Author(s): KINOSHITA, M., MAEO, S.1, KOBAYASHI, Y.1, EIHARA, Y.1, NISHIZAWA, N.1, OHASHI, C.1, KUSAGAWA, Y.1, SUGIYAMA, T.1, WAKAHARA, T.2, KANEHISA, H.3, ISAKA, T.1, Institution: RITSUMEIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 1640

INTRODUCTION:
Single-joint knee extension (KE) and multi-joint leg press (LP) are commonly used as a resistance training exercise for the quadriceps femoris (QF). However, their comparative effectiveness for QF hypertrophy is unclear. Furthermore, although LP can theoretically train multiple muscles at the same time, it is unknown which muscles are trained/hypertrophied by LP. Therefore, this study aimed to compare the hypertrophic effects of KE and LP on QF and other lower-limb muscles.
METHODS:
Seventeen untrained healthy young adults (11 males and 6 females) performed KE with one leg and LP with the other leg at 50-70% of one repetition maximum (1RM) of the corresponding task. Each leg performed 5 sets of 10 repetitions per session (2 s for each of the concentric/eccentric phases), 2 sessions per week for 12 weeks. Before and after the intervention, T1-weighted axial 3-T MR images (field of view: 275×275 mm, slice thickness & gap: 5 mm) were obtained to assess muscle volume of the individual QF and gluteus muscles, as well as the whole QF, hamstrings (HAM), and adductor muscles (ADD). In a follow-up experiment, electromyograms (EMGs) during KE and LP (10 reps at 50% 1RM) were measured in eleven males from the following muscles: rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris long head (BFL), semitendinosus (ST), and gluteus maximum (G-max). The EMG data were normalized to those obtained during maximal voluntary contraction of each muscle (%EMGmax).
RESULTS:
After the intervention, muscle volume of each and the whole QF significantly increased in both conditions (P ≤ 0.002), except for the RF of the LP (P = 0.290). The changes were significantly greater for the KE than LP in the RF (+13.2% vs +1.1%) and whole QF (+7.1% vs +4.9%) (P ≤ 0.005), but similar in the vasti muscles between KE and LP (VL: +6.4% vs +6.2%, VM: +7.2% vs +6.0%, vastus intermedius: +5.0% vs +4.4%, P ≥ 0.161). The LP significantly increased muscle volume of the G-max (+13.9%), gluteus medialis (+4.1%), HAM (+3.1%), and ADD (+3.8%) (P ≤ 0.020), while no such significant changes occurred after KE (+0.2%, -0.2%, +1.5%, and -0.5%, respectively, P ≥ 0.064). Changes in total muscle volume of analyzed muscles were significantly lower in KE than LP (+2.8 vs +5.9%, P < 0.001). The EMG analysis showed that %EMGmax values during KE compared to LP were significantly higher in the RF (38.0% vs 21.7%, P < 0.001), similar in the VL (36.9% vs 37.1%) and VM (32.4% vs 35.0%) (P ≥ 0.544), and lower in the BFL (7.3% vs 13.9%), ST (8.1% vs 18.9%), and G-max (8.8% vs 41.2%) (P ≤ 0.003).
CONCLUSION:
KE is more effective than LP for muscle hypertrophy of the QF, which is attributed to significant and insignificant hypertrophy of the RF after KE and LP, respectively. However, LP can indeed train/hypertrophy multiple lower-limb muscles and therefore can be considered more time-efficient exercise. The unique muscle hypertrophy of both KE and LP can be explained by muscle activity during each exercise.