Author(s): HITIER, M., EHEMBA, J.N., VIEIRA, D., DURIGAN, J.L.Q., BABAULT, N., Institution: UNIVERSITÉ DE BOURGOGNE, Country: FRANCE, Abstract-ID: 1589

INTRODUCTION:
Dynamic stretching is recommended during warm-up routines (Opplert and Babault, 2018). Mechanisms remained unclear and are partly related to a warm-up effect (Vieira et al., 2021). One can question whether increasing the intensity of dynamic stretching could exacerbate any warm-up effect. The present study aimed to explore the effects of various loading conditions during active dynamic stretching on hamstring muscle strength and range of motion.
METHODS:
12 physically active volunteers (3 women and 9 men) were included in this cross-over randomized study. Experimental sessions included a standardized comprehensive warm-up followed by 1 of the 3 experimental conditions: 1. unloaded dynamic stretch, 2. loaded dynamic stretch, and 3. control (no stretch). Dynamic stretching was 5 series of 15 repetitions at 1 Hz without or with an extra-load during the concentric phase (i.e., 20 or 40 N.m for women and men, respectively). Tests were performed before all sessions (Pre), after warm-up (Post-Warm), and after the experimental conditions (Post-Stretch). Tests included maximal voluntary isometric contractions of the hamstrings combined with the electromyographic activity (EMG) of biceps femoris (BF) and semitendinosus (ST) muscles and a passive maximal range of motion (ROM) test until maximal discomfort. Tests and experimental conditions were conducted on the right hamstrings on an isokinetic dynamometer. Two-way analysis of variances was used to compare conditions (unloaded vs. loaded stretch vs. control) and time (Pre vs. Post-Warm vs. Post-Stretch) effects.
RESULTS:
No significant condition x time interactions were obtained for the maximal torque (p=.456). A very slight increase in maximal torque was observed Post-Warm but did not reach the level of significance (p=.129). No interaction was observed for BF and ST EMG (p=.676 and p=.587, respectively). A significant time effect was obtained for ST EMG (p=.01) with lower values Post-Warm and Post-Stretch compared to Pre. No significant interaction was observed for the ROM (p=.134). A significant time effect revealed maximal ROM was significantly increased Post-Warm as compared to Pre (p=.001) and increased further Post-Stretch (p=.001).
CONCLUSION:
Active dynamic stretching whether performed unloaded or with an extra-load did not alter the force production capacity. Regardless of the extra-load, dynamic stretching increased the maximal ROM. Interestingly, dynamic stretch is not mandatory for ROM increases as it was already increased after the comprehensive warm-up. Thus, performing dynamic stretching within a warm-up routine remained questioned.
REFERENCES:
(1) Opplert J, Babault N. Sport Med, 2018, 48:299–325.
(2) Vieira D, Opplert J, Babault N. Eur J Appl Physiol, 2021, 121,957-967.