Recently watched this video by Jordan: https://youtu.be/OP4zPT45Ghk?si=WO1HwHTValIVRUPv
At around 6:04 you speak about motor unit loss with age, although you went over it pretty quick, so I had a few more questions.
Is this loss of motor unit inevitable or can it be delayed into late life?
If it is inevitable, you do say that this loss does not seem to cause much issue as long as a nearby motor unit can rescue the disconnected muscle fiber but also “when the rescue can no longer keep up with the losses muscle and strength suffer”. Is the rescue not being able to keep up with the losses factor also inevitable? If so, when does this typically happen? What’s the point at which loss of overall motor units is too much to keep up with for nearby motor units?
You mention that in autopsies people 75 and older have 30% less motor units than younger people. Does the decline begin close to 75 or does it start much earlier in life but only gets to 30% by 75?
And finally, if someone has lost motor units or nerves, can they reverse this and get it back again just like you can reverse loss of muscle mass, or is it irreversible once it’s gone?
We don’t really know if it can be 100% stopped, as it really hasn’t been investigated with long term observational studies in those who lift vs those who don’t. I think it’s likely that activity (specifically lifting) attenuates motor unit loss, but I think it’s unlikely that it can be 100% avoided forever.
I suspect this is somewhat inevitable, though to what degree it’s going to happen “no matter what”, I can’t speak confidently on. I suspect humans vary widely due to genetics, activity levels, and other factors. Conceptually, when the rescue can no longer keep up with the rate of loss, a person will lose active muscle fibers.
Motor unit loss starts much earlier…perhaps in the 3rd decade of life, though this isn’t well established. There’s some normal turnover here too.
The lost motor units are gone, but existing muscle tissue can improve function with training at nearly any age.
3rd decade, that’s the 20’s right? Why do most strength athletes typically peak in their 30’s then? Is this the point where motor units are declining but nearby surviving one’s are able to rescue the disconnected muscle fiber and keep up with the losses, thus muscle and strength is largely unaffected like you mentioned?
Yes. I think it’s important to distinguish between 3 things: 1) normal turnover/refinement of motor units, 2) loss with disuse, vs 3) rescue and improvement in function with training. We don’t know much about normal turnover/refinement and/or longitudinal changes from ages ~20 to 40.
One might wonder why I didn’t spend too much time on this in the video. Between little definitive data on the topic and overall lack of importance in management (until I get good at pharmaceutical r/d), I didn’t want to focus on this.
Hmm interesting. If a powerlifter begins/continues training from let’s say 20 and maintains their strength until 50, would it be correct to assume this person still has similar amounts of motor units or rescue at 50 to what they did as when they were much younger? Or have they lost MUs and rescue capacity like everyone else but are able to maintain strength through some other mechanism?
Just trying to figure out how important MUs are for performance or if it’s even something worth worrying about since you say they typically lack importance in management.
I would hope they would get much stronger during this 30 year training period, wouldn’t you? I would predict their strength would peak in powerlifting before 40, though individuals will vary and there are a lot of other factors going on here.
We don’t really know for sure. I’d suspect they would have the same amount of muscle fibers and that these muscle fibers are larger than when they started training.
A motor unit is the motor nerve and all the muscle fibers it supplies. By definition, they are very important. As far as what we can do to improve performance, we can’t add more motor units or more muscle fibers really, but we can make the stuff we have work better and grow. That is what I would focus on rather than preserving motor units per se’, though training should reduce the loss of motor units over time.
From a practical application perspective, I never worry about motor units when it comes to program design.
Haha, that is what I meant, sorry if it was unclear. I meant them maintaning their peak until 50, not that they already peaked at 20 and maintained until 50. If I were to give an example of what I meant then someone like Jennifer Thompson would likely do it. Was asking if someone in her situation would have the same amounts of MUs as they did at 20.
I see, so I guess it isn’t unreasonable to assume someone still has all or most of their motor units if they are not getting weaker, even if they are older, but as you say I guess we can’t be sure. Thank you for your answers.
Probably! Again, we don’t really know as we’d have to test someone before and after training, then longitudinally reassess. To my knowledge, this has not been done in a barbell sport athlete.
Even if they are weaker, they still may have the same number of motor units. It’s a fine question you ask, but as I mentioned a few times, not a ton of solid answers on specifics pertinent to you (or me).
It’s a solid question from an academic perspective, though I don’t think the answer would change what we do in practice.
What would cause them to get weaker if they are still maintaining motor units and muscle fibers? Just simply lack of motivation and other environmental factors?
Not necessarily. as this assumes continued exercise. Changes in excitation-contraction coupling, changes to the muscle fibers themselves, energy liberation, central nervous system efficiency, and so on are all possible mechanisms.
