TEMPORAL EFFECT OF MUSCLE-CONTRACTION ON RESPIRATORY SINUS ARRHYTHMIA

The purpose of this investigation was to compare the heart rate variab ility at respiratory frequency (HRVRF) in muscle contractions during t he inspiratory phase with that during the expiratory phase. Eight volu nteers performed pedaling on a cycle ergometer, twice a cycle of respi ration (4 sec) against a load of 0.25 Nm/kg BW, of which the timing wa s adjusted to twice during the inspiration phase (I), once during the expiration, once during the inspiration (El), or twice during the expi ration phase (E). Spectral analysis was applied to the R-R intervals o f each condition. The amplitude of HRVRF in E was less than half of 1 (9 +/- 2 msec versus 23 +/- 2 msec). The results indicate that the tim ing of muscle contraction can affect the heart rate variability even a t the frequency band of respiration.