Skating Crossovers on a Motorized Flywheel

A Preliminary Experimental Design to Test Effect on Speed and on Crossovers

Abstract

Smith, AM, Krause, DA, Stuart, MJ, Montelpare, WJ, Sorenson, MC, Link, AA, Gaz, DV, Twardowski, CP, Larson, DR, and Stuart, MB. Skating crossovers on a motorized flywheel: a preliminary experimental design to test effect on speed and on crossovers. J Strength Cond Res 27(12): 3412–3418, 2013—Ice hockey requires frequent skater crossovers to execute turns. Our investigation aimed to determine the effectiveness of training crossovers on a motorized, polyethylene high-resistance flywheel. We hypothesized that high school hockey players training on the flywheel would perform as well as their peers training on ice. Participants were 23 male high-school hockey players (age 15–19 years). The study used an experimental prospective design to compare players who trained for 9 sessions on the 22-foot flywheel with players who trained for 9 sessions on a similarly sized on-ice circle. Both groups were compared with control subjects who were randomly selected from the same participant pool as those training on ice. All players were tested before and after their 3-week training regimens, and control subjects were asked to not practice crossovers between testing. Group 1 trained in a hockey training facility housing the flywheel, and group 2 trained in the ice hockey arena where testing occurred. Primary outcome measures tested in both directions were: (a) speed (time in seconds) required to skate crossovers for 3 laps of a marked face-off circle, (b) cadence of skating crossovers on the similarly sized circles, and (c) a repeat interval speed test, which measures anaerobic power. No significant changes were found between groups in on-ice testing before and after training. Among the group 1 players, 7 of 8 believed they benefited from flywheel training. Group 2 players, who trained on ice, did not improve performance significantly over group 1 players. Despite the fact that no significant on-ice changes in performance were observed in objective measures, players who trained on the flywheel subjectively reported that the flywheel is an effective cost-effective alternative to training on ice. This is a relevant finding when placed in context with limited availability of on-ice training.

Introduction

Use of specialized exercise equipment to maintain fitness, train, and test for specific sports is now commonplace (^3,4,13). Many hockey players participate in skating treadmill programs, such as Acceleration (¹³). Kinematic variables (^5–7) and physiologic variables of players skating forward and backward on ice and on skating treadmills have been studied (^2,8). No empirical evidence shows that skating treadmills enhance on-ice performance, and performance benefit claims are usually anecdotal. Optimally, sports medicine providers and strength and conditioning coaches should be informed of the potential benefits and risks of the skating treadmills.

Although skating treadmills can be used to train forward and backward skating, 60–80% of the skating in a hockey game involves turning by gliding and crossovers (²). To facilitate off-ice crossover simulation, a 22-foot polyethylene motorized disc (called a flywheel) with controllable speed and incline was developed to train skaters performing forward and backward crossovers in clockwise and counterclockwise directions (Figure 1: Competitive Edge Hockey, http//www.hattrickarena.com/page/show/77918). Our preliminary kinematic analysis was a pilot test to compare on- and off-ice skating crossover technique. Participants were 5 Division III college hockey players who were not trained on crossovers during the pilot described. (⁵) Participants were briefly instructed in the testing procedure, introducing them to the Borg Rate of Perceived Exertion Scale (¹), and had time to warm up before being tested. Rate of perceived exertion (RPE) during the pilot showed RPE averaging 10 (on a scale of 6–20), corresponding to a heart rate of 100 b·min⁻¹ skating crossovers on ice, compared with 12.8 RPE, corresponding to 128–130 b·min⁻¹ skating crossovers on the flywheel (¹).

Figure 1: Hockey crossover flywheel.

Critical stride components measured on ice and on the flywheel were (a) point of maximum extension of the outside leg (crossover leg), (b) point of contact of outside leg (after crossover), (c) point of maximum extension with inside leg, and (d) point of contact with inside foot. As flywheel speed and incline increase, it is necessary for skaters to increase their stride rate (⁵). To determine the angles of inclination for the flywheel, the following formula was used by the flywheel developer/trainer:

. Greater lean on ice was attributed to low friction coefficients and centrifugal and centripetal forces (Figure 2). The angles of hips, knees, and ankles of participants skating on the flywheel were more vertical than when skaters performed crossovers on ice (^5,6); however, no injuries were reported. Incorporating what was learned from the pilot study, the present study was designed to compare the benefit of training crossovers on ice to training crossovers on the skating flywheel. Current climate changes limiting outdoor ice, the growth of hockey in southern states, and the overall expense of on-ice practice limit the opportunity for individual, instructive on-ice practice. Flywheel training facilitates an environment conducive to direct coach-player interaction and feedback, which is difficult to mimic in a full-team on-ice setting. Thus, if the flywheel enhances performance of crossovers, it would be a viable alternative to training on ice. Hypothesized was that the training crossovers on the flywheel would provide a benefit comparable to on-ice training.

Figure 2: Skating kinematics on-ice and off-ice (flywheel).

Methods

Experimental Approach to the Problem

Three groups of hockey players were studied: those performing crossover training on the motorized flywheel (group 1), those performing on-ice crossover training (group 2), and the control (group 3). The study started 2 weeks after the conclusion of the Minnesota State High School Hockey Tournament. Testing was conducted before and after 9 training sessions for the intervention groups. The control group was asked to not train specifically for crossovers during the 3 weeks between pretraining and posttraining testing. Players in group 1 and 2 were asked to train their crossovers on the surface to which they were assigned, at maximum speed and exertion during their scheduled sessions. Groups 1 and 2 were instructed by competent coaches versed in proper crossover skating mechanics. Groups were matched for number of sessions and the work-rest ratio. Dependent variables were speed and cadence of skating crossovers and the time required to complete the Repeat Ice Skating Test (RIST) (Figure 3). (¹⁰) Independent variables were the training groups: group 1 (flywheel), group 2 (on-ice), and group 3 (control).

Figure 3: Repeat Ice Skating Test (RIST) outline.

Subjects

Funding and institutional review board approval was obtained. One investigator (A.M.S.) contacted athletic directors, coaches, parents, and high school hockey players to identify those eligible, explain the study, and arrange to obtain informed consent from players and parents. Players were eligible to participate in the study if they were male high school hockey players who were expected to play the next hockey season. Players were excluded from participation if they (a) had a medical issue that restricted participation in high school hockey or in this study or (b) if they had a current injury that would preclude them from participating in 2 testing and 9 training sessions during the designated 3-week period. Some study participants were also involved in spring sports such as baseball and lacrosse during the study period. Initial study participants were 23 high school players, 8 of whom comprised group 1. One player from group 2 did not complete the study beyond pretesting; thus, the sample size for subsequent training and testing was 22. Players of group 1 were from 2 high schools and homes within 40 miles of the flywheel training facility. Their proximity to the facility increased the likelihood of them attending all 9 training sessions. Fifteen players from high schools and homes in proximity to the testing and on-ice training facilities (90 miles further south) were randomly assigned to on-ice training (group 2) and a control group (group 3). The players were offered a $200.00 stipend for their participation, payable after completion of the study. All parents provided consent, and all players signed informed consent. The subject demographics and their hockey characteristics are depicted in Tables 1 and 2.

Table 1: Demographic characteristics (N = 22 participants).

Table 2: Hockey-specific subject characteristics (N = 22 participants).

Procedures

The flywheel group (n = 8) wore safety harnesses, helmets, gloves, freshly sharpened skates, and carried sticks while training against increased velocity and incline on the flywheel. The on-ice group (n = 7) wore helmets, gloves, skates, and carried their sticks during training. All 3 groups were attired in this manner for pretesting and posttesting. Both the groups trained in 9 similarly structured sessions skating forward crossovers in both directions. One hour of time was booked for each of the 9 on-ice training sessions. The on-ice training minutes were supervised by a co-investigator, who was also a hockey coach (D.A.K.). The on-ice and flywheel minutes were matched as closely as possible between the experimental groups. For those training on the flywheel (group 1) the skaters met with the owner and trainer 9 times between the 2 testing sessions. Slope and speed were adjusted as each individual adapted. Both training groups were asked to follow, as closely as possible, a 1:3–4 work-rest ratio. On-ice testing and training rotated between corner face-off circles to ensure that the ice surface was as consistent as possible. Zamboni machines resurfaced the ice on request, and drinking water was made available at both venues.

Tests and Measures

The order of testing for on-ice measures was kept the same throughout. For example, player 3 would always follow player 4 for each round. This allowed for as close to a full rest cycle as possible.

1. Demographic characteristics of height, weight, and vital signs were obtained, and perceived competency ratings were surveyed. Weight was measured using a Seca Delta Model 707 (maximum weight of 200 kg and a minimum of 5 kg [0.45 kg·lb⁻¹]; Seca, Hanover, MD, USA). Height was measured using the SECA instrument (recorded in cm [2.54 cm·in⁻¹]). Vital signs (blood pressure and pulse rate) were obtained using an automatic blood pressure machine similar to the Welch Allyn model (www.welchallyn.com). A variety of cuff sizes were on hand, and arms of the players were sized appropriately.
2. The RIST is a hockey-specific on-ice test of anaerobic power (¹⁰). Players warmed up before skating 3 sprints from center ice, behind the net, and back the other side. See the Repeat Ice Hockey Skating Test—A coach's guide to conducting the Repeat Ice Skate Test for minor hockey players, produced by the Play it Cool Team (Power A. October 2010). In accordance with the RIST guide, players rested for 10 seconds between sprints, and their carotid pulse rate and RPE were recorded before the first and after the third sprints. Participants rested for 20 minutes before repeating the RIST. Pretesting and posttesting of the RIST were completed 3 weeks apart. Verbal encouragement was provided to all skaters during the RIST.
3. Speed of crossovers: players had 4 or 5 strides skating on the face-off circles before setting their optimal fast pace. An optimal fast pace was defined to the player as being the stride rate at which the player felt he was performing crossovers quickly while adhering closely to the outer line of the face-off circle (skating on the edge of their “comfort zone”). A verbal “start” coincided with timing of 3 laps in both directions.
4. Cadence of crossovers: after resting, skaters again established their optimal fast pace around the face-off circle. The metronome was used to record a player's pace or rhythm. The click of the metronome was set to match the crossover foot touchdown and required having the skater complete 3–5 laps to ensure it was synched to the best of our ability. Cadence served as our measure of stride rate to ensure speed was not accomplished by a few quick strides followed by gliding.

Format for Testing

On both pretesting and posttesting days, players in group 1 boarded a bus, contracted by the investigators, at the Flywheel Training Facility (Rogers, MN, USA) at 6 AM and were driven to Rochester (MN, USA). Food (fruit and bagels) and beverages (water) were provided. The bus ride was almost 2 hours. Participants met the co-investigators and research assistants at the testing facility on 2 Saturdays, 3 weeks apart at 8 AM. Water, juice, and bagels were available, and a sandwich lunch was provided at noon. On the first testing day, the demographics, weight, height, and vital signs were obtained, and on both testing days, on-ice measures were completed and the players were dismissed by 2:30 PM. Group 1 was returned to Rogers by bus.

Statistical Analyses

The accepted level of significance was p ≤ 0.05 (¹²). An analysis of variance model was used to evaluate differences in the speed or cadence of crossovers to the left or right between groups or testing times. The speed of crossovers was analyzed, and pulse rates and RPE scores were tracked. The reliability of the RIST was assessed by calculating the intraclass correlation coefficient between the 2 sets of times (6 trials) on 1 day of testing. The coefficient of repeatability was also calculated as an additional measure of reliability.

Results

The mean values, SDs, and level of significance (¹²) for pretesting and posttesting of cadence and speed of crossovers in both directions, left and right, in addition to the RIST by groups are depicted in Table 3.

Table 3: Cadence, speed, and repeat Ice skating test scores by group during pretesting and posttesting.

The cadence at which players performed crossovers to the left was also examined for time between groups (F = 4.00, p = 0.06) and testing time × group (F = 0.756, p = 0.483). The cadence of crossovers to the right was measured for time (F = 1.91, p = 0.183) and for time × group (F = 1.25, p = 0.31). The RIST times were tested between groups and within groups. Speed of crossovers was examined between groups going both to the left for time (F = 1.19, p = 0.29) and time × group (F = 1.48, p = 0.25). Speed (time in seconds) was also examined skating crossovers to the right (F = 6.92, p = 0.016) and between time × group (F = 5.19, p = 0.016).

The mean time for the RIST on pretesting for the 8 skaters in group 1 (flywheel) was 8.98 (SD = 0.30) seconds, for 7 skaters in group 2 (on-ice) was 8.99 (SD = 0.44) seconds, and for group 3 (control) for 7 skaters was 8.99 (SD = 0.33) seconds. Posttesting scores were as follows: 8.93 (SD = 0.25) seconds for group 1, 8.99 (SD = 0.41) seconds for group 2, and 8.67 (SD = 0.56) seconds for group 3. Pulse rates (in beats per minute) and RPE (¹) scores related to the trials on the RIST are depicted in Table 4.

Table 4: Results of the 3 RIST testing trials of high school hockey players.^*

The intraclass correlation coefficient between the 2 sets of times on the pretraining RIST (N = 23) was 0.79, the 95% confidence intervals (CIs) ranged between 0.383 and 0.921, and the coefficient of repeatability was 1.437 (¹²). This was calculated by taking 1.96 times the SD of the difference between the 2 measurements, which in this study was based on time in seconds. Although statistical differences were not noted according to the group, 4 (50%) of the flywheel-trained players (group 1) improved on the objective RIST posttest in both sets. (¹⁰) Because the flywheel was a new training device being evaluated, subjective comments regarding perceptions of the participants were invited. All 8 players in group 1 reported improvement in their crossovers (range of perceived improvement was 16–91%), and 73.3% thought that the flywheel was a better workout than on-ice training. Of these 8 hockey players, 81.6% would recommend it, and 80.4% would pay to use it.

Discussion

The fact that there were no significant differences in speed or cadence of crossovers to the left or right between groups or testing times provided partial support for our hypothesis. However, when speed of crossovers to the right was analyzed by time and group, an interaction showed that the on-ice training group and the control group improved (F = 5.196; p < 0.02). In general, players training on the flywheel (group 1) performed as well as those training on-ice (group 2), despite the lack of opportunity for group 1 to reacclimatize to a different surface for on-ice testing. Although subjective feedback is not always valued, it is important to recognize that subjects in this research study averaged 12.5 years of hockey experience. Their positive feedback about the flywheel training experience to nonbiased investigators should be considered.

Including the RIST to measure anaerobic capacity in a high school, hockey study is important. For many years, ice hockey players competing for selection at a variety of participation levels, such as national and international teams, are tested for anaerobic power using the Wingate test, performed on a bicycle ergometer. Although the Wingate (¹¹) is appropriate for cyclists, its relationship to a skating sport performed on ice has long been questioned (⁹). When the RIST was compared with the Wingate test (in watts), it had a correlation of R = 0.91 (95% CI = 0.76–0.97), and when compared with the vertical jump, the correlation was R = 0.78 (95% CI = 0.47–0.92) (¹⁰). Thus, while the RIST has shown test-retest reliability in Bantam ice hockey players (¹⁰), it had never been studied in high school hockey players. Therefore, these testing sessions provided an opportunity to obtain data and establish reliability of the RIST in this level of participation. Additionally, we were able to use the RIST as a measure of speed to evaluate the effectiveness of flywheel vs. on-ice training. The 2 tests are completed with only a 20-minute rest period and the heart rate, RPE, and times per trial reflect some fatigue. Use of the RIST in testing the anaerobic power of hockey players should be encouraged, as accumulation of data at all levels of participation can be used to contribute to its validity.

It is important that in the pilot test, when hockey players of both genders were tested on ice and on the flywheel (N = 5), no injuries were reported. Furthermore, no injuries were reported during this study in the 9 training sessions or during the 2 testing periods (N = 22).

Cadence, an indicator of stride rate, was slightly faster after 3 weeks of training for group 1 (pretesting mean = 65.4 [SD = 20.2] stride rate per minute vs. a posttesting mean of 68.4 [SD 6.5]) strides per minute. Important also are the smaller SDs accompanying the faster stride rates. The demand of the incline (angle) and speed of the flywheel require a quicker skate turnover, resulting in greater physiological expenditure. These subtle changes suggest that future studies of less mature and less accomplished players may find the flywheel to be an adjunct for training “quick feet.” As a result, younger players may also demonstrate larger delta (change) scores when studied.

The study has several limitations:

• The high school players had played hockey on average 12.5 years. Investigators, after seeing the enrolled study participants skate, anticipated that a margin for improvement might be small, as a result of elevated skill level of those enrolled.
• The flywheel group (group 1) and the on-ice group (group 2) both completed 9 training sessions, the final session for both groups being the night before posttesting.
• Group 1, after training the night before posttesting, boarded a bus at 6 AM to ride to the 8 AM posttesting site 125 miles away. This group had only 10 minutes to adjust from 9 flywheel training sessions to skating on ice (a low friction coefficient) before being tested on the RIST and then on the speed and cadence of their crossovers.
• Group 2 completed 9 sessions on the face-off circles they were tested on and lived a short distance away from the testing and training facility.
• Female players were not included and the sample size was fairly small. Budget limitations restricted sample size and dictated the lack of female players.
• The short window of time that these athletes had between sports and extracurricular activities, limited the feasible testing dates available.

Practical Applications

Indoor ice time is expensive for individual practice ($150 per sheet per hour in Rochester, MN, USA) and outdoor ice time is increasingly less available. The players who trained on ice in the same manner as they were tested did not improve significantly, in part, because of our small sample sizes and to a small margin for improvement in each of the 3 groups. This result suggests that in accordance with the subjective player feedback of group 1, the flywheel may be of comparable value in crossover training to on-ice training. The improvements posited may have been better supported by objective measures had investigators scheduled posttesting after flywheel-trained players rested and had a session or 2 to acclimate before on-ice testing.

Ice hockey has long been without a sport-specific (skating) test of anaerobic power. The RIST (¹⁰) was used in these high school hockey players in 2 ways. The first was to compare the results of set 1 and set 2, both obtained during pretesting to establish reliability for the RIST in high school age hockey players. The second way was to compare the speed of 6 trials skated during pretesting to the 6 trials skated during posttesting to determine if significant differences in times existed between the 3 groups. As such, reliability data were obtained for the high school hockey level of participation, demonstrating its utility for coaches and conditioning managers of high school hockey players. According to the Play it Cool manual (interactive education program used in Canadian minor hockey), the RIST, which also measures anaerobic power (in watts) only requires 30 minutes of practice time per set. Another advantage to the RIST for hockey coaches and trainers is that while hockey players are being tested, they are simultaneously involved in a sport-specific training session.

The use of a metronome and the decision to measure cadence was novel. It is a difficult task and requires 2 persons. Hockey experts often attribute success on ice to quick feet, while maintaining stride efficiency, comprising stride length and stride power. The method used to measure stride rate, in terms of the effectiveness of a metronome could certainly be debated. Our rationale was to prevent reliance solely on timed speed that could potentially have been accomplished by a stroke and glide or a power turn. Experienced coaches may want to critique this measure. Alternatively, the slight improvement in cadence on ice in the flywheel group (the flywheel requires a faster stride rate) may provide support for our decision.

Of interest was that players in the control group, who did not train specifically on crossovers, performed as well as the 2 intervention groups. Perhaps, the control group demonstrated the benefit of fresh legs, whereas the 2 experimental groups were tested inadvertently on tired legs. Although admittedly a subjective finding, the 8 high school players who trained 9 times on the skating flywheel believe they improved and appeared strong and competent. In small samples, all it takes is 1 player skating on an inexpedient angle to offset the hard earned gains of a group who had trained in either of the experimental groups. Health care providers and coaches may want to know that participants in group 1, who trained on the flywheel, would pay to use it and would recommend it to their coaches. A coach monitoring a player on the flywheel is able to focus all attention on the individual skater and provide constant feedback during a training session. On-ice practices often involve a high player to coach ratio, limiting the interaction a coach has with a player, and therefore decreasing the amount of constructive feedback a player receives. Future studies, on larger samples, ideally of hockey players who may have a larger window for improvement, using methods similar to those used in this preliminary investigation are needed to determine if these perceptions are valid. Barriers to obtaining individual ice for practice of crossovers are the expense and the increasingly limited outdoor ice availability.

Acknowledgments

The authors express their appreciation to USA Hockey and to the Orthopedic Research Review Committee, Mayo Clinic, for their financial support of this project. The authors thank Sophie Harrison for her assistance in preparing the manuscript. They also express their appreciation to Moira McPherson, PhD and Carlos Zerpa, MEd at Lakehead University, Thunder Bay, Ontario, Canada, for their contributions to the pilot study that preceded this work.