Energy expenditure is accurately and reliably determined by measuring oxygen consumption (V[Combining Dot Above]O2) (30). However, direct measurement of V[Combining Dot Above]O2 is often not practical, as it requires trained personnel and expensive laboratory equipment and can only accommodate 1 person at a time. A commonly used alternative for estimating energy expenditure in field-based settings is heart rate (1,32). There are several benefits to use heart rate in field settings. First of all, heart rate is easily measured by palpation or with a monitor, making assessment inexpensive and relatively easy to manage with minimal training (1). Secondly, heart rate shares a linear relationship with V[Combining Dot Above]O2 during lower-body exercise, such as walking, running, and cycling, performed over a wide range of intensities above basal and below maximal output (6,9,11). Based on this relationship, algorithms that predict energy expenditure have been developed using heart rate along with a variety of other factors that include, but are not limited to, age, aerobic fitness, and gender (22). In fact, commercially available heart rate monitors that use such algorithms have become the most commonly used methods of estimating energy expenditure during field-based exercise (1).
Despite the popularity of heart rate monitors, a review of the results from research studies investigating the heart rate-V[Combining Dot Above]O2 relationship suggests that the accuracy of heart rate monitors in estimating energy expenditure may depend on whether arm movements are involved in the exercise mode. For instance, although the linear heart rate-V[Combining Dot Above]O2 relationship is fairly strong during leg-only exercise, this relationship weakens during arm-only exercise. Specifically, research has shown that sustained arm-only exercise results in a higher heart rate per given V[Combining Dot Above]O2 than leg-only exercise (3,26,40). This disproportionate rise in heart rate compared with V[Combining Dot Above]O2 has been suggested to be because of an increase in sympathetic output that accompanies the involvement of upper body musculature, especially when performed overhead (4,8,28). Thus, caution should be employed when using heart rate monitors as a predictor of energy expenditure during arm-only exercise.
The relationship between heart rate and V[Combining Dot Above]O2 is not clear when leg and arm exercises are combined, such as during popular forms of group exercise. For instance, investigators have observed a disproportionate increase in heart rate relative to V[Combining Dot Above]O2 when comparing aerobic dance with arm movements to treadmill running at the same V[Combining Dot Above]O2 (28), aerobic dance with arm movements performed above the shoulder vs. below the shoulder (10), and aerobic dance with more arm movement vs. less arm movement (14). In contrast, other investigators have observed a comparable heart rate-V[Combining Dot Above]O2 relationship during the same aerobic dance routine performed with and without arm movements (5) and during treadmill running, aerobic dance with arm movements performed above the shoulder, and aerobic dance with arm movements performed below the shoulder at the same V[Combining Dot Above]O2 (7). Despite the obvious inconsistencies in the research, it is widely accepted that heart rate is likely to increase to a greater extent than V[Combining Dot Above]O2 during many different forms of group exercise involving combined leg and arm movements, including aerobic dance, aerobic bench stepping, and kickboxing (10,14,19,21,28,33,35,41). If heart rate indeed rises more than V[Combining Dot Above]O2 during group exercise, then reliance on heart rate monitors alone will result in an overestimation of energy expenditure. In fact, Lowe et al. (21) observed that the Polar F6 heart rate monitor overestimated energy expenditure by approximately 2 kCal·min−1 during aerobic bench stepping with choreographed arm and leg movements while stepping on and off a bench to music and suggested that the overestimation error was because of the involvement of arms.
This study is a follow-up to the Lowe et al. (21) study with the primary purpose of determining whether the overestimation in energy expenditure by the Polar F6 heart rate monitor was indeed because of choreographed arm movements performed during aerobic bench stepping. A secondary purpose was to characterize the effects of these arm movements on the cardiorespiratory responses measured during the aerobic bench stepping. To this end, the experiment was designed in such a way to isolate the effects of the arm movements on the accuracy of the Polar F6 heart rate monitor. Based on previous research observing elevated heart rates relative to V[Combining Dot Above]O2 during arm-only vs. leg-only exercise (3,26,39) as well as during combined arm and leg exercise (10,14,28), we hypothesized that when arms are immobilized during aerobic bench stepping: (a) the accuracy of the Polar F6 heart rate monitor in estimating energy expenditure will improve; and (b) oxygen pulse (V[Combining Dot Above]O2 per heart rate) will be higher. If this study shows that arm movements affect the accuracy of the Polar F6 heart rate monitor in estimating energy expenditure, then these results may suggest that the Polar F6 monitor may also be inaccurate in estimating energy expenditure when used during other forms of group exercise that involve arm movements.
Experimental Approach to the Problem
The approach to this problem was to isolate the effect of choreographed arm movements performed during aerobic bench stepping on the accuracy of the Polar F6 heart rate monitor and on the cardiorespiratory responses. All subjects completed 2 trials that consisted of performing a 20-minute choreographed aerobic bench stepping routine. The only difference between the trials was that one involved choreographed arm movements and the other involved immobilization of arms by placing hands on hips, directly above the iliac crest. The trial order was randomly assigned for each subject. During the trials, V[Combining Dot Above]O2 was measured through indirect calorimetry, and both heart rate and energy expenditure were determined through the Polar F6 heart rate monitor.
The research questions for this study were investigated according to the following hypothesis:
- Hypothesis 1: The accuracy of the heart rate monitor in estimating energy expenditure during aerobic bench stepping will improve when hands are placed on the hips, thereby immobilizing the arms.
- Hypothesis 2: Oxygen pulse (V[Combining Dot Above]O2 per heart rate in ml·b·min−1) will be higher when arms are immobilized during aerobic bench stepping.
To evaluate the tenability of our hypotheses, we conducted planned contrasts with the Bonferroni adjustment (22). The independent variable (i.e., study condition within subjects) was the inclusion of choreographed arm movements in the aerobic bench stepping routine. Two separate analyses were conducted to test our research hypotheses. In analysis 1, we determined whether the arm movements affected the accuracy of the Polar F6 heart rate monitor in estimating energy expenditure. For this analysis, the dependent variable was calculated as the difference between the energy expenditure estimated from the heart rate monitor (EE-HRM) and the energy expenditure determined through indirect calorimetry (EE-IC) for each of the same subjects; and this variable was compared between the 2 trials within subjects. In analysis 2, we characterized the effects of the arm movements on the cardiorespiratory responses by comparing the dependent variables, heart rate, V[Combining Dot Above]O2, and oxygen pulse (V[Combining Dot Above]O2 per heart rate in ml·b·min−1), for each of the same subjects, between the 2 trials.
Subjects were 32 college-aged female volunteers enrolled during a spring semester in a 2-day per week university group exercise class that fulfilled one of the 2-hour state-mandated physical activity class requirement for all majors. To ensure that the volunteers (18 to 25 years of age) were able to follow a videotaped aerobic bench stepping routine and also to reduce the risk of injury or other health complications, the criteria for participation included a minimum of 1 month of regular attendance (at least 2 days per week) in the group exercise class and being classified as low risk for cardiovascular disease as determined by a standard health appraisal survey (2).
Table 1 reports the subjects' descriptive statistics. The aerobic fitness levels of the participants ranged from poor to excellent, according to their maximal oxygen consumption (V[Combining Dot Above]O2max) measurements (2). Therefore, the results from this sample can be generalized to young, college-age women of varying fitness levels who are familiar with the techniques required for aerobic bench stepping.
This investigation was approved by Texas State University Institutional Review Board. Before the study began, subjects were informed of the experimental protocol, including any potential risks, and signed a consent form.
Subjects visited the laboratory in the afternoon on 4 separate occasions, 2–7 days apart. Before their first visit, the subjects were given strict instructions to adhere to during the study period to control factors that could potentially affect cardiovascular responses and the outcomes of this study. Subjects were asked to: (a) drink plenty of fluids over the 24-hour period preceding the test; (b) avoid food, caffeine, and tobacco products for at least 3 hours before the test and alcohol the day of the test; (c) avoid strenuous physical activity the day of the test; and (d) maintain their current level of physical activity during the relatively short study period (2). All data were collected by the same well-trained technician. Subjects were tested in a temperature-controlled room (approximately 22° C).
During visit 1, participants: (a) signed a consent form; (b) completed a comprehensive health appraisal; (c) were measured for height and weight (in exercise clothes, without shoes) using a calibrated physician's scale (Detecto Scale Co., Jericho, NY, USA); and (d) were familiarized with the equipment and with both the maximal and submaximal exercise protocols by practicing walking and running on the treadmill and performing the aerobic bench stepping routine while wearing the headgear, mouthpiece, and nose clip.
During visit 2, resting heart rate was measured while each subject sat quietly until their heart rate decreased to a resting level and remained constant for 5 minutes. Heart rate was recorded at the end of each minute. The resting heart rate was the average of the final 5 minutes of the resting protocol. During all tests, including resting, maximal, and submaximal exercise tests, heart rate was measured with a Polar F6 heart rate monitor (Polar Electro Oy [Polar], Stanford, CT, USA).
Also during visit 2, subjects performed a Bruce graded maximal exercise test (2) on a Trackmaster treadmill (FullVision, Newton, KS, USA). The test was terminated when the subjects achieved volitional exhaustion, or if they exhibited contraindications to exercise (2). Peak V[Combining Dot Above]O2 was considered as V[Combining Dot Above]O2max if 2 of the following criteria were met: (a) a plateau in V[Combining Dot Above]O2 despite an increase in workload; (b) a heart rate that was ±10 b·min−1 within the subject's age-predicted maximal heart rate (HRmax = 206.9 − [0.67 × age]) (16); and (c) a respiratory exchange ratio (RER) ≥1.15 (24). If the subject did not achieve V[Combining Dot Above]O2max, then she returned to the laboratory after at least a 48-hour rest period to repeat the Bruce protocol. All subjects achieved V[Combining Dot Above]O2max in 1 or 2 attempts. During maximal and submaximal exercise tests, expired air was analyzed with a PARVO Medics metabolic analyzer (Salt Lake City, UT, USA). V[Combining Dot Above]O2, carbon dioxide production (V[Combining Dot Above]CO2), minute ventilation (VE), RER, and energy expenditure were determined from 60-second averages. Calibration was performed before each test using a certified gas mixture (O2 = 16% and CO2 = 4%; Scott Medical Products, Plumsteadville, PA, USA).
During visits 3 and 4, subjects were randomly assigned to follow exactly either the arm and leg movements or the legs-only movements of a videotaped, 20-minute aerobic bench stepping routine. When performing the legs-only trial, subjects were instructed to place their hands on their hips. Bench stepping took place using a 20.32 cm (8-in) bench at a cadence of 128 b·min−1. The cadence was verified by a metronome. For both visits, user data (i.e., age, height, weight, gender, resting heart rate, V[Combining Dot Above]O2max, and HRmax) were first entered into a Polar F6 heart rate monitor. Once programmed, the heart rate monitor (i.e., receiver) was affixed to the subject's left wrist. A heart rate strap (i.e., transmitter) was affixed to the subject's chest. Damp sponges were placed between the chest and the strap to ensure that heart rate was recorded throughout the entire testing session.
The primary investigator collaborated with an Aerobics and Fitness Association of America-certified group exercise leader with 2 years of aerobic dance and aerobic bench stepping teaching experience to develop and videotape a 20-minute choreographed routine of moderate to hard intensity consisting of movements commonly cited in step instructor textbooks (23,31) and used in aerobic bench stepping classes (39). The rhythmical routine was set to music and consisted of basic stepping, alternating kicks, knee lifts, leg curls, back leg lifts, turn stepping, and traveling back and forth over the top of the bench. Various arm movements, including opening and closing the arms overhead and across the chest, and lateral and forward raises to shoulder height, were performed simultaneously with bench stepping. The arms were never held above the shoulders for an extended period of time and their range of movement was constant and within both the horizontal and vertical planes.
For the aerobic bench stepping trials involving arm movements, subjects were fitted with heart rate monitors and headgear that housed the breathing apparatus. Subjects then rested for 15 minutes and, as instructed, followed the exact movements of the aerobic bench stepping routine. Before the beginning of each trial, the bench was positioned so that the subject could perform the routine. The gas collection tubing was suspended overhead and to the side of each subject, extending from the metabolic cart through a plastic loop support. With the continuous aid of a technician to control the slack in the tubing, the exercise trials were completed with minimal interference in movement from the metabolic apparatus. To ensure that steady-state data were used for data analysis, the physiological measurements of all metabolic data (i.e., V[Combining Dot Above]O2, V[Combining Dot Above]CO2, VE, RER, EE, and heart rate) for minutes 6 through 20 were used. For the aerobics bench stepping trials performed without arm movements, the same protocol describe above was followed with 1 exception; the subjects were asked to immobilize their arms by placing hands on hips (i.e., placing fists laterally above the iliac crest).
To recap, the primary purpose of this study was to examine the effects of arm movements performed during aerobic bench stepping on the accuracy of the Polar F6 heart rate monitor. Hypothesis 1 stated that the accuracy of the heart rate monitor in estimating energy expenditure during aerobic bench stepping will improve when hands are placed on the hips, thereby immobilizing the arms. To this end, mean and SDs for EE-HRM and EE-IC measured for each subject during each trial were calculated. Also, the difference between EE-IC and EE-HRM was calculated for each individual for each of the 2 trials (i.e., aerobic bench stepping with and without arm movements). Then, paired sample t-tests were used to compare the differences for each subject between the 2 trials.
The secondary purpose of this study was to further characterize the effects that arm movements have on cardiopulmonary responses to aerobic bench stepping. Hypothesis 2 stated that oxygen pulse (V[Combining Dot Above]O2 per heart rate in ml·b·min−1) will be higher when arms are immobilized during aerobic bench stepping. To this end, mean and SDs for each subject during each trial were calculated. Then, paired sample t-tests were used to compare the cardiopulmonary measures for each subject between the 2 trials.
Type 1 error rate was corrected for multiple comparisons using the Bonferroni correction (22). Based on this correction, type 1 error rate was set to 0.01. Standardized mean difference (SMD = mean difference divided by the pooled SD) was also calculated and referenced against Hopkins' criteria (or Cohen's d) of trivial (0.0–0.2), small (0.21–0.6), moderate (0.61–1.2), and large (>1.2) (12).
Before conducting data analysis, the outcome measures (dependent variables) were screened for general linear model assumptions of: (a) normality, (b) homogeneity of variance between time points of measurement, and (c) linearity (20,25). The assumption of normality was evaluated based on a review of normal Q-Q plots and the Kolmogorov-Smirnov test. Homogeneity of variance was evaluated based on Levine's test, whereas the assumption of linearity was evaluated based on a review of the residual plots (38). Based on review of these assumptions with our data, no violations were found.
To ensure adequate statistical power to detect a difference between means when one actually existed, we conducted a power analysis and determined the minimum sample size to be N = 28 to achieve a power of 0.82 with type error rate of 0.01 and effect size of 3-quarters of 1 SD (12,18).
The average energy expended during the same aerobic bench stepping routine performed with and without arm movements and measured through indirect calorimetry and estimated using the Polar F6 heart rate monitor is provided in Table 2. The EE-HRM was greater than EE-IC by 27% (Δ1.96 kCal·min−1, t = 11.599, df = 31, p < 0.001, 95% confidence interval (CI) = 1.62–2.31, effect size = 2.05) when arm movements were included and by 26% (Δ1.73 kCal·min−1, t = 9.126, df = 31, p < 0.001, 95% CI = 1.34 to 2.12, effect size = 1.61) when arms were immobilized. The calculated difference between EE-IC and EE-HRM, however, was not significantly different between the aerobic bench stepping routine performed with and without arm movements (p ≥ 0.05). Therefore, the results of this study do not support hypothesis 1, which predicted that the accuracy of the heart rate monitor would improve when the routine was performed without arm movements.
The average cardiorespiratory responses to the same aerobic bench stepping routine performed with and without arm movements are reported in Table 3. All of the responses measured during aerobic bench stepping with arm movements were significantly different than those measured during the same routine performed without arm movements (p < 0.001). Specifically, when arm movements were included in the routine, V[Combining Dot Above]O2 increased by 9% (Δ+2.0 ml·kg−1·min−1, t = 6.687, df = 31, p < 0.001, 95% CI = 1.39–2.62, effect size = 1.48) and heart rate increased by 29% (Δ+36.3 b·min−1, t = 8.378, df = 31, p < 0.001, 95% CI = 27.5–45.2, effect size = −0.9549), whereas oxygen pulse decreased by 16% (Δ−1.7 ml per beat, t = −5.402, df = 31, p < 0.001, 95% CI = −1.09 to −2.41, effect size = 1.18). Therefore, the results of this study support hypothesis 2, which predicted that oxygen pulse (V[Combining Dot Above]O2 per heart rate) would be higher when the arms were immobilized during an aerobic bench stepping routine.
The Pearson product moment correlation was used to evaluate the consistency of measurement (i.e., reliability) across trials. The correlation between trials was observed as 0.66 for V[Combining Dot Above]O2, 0.42 for heart rate, 0.88 for EE-IC, and 0.82 for EE-HRM. All correlation coefficients support acceptable consistency of measurement across trials (>0.80) except for heart rate (0.42) and marginally for V[Combining Dot Above]O2 (0.66) (27).
This study was designed to isolate the impact of arm movements on the accuracy of the Polar F6 heart rate monitor in estimating energy expenditure. We fully expected the Polar F6 monitor to accurately estimate energy expenditure during aerobic bench stepping with no arm movement, but to overestimate energy expenditure when the routine involved arm movements because: (a) heart rate has long been shown to share a linear relationship with V[Combining Dot Above]O2 during lower-body aerobic exercise (6,9,11), but not during upper body aerobic exercise (3,26,40) or combined upper- and lower-body aerobic exercise (10,14,28); and (b) the Polar F6 heart rate monitor has been shown to overestimate energy expenditure during aerobic bench stepping involving arm movements (21). Surprisingly, the degree of accuracy of the Polar F6 monitor was similar during aerobic bench stepping with and without arm movements. For both trials, the Polar F6 monitor overestimated energy expenditure by almost 2 cal·min−1.
Since the monitor was equally inaccurate with and without arm movements, there must have been at least 1 variable other than arm movements that impacted the prediction of energy expenditure by the heart rate monitor. To consider other possible sources of error, a general understanding of how the Polar F6 heart rate monitor is designed to predict energy expenditure is warranted. Briefly, Polar uses “OwnCal,” a software system that estimates energy expenditure from the user's exercise heart rate and personal data, including age, gender, height, weight, V[Combining Dot Above]O2max, and maximal heart rate (HRmax) (29). In most settings, however, it is not feasible to obtain actual V[Combining Dot Above]O2max and HRmax measurements. Thus, the Polar F6 heart rate monitor includes a feature in which V[Combining Dot Above]O2max and HRmax can be estimated from the user's personal data. In short, V[Combining Dot Above]O2max and HRmax can be predicted by the monitor itself. Errors in such predictions could be a potential source of the variation in energy expenditure observed when using Polar heart rate monitors (13). To eliminate this source of error in this study, we measured V[Combining Dot Above]O2max and HRmax and manually entered these values into the monitor for each subject. Thus, although the design of this study allowed us to rule out arm movements and monitor-estimated V[Combining Dot Above]O2max and HRmax as potential sources of error, the fact remains that, in this study, the Polar F6 heart rate monitor overestimated energy expenditure during choreographed aerobic bench stepping performed with and without arm movements. Future research is needed to identify the true source(s) of error during group exercise that involves full body movements. In the meantime, users should be cautious when relying on a Polar F6 monitor during group exercise. For instance, in a typical 45-minute aerobic bench stepping session, the error observed in this study would translate to an overprediction of almost 90 cal by the Polar F6 monitor.
The second purpose of this study was to characterize the effects of choreographed arm movements on cardiopulmonary responses during aerobic bench stepping because most relevant research was performed about 2 decades ago and produced conflicting results (5,7,10,14,28). Results of this study revealed that V[Combining Dot Above]O2 and heart rate were higher while oxygen pulse was lower during aerobic bench stepping with arm movements compared with aerobic bench stepping without arm movements. While both V[Combining Dot Above]O2 and heart rate increased when arm movements were added to the aerobic bench stepping routine, heart rate increased to a greater extent than V[Combining Dot Above]O2. These results provide further evidence that V[Combining Dot Above]O2 and heart rate do not share a linear relationship during choreographed group exercise involving both leg and arm movements. In previous studies, lower oxygen pulses were also observed when aerobic dance was compared with more common modes of exercise (14,28) or during aerobic dance with arm movements performed above the shoulder vs. below the shoulder (10). Unlike this study, these studies did not compare the V[Combining Dot Above]O2-heart rate relationship for the same group exercise routine with and without arm movements.
Because we observed that heart rate rose to a greater extent than V[Combining Dot Above]O2 when arms were added to the aerobic bench stepping routine, we felt that a post hoc analysis regarding the usefulness of heart rate as a measure of exercise intensity during aerobic bench stepping with arms movements was warranted. Briefly, heart rate can be used to determine percent heart rate reserve (% HRR, i.e., [Exercise heart rate − Resting heart rate]/[Maximal heart rate − Resting heart rate]) (2). Percent HRR is considered a valid measure of intensity because, as with heart rate and V[Combining Dot Above]O2, %HRR has been shown to share a linear relationship with percent oxygen consumption reserve (% V[Combining Dot Above]O2R = [Exercise V[Combining Dot Above]O2 − Resting V[Combining Dot Above]O2]/[V[Combining Dot Above]O2 − Resting V[Combining Dot Above]O2]). Although it is clear that the % V[Combining Dot Above]O2R-% HRR relationship is linear during lower-body exercise, such as running and cycling (15,36,37), it is unclear whether this relationship exists during exercise involving upper-body exercise. Some research has shown, for instance, that the % HRR rises to a greater extent than % V[Combining Dot Above]O2R during upper-body exercise (34) and during combined upper- and lower-body exercise (35), whereas other research has shown a proportionate rise in % HRR compared with % V[Combining Dot Above]O2R during upper-body exercise (17). If % HRR indeed rises more than % V[Combining Dot Above]O2R when arm movements are performed along with leg movements, then % HRR may not be appropriate for monitoring exercise intensity during certain formats of group exercise, and reliance on heart rate monitors may lead group exercise participants to erroneously assume that they are working at a harder intensity than they actually are.
Post hoc analysis revealed that % HRR was significantly higher than % V[Combining Dot Above]O2R when arms were added to the step routine (t = 14.481, df = 31, p < 0.001). Specifically, % HRR was 34% higher than % V[Combining Dot Above]O2R during aerobic bench stepping with arm movement (Δ+19.0, 74.2 vs. 55.2%, respectively). Also, but as expected, there was no significant difference between % HRR and % V[Combining Dot Above]O2R during aerobic bench stepping performed without arm movements (p ≥ 0.05, Table 2). From a practical standpoint, the involvement of arm movements in this study led to a difference in classification of intensity depending on the method used. The average relative intensity during the aerobic bench stepping routine with arm movements was “hard” when using the average % HRR (74%) and “moderate” when using the average % V[Combining Dot Above]O2R (55%) (2). In contrast, the average relative intensity of the aerobic bench stepping routine without arms was moderate regardless of the method used. Thus, the data show that when arms are involved during aerobic bench stepping, the % HRR is not a valid measure of intensity, as it will most likely lead to an overestimation in exercise intensity. In practical terms, aerobic bench stepping instructors and class participants who use heart rate to characterize and monitor exercise intensity, regardless of how heart rate is measured, may believe that they are exercising harder than they actually are.
There were strengths to this study. To our knowledge, this is the first study to isolate the effects that choreographed arm movements during aerobic bench stepping have on the accuracy of the Polar F6 heart rate monitor in predicting energy expenditure. Second, compared with many studies, this study used a relatively large sample size. However, this study was not without limitations. The sample was essentially a convenience sample and thus not a representative of older women, men of any age, or obese men and women. Furthermore, the results are limited to aerobic bench stepping on an 8-in bench. Despite the limitations, we can glean that the involvement of arm movements is not the cause of the prediction error in energy expenditure by the Polar F6 heart rate monitor in young, healthy, relatively fit women participating in aerobic bench stepping.
Heart rate monitors have been shown to be accurate in estimating energy expenditure and monitoring exercise intensity during common forms of lower-body exercise, such as cycling, walking, and running (6,9,11), and inaccurate during aerobic bench stepping, an exercise that involves both the lower and upper body (21). In light of this, this study isolated the impact of the arm movements during aerobic bench stepping. The major finding of this study was that the arm movements did not account for the overestimation of energy expenditure by the Polar F6 monitor. Nevertheless, it remains evident that the Polar F6 heart rate monitor is not an accurate tool for estimating energy expenditure during aerobic bench stepping. Thus, aerobic bench stepping participants should be cautious when using a Polar F6 heart rate monitor to estimate energy expenditure.
We sincerely acknowledge Ms. Annie Lowe for supervising data collection. She ran a “tight ship” and ensured that all data were measured accurately and in a timely manner.
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