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The Long-Term Effects Of Resisted Sprint Training Using Weighted Sleds Versus Weighted Vests

Clark, Kenneth; Walts, Cory; Miller, Anthony; Stearne, David

The Journal of Strength & Conditioning Research: January 2010 - Volume 24 - Issue - p 1
doi: 10.1097/01.JSC.0000367084.42886.88

Linear sprinting is composed of acceleration and maximum velocity (MV) phases, and improving performance in each phase may require specific training methods. Although resisted sprint training using weighted sleds (WS) or weighted vests (WV) has recently become common practice, empirical evidence supporting their effectiveness for improving MV sprint performance is lacking. Furthermore, it has been suggested that these modalities may have different long-term effects on sprint kinematics, with WS potentially increasing stride length and WV decreasing ground-contact time and thus increasing stride rate. To determine the long-term effects of WS and WV training on MV sprint performance and kinematic parameters. 20 male NCAA Division-III lacrosse players (age: 19.82 ± 0.95 years, mass: 83.13 ± 11.69kg) voluntarily participated as part of their off-season training program. Subjects were randomly divided into a WS group (n = 7), a WV group (n = 6), and an unresisted (UR) active control group (n = 7). All subjects completed 13 60-minute training sessions over a 7-week period. WS subjects towed loads of 10% body mass, and WV subjects were loaded with 18.5% body mass. Pilot testing indicated these loads elicited acute decreases in MV approaching 10% and thus were appropriate for long-term training based on recommendations from the literature. Pre-and post-test measures of sprint time and average velocity across the distance interval of 18.3-54.9m were used to assess MV sprint performance, while high-speed video (300 Hz) and motion-analysis software were used to analyze kinematic measures of stride length (SL), stride rate (SR), average step ground time (GT), and average step flight time (FT). A 3 (training group) × 2 (time) repeated measures ANOVA revealed no significant between-group differences for either 18.3-54.9m sprint times or average velocities. Effect size statistics (ES) suggested small improvements in average velocity for the UR group (ES = 0.63) but only trivial improvements for the WS (ES = 0.02) and WV groups (ES = 0.24). A 3 × 2 repeated measures ANOVA also revealed no significant between-group differences for any of the kinematic stride cycle measures. Effect size statistics suggested small increases in SR (ES = 0.42) and decreases in GT (ES = 0.38) for the UR group, small decreases in SL (ES = 0.42) for the WS group, as well as small decreases in SL (ES = 0.37), moderate increases in SR (ES = 0.78), and large decreases in FT (ES = 1.00) for the WV group. The results indicate that WS and WV training had no beneficial effect compared with UR training. In fact, for the loads employed by WS and WV in this study, UR training may actually be superior for improving MV sprint performance in the 18.3-54.9m interval. Also of note, the WS group did not demonstrate significant increases in SL and the WV group did not demonstrate significant decreases in GT as expected. For the loading schemes employed in this study, the results suggest that MV sprint performance might be most effectively enhanced by UR training protocols. Future research should be directed at manipulating the resistance load for the WS and WV groups to explore the effects of lighter loads that more closely match the kinematics of UR sprinting or heavier loads that increase the resistive training stimulus. This investigation was supported by an NSCA Student Research Grant.

© 2010 National Strength and Conditioning Association