Different muscles in the front of the thigh may respond differently to how close to failure you train: the vastus lateralis may grow more when trained to complete fatigue, while the rectus femoris...
Mechanism
Synthesis from 1 study
When you do leg presses first and then leg extensions, pushing the leg press to failure makes the vastus lateralis grow more because it gets the most work when tired, but stopping short lets you do better leg extensions, which makes the rectus femoris grow more — this is why different parts of the...
Most probable mechanism
When you do leg presses first and then leg extensions, the leg press fatigues the vastus lateralis more, so pushing it to failure makes it grow a bit more because it gets the most tension. But if you stop short of failure on the leg press, you stay less tired, so when you do the leg extension, your rectus femoris gets more work and grows a bit more — this is why one muscle prefers going all the way to failure and the other prefers leaving a few reps in reserve, based on the order of exercises (10.1080/02640414.2024.2321021).
Multi-joint exercises like leg press preferentially activate and impose high mechanical tension on the vastus lateralis due to its biomechanical leverage during hip and knee extension (10.1080/02640414.2024.2321021).
Single-joint exercises like leg extension preferentially activate the rectus femoris due to its anatomical role in pure knee extension without hip involvement (10.1080/02640414.2024.2321021).
Training to momentary muscular failure during leg press induces greater neuromuscular fatigue in the vastus lateralis, maximizing its mechanical tension exposure and hypertrophic response (10.1080/02640414.2024.2321021).
Training with 1–2 repetitions-in-reserve during leg press preserves neuromuscular function, reducing fatigue and allowing higher-quality leg extension performance, which enhances rectus femoris activation and hypertrophy (10.1080/02640414.2024.2321021).
Differential fatigue accumulation across quadriceps subunits alters the relative mechanical tension experienced by vastus lateralis versus rectus femoris during subsequent exercises, leading to muscle-specific hypertrophic adaptations (10.1080/02640414.2024.2321021).
Less supported by current evidence, but not ruled out
Both training to failure and training with reps in reserve can cause muscle growth by stretching and pulling muscle fibers hard enough to trigger molecular signals that build more muscle protein, as long as the total amount of tension over time is similar (10.1080/02640414.2024.2321021).
Resistance training applies mechanical tension to muscle fibers during concentric and eccentric contractions, activating mechanosensors such as integrins and focal adhesion kinase (10.1080/02640414.2024.2321021).
Mechanosensor activation triggers the PI3K/Akt/mTOR signaling pathway, which increases ribosomal production and protein synthesis rates (10.1080/02640414.2024.2321021).
Net positive protein balance leads to sarcomere addition and increased muscle fiber cross-sectional area, regardless of whether sets are performed to failure or with repetitions-in-reserve, as long as total volume is matched (10.1080/02640414.2024.2321021).
Evidence from Studies
Supporting (1)
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