Steve McGregor wrote:
Well, we really don't *know* which fibers are being recruited in humans due to ethics and subject availability, but most of the evidence indicates that around 75% VO2 max (depending on the fitness of the subject) one will recruit most, if not all of their Type I and IIa fibers, which leaves the highly fatiguable IIx. So, one might argue an effective way to overload the IIxs would be to ran at approximately 75% (the LT?... Hmm) for a very long time in order to slowly recruit the highly fatiguable IIxs, or to run faster for a shorter amount of time, to recruit them faster. No magic formulas are likely needed though. Run at or above the LT/MLSS, but below the VO2max and you're good.
Steve
Steve,
The latest research data I'm familiar with has shown a wide range (up to 129x) of fatigue in fibers of the same types. For example, I recall a study that found a range of fatigue in fast twitch fibers of about 13 seconds to 34 minutes, with an inverse relationship between a fiber's rate of fatigue and it's level of strength.
It's clear we have fibers that fatigue in a few seconds (think very heavy weight lifting) and all the way out to those that take hours to fatigue (think marathon and ultras).
How does one overload fibers that takes 4 hours to fatigue? Those that take 2 hours to fatigue? Those that take 1 hour to fatigue? Those that fatigue in 30 minutes? 15 minutes? 5 minutes? 1 minute?
I suggest that all the fibers that are active during an athlete's chosen sport should be regularly trained to overload if maximum performance is desired. If all the active fibers are not specifically overloaded, they won't adapt optimally, and performance will be less than what is possible.