmed explained that understanding the neural basis of how we move, from simple tasks like reaching to more complex ones like walking and talking, is crucial for aging research and Parkinson’s disease studies.
To conduct the study, the researchers asked participants aged between 18 and 35 and 66 to 87 to complete a seemingly straightforward task: reaching for a target on a screen. By analyzing the patterns of these reaches, the researchers identified that older adults adjusted their movements to save energy under certain circumstances.
Both young and old individuals are driven to maximize rewards while minimizing effort, said Erik Summerside, a co-lead author of the study. However, older adults may have less efficient muscles, requiring more energy to perform the same tasks as younger adults. Alternatively, aging could impact the reward circuitry in the human brain, leading to reduced motivation to move.
To explore this further, the researchers asked participants to grab the handle of a robotic arm, which controlled the cursor on a computer screen. The subjects reached forward, aiming for a target. If they reached the target, they received a reward. Sometimes, the targets would explode, granting additional points and a ‘bing bing’ sound.
The younger adults moved their arms faster towards the reward when they knew they would hear the ‘bing bing’ sound. In contrast, older adults improved their reaction times, starting their reaches about 17 milliseconds earlier on average. When the researchers added an 8-pound weight to the robotic arm for the younger subjects, the differences between the two groups disappeared.
The brain appears to detect even minor changes in energy usage and adjusts our movements accordingly, said Robert Courter, a co-lead author of the study. When moving with just a few extra pounds, reacting quicker became the more energy-efficient option for young adults, causing them to mimic the older adults’ behavior.
The study suggests that older adults’ slower movements may be due to the increased effort costs of reaching, according to Ahmed. However, the research doesn’t entirely rule out the brain’s reward centers as a contributing factor. By identifying where and how these changes originate within the body, scientists may develop treatments to mitigate the effects of aging and related diseases.