Reproducibility of Computerized Measurements of QT Interval from Multiple Leads at Rest and During Exercise

Background: Accurate measurement of the QT interval is important for diagnosing long QT syndrome (LQTS), and in research on determinants of ventricular repolarization time. We tested automatic analysis of QT intervals from multiple ECG leads on chest. Methods: Eleven healthy volunteers and 10 genotyped LQTS patients were tested at rest and during exercise with a bicycle ergometer twice 1–31 months apart. Electrocardiograms were recorded with the body surface potential mapping system, and 12 precordial channels were selected for analysis. Averaged QT peak and QT end intervals were determined with an automated algorithm, and the difference QT end minus QT peak (Tp‐e) was calculated. Repeatability was assessed by coefficient of variation (CV) between measurements. Results: Within one test at rest the QT end intervals were highly repeatable with CV 0.6%. In repeated tests CV was 4.4% for QT end interval and 3.5% when the QT interval was corrected for heart rate. In exercise test at specified heart rates, mean CV was 3.0% for QT end and 2.9% for QT peak interval. The CV of Tp‐e interval was 10.2% at rest, and 9.3% in exercise test. Reproducibility was comparable between healthy subjects and LQTS patients. Conclusions: The BSPM system with automated analysis produced accurate and highly repeatable QT interval measurements. Reproducibility was adequate also over prolonged time periods both at rest and in exercise stress test. The method can be applied in studying duration of ventricular repolarization time in different physiologic and pharmacologic interventions.     

Differences in leisure-time physical activity levels between blacks and whites in population-based samples: The Minnesota heart survey

Energy expenditure in leisure-time physical activity (LTPA) was measured using the Minnesota LTPA Questionnaire in 35- to 74-year-old black and white residents of Minneapolis-St. Paul, Minnesota. Estimates of the geometric mean LTPA energy expenditure were 129 and 204 kcal per day for black and white men (p<.05) and 91 and 123 kcal per day for black and white women (p<.05). The percentage of individuals expending 2000 kcal or more per week in LTPA was significantly lower in black men than white men (25 vs. 35%; p=.01) but was not different in black versus white women (18 vs. 17%). Although black men and women reported greater occupational physical activity than their white counterparts, LTPA and job activity were unrelated in all race and sex groups. In both races, LTPA energy expenditure declined with age. LTPA increased with level of formal education, and the largest LTPA difference between blacks and whites was observed in those who had a high-school diploma or less. Blacks had lower participation rates than whites in most of the individually assessed physical activities. Additional research is needed on the determinants and promoters of LTPA in population subgroups.The research was funded by National Heart, Lung, and Blood Institute Research Grant R01 HL 23727 and National Research Award T32 HL 07328-10.     

The energy cost of walking or running on sand

Summary Oxygen uptake ( O₂) at steady state, heart rate and perceived exertion were determined on nine subjects (six men and three women) while walking (3–7 km · h^–1) or running (7–14 km · h^–1) on sand or on a firm surface. The women performed the walking tests only. The energy cost of locomotion per unit of distance (C) was then calculated from the ratio of O₂ to speed and expressed in J · kg^–1 · m^–1 assuming an energy equivalent of 20.9 J · ml O₂ ^–1. At the highest speedsC was adjusted for the measured lactate contribution (which ranged from approximately 2% to approximately 11% of the total). It was found that, when walking on sand,C increased linearly with speed from 3.1 J · kg^–1 · m^–1 at 3 km · h^–1 to 5.5 J · kg^–1 · m^–1 at 7 km · h^–1, whereas on a firm surfaceC attained a minimum of 2.3 J · kg^–1 · m^–1 at 4.5 km · h^–1 being greater at lower or higher speeds. On average, when walking at speeds greater than 3 km · h^–1,C was about 1.8 times greater on sand than on compact terrain. When running on sandC was approximately independent of the speed, amounting to 5.3 J · kg^–1 · m^–1, i.e. about 1.2 times greater than on compact terrain. These findings could be attributed to a reduced recovery of potential and kinetic energy at each stride when walking on sand (approximately 45% to be compared to approximately 65% on a firm surface) and to a reduced recovery of elastic energy when running on sand.     

Does the amount of exercising muscle alter the aerobic demand of dynamic exercise?

The primary purpose of this study was to determine if the aerobic demand for production of specified power outputs is altered by distribution of work between the arms and legs compared with when all the work is performed by the legs. Because of the important exercise training implications, a secondary purpose of this study was to determine if the exercising muscle mass affects the cardiorespiratory demands at specified rating of perceived exertion (RPE) levels and blood lactate concentrations. Nine healthy adults completed leg cycling and combined arm and leg exercise on an Airdyne using a discontinuous protocol. Repeated measures ANOVA revealed that oxygen uptake for the combined arm and leg exercise averaged 0.04 l·min⁻¹ greater (p<0.05) than for leg cycling at the same external power outputs. However, RPE levels at specified power outputs were lower (p<0.05) with combined arm and leg exercise than leg cycling. At specified RPE levels and blood lactate concentrations, oxygen uptake and heart rate values were higher (p<0.05) for combined arm and leg exercise than leg cycling. From these findings we conclude that: (1) the addition of arm exercise to leg cycling results in a reduction in RPE, but a minimal increase in oxygen consumption to perform a given power output, and (2) if training intensity is established by RPE or blood lactate concentration, use of a muscle mass larger than that used in leg cycling should allow a greater cardiorespiratory training effect.     

Validity of heart rate and ratings of perceived exertion as indices of exercise intensity in a group of children while swimming

Summary The purpose of this study was to investigate the validity of heart rate (f _c) and ratings of perceived exertion (RPE) as indices of exercise intensity in a group of children while swimming. Six healthy male swimmers, aged 10–12, swam tethered using the breast-stroke in a flume. The resistance started at 1.0 kg and increased in 1.0 kg steps up to the point of their exhaustion. The subjects swam for 5 min during each period, with a rest of 10–20 min until they had returned to their resting f _c level. The last exercise intensity was with the maximal mass the subjects could support for 2 min. The last min of oxygen consumption (VO₂) and 30 s of f _c were measured during each exercise period. The subjects gave their RPE assessment at the end of exercise.The individual relationships between f _c and VO₂, and percentage maximal oxygen consumption (% VO_2max, were linear with a high correlation r=0.962–0.996 and r=0.962–0.996, respectively. Therefore, it was concluded that f _c was valid as an index of the exercise intensity of children while swimming. Compared to the results found in adults using a similar protocol, the children's f _c were 8.3–26.9 beats·min^–1 higher than those of the adults at the given % VO_2max. The present study showed two different patterns in the relationship between VO₂ and RPE in individuals. In two subjects the RPE increased linearly with VO₂ while in the other four subjects the increase was discontinuous. If f _c and RPE were to be applied to the setting and evaluation of exercise intensity during swimming, it would seem that f _c would be a more useful guide than RPE for some children.     

Exercise for older women: a training method and its influences on physical and cognitive performance

Summary The decline in physical and mental ability often associated with increasing age in adults has both social and economic implications that affect most nations. Hence, the maintenance of functional capacity and independence of the older person are beneficial both for the individual and society alike. One way to enhance functioning in old age is physical exercise. However, few methods exist that enable older people to monitor and regulate exercise intensity without using expensive apparatus. Utilizing the individual's subjective feeling of perceived exertion through the use of a simple rating scale is an approach that differs markedly from those previously employed. The present study used the ratings of perceived exertion (RPE) scale to induce different exercise intensities in groups of older women. Walking was chosen as the type of exercise since most older women are unfamiliar with, or affraid to engage in, other types of physical exercise such as bicycling or running. Results indicated that physical exercise capacity increased after 3 months of regular low-intensity walking in the exercise groups but not in nonexercising controls. Furthermore, these changes were accompanied by improved digit span performance. In conclusion, this study has shown that the RPE scale may be used for exercise regulation and that older women would seem to be able to use the scale to monitor and regulate their exercise intensity in an outdoor environment in much the same way as younger individuals.     

Oxygen uptake during whole-body vibration exercise: comparison with squatting as a slow voluntary movement

In this study we investigated metabolic power during whole-body vibration exercise (VbX) compared to mild resistance exercise. Specific oxygen consumption ( ) and subjectively perceived exertion (rating of perceived exertion, RPE; Borg scale) were assessed in 12 young healthy subjects (8 female and 4 male). The outcome parameters were assessed during the last minute of a 3-min exercise bout, which consisted of either (1) simple standing, (2) squatting in cycles of 6 s to 90° knee flexion, and (3) squatting as before with an additional load of 40% of the subject's body weight (35% in females). Exercise types 1–3 were performed with (VbX+) and without (VbX–) platform vibration at a frequency of 26 Hz and an amplitude of 6 mm. Compared to the VbX– condition, the specific was increased with vibration by 4.5 ml·min^–1·kg^–1. Likewise, squatting and the additional load were factors that further increased . Corresponding changes were observed in RPE. There was a correlation between VbX– and VbX+ values for exercise types 1–3 (r=0.90). The correlation coefficient between squat/no-squat values (r=0.70 without and r=0.71 with the additional load) was significantly lower than that for VbX–/VbX+. Variation in specific was significantly higher in the squatting paradigm than with vibration. It is concluded that the increased metabolic power observed in association with VbX is due to muscular activity. It is likely that this muscular activity is easier to control between individuals than is simple squatting. Electronic Publication     

Blood lactate response to overtraining in male endurance athletes

Many physiological markers vary similarly during training and overtraining. This is the case for the blood lactate concentration ([La⁻]_b), since a right shift of the lactate curve is to be expected in both conditions. We examined the possibility of separating the changes in training from those of overtraining by dividing [La⁻]_b by the rating of perceived exertion ([La⁻]_b/RPE) or by converting [La⁻]_b into a percentage of the peak blood lactate concentration ([La⁻]_b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test and a time trial were performed before (baseline) and after this period of overtraining, and after 2 weeks of recovery (REC). The [La⁻]_b and RPE were measured during the recovery of each stage of the incremental test. We diagnosed overtraining in seven athletes, using both physiological and psychological criteria. We found a decrease in mean [La⁻]_b,peak from baseline to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol · l⁻¹, for the three tests, respectively; P < 0.05] and a right shift of the lactate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of mean [La⁻]_b/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in the three tests, respectively; P < 0.05), but no difference in RPE, its variability accounting for less than 25% of the variability of [La⁻]_b/RPE (r=0.49). Consequently, [La⁻]_b/RPE provides little additional information compared to [La⁻]_b alone. Expressing [La⁻]_b as a %[La⁻]_b,peak resulted in a suppression of the right shift of the lactate curve, suggesting it was primarily the consequence of a decreased production of lactate by the muscle. Since the right shift of the curve induced by optimal training is a result of improved lactate utilization, the main difference between the two conditions is the decrease of [La⁻]_b,peak during overtraining. We propose retaining it as a marker of overtraining for long duration events, and repeating its measurement after a sufficient period of rest to make the distinction with overreaching. Accepted: 26 September 2000     

The use of ratings of perceived exertion for regulating exercise levels in rowing ergometry

The purpose of this study was to examine the validity of the use of ratings of perceived exertion (RPE) to estimate and regulate exercise intensity during rowing ergometry. Nine competitive male rowers [mean age 28.6 years, (SD 6.3)] completed two rowing trials on an ergometer. The first trial (estimation) consisted of an incremental protocol designed to elicit a range of work outputs (WO) and heart rates (HR). The subjects indicated their perception of effort using a 15-point scale at each intensity level. In the second trial (production), 7–14 days later, the subjects were asked to produce exercise intensities corresponding to five levels of RPE: 15,11,17,13, and 19. Data analysis revealed high Pearson correlation coefficients between HR and RPE (r = 0.95,P < 0.01) and WO and RPE (r = 0.96,P < 0.01) during the estimation trial. In addition, significant correlations (P < 0.01) were obtained between the estimation and production trials for HR (r = 0.82) and WO (r = 0.84). Posthoc analysis of variance revealed that the observed differences in mean HR were not significant (P > 0.05) at three of the five intensity levels (RPE 15,17 and 19), but were at the two lowest RPE levels (11 and 13). Significant mean differences in WO were seen at all but RPE 17. These data support the validity of the RPE scale as a measure of physiological strain among competitive male rowers, and offer support for its use as a method of regulating the intensity of rowing ergometry, especially at higher levels.     

Effects of order of presentation of exercise intensities and of sauna baths on perceived exertion during treadmill running

Summary Thirteen male subjects performed a running test on the treadmill consisting of four standard exercise intensities [65%, 75%, 85%, 95% maximal O₂ uptake (VO_2max)] presented in ascending, descending or random order. At the end of each exercise intensity, O₂ consumption, heart rate (f _c), venous blood lactate concentration ([la]_b) and perceived exertion were assessed. This last variable was determined according to the Borg nonlinear CR-20 scale. The same variables were also determined during exercise at a standard intensity (65% or 95%VO_2max) performed before and after a Finnish sauna bath. Ratings of perceived exertion showed a good test-retest reliability (r=0.77); they were the same when the exercise intensity was expressed in relative (%VO_2max) or absolute (speed) terms, and were independent of the order of presentation of the exercise. The latter had no effect onf _c either but it did, however, influence [la]_b, which was significantly higher in the descending, as compared to the ascending or random modes of presentation. The sauna bath increasedf _c at a given exercise intensity, but left perceived exertion and [la]_b unchanged. It was concluded that at least under the present experimental conditions,f _c and venous [la]_b do not play a major role as determinants of perceived exertion.