Can HRV be used to evaluate training load in constant load exercises?

Area of Science:

• Exercise Physiology
• Sports Science
• Biomedical Engineering

Background:

• The overload principle necessitates sufficient training load (TL) to stimulate physiological adaptation.
• Objective measurement of TL remains a challenge due to the lack of a "golden standard".
• Heart rate variability (HRV) is a non-invasive physiological marker sensitive to autonomic nervous system changes.

Purpose of the Study:

• To investigate the potential of post-exercise heart rate variability (HRV) indices for evaluating training load (TL).
• To assess HRV responses to exercises of varying intensities and durations.
• To determine if HRV can serve as an objective measure for TL in field settings.

Main Methods:

• Thirteen endurance-trained males performed moderate (MODE), high-intensity (HI), and prolonged (PRO) running exercises.
• Heart rate variability (HRV) was analyzed using the short-time Fourier-transform method during rest, exercise, and recovery.
• Training load (TL) was concurrently assessed using rating of perceived exertion (RPE) and blood lactate (BLa).

Main Results:

• Rating of perceived exertion (RPE) and blood lactate (BLa) indicated significantly higher TL for HI and PRO compared to MODE.
• Post-exercise HRV recovery dynamics were similar across exercise conditions, but the absolute HRV level was lower after HI.
• Negative correlations were observed between RPE/BLa and HRV indices (HFP(120), LFP(120), TP(120)), indicating reduced HRV with higher TL.

Conclusions:

• Increased exercise intensity or duration negatively impacts immediate post-exercise HRV recovery.
• Post-exercise HRV, particularly within the first 2 minutes of recovery, may provide sufficient data for objective TL evaluation.
• HRV offers a promising, objective tool for assessing training load in practical, field-based training scenarios.