Changes in contractile properties after 24 weeks of stretching exercise

Abstract

Introduction: The effects of long-term stretching training and chronic stretching regimens on muscle performance have not yet been systematically investigated on a wider scale. Studies that have investigated possible correlations between stretching and muscular performance are scarce and inconclusive in the literature. Thus, the purpose of the present study was to examine the effect of long-term (24 weeks) stretching exercise on muscle contractile properties. Method: Eighteen subjects (five men and thirteen women; 21.82 ± 1.74 yrs, 71.80 ± 11.65 kg, 1.77 ± 5.56 m) volunteered to participate in this study. The training leg was randomly drawn and unilateral static stretching exercises (SS) were applied every day for twenty-four weeks. The SS protocol consisted of four repetitions of stretch, each lasting for one minute with a sixty second rest in between, aiming to increase the passive range of motion (ROM) in ankle dorsiflexion. The testing protocol consisted of measurements pre- and post-intervention in passive ROM, passive resistance torque (PRT), isometric maximal voluntary contractions (MVC) (10˚, 0˚, -5˚ and -10˚), isokinetic peak torque (PT) and angle at PT (30, 45, 60 and 90˚/sec). Results: The ROM significantly increased pre- to post-test for the training leg by 10.42˚ (58.42%) (P>0.05). For the PRT test a significant difference was found only at the angle of -10˚ between pre- to post-test for the training leg (P>0.05). No significant changes were observed for isometric MVC, isokinetic PT and angle at PT pre- to post-test or between groups (P>0.05). For the control leg no significant differences were found. Discussion: These results suggest that the present long-term stretching intervention was effective in increasing passive ROM. Despite this highly significant change in passive ROM, no changes were seen in muscle-contractile properties. Additional longitudinal interventions are needed to better understand the long-term effects of stretching training on the angle/torque relationship and the impact on force production throughout ROM.