Validity of a Jump Mat for assessing Countermovement Jump Performance in Elite Rugby Players

This study determined the validity of the Just Jump System (R) (JJS) for measuring flight time, jump height and peak power output (PPO) in elite rugby league players. 37 elite rugby league players performed 6 counter-movement jumps (CMJ; 3 with and 3 without arms) on a jump mat and force platform. A sub-sample (n = 28) was used to cross-validate the equations for flight time, jump height and PPO. The JJS systematically overestimated flight time and jump height compared to the force platform (P < 0.05), but demonstrated strong associations for flight time (with R-2 = 0.938; without R-2 = 0.972) and jump height (with R-2 = 0.945; without R-2 = 0.987). Our equations revealed no systematic difference between corrected and force platform scores and an improved the agreement for flight time (Ratio limits of agreement: with 1.00 vs. 1.36; without 1.00 vs. 1.16) and jump height (with 1.01 vs. 1.34; without 1.01 vs. 1.15), meaning that our equations can be used to correct JJS scores for elite rugby players. While our equation improved the estimation of PPO (with 1.02; without 1.01) compared to existing equations (Harman: 1.20; Sayers: 1.04), this only accounted for 64 and 69 % of PPO.