The association between National Aeronautics and Space Administration Task Load Index subscales, training-induced fatigue, and physiological responses in endurance athletes

Purpose: Traditional training metrics do not distinguish between the different components of internal training load contributing to training-induced fatigue, whereas the National Aeronautics and Space Administration Task Load Index (NASA-TLX) may offer a compelling multidimensional alternative. However, the NASA-TLX subscales have been overlooked in the context of endurance training. Therefore, this study investigated whether the NASA-TLX subscales are associated with acute performance decrement (APD) and physiological responses across different endurance training sessions. Methods: Twelve well-trained runners (10 males, 2 females; age 26.8 [6.9] y; maximal oxygen uptake [VO2max] 65.6 [6.4] mL·kg−1·min−1) completed 6 visits in the laboratory, an incremental test, a time to exhaustion (TTE) test, and 4 experimental training sessions in randomized order. A TTE test was performed at baseline and after each of 4 exercise sessions: low-intensity training, medium-intensity training, long-interval high-intensity (HITlong), and short-interval high-intensity (HITshort). APD was calculated as the percentage drop in TTE compared to baseline. The NASA-TLX questionnaire was administered between each training session and the TTE test to assess mental demand, physical demand, temporal demand, effort, frustration, and perceived performance. Results: All sessions led to significant APD (P = .041), with HITlong producing greater APD than low-intensity training (P = .035). Subscale analysis showed lower mental, physical, temporal, and effort scores after low-intensity training compared to HIT sessions (P < .001). All subscales were significantly correlated with APD and key physiological ventilatory and metabolic parameters (P < .001). Conclusion: NASA-TLX subscales appear valid and may help athletes to discriminate distinct components of perceived workload.