tjfry wrote:
domingjm wrote:
So what is the mechanism whereby easy efforts contribute to enhanced performance? It's not enhanced fat metabolism; our capacity for peripheral lipolysis already exceeds our capacity to deliver it to the muscles. My best guess (and what seems to be suggested by these coaches) is that it's a compromise: predominantly high intensity efforts are largely unsustainable from a psychological and physiological platform. And if you have burned-out or sick athletes, those are non-exercising athletes. So the next best thing is to pile on tons of volume, sprinkle in some intensity, and keep everyone healthy and exercising. There's plenty of published observational data to suggest that this approach works, but to my knowledge, no one has even proposed a mechanism attempting to explain the direct superiority of easy vs hard.
There are actually a number of mechanisms. The biggest is the capillarization of the specific muscle groups. VO2, threshold, etc are important, the but delivery system is overlooked in discussions like this. Aerobic activity promotes this best. Delivering the fuel and oxygen to the working muscle can be more important that the uptake itself if the O2 is stuck in traffic. There's also a nervous system piece to it. The growth and thickening of the nerves that deliver the impulse is a long and slow process. Working harder doesn't speed this up as far as I've read. It takes time. It takes tons and tons of repetition. The result is a stronger, more precise and more direct impulse the muscle. Sometimes referred to as muscle memory, but it's more than that. The stride of an elite runner or the pull of an elite swimmer is not just more efficient because it's performed correct, it's also not wasting any energy firing 'helper' muscles. It's dialed in and only firing the exact muscles needed. Less noise. There's also a hormonal piece that really starts getting above my head pretty quick. There's other benefits too...
So it's not a huge surprise that all the good guys train a ton of volume. Intensity has it's place, but it's much more limited in it's benefits when you're dealing with athletes with few time constraints.
Edit: Sorry, in advance, if I come across as pedantic or terse. I was just trying to be concise.
Sure, in addition to enhanced hyperemia, increased capillary density is important and contributes to the percent of VO2 max that an athlete can maintain. But again, this chronic acclimation is thought to be highly related to the acute release of nitric oxide from the vascular endothelium, which is induced by shear stress. The absolute quantity of NO released is determined by both the duration and magnitude of the stimulus (for how long blood flow is elevated through the arterioles). By the transitive property, higher cardiac output (thus elevated blood flow through arterioles of exercising muscle) should generate a greater stimulus for angiogenesis than lower cardiac output. I don't know if those comparisons have been made empirically, but it’s quite safe to assume that the inverse relation is not true (i.e., lower cardiac output providing a greater angiogenic stimulus).
I'm not quite sure what you mean about O2 being stuck in traffic, but for clarity, O2 delivery (in healthy humans) to muscle during submaximal exercise (i.e., not at VO2 max) does not limit performance. For example, oxygen saturation from venous samples during submaximal exercise is in the range of 30 to 50%, whereas venous samples from very high intensity exercise are closer to 10%. If blood flow or capillary density limits submaximal exercise performance, it's likely due to insufficient removal of the metabolites of contraction.
Change in nerve diameter is not a training acclimation. And the strength of a single impulse from the alpha motor neuron to its innervated muscle fiber is related neither to increased strength of contraction nor improved mechanics. These are all-or-none impulses, which either reach voltage required for depolarization or they don't. End plate potential. There’s some data to suggest that the thresholds can be modulated, such that they require less of an impulse from the motor neuron in order to depolarize, but that’s far from conclusive as a training acclimation at this point.
And about efficiency and improved motor unit recruitment....if we train at 8:00 pace but want to race at 6:30 pace, how is our training positively contributing to the precise motor unit recruitment patterns that we're going to require at 6:30 pace? Biomechanically, these two speeds look quite different when performed by the same individual. If we're trying to optimize efficiency and motor unit recruitment patterns, and if repetition accomplishes that, why would we not want to run the bulk of our miles at 6:30? Maybe someone else can chime in on this. Maybe they're close enough; I'm certainly not a biomechanics expert.
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