Are three recovery days enough? Elevated match day creatine kinase levels under congested schedules in youth soccer

We examined if creatine kinase (CK) activity differed between congested (CS) and non-congested schedules (NCS) in elite youth national team soccer players. The CK activity of 188 players (16.53 ± 1.78 years) was measured in national team training camps (2489 individual data points). Training load one day before the match (MD-1) was monitored with global positioning system (GPS) devices. CS occurred, when the athlete played at least 60 minutes in the previous 3 days leading into the match (MD). CK_MD was significantly higher in CS than in NCS (median: 309 vs 220 U/L, p < 0.05). More recovery days between matches were associated with lower values on the second CK_MD. CK values one (CK_MD+1: 678 vs 487 U/L) and two days after the match (CK_MD+2: 395 vs 303 U/L) were higher for CS (p < 0.05), however relative CK changes from MD to one (CK_MD→MD+1%: 181 vs 135%) or two days after (CK_MD→MD+2%: 74 vs 44%) were higher for NCS (p < 0.05). 11 out of 15 MD-1 training load parameters were significantly higher for NCS (p < 0.05). CK_MD was sensitive to congested schedule and the number of recovery days between matches. Therefore three recovery days between matches might be inadequate for complete recovery. Higher CK_MD, CK_MD+1 and CK_MD+2 values, but lower CK_MD→MD+1% and CK_MD→MD+2% changes were found for CS than for NCS. MD-1 training load was lower in CS than in NCS, making it an unlikely cause of the elevated CK_MD and CK_MD+1 values. Instead, it might be the result of residual fatigue from the last match.