Maximal strength and power capabilities of athletes are often trained in an attempt to enhance maximal power output and sport-specific performance. Recently, there has been consdierable research focused on identifying the load which maximises peak concentric mechanical power (Pmax) (1,2,3). Researchers have suggested that the power outputs at loads either side of the identified load for Pmax are insubstantial (1,3) and the preoccupation with identifying Pmax is unwarranted (3). As such the concept of adopting a `bandwidth` of loads approach for training prescription is gaining momentum, yet despite the prevalence of this practice, no research to date has quantified what a `substantial` or `insubstantial` difference in power output across loads is for the incremental load-power profile. The purpose of this study therefore was to quantify the smallest substantial difference in peak concentric mechanical power across a spectrum of loads in the jump squat (countermovement jump) for team sport athletes. Methods To quantify the substantial difference in power output for the load power profile, 16 elite Australian Rules Football and 20 highly trained Rugby Union players performed 3 jump squats across a spectrum of incremental loads (0, 10, 20, 30, 40, 50, and 60kg). Measurement of force-time and displacement-time data was collected at a sampling frequency of 200Hz using a force plate (400 Series Performance Force Plate, Fitness Technology, Adelaide, Australia) and linear position transducer (Ballistic Measurement System, Fitness Technology, Adelaide, Australia) for calculation of power output using the system mass. To estimate the load which elicited Pmax, a quadratic was fitted to the log transformed peak concentric power output (mean of 3 jump squats) and load of each player. To quantify the substantial difference in power output across loads, the quadratic was used to estimate power output at each load. The smallest substantial difference was then calculated as 0.2 of the log transformed between athlete SD for peak power at each load. Back transformation of the log data was applied to express the smallest substantial difference as a percent. Results Mean Pmax for elite Australian Rules Football players was 5151.0 ± 996.7 W and occurred at a load of 0.0 ± 0.0kg. Mean Pmax for highly trained Rugby Union players was 6193.9 ± 1101.9 W, corresponding to a load of 0.0 ± 0.0kg. The smallest substantial difference in power output across loads for elite Australian Rules Football and Rugby Union players was 4.1% (90% CI: 3.2-5.9%) and 3.5% (90% CI: 2.8-4.8%) respectively. Discussion/Conclusion The optimal load for production of peak power in the jump squat in elite Australian Rules Football and highly trained Rugby Union players occurred at an external load of 0kg. Loads corresponding to peak powers that are within 3.5% and 4.1% of Pmax for Australian Rules Football and Rugby Union players are not substantially different from the Pmax and can be prescribed for jump squat training. Practitioners should consider the smallest substantial difference in power output across loads when interpreting the load-power profile for adequate prescription of training loads to enhance peak mechanical power.
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