Hypertrophic Effects of Single- versus Multi-Joint Exercise: A Direct Comparison between Knee Extension and Leg Press.

Abstract

Single-joint knee extension (KE) and multi-joint leg press (LP) are commonly used exercises to train the quadriceps femoris (QF), the largest muscle group in humans. However, their comparative effectiveness for inducing QF hypertrophy remains unclear. Furthermore, the specific muscles hypertrophied by LP are not well characterized. This study compared the hypertrophic effects of KE and LP on the QF and other lower-limb muscles. Seventeen untrained adults performed KE with one leg and LP with the contralateral leg at 70% of one-repetition maximum, 10 reps/set, 5 sets/session, 2 sessions/week for 12 wk. Magnetic resonance imaging was used to assess pre- and post-training muscle volumes of 17 individual muscles, including the four QF heads, gluteus muscles, hamstrings, and adductors. Muscle volumes of the individual and whole QF significantly increased in both conditions ( P ≤ 0.026), except for the rectus femoris in the LP condition ( P = 0.379). Rectus femoris volume gains were greater for KE than LP (+13.2% vs +1.1%, P ≤ 0.001), but gains in the vasti muscles (+5.0%-7.2% vs +4.4%-6.2%) and whole QF (+7.1% vs +4.9%) were comparable between conditions ( P ≥ 0.319). LP, but not KE, increased volumes of the gluteus maximus (+15.4%) and the adductor magnus (+6.2%) ( P ≤ 0.001). A follow-up experiment using surface electromyography showed that muscle excitation patterns during KE and LP generally mirrored the between-condition hypertrophic differences and similarities observed after the training intervention. LP induces significant hypertrophy in the gluteus maximus and adductor magnus while producing similar vasti and overall QF growth as KE, indicating that LP is a highly time-efficient exercise. However, KE is essential for effectively targeting the rectus femoris, which may have clinical relevance given its high susceptibility to strain injuries.