Performing multiple sets of resistance exercise with sustained tension and fatigue leads to greater activation of muscle fibers and results in an increase in muscle size.
Mechanism
Synthesis from 3 studies
When muscles get tired from lifting weights, waste products build up and make it harder for them to push hard. To keep going, your body turns on more muscle fibers than before. Doing this over several sets puts more stress on those fibers, which makes them grow bigger over time.
Most probable mechanism
When you lift weights until you're tired, your muscle cells build up waste products that make it harder for the muscle fibers to generate force. To keep pushing, your body turns on more muscle fibers than before, and doing this over several sets causes the muscles to grow bigger over time.
ATP hydrolysis during repeated muscle contractions releases inorganic phosphate (Pi) and protons (H+) into the muscle cell cytoplasm.
Accumulated Pi binds to the myosin head, promoting detachment from actin and inhibiting the transition to a force-generating state.
Accumulated H+ binds to the actin-myosin complex, preventing the conformational change needed for strong cross-bridge formation and force generation.
The combined inhibition of cross-bridge cycling by Pi and H+ reduces the force output per muscle fiber.
Reduced force output from active motor units triggers the central nervous system to recruit additional motor units to maintain the required level of tension.
Repeated recruitment of additional motor units across multiple sets increases mechanical load on previously underused muscle fibers, stimulating hypertrophic signaling pathways.
Less supported by current evidence, but not ruled out
When you lift weights quickly, your muscles use oxygen more efficiently to keep producing energy, letting you do more reps without getting as tired from acid buildup. More reps mean your muscles are under tension longer overall, which helps them grow.
High-velocity contractions increase power output and rate of ATP demand per unit time.
Elevated ATP demand increases oxygen uptake and shifts energy production toward aerobic metabolism.
Greater aerobic contribution sustains ATP production without proportional accumulation of metabolic byproducts like lactate or H+.
Sustained ATP availability allows more repetitions to be completed, increasing total volume load while maintaining time under tension.
Higher volume load increases cumulative mechanical tension across muscle fibers, enhancing hypertrophic stimulus.
Evidence from Studies
Supporting (2)
Community contributions welcome
Bench-Press Performed With a Velocity- and Tempo-Based Approach: Are There Differences in Volume Load, Time Under Tension, and Metabolic Demands?
Cross-bridge model-based quantification of muscle metabolite alterations leading to fatigue during all-out knee extension exercise
Contradicting (1)
Community contributions welcome
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