Effects of antecedent flexibility conditioning on neuromuscular and sensorimotor performance during exercise-induced muscle damage

The aim of this study was to assess the effects of two modes of antecedent flexibility conditioning on neuromuscular and sensorimotor performance during a subsequent episode of exercise-induced muscle damage (EIMD). Twenty-four males (age 20.9 ± 2.3 years; height 1.78 ± 0.06 m; body mass 72.3 ± 7.4 kg, mean ± SD) were randomly assigned to interventions comprising 6 weeks of thrice-weekly flexibility conditioning of the hip region and knee flexor musculature in the dominant limb involving proprioceptive neuromuscular facilitation (n = 8), passive exercise (n = 8), or no exercise as a control (n = 8). Musculoskeletal, neuromuscular, and sensorimotor assessments were carried out at baseline, after conditioning, and before and up to 168 hours after damaging exercise of the ipsilateral knee flexors. Flexibility conditioning and EIMD elicited transient performance decreases in volitional electromechanical delay (up to 40.1% compared to baseline; 67.5 ± 12.3 milliseconds vs. 47.9 ± 9.7 milliseconds, mean ± SD, 48-hour post- vs. pre-EIMD; p < 0.01), passive hip flexibility (up to 19.9%; 96.7° ± 8.2° vs. 120.7° ± 11.0°, p < 0.001) and sensorimotor capability (manifold error increase to 10.8%; 10.8% ± 6.9% vs. 0.3% ± 3.7%, p < 0.05) and exceeded the effects of eccentric exercise alone. EIMD-related performance decreases were especially prominent when preceded by passive flexibility conditioning, and were sufficiently potent following both modes of antecedent conditioning to raise concerns about compromised capability for rapid and dynamic stabilization of synovial joints.