Heart Rate Variability (HRV) and Galvanic Skin Response (GSR) offer athletes a window into the autonomic nervous system — the machinery that governs stress, arousal, and recovery. HRV reflects the balance between the body's "fight-or-flight" and "rest-and-digest" branches, while GSR directly tracks sympathetic arousal through sweat gland activity. Read together, their patterns tell an athlete whether the body is primed to absorb hard training or signaling that recovery should come first. This article explains the physiology behind both signals, presents a model for interpreting them in combination, and shows how to apply that model across the preparation, competition, and transition phases of a training cycle.
Understanding Biofeedback for Athletes: HRV and GSR
Biofeedback is the practice of measuring physiological processes in real time so that a person can observe, and ultimately influence, states that normally operate below conscious awareness. For athletes, the two most relevant signals here are HRV and GSR. HRV analyzes the subtle fluctuations in timing between heartbeats, and it is widely used as a measure of how well the autonomic nervous system is functioning, with the goal of improving physiological resilience. GSR — also called electrodermal activity or skin conductance — measures the electrical conductivity of the skin, which changes with sweat gland activity.
The physiological logic is straightforward. Because sweat glands are controlled by the sympathetic nervous system, skin conductance is described by biofeedback practitioners as one of the most sensitive indicators of emotional arousal and stress: when a person feels tense, anxious, or excited, skin conductance rises. HRV adds a complementary layer of insight into autonomic balance, showing how the calming parasympathetic response and the activating sympathetic response are negotiating from beat to beat.
The Autonomic Nervous System and Athletic State
Every training decision ultimately rests on which branch of the autonomic nervous system is dominant. The sympathetic branch mobilizes the body — elevating arousal, sweating, and stress hormones — while the parasympathetic branch restores it. A systematic review and Bayesian meta-analysis published in Frontiers in 2025 by Xuda Zhang and colleagues frames the core mechanism of biofeedback interventions as enhancing an individual's ability to regulate autonomic nervous system activity, particularly heart rate variability. Drawing on Herbert Benson's "relaxation response" theory, the review notes that by regulating the autonomic nervous system, biofeedback can reduce levels of stress hormones such as cortisol and alleviate the stress response.
The two metrics capture this balance from different angles, and that difference matters for interpretation. GSR is a direct readout: it picks up changes in sweat gland output, making it a highly responsive marker of psychological stress and emotional activation. HRV is an indirect readout: because increased HRV is associated with increased parasympathetic activity, a rising HRV suggests the recovering, restorative branch is gaining influence, while a falling HRV implies sympathetic dominance or accumulated stress. An athlete who understands this asymmetry — GSR measures sympathetic activity directly, HRV reflects the overall autonomic balance — can interpret both signals without conflating them.
