Effect of instructions on EMG during the bench press in trained and untrained males

- Muscle activation does not differ between trained and untrained males in the bench press.
- Instructions to emphasize activation of the chest muscles may reduce triceps activity at 80% 1-RM.
- Selective activation of the pectoral muscles in the bench press does not occur at 80% 1-RM.

Strength and rehabilitation professionals strive to emphasize certain muscles used during an exercise and it may be possible to alter muscle recruitment strategies with varying instructions. This study aimed to determine whether resistance trained and untrained males could selectively activate the pectoralis major or triceps brachii during the bench press according to various instructions. This study included 13 trained males (21.5 ± 2.9 years old, 178.7 ± 7.0 cm, 85.7 ± 10.7 kg) and 12 untrained males (20.3 ± 1.6 years old, 178.8 ± 9.4 cm, 74.6 ± 17.3 kg). Participants performed a bench press one-repetition maximum (1-RM) test, 3 uninstructed repetitions at 80% 1-RM and two more sets of three repetitions with instructions to isolate the chest or arm muscles. Electromyography (EMG) was obtained from the pectoralis major, anterior deltoid, and the long head and short head of the triceps brachii. Maximum EMG activity normalized to 1-RM for each muscle was averaged over the three repetitions for each set and compared between the uninstructed, chest-instructed and arm-instructed conditions among the groups. The trained participants had a greater 1-RM (126.2 ± 30.6 kg) than the untrained participants (61.6 ± 14.8 kg) (P < 0.01). EMG activity was not different between the groups for any of the instructions (P > 0.05). When the group data was combined, short head of the triceps activity was significantly lower in the chest instruction (80.1 ± 19.3%) when compared to the uninstructed (85.6 ± 23.3%; P = 0.01) and arm-instructed (86.0 ± 23.2; P = 0.01) conditions. It can be concluded that instructions can affect muscle activation during the bench press, and this is not dependent on training status.