Decline, decrease, deteriorate—all words associated with the aging process. Preventing “D” words is important to keep older people healthy. The loss of muscle is one of the most obvious age-related decreases we experience. Bulky muscles on a person that lifts a lot of weights or the sleek tone of a person that runs a lot of miles shows you that muscles of young people are amazing in their ability to change with the demands put on them. Scientists call this ability to change “plasticity.” When and why does muscle plasticity decline?
As individuals age, large muscle fibers that allow explosive types of movements, such as jumping or lifting a heavy weight, disappear more than small muscle fibers that allow slow, low-force movements such as grabbing a cup or adjusting posture. A recent Journal of Applied Physiology podcast discusses a research article that looked at small, medium and large muscle fibers from a group of subjects who were ages 87 to 90. At this age a substantial decline in strength is expected. However, the study showed that even though large muscle fibers are lost in old age, medium-sized muscle fibers become very strong for their size to compensate for that loss. The amount of force the medium-sized fibers could generate for their size was greater than muscle fibers from a group of young subjects and was similar to a world-class sprinting athlete. Therefore, the medium-sized fibers in the muscle of a very old group of subjects were plastic and adapted to the loss of bigger more explosive muscle fibers.
Future research is needed to determine if this plasticity is apparent in all old individuals or whether it was unique to this group that was still fairly active. Also, it is still unknown why some types of fibers keep this plasticity and others do not. Although older muscle does decline, decrease and deteriorate, plasticity appears to remain, which provides an interesting avenue to prevent the “D” words.
Benjamin Miller, PhD, is an associate professor in the department of Health and Exercise Science at Colorado State University. He co-directs the Translational Research in Aging and Chronic Disease (TRACD) Laboratory with Karyn Hamilton, PhD.