Abstract
The primary aim of this investigation was to determine the effects of a four-week period of in-season strength training on the dynamic strength index (DSI). Pre and post a four-week period of strength-based training, twenty-four collegiate athletes (age = 19.9 ± 1.3 years; height = 1.70 ± 0.11 m; weight 68.1 ± 11.8 kg) performed three isometric mid-thigh pulls and countermovement jumps to permit the calculation of DSI. T-tests and Cohen’s effect sizes revealed a significant but small (p = 0.009, d = 0.50) decrease in DSI post-training (0.71 ± 0.13 N·N−1) compared to pre-training (0.65 ± 0.11 N·N−1); however, when divided into high and low DSI groups, differential responses were clear. The low DSI group exhibited no significant or meaningful (p = 1.000, d = 0.00) change in DSI pre to post-training (0.56 ± 0.05 N·N−1, 0.56 ± 0.09 N·N−1, respectively), whereas the high DSI group demonstrated a significant and large decrease (p = 0.034, d = 1.29) in DSI pre to post-training (0.85 ± 0.05 N·N−1, 0.74 ± 0.11 N·N−1, respectively), resulting in a significant and moderate difference (p = 0.034, d = 1.29) in the change in DSI between groups. These results demonstrate that DSI decreases in response to strength training, as expected, due to an increase in isometric mid-thigh pull peak force, with minimal change in dynamic (countermovement jump) peak force.
Highlights
To ensure that the previous phase of training has resulted in the desired changes in performance and to identify priorities for subsequent phases of training, accurate monitoring of changes in performance in response to training is essential [1]
In response to different training stimuli have been reported by researchers. The aims of this investigation were to determine the effects of a four-week period of in-season strength training on dynamic strength index (DSI), the components of DSI, jump height, and time to take-off (TTT) during the countermovement jump (CMJ)
The between-subject approach was used to determine if any differences in changes in dependent variables were observed between high and low-DSI groups, with an a priori power calculation determining that a minimum of 7 subjects per group was required for a statistical power of ≥0.80 at an a priori alpha level of p < 0.05
Summary
To ensure that the previous phase of training has resulted in the desired changes in performance and to identify priorities for subsequent phases of training, accurate monitoring of changes in performance in response to training is essential [1]. Appropriate analysis of CMJ force-time data can provide detailed insight into changes in jump height and jump strategy, with time to take-off (TTT) (sometimes referred to as contraction time) being indicative of changes in movement time and countermovement displacement (squat depth) [5,6,7]. To date, no data illustrating the changes in DSI in response to different training stimuli have been reported by researchers The aims of this investigation were to determine the effects of a four-week period of in-season strength training on DSI, the components of DSI (namely, CMJ PF and IMTP PF), jump height, and TTT during the CMJ. It was hypothesized that both the low and high DSI groups would demonstrate a decrease in DSI as a result of an increase in IMTP PF, in line with previous suggestions [15]
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