Comparative Effect of Reciprocal Inhibition and Static Stretching Technique on Hip Flexion Range of Motion in Individuals with Iliopsoas Tightness

Abstract

Background: Iliopsoas tightness is common in individuals with prolonged sedentary exposure and may restrict hip extension, alter lumbopelvic mechanics, and contribute to compensatory movement. Reciprocal Inhibition (RI) and Static Stretching (SS) represent two different approaches to improving muscle length: RI uses an antagonist contraction to facilitate reflex relaxation of the iliopsoas, whereas SS relies on sustained passive mechanical elongation. Objective: To compare the effect of RI and SS on hip flexion range of motion, quantified through hip extension capability, in individuals with iliopsoas tightness. Methods: A randomized experimental pre-test/post-test comparative study included 30 participants aged 20–40 years with a positive Modified Thomas Test and sedentary occupations involving more than six hours of sitting per day. Participants were allocated equally to Group A (RI, n=15) and Group B (SS, n=15). Interventions were delivered for two weeks, six sessions per week. Hip extension ROM was measured with a universal goniometer in the Modified Thomas Test position. Paired and independent t-tests, Pearson correlation, chi-square analysis, and Cohen’s d were used. Results: RI increased mean hip extension ROM from 171.42±3.25° to 185.24±2.88° (mean gain 13.82°, p<0.001), while SS increased ROM from 172.15±3.10° to 180.30±2.95° (mean gain 8.15°, p<0.001). The mean between-group difference in improvement was 5.67° (p<0.001). Post-treatment Modified Thomas Test negativity was 93.3% with RI and 46.7% with SS. Baseline ROM correlated negatively with BMI (r=-0.684) and daily sitting hours (r=-0.742), both p<0.001. Conclusion: Both techniques improved iliopsoas flexibility, but RI produced substantially larger ROM gains and a higher clinical normalization rate than SS over the two-week intervention period.