Effects Of Induced Physical Fatigue On Heart Rate Variability

Detecting physical fatigue can help prevent over-exertion. While physical fatigue is commonly defined at the muscle level, defining systemic fatigue is less clear. HRV was shown to be associated with the adaptability of the autonomic nervous system to physical stressors, which could potentially serve as a biomarker of fatigue. While prior studies primarily used subjective ratings to assess fatigue, this study incorporated vertical jump height as an objective criterion. PURPOSE: (1) Compare HRV data between baseline standing (Stand), baseline walking (PRE), and post-fatigued walking (POST); and (2) identify baseline HRV measures that correlate with the total fatiguing time. METHODS: 20 subjects (9 F, age: 23.4 ± 5.0 yrs) walked on the treadmill at 1.25 m/s with progressively increased incline. Physical fatigue criteria include: (1) rating of perceived exertion >17/20, (2) 85-90% of maximum predicted heart rate, and (3) vertical jump height reduced by ≥20%. Otherwise, another round(s) of treadmill walking would be resumed. Raw R-R interval data were collected at 256 Hz and HRV metrics were derived and natural log transformed. RESULTS: lnRMSSD was significantly reduced at POST compared to PRE or Stand (Table). DFA-α1 and lnApEn were reduced at POST, indicating heart rate signals became more tightly controlled. lnPoincaré SD2/SD1 was significantly increased at POST, reflecting increased sympathetic activation. lnRMSSD, lnPoincaré SD2/SD1, lnApEn values at PRE, and lnLH/HF at Stand were significantly correlated to their total fatiguing time. CONCLUSION: Significantly reduced HRV was manifested during post-fatigued walking. Having greater HRV and smaller LF/HF ratio at baseline (i.e., increased parasympathetic activity) was associated with better endurance during physical activities. Time-domain and non-linear measures may be more sensitive to fatigue, while resting frequency-domain parameters may be useful for predicting endurance during activity.Partially supported by NSF IIS-1955979