The ability to rapidly change direction is an important action associated with successful performance in multidirectional sports. For example, soccer players can perform ~600 cuts of 0–90° and ~100 turns of 90– 180° during matches.
A change of direction (COD) typically involves an athlete adopting a lateral foot plant to change their base of support relative to their COM to redirect and accelerate towards the new intended direction. The lateral foot plant is commonly described as the final foot contact (FFC) and plays a crucial role in facilitating effective COD. Additionally, in order to reduce momentum prior to the FFC, athletes decelerate whereby high braking forces are produced over the penultimate foot contact (PFC) (second to last foot contact involved with COD) and potentially steps prior. Importantly, the biomechanical demands of COD are “angle-dependent”, whereby the deceleration and reacceleration requirements (performance variables), GRF, knee injury risk surrogates, trunk and lower limb kinematics and kinetics, and lower-limb muscle activity vary across CODs of different angles.
Currently, there is a paucity of research that has comprehensively examined the effects of angle on COD biomechanics, while considering PFC braking characteristics and knee internal rotation moments (KIRMs). The aim of this study was three-fold: 1) to compare COD performance, knee injury risk surrogates, GRF, and trunk and lower-limb kinetics and kinematics between CODs of 45°, 90°, and 180°; 2) to examine the inter-task relationships in the aforementioned biomechanical variables between different COD angles; and 3) to assess agreements in “high” and “low” knee joint load classification for KAMs and KIRMs between COD angles.
Twenty-seven men (age: 22.9 ± 5.1 years, mass: 77.6 ± 12.5 kg, height: 1.78 ± 0.07 m) from multiple sports (soccer n = 19, rugby n = 7, field-hockey n = 1) participated in this study. Participants performed six trials each of a 45° (COD45), 90° (COD90) and 180° (COD180) COD task as fast as possible in a sequential order. The 45° and 90° COD tasks consisted of a 5-m entry and 3-m exit, whereas the 180° COD consisted of a 5-m entry and exit, and were performed on an indoor running track.
The lower-limb and trunk kinematics and kinetics were assessed via 3D motion and ground reaction force (GRF) analysis. Prior to the COD tasks, reflective markers were placed on lower-limb and torso bony landmarks of each participant. Marker and GRF data were collected over the PFC and FFC using ten infrared cameras (240 Hz), and GRFs were collected from two 600 mm × 900 mm force platforms embedded into the running track sampling at 1200 Hz.
Percentage agreements in “high” and “low” knee joint load classification for peak KAMs and KIRMs were performed between tasks, with moments greater than mean + 0.5 standard deviations considered “high” and moments lower than this threshold considered “low”. Like-for-like identifications in “high” or “low” knee joint loads classifications between the three COD tasks were performed and subsequent percentage agreements were calculated. Percentage agreements were interpreted with the following: excellent (>80%), moderate (51–79%), and poor (<50%).
Key mechanical differences in velocity profiles, GRF, sagittal joint angles and moments, multiplanar knee joint moments, and technical parameters existed between CODs. The primary findings were that as COD angle increased, velocity profiles decreased (p < 0.001, d = 1.56–8.96), ground contact times increased (p < 0.001, d = 3.00–5.04), vertical GRF decreased (p < 0.001, d = 0.87–3.48), and sagittal peak knee joint moments decreased (p ≤ 0.040, d = 0.62–2.73). These findings support the “angle-velocity trade-off” concept, whereby as COD angle increases, approach velocity and velocity during COD declines, while GCTs increase in order to perform the intended COD and deflect the COM.
Notably, the greatest peak knee internal rotation (KIRMs) and abduction moments (KAMs) and angles were observed during the 90° COD (p < 0.001, d = 0.88–1.81), indicating that this may be the riskiest COD angle.
Generally, athletes tended to display “high” or “low” KAMs consistently between tasks, with moderate to excellent percentage agreements in “high/low” KAMs classification observed. Conversely, the relationships and classifications in KIRMs between tasks were lower with weaker correlations and lower percentage agreements in “high/low” KIRMs classifications observed. Disagreements of ~20% and ~35% in “high/low” classification based on KAMs and KIRMs, respectively, were observed between COD angles. Therefore, evaluations at different COD angles are needed to develop an athlete’s biomechanical injury risk profile.
The authors concluded that COD angle has a significant and meaningful effect on COD biomechanics. The results of the study substantiate the concept that the biomechanical demands of COD are “angle- dependent”,which have important implications with respect to COD coaching, screening, and physical preparation.
Dos’Santos T et al. (2021) The effect of angle on change of direction biomechanics: Comparison and inter-task relationships, Journal of Sports Sciences.
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