The moderating effects of speed, strength and endurance capacities on match induced neuromuscular fatigue in U-18 English Premier League academy football players: a hypothesis-generating case report.

Purpose: To identify new hypotheses relating to the moderating effects of speed, strength and endurance capacities on match-induced neuromuscular fatigue. Methods: 14 U-18 outfield players from one EPL academy team completed countermovement jump (CMJ) and isometric adductor (IADS) and posterior chain (IPCS) strength tests one day before match day (MD) (i.e., MD-1) and on MD+2 around 8 competitive games. Explosive strength (CMJ), reactive strength (30 cm drop jump (DJ)), speed (10m and 30m), maximal strength (isometric mid-thigh pull (IMTP)) and endurance (1 km Time Trial (TT)) were measured at 4 time points across the season. Relationships between the average match induced change to each NMF measure and the average of each physical capacity measure were examined using Pearson’s R (r) (when normally distributed) or Spearman’s rank (rho) (when not normally distributed) correlation coefficients. Results: Moderate positive relationships were observed between CMJ-JH change () and DJ-RSI (rho=0.36;p=0.16) and IMPT (r=0.46;p=0.06). Small negative relationships were observed between IADS-PF  and 10m speed (rho=0.27;p=0.29), 30m speed (r=0.22;p=0.41), CMJ-JH (rho= 0.29;p=0.26) and DJ-RSI (rho=0.36;p=0.16), and between IPCS-PF  and 10m speed (rho=0.20;p=0.45) and 1kmTT (rho=0.26;p=0.33). Conclusions: These results generate important hypotheses relating to the potential mitigating effects that reactive strength, maximal strength and endurance capacities might exert on match induced NMF in U-18 academy football players. These relationships warrant further investigation in larger research designs spanning both older and younger player age groups (i.e., across other youth development and professional development phase players) and competition levels (i.e., elite and sub-elite players).