Robert J. Robertson

Evaluation of the SenseWear Pro Armband to assess energy expenditure during exercise.

PURPOSE To assess the accuracy of the SenseWear Pro Armband for estimating energy expenditure during exercise. METHODS : Forty subjects (age = 23.2 +/- 3.8 yr; body mass index = 23.8 +/- 3.1 kg x m) performed four exercises (walking, cycling, stepping, arm ergometry) with each exercise lasting 20-30 min and workload increasing at 10-min intervals. Subjects wore the SenseWear Pro Armband on the right arm, and energy expenditure was estimated using proprietary equations developed by the manufacturer. Estimated energy expenditure from the SenseWear Pro Armband was compared with energy expenditure determined from indirect open-circuit calorimetry, which served as the criterion measure. RESULTS : When a generalized proprietary algorithm was applied to the data, the SenseWear Pro Armband significantly underestimated total energy expenditure by 14.9 +/- 17.5 kcal (6.9 +/- 8.5%) during walking exercise, 32.4 +/- 18.8 kcal (28.9 +/- 13.5%) during cycle ergometry, 28.2 +/- 20.3 kcal (17.7 +/- 11.8%) during stepping exercise, and overestimated total energy expenditure by 21.7 +/- 8.7 kcal (29.3 +/- 13.8%) during arm ergometer exercise (P < or = 0.001). At the request of the investigators, exercise-specific algorithms were developed by the manufacturer and applied to the data that resulted in nonsignificant differences in total energy expenditure between indirect calorimetry and the SenseWear Pro Armband of 4.6 +/- 18.1 kcal (2.8 +/- 9.4%), 0.3 +/- 11.3 kcal (0.9 +/- 10.7%), 2.5 +/- 18.3 kcal (0.9 +/- 11.9%), and 3.2 +/- 8.1 kcal (3.8 +/- 9.9%) for the walk, cycle ergometer, step, and arm ergometer exercises, respectively. CONCLUSIONS It appears that it is necessary to apply exercise-specific algorithms to the SenseWear Pro Armband to enhance the accuracy of estimating energy expenditure during periods of exercise. When exercise-specific algorithms are used, the SenseWear Pro Armband provides an accurate estimate of energy expenditure when compared to indirect calorimetry during exercise periods examined in this study.

The validity of regulating exercise intensity by ratings of perceived exertion.

DUNBAR, C. C., R. J. ROBERTSON, R. BAUN, M. F. BLANDIN, K. METZ, R. BURDETT, and F. L. GOSS. The validity of regulating exercise intensity by ratings of perceived exertion. Med. Sci. Sports Exerc., Vol. 24, No. 1, pp. 94–99, 1992. The purpose of this investigation was to examine the regulation of ex

Central signals of perceived exertion during dynamic exercise.

The purpose of this review is to examine the evidence that links specific physiological processes with central signals of perceived exertion during dynamic exercise. The physiological processes thought to be associated with a central signals of exertion include heart rate (HR), ventilation (VE), respiratory rate (RR), and oxygen uptake (VO2). Parallel changes in HR and ratings of perceived exertion (RPE) were not apparent when HR was manipulated experimentally. Heart rate does not appear to be associated with a strong central signal of exertion. Sensations of ventilatory function and discomfort are the only central signals that are consciously monitored. Corresponding changes in VE and RPE were noted when ventilatory drive was altered by hypnosis, induced erythrocythemia, hypoxia, or hyperoxia. Ventilation begins to provide potent sensory signals between 45-70% VO2max. Both the absolute and relative (percent VO2) oxygen uptake have been proposed as central signals. For a fixed VO2, RPE differed when comparisons were made between various experimental conditions. In contrast, RPE did not differ between conditions when expressed as a function of percent of VO2max. The relative VO2 is more likely to be associated with a strong sensory signal. Central signals involving VE and the relative VO2 are proposed to act as an amplifier that potentiates local signals in proportion to the aerobic metabolic demand.

Perceived exertion, electromyography, and blood lactate during acute bouts of resistance exercise.

PURPOSE This study examined ratings of perceived exertion (RPE) during resistance exercise in women. In addition, changes in blood lactic acid and biceps muscle activity assessed using electromyography (EMG) were investigated as potential mediators of RPE during resistance exercise. METHODS Twenty female volunteers (age, 25 +/- 4 yr) performed one set of biceps curl exercise at 30%, 60%, and 90% of their one-repetition maximum (1-RM). Total work was held constant by varying the number of repetitions during each of the three intensities. The three intensities were performed in random order. RPE responses were assessed for both the active muscle (RPE-AM) and the overall body (RPE-O) following each intensity. EMG data were collected from the biceps brachii muscle during each intensity. Blood samples were taken before and following the intensities and analyzed for blood lactic acid concentration. RESULTS A two-factor repeated-measures ANOVA showed a significant RPE (region) x intensity interaction (P < 0.02). Both RPE-AM and RPE-O increased as the intensity of exercise increased. EMG activity increased significantly (P < 0.01) as the intensity of exercise increased. A two-factor repeated measures ANOVA performed on the blood lactate data showed a significant (P < 0.04) time x intensity interaction. Postexercise [Hla] was significantly greater (P < 0.01) at 90% 1-RM than at 30% 1-RM. No significant differences were found in [Hla] between 30% and 60% 1-RM, or between 60% and 90% 1-RM. CONCLUSION These results indicate that monitoring RPE may be a useful technique for regulating resistance exercise intensity. Moreover, blood lactate and activity of the involved muscle may mediate the relation between RPE and resistance exercise intensity.

Construct validity of the OMNI resistance exercise scale.

This study examined the construct validity of the Adult OMNI Perceived Exertion Scale for Resistance Exercise (OMNI-RES). Forty (20 men and 20 women) subjects performed 1 repetition of the knee extension exercise at 40, 50, 60, 70, 80, and 90% of the 1 repetition maximum. Active muscle and overall body ratings of perceived exertion (RPE) were collected from the Borg 15-category RPE scale and the OMNI-RES immediately following each repetition. Construct validity was established by correlating RPE from the OMNI-RES with RPE from the Borg RPE scale using regression analysis. The results indicated a positive and linear relationship between RPE from the OMNI-RES and RPE from the Borg scale for both men and women. Validity coefficients ranged from r = 0.94 to 0.97. The high level of construct validity indicates that the OMNI-RES measures the same properties of exertion as the Borg RPE scale during resistance exercise and suggests that the 2 scales can be used interchangeably during resistance exercise.

The accuracy of the TriTrac-R3D accelerometer to estimate energy expenditure.

PURPOSE This study examined the reliability and validity of the TriTrac-R3D triaxial accelerometer to estimate energy expenditure during various modes of exercise. METHODS Twenty subjects (age = 21.5+/-3.4 yr; body mass index = 23.3+/-3.6 kg x m(-2)) performed five exercises (treadmill walking, treadmill running, stepping, stationary cycling, and slideboard), with each lasting 20-30 min and workload increased at 10-min intervals. To test the inter-TriTrac reliability, two TriTrac-R3D accelerometers were worn during each exercise period, and to examine validity, a simultaneous measurement of energy expenditure was made using indirect calorimetry (SensorMedics 2900 Metabolic Cart). RESULTS Results showed a significant correlation between the two TriTrac-R3D accelerometers during all exercises. The difference in estimated energy expenditure between the two accelerometers during the walking, stepping, and slideboard exercises was less than 1 kcal x min(-1) but statistically significant (P<0.05). There was also a significant correlation between energy expenditure estimated by each of the TriTrac-R3D accelerometers and indirect calorimetry during walking, running, stepping, and slideboard exercise (P<0.05). The interaction of Method x Workload was significant (P<0.05) for each exercise, indicating that the TriTrac-R3D underestimates energy expenditure and that the magnitude of this underestimation increases as workload increases. CONCLUSIONS Therefore, energy expenditure estimated via triaxial accelerometry does not increase with increasing workloads. These results suggest that there are limitations to using triaxial accelerometry to quantify energy expenditure.

Activity in the spinal cord-injured patient: an epidemiologic analysis of metabolic parameters

Individuals with traumatic spinal cord injury (SCI) represent a population with extreme inactivity. The purpose of the current research was to investigate the metabolic differences between extremely inactive disabled individuals (SCI sedentary group), active disabled individuals (SCI athletes), and able-bodied individuals. Fasting morning blood samples were obtained for the determination of high density lipoprotein cholesterol (HDLc) subfractions, glucose, and insulin. The sedentary SCI group was comprised of 77 consecutive male admissions to a rehabilitation center. The 17 SCI athletes were recruited prior to competition at the annual National Wheelchair Games. Total HDLc and both its subfractions were significantly lower (P less than 0.01) in the male SCI sedentary population than in the SCI athletes or able-bodied controls. HDL2 was significantly elevated (P less than 0.01) in the SCI athlete compared to the SCI sedentary group (42.7 vs 34.1 mg X dl-1) and was similar to the control population (46.1 mg X dl-1). Glucose levels were similar in the two SCI groups but were both significantly lower (P less than 0.05) than in the able-bodied controls. These data suggest that the extreme inactivity observed in disabled populations is associated with lower HDLc concentrations and presumably an increase in coronary heart disease risk if these values were to persist over time. Additionally, it appears that physical activity is associated with increases in total HDLc, primarily through the HDL2 subfraction. Glucose and insulin were similar for both SCI groups despite the marked difference in activity levels, suggesting that these parameters may not be associated with activity.

Reproducibility of the oral glucose tolerance test in overweight children.

OBJECTIVE We examined the reproducibility of the oral glucose tolerance test (OGTT) in overweight children and evaluated distinguishing characteristics between those with concordant vs. discordant results. DESIGN Sixty overweight youth (8-17 yr old) completed two OGTTs (interval between tests 1-25 d). Insulin sensitivity was assessed by the surrogate measures of fasting glucose to insulin ratio, whole-body insulin sensitivity index, and homeostasis model assessment of insulin resistance, and insulin secretion by the insulinogenic index with calculation of the glucose disposition index (GDI). RESULTS Of the 10 subjects with impaired glucose tolerance (IGT) during the first OGTT only three (30%) had IGT during the second OGTT. The percent positive agreement between the first and second OGTT was low for both impaired fasting glucose and IGT (22.2 and 27.3%, respectively). Fasting blood glucose had higher reproducibility, compared with the 2-h glucose. Youth with discordant OGTTs, compared with those with concordant results, were more insulin resistant (glucose/insulin 2.7+/-1.4 vs. 4.1+/-1.8, P=0.006, whole-body insulin sensitivity index of 1.3+/-0.6 vs. 2.2+/-1.1, P=0.003, and homeostasis model assessment of insulin resistance 10.6+/-8.1 vs. 5.7+/-2.8, P=0.001), had a lower GDI (0.45+/-0.58 vs. 1.02+/-1.0, P=0.03), and had higher low-density lipoprotein cholesterol (117.7+/-36.6 vs. 89.9+/-20.1, P=0.0005) without differences in physical characteristics. CONCLUSIONS Our results show poor reproducibility of the OGTT in obese youth, in particular for the 2-h plasma glucose. Obese youth who have discordant OGTT results are more insulin resistant with higher risk of developing type 2 diabetes mellitus, as evidenced by a lower GDI. The implications of this remain to be determined in clinical and research settings.

The decline of grip strength in the menopause: Relationship to physical activity, estrogen use and anthropometric factors

The focus of this study was the relationship of grip strength to age, physical activity and anthropometric factors, in a population of 255 post-menopausal women not on estrogen therapy (mean age = 57.6) and 55 women currently on estrogen replacement therapy (mean age = 56.9). Grip strength was measured as an indicator of muscular strength in the upper limbs. The grip strength of the estrogen users was significantly higher than that of the estrogen abstainers. Grip strength was related to age (r = -0.25, p less than 0.01), and the body habitus parameters of height (r = 0.36, p less than 0.01) and weight (r = 0.18, p less than 0.01). Although estrogen use was univariately correlated with strength (r = 0.16, p less than 0.05), multiple regression analyses revealed that only the height, age and physical activity were independent determinants of grip strength. These data suggest: height is the major determinant of upper body strength in older women; the reduction in physical activity with advancing age may contribute to strength decline, and modest increase in physical activity may retard the loss of strength that accompanies aging; the loss of ovarian estrogen in menopause may be related to the loss of strength in postmenopausal women.

Accuracy and reliability of the Caltrac accelerometer for estimating energy expenditure.

The Caltrac accelerometer is designed to assess energy expenditure during normal activity. The aims of the present study were (a) to determine the interinstrument and intersession reliability of the Caltrac and (b) to validate these instruments with measures of oxygen uptake (VO2) and determine whether Caltracs accurately reflect differences in energy expenditure due to sex, body weight, and speed. Caltracs were found to have very good interinstrument and intersession reliability and to accurately reflect differences in expenditure due to sex, weight, and speed. However, Caltracs consistently over-estimated energy expenditure by an average of 9-13%. The absolute percent error (percent error without consideration of the sign) of the Caltrac was greater, averaging 23%. The correlations between Caltrac and VO2 averaged 0.68-0.74. Thus, the Caltracs seem well suited for studies of activity level of groups, but may be less useful in estimating an individuals activity.