Resting heart rate variability (HRV) profile was compared between sedentary and active females before, during, and after a 2-week overreaching protocol. Twenty currently active and 20 sedentary females were subdivided within their groups to either an experimental or control group. The active and sedentary experimental groups completed an overreaching protocol; endurance exercise, 40 minutes per session at an intensity of 70-90 % heart rate reserve, 7 d.wk(-1). The active experimental group showed an increase in low frequency power and a decrease in high frequency power over the intervention weeks (LF : HF ratio; Baseline = 2.0 [1.1], End week 1 = 2.4 [1.9], End week 2 = 3.2 [1.9], Recovery = 1.9 [1.0] mean [SD]) although this was not statistically significant (p > or = 0.05) for within group effects. The sedentary experimental group however, showed a significant (p < or = 0.05) increase in low frequency power and a decrease in high frequency power during the overreaching phase suggesting a move towards a predominance of resting sympathetic cardiac modulation (LF:HF ratio; Baseline = 1.6[1.1], End week 1 = 3.4 [1.6], End week 2 = 4.4 [3.0], Recovery = 1.8 [0.9]). These findings arose in the absence of any significant change in resting heart rate. Time domain analysis however failed to provide similar findings in either experimental group. Neither control group showed any significant changes. These data suggest a more marked change in sympathovagal balance in sedentary people when exposed to an overreaching protocol than in active individuals.