Application of heart rate at lactate threshold to Karvonen's formula in cases of multiple risk factors

Abstract

Heart rate (HR) corresponding to lactate threshold (LT) was evaluated in patients with multiple risk factors and applied to determine the target HR by Karvonen's formula calculated from the predicted HR max. The subjects were 52 outpatients (33 men and 19 women) aged from 23 to 70 years old (mean 46.9) with more than 2 risk factors including obesity, hypertension, diabetes mellitus, impaired glucose tolerance, dyslipidemia, hyperuricemia, and hyperinsulinemia. A multistage graded test of submaximal exercise on electric bicycle ergometer was performed for each subject before starting exercise therapy. The workload was increased every 4 minutes, and heart rate, blood pressure, and blood lactate concentration were measured during the last 1 minute of each stage. The LT-HR ranged from 80 to 120 beats/min (mean 101±10) and Karvonen's coefficients ranged from 0.08 to 0.40 (mean 0.22±0.08). Because of these differences and variance, it is suggested that LT-HR should be measured directly or about 20% HR reserve should be prescribed at least when starting exercise therapy for these cases.