Conflicting reports have been presented regarding the potential cardiorespiratory benefits attainable from in-line skating as compared with more traditional forms of aerobic exercise. The heart rate (HR) responses to in-line skating have been reported to be higher than treadmill running(8) and skate-skiing (5) at the same level of oxygen consumption (˙VO2). These results suggest that a higher steady rate HR is required during in-line skating to achieve cardiorespiratory benefits similar to other forms of aerobic exercise, particularly in highly fit individuals (5). However, several investigators have concluded that an appropriate training stimulus is achievable with in-line skating independent of fitness level or skating ability (2,4,7,10). In a study from our laboratory (7), the metabolic responses during running and in-line skating were compared at self-selected exercise intensities. Although running elicited a significantly higher steady rate˙VO2 (44.0 ± 1.7 vs 42.0 ± 0.2 ml·kg-1·min-1), the small difference between exercise modes suggests that running and in-line skating at self-selected speeds may offer a similar training stimulus.
No definitive statements regarding the cardiorespiratory benefits of in-line skating can be proposed until the adaptations to an in-line skate training program are examined. Furthermore, as in-line skating is generally considered an alternative exercise training modality to running, data that quantify and compare adaptations to these two modes of exercise are needed. This study was designed to test the hypotheses that: 1) in-line skate training at intensities recommended by the ACSM will increase maximal aerobic capacity(˙VO2max); and 2) increases in ˙VO2max will be equivalent to those elicited by a running program similar in training volume and intensity.
Subjects. Participants were recruited from undergraduate exercise science classes and were enrolled in a special section of a physical education course. Potential subjects were carefully screened regarding their physical activity levels to obtain a sample that was neither highly fit nor sedentary. Volunteers who reported any form of systematic aerobic training over the previous 6 months were excluded. Systematic aerobic training was defined as participation in any dynamic activity involving the lower extremity (e.g., cycling, running), performed two or more times per week for 6 wk or longer with the specific goal of improving fitness. Based on questionnaire responses, the subjects were classified as moderately physically active.
Thirty-eight subjects were selected from the initial screening and assigned to one of the training groups. To eliminate a learning effect, the in-line skate training group consisted only of individuals who demonstrated the ability to safely skate, turn, and brake (N = 21). Remaining subjects (N = 17) were assigned to the running group. A third group(N = 7) served as controls who were asked not to alter their exercise patterns over the course of the study. The same physical activity screening procedures were used for the controls. All subjects provided informed written consent in accordance with the university Human Subjects Review Committee Guidelines.
Subject descriptive characteristics are presented inTable 1. Two skaters and one runner did not satisfy requirements of the training program. Therefore, the final sample consisted of 19 skaters, 16 runners, and 7 controls. Although female runners were significantly older than female controls, the groups were homogeneous with respect to all other physical characteristics. No significant changes in body mass were observed over the course of the study in any of the three groups.
Training protocol. Training sessions were conducted three times each week for 9 wk. All sessions were supervised, and subjects were asked not to alter their regular activity patterns outside of training. To be included in the final analysis, subjects were required to attend a minimum of 90% of the training sessions (24 of a possible 27 sessions). Running sessions during the first week were conducted indoors on a 160-m rubberized surface track. After the first week runners were given the option of training outdoors but were provided with prescribed courses to ensure that all training was conducted on level terrain. In-line skating sessions were conducted at an indoor skating facility (115-m oval) with a hardwood polished surface.
Exercise intensity was based on a percentage of the exercise-specific maximal heart rates (HRmax) observed during ˙VO2max testing. The training program was designed to satisfy the ACSM guidelines for improving cardiorespiratory fitness (1) and was divided in two stages. The first stage (weeks 1-4) imposed a gradual increase in exercise duration and intensity and consisted of continuous exercise. Duration and intensity were gradually increased from 20 min per session at 80% HRmax during the first week, to 40 min at 90% HRmax by the end of the fourth week. In the second stage (weeks 5-9), training days alternated between long, high intensity bouts (40 min at 85% HRmax), and interval workouts. A sample interval workout is presented in Table 2.
During all training sessions, subjects wore a heart rate telemetry system(AMF Quantum XL Heart Watch, Polar Electro, Inc., Kempele, Finland). The duration and desired HR zone for each subject's workout was pre-programmed into memory. If HR was not maintained within ±5 beats·min-1 of the desired intensity, an alarm sounded signaling the subject to either increase or decrease speed to restore HR to the target zone. All training heart rate data were downloaded to a personal computer and reviewed after each training session to ensure that subjects were adhering to the training program.
Maximal oxygen consumption. Pre- and post-training, runners and controls performed an incremental running test to volitional exhaustion, and skaters performed both a running and skating test (separated by at least one but not more than 7 d). All ˙VO2max tests were performed on a customized motor driven treadmill (2.4 m long × 1.8 m wide) designed to accommodate in-line skating (Trackmaster, JAS Fitness Systems, Pensacola, FL). Subjects were required to practice running on the treadmill prior to the pre-training test. Skaters also practiced skating on the treadmill. To ensure safety during skating trials, subjects wore a nonrestrictive harness suspended from the ceiling. Subjects ran or skated at several different grades to become familiarized with the testing protocol. At the end of the practice session, subjects selected a comfortable speed for use during pre- and post-training testing. Treadmill speed was verified using a high precision digital tachometer (Biddle, Inc., Plymouth Meeting, PA).
A constant speed, incremental grade protocol was used with 2-min stages. Running tests began at 0% grade with increments of 2.5%, and in-line skating tests began at a 2% grade with increments of 2%. The skating protocol was modified because pilot testing indicated that skating on a level grade was technically difficult due to lack of resistance against the moving belt and that increments of 2.5% caused most subjects to terminate the test prior to attaining criteria acceptable for ˙VO2max. Each ˙VO2max test was preceded by a 5-min warm-up at the speed and grade used during the initial stage. To be considered ˙VO2max, two of the following criteria had to be satisfied: 1) a respiratory exchange ratio (RER) ≥1.0; 2) HR within 15 beats·min-1 of age predicted maximal heart rate; 3) a leveling off in ˙VO2 despite an increase in workload(6).
˙VO2max was determined using indirect calorimetry. Subjects breathed through a Hans Rudolph high velocity two-way non-rebreathing valve(model 2700, dead space 95 ml, Kansas City, MO). Inspired volume of air was measured with a calibrated dry gas meter (Rayfield Equipment, Waitsfield, VT). Expired gases were dried and analyzed using Ametek (Pittsburgh, PA) O2(Model S-3A1) and CO2 (Model CD-3A) analyzers. The analyzers were calibrated before each test using verified gases of known concentration. Analog data from the analyzers and dry gas meter were converted to digital signals and transmitted to a personal computer. An on-line program(˙VO2PLUS, Exeter Research, Exeter, NH) sampled data every 30 s and automatically calculated ventilation (˙VE), oxygen consumption, carbon dioxide production, and the respiratory exchange ratio (RER). Heart rate was monitored using a heart-rate telemetry system and was sampled every 30 s.
Data Analysis. A two-factor (group × time) repeated measures ANOVA was used to determine differences in running ˙VO2max and maximal treadmill time. To determine differences in training-specific adaptations, the magnitude of changes in running data from the runners and controls were compared to skating data from the skaters using a two-factor repeated measures ANOVA. Post-hoc comparisons for all ANOVAs were performed using the Scheffe test. Running and skating ˙VO2max data from the skaters only were compared using paired t-tests. Correlations were calculated using the Pearson product-moment formula. An alpha level of 0.05 was required for statistical significance.
The groups did not differ in pre-training running ˙VO2max(absolute or relative) or maximal treadmill time (seeFigs. 1-3). After 9 wk of training, significant increases in running absolute ˙VO2max (Fig. 1) were observed in runners (3.0 ± 0.2 to 3.3 ± 0.2 l·min-1) and skaters (3.1 ± 0.2 to 3.3± 0.2 l·min-1), but not in controls (2.9 ± 0.3 to 3.0 ± 0.3 l·min-1). Likewise, significant increases in running relative ˙VO2max (Fig. 2) were observed in runners (46.3 ± 1.8 to 50.8 ± 1.9 ml·kg-1·min-1) and skaters (46.1 ± 1.7 to 48.9 ± 1.7 ml·kg-1·min-1), but not in controls (46.7 ± 2.7 to 47.7 ± 2.8 ml·kg-1·min-1). Post-training running˙VO2max (absolute and relative) of the skaters and runners were significantly higher than that of the controls (P < 0.001), but not different between the two training groups. Significant increases were also observed in running maximal treadmill time (Fig. 3) in runners (625.9 ± 35.4 to 716.6 ± 33.7 s) and skaters (621.6± 32.4 to 665.9 ± 30.9 s), but not in controls (639.0 ± 35.4 to 648.6 ± 50.9 s). Skaters also significantly increased their skating ˙VO2max (2.8 ± 0.2 to 3.1 ± 0.2 l·min-1) and maximal treadmill time (549.5 ± 22.0 to 592.1 ± 24.3 s).
Evaluation of the individual responses revealed that all but one of the runners improved running ˙VO2max (mean ± SE = 9.3 ± 1.3%). The one subject who did not improve remained at pre-training level. Similarly, all but one of the skaters increased running ˙VO2max(6.2 ± 0.8%). The one subject who did not improve had a small decrease in running ˙VO2max (-0.8%). The magnitude of increase in running˙VO2max was not different between the two groups. Two skaters had decreases in skating ˙VO2max (-5.1% and -2.9%) despite having small increases in running ˙VO2max (+3.6% and +0.9%). All other skaters had an increase in skating ˙VO2max. The magnitude of increase in skating ˙VO2max (8.6 ± 1.8%) in the skating group was not different from the increase in running ˙VO2max of the runners (9.3± 1.3%).
Interestingly, a comparison of the running and skating ˙VO2max data for the skaters before and after training showed that the running protocol elicited greater absolute and relative ˙VO2max values(P < 0.001) but no differences in HRmax or˙VEmax. Using pooled data from pre- and post-training, the correlation (r = 0.98) between running and skating ˙VO2max was strong.
The magnitude of increases in ˙VO2max observed in this study are consistent with previous running studies that used previously untrained subjects and programs of similar frequency, duration, and intensity(3,11). Our results support the hypothesis that a cardiorespiratory training effect is achievable with an in-line skating exercise program (2,4,7,10). Our second hypothesis was that increases in ˙VO2max resulting from running and skating programs similar in training volume and intensity would be equivalent. There was no difference in post-training running˙VO2max between the two training groups. Furthermore, the magnitude of increases in running ˙VO2max of the runners and skating˙VO2max of the skaters were not different. In conclusion, in moderately active college-aged students, similar improvements in˙VO2max may be achieved with running and in-line skating exercise programs.
To our knowledge, this is the first investigation that has measured˙VO2max using an incremental graded protocol while in-line skating on a motorized treadmill. Paired t-tests indicated no differences in˙VEmax or HRmax between running and skating˙VO2max at pre- and post-training. Moreover, there was a high correlation between running and skating ˙VO2max. However, the skating protocol produced lower ˙VO2max values than running both before (2.8 ± 0.2 vs 3.1 ± 0.2 l·min-1) and after(3.1 ± 0.2 vs 3.3 ± 0.2 l·min-1) training. The reason for this difference is not readily apparent but is consistent with the findings of Wallick et al. (10) who reported lower˙VO2peak values during in-line skating over level terrain as opposed to treadmill running. They suggested that the lower values during in-line skating may have been a result of the inability of their subjects to skate fast enough at 0% grade to maximally challenge the cardiovascular system. However, in this study, the running and skating protocols elicited similar maximal values for heart rate and ventilation. Our data suggest that differences in ˙VO2max may be due to the oxygen demands of the active musculature. The exact cause of this difference remains to be elucidated.
We are unable to explain why two skaters had lower skating˙VO2max after training despite having small increases in running˙VO2max. However, several subjects suggested that the in-line skating test was more difficult than the running test due to the novelty of skating on a treadmill at an elevated grade.
True differences in the HR/˙VO2 relationship of running and in-line skating remain equivocal at this time. Several investigators have reported a disproportionate increase in HR relative to ˙VO2 during in-line skating (4,5,8). Snyder et al.(8) reported that compared with treadmill running at a given HR, in-line skating elicited a lower ˙VO2. However, in-line skating was performed over a 200-m Tartan-surfaced track, which may have increased the rolling resistance (and thus the metabolic responses) above that which would be encountered while skating over other surfaces, particularly concrete and asphalt. In addition, skating on an oval track increases the frequency of turning, which may effect the achievement of a steady state response (4). Fedel et al. (4) also reported a higher HR response relative to ˙VO2 during in-line skating at 60 and 80% of ˙VO2peak compared to the ACSM guidelines(1). However, their study used competitive in-line skaters who may assume a more horizontal thigh position during the glide phase than recreational or untrained skaters. This position produces a static contraction of the thigh muscles that may produce a pressor response and elevate heart rate (9). Recreational skaters assume a less horizontal position and probably for a shorter duration of each stride; thus, they may be less likely to experience a disproportionate increase in HR during in-line skating.
In contrast, Wallick et al. (10) reported no difference in the HR/˙VO2 curves of treadmill running and in-line skating using subjects not previously trained as in-line skaters. In the present study, most training was performed in the 80-90% HRmax range, which resulted in similar increases in ˙VO2max for both groups. Therefore, we believe there is sufficient evidence to support prescribing in-line skating exercise intensity as a percentage of HRmax in inactive and moderately active individuals. However, a higher exercise HR may be required in trained or competitive in-line skaters to elicit cardiovascular benefits similar to running.
We conclude that in-line skating provides an adequate stimulus for improving cardiorespiratory fitness in moderately active individuals. To achieve cardiovascular training effects similar to those in running, in-line skate training programs should be similar in frequency, duration, and intensity. As there were no differences in HRmax for running and in-line skating, it appears that in-line skating exercise intensity can be prescribed for moderately active individuals using the traditional percentage of age predicted maximal heart rate.
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Keywords:©1996The American College of Sports Medicine
AEROBIC ENDURANCE TRAINING; MAXIMAL OXYGEN UPTAKE