OBJECTIVE -Individuals with diabetic autonomic neuropathy (DAN) exhibit an increased resting heart rate but depressed maximal heart rate. Thus, the purpose of this study was to examine the validity of using either percent of heart rate reserve (HRR) or a rating of perceived exertion (RPE) scale to prescribe exercise intensity in diabetic individuals both with and without DAN.RESEARCH DESIGN AND METHODS -The subjects consisted of 23 individuals with type 2 diabetes, ages 45-75 years, with (DAN; n ϭ 13) or without (No DAN; n ϭ 10) clinical signs of DAN, as assessed by heart rate variability using the expiration-to-inspiration ratio of the R-R interval. Peak aerobic capacity was determined using a graded protocol on a cycle ergometer, with RPE, heart rate, and VO 2 values recorded at each stage.RESULTS -The subjects were similar with the exception of depressed autonomic function in DAN subjects. Peak respiratory exchange ratio values were significantly higher (P Ͻ 0.05) in the DAN group (1.08 Ϯ 0.02 vs. 1.02 Ϯ 0.01 in No DAN subjects), although DAN subjects exhibited a significantly lower (P Ͻ 0.05) peak exercise heart rate. A similarly highly linear relationship between %HRR and percent VO 2 reserve (VO 2 R) existed for both groups (r ϭ 0.98). A similar slightly weaker relationship (r ϭ 0.94) was found between RPE and %VO 2 R.CONCLUSIONS -In conclusion, in diabetic individuals, %HRR provides an accurate prediction of %VO 2 R and can be used to prescribe and monitor exercise intensity, regardless of the presence of DAN. The RPE scale is also a valid, albeit slightly less accurate, method to monitor exercise intensity in diabetic individuals.
Diabetes Care 26:986 -990, 2003U ntil recently, the linear relationship between the percent of heart rate reserve (HRR) and percent of maximal aerobic capacity (VO 2max ) led to the use of %HRR to quantify a given percentage of VO 2max . Recent studies in healthy adults, however, have shown that the two were not equivalent-rather that %HRR is equivalent or more closely related to the percent VO 2 reserve (VO 2 R) (i.e., a percentage of the difference between resting and maximal VO 2 at which an individual is exercising) than to %VO 2max (1,2). These findings led the American College of Sports Medicine to adopt %VO 2 R in place of %VO 2max for the prescription of exercise intensity, which in normal individuals is now generally prescribed as a percentage of maximal heart rate (60 -90%), VO 2 R (50 -85%), or HRR (50 -85%) (3,4). An alternate method of prescribing intensity is with the rating of perceived exertion (RPE) scale (5), which uses a subjective rating from 6 to 20 to quantify an individual's perceived exercise intensity.Individuals with diabetic autonomic neuropathy (DAN) do not have a normal hemodynamic response to exercise. Autonomic neuropathy interferes with normal heart rate regulation during exercise by depressing maximal heart rate and blood pressure and at rest by increasing resting heart rate (6,7). Such individuals exhibit a lower peak heart rate response, lower...