Pattern of energy expenditure during simulated competition

PURPOSE: To determine how athletes spontaneously use their energetic reserves when the only instruction was to finish in minimal time, and whether experience from repeated performance changes the strategy of recreational athletes. METHODS: Recreational road cyclists/speed skaters (N = 9) completed three laboratory time trials of 1500 m on a windload braked cycle. The pattern of energy use was calculated from total work and from the work attributable to aerobic metabolism, which allowed computation of anaerobic energy use. Regional level speed skaters (N = 8) also performed a single 1500-m time trial with the same protocol and measurements. RESULTS: The serial trials were completed in (mean +/- SD) 133.8 +/- 6.6, 133.9 +/- 5.8, 133.8 +/- 5.5 s (P > 0.05 among trials); and in 125.7 +/- 10.9 s in the skaters (P < 0.05 vs cyclists). The [OV0312]O(2peak) during the terminal 200 m was similar within trials (3.23 +/- 0.44, 3.34 +/- 0.44, 3.30 +/- 0.51 (P > 0.05)) versus 3.91 +/- 0.68 L.min-1 in the skaters (P < 0.05 vs cyclists). In all events, the initial power output and anaerobic energy use was high and decayed to a more or less constant value ( approximately 25% of peak) over the remainder of the event. Contrary to predictions based on an assumed "all out" starting strategy, the subjects reserved some of their ability to perform anaerobic work for a terminal acceleration. The total work accomplished was not different between trials (43.53, 43.78, and 47.48 kJ in the recreational athletes, or between the cyclists and skaters (47.79 kJ). The work attributable to anaerobic sources was not different between the rides (20.67, 20.53, and 21.12 kJ in the recreational athletes). In the skaters, the work attributable to anaerobic sources was significantly larger versus the cyclists (24.67 kJ). CONCLUSION: Energy expenditure during high-intensity cycling seems: 1) to be expended in a manner that allows the athlete to preserve an anaerobic energetic contribution throughout an event, 2) does not appear to have a large learning effect in already well trained cyclists, and 3) anaerobic energy expenditure may be the performance discriminating factor among groups of athletes.     

Effect of competitive distance on energy expenditure during simulated competition

Concepts of how athletes should expend their aerobic and anaerobic energetic reserves are generally based on results of tests where an "all out" strategy is imposed on/required from the athlete. We sought to determine how athletes spontaneously expend their energetic reserves when the only instruction was to finish the event in minimal time, as in competition. Well trained, and task habituated, road cyclists (N = 14) completed randomly ordered laboratory time trials of 500 m, 1000 m, 1500 m and 3000 m on a windload braked cycle ergometer. The pattern of aerobic and anaerobic energy use was calculated from total work accomplished and V.O (2) during the trials. The events were completed in 40.3 +/- 0.6 s, 87.4 +/- 4.1 s, 133.8 +/- 6.6 s and 296.0 +/- 7.2 s. The peak V.O (2) during the terminal 200 m of all events was similar (2.72 +/- 0.22, 3.01 +/- 0.34, 3.23 +/- 0.44 and 3.12 +/- 0.13 l x min (-1)). In all events, the initial power output and anaerobic energy use was high, and decreased to a more or less constant value over the remainder of the event. However, the subjects seemed to reserve some ability to expend energy anaerobically for a terminal acceleration which is contrary to predictions of an "all out" starting strategy. Although the total work accomplished increased with distance (23.14 +/- 4.24, 34.14 +/- 6.37, 43.54 +/- 6.12 and 78.22 +/- 8.28 kJ), the energy attributable to anaerobic sources was not significantly different between the rides (17.29 +/- 3.82, 18.68 +/- 8.51, 20.60 +/- 6.99 and 23.28 +/- 9.04 kJ). The results are consistent with the concept that athletes monitor their energetic resources and regulate their energetic output over time in a manner designed to optimize performance.     

Describing and understanding pacing strategies during athletic competition

It is widely recognized that an athlete's 'pacing strategy', or how an athlete distributes work and energy throughout an exercise task, can have a significant impact on performance. By applying mathematical modelling (i.e. power/velocity and force/time relationships) to athletic performances, coaches and researchers have observed a variety of pacing strategies. These include the negative, all-out, positive, even, parabolic-shaped and variable pacing strategies. Research suggests that extremely short-duration events (< or =30 seconds) may benefit from an explosive 'all-out' strategy, whereas during prolonged events (>2 minutes), performance times may be improved if athletes distribute their pace more evenly. Knowledge pertaining to optimal pacing strategies during middle-distance (1.5-2 minutes) and ultra-endurance (>4 hours) events is currently lacking. However, evidence suggests that during these events well trained athletes tend to adopt a positive pacing strategy, whereby after peak speed is reached, the athlete progressively slows. The underlying mechanisms influencing the regulation of pace during exercise are currently unclear. It has been suggested, however, that self-selected exercise intensity is regulated within the brain based on a complex algorithm involving peripheral sensory feedback and the anticipated workload remaining. Furthermore, it seems that the rate and capacity limitations of anaerobic and aerobic energy supply/utilization are particularly influential in dictating the optimal pacing strategy during exercise. This article outlines the various pacing profiles that have previously been observed and discusses possible factors influencing the self-selection of such strategies.     

Nutritional conditioning for athletic competition

Diet in itself cannot provide fitness or championship form, but a poor diet can ruin both. Optimal nutrition is a basic component of training that is necessary for the development and maintenance of top physical performance. Appropriate application of recent research findings can have a beneficial impact on exercise performance.     

Total energy expenditure during arduous wildfire suppression

PURPOSE: The purpose of this investigation was to determine the total energy expenditure (TEE) by using the doubly labeled water (DLW) methodology during 5 d of wildfire suppression in Montana, California, Florida, Washington, and Idaho. METHODS: Seventeen wildland firefighters (from three Interagency Hot Shot crews, N = 8 men, height = 177 +/- 7 cm, weight = 74.6 +/- 6.4 kg, age = 24.5 +/- 1.8 yr; N = 9 women, height = 170 +/- 7 cm, weight = 65.2 +/- 8.0 kg, age = 25.0 +/- 1.3 yr) served as subjects. Before wildland fire suppression, each subject was given an oral dose of 2H2O and H218O (approximately 0.23 g 2H2O.kg estimated TBW-1 and 0.39 g H218O.kg estimated TBW-1). Urine samples were collected between 0400 and 0600 daily. TEE was calculated using the two-point method for days 1-3 and 1-5, with the TEE for days 4-5 calculated by extrapolation. Urine samples from other crew members not participating in the DLW protocol were collected at the same times and used to adjust calculations of isotopic elimination for background shifts. RESULTS: TEE was 17.4 +/- 3.7 and 17.5 +/- 6.9 MJ.d-1 during days 1-3 and 4-5, respectively. The energy expenditure associated with physical activity (EEA) was 8.8 +/- 3.0 and 8.9 +/- 6.1 MJ.d-1 for days 1-3 and 4-5, respectively. CONCLUSION: The current data demonstrate consistently high daily energy expenditure in the wildland firefighter. These data also demonstrate that the doubly labeled water methodology is an appropriate methodology for the measure of TEE during unpredictable field operations if adjustments are made for changes in background enrichment and elevated water turnover.     

Mild overcooling increases energy expenditure during endurance exercise

Intensive cooling has been shown to increase energy expenditure (EE) during work as well as to decrease physical performance. Two different levels of moderate cooling (10°C vs 15°C) were studied during light endurance exercise in order to examine the effect of the increased heat loss on EE. Twelve subjects performed a 90-min low intensity exercise (100 W) on a cycle ergometer, wearing a water-cooled calorimeter suit for controlled cooling. The lower temperature resulted in a 4.3±3.8% (mean±SD) higher EE, increased total heat loss and lowered skin temperatures. No differences in central core body temperature, heart rate or respiratory quotient (RQ) were recorded. There was a relation between differences in the rate of heat loss and the corresponding increase in EE. Even a small increase in cooling during endurance exercise increased EE which may be a relevant problem in winter sports.     

Determining energy expenditure during some household and garden tasks

PURPOSE: This study: a) calculated the reproducibility (intraclass correlation coefficient, ICC) and precision (technical error of measurement, TEM) for VO2 during moderate paced walking, self-paced sweeping, window cleaning, vacuuming and lawn mowing; b) determined which of the five activities rated >or= 3.0 when exercise intensity was calculated in METs (1 MET or metabolic equivalent = VO2 of 3.5 mL.kg-1.min-1) and multiples of the measured resting metabolic rate (RMR); and c) expanded the limited database on energy expenditure during household and garden activities. METHODS: Twelve men and 12 women (mean +/- SD: 39.3 +/- 3.4 yr; 171.6 +/- 9.6 cm; 81.0 +/- 15.5 kg) were measured for RMR and VO2 during the five activities on two separate days via indirect calorimetry by using the Douglas bag method. RESULTS: The interday ICCs and TEMs for the five activities ranged from 0.81 to 0.97 and from 2.1 to 7.0%, respectively. The means were significantly (P < 0.001) above 3.0 for moderate paced walking (range = 3.3-8.7), sweeping (2.9-6.7), window cleaning (3.0-6.0), vacuuming (2.6-4.4), and lawn mowing (4.9-7.5) when VO2 was divided by measured RMR, but one and five subjects scored below 3.0 for sweeping and vacuuming, respectively. Division of exercise VO2 by the convention of 3.5 mL O2.kg-1.min-1 significantly decreased (P < 0.001) each mean, and lawn mowing (5.0 METs) was the only activity where all subjects scored above 3.0 METs (P < 0.001; 3.8-6.4); nevertheless, the means for walking (3.7 METs), sweeping (3.2 METs), and window cleaning (3.6 METs) were also in the moderate intensity category of 3-6 METs. CONCLUSIONS: These data: a) emphasize that the VO2 during self-paced moderate intensity walking and self-paced household and garden activities can be measured with reproducibility and precision, b) demonstrate that expressing energy expenditure in conventional METs yields lower values than when it is presented as a multiple of measured RMR, c) suggest that all activities except vacuuming are performed at moderate intensity when energy expenditure is expressed in conventional METs, and d) highlight the biological variability in energy expenditure when different people perform the same task.     

Determining the intensity and energy expenditure during commuter cycling

Objectives

To determine the intensity and energy expenditure during commuter cycling, and to investigate whether cycling to work at a self‐chosen intensity corresponds to recommendations of the Centers for Disease Control and Prevention (CDC) and American College of Sports Medicine (ACSM) for health improvement and ACSM recommendations for fitness improvement.

Methods

18 healthy, untrained middle‐aged people, who did not cycle to work, underwent two maximal exercise tests (MT and MT2) in order to measure their maximal heart rate and oxygen consumption (VO₂). MT2 was performed 24 weeks after MT. Participants were asked to cycle at least three times a week to their workplace over a one‐way minimum distance of 2 km. Data on cycling were recorded in a diary. 12 weeks after MT, a field test was conducted, where participants had to cycle to or from their workplace. The same measurements were taken as during MT as markers of exercise intensity. Metabolic equivalents (METs) and energy expenditure were calculated.

Results

The intensity during the field test was >75% of their maximal aerobic capacity. The mean (SD) MET value was 6.8 (1.9). The energy expenditure during the field test was 220 (115) kcal or 540 (139) kcal/h and 1539 (892) kcal/week. Men consumed significantly (p<0.01) more energy per hour than women.

Conclusion

Commuter cycling at a self‐selected intensity meets the CDC and ACSM recommendations for health improvement and the ACSM recommendations for improvement of cardiorespiratory fitness. However, as the participants cycled faster during the field test than during daily cycling, the results should be interpreted with caution.Despite warnings about the potentially negative health consequences of a sedentary lifestyle, a large proportion of adults are physically inactive.¹ Compelling evidence suggests that physical inactivity is a contributing factor in several chronic diseases. People of all ages, both men and women, can improve their general health, fitness and mental health by becoming even moderately active.¹At the population level, the substantial health‐enhancing potential of physical activity can be accomplished preferentially by incorporating physical activity into the daily routine. Physically active commuting to work provides a promising mode for such activity.² Daily cycling to work has been shown to improve physical performance^3,4 and health⁵ in men and women.Reliable estimates of self‐selected intensity in cycling are essential to exercise research on epidemiology for two reasons. Firstly, self‐selected exercise intensity must be determined to assess energy expenditure accurately. Secondly, information about self‐selected cycling can be used in conjunction with prospective health data on cycling to help clarify the relationship between exercise intensity and health.⁶Many of the health and fitness benefits are related to the total amount of work (volume) performed.^1,7,8,9 The American College of Sports Medicine (ACSM) Position Stand⁸ makes the following recommendations for the quantity and quality of exercise for developing and maintaining cardiovascular fitness: frequency, 3–5 days/week; intensity, 55–90% of the maximal heart rate; and duration, 20–60 min of continuous or intermittent aerobic activity. Lower levels of physical activity (particularly intensity) may reduce the risk of certain chronic degenerative diseases and improve metabolic fitness, and yet may not be of sufficient quantity or quality to improve maximal oxygen uptake capacity. Many of the health benefits from physical activity can be achieved at lower intensities of exercise if frequency and duration are increased appropriately.⁸ According to the recommendations of the Centers for Disease Control and Prevention (CDC) and the ACSM,¹ considerable health benefits can be achieved by engaging in physical activity of moderate intensity for at least 30 min per session on most, and preferably all, days of the week. Moderate physical activity is defined as activities performed at an intensity of 3–6 metabolic equivalents (METs; 3.5–7 kcal/min). For people who are quite unfit, the lower intensity values—that is, 55–64% of the maximum heart rate—are most applicable.⁸The interaction of intensity, duration and frequency of physical activity determines the net energy expenditure from the activity. The ACSM⁸ views exercise or physical activity for health and fitness in the context of an exercise dose continuum. Benefits are derived through varying quantities of physical activity ranging from about 700 to 2000 kcal per week.⁸ The lower end of this range represents a minimal energy threshold of about 1050 kcal/week, which is associated with a considerable (20%–30%) reduction in risk of all‐cause mortality^7,9,10; this should be the initial goal for previously sedentary people.Little is known about the self‐selected intensity and energy cost of unsupervised cycling, and least of all about commuter cycling. Therefore, the primary purpose of this study was to measure the cycling intensity and energy expended by healthy untrained volunteers during a typical cycling trip to work. The second purpose was to examine whether commuter cycling meets both the recommendations of the ACSM⁸ and the CDC and those of the ACSM recommendations¹ regarding exercise intensity for the improvement of cardiovascular fitness and health, respectively. Heart rate and oxygen uptake, measured during cycling to work at a self‐chosen intensity, were used as markers of exercise intensity, and compared with previous in‐house maximal graded exercise test data. Energy expenditure and METs were calculated as additional markers of exercise intensity.     

A practical method of estimating energy expenditure during tennis play

This study aimed to develop a practical method of estimating energy expenditure (EE) during tennis. Twenty-four elite female tennis players first completed a tennis-specific graded test in which five different Intensity levels were applied randomly. Each intensity level was intended to simulate a "game" of singles tennis and comprised six 14 s periods of activity alternated with 20 s of active rest. Oxygen consumption (VO2) and heart rate (HR) were measured continuously and each player's rate of perceived exertion (RPE) was recorded at the end of each intensity level. Rate of energy expenditure (EE(VO2)) during the test was calculated using the sum of VO2 during play and the 'O2 debt' during recovery, divided by the duration of the activity. There were significant individual linear relationships between EE(VO2) and RPE, EE(VO2) and HR (r > or = 0.89 & r > or = 0.93; p < 0.05). On a second occasion, six players completed a 60-min singles tennis match during which VO2, HR and RPE were recorded; EE(VO2) was compared with EE predicted from the previously derived RPE and HR regression equations. Analysis found that EE(VO2) was overestimated by EE(RPE) (92 +/- 76 kJ x h(-1)) and EE(HR) (435 +/- 678 kJ x h(-1)), but the error of estimation for EE(RPE) (t = -3.01; p = 0.03) was less than 5% whereas for EE(HR) such error was 20.7%. The results of the study show that RPE can be used to estimate the energetic cost of playing tennis.     

A comparison of energy expenditure during rowing and cycling ergometry

Metabolic and cardiorespiratory responses of healthy adults were compared at similar incremental power outputs during a variable-resistance rowing exercise and a fixed-resistance cycle ergometer exercise. Repeated measurements of power (watts), VEBTPS, VO2 STPD, and HR were obtained on 60 men and 47 women ranging in age from 20 to 74 yr. Average maximal power output for the men was significantly higher (P less than 0.05) for cycling than rowing: 207 +/- 5.2 W vs 195 +/- 58 W (mean +/- SE). A similar difference was also observed for women favoring cycling: 135 +/- 4.1 W vs 126 +/- 4.9 W (mean +/- SE). VEBTPS, VO2 STPD, and HR were significantly higher at all power increments during the rowing graded exercise test (RGXT) when compared with the same exercise intensity during the cycle graded exercise test (CGXT). Consistent linearity was found between VEBTPS and VO2 STPD and between HR and VO2 STPD for both exercises. The linear relationship between VEBTPS and VO2 STPD for men during RGXT was r = 0.976, P less than 0.001, slope = 44.6 +/- 1.03, and for women during RGXT it was r = 0.990, P less than 0.001, slope = 19.6 +/- 0.36. The relationship between HR and VO2 STPD for men during rowing was r = 0.989, P less than 0.001, slope = 29.1 +/- 0.76, and for women during rowing it was r = 0.971, P less than 0.001, slope = 35.7 +/- 0.89. The linear relationship between VEBTPS and VO2 STPD for men during CGXT was r = 0.991, P less than 0.001, slope = 31.1 +/- 0.98, and for women it was r = 0.959, P less than 0.991, slope = 29.6 +/- 0.87. The relationship between HR and VO2 STPD for men during CGXT was r = 0.997, P less than 0.001, slope = 28.1 +/- 0.83, and for women it was r = 0.990, R less than 0.001, slope = 35.9 +/- 0.96. Results indicated that energy costs for rowing ergometry was significantly higher than cycle ergometry at all comparative power outputs including maximum levels. It was concluded that rowing ergometry could be an effective alternative activity for physical fitness and exercise rehabilitation programs.     

Heart rate and estimated energy expenditure during ballroom dancing.

Ten competitive ballroom dance couples performed simulated competitive sequences of Modern and Latin American dance. Heart rate was telemetered during the dance sequences and related to direct measures of oxygen uptake and heart rate obtained while walking on a treadmill. Linear regression was employed to estimate gross and net energy expenditures of the dance sequences. A multivariate analysis of variance with repeated measures on the dance factor was applied to the data to test for interaction and main effects on the sex and dance factors. Overall mean heart rate values for the Modern dance sequence were 170 beats.min-1 and 173 beats.min-1 for males and females respectively. During the Latin American sequence mean overall heart rate for males was 168 beats.min-1 and 177 beats.min-1 for females. Predicted mean gross values of oxygen consumption for the males were 42.8 +/- 5.7 ml.kg-1 min-1 and 42.8 +/- 6.9 ml.kg-1 min-1 for the Modern and Latin American sequences respectively. Corresponding gross estimates of oxygen consumption for the females were 34.7 +/- 3.8 ml.kg-1 min-1 and 36.1 +/- 4.1 ml.kg-1 min-1. Males were estimated to expand 54.1 +/- 8.1 kJ.min-1 of energy during the Modern sequence and 54.0 +/- 9.6 kJ.min-1 during the Latin American sequence, while predicted energy expenditure for females was 34.7 +/- 3.8 kJ.min-1 and 36.1 +/- 4.1 kJ.min-1 for Modern and Latin American dance respectively. The results suggested that both males and females were dancing at greater than 80% of their maximum oxygen consumption. A significant difference between males and females was observed for predicted gross and net values of oxygen consumption (in L.min-1 and ml.kg-1 min-1).     

Energy intake and energy expenditure of elite cyclists during preseason training

In the last years, the interest in sport nutrition has increased. The purpose of this study was to quantify the nutritional status of eleven cyclists of a professional team (age: 28.7+/-4.2 yr; height: 181.0+/-4.2 cm; weight: 71.0+/-5.2 kg; body fat: 10.2+/-2.4%), during basic pre-season training. The athletes trained on five days (160 km per day) and respected one rest-day (33 km). The food of the cyclists, which was chosen by the riders themselves, was weighed and recorded for six days, the protocols were analysed through the PRODI 4.3 EXPERT database. The daily energy intake which averaged 13.5 MJ (59% carbohydrates, 19% proteins, and 21% fat), was compared to the mean daily consumption of energy (19.1 MJ), which was calculated from the basal metabolic rate and the energy turnover while training (directly measured through the SRM Training system). The daily energy expenditure was 30% higher than the daily energy intake. The analysis of the food diary showed that these experienced riders composed a carbohydrate-rich and low-fat diet by themselves as recommended for high-performance endurance athletes. When compared to nutritional guidelines, the composition of the diet in the present study can be considered as adequate.     

Validity of energy expenditure estimation methods during 10 days of military training

Wearable physical activity (PA) monitors have improved the ability to estimate free‐living total energy expenditure (TEE) but their application during arduous military training alongside more well‐established research methods has not been widely documented. This study aimed to assess the validity of two wrist‐worn activity monitors and a PA log against doubly labeled water (DLW) during British Army Officer Cadet (OC) training. For 10 days of training, twenty (10 male and 10 female) OCs (mean ± SD: age 23 ± 2 years, height 1.74 ± 0.09 m, body mass 77.0 ± 9.3 kg) wore one research‐grade accelerometer (GENEActiv, Cambridge, UK) on the dominant wrist, wore one commercially available monitor (Fitbit SURGE, USA) on the non‐dominant wrist, and completed a self‐report PA log. Immediately prior to this 10‐day period, participants consumed a bolus of DLW and provided daily urine samples, which were analyzed by mass spectrometry to determine TEE. Bivariate correlations and limits of agreement (LoA) were employed to compare TEE from each estimation method to DLW. Average daily TEE from DLW was 4112 ± 652 kcal·day^?1 against which the GENEActiv showed near identical average TEE (mean bias ± LoA: ?15 ± 851 kcal^.day^?1) while Fitbit tended to underestimate (?656 ± 683 kcal·day^?1) and the PA log substantially overestimate (+1946 ± 1637 kcal·day^?1). Wearable physical activity monitors provide a cheaper and more practical method for estimating free‐living TEE than DLW in military settings. The GENEActiv accelerometer demonstrated good validity for assessing daily TEE and would appear suitable for use in large‐scale, longitudinal military studies.     

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.     

Protein and energy metabolism during prolonged exercise in trained athletes

Eight elite triathlon athletes participated in a laboratory study of the effects of endurance exercise on protein and energy metabolism. The study consisted of 3 h of cycling and 5 h of treadmill running; 3.5 h before beginning the exercise, a primed constant infusion of 1-13C leucine and 6,6(-2)H glucose was begun. Serial blood samples were collected during the rest and exercise periods for isotopic analysis. Respiratory gas exchange was determined every half hour. Results: the subjects exercised at an average of 53% +/- 3% of peak VO2. During the 8-h exercise period there was a decline in glucose utilization and an increase in lipid oxidation. For the first part of the exercise, most of the glucose oxidized was of muscle origin. Hepatic glucose production increased with exercise from 20 g/h to a maximum of about 60 g/h after 4 h of exercise and then decreased toward the pre-exercise rate. The plasma urea concentration was unchanged during the study. The leucine flux decreased during the first 4 h of exercise and then attained a new plateau about 20% lower than the pre-exercise value indicating an adaptive reduction in protein turnover.     

Load carriage energy expenditure with and without hiking poles during inclined walking

The purpose of this study was to compare load carriage energy expenditure with and without using hiking poles. Twenty male volunteers aged 20-48yr (Mean=29.8yr) completed two randomly ordered submaximal treadmill trials with poles (E) and without poles (C). Poles and load (15 kg backpack) were fitted for each subject according to the manufacturers' suggestions. Heart rates (HR), minute ventilation (V(E)), oxygen consumption (O2), caloric expenditure (Kcal), and rating of perceived exertion (RPE) were recorded at the end of each minute. Two trials separated by one week consisted of a constant treadmill speed of 1.5 mph and 1 min at 10% grade, 2 min at 15% grade, 2 min at 20% grade, and 10 min. at 25% grade. Mean HR (E = 144.8 +/- 24.4 b x min(-1); C = 144.0 +/- 25.7 b x min(-1)) and mean V(E) (E=51.4 +/- 15.8L x min(-1); C=50.8 +/- 17.0L x min(-1)), VO2 (E = 26.9 +/- 6.1 ml x kg(-1) x min(-1); C = 27.4 +/- 6.6 ml x kg(-1) x min(-1)), and Kcal (E = 10.6 +/- 2.9 Kcal x min(-1); C = 10.8 +/- 3.1 Kcal x min(-1)) were not significantly different between the two conditions. RPE (E = 13.28 +/- 1.2; C = 14.56 +/- 1.2) was significantly lower (P < 0.05) with hiking poles. Analysis of paired time points yielded no significant differences in HR, VO2, V(E), and Kcal, however, RPE means were significantly lower for 5 of the last 7 trial minutes with the use of poles. These results suggest that during load carriage on moderate grade, the weight and use of hiking poles does not increase energy expenditure but may provide reduced perceptions of physical exertion.