Share this article on:

Trekking Poles Increase Physiological Responses to Hiking Without Increased Perceived Exertion

Saunders, Michael J; Hipp, G Ryan; Wenos, David L; Deaton, Michael L

Journal of Strength and Conditioning Research: September 2008 - Volume 22 - Issue 5 - p 1468-1474
doi: 10.1519/JSC.0b013e31817bd4e8
Original Research

Saunders, MJ, Hipp, GR, Wenos, DL, and Deaton, ML. Trekking poles increase physiological responses to hiking without increased perceived exertion. J Strength Cond Res 22(5): 1468-1474, 2008-Trekking poles are used by hikers for improved stability and lowered leg fatigue due to increased upper body muscle involvement. However, the weight of the poles and exaggerated upper body movement when using poles may increase total energy expenditure at a given walking speed. Few studies have investigated the physiological responses of hiking with trekking poles outside the laboratory setting. The purposes of this study were to determine if trekking poles altered physiological responses to hiking on varied terrain, and whether responses between trials were dependent on the grade of the terrain. Fourteen recreational hikers completed four hiking trials over a course that included sustained sections of flat (0 ± 1% grade), steep uphill (>10% grade), gradual uphill (5% grade), gradual downhill (−5% grade) and steep downhill (<−10% grade) terrain. Subjects walked at a self-selected speed that was matched across trials using time-splits and a metronome. Two trials were conducted with hiking poles and two without poles. O2 was significantly elevated (p <0.05) during the pole trials (1502.9 ± 510.7 ml/min) compared to the no-pole trials (1362.4 ± 473.2 ml/min). Similarly, ventilatory efficiency (E) (43.1 ± 9.6; 38.3 ± 10.1 L/min) and heart rate (HR) (112.1 ± 9.7; 105.7 ± 10.4 bt/min) were significantly higher during the pole trials than the no-pole trials. However, ratings of perceived exertion (RPE) was not altered by pole condition (8.5 ± 0.7; 8.4 ± 0.8). Comparisons within each grade revealed significantly higher physiological responses for O2, E and HR in the pole-condition at all grades, with no significant variable*grade interactions. RPE measures were not significantly different between pole trials at any grade. These data suggest that trekking poles may be a beneficial tool for increasing caloric expenditure, as energy production increased during exercise without increased perceptions of effort.

Human Performance Laboratory, Department of Kinesiology, James Madison University, Harrisonburg, Virginia

Address correspondence to Dr. Michael J. Saunders, saundemj@jmu.edu.

Back to Top | Article Outline

Introduction

Trekking poles have been used by hikers for a variety of putative benefits, including increased stability, decreased muscular strain on the lower extremities, increased climbing potential during rugged hikes, and aid for orthopedic problems (3, 7, 15). More recently, fitness practitioners have suggested using poles to increase arm activity and caloric expenditure during walking. However, evidence regarding the potential benefits of pole use is inconclusive and difficult to generalize.

Pole use has been studied during walking on flat surfaces or easy to moderate grades on treadmills. In these controlled laboratory settings, researchers have observed increased physiological responses, such as heart rate (HR), oxygen uptake, and caloric expenditure, compared to walking without poles (4,10,13,14). These findings are logical because added weight (1,5,6) or exaggerated arm motion (12) can increase upper-body muscular recruitment and oxygen demand at a given walking speed. However, at least 2 studies have reported no differences in physiological responses between hiking trials with and without poles (8,9). It is notable that both of these studies compared hiking trials performed with relatively large elevation gains, suggesting that physiological responses to pole use may depend on the steepness of the slope hiked.

Increased physiological responses to hiking are beneficial to recreational exercisers who wish to maximize caloric consumption during exercise. However, most recreational exercisers gauge their exercise intensity using perceptions of effort during exercise and would likely decrease their speed if the added caloric expenditure was accompanied by increased effort. Thus, it is significant that some investigators have observed increases in caloric expenditure with pole use without changes in ratings of perceived exertion (RPE) (4,14). Other researchers have reported increased (13) or decreased (10) RPE with pole use during flat or minimally steep walking. There are at least 2 reports of lowered RPE during hiking on relatively steep slopes (8,9), suggesting that responses to pole use may depend on variations in surface grade.

These referenced data illustrate inconsistencies in the literature regarding pole use during walking or hiking. Collectively, it appears that pole use increases physiological responses during walking on flat or minimal grades without consistent changes in RPE. However, these data are limited by the lack of information regarding the effects of grade on responses to pole use. In addition, almost all studies performed to date have examined pole use during walking on treadmills or tracks. It is unclear whether these data may be generalized to hiking on outdoor trails. The only directly related field study on this topic showed no difference in HR between pole and nonpole trials over steep, rugged terrain (9). It is possible that the use of hiking poles on outdoor trail surfaces may decrease the muscular activity of the lower extremity (10) while allowing the upper extremity to share in workload production, which could result in no change in overall caloric cost of activity. However, the authors are aware of no studies that have directly examined the effects of trekking poles on physiological measures, such as oxygen uptake, ventilation, and caloric expenditure, in a field setting. Therefore, the current study was designed to address 2 purposes: to compare the physiological (i.e., o2, HR, and ventilation) and subjective (i.e., RPE) effects of walking along an outdoor hiking trail with and without poles and to examine the effect of terrain grade on differences between responses to hiking with and without poles.

Back to Top | Article Outline

Methods

Experimental Approach to the Problem

As the information above illustrates, data obtained during hiking are difficult to generalize to all conditions. Therefore, the current study was designed to clarify and extend previous research on this topic by using design elements that were unique from previous studies. For practical reasons, most previous data have been collected on laboratory treadmills or running tracks. These settings do not closely replicate the conditions under which hiking poles are typically used by exercisers. Therefore, exercise in this study was performed outside the laboratory setting on a mixed dirt and gravel trail (see “Hiking Course” for details).

The population studied may also influence the responses to exercise with hiking poles. This study aimed to examine the effects of poles used for fitness walking, as opposed to through-hiking on very loose or demanding terrain, or other activities. Therefore, subjects were fit but not highly experienced hikers, and they were permitted to choose a walking pace in their first trial, which was controlled across subsequent trials. In addition, the course included varied but stable terrain considered typical for recreational walking or hiking.

Inconsistencies from previous research suggested that the steepness of terrain may influence physiological and perceptual responses to hiking with and without poles. Therefore, a hiking course was selected that contained differing grades. A distinguishing element of the course was that it included sustained segments at each grade (i.e., approximately 200 m of flat terrain followed by approximately 200 m of 10% grade and so forth). This feature allowed comparisons across grades that would not have been possible with a more undulating course. In addition, the terrain chosen included elevations that ranged from -10% to +10%. This range is within the levels examined by most previous studies (10,13,14), but considerably less than those of a few studies (8,9). Although the grades examined in the current study were not as tightly controlled or consistent as those in laboratory studies, they more closely resembled typical walking or hiking terrain.

Back to Top | Article Outline

Subjects

Fourteen men (mean age, 22.1 ± 2.1 years; mean weight, 80.9 ± 16.0 kg; mean height, 174.8 ± 9.0 cm) completed the study. All subjects reported moderate physical activity at least 3 times per week, including aerobic conditioning and resistance training. None of the subjects were involved in training for competitive sport, and all could be classified as recreationally active, novice hikers. Before testing, all subjects signed an informed consent form and completed a comprehensive medical questionnaire to determine the presence of any risk factors associated with coronary artery disease. All subjects were asymptomatic and had fewer than 2 risk factors according to American College of Sports Medicine guidelines (1). In addition, all subjects were free of any upper- or lower-body orthopedic conditions that could affect participation in the study. All procedures and protocols were approved by the James Madison University Institutional Review Board.

Back to Top | Article Outline

Procedures

Subjects completed a total of 3 testing sessions. The first session was a practice trial, in which subjects were provided instructions regarding how to properly use the trekking poles and walked the course once with the poles. Subjects returned 2 to 4 days later and performed the second trial. On this day, the subjects hiked the course twice: once with poles and once without poles. Data were obtained throughout these trials as described below. The order of pole conditions (i.e., poles or no poles) was randomly assigned. Each subject rested for 10 minutes between trials and consumed 8 oz of water during this time. A metronome and time splits for each trail segment were used to control for speed of hiking between pole trials. After this trial, subjects returned 2 to 4 days later to complete the final test session. All procedures from trial 2 were repeated, with the order of pole conditions reversed; for example, if a subject received the nonpole trial first during session 2, he received the pole trial first during session 3.

Subjects were asked to refrain from using tobacco products or ingesting alcohol, caffeine, or food for 3 hours before data collection. In addition, subjects were asked to abstain from heavy exercise for 24 hours before data collection. Subjects recorded their daily exercise and dietary intake for 48 hours before the first hiking session and were requested to replicate these dietary and exercise habits before subsequent trials. The time of day when data collection was completed was kept constant between trials for each subject to control for any variations in responses associated with circadian rhythms. All data were collected in March and April, with dry trail conditions and mild to warm temperatures lower than 25°C. Testing temperatures were similar between trials for each subject.

Back to Top | Article Outline

Hiking Course

A hiking course was created in the arboretum of the campus of James Madison University. The specific trail was chosen based on 3 criteria. First, it offered a variety of prolonged, consistent grades. Second, it could be hiked in a continuous loop. Finally, it was proximal to the university campus to allow for rapid recalibration of testing equipment, if necessary. The first data collection area was approximately 250 m long and flat (grade, 0 ± 1%). The next 2 data collection areas were uphill; the first was150 to 200 m long, with a grade of approximately 10%, and the second was 150 to 200 m long, with a grade of approximately 5%. At the top of the climb, subjects completed a short flat section of trail, turned around a cone placed in the trail, and then descended the same sections of terrain. Thus, each subject walked on flat, uphill, and downhill portions of the course. The total length of the course was approximately 1.25 km, as measured by a global positioning system device (Magellen GPS 315; Magellan Navigation, Inc., Santa Clara, CA).

Back to Top | Article Outline

Trekking Poles

The trekking poles used were Super Makalu COR-TEC (Leki USA, Inc., Buffalo, NY). These poles were telescopic to enable adjustment between 80 and 140 cm, had carbine tips, and weighed approximately 615 g per pair. A 15° grip angle maintained a neutral wrist position throughout the planting motion. There was also an “antishock” feature built into the poles. However, this feature was disengaged during data collection to standardize trials. The trekking poles were adjusted so that a 90° angle was created at the elbow of each hiker, as measured with a goniometer.

Back to Top | Article Outline

Data Collection

Physiological measures (i.e., o2, ventilatory efficiency [E], and HR) were obtained continuously during all hiking trials by using a portable metabolic unit (K4 b2, Cosmed USA, Inc., Chicago, Ill.) This unit was attached to each subject with a harness and Hans-Rudolph mask that fit over the nose and mouth to collect expired gases. Unit calibration procedures were conducted according to the manufacturer's guidelines before each test session after a 45-minute warm-up. Ambient air and reference gas calibrations (i.e., 16.00% for O2 and 5.00% for CO2) were conducted daily. Gas delay calibration was conducted weekly, and turbine flowmeter gain was calibrated quarterly and conducted with a 3-L syringe. Relative humidity was measured with a portable hand hygrometer and entered before each test. A heart rate monitor was worn across the chest that transmitted directly to the portable metabolic unit. A researcher recorded time splits for each of the 5 recorded sections (i.e., flat, 10% uphill, 5% uphill, 5% downhill, and 10% downhill). Physiological data were averaged across the entire period for each of the 5 sections of trail. Perception of effort was obtained by using Borg's 6 to 20 RPE scale. Measurement of RPE was obtained in the last 15 seconds of each hiking segment.

Back to Top | Article Outline

Statistical Analyses

Data for each dependent measure (i.e., o2, VE, HR, and RPE) were averaged across the 2 repeat trials for each pole condition. Coefficients of variation between repeated trials (i.e., within the same pole condition and terrain steepness) ranged between 4.8% and 12.7% for all variables. Dependent t-tests revealed no significant differences in any dependent measures between repeat trials. All further statistical analyses were performed by using these mean values, averaged across the 2 trials for each pole condition.

Differences between pole conditions for each dependent measure were calculated by examining the main effect (i.e., pole condition) in a 2-way repeated-measures analysis of variance. The effect of terrain grade was determined by examining the pole condition × terrain interaction in the same repeated-measures analysis of variance. Statistical analyses were performed with SPSS statistical software, version 13.0 (SPSS, Inc., Chicago, IL).

Fourteen subjects exceeded the minimum sample size needed to detect treatment differences in the dependent measures (i.e., o2, VE, HR, and RPE) with a power of 0.80. This power calculation (11) was based on estimated effect sizes of 1.0 SD units, a 2-tailed α level of 0.05, and intraclass correlations for repeated measures of 0.60 and 0.92. Intraclass correlations were based on previous data collected in the authors' laboratory, while effect sizes were estimated based on data from pilot data in which effect sizes of 1.00 and 1.2 SD units were observed for treatment differences in dependent measures.

Back to Top | Article Outline

Results

Data for each dependent measure were averaged for each segment of trail (i.e., separate mean values for flat, steep uphill, gradual uphill, gradual downhill, and steep downhill sections). No statistically significant (p < 0.05) differences were observed between any measures during trial 1 and trial 2, within either pole condition. As a result, overall mean data were calculated for each pole condition as the average of the 2 within-treatment trials.

The overall effects of poles versus no poles (independent of grade) were compared by examining the main effects from the repeated-measures analysis of variance. o2 was significantly elevated (p < 0.05) during the pole trial (1502.9 ± 510.7 mL·min-1) compared to the nonpole trial (1362.4 ± 473.2 mL·min-1). Similarly, VE (43.1 ± 9.6 L·min-1 versus 38.3 ± 10.1 L·min-1) and HR (112.1 ± 9.7 b·min-1versus 105.7 ± 10.4 b·min-1) were significantly higher during the pole trial than the nonpole trial, respectively. However, RPE was not significantly altered by pole condition (8.5 ± 0.7 versus 8.4 ± 0.8).

Analyses of means for each dependent measure across grades were performed using 2-way (grade × pole condition) repeated-measures analyses of variance for each dependent measure. If that interaction was significant, it would imply that the physiological response to trekking poles may vary, depending on the grade of the terrain. The results of these analyses are discussed below.

Back to Top | Article Outline

Oxygen Consumption

Mean o2 for the flat, steep uphill, gradual uphill, gradual downhill, and steep downhill were 1280 ± 301 mL·min-1, 2038 ± 407 mL·min-1, 1856 ± 422 mL·min-1, 1125 ± 306 mL·min-1, and 947 ± 279 mL·min-1, respectively. A significant (p < 0.05) main effect was present for the pole condition. However, there was no significant pole × grade interaction. Individual comparisons for o2 measures between pole conditions within each grade revealed significantly higher (p < 0.05) o2 measures at each individual grade (Figure 1).

Figure 1

Figure 1

Back to Top | Article Outline

Heart Rate

Mean HR for the flat, steep uphill, gradual uphill, gradual downhill, and steep downhill were 102.6 ± 18.3 b·min-1, 122.3 ± 14.2 b·min-1, 116.9 ± 15.2 b·min-1, 102.3 ± 15.9 b·min-1, and 100.3 ± 14.3 b·min-1, respectively. A significant (p < 0.05) main effect was present for the pole condition. However, there was no significant pole × grade interaction. Individual comparisons for HR measures between pole conditions within each grade revealed significantly higher (p < 0.05) HR measures at each individual grade (Figure 2).

Figure 2

Figure 2

Back to Top | Article Outline

Ventilation

Mean VE for the flat, steep uphill, gradual uphill, gradual downhill, and steep downhill were 36.4 ± 7.5 L·min-1, 54.3 ± 10.0 L·min-1, 47.7 ± 9.5 L·min-1, 33.4 ± 7.6 L·min-1, and 31.7±7.6 L·min-1, respectively. A significant (p < 0.05) main effect was present for the pole condition. However, there was no significant pole × grade interaction. Individual comparisons for VE measures between pole conditions within each grade revealed significantly higher (p < 0.05) VE measures at each individual grade (Figure 3).

Figure 3

Figure 3

Back to Top | Article Outline

Ratings of Perceived Exertion

Mean RPE for the flat, steep uphill, gradual uphill, gradual downhill, and steep downhill were 7.9 ± 1.0, 9.6 ± 1.8, 8.6 ± 1.2, 8.0 ± 1.1, and 8.2 ± 1.0, respectively. No significant differences were observed between the pole conditions. In addition, there was no significant pole × grade interaction (Figure 4).

Figure 4

Figure 4

Back to Top | Article Outline

Discussion

The primary finding of this study was that hiking poles increased physiological responses to hiking at a given speed, without increasing the hiker's RPE. Specifically, hiking with poles increased levels of oxygen consumption, ventilation, and HR compared to hiking without poles at the same hiking speed over the same varied outdoor terrain. A number of studies have observed similar elevations in physiological responses to pole use while hiking on treadmills at similar grades used in the current study (10,13,14). These findings appear logical, as the use of hiking poles could increase upper-body muscle recruitment, causing increased oxygen demand in the upper body. This increased oxygen use could be the result of carrying the weight of the poles. Auble et al. (2) and Graves et al. (5,6) showed statistically significant increases in physiological parameters associated with exercising with hand or wrist weights. The similarities of these studies suggest that using trekking poles while hiking could be similar to walking with hand or wrist weights. However, data from Owens et al. (12) suggested that unless the weight is greater than 2.27 kg, the elevated oxygen demand is more likely caused by exaggerated arm movement when carrying weights. Because of the low weight of the poles used in this study, it seems plausible that much of the difference in physiological responses to hiking with poles was due to this exaggerated arm motion. Some researchers observed no differences in physiological responses to hiking with poles versus without poles (8,9). However, these studies were conducted on grades of 10% to 40%, which considerably exceeded those used in the current study or aforementioned studies. In addition, it is possible that the failure to find a difference in these studies may have been related to insufficient sample sizes. Because these studies were performed in a less controlled environment than the studies that showed a significant effect of trekking poles, it is likely that there was more experimental variation in the results. As a result, more subjects may have been required to have sufficient power to find a difference.

Despite the elevated physiological responses in the pole trials in the current study, there were no differences in RPE, and the same response was observed by Rodgers et al (14). In the other 2 studies in which physiological responses were elevated during pole hiking, 1 study showed increased RPE (13) and 1 study showed decreased RPE (10) during pole trials. Collectively, these studies suggest that hiking on minimal grades, where physiological responses are elevated by pole use, there is no consistent change in RPE. In studies conducted on steep grades, where physiological responses were equal between pole trials, RPE responses to hiking were consistently lower in pole trials (8,9).

Because of the general observation that responses to pole use were altered with increased trail elevation, it was hypothesized that there would be an interaction between hiking responses and grade in the current study. However, there were no variable × grade interactions for any of the measures in this study. As previously stated, overall physiological responses were significantly elevated in the pole trial. In addition, all these variables were also significantly elevated at each of the individual sections that were analyzed. This finding and the lack of grade × pole interactions indicate that the effect of trekking poles in this study is independent of the terrain grade. Similarly, while overall RPE measures were no different between pole trials, there were likewise no significant differences in RPE at any of the individual grades. Therefore, any differences in physiological and RPE responses between pole trials were independent of grade in this study.

The findings of this study were inconsistent with those of the aforementioned studies. However, it should be noted that the grades used in the current study varied from approximately -10% to +10%. Studies that have demonstrated similar physiological responses and lowered RPE responses with hiking poles have been conducted at grades that were considerably steeper than 10% (8,9). Electromyographic data from Knight and Caldwell (10) showed decreased lower leg activity of muscles in the lower extremity while hiking with trekking poles, as upper-body force production assists forward propulsion. It seems reasonable that this upper-body assistance would be greater on steeper slopes, thus increasing the potential benefits of hiking pole use. Therefore, the finding should not be generalized to hiking conditions where the grade exceeds 10%. In addition, the relatively low RPE, o2 and HR measures elicited during hiking could have minimized the overall effect of pole use in the current study. Future researchers should validate these findings at a variety of hiking speeds and grades to provide specific recommendations for hikers regarding pole use.

Despite the aforementioned limitations, the data from the current study have several important implications. Hiking with poles at low to moderate speeds, on trails of -10% to +10% grade, elicits increased physiological responses without concomitant increases in perceived exertion. From a general fitness point of a view, this information could be helpful for individuals who want to maximize the benefits of exercising over a given period. Logically, most people exercise at self-selected paces that are dictated by comfort. If hiking poles increase physiological responses to activity at this pace without altering comfort level, greater caloric expenditure and fitness improvements may be derived from activity with poles. Another advantage to using poles is that they involve the upper body and allow for a full body workout without the use of a separate workout. Because using trekking poles turns walking into a full body workout and also raises the physiological parameters, it could be considered an efficient exercise.

From a hiking performance perspective, the data suggest that an increased amount of energy expenditure will occur when using poles at a given hiking speed. During hikes without extreme grade or elevation changes, this could be perceived as a negative outcome, as movement economy is decreased. In effect, the relative exercise intensity of the activity is increased at a given speed by the use of poles. Ultimately, this could have a negative effect on total hiking duration, effort, and efficiency. During extended hikes, the increased energy expenditure could also mean more food must be carried to compensate for the elevated energy expenditure. However, further research is needed to establish whether trekking poles decreases the amount of work done by the lower extremity, as suggested by Knight and Caldwell (10). If this hypothesis is true, by spreading out the work throughout the whole body, there could be a leg-saving response. This could effectively lower long-term fatigue related to localized fatigue, despite the increased total energy demand created by the use of poles.

Back to Top | Article Outline

Practical Applications

The use of trekking poles increased physiological responses to hiking without altering RPE, regardless of the grade of terrain. This finding suggests that trekking poles may be effective at increasing caloric expenditure in those walking at self-selected paces over varied terrain. These findings were observed in moderately active, novice hikers walking at low to moderate intensities over well-groomed, moderate-grade trails without a load. It remains to be shown whether these findings can be generalized to conditions such as intense paces, steep slopes, load-carrying conditions, and highly experienced hikers.

Back to Top | Article Outline

Acknowledgments

The authors wish to thank Leki USA, Inc. for providing the trekking poles used in this research project. The results of this study do not constitute endorsement of any products by the authors or by the National Strength and Conditioning Association.

Back to Top | Article Outline

References

1. American College of Sports Medicine. Guidelines for Exercise Testing and Prescription (6th ed.). Baltimore: Lippincott Williams & Wilkins, 2000. p. 79.
2. Auble, TE, Schwartz, L, and Robertson, RJ. Aerobic requirement for moving handweight through various ranges of motion while walking. Physician Sportsmed 15: 133-140, 1987.
3. Bohne, M and Adendroth-Smith, J. Effects of hiking downhill using trekking poles while carrying external loads. Med Sci Sports Exerc 39: 177-183, 2007.
4. Church, TW, Earnest, CP, and Morss, GM. Field testing of physiological responses associated with Nordic Walking. Res Q Exerc Sport 73: 296-301, 2002.
5. Graves, JE, Martin, AA, Miltenberger, LA, and Pollock, ML. Physiological responses to walking with hand weights, wrist weights, and ankle weights. Med Sci Sports Exerc 20: 265-271, 1987.
6. Graves, JE, Pollock, ML, Montain, SJ, Jackson, AS, and O'Keefe, JM. The effect of hand-held weight on the physiological responses to walking exercise. Med Sci Sports Exerc 19, 260-265, 1986.
7. Jacobson, BH, Caldwell, B, and Kulling, FA. Comparison of hiking stick use on lateral stability while balancing with and without a load. Percept Mot Skills 85: 347-350, 1997.
8. Jacobson, BH, Wright, T, and Dugan, B. Load carriage energy expenditure with and without hiking poles during inclined walking. Int J Sports Med 21: 356-359, 2000.
9. Jacobson, BH and Wright, T. A field test comparison of hiking stick use on heart rate and rating of perceived exertion. Percept Mot Skills 87: 435-438, 1998.
10. Knight, CA and Caldwell, GE. Muscular and metabolic costs of uphill backpacking: are hiking poles beneficial? Med Sci Sports Exerc 32: 2093-2101, 2000.
11. Owens, SG, Al-Ahmed, A and Moffat, RJ. Physiological effects of walking and running with hand-held weights. J Sports Med Phys Fitness 29: 384-387, 1989.
12. Porcari, JP, Hendrickson, TL, Walter, PR, Terry, T, and Walsko, G. The physiological responses to walking with and without Power Poles on treadmill exercise. Res Q Exerc Sport 68: 161-167, 1997.
13. Rodgers, CE, Vanheest, JL, and Schachter, CL. Energy expenditure during submaximal walking with Exerstriders. Med Sci Sports Exerc 27: 607-611, 1995.
14. Schwameder, H, Roithner, R, Muller, E, Niessen, W, and Rashchner, C. Knee joint forces during downhill walking with hiking poles. J Sports Sci 17: 969-978, 1999.
Keywords:

energy expenditure; exercise prescription; weight management

© 2008 National Strength and Conditioning Association