Clarification on explosiveness

[adamanderson]

Coach,

A muscle is made up of fibers. Every fiber is capable of producing some amount of force. Force is what moves (accelerates) things, like your limbs, that in turn move (accelerate) weights.

Everyone can get stronger; we can create more fibers + program our bodies to activate a greater percentage of them simultaneously.

Now, explosiveness is largely genetic. We all have a limit as to how quickly we can produce force. This is seen in the fact that a better squat will not greatly improve ones vertical jump. It's a short motion that takes little time, so the added strength will not help, i.e. the small amount of time that the movement takes doesn't allow for all that new force production ability (strength) to be used.

... what I don't get is this: every fiber produces some amount of force in a certain amount of time. If a muscle has 10 fibers that produce 1 unit of force each per 1 second. How come that, if we double the thickness i.e. amount of fibers, and we now have 20 fibers in that muscle that all produce 1 unit of force each per 1 second .. how come we are NOT now two times as explosive? Say the jump takes .3s to do (not counting airborne time of course), why aren't we propelling our bodies into the air with twice the force as before? I know we aren't, but what are the mechanics here? I know we're genetically limited in how much force we can produce in those .3s, and that going from a 220 to a 700 squat won't make our VJ 700/220=3.18 times better (we'd have to account for the weight of the added muscle mass, but, that can't be the only reason) ... I don't understand why. What am I missing? Why does the force production per time unit ability that we possess, not increase linearly with force production ability?

[Mark Rippetoe]

Because 1. when the fiber doubles in thickness, it's still just one fiber, hooked up to the same nerve within the same motor unit. And 2. the force produced is only acting against the force of gravity on your bodyweight, an insignificant amount of force for a 700 squatter to produce. The number of motor units in recruitment is the key -- you have not used the term "motor unit", and I don't think you understand the concept.

Practical Programming for Strength Training | The Aasgaard Company

[adamanderson]

I looked it up and think I understand it now.

But a thicker fiber = more force, right? If the same number of fibers are recruited in the movement as before, and the fibers have doubled in thickness, wouldn't that still produce twice the force in whatever amount of time the contraction takes? ... OR ... this is my alternative guess: No. The fiber is capable of producing twice the force now, however, it takes twice the time, and therefore a heavy squat, which is slow, gets better, but the jump, doesn't?

And on point 2 ... I think what you mean is that a genetically explosive person, is explosive, because he recruits fibers more easily i.e. he needs less external resistance to activate more fibers and --> he produces more force per time?

Summary: A fiber's thickness corresponds to the force it can produce, but the thicker i.e. stronger a fiber is, the more time it takes for that fiber to max out on its force and a jump takes so little time that it never gets to use all of the fiber's potential force ... AND ... what therefore matters in "explosiveness" is # of motor units in recruitment, because obviously the more fibers that are activated, the greater the sum of the forces, even if every fiber only uses 10% of their max force ... also, I'm guessing that fast twitch fiber percentage would make a difference, because they get closer to their max force potential in less time, like during the jump motion.

[adamanderson]

I made a comment before this one and deleted it, I hope it doesnt show up here as it's the same question as this one

I looked it up and think I understand it now, thanks.

I think what you mean is that when a fiber thickens, it does become capable of producing more force(!), however, it also takes longer now for that fiber to reach its max force potential, and the jump motion taking so little time, the added force potential of a single fiber doesn't help, whereas it does in the squat cuz the squat takes more time to complete? So therefore what makes a difference is # motor units in recruitment, because obviously the sum of the forces from more fibers is greater?

On point 2 ... Do you mean that what makes a person explosive, is that they activate more fibers more easily, like from the small force of gravity on their bw?

Lastly, I would guess that the ratio of fast twitch fibers also matters, because they get closer to their max force potential in less time?

[danomite!]

This is good reading for this thread.

Neuromuscular Efficiency for the Strength-Lifter | CJ Gotcher