Self-selected speeds and metabolic cost of longboard skateboarding Wayne J. Board & Raymond C. Browning European Journal of Applied Physiology ISSN 1439-6319 Eur J Appl Physiol DOI 10.1007/s00421-014-2959-x 1 23 Your article is protected by copyright and all rights are held exclusively by SpringerVerlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Eur J Appl Physiol DOI 10.1007/s00421-014-2959-x Original Article Self‑selected speeds and metabolic cost of longboard skateboarding Wayne J. Board · Raymond C. Browning Received: 26 March 2014 / Accepted: 15 July 2014 © Springer-Verlag Berlin Heidelberg 2014 Abstract Purpose The purpose of this study was to determine selfselected speeds, metabolic rate, and gross metabolic cost during longboard skateboarding. Methods We measured overground speed and metabolic rate while 15 experienced longboarders traveled at their self-selected slow, typical and fast speeds. Results Mean longboarding speeds were 3.7, 4.5 and 5.1 m s−1, during slow, typical and fast trials, respectively. Mean rates of oxygen consumption were 24.1, 29.1 and 37.2 ml kg−1 min−1 and mean rates of energy expenditure were 33.5, 41.8 and 52.7 kJ min−1 at the slow, typical and fast speeds, respectively. At typical speeds, average intensity was ~8.5 METs. There was a significant positive relationship between oxygen consumption and energy expenditure versus speed (R2 = 0.69 (P < 0.001), and R2 = 0.78 (P < 0.001), respectively). The gross metabolic cost was ~2.2 J kg−1 m−1 at the typical speed, greater than that reported for cycling and ~50 % smaller than that of walking. Conclusion These results suggest that longboarding is a novel form of physical activity that elicits vigorous intensity, yet is economical compared to walking. Communicated by Guido Ferretti. W. J. Board Department of Health and Exercise Science, Colorado State University, 220 Moby B Complex, Fort Collins, CO 80523, USA R. C. Browning (*) Department of Health and Exercise Science, Colorado State University, 215C Moby B Complex, Fort Collins, CO 80523‑1582, USA e-mail: [email protected] Keywords Metabolic rate · Oxygen consumption · Energy expenditure · Active transport Abbreviations ACSMAmerican College of Sport Medicine ANOVAAnalysis of variance GPSGlobal positioning system HzHertz JJoules kgKilogram kmKilometer kJKilojoule METMetabolic equivalent mMeter minMinute mlMilliliters MPHMiles per hour sSecond SEEStandard error of the estimate Introduction Longboarding is a form of skateboarding in which participants use a skateboard with a longer deck (~0.85–1.05 m) and wheelbase (~0.75 m) than found on a traditional skateboard (Fig. 1). While traditional skateboards are typically used for performing tricks (e.g. kickflip or ollie), longboards are designed for traveling at faster speeds, as they are more stable due to their length, deck height and wide trucks (connection between wheels and the deck) and have larger, softer wheels that provide relatively good lateral traction. While longboards are used to descend hills at fast speeds, they are also used by adolescents and young adults as a means of active transportation. The increasing 13 Author's personal copy Eur J Appl Physiol Fig. 1 a Anatomy of a longboard. Deck length measured from tip to tail of board. Wheelbase is measured as the distance between the inside truck bolt mounts. b Participant longboarding during the study popularity of longboarding as a form of active transportation is likely due to a combination of their affordability, portability, relatively fast travel speeds on level and downhill terrain, and the “cool” image associated with the activity. To evaluate longboarding as a mode of active transportation, it is insightful to compare the overground speeds and metabolic cost of longboarding to other common forms of active transportation. Walking and bicycling are the two most common forms of active transportation (American College of Sports Medicine 2006). These activities are popular because they are convenient, easy to learn, relatively safe and use the existing transportation infrastructure. They are also health promoting, in that they elevate metabolic rate and increase daily energy expenditure (Frank 2000; Frank and Engelke 2001; Oja et al. 1998; Saelens et al. 2003; Sallis et al. 2004). Many studies have quantified self-selected speeds and metabolic energetics of walking in adults (Inman et al. 1994; Ralston 1958), and these studies report that selfselected speeds are ~1.3 m s−1 (~4.7 km h−1) (Bornstein and Bornstein 1976; Browning et al. 2006; Martin et al. 1992). It has also been well established that adults walk at the speed that minimizes the gross metabolic cost, with gross metabolic cost values of ~3.0 J kg−1 m−1 typically reported for normal weight adults (Rubenson et al. 2007). The energetics of bicycling are also well described in the literature, primarily during cycle ergometry (Burke 2002). To our knowledge, preferred commuting cycling speed have only been quantified by one study that reported mean commuting speeds of ~4.9 m s−1 (17.7 km h−1) (Dill 2009). The metabolic cost of cycling increases with speed, though, at typical commuting speeds, is ~1.0–1.4 J kg−1 m−1 (ACSM 2006; Minetti et al. 2001; di Prampero 1986). The metabolic costs of legged locomotor activities are primarily determined by body position, biomechanics and 13 aerodynamics. As in walking, longboarding utilizes an upright body position and requires that the legs be continually repositioned to provide the propulsion necessary to maintain a steady speed (di Prampero 1986). However, longboarding also has a period of coasting or gliding between propulsive periods, which may result in a lower metabolic cost of longboarding compared to walking even though the metabolic cost required to overcome aerodynamic forces would be greater during longboarding compared to walking due to faster speeds. Compared to longboarding, bicyclists utilize a more seated or crouched posture (reducing metabolic cost associated with overcoming aerodynamic forces), support some of their weight via the saddle/handlebars and do not need to actively reposition their limbs to provide propulsion to maintain a steady speed (i.e. there are smaller acceleration-deceleration phases). As a result, we would expect the metabolic cost of bicycling to be less than the metabolic cost of longboarding. The form of locomotion most similar to longboarding is classic style cross-country skiing (i.e. diagonal stride Nordic skiing). Both classic style cross-country skiing and longboarding utilize similar body positions and biomechanics (i.e. alternating phases of propulsion and gliding phases, di Prampero 1986). As a result, the gross metabolic cost of longboarding may be similar to that of classic cross-country skiing, which has been reported to be ~2.3–2.6 J kg−1 m−1 (Formenti et al. 2005; Bellizzi et al. 1998). To date, there have been no studies that have measured typical longboarding speeds or the metabolic rate and cost required to longboard. Providing metabolic data for longboarding will allow this activity to be assessed as a form of physical activity. Given the prevalence of sedentary lifestyles among adolescents and young adults (Rey-López et al. 2008), public health professionals could benefit from the inclusion of a form of physical activity and active Author's personal copy Eur J Appl Physiol transportation that appeals to some younger individuals. In addition, self-selected speed and physiological data will assist in evaluating longboarding’s potential as a form of active transportation and may help transportation planners as they consider if/how to integrate longboarding into comprehensive transportation plans. The purposes of this study were to measure typical longboarding speeds and quantify the physiological requirements of longboarding. We hypothesized that: (1) selfselected longboarding speeds would be faster than those reported for walking and similar to commuter cycling, and (2) longboarding would require less metabolic energy per distance traveled (i.e. metabolic cost) than that reported for walking, greater than the reported metabolic cost of bicycling, and similar to cross-country skiing. overground speed. To calculate push frequency, we also measured and timed the number of pushes by their feet per 100 m, as observed in one section of the rectangular loop. Experimental data Methods Overground speed was measured by the GPS unit. GPS unit speed was verified by comparing average loops speeds from the GPS unit to speeds calculated with times to complete each loop measured and the distance of the loop. To determine metabolic rate and energy expenditure during longboarding, we measured rates of oxygen consumption and carbon dioxide production with a portable metabolic measurement system (Oxycon Mobile, Yorba Linda, CA) that has been validated for use in field studies (Rosdahl et al. 2010). We calibrated the system prior to data collection, and participants were allowed 4 min to reach steady state. Participants Data and statistical analysis Seventeen individuals were recruited and participated in the study. However, data from two participants were not used due to equipment malfunction (GPS unit loss of satellite positioning), thus data from fifteen individuals (2 female, 13 male) were used in the study. Participants were experienced longboarders (at least 1 year of longboarding 2 or more times/week), who were in good health with no known diseases or limitations to physical activity. Mean age, body mass and height of participants were 21.0 (1.7) years, 71.5 (8.2) kg and 1.77 (0.07) m, mean (SD), respectively. Participants gave written informed consent that followed the guidelines of and was approved by the Colorado State University Human Research Institutional Review Board. The Garmin GPS data were downloaded and exported using Garmin software. Distance and speed data were computed from the 1 Hz GPS coordinates and averaged over the duration of each trial using a custom program in Matlab (Matlab v 12.0, Mathworks, Natick, MA). We calculated the average overground speeds, rates of oxygen consumption and carbon dioxide production for the final 2 min of each trial. We used the overground speed and the rate of oxygen consumption and carbon dioxide production data to calculate metabolic rate and metabolic cost (metabolic rate speed−1) using standard techniques (Brockway 1987). Descriptive statistics were calculated for overground speed, rate of oxygen consumption, metabolic rate, metabolic cost, and energy expenditure. We used linear regression to determine the relationship between oxygen consumption and energy expenditure versus longboarding speed. One-way, repeated measures ANOVAs were performed on outcome variables to determine if there were significant differences due to speed: P < 0.05 defined significance. If significant main effects were observed, we used the Holm-Sidak method to perform post hoc pairwise multiple comparisons. SigmaPlot version 11.0 (Systat Software, Inc., San Jose, CA) was used for all statistical analyses. Experimental protocol Participants attended one data collection session. Prior to data collection, participants were asked to longboard for 10–15 min at a low-intensity effort to warm-up and become familiar with the longboard model used in this study. Participants then completed three ~6 min trials while traveling at a self-selected slow, typical and fast speeds and using this standard longboard (Model PF124/Mini Shaka Complete, Sector 9, San Diego, CA). Participants were instructed to maintain a steady speed during each trial and monitored their speed throughout each trial using a wristmounted global positioning system (GPS) unit (Garmin Forerunner 150, Garmin, Olathe, KS) and handheld stopwatch. Each trial consisted of completing multiple ~350 m laps on a level street/sidewalk (Fig. 1). The road surface was ~75 % concrete and 25 % asphalt. During each trial, we continuously measured oxygen consumption and Results Mean (SE) longboarding speeds were 3.7 (0.1), 4.5 (0.1) and 5.1 (0.1) m s−1 (13.3, 16.2, and 18.4 km h−1), during the slow, typical and fast trials, respectively. Speeds 13 Author's personal copy Eur J Appl Physiol Fig. 3 Mass-specific gross metabolic cost across the range of speeds tested. Error bars are SD. Metabolic cost was greater at that fastest speed compared to the slowest speed. Asterisk indicates significant difference between fastest and slowest speeds Fig. 2 Gross mass-specific oxygen consumption (a) and energy expenditure (b) across the range of speeds used by participants. Both oxygen consumption and EE increased with speed. Linear regression equations: VO2 = −9.98 + 9.054 speed (R2 = 0.69, SEE = 4.53, P < 0.001), EE = −6.11 + 3.68 speed (R2 = 0.78, SEE = 1.47, P < 0.001), respectively ranged from 2.8 to 5.9 m s−1 (10.1–21.2 km h−1). As expected, rates of oxygen consumption and energy expenditure increased with speed (Fig. 2). Mean (SE) rates of oxygen consumption were 24.1 (1.1), 29.1 (1.5) and 37.2 (1.4) ml kg−1 min−1 at the slow, typical and fast speeds, respectively. Mean (SE) rates of energy expenditure were 33.2 (2.2), 41.9 (2.4) and 52.9 (2.9) kJ min−1 at the slow, typical and fast speeds, respectively. At typical speeds, average intensity was ~8.5 METs, indicating 13 Fig. 4 Push frequency across the range of speeds used by participants. Linear regression equation: frequency = −0.421 + 0.20 speed (R2 = 0.42, SEE = 0.172, P < 0.001) the activity would be classified as vigorous exercise. Mean respiratory exchange ratios were 0.74 (0.02), 0.80 (0.02), and 0.84 (0.02) at slow, typical, and fast speeds, respectively. There was a significant positive relationship between rates of oxygen consumption and energy expenditure versus speed (R2 = 0.69 (P < 0.001) and 0.71 (P < 0.001), respectively; Fig. 2). Gross metabolic cost increased slightly with speed (Fig. 3). There was a significant difference between the metabolic cost at the slowest and fastest speeds. Push frequency increased with speed (Fig. 4). Mean (SE) push frequencies were 0.30 (0.02), 0.41 (0.05) and 0.54 (0.06) Hz at the slow, typical and fastest speeds, respectively. Author's personal copy Eur J Appl Physiol Discussion Our results demonstrate that longboarders travel at relatively fast speeds, and that the activity elicits a high metabolic rate (i.e. is classified as vigorous intensity exercise) while having a relatively low metabolic cost per distance. As we hypothesized, typical longboarding speeds were ~3.5-times faster than reported self-selected walking speeds (1.3 vs. 4.5 m s−1) and similar to or slightly slower than bicycle commuting speeds (4.9 vs. 4.5 m s−1). We found that gross metabolic cost was ~2.2 J kg−1 m−1, indicating that longboarding metabolic cost (i.e. economy) is nearly 50 % better than that of walking. The gross metabolic cost of cycling has been reported to be ~1.0 J kg−1 m−1 at commuting speeds (Tucker 1975) and classic cross-country skiing of ~2.4 J kg−1 m−1 (Formenti et al. 2005; Bellizzi et al. 1998), thus we also accept our second hypothesis that longboarding metabolic cost would be lower than walking, higher than bicycling and similar to cross-country skiing. Our results suggest that longboarding may be a physically active way to travel from place to place while expending metabolic energy. Given the self-selected speeds of ~4 m s−1, longboards can be used to travel reasonable distances relatively rapidly. For example, an individual using a longboard could travel 1.5 km in ~6 min if they used the typical speeds measured in this study. It would take ~20 min to walk the same distance. The metabolic data indicate that longboarding at typical speeds requires a vigorous intensity effort of ~8.5 METs. Although similar to a study that found traditional skateboarding elicited an intensity of ~8.2 METS when used as a means of physical activity (Hetzler et al. 2011), we were surprised to find this level of intensity in our study given that other forms of active transportation are typically performed at light-moderate intensities (2.5–5 METs) (Oja et al. 1998). One possible explanation is that participants in this study were traveling faster than they would during a typical trip. This could have been due to their interpretation of the instructions to travel at “normal” or “typical” speeds. Our results indicate that slower speeds of ~3.0 m s−1 would still require a moderatevigorous effort of ~5–6 METs. Given the need for more individuals, particularly adolescents and young adults, to engage in moderate-vigorous physical activity (Rey-López et al. 2008), our results suggest that longboarding may be a good activity for transportation and improved health. The metabolic rate (oxygen consumption) and metabolic cost of longboarding increased linearly with speed. Metabolic rate/cost has been shown to increase curvilinearly with speed in other forms of legged locomotion (di Prampero 1986), but across a much wider range of speeds than reported here. We anticipate that the same relationship would exist during longboarding had we collected data at faster and slower speeds. The increase in metabolic rate with speed is likely due to an increase in both non-aerodynamic and aerodynamic factors, although quantification of these contributions will require further study. Metabolic rate during longboarding is similar to that reported for classic style cross-country skiing at a similar speed using only the legs (i.e. no poling, Bellizzi et al. 1998). The similar rates of oxygen consumption during longboarding and cross-country skiing are not surprising given the similarities between the two activities in terms of body posture, and the relatively energy inefficient acceleration-deceleration phases associated with the phases of propulsion and glide (di Prampero 1986). Furthermore, the gliding phase during longboarding and cross-country skiing decreases gross metabolic cost compared to walking and running (Formenti et al. 2005). Longboarding is a metabolically economical form of physical activity. This is not surprising given the mechanics of the task. Individuals push the board every 2–3 s (0.3–0.5 Hz) and then stand on the board and coast or glide. Push frequency increased with speed, with values similar to those found during cross-country skiing (0.6 Hz) (Bellizzi et al. 1998) but lower than typical walking or running stride frequencies (1–2.5 Hz). Bicycling is regarded as one of the most metabolically economical forms of humanpowered travel, with an estimated gross metabolic cost of ~1.0 J kg−1 m−1 (Tucker 1975). The difference between bicycling and longboarding metabolic cost is likely due to differences in body position, bodyweight support and propulsion mechanics. During bicycling, individuals are in a crouched sitting position, with the majority of bodyweight being supported by the saddle. The standing position adopted during longboarding requires the legs to support the body and also results in a greater frontal area exposed to air resistance. The combination of active weight support (non-aerodynamic), increased aerodynamic drag and a less efficient propulsion system may contribute to the greater metabolic cost during longboarding compared to bicycling (di Prampero 1986). While longboarding is relatively economical when the terrain is level, it is likely that economy would be reduced when traveling uphill. Longboards likely decelerate quickly when going uphill (particularly on steeper grades) and the need to push would increase. There is most likely a grade above which it becomes less metabolically costly to walk. Future studies that quantify longboarding energetics at varying grades would confirm this hypothesis. Conversely, longboarding downhill should have an economy similar to that of cycling downhill (coasting). Of course, as the downhill grade increases, the need to brake may increase and potentially increase the metabolic cost. Given the challenges of longboarding uphill combined with the potential risks of longboarding downhill, longboarding as a form of physical activity seems best suited for relatively flat terrain. 13 Author's personal copy While longboarding may be considered a good form of physical activity, it does have risks unique to the activity. Namely, longboarding requires a level of skill to propel, steer and stop the board. This skill is probably equal or greater than that required for cycling and, thus, highlights the need for individuals to practice the activity in order to acquire the necessary skills. In particular, stopping a longboard can be challenging for a novice, particularly if the rider is moving relatively fast. Successful integration of longboarding as a physical activity alternative could be facilitated with programs that teach the basic skills of riding (similar to bicycling safety/skill programs for children). In addition, the difference between longboarding and walking speeds highlights the challenge associated with longboarders and walkers sharing the same path. Given the similarity of travel speeds of longboarding and bicycling, it may be more reasonable to have these two forms of activity share the same infrastructure (e.g. a bike lane) when possible. It should be noted that longboards are not particularly well suited to be ridden in inclement weather, as the risk of the board slipping laterally increases considerably. This risk may limit the broad, year-round adoption of longboarding in regions where rain and/or snow are common. Conclusions Longboarding is a novel form of physical activity that elicits moderate-vigorous intensity yet is metabolically economical. Travel speeds are similar to commuter cycling but considerably faster than walking, at least on level terrain. Given its popularity, longboarding may be an attractive active transportation option for young adults. Acknowledgments This research was supported by a grant from AEND Industries. Conflict of interest The authors declare that they have no conflict of interest. Ethical standards This experiment complies with the current laws of the United States of America. 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