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Energy expenditure during recreational backpacking: A case study
Abstract
The purpose of this study was to determine the exertional intensities and energy costs of backpacking for a single subject and assess the energy expenditure during a two-day backpacking excursion. A heart rate versus oxygen uptake regression was developed for backpacking by submaximal testing with simultaneous measurement of heart rate and oxygen uptake. Heart rate was measured using a Polar Vantage XL monitor and physical activity was assessed using the Tritrac-R3D. The average VO2 values while hiking uphill were measured as 49% VO2max and ranged from 39% to 66%, while hiking downhill the average VO2 values were measured as 28% VO2max and ranged from 22% to 35%. The Tritrac activity monitor underestimated the energy expenditure hiking on the downhill gradient and vastly underestimated the energy expenditure hiking on the uphill gradient. The analysis of caloric expenditure during the two days revealed that backpacking requires a moderate level of energy expenditure. Average caloric expenditure during the uphill hike was calculated to be 9.85 kcal/ min. In addition, the average caloric expenditure during the downhill hike was calculated to be 5.64 kcal/min. The data storage capability of heart rate monitors allows for the long-term estimation of energy expenditure for future backpacking studies.
The purpose of this study was to develop a heart rate - energy expenditure regression and then evaluate heart rate (HR) responses during a seven-day backpacking trip in order to estimate caloric expenditure during backpacking. The selected route was 122km of trails in the Grand Canyon National Park, Arizona. In order to estimate caloric expenditure during the expedition, a HR-VO2 regression was developed by simultaneous measurement of HR (Polar Vantage XL monitor) and VO2 (Aerosport KB1-C). The average hiking heart rates ranged from 60% to 73% HRmax during the expedition. The average rate of estimated caloric cost during backpacking ranged from 6.8 to 10.6kcals·min-1 (equivalent to 408 to 636kcals·hr-1) indicating a relatively moderate level of exertion. Knowledge of the caloric cost of backpacking is important since the nutritional requirements need to be planned prior to undertaking an expedition.
The purpose of this study was to evaluate heart rate responses during a seven-day backpacking trip. The selected route was 122km of trails in the Grand Canyon National Park, Arizona. Heart rate was measured using a Polar Vantage XL monitor. The analysis of heart rate data demonstrated the variability related to terrain (downhill, uphill, or uneven), with respect to the difficulty of the terrain (switchbacks vs. steps) and speed of the hiking gait. The average hiking heart rates ranged from 64% to 74% HRmax during the expedition. This study assessed the heart rate responses while backpacking on an extended expedition, which have never been assessed previously.
Eleven female subjects (ages 18-33 years) walked on a motor-driven treadmill at 86 m/min for 1 h carrying 33% of their body weight in a backpack. The grade of the treadmill alternated every 15 min between 0 and 3%. Each subject carried an internal frame backpack for one trial and an external frame backpack for another trial on a separate day. The variables measured during the two load-carrying experiments included oxygen consumption (VO2), heart rate (HR), respiratory exchange ratio (R), minute ventilation VE, and the ratings of perceived exertion for the chest (RPE-chest), shoulders (RPE-shoulders), and legs (RPE-legs). When oxygen uptake measured during load-carrying was expressed as a percentage of VO2max, the average values were 40.1% (63.5% HRmax) at 0% grade and 49.0% (69.6% HRmax) at 3% grade for both backpacks. No significant differences were found between the two packs for any of the metabolic, cardiorespiratory, or perceptual variables measured. Changes in treadmill grade had a significant effect on VO2, HR, and VE, regardless of the type of pack carried. Minute ventilation was the only physiological response to load-carrying that increased significantly as exercise duration increased. The values for RPE-chest, RPE-shoulders, and RPE-legs were significantly increased by both exercise time and treadmill slope, regardless of the type of pack frame carried. Thus despite relatively constant metabolic responses over time, increased perception of effort could compromise completion of the load-carrying task. It was concluded that differences in backpack frame design were not great enough to produce significant differences in the energy cost or perception of carrying a moderately heavy load on the back.
Our primary purpose was to characterize cardiac frequency during aerobic dancing. A continuous ECG tape recording was obtained on 13 women (21 ± .5 yrs; [Xbar]± SEM) during aerobic dance classes. The tape was subsequently analyzed by microcomputer for min-by-min heart rate (HR) characteristics. During the main dancing phase of 35 min, the total elapsed time the subjects' HR was greater than or equal to HR reserve thresholds of 60%, 70%, and 80% was 23.9 ± 2.29 min, 17.2 ± 2.75 min, and 9.5 ± 2.24 min, respectively. The longest continuous time that HRs exceeded the minimal threshold of 60% was 17.8 ± 2.64 min; this value decreased at the higher thresholds of 70% and 80% to 12.4 ± 2.28 and 6.8 ± 1.80 min, respectively. Aerobic dancing can sustain an elevated cardiac frequency, although not all participants demonstrated this response. The caloric cost of aerobic dancing was estimated from HR during dance and the subjects' HR - oxygen consumption relationship determined in the laboratory. The caloric cost during the main dancing phase of the class was estimated to be 8 ± 1.3 kcal/min.
Thirty-two subjects marched 20 km with 3 different back loads; 20, 25 and 30 kg. Their heart rate, rectal temperature and VO 2max, immediately following the march, were compared to initial values. A mean drop of more than 20% in VO 2max was found in the group carrying the 30 kg load, while no significant decrease in VO 2max occurred in the subjects carrying 20 and 25 kg loads. No correlation was found between the change in VO 2max and the weight of the subjects or the percentage of the load from the body weight. Since those who carried the 30 kg load were in excellent physical condition (VO 2max more than 50 ml O 2/min x kg B.W.) and those who carried the 25 kg load were only of a good one (VO 2max 40-49 ml O 2/min x kg B.W.), it is suggested that to avoid significant decrease in VO 2max, the maximal back load carried by an individual in good physical condition for long distances under field conditions, should not exceed 25 kg.
Eleven healthy male volunteer soldiers (mean [SD] age 24.0 [2.8] years, stature 174.1 [5.2] cm, body weight 73.2 [10.8] kg, body fat 14.2 [5.0]% and maximal oxygen uptake 4.1 [0.4] 1 min-1) walked at 4.8 km h-1 on a motor driven treadmill for 5 min at each of three gradients (0, 2.5 and 5%) whilst carrying a two-part 26 kg load either on each shoulder or strapped to a backpack frame. The load was made up of two cylinders, one weighing 18.4 kg and the other weighing 7.6 kg. For all treadmill gradients the mean (SD) backpacking heart rates and oxygen uptakes (0% gradient, 122 [10] beats min-1, 1.51 [0.11] 1 min-1; 2.5% gradient, 135 [10] beats min-1, 1.81 [0.13] 1 min-1; 5% gradient, 155 [7] beats min-1, 2.21 [0.11] 1 min-1) were significantly (p less than 0.001) lower than for shoulder load carriage (0% gradient, 130 [9] beats min-1, 1.70 [0.12] 1 min-1, 2.5% gradient, 147 [8] beats min-1; 2.01 [0.10] 1 min-1; 5% gradient 164 [9] beats min-1, 2.39 [0.11] 1 min-1). The relative oxygen cost of backpacking was 4.3-4.7% VO2 max lower than for shoulder load carriage. It is concluded that the metabolic cost of backpacking an asymmetric two part 26 kg load was significantly less than for shoulder load carriage when walking at 4.8 km h-1 on a treadmill over gradients of 0-5%.(ABSTRACT TRUNCATED AT 250 WORDS)
Previous studies have investigated the oxygen cost ([Vdot]02) of increasing boot weight during unloaded walking or running, and have shown that for each 100 g increase in weight of footwear there is a 0·7-1·0% increase in [Vdot]O2 In reality (except in athletic events) the use of heavy footwear is associated with load carriage, usually backpacking. We therefore investigated the effects of increasing boot weight by 5% of body weight on the [Vdot]02 of backpacking a load amounting to 35% of the body-weight in five healthy young males who walked at 4·5 km/hour (0% grade) on a motor-driven treadmill. The results indicated a mean increase of 0·96% in [Vdot]02 whilst backpacking for each 100thinsp;-g increase in boot weight. In contrast the oxygen cost of increasing the backpack load was only 0·15% indicating that it was 6·4 times more expensive to carry weight on the feet as compared to the back. It is concluded that the relation between boot weight and oxygen cost, previously developed for unloaded walking and running, can reasonably be extended to include heavier boots and backpacking.
This study was designed to investigate the cardiorespiratory, metabolic, and subjective responses to carrying a load close to the trunk in five different ways. Each of five subjects carried a load equivalent to 35% body weight (BW) for one hour at 4-5 km hr and 0%grade on a motor driven treadmill using each of the following modes of load carriage: (1) the total load carried in a backpack with frame (BP/F), (2) the total load carried in a backpack with no frame (BP/NF), (3) half the load in a backpack (with frame) and half in pouches attached to a waist belt (BP/WB), (4) half the load in a backpack (with frame) and half in a front pack on the chest (BP/FP), and (5) the total load carried as a trunk jacket (TJ), i.e. a military type ‘flak’ jacket with weights inserted in pockets evenly distributed about the trunk. There were no statistically significant differences in the mean cardiorespiratory and metabolic costs associated with each of the five modes of load carriage. However, BP/FP and TJ were subjectively rated as significantly (P < 001) more comfortable than BP/F and BP/NF, suggesting that there may be physiological differences between the five modes of load carriage which were not detected by the cardiorespiratory and metabolic measurements used in this study (i.e. heart rate, oxygen consumption and minute ventilation). In contrast, the BP/FP was reported to be the hardest to don and doff and was associated with a statistically significant (P
We examined the ability of the Tritrac-R3D to estimate daily energy expenditure (EE) and characterize the physical activity patterns of free-living humans. Daily EE was estimated by the Tritrac, a 3-d physical activity log (PAL), and a 7-d recall (SDR). Digital storage of activity data by the Tritrac allowed us to tabulate the number of minutes the monitor recorded EE at specific activity intensities. Twenty-five men and women (mean age and body mass 26.7 yr, 72.5 kg) wore the monitor for 7 d. The Tritrac significantly underestimated daily EE compared with the PAL and SDR, 2552.7 vs 2915.5 kcal.d-1 and 2530.0 vs 2840.3 kcal.d-1, respectively (both, P < 0.01). Correlations between the Tritrac and PAL and the SDR were r = 0.82 and r = 0.77 (both, P < 0.001). Compared with the PAL, the Tritrac overestimated time accumulated in sedentary activities (862.7 vs 827.2 min.d-1) but underestimated time accumulated in active behaviors (37.5 vs 78.0 min.d-1). In conclusion, these data suggest the Tritrac ranks activity levels similarly to the PAL and SDR but it significantly underestimates free-living energy expenditure.
None of the various methods used to measure habitual physical activity over days, weeks, or years in the general population have yet proven entirely satisfactory. A major problem is that no "gold standard" exists for the validation of various questionnaires, logs, or diaries that can be used in large sample population studies. Attempts have been made to accurately measure the activity profile by using heart rate or various motion sensors or accelerometers, but each approach has had significant limitations. The availability of new solid state recording techniques and computer-based analytic and display procedures now makes it possible to simultaneously record heart rate and body movement continuously for days and to combine the analysis of these data using customized software. Preliminary evaluation of this concept of simultaneous recording and analysis of heart rate and body motion via movement sensors on an arm and leg were conducted in 19 men. Subjects performed a variety of exercises in the laboratory during which heart rate, leg motion, arm motion, and oxygen uptake were recorded. Various issues regarding the prediction of energy expenditure from heart rate and body movement independently and in combination were evaluated. The results demonstrate that the accuracy of estimating oxygen uptake during a wide range of activities is improved when individualized heart rate--oxygen uptake regressions are used and heart rate and body movement are analyzed simultaneously rather that separately.
The present study evaluated the utility of a portable metabolic measurement system, the Aerosport TEEM 100. A total of 505 data points [242 from incremental (INC) and 263 from constant load (CL) exercise] were collected on 12 subjects (age = 25 +/- 4 yr), by placing the Aerosport TEEM 100 medium flow pneumotach and mouthpiece in-line with a validated system, the Rayfield system. When VO2 values were separated into categories (< 1.5, 1.5-2.0, 2.0-2.5, 2.5-3.0, > 3.0 l.min-1), there was a small but statistically significant difference between the two metabolic measurement systems for VO2, VCO2, VE, RER, %ECO2, and %EO2 during both INC and CL exercise and measurement error for VO2 ranged between 2% and 11%. Correlations for VO2 values during INC and CL exercise between the two systems were r = 0.95 (SEest +/- 0.18 l.min-1) and r = 0.96 (SEest +/- 0.29 l.min-1), respectively. Correlations for RER were r = 0.82 (SEest +/- 0.08) and r = 0.47 (SEest +/- 0.11), for INC and CL, respectively. Results from the present investigation indicate that the Aerosport TEEM 100 has utility for the assessment of VO2, but the estimation of carbohydrate and fat utilization from RER should be used with caution.