Author(s): STOCKERT, A., RASP, D.M., VOGL, A.M., PATERNOSTER, F.K., Institution: TECHNICAL UNIVERSITY OF MUNICH, Country: GERMANY, Abstract-ID: 2489

INTRODUCTION:
The leg press is widely used to assess lower-limb strength in elite sports. While muscle activation of the lower extremities is influenced by joint angles, hand grip positioning is rarely standardized and varies across Olympic training centers despite its potential impact on maximal force output and neuromuscular activity. This study investigated, whether different hand grip positionings during the leg press affect maximal voluntary isometric force and surface EMG activity in lower and upper body muscles.
METHODS:
Fifteen healthy participants (9 males and 6 females; age: 24.2 ± 2.9 years; body height: 180.1 ± 7.6 cm; body mass: 75.2 ± 8.9 kg) performed maximal isometric trails of the leg press exercise on the IsoMed2000 leg press device at 90° knee flexion. Three hand grip positionings were tested in randomized order: side grips, arms crossed over the chest, and hands on the shoulder attachment. For each condition, three 5-s trials were completed, with a 1-min rest between trials and a 5-min rest between conditions. Peak force was recorded with a force plate, attached to the devices foot plate, and normalized to body mass. Surface EMG was used to record the muscle activity of the mm. vastus lateralis, rectus femoris, biceps femoris long head, latissimus dorsi, and pectoralis major. All data were sampled at 2000 Hz. EMG signals were band-pass filtered (10–500 Hz, Butterworth) and rectified, and both EMG and force data were subsequently low-pass filtered at 6 Hz. Repeated measures ANOVA were calculated to analyze the effect of the hand grip positioning on the peak force and the respective muscle activities. The level of significance was set at α = 0.05 and Bonferroni-corrected during the post-hoc tests in case of a significant ANOVA.
RESULTS:
Peak force did not differ significantly between hand grip positioning (crossed: 25.5 ± 2.93 N·kg⁻¹; shoulder: 25.12 ± 2.70 N·kg⁻¹; side: 26.19 ± 2.57 N·kg⁻¹; p = 0.11, η² = 0.14). Mean EMG activity of the lower-limb muscles and the latissimus dorsi showed no significant differences between conditions. In contrast, pectoralis major activation differed significantly across hand grip positioning (p = 0.002, η² = 0.38). Bonferroni-adjusted post hoc analyses revealed higher activation in the side-grip condition compared to the shoulder condition (p = 0.008, Cohen’s d = 1.08), while no other pairwise comparison reached significance.
CONCLUSION:
Maximal voluntary isometric force and lower body muscle activity did not differ significantly between hand positions. Pectoralis major activity was significantly higher when participants held the side grips compared to the shoulder condition. This likely reflects active pushing against the side grips, pressing the upper body into the backrest. Based on the descriptive results, the crossed-arms condition may seem favorable for standardizing testing procedures, as it minimizes upper-body involvement and promotes a more isolated assessment of lower-limb muscle strength.