Q: At your suggestion, I've been including higher-rep sets in many of my workouts. I'm seeing much more size and vascularity. My question is, do sets of around 20 reps work because I'm getting growth in more slow-twitch fibers or are the fast-twitch ones getting larger as well?
A: Yes, both—and as bodybuilders, we want to maximize ALL hypertrophic pathways, even size in the slow-twitch fibers. Higher-rep sets also give you anabolic hormone surges…
According to Brad Schoenfeld, Ph.D., who conducts studies on muscle hypertrophy,
"Sets that last longer than 20 to 30 seconds substantially increase metabolic stress." Hydrogen ion that fill your muscles during long tension times lower the muscles' pH due to lactic acid. "That seems to make them bigger by stimulating the production of proteins and HORMONES that act as growth factors for muscle tissue."
As for muscle fiber activation, Schoenfeld says,
"[Longer tension-time sets] recruit more muscle fibers, including your fast-twitch [high-growth] fibers, which typically don't report for duty unless you're lifting 80 percent or more of your one-rep max. Longer-lasting sets with lighter weights call them into action by thoroughly exhausting your lower-threshold (i.e., slow-twitch) fibers…. Just make sure you hit that sweet spot, when your legs are shaking from fatigue."
[Men's Health, July/August '13]
One way to flip on that slow-twitch to fast-twitch growth switch is with our MMX method, based on a Brazilian study published in the European Journal of Applied Physiology. Researchers had one group do a preliminary set of leg extensions to failure with 20 percent of their one-rep-max before moving to heavier sets. The other group did only standard sets with 75 percent of their 1RM. Rests between sets for both groups were 30 seconds to one minute…
More muscle size and strength occurred in the group that included a preliminary high-rep set because:
"muscle failure (principally of [slow-twitch] type-1 fibers) and metabolic accumulation induced by prior exhaustive exercise [promoted] a greaterglobal recruitment of type-2 [high-growth] fibers during traditional training sets and, thus, further stimulate muscle performance and adaptations."
While the scientists in that Brazilian study surmised that the initial high-rep set fatigued the slow-twitch fibers so that more fast-twitch growth fibers could be stimulated on the heavier sets after, that's only one of many hypertrophic pathways in which a high-rep set can force new muscles growth. High reps can also…
1) Hypertrophy those slow-twitch endurance fibers that were pre-fatigued.
2) Trigger more growth in the 2A power-and-endurance (dual-component) fibers.
3) Cause extreme sarcoplasmic, or energy fluid, expansion via mitochondrial growth, glycogen storage, etc. in all fiber types
OR maybe it was ALL of the above, which would boost muscle size significantly….
Give that MMX method a try to pack on new size.
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Till next time, train hard—and smart—for BIG results.