Monitoring Elite Youth Football Players' Physiological State Using a Small-Sided Game: Associations With a Submaximal Running Test

Purpose: To examine the utility of a standardized small-sided game (SSG) for monitoring within-player changes in mean exercise heart rate (HRex) when compared with a submaximal interval shuttle-run test (ISRT). Methods: Thirty-six elite youth football players (17 [1] y) took part in 6 test sessions across an in-season period (every 4 wk). Sessions consisted of the ISRT (20-m shuttles, 30 '':15 '' work:rest ratio, 70% maximal ISRT) followed by an SSG (7v7, 80 x 56 m, 6 min). HRex was collected during both protocols, with SSG external load measured as high-speed running distance (>19.8 km center dot h-1) and acceleration distance (>2 m center dot s-2). Data were analyzed using linear mixed-effect models. Results: Controlling for SSG external load improved the model fit describing the SSG-ISRT HRex relationship (chi 2 =12.6, P = .002). When SSG high-speed running distance and SSG acceleration distance were held constant, a 1% point change in SSG HRex was associated with a 0.5% point change in ISRT HRex (90% CI: 0.4 to 0.6). Inversely, when SSG HRex was held constant, the effects of a 100-m change in SSG high-speed running distance and a 21-m change in SSG acceleration distance on ISRT HRex were -1.0% (-1.5 to -0.4) and -0.6% points (-1.1 to 0.0), respectively. Conclusions: An SSG can be used to track within-player changes in HRex for monitoring physiological state. Given the uncertainty in estimates, we advise to only give meaning to changes in SSG HRex >2% points. Additionally, we highlight the importance of considering external load when monitoring SSG HRex.