Can We Just Play? Internal Validity of Assessing Physiological State With a Semistandardized Kicking Drill in Professional Australian Football.

Abstract

To examine associations between exercise heart rate (HRex) during a continuous-fixed submaximal fitness test (CF-SMFT) and an intermittent-variable protocol (semistandardized kicking drill [SSD]) in Australian Football athletes, controlling for external intensities, within-session scheduling, and environmental conditions. Forty-four professional male Australian Football athletes (22.8 [8.0]y) were monitored over 10 sessions involving a 3-minute CF-SMFT (12km·h-1) as the first activity and a SSD administered 35.7 (8.0)minutes after the CF-SMFT. Initial heart rate and HRex were collected, with external intensities measured as average velocity (in meters per minute) and average acceleration-deceleration (in meters per second squared). Environmental conditions were sampled. A penalized hierarchical linear mixed model was tuned for a Bayesian information criterion minima using a 10-fold cross-validation, with out-of-sample prediction accuracy assessed via root-mean-squared error. SSD average acceleration-deceleration, initial heart rate, temperature, and ground hardness were significant moderators in the tuned model. When model covariates were held constant, a 1%-point change in SSD HRexassociated with a 0.4%-point change in CF-SMFT HRex(95% CI, 0.3-0.5). The tuned model predicted CF-SMFT HRexwith an average root-mean-squared error of 2.64 (0.57) over the 10-fold cross-validation, with 74% and 86% of out-of-sample predictions falling within 2.7%-points and 3.7%-points, respectively, from observed values, representing the lower and upper limits for detecting meaningful changes in HRexaccording to the documented typical error. Our findings support the use of an SSD to monitor physiological state in Australian Football athletes, despite varied scheduling withinsession. Model predictions of CF-SMFT HRexfrom SSD HRexclosely aligned with observed values, considering measurement imprecision.