The relationship between resistance training proximity to failure and muscle hypertrophy exhibits a detectable dose-response to repetitions in reserve (RIR), whereas the relationship with strength does not, indicating that optimal training strategies for maximizing muscle growth may differ from those for maximizing strength gain.

When you train close to failure, your body recruits more muscle fibers and builds up metabolic byproducts like lactate and hydrogen ions. These signals trigger muscle cells to increase protein synthesis and grow larger. When you stop short of failure, fewer fibers are activated and less metabolic stress occurs, so muscle growth is smaller. Strength gains, however, depend more on how often and how forcefully you contract muscles, not how close you get to exhaustion.