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side stepping

An important steering task in team sports is cutting and side-stepping (SS), a maneuver performed to evade oncoming opponents. Sidestepping during game situations is complex, as athletes are generally traveling at higher velocities and often required to sidestep under unpredictably high temporal constraints when responding to opponents’ defensive movements or other situational demands. Frontal plane trunk displacement during SS has been reported to increase knee valgus loading which is associated with anterior cruciate ligament (ACL) injuries.

It was suggested that the central nervous system, depending on the level of temporal constraints, employs two separate strategies to redirect the centre of mass when steering. Planned situations without temporal constraints afford sufficient time for the adoption of a support foot placement strategy prior to initial contact of the push-off foot to initiate directional change. In unplanned situations with high temporal constraints, a strategy using trunk lateral flexion is adopted instead.

The authors of present study have previously shown that SS biomechanics is further differentiated by the game realism of the visual stimuli used to elicit unplanned SS, compared with those elicited using lights and planned sidesteps.

This study aimed to investigate how athletes reorient their bodies from the penultimate step to foot-off when SS in response to different types of visual stimuli and examine if the types of visual stimuli affect the body orientation strategies differently in players of varying levels of expertise.

The quasi-game-realistic stimuli were three-dimensional video projections of defensive opponent(s), consisting of a one-defender scenario (1DS) and a two-defender scenario (2DS). Sidesteps performed to avoid the projected defender(s) in these scenarios were further compared with those performed in response to the traditionally employed, two-dimensional arrow-planned condition (AP) and arrow-unplanned condition (AUNP). Selected frontal plane trunk and foot kinematics, and spatiotemporal variables were recorded due to their relevance in redirecting CM and with ACL injury risk.

15 high- and 15 low-level soccer players were recruited for this study. Participants performed sidestep and crossover cutting in response to four different stimuli conditions (AP, 1DS, 2DS, and AUNP). Each stimulus imposed a different level of visuospatial and temporal constraints that participants had to cope with in order to sidestep or crossover cut successfully on their dominant leg. The 2DS imposed the highest level of visuospatial constraints followed by the 1DS. The arrow conditions imposed minimal visuospatial constraints. The temporal constraints imposed by the stimuli conditions increased in the following order: AP, 1DS, 2DS, and AUNP. Cutting trials were considered successful when participants maintained an approach velocity of 4.5 ± 0.5 m/s between two infrared timing gates and achieved a cut angle of 45° ± 10° in all stimuli conditions.

A stereoscopic system was used to present the stimuli conditions. Participant three-dimensional motion data were collected synchronously at 250 Hz using a 12-camera Vicon MX motion analysis system during the cutting tasks. A 1.2 x 1.2 m AMTI force plate served as a standardized location for foot contact of the dominant push-off foot. No ground reaction force data were analyzed in this study.

Various trunk and foot kinematic parameters were measured and analyzed across both the preparation and execution phases of SS. Within and between group differences were ascertained using a 4 x 2 (stimuli x skill level) mixed design ANOVA.

Consistent across the two skill levels, stimuli type significantly affected (P < 0.05) all SS biomechanical and timing measurements. No interactions between stimuli type and skill level were found. Irrespective of stimuli type, only push-off foot placement was significantly different between skill levels.

Post-hoc testing revealed that step length was greater in the AUNP compared with the AP, 1DS, and 2DS. Additionally, step length in the AP was greater than the 1DS.

Placement of the support foot moved medially, crossing the pelvic midline for all stimuli conditions except for the AUNP, and was more medial in the AP compared with the other stimuli conditions. Conversely, support foot placement in the AUNP was more lateral compared with the AP, 1DS, and 2DS. Push-off foot placement was more lateral to the pelvic midline by approximately 2 cm in the 1DS and 2DS, compared with the AP and AUNP. Post-hoc testing further revealed that the high-level players placed their push-off foot 2.5 cm closer to their pelvic midline when SS in the AP and 4.6 cm in the 2DS, compared with the low-level players.

Peak trunk flexion contralateral to the sidestep direction decreased by approximately 3° in the AP compared with the 1DS and 2DS, and by approximately 5° compared with the AUNP. Furthermore, peak trunk contralateral flexion decreased by approximately 2° in the 2DS compared with the AUNP. The timing of peak contralateral trunk flexion occurred at a similar time in the AP and 1DS conditions in the selected mid-swing to foot-off phase of the dominant push-off leg. This occurred 9% later in the 2DS and AUNP conditions.

The ability of the high-level players to maintain their push-off foot closer to their base of support in complex quasi-game-realistic conditions (2DS) suggests that these players may possess a safer VPM strategy to sidestep and warrants further investigation. An understanding of the input parameters of this neuromuscular strategy could potentially be trained in lesser skilled players to reduce high ACL loads associated with dangerous SS postures.

 

Source:

Lee MJC et al. (2016) Different visual stimuli affect body reorientation strategies during sidestepping. Scand J Med Sci Sports.