Jessica L. Unick1*, Sarah Gaussoin2, Judy Bahnson2 Richard Crow3, Jeff Curtis4, Tina Killean5, Judith G Regensteiner6, Kerry J Stewart7, Rena R Wing1, John M Jakicic8 and The Look AHEAD Research Group
1Weight Control and Diabetes Research Center, The Miriam Hospital and Brown Medical School, Providence, RI, USA
2Wake Forest University School of Medicine, Winston-Salem, NC, USA
3Universitiy of Minnesota, Minneapolis, MN, USA
4Phoenix Epidemiology and Clinical Research Branch, NIDDK, NIH, Phoenix, AZ, USA
5Northern Navajo Medical Center, Shiprock, NM, USA
6Center for Women’s Health Research, Divisions of General Internal Medicine and Cardiology, Department of Medicine, University of Colorado School of Medicine, Aurora, CO, USA
7Johns Hopkins University, Baltimore, MD, USA
8Department of Health and Physical Activity, Physical Activity and Weight Management Research Center, University of Pittsburgh, Pittsburgh, PA, USA
Received: 12 June, 2014; Accepted: 05 July, 2014; Published: 07 July, 2014
Jessica Unick, Ph.D., Warren Alpert Medical School at Brown University and The Miriam Hospital’s Weight Control and Diabetes Research Center, 196 Richmond Street, Providence, RI 02903, USA, Tel: 401-793-8966; Fax: 401-793-8944; Email: firstname.lastname@example.org
Unick JL, Gaussoin S, Bahnson J, Crow R, Curtis J, et al. (2014) Validity of Ratings of Perceived Exertion in Patients with Type 2 Diabetes. J Nov Physiother Phys Rehabil 1(1): 004-012. DOI: 10.17352/2455-5487.0000002
© 2014 Unick JL, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Optokinetic chart stimulation; Epley’s manouvre; BPPV; Ménière’s disease; vestibular rehabilitation; Care of the elderly
Exercise prescription; Diabetes; Obesity; Ratings of perceived exertion; Exercise; Type 2 diabetes
Purpose: To examine whether a subjective measure of moderate-intensity exercise (12-13 on Borg’s ratings of perceived exertion scale; RPE) corresponds to the target heart rate for moderate-intensity exercise (40-59% heart rate reserve; %HRR) and to determine the characteristics of those for whom RPE does not appropriately estimate exercise intensity.
Methods: 3582 individuals with type 2 diabetes (age: 58.3±6.8 years; BMI: 35.9±5.9 kg/m2) underwent a maximal exercise test and minute-by-minute HR and RPE were recorded. Linear regression was used to determine the %HRR corresponding to an RPE of 12 and 13 for each individual.
Results: At an RPE of 12 or 13, 57% of participants fell within the target 40-59% HRR range, while 37% and 6% fell above and below this range, respectively. Participants with a %HRR ≥60% (above range) were more likely to be female (OR: 1.19; 95% CI: 1.01,1.40), African American (OR: 1.65; 95% CI: 1.35, 2.02) or Hispanic (OR: 1.57; 95% CI: 1.27, 1.95), have a higher BMI (OR: 1.03; 95% CI 1.01, 1.04) and HRmax (OR: 1.02; 95% CI: 1.01, 1.02), and lower fitness (OR: 0.90; 95% CI: 0.85, 0.94) and RPEmax (OR: 0.68; 95% CI: 0.63, 0.73), compared to those within the target 40-59%HRR range (p-values’<0.05).
Conclusions: RPE appropriately gauges exercise intensity in approximately half of overweight individuals with type 2 diabetes; however, more than one-third of participants were at an increased risk of exercising at a higher than prescribed intensity when using RPE. Future studies should continue to examine the characteristics of individuals for whom RPE appropriately estimates exercise intensity and for those whom it does not.
Regular exercise is associated with physiological and psychological health benefits [1-5], and is particularly important for individuals with type 2 diabetes, given the effect of exercise on body mass, insulin action and glucose control . Implementation of an individually tailored exercise program may be necessary to optimize these health benefits. For example, exercise should be performed at intensity great enough to elicit a physiological training effect, but not too vigorous that it would increase the likelihood of abnormal clinical signs or symptoms, or increase the risk of musculoskeletal injury in high-risk populations . Exercise regimens are often prescribed based on patient-reported subjective measures of intensity or the degree of physiological stress induced, often measured by heart rate; however, the relationship between subjective reporting and the physiologic response in type 2 diabetes, where neuropathy and other diabetes related factors may alter the relationship, has not been established.
The American College of Sports Medicine (ACSM) recommends that individuals with diabetes engage in 150 minutes/week (5 days/week) of moderate-intensity exercise in bouts lasting ≥10 min with no more than 2 consecutive days between bouts [6,7]. Furthermore, moderate-intensity exercise is defined as 40-59% heart rate reserve (HRR) or 40-59% oxygen uptake reserve (VO2R). However, assessing heart rate (HR) or oxygen consumption (VO2) is not practical in many situations; therefore more convenient methods for monitoring exercise intensity are often utilized. For example, the ratings of perceived exertion (RPE) scale has been shown to be an accurate and reliable tool for monitoring and self-regulating exercise intensity in selected populations [8,9]. Although subjective, the RPE scale has been shown to correlate with physiological variables such HR, ventilation, respiration, oxygen uptake, and blood lactate [10-12]. Additionally, an RPE of 12-13 on Borg’s RPE scale  range 6-20, has been suggested to correspond with 40-59% HRR, the physiological threshold for defining moderate intensity activity . However, there are limited data examining the correspondence between these methods for monitoring exercise intensity among individuals with type 2 diabetes. It is possible that symptoms associated with diabetes (i.e., pain, peripheral neuropathy, etc.) might influence one’s subjective exercise experience. For example, women with type 2 diabetes were found to report a greater effort at low exercise workloads compared to those without type 2 diabetes . Moreover, autonomic neuropathy, which is highly prevalent in this population, could influence maximal heart rate, thereby impacting %HRR and the concordance between these measures and RPE.
In a small sample (n=23), Colberg et al.  examined the validity of using %HRR or RPE to prescribe and monitor exercise intensity in adults with type 2 diabetes. A highly linear relationship between %HRR and %VO2R (r=0.98) and between RPE and %VO2R (r=0.94) was reported, suggesting that RPE and %HRR can appropriately monitor exercise intensity in individuals with diabetes, regardless of the presence of diabetic autonomic neuropathy. However, this study was limited by a small sample size, with further division of these subjects into those with (n=13) and without diabetic autonomic neuropathy (n=10). Further, the data presented were purely correlational, and did not assess whether the clinical cut-points for moderate-intensity exercise are appropriate in this population and whether there were any factors which influenced the association between HR and RPE.
The primary aim of this paper is to examine whether an RPE of 12-13, a subjective measure of moderate-intensity exercise, corresponds to 40-59% HRR, a physiological measure of moderate-intensity, during a maximal graded exercise test in individuals with type 2 diabetes who were not currently on β-adrenergic blocking medication (β-blockers). Based on the current literature, we hypothesized that the RPE and %HRR ranges for moderate-intensity exercise would appropriately correspond with one another. To increase the generalizability of these findings to clinical practice, this study also examined the characteristics of individuals for whom RPE appropriately estimated exercise intensity and for those whom it did not.
Data were obtained from participants enrolled in the Look AHEAD trial, a multi-center randomized clinical trial examining the long-term effects (up to 13.5 years) of an intensive lifestyle intervention program on cardiovascular morbidity and mortality in overweight or obese persons with type 2 diabetes. Characteristics of the 5,145 subjects enrolled in the Look AHEAD trial have been previously reported . In short, participants had type 2 diabetes, were 45-76 years of age, had a BMI ≥25 kg/m2 (or ≥27 kg/m2 if taking insulin), HbA1c ≤11%, triglycerides <600mg/dL, and systolic and diastolic blood pressure ≤160 and ≤100 mmHg, respectively. All participants provided written informed consent, and study procedures were approved by each center’s institutional review board.
A total of 3991 individuals were considered in the analyses after excluding participants who reported using β-blockers given that β-blockers have been shown to blunt the HR response. Participants were further excluded for not achieving a maximal effort on the graded exercise test (GXT) as determined by the technician (n=168) or if the test was stopped by the physician due to EKG abnormalities or abnormal clinical signs or symptoms (n=215). If EKG abnormalities were observed, yet the physician did not terminate the test, these individuals were also included in the analyses given that they met the criteria for randomization into the Look AHEAD trial. This suggests that these individuals only had mild-to-moderate abnormalities that would not preclude them from safely engaging in exercise. Finally, participants missing HR data or RPE data at any given stage of the GXT (n=128) were also excluded from the analyses; thus ending with a total sample of n=3582 participants who were included in the following analyses (Note: some participants were excluded for more than one reason mentioned above and thus were included under multiple categories).
Graded exercise test
Prior to undergoing the graded exercise test, participants were instructed to talk with their physician whether they needed to reduce their insulin/sulphonyl urea dose on the day of testing. On the exercise testing day, participants completed a maximal GXT where the treadmill speed was determined based upon the preferred speed of the participant as well as their HR response during the first minute of a baseline test. The available speeds were 1.5, 2.0, 2.5, 3.0, 3.5, or 4.0 mph (2.41, 3.22, 4.02, 4.83, 5.63, 6.44 km/hr respectively). Using the pre-determined speed, the GXT began at a 0% grade which increased by 1% every minute until test termination at volitional fatigue or at the point where American College of Sports Medicine (ACSM) test termination criteria were observed . During the test, participants were prohibited from holding onto the hand rails, except for brief balance. Heart rate was assessed using a 12-lead electrocardiogram (EKG) every minute during the final 10-15 seconds of each exercise stage and at the point of test termination. Maximal fitness was calculated using the grade and speed of the treadmill at test termination and was expressed in metabolic equivalents (METs) . Heart rate recovery was calculated as maximal HR minus HR at two minutes post-test termination. Participants were instructed to take all medications as usual prior to this test.
Measurement of % heart rate reserve and ratings of perceived exertion
During each stage (every minute) of the GXT and at test termination, participants used the Borg scale to rate their RPE . This scale has previously been shown to be valid and reliable in both healthy and clinical populations, as well as obese adults [18-21]. Before beginning the test, clinic staff read each participant a standardized script to explain and anchor the RPE scale. This RPE scale considers a rating of 6 to be “no exertion at all” whereas a 20 is considered to be “maximal exertion”.
Resting HR (HRrest) was measured via EKG on the day of the exercise test following a 5 minute rest period with the subject placed in a supine or semi-supine position. Although resting HR is sometimes measured in a seated position, prior studies, including the original Karvonen study, have used a supine HR measurement in the calculation of HRR [22,23]. Maximal HR (HRmax) was recorded at the point of test termination when the subject indicated that they had achieved volitional fatigue. Heart rate reserve for each individual was calculated as follows: (HRR=HRmax – HRrest).
Additional assessment measures
Fasting serum glucose and HbA1c were analyzed by the Central Biochemistry Laboratory (Northwest Lipid Research Laboratories, University of Washington, Seattle, WA) using methods described elsewhere . Use of insulin and other diabetes medications were determined via standardized interviewer-administered questionnaires and participants were asked whether a physician has ever diagnosed diabetic neuropathy. Waist circumference was measured at the level of the iliac crest to the nearest 0.1 cm using the Gulick II tape measure and the average of two measures was used to represent the waist circumference. Physical activity (expressed in kcal/wk) was assessed using Paffenbarger Physical Activity Questionnaire (PPAQ) , but was only assessed at approximately half of the study sites given that this was a process measure and was not a primary aim of the larger trial.
The HR and RPE during each stage of the GXT were used to develop individual regression lines for each participant. Using this regression equation, the percent heart rate reserve (%HRR) was calculated for each participant at an RPE of 12 using the following equation: % HRRRPE=12 = [(HRRPE=12 – HRrest) / (HRmax – HRrest)]. Similar methods were used to calculate the %HRR at an RPE of 13. The %HRR which corresponded to both an RPE of 12 and 13 was identified and then used to determine if it fell within the target 40-59% range. Participants were then categorized into 1 of 3 groups: Below target: < 40%HRR at both an RPE of 12 and 13; at target: 40-59%HRR at an RPE of 12 or 13, and above target: ≥60%HRR at an RPE of 12 and 13. The percentage of participants falling into each of these categories was computed and a Pearson correlation was used to examine the relationship between HR and RPE throughout the GXT. Demographic variables (e.g., BMI, waist circumference, age, gender, race/ethnicity, lab measures, etc.), diabetes-specific variables (e.g., diabetes medication use, neuropathy, duration of diabetes, etc.), and exercise-related variables (e.g., HRmax, fitness, RPEmax, physical activity, etc.) were compared between the 3 %HRR groups using bivariate Analysis of Variance (ANOVA). In order to determine characteristics of those above and below target for %HRR, those variables which significantly differed across groups were entered as independent variables into two separate logistic regression models. Backwards selection methods were utilized. All analyses were performed using SAS version 9.2 (SAS Institute, Cary, NC).
Demographic characteristics of the 3582 participants are shown in table 1. On average, participants were 58.3 ± 6.8 years of age, had a BMI of 35.9 ± 5.9 kg/m2, and 62.1% were Caucasian. Moreover, the majority of participants had relatively “poor” fitness (max METs = 7.3 ± 2.0 METs) and 70% of participants reported engaging in <1000 kcal/week of leisure time physical activity .
There was a linear relationship (r=0.62, p<0.001) between HR and RPE throughout the GXT. At maximal effort, the mean HRmax was 154.3 ± 12.9 bpm which is equivalent to 95.7 ± 7.2% of age-predicted maximal heart rate (calculated as 220-age). Additionally, the mean RPE at maximal effort was 19.4 ±1.0.
Figure 1 illustrates the variability in %HRR at a self-reported RPE of 12 and 13. %HRR was normally distributed with a mean of 55% at an RPE of 12 and 62% at an RPE of 13. Fifty-seven percent of participants fell within the target 40-59%HRR range at an RPE of 12 or 13. However, 37% were exercising above the physiological threshold for moderate intensity (≥ 60% HRR; “Above target” group) at both an RPE of 12 and 13. The mean exercise intensity for these individuals was 69.0%HRR and 74.4%HRR at an RPE of 12 and 13 respectively. Six percent of participants fell below the moderate-intensity threshold at an RPE of 12 and 13 (<40%HRR; “Below target” group). When participants who may not have reached a true maximal effort (defined as maximal RPE < 17; n=106 or HRmax <85% of age-predicted maximum; n=63) were excluded from the analyses, the results were unchanged.
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