comparison of muscular performance induced by maximum voluntary isometric contraction durationsin pnf training

proprioceptive neuromuscular facilitation (pnf) training (contraction - relaxation method), in compared to the other methods of static and dynamic stretching exercises; has higher and safer effects on enhancement of hamstring muscle's flexibility, strength and endurance. achieving the optimal combination of contraction and stretching phases in pnf training that can increase these factors of physical fitness is controversial. therefore, this quasi-experimental study was conducted to determine and compare of the effects of combined phases of 5, 10, and 15 seconds of maximum voluntary isometric contraction and 10 seconds of passive stretching (up to pain threshold) in pnf training (contraction - relaxation method) on flexibility, strength, and endurance of hamstring muscle in nonathlete men. 40 men were selected from 55 non-athlete volunteer men of 20-25 years old eligible. the participants were divided into 4 groups, each with 10 men. the training was performed three times a week for 6 weeks, and each session lasted one hour according to the progressive overload principle. muscle strength was measured by using one repetition maximum (1rm) test. muscle endurance was measured by using number of repetitions with 70% of 1rm (70%*1rm) of hamstring muscle. flexibility of hamstring muscle was measured with modified srt (sit & reach test). within group's comparison were done with two tailed paired sample t-test. between groups comparison were done with one-way anova and tukey post hock test. all tests significant level was set at p0.05. between group's differences of muscle strength and endurance were significant in post-test (p 0.001*). within group's difference of muscle strength were significant in 5sec (p 0.001*), 10sec (p 0.001*), and 15sec groups (p 0.001*). within group's difference of muscle endurance was significant in 10sec (p 0.001*) and 15sec groups (p 0.001*). between group's differences of flexibility was not significant in post-test (p = 0.155). within group's difference of flexibility were significant in 5sec (p 0.001*), 10sec (p 0.001*), and 15sec groups (p 0.001*). therefore, this training can increase the flexibility, strength, and endurance of hamstring muscle in non-athlete men. keywor