Determining the Effects of a 6-Week Training Intervention on Reactive Strength: A Single-Case Experimental Design Approach.

Objectives: Single-case experimental designs (SCEDs) provide a robust way to observe adaptations to training in highly specific populations. Furthermore, they provide unique insights into inter-participant variance in responses to interventions, which traditional randomized control trials cannot obtain. However, there is limited sports science literature that has applied this methodology to assess the effectiveness of training interventions. Thus, the aim of this study was to determine the individual and combined changes to reactive strength following a 6-week strength and plyometric training intervention. Methods: A non-concurrent multiple baseline SCED was used, where four participants completed weekly 10/5 repeated jump (RJ), drop jump (DJ), and loaded squat jumps during a 5-7-week baseline phase and a 6-week intervention phase. The intervention consisted of traditional resistance and plyometric training. Results: The results found inter-participant variance in changes to reactive strength, with some individuals having significant improvements whilst others declined. The combined results found that during the intervention, the reactive strength index (RSI) of the RJ significantly decreased (baseline: 2.15 vs. intervention: 2.0) whilst no change in DJ occurred. This led to a significant increase in the reactive quality ratio (RQR) (baseline: 1.02 vs. intervention: 1.08). Conclusions: These findings highlight the importance of considering individual responses to training reactive strength rather than cohort observations alone, and the SCED is a viable methodology to achieve this. Practitioners should consider exercise selection, maximum strength levels and responsiveness of individuals when prescribing plyometric exercise to improve high and low amplitude reactive strength qualities.