A Standardized Small Sided Game Can Be Used to Monitor Neuromuscular Fatigue in Professional A-League Football Players

Abstract

Introduction: Training and competition load can cause neuromuscular fatigue (NMF) and modified movement strategy such as an increase in the contribution of the medio-lateral [PlayerLoad^TM_ML(%)] and decrease in the % vertical [PlayerLoad^TM_V(%)] vectors, to total PlayerLoad^TM (accelerometer derived measurement in vertical, medio-lateral, and anterior-posterior planes) in matches. NMF assessment involves expensive equipment, however, given the modification of match movement strategy with NMF, this may be present in a standardized drill. The aim of this study was to determine the utility of a small sided game (SSG) for the measurement of NMF. Materials and Methods: Data was collected throughout a competitive football season. External load was quantified using global positioning system (GPS) and accelerometry, and internal load by session rating of perceived exertion (sRPE). A 5 vs. 5 SSG and countermovement jump (CMJ), for determination of flight time:contraction time (FT:CT), were performed the day prior to each match. Weekly volume from GPS, PlayerLoad^TM and sRPE were calculated across the season. Weekly SSG activity profile and FT:CT was compared between "high" and "low" load weeks determined relative to season average. SSG activity profile was assessed between weeks where FT:CT was above or below pre-season baseline. Impact on match activity profile was examined between weeks where FT:CT and SSG activity profile were higher or lower than baseline. The difference (high vs. low load and < or > pre-season baseline) was calculated using the effect size (ES) ± 90% CI and practically important if there was a >75% likelihood of exceeding an ES of 0.2. Results: All weekly load metrics increased SSG PlayerLoad^TM⋅m⋅min^-1 when above season average, however, the impact on FT:CT was trivial. Reduced weekly FT:CT compared to baseline resulted in lower SSG PlayerLoad^TM⋅min^-1 and PlayerLoad^TMSlow⋅min^-1. FT:CT below baseline increased match PlayerLoad^TM_ML(%) and decreased PlayerLoad^TM_V(%) during subsequent match play. Similarly, a reduction in SSG PlayerLoad^TM⋅m⋅min^-1 was followed by increased match PlayerLoad^TM_ML(%). Conclusion: Changes in select match activity profile variables following a reduction in SSG PlayerLoad^TM m.min^-1, mirror those seen when FT:CT is reduced. Increased PlayerLoad^TM_ML(%) during matches likely represents fatigue driven modification to movement strategy. Small-sided games may be a useful tool to detect NMF.

Keywords: GPS; PlayerLoadTM; accelerometer; countermovement jump; soccer; training load.

FIGURE 1

Diagrammatic representation of the steps of analysis. Small-sided game; SSG, Flight time:Contraction time ratio; FT:CT.

FIGURE 2

Change in small-sided game; SSG activity profile metrics (A) and match exercise intensity (B) based on flight time:contraction time; FT:CT < and > baseline by more than the 8 %CV. Symbols denote a ^∗∗likely, ^∗∗∗very likley, and ^∗∗∗∗most likley chance that the change has exceeded the smallest worthwile change of 0.2 (shaded in gray).

FIGURE 3

Change in match exercise intensity based on small-sided game; SSG PlayerLoad^TM per relative distance (meter per minute); PL⋅m⋅min^-1 < and > baseline, by more than 1.0, 1.5, and 2.0x %CV. Symbols denote a ^∗∗likely, ^∗∗∗very likely, and ^∗∗∗∗most likely chance that the change has exceeded the smallest worthwile change of 0.2 (shaded in gray).

FIGURE 4

Change in match exercise intensity based on small-sided game; SSG PlayerLoad^TM Slow per minute; PLSlow⋅min^-1 < and > baseline, by more than 1.0, 1.5, and 2.0x %CV. Symbols denote a ^∗∗likely, ^∗∗∗very likley, and ^∗∗∗∗most likley chance that the change has exceeded the smallest worthwile change of 0.2 (shaded in gray).

FIGURE 5

Diagrammatical representation of the impact of high weekly load compared to low weekly load, on small-sided game; SSG accelerometer derived metrics and flight time:contraction time ratio; FT:CT, the related change in match activity profile due to increased small-sided game; SSG activity profile and the impact of suppressed small-sided game; SSG activity profile and flight time:contraction time; FT:CT on subsequent match activity profile.