Investigating the effects of pre-exhausting a synergist prior to a compound exercise. : An electromyographic study

Abstract: Background: Pre-exhausting a synergist prior to a compound exercise has been shown to alter the firing patterns in the muscles during the exercise. Pre-exhausting a muscle is done by exercising a muscle group to fatigue with a single joint exercise prior to an exercise. Aim: The purpose of this study was to further investigate the effects of pre-exhausting the triceps brachii prior to performing a bench press, measuring the EMG activity in pectoralis major, triceps brachii and deltoid anterior. Methods: 30 participants, men (n=15) and women (n=15), performed two different protocols (T1 and T2) while the muscle activity was measured with surface EMG. Electrodes were placed on pectoralis major, triceps brachii and deltoid anterior. Maximum voluntary isometric contraction (MVIC) was performed prior to performing protocols in order to get reference values. Results: Pectoralis major and deltoid anterior activation was significantly higher when preexhausting triceps brachii before bench press compared to no PRE, but no significant increase was seen in triceps brachii (p=0.000, p=.0009 and p=0.405 respectively) MVIC expressed in percentages and mean values ± standard deviation during protocol T1 for pectoralis major 45.3(±12.4), triceps brachii 56.28(±15.9) and deltoid anterior 63.45(±31.4) and during protocol T2 pectoralis major 56.41(±18.4), triceps brachii 58.49(±20.07) and deltoid anterior 71.65(±42.7). Conclusion: These results suggest that pre-exhausting a synergist prior to a compound exercise may change the muscle activity in the involved muscles. This can be used in a practical sense to develop weak points in the muscles by changing the activation pattern in the muscles hence being able to target specific muscles better.