In previously trained adults, 5 weeks of resistance training with matched total volume results in no significant difference in vastus lateralis muscle cross-sectional area at proximal or mid-thigh sites when comparing training performed near failure (0–1 RIR) versus training performed with higher rep reserves (4–6 RIR).

When people who already lift weights do the same total amount of work, whether they push to exhaustion or stop short, their muscles grow the same amount because the body recruits the same number of muscle fibers over time — just in different patterns. Training to failure fires the same muscle fibers more often under fatigue, but stopping short of failure spreads the same total work across more sessions with less fatigue per set. In both cases, the total number of times muscle fibers are activated and stressed reaches the same level, so the signal to grow doesn't change.