The aim of this study was to evaluate the acute effect of the use of stable and unstable surfaces on electromyography (EMG) activity and coactivation of the scapular and upper-limb muscles during the push-up plus (with full protraction of the scapula). Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major, biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) levels and coactivation index were determined by surface EMG in 20 young men during push-up plus performed on a stable and unstable condition (2 unstable devices applied to hands and feet). The paired t test and Cohen d were used for statistical analysis. The results showed that during the execution of the push-up plus on the unstable surface an increased EMG activity of the scapular stabilizing muscles (SA, MT, and LT) was observed, while AD and PD muscles showed a decrease. During exercise execution on the unstable surface there was a higher index of coactivation of the scapular muscles (SA-MT and UT-LT pairs). No significant differences were observed in TB-BB and AD-PD pairs. These results suggest that the push-up-plus exercise associated with unstable surfaces produced greater EMG activity levels and coactivation index of the scapular stabilizing muscle. On the other hand, the use of an unstable surface does not promote the same effect for the shoulder muscles.
Context: It is believed that conscious abdominal contraction (CAC) during exercise encourages greater periscapular activation through existing myofascial connections. On the other hand, it is postulated that the use of unstable surfaces would promote greater neuromuscular demand. Objective: To analyze the effect of CAC on periscapular muscle activity during push-up plus exercise on stable and unstable surfaces and to evaluate the correlation between electromyographic (EMG) activity of the serratus anterior (SA) and abdominal oblique muscles. Design: Repeated-measures design in a single group, pre–post CAC. Setting: Biomechanics laboratory. Participants: Twenty-three male volunteers without a history of lesions in the upper limbs participated in the study. Main Outcome Measures: Five repetitions of push-ups on stable and unstable surfaces were performed with and without instruction for CAC. The normalized amplitude of the EMG activity was obtained from the muscles of the upper, middle, and lower trapezius, SA upper (SA_5th) and lower (SA_7th) portions, external oblique (EO), and internal oblique. Results: CAC increased the activity of the EO, internal oblique, middle trapezius, and SA (P < .05) in both surfaces. The use of the unstable surface increased the EMG activity of the EO, SA_7th, and middle trapezius and decreased the EMG activity of the SA_5th. However, all changes observed in EMG signals were of low magnitude, with effect sizes lower than 0.45. There was a weak correlation between the EMG activity of the EO and SA_5th (r = .24) and a strong correlation between the EO and SA_7th (r = .70). Conclusion: The isolated use of CAC or unstable surface during push-up seems to present no practical relevance, but the combined use of these strategies may increase activation of the SA_7th and middle trapezius muscles.
Background/aims Core training has been recommended in shoulder rehabilitation programs. However, the evidence on this topic is still scarce. The aim of this study was to investigate the effect of conscious abdominal contraction combined with unstable surfaces on electromyographic activity of periscapular muscles during the plus phase of a push-up. Methods A total of 20 male participants (22.8 ± 2.5 years) were evaluated. Electromyographic signals were collected from the upper, middle and lower trapezius, serratus anterior, and external and internal oblique muscles during push-up exercises on a stable and unstable surface with and without the conscious abdominal contraction. Each participant performed four variations of the plus phase of a push-up. Results The results demonstrated that the conscious abdominal contraction caused an increase in the electromyographic activity of external oblique, internal oblique, serratus anterior and lower trapezius muscles (P≤0.008). The unstable surface caused only a relevant increase in electromyographic activity of the abdominal muscles (P≤0.025). Combining the two strategies did not increase the electromyographic activity of any muscles (P≥0.238). Conclusions The conscious abdominal contraction seems to be a viable strategy to increase the electromyographic activity of the periscapular muscles.
This study evaluated the effects of instability on the EMG activity of scapular stabilizing and upper limb muscles during exercises with axial and rotational load. Twenty male volunteers (20.9 ± 1.8 years, 174.1 ± 0.04 cm, 73.17 ± 8.77 kg) experienced in strength training participated in a crossover design. Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major (PM), biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) were determined on both conditions. Participants performed a single series of 10 repetitions of bench press and fly exercises on stable (bench) and unstable (proprioceptive disc) conditions at 60% of 1-RM. The Friedman test and post hoc Dunn's indicated that the unstable condition showed greater EMG activity for AD (P = .001) and BB (P = .002) on the fly exercise, SA (P = .001) and LT (P = .048) on the bench press, and PM (P ≤ .002) on both exercises. These results show that using an unstable surface in exercises with rotational load provides superior EMG activity of the agonist muscles, while in exercise with axial load, the instability favors EMG activity of the scapular stabilizing muscles.
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