Sports Biomechanics
ISSN: 1476-3141 (Print) 1752-6116 (Online) Journal homepage: http://www.tandfonline.com/loi/rspb20
Skating mechanics of change-of-direction manoeuvres in ice hockey players Antoine Fortier, René A. Turcotte & David J. Pearsall To cite this article: Antoine Fortier, René A. Turcotte & David J. Pearsall (2014) Skating mechanics of change-of-direction manoeuvres in ice hockey players, Sports Biomechanics, 13:4, 341-350, DOI: 10.1080/14763141.2014.981852 To link to this article: http://dx.doi.org/10.1080/14763141.2014.981852
Published online: 24 Nov 2014.
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Date: 17 October 2017, At: 07:37
Sports Biomechanics, 2014 Vol. 13, No. 4, 341–350, http://dx.doi.org/10.1080/14763141.2014.981852
Skating mechanics of change-of-direction manoeuvres in ice hockey players ANTOINE FORTIER, RENE´ A. TURCOTTE, & DAVID J. PEARSALL Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada
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(Received 17 June 2013; accepted 25 October 2014)
Abstract Ice hockey requires rapid transitions between skating trajectories to effectively navigate about the ice surface. Player performance relates in large part to effective change-of-direction manoeuvres, but little is known about how those skills are performed mechanically and the effect of equipment design on them. The purpose of this study was to observe the kinetics involved in those manoeuvres as well as to compare whether kinetic differences may result between two skate models of varying ankle mobility. Eight subjects with competitive ice hockey playing experience performed rapid lateral (908) left and right change-of-direction manoeuvres. Kinetic data were collected using force strain gauge transducers on the blade holders of the skates. Significantly greater forces were applied by the outside skate (50 – 70% body weight, %BW) in comparison to the inside skate (12 – 24%BW, p , 0.05). Skate model and turn direction had no main effect, though significant mixed interactions between leg side (inside/ outside) with skate model or turn direction ( p , 0.05) were observed, with a trend for left-turn dominance. This study demonstrates the asymmetric dynamic behaviour inherent in skating changeof-direction tasks.
Keywords: Ankle mobility, turns, kinetics, agility, skate design
Introduction Studies of ice skating mechanics have focused primarily on kinematic variables corresponding to performance of forward skating tasks (Marino, 1977; Upjohn, Turcotte, Pearsall, & Loh, 2008), and yet in skating, as in other forms of physical activity study, the measurement of ground reaction forces (GRF) is equally as important to understand the mechanical interactions necessary to successfully perform various movement techniques. Obtaining direct kinetic measurements in an ice environment, however, can be quite challenging from a technical perspective; the development of a means to quantify dynamics in this environment, therefore, is necessary to enhance the ability of researchers to explain skating mechanics. Few previous studies have attempted to capture skating dynamics. In a study examining push-off manoeuvres with a regular hockey skate on a force plate, Sim and Chao (1978) reported GRFs of 1.5 –2.5 times the body weight (BW), with a backward push off force of approximately 688 N and a lateral force of approximately 353 N. With regard to measures on Correspondence: David J. Pearsall, Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, Quebec, Canada H2W 1S4, E-mail: [email protected] q 2014 Taylor & Francis
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ice, Gagnon, Dore´, and Lamontagne (1983) and Lamontagne, Gagnon, and Dore´ (1983) demonstrated the feasibility of estimating GRFs using strain gauge force transducers attached to the skate blade, reporting ice maximum GRFs during parallel stops of more than 900 N. To overcome the latter system’s limited range for skating movement, speed skating researchers developed a portable strain gauge chassis placed between the skater’s boot and blade that estimated force and frictional properties while skating unrestricted about the open ice surface (de Boer et al., 1987; de Koning, de Groot, & van Ingen Schenau 1992; Jobse, Schuurhof, Cserep, Wim Schreurs, & de Koning, 1990). The measurement chassis, however, substantially disrupted and added weight to the original skate design. More recently, a portable and non-destructive strain gauge force transducer approach was developed for the collection of GRFs in forward skating for ice hockey (Stidwill, Pearsall, Dixon, & Turcotte, 2010) that allowed for unencumbered skater movement and accurate force vector estimates. Adopting this measurement approach, Robert-Lachaine, Turcotte, Dixon, and Pearsall (2012) could detect force increases related to decreased ankle boot stiffness during forward skating tasks. The investigation of the dynamics of other skating skills is warranted; in particular, change-of-direction agility tasks. As agility is paramount in a player’s ability to outmanoeuvre the opponents, these tasks are fundamental to the game of ice hockey. There are many variations of change-of-direction tasks but common to all is the ability to effectively change one’s speed and movement heading to evade and/or obstruct the opponent’s movements. Much is unknown with regard to the specific dynamics required for these tasks, let alone the impact of increased foot and ankle complex stiffness on skating dynamics. Theoretically, asymmetric bi-lateral forces (both medial versus lateral forces, and left and right foot normal forces) need to occur to generate the impulse to change the direction over ground. To what extent does this occur when moving on ice? Further, do skaters favour turn directions by way of generating greater skate dynamic? In terms of practical applications, understanding these key mechanical traits for proficient change-of-direction tasks may enhance coaches’ skill development in young players. Hence, the purpose of this study was to examine, first, the bilateral GRF dynamics during rapid 908 change-of-direction tasks in both left and right directions and between both skates (inside and outside to the turn radius), and second, the effect of a planned skate design change (i.e. decreased plantar-dorsi flexion boot stiffness about the foot – ankle complex) on these dynamics. It was hypothesized that turn direction as well as the skates’ position within the turn (i.e. inside versus outside) would result in asymmetric kinetic differences. Conversely, the design change in skate boot stiffness was not expected to alter the mediolateral stability of the foot – ankle complex and thus the GRF dynamics would not differ from the conventional skate model.
Methods Participants Eight adult male hockey players participated in this study (24.1 ^ 2.6 years, 77.5 ^ 8.1 kg; seven forwards and one defence). Prior statistical power analysis identified a minimum of six participants were needed to discriminate differences of 10%BW. Participants’ competitive level ranged from recreational to Midget ‘AAA’ and had a large amount of playing experience (17.1 ^ 3.6 years). The study was approved by the McGill University Research Ethics Committee. Each participant completed and signed an informed consent document before testing.
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Instrumentation Before testing, the strain gauge force transducer measurement system had to be assembled to the respective skate models. Once this was completed, it had to be combined to a data recording system and calibrated (Figure 1A). The following are the steps that were taken to complete these requirements. Five force transducer strain gauges were placed (350 V, 0.3175 cm; Vishay, Malvern, PA, USA) in five strategic locations on the front post, the rear post, and the mid-beam of the blade holder. The gauges were connected to bridge circuits through connective wires with sufficient length so that once trials began movement was not inhibited in any way. This configuration allowed the collection of ice reaction forces based on the strain in the vertical and mediolateral directions of the blade holder (Figure 1B). This configuration has been proven to be effective at collecting kinetic on-ice data (Stidwill et al., 2010). In terms of mediolateral forces, a positive %BW value represents a force value towards the lateral side of the skate blade, whereas a negative value represents a force value towards the medial side of the skate blade (Figure 1C). The skate models that were used for this study were an unmodified (regular) and modified version of the Nike-Bauer Supreme One95 skate. These skate models were identical except for the modified skates’ having a more flexible Achilles guard, an elastic tongue and higher lacing eyelets. In terms of performance, the skates were sharpened by stone grinding to hollow radii of 3/8 – 1/2 inch (0.95 – 1.27 cm) before each testing period and methods to ensure optimal blade sharpness could be taken in future studies as blade design and sharpness do affect the performance of change-of-direction manoeuvres (Federolf, Mills, & Nigg, 2007). Data for this study were collected at 100 Hz using a portable 13-bit analog-to-digital data acquisition system (DataLOG P3X8, Biometrics Ltd, Gwent, UK). The DataLOG was used to provide voltage (2 V ^ 2%) to force transducer strain gauge circuits. The data were then stored in .RWX format to a flash memory card (MMC 32 MB, Kingston Technology, Fountain Valley, CA, USA) that was inserted inside the DataLOG before testing. The measurement output range was set to 10 mV with a resolution of 0.0025 mV.
Figure 1. Strain gauges were adhered to the skate blade holder (a) with wire leads directed up to a 15-pin connector to (b) to the bridge circuit box (c) and portable DataLOG digital acquisition device (d) (A). The strain gauges were position to measure mediolateral and vertical forces with respect to skate (B, C).
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After placing the strain gauges on the skate blade holder, to convert micro-strain voltages to force estimates, controlled static forces were applied simultaneously through the skate onto a force plate (Stidwill et al., 2010). To generate consistent vertical forces, a surrogate foot placed within the skate was loaded by means of a lever up to 1000 N. For the mediolateral force calibration of the skate, the skate blade was placed along the force plate with the medial side of the skate facing downwards for the medial calibration in the front and rear post strain gauge arrays, followed by placing the lateral side of the skate facing downwards on the force place for the lateral calibration.
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Protocol Participants were asked to wear comfortable sports clothing in order to perform the changeof-direction tasks with as little encumbrance as possible. Participants were given appropriate skates sizes. The wire bundles from the gauges were passed through the inside of their pant legs to avoid being tangled during testing. The pin connectors of the wire bundles for the left and right skate were then plugged into their respective bridge circuits and in turn to the DataLOG unit. This unit (about 1.7 kg) was carried in a backpack worn by the participants during testing (Figure 1). Skaters were also provided with a hockey helmet, gloves, and a hockey stick to their shooting side. Two pairs of cones were placed on the ice, one pair at one end of the blue line and the other 1 m behind the opposite blue line (Figure 2). Participants were given approximately 10 min to warm up with their respective pair of instrumented skates and backpack. Prior to testing data, the strain channels of both left and right skates were set to zero in the DataLOG while non-weight bearing, followed by full weight bearings measures. The change-of-direction tasks performed by the participants were as follows. Behind one of the two sets of cones, after the DataLOG had been started, the researcher signalled for the participant to start. The skater accelerated as fast as possible towards the turning point, identified by a cone (Figure 2). The participant was instructed to fully stop forward progression, before accelerating 908 towards the left or right side (predetermined before the trial). This change-of-direction execution pattern was chosen to simulate one common technique used in a hockey game. This was controlled with post-task video analysis of each trial. The participant then stopped the DataLOG unit data collection by pressing the external trigger. Each skater performed three consecutive change-of-direction trials both towards the left and right sides for each skate model type starting with the regular skates first. Demonstrations of the tasks were given by one of the testers (an experienced hockey player) before testing commenced. If the participants showed signs of high fatigue, they were given a 2-min rest period before starting the next trial. After every three trials collected, the participant returned to the bench and the MultiMediaCard (MMC) flash card inside the DataLOG unit was temporarily taken out of the DataLOG unit to be placed inside the MMC reader connected to a laptop computer (ThinkPad X201, Lenovo Canada, North York, Ontario, Canada) to be viewed in the DataLOG Software (v.3.0; Biometrics Ltd). Once data for one skate model had been collected, the participant changed skate models and repeated the same test protocol. Each skater was given ample time to rest in between skate trials. Analysis The start point of each change-of-direction manoeuvre was determined by the end of the skating strides and the beginning of the stopping manoeuvre as shown by the force data in the
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Figure 2. Sequence of left- and right-turn direction at the cones. Note inside and outside leg defined with respect to the turn direction.
post-processing phase (Figure 3). The end point of each manoeuvre was determined as just before the skater recommenced his skating strides. Because prior investigation (RobertLachaine et al., 2012; Stidwill et al., 2010) looked primarily at the forward skating stride portion of the data, the focus of this study was directed primarily at the forces generated during the change-of-direction manoeuvre. The average force of each leg for each task was calculated by the sum of forces over the duration of the task (start and end). The sampling rate was set at 100 Hz and force values were rescaled to body weight percentage (%BW). The dependent variables included the peak vertical, mediolateral, and total force magnitudes during each change-of-direction manoeuvre, as well as contact time and impulse estimates. Statistical analysis used three-way MANOVAs with the main factors being turn direction (left and right), skate model (regular and modified), and leg side (inside and outside with respect to turn axis). Statistical significance was set at a ¼ 0.05 and Bonferroni post hoc tests were performed when indicated. All statistical analyses were performed using SPSS (v.17, IBM, Chicago, IL, USA). Results In general, small differences between skate models ( p ¼ 0.683) were observed, with average forces of 49.9 ^ 15.4%BW and 46.3 ^ 21.0%BW, respectively, for the regular and modified skates worn. Left-turn directions tended to show greater average forces than right turns (52.1 ^ 19.7%BW and 44.0 ^ 15.9%BW, respectively), though not statistically different
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Figure 3. Example processing of sample data set for a left turn using the modified left skate model.
( p ¼ 0.065). Conversely, leg side (i.e. inside versus outside with respect to the rotation axis) was shown to have a significant main effect on average normal forces (62.9 ^ 7.4%BW versus 33.2 ^ 6.5%BW, respectively). Furthermore, significant interactions between leg side and skate model ( p , 0.01) and leg side and turn direction ( p , 0.001) were noted (Table I). The latter interactions were generally manifest as lower forces for right turns in combination with skate model or leg side than left-turn combinations (Table I). Similar observations were found for total impulse, given that contact times were relatively constant (1.00 – 1.10 s). In general, the inside skate blade pressed medially eliciting a lateral reaction force, while the inverse occurred for the outside skate blade (i.e. medial reaction force). The outside blade’s forces were approximately twice as large as on the inside blade, though both were much lower than the magnitude of average vertical forces (1 –27%BW). Similar trends were
23.7 ^ 6.3 3.9 ^ 0.9 37.2 ^ 13.7
60.5 ^ 3.7* -9.7 ^ 5.4* 62.5 ^ 10.3*
Outside 18.4 ^ 4.4 9.3 ^ 3.3 29.2 ^ 1.9
Inside 62.1 ^ 7.8* -19.5 ^ 3.6* 63.4 ^ 1.8*
Outside
Modified modela
23.6 ^ 4.9 4.0 ^ 4.4 30.4 ^ 4.9
Inside
54.0 ^ 2.2* -7.9 ^ 7.4 57.6 ^ 10.3*
Outside
Right turnb
18.4 ^ 5.7 9.2 ^ 2.1 36.0 ^ 6.9
Inside
68.7 ^ 9.4* -21.3 ^ 1.6* 68.3 ^ 1.7*
Outside
Left turnb
Note: Leg side was identified to have significant interactions with both skate model and turn direction. *Significantly different from the inside condition ( p , 0.05). a Turn conditions pooled; b Model conditions pooled.
Average force (%BW) Vertical Mediolateral Total impulse (%BWs)
Inside
Regular modela
Table I. Force and impulse measures by skate model and turn direction (M ^ SD).
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observed for both front and rear posts of the blade holder. In general, these mediolateral forces were not substantially different between skate models.
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Discussion and implications Several significant main effects for turn direction and skate side were noted. In addition some significant interaction effects between model and turn direction, as well as turn direction and skate side were identified, though not consistently observed across all factor combinations. Turn direction had a significant effect on force magnitudes; in general, left turns yielded higher outside leg forces than right (, 4%BW to 10%BW). This could be explained by the fact that all subjects were noted as being right leg dominant, which could affect their confidence to apply forces during a turn in the left direction where the outside limb would be the right leg. A study observing the reaction forces between dominant and non-dominant legs of recreational athletes (who were right leg dominant) during drop landing to cutting manoeuvres also found the kinetics to be greater during cutting in the left direction (Rosado, 2006). These turn asymmetry findings are similar to another non-skating change-ofdirection study where during over-ground speed tests subjects who possessed significantly greater reactive strength in the right leg executed faster change-of-direction manoeuvres in the left direction (Young & Farrow, 2006). Another study identified subjects’ GRFs as being 41.4% greater in their dominant limb than in their non-dominant limb during ground-based cutting manoeuvres (Cowley, Ford, Myer, Kernozek, & Hewett, 2006). We can speculate then that for hockey players in a game situation, right leg-dominant players may be more inclined to perform a change-of-direction manoeuvre in the left direction because of the confidence to apply forces in that direction, which would lead them to favour certain positions on the ice, that is being a right or left wing player. Significant differences were found between skate leg sides; that is, the outside leg carried greater forces (, 51%BW to 70%BW), compared with the inside leg (, 12%BW to 24% BW). These findings are similar to a study observing forces and path radius of turning in downhill skiing as the forces carried by the foot of the outside ski were found to be greater than forces carried by the foot of the inside ski (Yoneyama, Scott, Nagawa, & Osada, 2008). Another downhill skiing study had similar findings for GRFs; that is, during the turning and ploughing tasks, whenever the foot was on the outside of the turning phase during kinetic measures were seen to be greater than when it was on the inside of the turning phase (Nakazato, Scheiber, & Mu¨ller, 2011). What was also observed from the corresponding video log trials of each change-of-direction task is that the skate to be first placed on the outside was followed rapidly (, 40 ms) by the inside skate, which was placed adjacent and parallel to the other. During the time of the change-of-direction task when both skates are in full contact with the ice (, 1.0 s), the skates pivot and plough under the player so as to point towards a new direction of travel followed by the inside skate moving forward in tandem with the outside skate towards the end of the task. The inside skate is then lifted and quickly stepped towards the turn direction immediately before the end of the changeof-direction task. In general, skate model (regular versus modified) did not significantly affect either the vertical or mediolateral forces. This was surprising, given the prior findings by RobertLachaine et al. (2012) the modified skate demonstrated modest yet significant force increases during forward skating tasks. However, considering the intent of the modified skate design was solely to enhance plantar-dorsi flexion range of motion (in the sagittal plane of the ankle complex) without foregoing side-to-side stiffness (in the frontal plane)
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the differences in force outcomes between studies is reasonable; that is, both skate models provided the same mediolateral stability during these particular change-of-direction manoeuvres. Further study with more participants is warranted to determine whether the main and interaction effects consistently present. Several limitations of this study exist. Though all subjects successful executed the same defined change-of-direction manoeuvre, the specific movement technique employed by subjects varied; for example, from video logs, subjects displayed differences in the relative inside – outside skate positions during the task (varying from tandem to adjacent) that in turn may modify their respective kinetic bearing. Other questions remain: For examples, to what extent these findings extend to other change-of-direction manoeuvres? How representative are these tasks performed in a non-game, pre-planned format to that of an open game format? It is also possible for a long-term habituation effect, due to a player’s possible preferred position, to influence performance of the change-ofdirection manoeuvres which was not controlled for in this study. Because leg dominance appears to be a main issue in the results, a formalized testing methodology to determine the subject’s true leg dominance would be beneficial to the study as well as controlling for leg dominance. Stick side of each subject was noted; however, a method of examining its relationship to the performance of change-of-direction manoeuvres could be developed in a future study. As the first study to examine change-of-direction kinetics in ice hockey, these findings may have coaching implications; for example, the need to enhance these manoeuvres with equal proficiency for both turning directions regardless of leg dominance. The challenge will be to define the coaching cues necessary to elicit greater outside leg force generation during the change-of-direction manoeuvre. Furthermore, the observation that upper boot flexibility (dorsi-plantar flexion) did not compromise the manoeuvre dynamics that refutes the common perception among players that high boot stiffness is required. Conclusion The results demonstrated that the use of a portable strain-gauge force transducer system can be used to assess on-ice change-of-direction manoeuvres in ice hockey. Clear force asymmetry between skate sides was noted during the task. The kinetic strategies seen during skating change-of-direction tasks were similar to other sports such as alpine skiing, rugby, soccer, and basketball. These findings provide a comprehensive understanding of the mechanics of change-of-direction tasks that is relevant to athletic skill development. In addition, the ability to distinguish mechanical performance differences between the two skate models tested further demonstrates the potential of direct force measurement as a sensitive metric to differentiate subtle glide and traction properties fundamental to skating performance. Future studies utilizing this measurement technology to more fully explore the many other skill combinations are warranted. Funding The authors would like to thank Bauer Hockey Corp. for their significant financial and material contributions to the study, as well as Natural Sciences and Engineering Research Council of Canada for their matching financial support as part of the Industrial Partnership Collaborative Research and Development Grant.
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References Cowley, H. R., Ford, K. R., Myer, G. D., Kernozek, T. W., & Hewett, T. E. (2006). Differences in neuromuscular strategies between landing and cutting tasks in female basketball and soccer athletes. Journal of Athletic Training, 41, 67– 73. de Boer, R. W., Cabri, J., Vaes, W., Clarijs, J. P., Hollander, A. P., de Groot, G., & van Ingen Schenau, G. J. (1987). Moments of force, power, and muscle coordination in speed-skating. International Journal of Sports Medicine, 8, 371–378. de Koning, J. J., de Groot, G., & van Ingen Schenau, G. J. (1992). Ice friction during speed skating. Journal of Biomechanics, 25, 565–571. Federolf, P. A., Mills, R., & Nigg, B. (2007). Agility characteristics of ice hockey players depend on the skate blade design. Journal of Biomechanics, 40, S235. Gagnon, M., Dore´, R., & Lamontagne, M. (1983). Development and validation of a method for determining tridimensional angular displacements with special adaptations to ice hockey motions. Research Quarterly for Exercise and Sport, 54, 136–143. Jobse, H., Schuurhof, R., Cserep, F., Wim Schreurs, A., & de Koning, J. J. (1990). Moments of push-off force and ice friction during speed skating. International Journal of Sport Biomechanics, 6, 92–100. Lamontagne, M., Gagnon, M., & Dore´, R. (1983). Development, validation and application of dynamic skate system. Canadian Journal of Sport Sciences, 8, 169 –183. Marino, G. W. (1977). Kinematics of ice skating at different velocities. Research Quarterly, 48, 93–97. Nakazato, K., Scheiber, P., & Mu¨ller, E. (2011). A comparison of ground reaction forces determined by portable force-plate and pressure-insole systems in alpine skiing. Journal of Sports Science and Medicine, 10, 754–762. Robert-Lachaine, X., Turcotte, R. A., Dixon, P. C., & Pearsall, D. J. (2012). Impact of hockey skate design on ankle motion and force production. Sports Engineering, 15, 197–206. Rosado, L. (2006). Impact and push-off force symmetry in dominant versus non-dominant legs during a jump landing/cutting task. McNair Scholars Research Journal, 2, 47– 51. Sim, F. H., & Chao, E. Y. (1978). Injury potential in modern ice hockey. American Journal of Sports Medicine, 6, 378–384. Stidwill, T. J., Pearsall, D. J., Dixon, P., & Turcotte, R. (2010). Force transducer system for measurement of ice hockey skating force. Sports Engineering, 12, 63–68. Upjohn, T., Turcotte, R. A., Pearsall, D., & Loh, J. (2008). Three dimensional kinematics of the lower limb during forward ice hockey skating. Sports Biomechanics, 7, 205 –220. Yoneyama, T., Scott, N., Nagawa, H., & Osada, K. (2008). Ski deflection measurement during skiing and estimation of ski direction and edge angle. Sports Engineering, 11, 2–13. Young, W., & Farrow, D. (2006). A review of agility: Practical applications for strength and conditioning. Strength and Conditioning Journal, 28, 24–29.
ISSN: 1476-3141 (Print) 1752-6116 (Online) Journal homepage: http://www.tandfonline.com/loi/rspb20
Skating mechanics of change-of-direction manoeuvres in ice hockey players Antoine Fortier, René A. Turcotte & David J. Pearsall To cite this article: Antoine Fortier, René A. Turcotte & David J. Pearsall (2014) Skating mechanics of change-of-direction manoeuvres in ice hockey players, Sports Biomechanics, 13:4, 341-350, DOI: 10.1080/14763141.2014.981852 To link to this article: http://dx.doi.org/10.1080/14763141.2014.981852
Published online: 24 Nov 2014.
Submit your article to this journal
Article views: 477
View related articles
View Crossmark data
Citing articles: 1 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=rspb20 Download by: [UQ Library]
Date: 17 October 2017, At: 07:37
Sports Biomechanics, 2014 Vol. 13, No. 4, 341–350, http://dx.doi.org/10.1080/14763141.2014.981852
Skating mechanics of change-of-direction manoeuvres in ice hockey players ANTOINE FORTIER, RENE´ A. TURCOTTE, & DAVID J. PEARSALL Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada
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(Received 17 June 2013; accepted 25 October 2014)
Abstract Ice hockey requires rapid transitions between skating trajectories to effectively navigate about the ice surface. Player performance relates in large part to effective change-of-direction manoeuvres, but little is known about how those skills are performed mechanically and the effect of equipment design on them. The purpose of this study was to observe the kinetics involved in those manoeuvres as well as to compare whether kinetic differences may result between two skate models of varying ankle mobility. Eight subjects with competitive ice hockey playing experience performed rapid lateral (908) left and right change-of-direction manoeuvres. Kinetic data were collected using force strain gauge transducers on the blade holders of the skates. Significantly greater forces were applied by the outside skate (50 – 70% body weight, %BW) in comparison to the inside skate (12 – 24%BW, p , 0.05). Skate model and turn direction had no main effect, though significant mixed interactions between leg side (inside/ outside) with skate model or turn direction ( p , 0.05) were observed, with a trend for left-turn dominance. This study demonstrates the asymmetric dynamic behaviour inherent in skating changeof-direction tasks.
Keywords: Ankle mobility, turns, kinetics, agility, skate design
Introduction Studies of ice skating mechanics have focused primarily on kinematic variables corresponding to performance of forward skating tasks (Marino, 1977; Upjohn, Turcotte, Pearsall, & Loh, 2008), and yet in skating, as in other forms of physical activity study, the measurement of ground reaction forces (GRF) is equally as important to understand the mechanical interactions necessary to successfully perform various movement techniques. Obtaining direct kinetic measurements in an ice environment, however, can be quite challenging from a technical perspective; the development of a means to quantify dynamics in this environment, therefore, is necessary to enhance the ability of researchers to explain skating mechanics. Few previous studies have attempted to capture skating dynamics. In a study examining push-off manoeuvres with a regular hockey skate on a force plate, Sim and Chao (1978) reported GRFs of 1.5 –2.5 times the body weight (BW), with a backward push off force of approximately 688 N and a lateral force of approximately 353 N. With regard to measures on Correspondence: David J. Pearsall, Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, Quebec, Canada H2W 1S4, E-mail: [email protected] q 2014 Taylor & Francis
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ice, Gagnon, Dore´, and Lamontagne (1983) and Lamontagne, Gagnon, and Dore´ (1983) demonstrated the feasibility of estimating GRFs using strain gauge force transducers attached to the skate blade, reporting ice maximum GRFs during parallel stops of more than 900 N. To overcome the latter system’s limited range for skating movement, speed skating researchers developed a portable strain gauge chassis placed between the skater’s boot and blade that estimated force and frictional properties while skating unrestricted about the open ice surface (de Boer et al., 1987; de Koning, de Groot, & van Ingen Schenau 1992; Jobse, Schuurhof, Cserep, Wim Schreurs, & de Koning, 1990). The measurement chassis, however, substantially disrupted and added weight to the original skate design. More recently, a portable and non-destructive strain gauge force transducer approach was developed for the collection of GRFs in forward skating for ice hockey (Stidwill, Pearsall, Dixon, & Turcotte, 2010) that allowed for unencumbered skater movement and accurate force vector estimates. Adopting this measurement approach, Robert-Lachaine, Turcotte, Dixon, and Pearsall (2012) could detect force increases related to decreased ankle boot stiffness during forward skating tasks. The investigation of the dynamics of other skating skills is warranted; in particular, change-of-direction agility tasks. As agility is paramount in a player’s ability to outmanoeuvre the opponents, these tasks are fundamental to the game of ice hockey. There are many variations of change-of-direction tasks but common to all is the ability to effectively change one’s speed and movement heading to evade and/or obstruct the opponent’s movements. Much is unknown with regard to the specific dynamics required for these tasks, let alone the impact of increased foot and ankle complex stiffness on skating dynamics. Theoretically, asymmetric bi-lateral forces (both medial versus lateral forces, and left and right foot normal forces) need to occur to generate the impulse to change the direction over ground. To what extent does this occur when moving on ice? Further, do skaters favour turn directions by way of generating greater skate dynamic? In terms of practical applications, understanding these key mechanical traits for proficient change-of-direction tasks may enhance coaches’ skill development in young players. Hence, the purpose of this study was to examine, first, the bilateral GRF dynamics during rapid 908 change-of-direction tasks in both left and right directions and between both skates (inside and outside to the turn radius), and second, the effect of a planned skate design change (i.e. decreased plantar-dorsi flexion boot stiffness about the foot – ankle complex) on these dynamics. It was hypothesized that turn direction as well as the skates’ position within the turn (i.e. inside versus outside) would result in asymmetric kinetic differences. Conversely, the design change in skate boot stiffness was not expected to alter the mediolateral stability of the foot – ankle complex and thus the GRF dynamics would not differ from the conventional skate model.
Methods Participants Eight adult male hockey players participated in this study (24.1 ^ 2.6 years, 77.5 ^ 8.1 kg; seven forwards and one defence). Prior statistical power analysis identified a minimum of six participants were needed to discriminate differences of 10%BW. Participants’ competitive level ranged from recreational to Midget ‘AAA’ and had a large amount of playing experience (17.1 ^ 3.6 years). The study was approved by the McGill University Research Ethics Committee. Each participant completed and signed an informed consent document before testing.
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Instrumentation Before testing, the strain gauge force transducer measurement system had to be assembled to the respective skate models. Once this was completed, it had to be combined to a data recording system and calibrated (Figure 1A). The following are the steps that were taken to complete these requirements. Five force transducer strain gauges were placed (350 V, 0.3175 cm; Vishay, Malvern, PA, USA) in five strategic locations on the front post, the rear post, and the mid-beam of the blade holder. The gauges were connected to bridge circuits through connective wires with sufficient length so that once trials began movement was not inhibited in any way. This configuration allowed the collection of ice reaction forces based on the strain in the vertical and mediolateral directions of the blade holder (Figure 1B). This configuration has been proven to be effective at collecting kinetic on-ice data (Stidwill et al., 2010). In terms of mediolateral forces, a positive %BW value represents a force value towards the lateral side of the skate blade, whereas a negative value represents a force value towards the medial side of the skate blade (Figure 1C). The skate models that were used for this study were an unmodified (regular) and modified version of the Nike-Bauer Supreme One95 skate. These skate models were identical except for the modified skates’ having a more flexible Achilles guard, an elastic tongue and higher lacing eyelets. In terms of performance, the skates were sharpened by stone grinding to hollow radii of 3/8 – 1/2 inch (0.95 – 1.27 cm) before each testing period and methods to ensure optimal blade sharpness could be taken in future studies as blade design and sharpness do affect the performance of change-of-direction manoeuvres (Federolf, Mills, & Nigg, 2007). Data for this study were collected at 100 Hz using a portable 13-bit analog-to-digital data acquisition system (DataLOG P3X8, Biometrics Ltd, Gwent, UK). The DataLOG was used to provide voltage (2 V ^ 2%) to force transducer strain gauge circuits. The data were then stored in .RWX format to a flash memory card (MMC 32 MB, Kingston Technology, Fountain Valley, CA, USA) that was inserted inside the DataLOG before testing. The measurement output range was set to 10 mV with a resolution of 0.0025 mV.
Figure 1. Strain gauges were adhered to the skate blade holder (a) with wire leads directed up to a 15-pin connector to (b) to the bridge circuit box (c) and portable DataLOG digital acquisition device (d) (A). The strain gauges were position to measure mediolateral and vertical forces with respect to skate (B, C).
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After placing the strain gauges on the skate blade holder, to convert micro-strain voltages to force estimates, controlled static forces were applied simultaneously through the skate onto a force plate (Stidwill et al., 2010). To generate consistent vertical forces, a surrogate foot placed within the skate was loaded by means of a lever up to 1000 N. For the mediolateral force calibration of the skate, the skate blade was placed along the force plate with the medial side of the skate facing downwards for the medial calibration in the front and rear post strain gauge arrays, followed by placing the lateral side of the skate facing downwards on the force place for the lateral calibration.
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Protocol Participants were asked to wear comfortable sports clothing in order to perform the changeof-direction tasks with as little encumbrance as possible. Participants were given appropriate skates sizes. The wire bundles from the gauges were passed through the inside of their pant legs to avoid being tangled during testing. The pin connectors of the wire bundles for the left and right skate were then plugged into their respective bridge circuits and in turn to the DataLOG unit. This unit (about 1.7 kg) was carried in a backpack worn by the participants during testing (Figure 1). Skaters were also provided with a hockey helmet, gloves, and a hockey stick to their shooting side. Two pairs of cones were placed on the ice, one pair at one end of the blue line and the other 1 m behind the opposite blue line (Figure 2). Participants were given approximately 10 min to warm up with their respective pair of instrumented skates and backpack. Prior to testing data, the strain channels of both left and right skates were set to zero in the DataLOG while non-weight bearing, followed by full weight bearings measures. The change-of-direction tasks performed by the participants were as follows. Behind one of the two sets of cones, after the DataLOG had been started, the researcher signalled for the participant to start. The skater accelerated as fast as possible towards the turning point, identified by a cone (Figure 2). The participant was instructed to fully stop forward progression, before accelerating 908 towards the left or right side (predetermined before the trial). This change-of-direction execution pattern was chosen to simulate one common technique used in a hockey game. This was controlled with post-task video analysis of each trial. The participant then stopped the DataLOG unit data collection by pressing the external trigger. Each skater performed three consecutive change-of-direction trials both towards the left and right sides for each skate model type starting with the regular skates first. Demonstrations of the tasks were given by one of the testers (an experienced hockey player) before testing commenced. If the participants showed signs of high fatigue, they were given a 2-min rest period before starting the next trial. After every three trials collected, the participant returned to the bench and the MultiMediaCard (MMC) flash card inside the DataLOG unit was temporarily taken out of the DataLOG unit to be placed inside the MMC reader connected to a laptop computer (ThinkPad X201, Lenovo Canada, North York, Ontario, Canada) to be viewed in the DataLOG Software (v.3.0; Biometrics Ltd). Once data for one skate model had been collected, the participant changed skate models and repeated the same test protocol. Each skater was given ample time to rest in between skate trials. Analysis The start point of each change-of-direction manoeuvre was determined by the end of the skating strides and the beginning of the stopping manoeuvre as shown by the force data in the
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Figure 2. Sequence of left- and right-turn direction at the cones. Note inside and outside leg defined with respect to the turn direction.
post-processing phase (Figure 3). The end point of each manoeuvre was determined as just before the skater recommenced his skating strides. Because prior investigation (RobertLachaine et al., 2012; Stidwill et al., 2010) looked primarily at the forward skating stride portion of the data, the focus of this study was directed primarily at the forces generated during the change-of-direction manoeuvre. The average force of each leg for each task was calculated by the sum of forces over the duration of the task (start and end). The sampling rate was set at 100 Hz and force values were rescaled to body weight percentage (%BW). The dependent variables included the peak vertical, mediolateral, and total force magnitudes during each change-of-direction manoeuvre, as well as contact time and impulse estimates. Statistical analysis used three-way MANOVAs with the main factors being turn direction (left and right), skate model (regular and modified), and leg side (inside and outside with respect to turn axis). Statistical significance was set at a ¼ 0.05 and Bonferroni post hoc tests were performed when indicated. All statistical analyses were performed using SPSS (v.17, IBM, Chicago, IL, USA). Results In general, small differences between skate models ( p ¼ 0.683) were observed, with average forces of 49.9 ^ 15.4%BW and 46.3 ^ 21.0%BW, respectively, for the regular and modified skates worn. Left-turn directions tended to show greater average forces than right turns (52.1 ^ 19.7%BW and 44.0 ^ 15.9%BW, respectively), though not statistically different
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Figure 3. Example processing of sample data set for a left turn using the modified left skate model.
( p ¼ 0.065). Conversely, leg side (i.e. inside versus outside with respect to the rotation axis) was shown to have a significant main effect on average normal forces (62.9 ^ 7.4%BW versus 33.2 ^ 6.5%BW, respectively). Furthermore, significant interactions between leg side and skate model ( p , 0.01) and leg side and turn direction ( p , 0.001) were noted (Table I). The latter interactions were generally manifest as lower forces for right turns in combination with skate model or leg side than left-turn combinations (Table I). Similar observations were found for total impulse, given that contact times were relatively constant (1.00 – 1.10 s). In general, the inside skate blade pressed medially eliciting a lateral reaction force, while the inverse occurred for the outside skate blade (i.e. medial reaction force). The outside blade’s forces were approximately twice as large as on the inside blade, though both were much lower than the magnitude of average vertical forces (1 –27%BW). Similar trends were
23.7 ^ 6.3 3.9 ^ 0.9 37.2 ^ 13.7
60.5 ^ 3.7* -9.7 ^ 5.4* 62.5 ^ 10.3*
Outside 18.4 ^ 4.4 9.3 ^ 3.3 29.2 ^ 1.9
Inside 62.1 ^ 7.8* -19.5 ^ 3.6* 63.4 ^ 1.8*
Outside
Modified modela
23.6 ^ 4.9 4.0 ^ 4.4 30.4 ^ 4.9
Inside
54.0 ^ 2.2* -7.9 ^ 7.4 57.6 ^ 10.3*
Outside
Right turnb
18.4 ^ 5.7 9.2 ^ 2.1 36.0 ^ 6.9
Inside
68.7 ^ 9.4* -21.3 ^ 1.6* 68.3 ^ 1.7*
Outside
Left turnb
Note: Leg side was identified to have significant interactions with both skate model and turn direction. *Significantly different from the inside condition ( p , 0.05). a Turn conditions pooled; b Model conditions pooled.
Average force (%BW) Vertical Mediolateral Total impulse (%BWs)
Inside
Regular modela
Table I. Force and impulse measures by skate model and turn direction (M ^ SD).
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observed for both front and rear posts of the blade holder. In general, these mediolateral forces were not substantially different between skate models.
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Discussion and implications Several significant main effects for turn direction and skate side were noted. In addition some significant interaction effects between model and turn direction, as well as turn direction and skate side were identified, though not consistently observed across all factor combinations. Turn direction had a significant effect on force magnitudes; in general, left turns yielded higher outside leg forces than right (, 4%BW to 10%BW). This could be explained by the fact that all subjects were noted as being right leg dominant, which could affect their confidence to apply forces during a turn in the left direction where the outside limb would be the right leg. A study observing the reaction forces between dominant and non-dominant legs of recreational athletes (who were right leg dominant) during drop landing to cutting manoeuvres also found the kinetics to be greater during cutting in the left direction (Rosado, 2006). These turn asymmetry findings are similar to another non-skating change-ofdirection study where during over-ground speed tests subjects who possessed significantly greater reactive strength in the right leg executed faster change-of-direction manoeuvres in the left direction (Young & Farrow, 2006). Another study identified subjects’ GRFs as being 41.4% greater in their dominant limb than in their non-dominant limb during ground-based cutting manoeuvres (Cowley, Ford, Myer, Kernozek, & Hewett, 2006). We can speculate then that for hockey players in a game situation, right leg-dominant players may be more inclined to perform a change-of-direction manoeuvre in the left direction because of the confidence to apply forces in that direction, which would lead them to favour certain positions on the ice, that is being a right or left wing player. Significant differences were found between skate leg sides; that is, the outside leg carried greater forces (, 51%BW to 70%BW), compared with the inside leg (, 12%BW to 24% BW). These findings are similar to a study observing forces and path radius of turning in downhill skiing as the forces carried by the foot of the outside ski were found to be greater than forces carried by the foot of the inside ski (Yoneyama, Scott, Nagawa, & Osada, 2008). Another downhill skiing study had similar findings for GRFs; that is, during the turning and ploughing tasks, whenever the foot was on the outside of the turning phase during kinetic measures were seen to be greater than when it was on the inside of the turning phase (Nakazato, Scheiber, & Mu¨ller, 2011). What was also observed from the corresponding video log trials of each change-of-direction task is that the skate to be first placed on the outside was followed rapidly (, 40 ms) by the inside skate, which was placed adjacent and parallel to the other. During the time of the change-of-direction task when both skates are in full contact with the ice (, 1.0 s), the skates pivot and plough under the player so as to point towards a new direction of travel followed by the inside skate moving forward in tandem with the outside skate towards the end of the task. The inside skate is then lifted and quickly stepped towards the turn direction immediately before the end of the changeof-direction task. In general, skate model (regular versus modified) did not significantly affect either the vertical or mediolateral forces. This was surprising, given the prior findings by RobertLachaine et al. (2012) the modified skate demonstrated modest yet significant force increases during forward skating tasks. However, considering the intent of the modified skate design was solely to enhance plantar-dorsi flexion range of motion (in the sagittal plane of the ankle complex) without foregoing side-to-side stiffness (in the frontal plane)
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the differences in force outcomes between studies is reasonable; that is, both skate models provided the same mediolateral stability during these particular change-of-direction manoeuvres. Further study with more participants is warranted to determine whether the main and interaction effects consistently present. Several limitations of this study exist. Though all subjects successful executed the same defined change-of-direction manoeuvre, the specific movement technique employed by subjects varied; for example, from video logs, subjects displayed differences in the relative inside – outside skate positions during the task (varying from tandem to adjacent) that in turn may modify their respective kinetic bearing. Other questions remain: For examples, to what extent these findings extend to other change-of-direction manoeuvres? How representative are these tasks performed in a non-game, pre-planned format to that of an open game format? It is also possible for a long-term habituation effect, due to a player’s possible preferred position, to influence performance of the change-ofdirection manoeuvres which was not controlled for in this study. Because leg dominance appears to be a main issue in the results, a formalized testing methodology to determine the subject’s true leg dominance would be beneficial to the study as well as controlling for leg dominance. Stick side of each subject was noted; however, a method of examining its relationship to the performance of change-of-direction manoeuvres could be developed in a future study. As the first study to examine change-of-direction kinetics in ice hockey, these findings may have coaching implications; for example, the need to enhance these manoeuvres with equal proficiency for both turning directions regardless of leg dominance. The challenge will be to define the coaching cues necessary to elicit greater outside leg force generation during the change-of-direction manoeuvre. Furthermore, the observation that upper boot flexibility (dorsi-plantar flexion) did not compromise the manoeuvre dynamics that refutes the common perception among players that high boot stiffness is required. Conclusion The results demonstrated that the use of a portable strain-gauge force transducer system can be used to assess on-ice change-of-direction manoeuvres in ice hockey. Clear force asymmetry between skate sides was noted during the task. The kinetic strategies seen during skating change-of-direction tasks were similar to other sports such as alpine skiing, rugby, soccer, and basketball. These findings provide a comprehensive understanding of the mechanics of change-of-direction tasks that is relevant to athletic skill development. In addition, the ability to distinguish mechanical performance differences between the two skate models tested further demonstrates the potential of direct force measurement as a sensitive metric to differentiate subtle glide and traction properties fundamental to skating performance. Future studies utilizing this measurement technology to more fully explore the many other skill combinations are warranted. Funding The authors would like to thank Bauer Hockey Corp. for their significant financial and material contributions to the study, as well as Natural Sciences and Engineering Research Council of Canada for their matching financial support as part of the Industrial Partnership Collaborative Research and Development Grant.
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