Despite its popularity as a form of exercise, no field study has been undertaken which directly compares the physiological demands of in-line skating with running. However, several investigations have used laboratory measures to compare in-line skating with other forms of exercise. Snyder et al. (14) reported that in-line skating elicited higher heart rate responses in nine trained subjects than treadmill running or stationary cycling at the same level of ˙VO2. Although it was concluded that in-line skating is an effective mode of aerobic exercise, a leftward shift was observed in the HR/˙VO2 curve for in-line skating compared with other forms of exercise. These results suggested that training adaptations for in-line skating may be less than running at a given heart rate (HR). In contrast, Wallick et al. (15) found no difference between the HR/˙VO2 curves of 16 “active males” during in-line skating and treadmill running.
The hypothesis that training adaptations resulting from in-line skating may be less than running is supported by Hoffman et al. (7). Based on extrapolation of ˙VO2 measured in 10 competitive male cross-country skiers during in-line skating at speeds between 14.6 and 18 km·h-1, it was suggested that highly fit individuals may need to travel at unsafe and technically difficult speeds to achieve appropriate training benefits from in-line skating. However, Fedel et al.(5) reported that 12 male competitive in-line skaters were capable of safely skating at speeds sufficient enough to elicit an adequate cardiovascular training stimulus. At speeds of 22.5 and 27.4 km·h-1, HR was 74% and 85% of peak, and ˙VO2 was 51% and 72% of peak. Similar results were reported by Wallick et al.(15) in 16 “active males.” They showed that between 17.7 and 20.9 km·h-1, ˙VO2 and HR were 60-75% and 75-90% of peak, respectively.
Although the HR/˙VO2 relationship between running and in-line skating may be different (7,14), the interpretation that in-line skating does not provide the same aerobic training benefit as running may be premature. Doing so ignores the possibility that participants may naturally self-select intensities that would provide similar cardiovascular overloads independent of exercise mode. Selection of exercise intensity is probably dependent upon a multitude of metabolic responses (e.g., HR, blood lactate, ventilation, respiratory rate). As recreational exercisers would find it impractical to measure these variables, and given the surge in popularity of in-line skating as a form of exercise, data are needed that directly compare the demands of running and in-line skating at preferred exercise intensities. Therefore, the purpose of this study was to compare the physiological demands of in-line skating and running at self-selected exercise intensity levels.
Ten males (24.7 ± 4.5 yr, 72.5 ± 5.6 kg, 179.2 ± 6.0 cm) and 10 females (25.7 ± 4.6 yr, 60.7 ± 8.2 kg, 167.8 ± 6.9 cm) provided informed written consent in accordance with the university Human Subjects Review Committee Guidelines. Subjects were required to demonstrate proficient in-line skating technique and reported previous experiences with in-line skates ranging from a few times (3 or 4) up to several years of experience. None of the subjects were considered novice in-line skaters. Several subjects reported in-line skating as a regular form of exercise during summer months, but none of the subjects were training as competitive in-line skaters. Although maximal aerobic capacity was not determined, subjects reported various forms and levels of regular physical activity.
Testing was conducted on two separate days during the months of July and August. On each day, subjects performed either 15 min of in-line skating or running. Tests were separated by at least 1 but no more than 7 d. The order of running and in-line skating trials was balanced across subjects. Testing was conducted outdoors over a rectangular course that measured 0.48 km (0.3 miles) on a smooth and level asphalt parking lot. Subjects were instructed to select an exercise intensity that would represent a cardiovascular or aerobic workout(an intensity high enough so that they would get a good workout), and to maintain a steady pace throughout the 15 min of exercise. Average speed over each 15-min trial was monitored by a cyclocomputer-equipped bicycle ridden approximately 3-5 m behind the subject. Subjects wore their own running shoes during the running trials, but the same model of in-line skates(Rollerblade® Macroblade Equipe™, Rollerblade, Inc., Minnetonka, MN) was used during skating trials. On at least one occasion before testing, subjects practiced skating while wearing the Macroblades. During in-line skating trials, subjects were provided a pair of knee, wrist, and elbow guards but were not given any instructions regarding skating technique.
During each trial, heart rate and ˙VO2 were monitored continuously via telemetry using a portable open-circuit spirometry system(Cosmed K2, Vacumetrics, Inc., Ventura, CA). The specifications and validity of the Cosmed K2 have been previously reported(8,9,11). The K2 was turned on at least 60 min before intended use and was calibrated prior to each trial. The K2 is not equipped with a carbon dioxide analyzer; therefore, an estimate of caloric expenditure was obtained by multiplying ˙VO2(l·min-1) by 5.05, which represents the caloric equivalent of a respiratory exchange ratio of 1.0 (10).
Before each trial standardized instructions for rating of perceived exertion (RPE) were read to each subject. After each trial, subjects were again read the instructions, and were asked to provide an overall rating of perceived effort during the exercise trial. The Borg 6-20 RPE scale was used to estimate perception of effort, with perceptual scale anchors established as previously reported (2).
One-factor analysis of variance (ANOVA) with repeated measures was used to detect differences in ˙VO2 over minutes 11-15. Pairedt-tests were performed on selected dependent measures to determine differences between running and in-line skating. Pearson product-moment correlation coefficients were used to compare running and in-line skating responses. All comparisons were considered significant at P < 0.05.
There were no differences in ˙VO2 over minutes 11-15 during either in-line skating (P = 0.41) or running (P = 0.71). Therefore, HR, ˙VO2, and energy expenditure for each subject were calculated as the mean values observed over the last 5 min of each trial.
Average speeds observed during the in-line skating and running trials are presented in Table 1, and mean values for dependent measures are presented in Table 2. No significant differences in ˙Ve (P = 0.72), HR (P = 0.69), or RPE(P = 0.91) were observed between in-line skating and running. However, ˙VO2 and energy expenditure were significantly higher during running (P = 0.03).
Consistent with previous investigations(5,7,14,15), we conclude that in-line skating is an appropriate mode of exercise for improving cardiovascular fitness. Preferred level of exertion corresponded to an intensity that was 73-98% of age-predicted maximal heart rate (HRmax) during in-line skating, and 66-97% HRmax during running (Fig. 1). These levels are considered sufficient to promote a cardiovascular training effect (1). The short duration of the trials (15 min) probably contributed to selection of an intensity higher than would be chosen for a longer (30-60 min) exercise bout. However, inspection ofFigure 1 suggests that subjects could reduce intensity and still be within the suggested range for improving cardiovascular fitness(1). Although pace was not controlled, maintenance of steady rate ˙VO2 suggests that subjects were in a physiological steady state during the last 5 min of both running and in-line skating.
In the present study, subjects perceived no differences in exercise intensity during self-selected speed running and skating although steady rate˙VO2 and energy expenditure were significantly lower during in-line skating (Table 2). However, because the magnitude of these differences in steady rate responses was small (0.2 l·min-1 (2.0 ml·kg-1·min-1), 0.7 kcal·min) we conclude that the intensity of exercise was equivalent during running and in-line skating.
The conclusion that intensity of exercise was equivalent during the in-line skating and running bouts assumes that RPE is a valid marker of relative exercise intensity independent of variations in ambient conditions, mode of exercise, or fitness level. Results from several published studies support this assumption. Potteiger and Weber (12) investigated the influence of temperature on HR and RPE and found no significant differences in HR or RPE during constant load cycle ergometry work performed at 14°, 22°, and 33°C. In the present study, there were also no differences in RPE and HR, and ambient temperature during testing varied within a narrow range (21-32°C). Dishman et al. (4) compared responses to preferred intensities of exertion by high-active and low-active men during 20 min of cycle ergometry. There were no differences in exercise intensity (%˙VO2peak) between groups during the last 10 min, and RPE was identical between groups for the entire 20 min. These results suggest that RPE is a valid indicator of exercise intensity independent of fitness levels. Finally, Robertson et al. (13) reported no differences in RPE during several modes of exercise (treadmill running, cycle ergometry, and bench stepping with hand weights) performed at 70% of the exercise-specific relative ˙VO2peak. Thus, it appears that RPE can be used to equate exercise intensity during various modes of exercise.
There have been conflicting results regarding the effectiveness of in-line skating as a form of aerobic exercise when compared with other exercises. Leftward shifts in the HR/˙VO2 curves have been reported when in-line skating was compared with treadmill running (14) and skate skiing (7). However, these results may have been affected by the environments in which testing was performed(5). In previous studies, in-line skating was performed on an indoor, 200-m Tartan track (14) or an outdoor, 432-m rubberized track (7). These relatively short courses resulted in more frequent turning and may have affected the achievement of a steady-state response (5), particularly in recreational or inexperienced skaters. In addition, in-line skating on these surfaces may have produced a higher coefficient of rolling resistance(5). In contrast to Snyder et al.(14) and Hoffman et al. (7), Wallick et al. (15) reported no difference in the HR/˙VO2 curves of treadmill running and in-line skating when in-line skating was performed over a straight, level, asphalt surface.
The present study was unique in that it compared the physiological responses to running and in-line skating in the environment in which they are normally performed, e.g., outdoors on an asphalt surface at preferred levels of exertion. Snyder et al. (14) reported that at 30 ml·kg-1·min-1 HR elicited by in-line skating was 14 beats·min-1 higher than running, and it appeared that this difference increased as ˙VO2 increased. In contrast, our results suggest that at a ˙VO2 of 42-44 ml·kg-1·min-1, in-line skating and running elicit similar HR responses (approximately 176 beats·min-1). The difference in experimental design between studies makes direct comparisons difficult. For example, Snyder et al. (14) compared responses over a broad range of exercise intensity (30-90%˙VO2max), whereas the present study compared responses only at a preferred level of exertion, and% ˙VO2max was not known. Furthermore, track conditions and lengths may have influenced the relationship between HR and˙VO2. Differences in the HR/˙VO2 relationships between running and in-line skating should be determined by comparing these exercises across a range of exercise intensities in a controlled, laboratory setting. Actual differences in cardiovascular adaptations cannot be determined until a controlled, systematic training study is completed.
It may be hypothesized that the weight of the protective gear and in-line skates may have significantly increased the energy cost and ˙VO2 of in-line skating as compared with running. Frederick et al.(6) reported that as little as 15 g added to each foot had significant effects on aerobic demands of running at certain speeds. The combined weight of the wrist, knee, and elbow guards is approximately 0.7 kg, but since they are not worn on the feet, this probably had negligible effects on ˙VO2. Although the weight of each in-line skate is approximately 1.8 kg, Carroll et al. (3) suggest that “the mechanical differences between running and skating, particularly in the recovery phase of the strides, suggest that skate weight would have less affect on the aerobic demand for the skater than would shoe weight for the runner, since in skating the foot stays closer to the ground.”
Wallick et al. (15) reported that in active males, in-line skating at speeds of 14.5, 17.7, 20.9, and 24.1 km·h-1,˙VO2 was 26.7, 34.5, 43.4, and 51.4 ml·kg-1·min-1, which corresponded to an intensity of 60-75% of ˙VO2peak. In collegiate hockey players, Carroll et al.(3) reported that at in-line skating speeds of 12.5, 16.5, and 20.5 km·h-1, ˙VO2 was approximately 19, 34, and 42 ml·kg-1·min-1, though no peak or maximal data were presented. In competitive in-line skaters, Fedel et al.(5) reported that at 27.4 km·h-1,˙VO2 was 40.8 ml·kg-1·min-1 (72% of˙VO2peak). In our heterogeneous sample, in-line skating at a mean speed of 21.7 km·h-1 elicited a ˙VO2 of 42.0 ml·kg-1·min-1, which corresponded to 73-98% HRmax. These results suggest that an appropriate cardiovascular training effect may be achieved with in-line skating in individuals of varying levels of fitness and skating ability.
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