VAGAL MODULATION OF HEART-RATE DURING EXERCISE - EFFECTS OF AGE AND PHYSICAL-FITNESS

Vagal modulation of heart rate during exercise; effects of age. and ph ysical fitness. Am. J. Physiol, 274 (Heart Circ. Physiol. 43): H424-E4 29, 1998.-This study was designed to assess the effects of age and phy sical fitness on vagal modulation of heart rate (HR) during exercise b y analyzing the instantaneous R-R interval variability from Poincare p lots (Sal) at rest and at different phases of a bicycle exercise test in a population of healthy males. SD1 normalized for the average R-R i nterval (SD1(n)), a measure of vagal activity, was compared at rest an d during exercise among subjects of ages 24-34 (young, n = 25), 35-46 (middle-aged, n = 30), and 47-64 yr (old, n = 25) matched for peak O-2 consumption ((V) over dot o(2peak)) and among subjects with (V) over dot o(2peak) Oi. 28-37 (poor; n = 25), 35-45 average, n = 36), and 46- 60 ml.kg(-1).min(-1) (good, n = 25) matched fur age. SDIn was higher a t rest in the young subjects than in the middle-aged or old subjects ( 39 +/- 14, 27 +/- 16, and 21 +/- 8, respectively; P < 0,001), but the age-related differences in SD1(n) were smaller during exercise Ee,g., 11 +/- 5, 9 +/- 5, and 8 +/- 4 at tile level of 100 W; P = not signifi cant, (NS)]. The age-matched subjects with good, aver age, and poor (V ) over dot o(2peak) showed no difference in SD1(n) at rest (32 +/- 17, 28 +/- 13, and 26 +/- 11, respectively; P = NS), but SD1, differed si gnificantly among the groups from a low to a moderate exercise intensi ty level (e.g., 13 +/- 6, 10 +/- 5, and 6 +/- 3 for good, average, and poor fitness groups, respectively; P < 0.001, 100 W), These data show that poor physical fitness is associated with an impairment of cardia c vagal function during exercise, whereas aging itself results in more evident impairment of vagal function at rest.