title: Changes in Sprint Kinetics or Kinematics Following Static or Dynamic Stretching
Creators: name: Bartel, Kristyne
Publisher: name: University of Nevada, Las Vegas
Year: 2015

description: The purpose of this study was to determine the effects of static or dynamic stretching on hip kinematics and kinetics during intermittent sprinting. To achieve this aim, intermittent sprint athletes were asked to complete either a static or dynamic stretch, followed by a repeated-sprint protocol. Hip joint kinematics and performance measures were evaluated during the sprint, including changes that occurred in these variables over the course of the sprint protocol. In addition, hip flexion torque was measured with an isokinetic dynamometer. Ten male (age = 25±2.3 years, 175±3.2 cm, 76.2±2.7 kg) and female (age = 20±1 years, 166±1.3 cm, 60±1.1 kg) recreational soccer players were recruited from the Las Vegas community. Participants reported to the Sports Injury Research Center for data collection on two days separated by at least 48 hours. Before providing consent (IRB Protocol #724261-2), participants were able to ask any questions and familiarize themselves with the isokinetic dynamometer. Data collection consisted of: 1) 5-minute walking warm up on a treadmill at a preferred speed, 2) baseline hip flexion torque measurements, 3) either a static or dynamic stretch, 4) post-stretch torque measurements, 5) 6 x 20-meter sprints with 2 minutes rest between each trial, and 6) post-sprint torque measurements. On day two, participants completed the alternate stretch condition (step 3). Hip flexion torque output values extracted using Biodex Software were entered into Microsoft Excel and peak torque values were identified for each measurement period (baseline, post stretch, post sprint) for each condition (dynamic stretch or static stretch). These values were analyzed using a 2 (stretch) x 3 (time), repeated measures factorial analysis of variance (ANOVA) with a Bonferroni adjustment using SPSS for Windows (IBM, v. 22, Armonk, NY). Multiple comparison post-hoc analysis was completed using a one-way repeated measures ANOVA and paired t-tests. Sprint times were recorded during collection and entered into Microsoft Excel, where the average sprint time for each condition was calculated, as well as the time difference between sprints 1 and 6. Two separate paired samples t-tests were completed for average sprint speed and T1-T6 differences for each condition with significance set to α=0.05. Hip angular velocity was calculated during the initial swing phase using MaxTRAQ software (Innovision Systems, Inc., Columbiaville, MI). Initial swing was defined as toe-off to maximum knee flexion. These identifying positions were determined using the markers placed prior to data collection. Angular position data for the hip and knee were filtered with a zero lag, low-pass, 4th order Butterworth filter with a cutoff frequency of 12 Hz. From the angular position data, instantaneous angular velocity was calculated for each frame that comprised the initial swing phase of sprints 1 and 6. The length in frames of the phase was normalized by percent, and the phase percent at which peak instantaneous velocity occurred was noted. Paired samples t-tests were completed for both peak instantaneous velocity and percent phase of peak instantaneous velocity for each condition with significance set to α=0.05. Results of statistical analysis yielded no significant results. However, angular velocity values and torque measurements were greater following dynamic stretch and sprint times were faster. The lack of statistical significance may be explained by several factors, specifically large variability within a small sample. Future research would benefit by increasing the sample size, matching participant experience and playing level, and potentially increasing the number and length of stretches performed.