Impaired heart rate recovery after sub-maximal physical exercise in people with multiple sclerosis

BACKGROUND: Heart Rate Recovery (HRR) after a physical exercise has been poorly investigated in people with multiple sclerosis (PwMS). OBJECTIVE: To evaluate the kinetics of HRR and its autonomic modulation in PwMS and to elucidate the interplay between HRR and subjective fatigue. METHODS: ECG was digitally acquired during rest (5 min), submaximal exercise (4 min at 10 W of upper limb cycling) and recovery (3 min) in 17 PwMS (EDSS: 5.9 ± 1.2, mean±standard deviation) and 17 healthy control (HC) subjects. Short-term (first 30 s) and long-term (up to180 s) validated indices of HRR were calculated. The time course of the parasympathetic index of heart rate variability RMSSD (Root Mean Square of Successive Differences) was computed every 30 s of recovery. Subjective fatigue was evaluated by the Borg scale applied to breathing and upper limbs. RESULTS: In comparison with HC, the short-term HRR indices were significantly slower (P < 0.05) in PwMS, whereas the long-term ones did not. The time course of RMSSD was significantly different in PwMS (P < 0.05). HRR and HRV indexes did not correlate with fatigue perception and baseline HRV values. CONCLUSION: The cardiac parasympathetic reactivation from a submaximal exercise was blunted in PwMS, thereby slowing the short-term phase of HRR. This may contribute to the higher cardiovascular risk in PwMS, but the mechanism needs further investigation. The parasympathetic impairment during post-exercise HR reactivation cannot be predicted by baseline HRV values and may therefore be revealed only by an appropriate provocative low-intensity physical test.