As an index for sympathetic response to exercise, the percentage P-R interval shortening (%P-R) during a maximal bicycle ergometer test was studied in 190 apparently healthy subjects (95 men and 95 women) divided into five subgroups according to age. The P-R interval measurements at rest and during exercise were highly reproducible. The %P-R was 28 ± 10 in men and 27 ± 11 in women. In both men and women the %P-R was similar in the three decades 20-49 years, whereas a highly significant reduction was noted in both genders ≥50 years of age (p <0.001). A more gradual age-related decline in maximal heart rate was observed. The %P-R correlated significantly with the maximal heart rate during exercise in both men (r = 0.72) and women (r = 0.52), but not with the heart rate at rest. As judged from the %P-R during exercise, the sympathetic reserve from rest to maximal exercise showed a significant decrease around the age of 50 years in both genders.

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