Force irradiation effects during upper limb diagonal exercises on contralateral muscle activation

The aim of this study was to explore the force irradiation effects of upper limb isometric diagonal exercises on shoulder muscle activities. Interactions among diagonal directions, contraction intensities (moderate and maximum) and sex were assessed. Thirty healthy subjects (11 males) performed isometric unilateral diagonal exercises based on proprioceptive neuromuscular facilitation technique in an isokinetic dynamometer with their dominant upper limbs. The second diagonal for flexion and for extension were assessed while the participants performed their maximum isometric torque (MIT) and at 25% of their MIT. During the exercise the muscle activity of the medial deltoid, pectoralis major and upper trapezius in the non-dominant (non-exercised) upper limbs of the participants was recorded by surface electromyography. The highest muscle activity occurred in the upper trapezius during the diagonal for flexion (27% of maximum isometric voluntary contractions). Upper trapezius and pectoralis major were more active during the diagonal for flexion than diagonal for extension (p < 0.001), while similar values between both diagonals were observed for the medial deltoid (p > 0.05). In conclusion, we observed that force irradiation during upper limb diagonal exercises is affected by diagonal direction, contraction intensity and sex when performed by healthy participants.