EMG Activity And Force Output In Fast And Slow Bench Press Repetitions Against Different Loads

PURPOSE: To compare muscle activation, applied force and movement velocity during bench press repetitions performed with moderate and low loads at different movement tempos. METHODS: Eight resistance trained men performed bench press repetitions under three conditions on separate, randomly assigned occasions one week apart: (a) three repetitions at maximal movement tempo (Tmax), (b) three repetitions at half of the maximum movement tempo (Thalf) and (c) three ballistic barbell throws (BALLt). The load for Tmax and Thalf was set at 70% of 1-RM, while the load for BALLt was 30% of 1-RM (65 ± 8 vs. 28 ± 4 kg; p < 0.001). The tempo for the Thalf condition was determined in a preliminary session. Mean, peak and eccentric velocities were measured using a linear position transducer. Surface EMG (sEMG) was recorded for the pectoralis major (PM), triceps brachii (TB) and anterior deltoid (AD), with values expressed as a percentage of sEMG in a maximal isometric contraction. Peak force was measured with a 3-D accelerometer. RESULTS: Peak, mean concentric and mean eccentric barbell velocities were higher in BALLt (2.06 ± 0.11, 1.46 ± 0.08, and 1.54 ± 0.11 m/s) than in Tmax (0.85 ± 0.10, 0.67 ± 0.08, and 1.03 ± 0.15 m/s; p < 0.01) and Thalf (0.54 ± 0.07, 0.41 ± 0.06, and 0.41 ± 0.07 m/s; p < 0.01). Peak force was significantly higher in Tmax (1179 ± 227 N) compared to Thalf (841 ± 105 N; p < 0.01) and BALLt (801 ± 121 N; p < 0.01) with no difference observed between Thalf and BALLt (p = 0.83). sEMG activity of PM and TB were higher in Tmax (100.5% ± 26.3% and 97.1% ± 18.6%) compared to BALLt (69.50 ± 12.5% and 76.6% ± 12.3%; p < 0.01) and Thalf (71.8 ± 17.9% and 66.9% ± 5.2%; p < 0.01) with no differences between Thalf and BALLt (p > 0.05). For the AD muscle, sEMG activity was higher in both Tmax and BALLt compared to Thalf (Tmax: 85.0 ± 18.5%, BALLt: 73.3 ± 13.7%, Thalf: 51.7 ± 11.8%; p < 0.01). CONCLUSIONS: Despite the much lower load in the BALLt compared with the other two conditions (30 vs. 70% of 1-RM), peak force and neuromuscular activation were similar to the Thalf condition, likely due to the higher acceleration, which compensated for the lower load. This highlights the importance of movement velocity in achieving higher actual loading and muscle activation when training against low resistance.