Lifting weights seems straight forward enough however once you start getting into the details it can get confusing. Greg Nuckols goes into detail on the different muscle fiber types and if you should structure your training around this.
- Most muscles in your body have a fairly even split of fast-twitch and slow-twitch muscle fibers; very few muscles are (on average) incredibly fast-twitch or slow-twitch dominant.
- There’s not a practical test to know whether a particular muscle is composed primarily of fast-twitch or slow-twitch fibers. The methods you’d typically use in a gym setting (seeing how many reps you’d get with a particular percentage of your 1rm) have virtually no predictive power.
- The idea that you should train muscles differently based on their predominant muscle fiber type comes from the notion that fast-twitch muscle fibers respond best to heavy weights and low reps, and that slow-twitch muscle fibers respond best to light weights and high reps. Evidence is still very mixed on this point – it’s not yet clear that particular training styles specifically target fast-twitch or slow-twitch fibers in the first place.
- Even if there was good evidence for fiber type specific hypertrophy, and even if there was a good, practical test to know a muscle’s fiber type breakdown, it still wouldn’t change the general recommendation to keep training that muscle with a variety of rep ranges.
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