Validity and sensitivity of a submaximal fitness test for assessing cardiorespiratory fitness and response to training load in female football players

Purpose: To evaluate the within-athlete sensitivity, longitudinal validity, and dose-response relationships of exercise heart rate (HRex) from a submaximal fitness test (SMFT) as a proxy measure of cardiorespiratory fitness (CRF).Methods: Observational, repeated measures design. Twenty-five female football players’ training loads (global positioning system and HR metrics) were collected throughout an 8-week pre-season period. A fixed-continuous SMFT protocol was administered weekly to evaluate HRex. A running time-trial assessment was conducted in week 2 and week 8 to calculate mean velocity (5:30vel) as a proxy measure of CRF. SMFT HRex measurement properties were determined via within- and between athlete correlations and linear-mixed models. Results: The overall preseason change in SMFT HRex derived from weekly repeated measures was –4.7 percentage points (90% CIs: –5.6 to –3.9). The association between SMFT HRex and 5:30vel changes was large (–0.55), with 90% CIs ranging from moderate to very large magnitudes (–0.71 to –0.31). A 1-% point decrease in SMFT HRex corresponded to an increase in 5:30vel of 0.13 [90% CIs: 0.03 to 0.24] km·h-1. Within-athlete correlations between training loads and SMFT HRex demonstrated moderate inverse relationships with external load parameters (–0.47 to –0.39), and small inverse relationships with HR-based internal metrics (–0.29 to –0.25). Accumulated high and very high-speed running throughout the entire preseason showed consistent dose-response relationships with SMFT HRex (moderate and large, respectively), while all other measures displayed unclear associations.Conclusions: SMFT HRex is a sensitive and valid tool to evaluate pre-season CRF changes in female football players.