In healthy young men, performing lower-body resistance training to concentric failure twice per week for six weeks is associated with improvements in multi-joint strength, with similar strength gains observed between 10-repetition maximum and 20-repetition maximum training protocols across most exercises, except for the lying leg-curl, where the 20-repetition maximum protocol resulted in greater gains.

When muscles are worked to failure with repeated contractions, the energy demand inside the muscle cells spikes, triggering the production of more energy factories called mitochondria. These mitochondria process oxygen faster, allowing the muscle to recover quickly between contractions and keep generating force. This happens whether the weights are heavy with fewer reps or light with more reps, which is why strength improves similarly in both cases. For the lying leg-curl, the higher-rep protocol may stress the hamstrings more continuously, leading to even greater mitochondrial adaptation and stronger gains.