Introduction/purpose: Negative mood symptoms occur frequently in sedentary populations, but individual vulnerability factors for developing these complaints have not been systematically evaluated. This investigation examined whether the autonomic nervous system (ANS) serves a role in the development of negative mood after controlled exercise withdrawal.
Methods: Forty participants (mean age of 31.3 +/- 7.5 yr, 55% women) who exercised regularly (>or= 30 min of continuous aerobic exercise at least three times a week during the past 6 months) were randomized either to withdrawal from regular aerobic exercise (N=20) or to continue regular aerobic exercise (N=20) for 2 wk. Measurements were taken before exercise withdrawal and at 2-wk follow-up. Various dimensions of negative mood were measured with the multidimensional fatigue inventory, profile of mood states, and Beck depression inventory-II. ANS activity was assessed by heart rate variability (HRV) analyses, examining low-frequency (0.04-0.15 Hz: lf) and high-frequency (hf) domains (0.15-0.40 Hz). The lf/hf ratio was used as index of sympathovagal balance. Protocol adherence was documented by ambulatory activity monitoring.
Results: Exercise withdrawal resulted in significantly higher negative mood scores at follow-up compared with control (P<0.05). Baseline lf/hf ratios correlated with the increases in symptoms (r>0.4; P<0.05) in the exercise-withdrawal group independently of gender, age, weight, baseline fitness level, and baseline symptom status. The exercise-withdrawal and control groups displayed no significant change in hf HRV, lf HRV, or lf/hf HRV during the 2 wk.
Conclusion: Reduced parasympathetic ANS activity as measured by HRV is predictive of the development of negative mood after deprivation of usual exercise activities. No significant changes in HRV were observed during the 2-wk exercise deprivation period. These findings are relevant to the understanding of mood changes in response to short-term exercise withdrawal, such as sports injuries and recovery from medical procedures.