"We can make him better, stronger..."

[rhoenix]

Human running speeds top out near 28 mph, if the record-breaking feats of Jamaican speed demon Usain Bolt prove anything. But scientists say that the biological limits of human running could theoretically reach 35 or even 40 mph -- assuming that human muscle fibers could contract faster and allow people to pick up their pace.

This provides a new twist on the old school of thought that speed limits depended on how much force a runner could exert against the ground. Past studies showed that sprinters can apply up to 1,000 pounds of force with a single limb during each sprinting step, and so researchers thought that humans simply could not push beyond that point.

The new study titled "The biological limits to running speed are imposed from the ground up" appears in the Journal of Applied Physiology. It involves testing runners on a treadmill at top speed while they run forward and backward and hop on one leg.

One-legged hopping produced ground forces greater than those applied during normal running by 30 percent or more, and active leg muscles also generated about 1.5 to 2 times greater force during one-legged hopping. That shows how humans don't exert the maximum possible force during the act of forward sprinting, the researchers say.

Going one step farther, the researchers also found that the "critical biological limit" depends upon how quickly runners can exert ground force while sprinting. Elite runners have foot-ground contact times of less than one-tenth of a second, and max out ground forces within one-twentieth of one second when their foot first hits the ground.

Bionic limbs and motorized exoskeletons could suggest a way forward for humans to overcome their biological limits. But ordinary runners can at least look to less expensive enhancements for a healthier gait, such as highly customizable shoes. Or they can consider a return to barefoot running.

This is cool by itself for the biology coolness factor, but what amazes me is what the human frame is capable of. This is going to have an impact on my project, to be certain.

[Batman]

I wasn't aware that we had REACHED our biological limits. IIRC (mind you, I don't exactly bother to keep up on these issues so my information may be woefully outdated) we simply CANNOT access the body's full physical potential intentionally, there's some sort of built in reserve for when we're in serious peril.

[frigidmagi]

Part of that is intentional, if you could go all out whenever you felt like it you would be more likely to hurt yourself. By setting it up that only the fight or flight reflex can trigger this it keeps folks form fucking themselves over.

[Batman]

Thank you.That was what I was talking about. I just wasn't sure if it was still valid.

[The Silence and I]

*Yawn* It's physics folks.

Muscle fiber contracts slowly compared to many modern mechanical devices. Leverage allows limbs to move with any appreciable speed (at a cost to force and/or torque) but there are limits. This speed of contraction limits the power a muscle can generate. Force x Velocity = Power; given two muscles of the same ability to apply force but with different contraction speeds the faster muscle will be more powerful.

A consequence of this relationship is that even if a muscle could produce constant power at any contraction speed (it cannot) the force it may produce must decrease as contraction speed increases. During a sprint the leg muscles are contracting as fast as possible and thus the force they apply is less than is possible at a lower speed. During one legged hopping the foot contacts the ground for much longer at a slower contraction speed and more force is possible (which is good because more force is needed as well).

During any given activity a balance between force and speed is achieved. At maximum running speed if you try to push yourself a little faster it'll come at a cost of muscle force and you'll fall on your face as you can no longer support your body going forward. If you were to "unlock" your mental limits and recruit more muscle fibers you'd have more available force, and could then move a little faster. But only to a point because muscle fibers only contract so quickly--no matter how strong your legs are they can never move faster than a fixed multiple of your muscle contraction speed. That is why the fastest running animals have longer legs--the extra length increases that multiple and allows their limbs' distal ends to move faster. This is also why fast animals take longer strides, not faster strides.