# Muscle size and explosivity

Seeing guys like Bruce Lee, there doesn't seem to be any correlation between muscle size and explosive power. Is this correct?

In terms of musculature, how does the body create explosive power?

• It might help if you defined what you mean by explosive power, and how you see it being applied.
– JohnP
Sep 19 '18 at 15:14
• Are you referring to 1" punch kind of stuff, when you say 'explosive power'? Trying to consider the exact context. Powerlifters for example can have explosive power in at least one sense, but are not built like Bruce Lee typically. Sep 21 '18 at 22:25
• Yes, I do mean punching and kicking Sep 21 '18 at 23:46

Physics wise, power is what we're typically talking about here:

That is, how much work can you do (Work = F * D) and how quickly can you do it.

We also know

• Force = mass * acceleration.

Furthermore, we can break up the Power equation to be,

• Power = Force * D/T,

which is,

• Power = Force * Velocity

In other words, we can clearly see force is part of the story, and something perhaps much more intuitive is how much force a muscle can generate is clearly related to how big it is.

So, ASSUMING you can generate more force over the same period of time, then having more muscle size will correlate with producing more power i.e. being more explosive.

A car analogy is often helpful. Throw a bigger engine in the car, it can produce more power.

But, you can't leave the rest of the car alone. At some point, a bigger engine is going to infringe on the limitations of other parts of the car. Maybe you need bigger bolts on the wheels. Or a bigger exhaust. Or a driver with less fear of pressing the pedal. I'm no auto expert, but I think you get the idea. You can't treat the entity as only one part.

This is where biology laughs at classical physics. It's just never straight forward. You simply can't tell someone "get more muscle" and assume they'll be more explosive.

Most obviously, a lot of people who try to gain muscle also gain a lot of fat. If they gain more weight than they gain power, their power to weight ratio would go down. They may very well end up slower! (And this is why drugs are so prevalent at extreme levels of performance. They make it a lot easier to gain muscle with less fat.)

## Some specific examples

Furthermore, the distance you're looking to generate your power over can change your "effective power" too. NFL athletes are a nice example.

If you want to generate a lot of power, but only very briefly? You might end up wanting to be very big, ala the linemen.

Want to generate that power for a bit longer period of time? You end up smaller, ala linebackers and running backs.

Want to generate the power over even longer distances? Even smaller, ala the defensive backs and receivers.

Track athletes also work. As we go from 100 meters to say, 800 meters, everybody gets skinnier.

In fact, I've heard Lance Armstrong talk at length about power to weight ratio. It doesn't get much longer distance than the Tour de France! And, consequently, athletes don't get much lighter than Tour de France cyclists.

As an aside, one reason I believe you see this inevitable decline in body size is the body's ability to dissipate heat is critical. Bigger body = more power = more heat generation. The body is incredibly good at not letting itself overheat.

Relatedly, one reason African Americans dominate power events (provided the event is running oriented) is because of their body structure, which is related to their more recent African descent, which is related to their ability to dissipate heat

The longer the (running) event is, the more dominant African Americans become.. (You see white NFL linemen. You don't see white NFL cornerbacks.)

## The Freaks

As for why you do come across some skinny dudes who hit like trucks, that's where the nervous system can come into play. As far as I'm aware, Charlie Francis, the best sprint coach, and probably best sport coach ever, first introduced this, paraphrasingly, "it's not just how fast you can contract. It's how fast you can relax."

When we contract a muscle, that generates stiffness. You can't go into a subsequent contraction until that contraction relaxes. If you flex your hip up to run, you need to relax that hip flexion so you can next go into hip extension.

More recently, I've seen Stuart McGill formalize this as "muscle pulsing." Applying it to MMA athletes. Here's a nice little read, that actually references Bruce Lee: https://www.backfitpro.com/documents/Strikefasterandharder.pdf

Maximum potential muscle strength is measured in PCSA

Muscle mass \cosine\fiber length

So muscle size is important for strength, math is not an opinion.

Potential overall strength also depends on sinew limit, most of the time sinew is the limit factor and not muscle because muscle is actually stronger than connective tissue.

MassLimit_{sinew} = TensileStrength_{sinew} \times (2 \times \pi \times Radius_{smallest load bearing bone} \times (Height \div 4 \times 0.1) \div Acceleration_{gravity}

And muscle efficiency is a thing too, some people can use a greater percentage of their muscle mass at once than other people, the difference is minimal most of the time but extraordinary rare exceptions do exist. Probably not the case for Bruce Lee most likely he just had really strong connective tissue and average muscle efficiency.

But you also have to consider that Bruce Lee was mostly training with isometrics and anecdotally speaking most trainees that use isometrics have great strength while being as skinny as Bruce Lee, look into calisthenics.

However I don't know any study that compares the outcomes between isometric training and normal training.

There's also the bone limit to take into consideration, no matter how strong your tendons and muscles get, if the skeleton can't keep the pace the body will just fall apart. The smallest bone by cross section to bear your weight will be your limit. The chain is as strong as the weakest link.

You can only pull up as much weight as your finger bones allow you or you can only squat as much weight as your feet allow you.

• This answer desperately needs references; Math is not an opinion, but biology is... And, the math you are referring to need biology and biomechanics to justify its usage; You know, just like physics formulas need postulates and experimental evidence to justify their usage. Apr 22 '19 at 18:47

Generally, while fast twitch muscles are "larger" in their cross-sections than slow twitch, that is not the reason for the increased force production. Muscles can be trained in a couple of ways, most regularly, hypertrophy, that is, increase in the cross sectional diameter, or explosively, meaning that the potential of force/strength of the contraction of the muscle increases. For this reason, you'll never see tried and true bodybuilders, whose ultimate goal is hypertrophy, performing gigantic numbers in the big three lifts, the Olympic lifts, vertical jump tests, or sprint tests. In fact, body-building in itself is inherently "unathletic," in the sense that doing high ranges of reps (12-20) produces tremendous growth, but no improvement in contractile potential. Bringing this back to Bruce Lee, one could guess that he never really lifted weights for hypertrophy, but most, if not all, of his strength and conditioning work was focused on very explosive, very quick-twitch based movements, which ultimately increased the contractile potential of his muscles, but not his size.

• Bruce Lee DID train for hypertrophy though. Sep 21 '18 at 16:29
• I don't think Bruce Lee's goal was hypertrophy. I'm not exactly sure, of course, but I never read anything about him saying his goal was to be as large as possible, or even large at all. His goal was explicitly martial arts related, meaning he trained for speed, quickness, and dexterity. Doing loads of pushups, sit ups, pull ups, and other body weight exercises does not count as "training for hypertrophy." If that was the case, no body builder would ever load up a barbell. Sep 26 '18 at 23:59

I think the biggest limiting factor for most people is that we do not have the ability to recruit all muscle fibers in a muscle at the same time. This is a property of the "electrical wiring" from the brain to the muscles and does not add size. Only a few people are born with this explosive ability. It can not be trained.

Type of muscle fibers also play a role; a person with mostly fast muscle fibers will have more power than another person same size with mostly slow but enduring muscle fibers.

Finally I think an "explosive punch" is only part strength. It is also technique and timing.

• Shouldn't this be a comment instead of an answer? I mean, you don't go in depth and start off with "I think", which strongly indicate that this is mere speculation. Apr 22 '19 at 18:39