Shedding Light on an Age-Old Problem: Researchers Probe Muscle Function Decline in Older Adults

With age, we often get smarter and wiser. Unfortunately, it is also true that the older we get, the more we are prone to slips and falls — and the debilitating injuries that can result.  

Generating movement quickly is crucial in those first few milliseconds after a slip or trip, so that we can catch ourselves before injury occurs. But around the age of 40, our muscles’ ability to produce force quickly, or rate of force development (RFD), begins to decline, and continues to decrease as we age.   

While it is well established that loss of muscle mass, stiffness, and changes to the nervous system all affect our ability to use our muscles as we age, very little is known about what is actually happening to individual muscle cells, and how this contributes to the decrease in RFD. 

Researchers in the Department of Human Health and Nutritional Sciences are working to change that. 

In a recent publication in the European Journal of Applied Physiology, graduate students Benjamin Dalton and Nicole Mazara, along with their supervisor Dr. Geoff Power, examined the age-related changes that occur in our muscles’ contraction machinery and found that the answer is likely to be more complicated than expected. 

For years, it has been assumed that there is a relationship between the contractile properties of single muscle fibres (cells) and whole-muscle RFD, but this has yet to be studied directly. 

“Our goal was to see if we could explain age-related reductions in strength and physical function by looking at mechanisms at the single fibre level,” explains Dalton. 

Using a new technique to isolate individual muscle cells, the researchers zeroed in on single muscle fibres collected and isolated from the quadriceps of both older (~ 70 years old) and younger males (~26 years old). They tested each cell’s RFD, and then compared this measurement to the RFD of the knee joint, which represents the full muscle RFD.

The researchers found only weak evidence of a potential relationship between the RFD in single muscle fibres and the knee joints in older adults.  And in younger adults, single fibre RFD values were completely unrelated to joint-level RFDs. 

The lack of a clear relationship between single and whole muscle RFD across age groups was unexpected.    

“What we’ve been assuming didn’t come to fruition when we tested it,” says Dalton. “But we now have a better understanding of what is going on, which will help direct future research.”   

More specifically, says Dalton, future studies can now go on to investigate other targets that may contribute to the muscle weakness associated with aging.

Dalton also highlights the need to explore sex differences in the mechanisms of muscle decline as well, since it is already known that muscle kinetics in females suffer greater age-related impairments than males.

So what can the rest of us do in the meantime while the research community continues to tackle this complex topic?

“Keep moving,” Dalton advises. “If people are worried about maintaining muscle function as they age, the most important thing is to keep exercising. Your function will be somewhat maintained, no matter how it is happening at the mechanistic level.” 

This study was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC). 

Read the full study in the European Journal of Applied Physiology. 

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