Evaluating the sensitivity of heart rate variability fractal correlation properties to training load variations: Implications for monitoring training readiness and durability

This study examined the utility of HRV detrended fluctuation analysis alpha-1 (DFAα1) to assess readiness-to-train and exercise durability under varying acute training loads. Nineteen trained cyclists completed two 20-minute time-trials (TT) under rested and fatigued conditions. DFAα1 was measured during a standardized warm-up (WU), 20-min TT, and standardized cool-down (CD). Power output (PO) and DFAα1 responses were compared across conditions, and associations with performance and fitness (W·kg −1 ) were examined. DFAα1 values declined with increasing WU and CD exercise intensity (p<0.001) and were significantly attenuated following the 20-min TT (p<0.001). While DFAα1 profiles did not differ significantly between rested and fatigued conditions, lower pre-TT DFAα1 was associated with reduced TT performance (p=0.022; r=0.55), suggesting relevance to training readiness. Additionally, an 18% decline in DFAα1 between 10- and 20-min during the TT (p=0.031), and lower post-TT values at matched intensities were observed (p<0.001), indicating physiological perturbation from the 20-min TT. Fitter participants exhibited lower DFAα1 values during the 20-min TT (p<0.001; r=−0.77), suggesting a greater capacity to sustain physiological stress. While DFAα1 is responsive to exercise intensity and stress, offering potential to assess training readiness and durability, more robust fatigue protocols are needed to validate DFAα1 as training load monitoring tool.