The reliability of isoinertial force–velocity–power profiling and maximal strength assessment in youth

The purpose of this study was to quantify the inter-session reliability of force–velocity–power profiling and estimated maximal strength in youth. Thirty-six males (11–15 years old) performed a ballistic supine leg press test at five randomized loads (80%, 100%, 120%, 140%, and 160% body mass) on three separate occasions. Peak and mean force, power, velocity, and peak displacement were collected with a linear position transducer attached to the weight stack. Mean values at each load were used to calculate different regression lines and estimate maximal strength, force, velocity, and power. All variables were found reliable (change in the mean [CIM] ¼ -1 to 14%; coefficient of variation [CV] ¼ 3–18%; intraclass correlation coefficient [ICC] ¼ 0.74–0.99), but were likely to benefit from a familiarization, apart from the unreliable maximal force/velocity ratio (CIM ¼ 0–3%; CV ¼ 23– 25%; ICC ¼ 0.35–0.54) and load at maximal power (CIM ¼ -1 to 2%; CV ¼ 10–13%; ICC ¼ 0.26– 0.61). Isoinertial force–velocity–power profiling and maximal strength in youth can be assessed after a familiarization session. Such profiling may provide valuable insight into neuromuscular capabilities during growth and maturation and may be used to monitor specific training adaptations