Motor units recruited per exercise and muscular development

[milk farts]

Why is it that the encouragement of muscular development is a function of both motor units recruited per exercise and motor units recruited per workout rather than only the latter?

My two guesses:
1) Exercises that recruit a greater number of motor units are better at training the body to recruit even more motor units next workout
2) Exercises that recruit a greater number of motor units trigger a greater release of muscle developing hormones by the body

Eh?

[Mark Rippetoe]

I don't know.

[JLascek]

Our Docs on staff can correct me if I'm wrong, but it is primarily the breakdown of muscle fibers that induces the hormonal response that repairs the damage from training instead of how many motor units were recruited to do so.

Rip, it seems like a simple answer to his weird question is that muscular development is a function of the muscle fibers getting stronger (especially for our purposes here). I haven't thought in terms of muscle fibers recruited in a work out, unless you just mean the musculature involved in the training session. In any case, more motor units recruited means increases in strength, which means more muscular development.

Eh?

[Mark Rippetoe]

Fuck, I guess so. Maybe Dr. Kilgore is interested enough in a theoretical internet physiology question to answer. Maybe I'll ask him if I see him. Meanwhile, I'll just ponder the significance of the difference between using my motor units in an exercise and using them in a workout that probably consists of exercises.

[milk farts]

Suppose Workout A and Workout B recruit the same number of motor units throughout the course of the workouts and put equal strain on the same muscles (that is, each muscle fiber is stressed in exactly the same way in both workouts), but Workout A uses fewer exercises and thus involves a greater number of motor units to be recruited per exercise. I presume this scenario could be achieved if Workout A worked a number of muscles in compound exercises that Workout B worked separately in isolation exercises.

What is the physiological explanation for the muscle fibers getting stronger as a result of Workout A?

(Then again, perhaps when muscle fibers are stressed in compound exercises as compared to the corresponding isolation exercises they cannot possibly be stressed in exactly the same way, in which case an explanation of why such a difference exists would provide the knowledge I am seeking.)

[eh9]

Why is it that the encouragement of muscular development is a function of both motor units recruited per exercise and motor units recruited per workout rather than only the latter?There are two kinds of adaptation: one in the muscle and another in the nervous system. Recruitment of motor units is neural process, and the adaptive stimulus for greater recruitment is different from that for the muscle.

[Mark Rippetoe]

This looks like a question for the Supertraining board.

[eh9]

Workout A uses fewer exercises and thus involves a greater number of motor units to be recruited per exercise. [...] What is the physiological explanation for the muscle fibers getting stronger as a result of Workout A?Specificity of adaption would seem to explain this just fine. If a motor unit does not fire during an exercise, the muscle fibers in the group are not stressed, and thus don't adapt. So if you exercise in such a way to recruit more motor units, you get adaptation in more muscle fibers. I've come to understand that this is one of the key benefits of fast lifts, that by their nature recruit more motor units for an explosive action. As a result, more muscle fibers adapt. The brain, however, seems to adapt as well, habitually recruiting more muscle units, helping future exercise to stress a greater fraction of the muscle fibers, and to do so habitually.

[JLascek]

(Then again, perhaps when muscle fibers are stressed in compound exercises as compared to the corresponding isolation exercises they cannot possibly be stressed in exactly the same way, in which case an explanation of why such a difference exists would provide the knowledge I am seeking.)

How could they be? You can't assume that they are when evidence shows they are not.

[milk farts]

Thanks for the responses so far. Since I'm asking the question I'm naturally in a position of ignorance so I'm going to try to avoid going on as though I know what I'm talking about. Though I would like to attempt to clarify my question and perhaps reveal any faulty premises that I hold to be true.


Specificity of adaption would seem to explain this just fine. If a motor unit does not fire during an exercise, the muscle fibers in the group are not stressed, and thus don't adapt. So if you exercise in such a way to recruit more motor units, you get adaptation in more muscle fibers. I've come to understand that this is one of the key benefits of fast lifts, that by their nature recruit more motor units for an explosive action. As a result, more muscle fibers adapt. The brain, however, seems to adapt as well, habitually recruiting more muscle units, helping future exercise to stress a greater fraction of the muscle fibers, and to do so habitually.

The same motor units are recruited and the same muscle fibers are stressed in both of my hypothetical workouts, it is just that fewer exercises are used to accomplish this in Workout A. For example, Workout A might work quadriceps and hamstrings together in the same exercise, but Workout B works these muscles separately in two different exercises. So more motor units are not recruited throughout the course of the Workout A, but more motor units are recruited per exercise. Why does Workout A result in a greater adaptation?


How could they be? You can't assume that they are when evidence shows they are not.

You have in mind the knowledge that can erase my ignorance forever and you tease me like this?! To someone like yourself I am sure the evidence of which you are speaking is so obvious that it need not be said, but to an ignorant fool such as myself this evidence could be enlightening indeed! Please JLascek, share your knowledge with me!

[Mark Rippetoe]

Troll? Big influx of these recently.