Dose-Response Relationship between Training Load and Changes in Aerobic Fitness in Professional Youth Soccer Players

Purpose: The aim of this study was to compare the dose-response relationship between, traditional arbitrary speed thresholds versus an individualised approach, with changes in aerobic fitness in professional youth soccer players. Methods: Fourteen youth soccer players, completed a 1500 metre time trial to estimate maximal aerobic speed (km.h-1, (MAS)) at the start and the end of a six week period. Training load was monitored on a daily basis during this study. External load measures were; total distance covered (TD), total acceleration and deceleration distance > 2m.s-2 (A/D Load). Arbitrary high speed running measures were; metres covered and time spent > 17 km.h-1 (m>HSD, t>HSD) and 21 km.h-1 (m>VHSD, t>VHSD). Individualised high speed running measures were; metres covered and time spent > MAS km.h-1 (m>MAS, t>MAS) and 30% anaerobic speed reserve (m>30ASR, t>30ASR). In addition, internal load measures were also collected; heart rate exertion (HRE) and rating of perceived exertion (RPE). Linear regression analysis was used to establish the dose-response relationship between mean weekly training load and changes in aerobic fitness. Results: Substantial very large associations were found between t>MAS and changes in aerobic fitness (R2 = 0.59). Substantial large associations were found for t>30ASR (R2 = 0.38) and m>MAS (R2 = 0.25). Unsubstantial associations were found for all other variables. Conclusion: An individualised approach to monitoring training load, in particular t>MAS, may be a more appropriate method than using traditional arbitrary speed thresholds when monitoring the dose-response relationship between training load and changes in aerobic fitness