Shoulder Muscle Activation Levels During Exercises With Axial and Rotational Load on Stable and Unstable Surfaces

in Journal of Applied Biomechanics
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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.

Nascimento, Torres, dos Santos, and Pitangui are with the Department of Physical Therapy, University of Pernambuco, Petrolina, Pernambuco, Brazil. Beltrão is with the Department of Physical Education, University of Pernambuco, Recife, Pernambuco, Brazil; and the Department of Physical Education, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil. Pirauá is with the Department of Physical Education, University of Pernambuco, Recife, Pernambuco, Brazil; and the Department of Physical Education, Asces College, Caruaru, Pernambuco, Brazil. De Oliveira and de Araújo are with the Department of Physical Therapy, University of Pernambuco, Petrolina, Pernambuco, Brazil; and the Department of Physical Education, University of Pernambuco, Recife, Pernambuco, Brazil.

Address author correspondence to Natália Barros Beltrão at nat.barros@gmail.com.