|Abstract or Summary
- PURPOSE: The purpose of this research was to quantify the effects of a warm-up with static or dynamic stretching on countermovement jump height, reaction time, muscle onsets for tibialis anterior (TA) and vastus lateralis (VL), and low back/ hamstring flexibility.
METHODS: Twenty one recreationally-active males (24.4 ± 4.5 yrs), recruited from the university community, completed 3 data collection sessions. Inclusion criteria were regular participation (30 minutes, 3 days per week) in exercise including resistance training, sprinting, or jumping, and no history of lower extremity injury in the past 6 months. Each session included a 5 minute treadmill jog followed by one of the stretch treatments: no stretching (NS), static stretching (SS), or dynamic stretching (DS). After the general warm-up and treatment, the participant performed a sit-and-reach test to assess low back and hamstring flexibility. Next, the participant completed a series of ten maximal-effort countermovement jumps (CMJ), during which he was asked to jump as quickly as possible after seeing a visual stimulus (light). The onset of movement and CMJ height were determined from force plate data, and muscle onsets (TA and VL) were obtained using surface electromyography (sEMG). Ground reaction forces were recorded at 2000 Hz using a portable force plate, and filtered at 25 Hz. Outcome measures included maximal jump height, reaction time, and muscle onset (TA and VL). A repeated measures 3 (treatment) by 8 (jump) ANOVA was used to assess CMJ height. Additional outcome measures
(reaction time, muscle onsets, flexibility) were assessed using separate repeated-measures one-way ANOVA.
RESULTS: Results of the 3x8 repeated-measures ANOVA for CMJ height revealed a significant main effect of treatment (p=.004). Post hoc analysis showed significant differences between NS (41.4cm) and DS (43.0cm) (p=.0045), and between SS (41.9cm) and DS (p=.0435), but not between NS and SS (p=.4605). Analysis also
revealed a significant main effect of jump (p=.005) on CMJ height: mean jump height progressively decreased from the early to the late jumps. No significant interaction between treatment and jump was observed (p=.571). The analysis of reaction time,
TA and VL sEMG onsets showed no significant effects. Treatment also had a main effect (p<.001) on flexibility. Post hoc analysis revealed improved flexibility after both SS (p=.002) and DS (p<.001) compared with NS, with no difference in flexibility between the two treatments (p=.530).
CONCLUSION: CMJ height was significantly higher during the DS condition compared to SS and NS, with no difference between NS and SS. Additionally, reaction time and muscle onsets were not influenced by either stretch technique.
Athletes in sports requiring lower-extremity power should use dynamic stretching
techniques in warm-up to enhance flexibility while improving performance.