Evaluation of muscle activity during a standardized shoulder resistance training bout in novice individuals

Momentary fatigue is an important variable in resistance training periodization programs. Although several studies have examined neuromuscular activity during single repetitions of resistance training, information is lacking in regard to neuromuscular fatigue indices throughout a full resistance training bout. The purpose of this study was to evaluate muscle activity during a shoulder resistance training bout with 15 repetitions maximum (RM) loadings in novice individuals. Twelve healthy sedentary women (age = 27-58 years; weight = 54-85 kg; height = 160-178 cm) were recruited for this study. Normalized electromyographic (nEMG) activity and median power frequency (MPF) of the upper, medial, and lower trapezius; the medial deltoid, infraspinatus, and serratus anterior was measured during 3 sets of 15RM during the exercises front raise, reverse flyes, shrugs, and lateral raise. For the majority of exercises, nEMG activity was high (>60% of maximal isometric contractions). From the first to the last repetition of each set nEMG-averaged for all muscles-increased 10. 0 ± 0.4% (p < 0.05) and MPF decreased -7.7 ± 0.5 Hz (p < 0.05). By contrast, nEMG activity and MPF were unchanged from the first to the third set (averaged for all muscles: 38.1 ± 23.6 vs. 47.6 ± 28.8% and 88.4 ± 21.3 vs. 82.1 ± 18.1 Hz, respectively). In conclusion, during a shoulder resistance training bout in novice individuals using 15RM loading muscle activity of the upper, medial, and lower trapezius, the medial deltoid, infraspinatus, and serratus anterior increased, and MPF decreased within each set-indicating momentary neuromuscular fatigue. By contrast, no such change was observed between the 3 sets. This indicates that momentary neuromuscular fatigue in shoulder resistance training is induced more efficiently within a set than between sets.