Influence of Inter-Set Stretching on Strength, Flexibility and Hormonal Adaptations

Adequate levels of strength and flexibility are important for the promotion and maintenance of health and functional autonomy as well as safe and effective sports participation. The aim of the present study was to analyze the effects of 8 weeks of strength training with or without inter-set static stretching on strength, flexibility and hormonal adaptations of trained men. Sixteen trained men were randomly divided into 2 groups: the static stretching group (SSG) and passive interval group (PIG). All participants performed 24 training sessions 3 times a week. The test and retest of 8RM, strength, flexibility, cortisol and growth hormone concentration in pre and post test conditions were also evaluated. To compare the differences between and within groups in pre- and post-training tests, ANOVA with repeated measures was performed (SSG(pre) x SSG(post); PIG(pre) x PIG(post); SSG(post) x PIG(post)). An alpha level of p<0.05 was considered statistically significant for all comparisons. Both groups showed significant increases in strength (SSG(pre) vs. SSG(post); PIG(pre) vs. PIG(post)) in the same exercises for leg extension (LE) and Low Row (LR). Specifically, in the SSG group, the parameters for LE were (p = 0.0015 and ES = 2.28 - Large), and the parameters for LR were (p = 0.002 and ES = 1.95 - Large). Moreover, in the PIG group, the parameters for LE were (p = 0.009 and ES = 1.95 - Large), and the parameters for LR were (p = 0.0001 and ES = 2.88 - Large). No differences were found between the groups (SSG(post) vs. PIG(post)). Both groups showed significant increases in flexibility but in different joints (SSG(pre) vs. SSG(post); PIG(pre) vs. PIG(post)). In the SSG group, only three joints showed significant increases in flexibility: shoulder extension (p = 0.004 and ES = 1.76 - Large), torso flexion (p = 0.002 and ES = 2.36 - Large), and hip flexion (p = 0.001 and ES = 1.79 -Large). In the PIG group, only three joints showed increases in flexibility: horizontal shoulder abduction (p = 0.003 and ES = 2.07 - Large), hip flexion (p = 0.001 and ES = 2.39 – Large), and hip extension (p = 0.02 and ES = 1.79 - Large). In-between group analyses (SSG(post) x PIG(post)) revealed differences in two joints: shoulder extension (p = 0.001) and horizontal shoulder abduction (p = 0.001). Hormonal profiles showed no significant differences in cortisol secretion or growth hormone concentration. In conclusion, both studied strength protocols (with and without inter-set static stretching) resulted in flexibility and strength gains without an effect on the anabolic and catabolic hormonal profile.