Objective: The aim of the present study was to compare the effect of ratios of contraction- Relaxation on the muscle strength and range of motion of hip joint in PNF exercises.

Methods: Thirty nine nonathletic male students (Mean±SD; age, 13±1.2 years; body mass, 55±9.8 kg) were assigned .Three groups designated as I, II and III groups. The ratios of contraction to relaxation periods for groups were 1, 2 and 3 respectively. Training program included three sessions per week (CR-PNF) for 6 weeks. Measurements of hip extensors muscles stretch and strength were performed at the beginning and at the end of training using an inclinometer (during leg raise test) and dynamometer. Data were analyzed using dependent samples t-test and one-way ANOVA.

Results: The results of the present study showed significant increases in hip extensor muscles flexibility and strength for three groups. This increase the in the strength in group I equaled 6 kg, in group II 4 kg and in group III 7 kg. The amount of increase in the hip extensor muscles flexibility in group I, II and II were 15, 8 and 12 degrees, respectively.  The increase in these two variables was significant and similar in all three groups.

Conclusion: Different contraction to relaxation ratio normally, 0.5, 1 and 2, did not show any meaningful differences on hip extensor muscular strength and hip range of motion.