When people lift weights until they can’t do another rep, both slow-twitch and fast-twitch muscle fibers grow at about the same rate — so fast-twitch fibers aren’t naturally better at getting bigger.
Scientific Claim
Training to failure at 60% 1RM produces similar fiber-type-specific hypertrophy in slow- and fast-typology individuals, contradicting the hypothesis that fast-twitch fibers are inherently more responsive to hypertrophic stimuli.
Original Statement
“No significant differences were found in fiber CSA adaptations between ST and FT groups (Type I 3x/week: p = 0.318; type II 3x/week: p = 0.096).”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
probability
Can suggest probability/likelihood
Assessment Explanation
The study shows no significant difference, but the small sample size and wide confidence intervals (e.g., p=0.096 for type II) mean it cannot definitively disprove a small effect — 'does not show' is more accurate than 'contradicts'.
More Accurate Statement
“Training to failure at 60% 1RM does not show a significant difference in fiber-type-specific hypertrophy between slow- and fast-typology individuals, suggesting that training to failure may equalize hypertrophic responses across fiber types, though small effects cannot be ruled out.”
Evidence from Studies
Supporting (1)
Can muscle typology explain the inter‐individual variability in resistance training adaptations?
Even if someone has mostly slow or fast muscle fibers, training to exhaustion with light weights made both types of fibers grow about the same — so fast fibers aren’t naturally better at getting bigger.