Acute static stretching does not alter balance control ability: the role of neuromuscular activation

Balance control (BC) is the resultant of an integrative network involving sight, hearing, vestibular function, and proprioceptive feedback. Perturbations of one of these contributors could turn into a worsening of BC regulation. Passive stretching (PS) has been reported to affect proprioceptive feedback, thus possibly decreasing BC ability. This study evaluated the acute effects of PS and active stretching (AS) of the lower limbs on static and dynamic BC parameters. Thirty-eight participants (age: 26±3 yrs; stature: 1.72±0.10 m; body mass: 69±17 kg) underwent PS, AS and control sessions randomly on different days. Stretching routines had similar durations and involved bilaterally the muscles acting around the knee and ankle. Before and after stretching, hip, knee and ankle range of motion (ROM), maximum voluntary isometric contraction (MVC), and maximum muscles activation [surface electromyography, sEMG, root mean square (RMS) from the investigated muscles] were measured. Static and dynamic BC parameters were determined by stabilometry in bipedal and monopedal conditions (with both open and closed eyes). sEMG was recorded during balance test and normalized to MVC. After stretching, ROM increased in all the joints (p<0.001) and MVC decreased (PS: p<0.001; AS: p=0.03) together with RMS (PS: p=0.01; AS: p=0.02) in all the investigated muscles. BC resulted unaffected. However, an overall significant increment in sEMG RMS was found in all the tested muscles during balance tests (p from 0.02 to <0.001).These findings suggest that, muscles directly involved in BC were more activated to maintain a similar performance, likely as a possible compensation to an altered proprioceptive feedback from the stretched muscles and joints.