Postural balance strategies during landing at the moment of return-to-sports after anterior cruciate ligament reconstruction.

Most athletes that return to sport (RTS) after Anterior Cruciate Ligament (ACL) injury undergo reconstruction (ACLR) to restore their knee stability. The major concern for RTS is for the patient to be able to perform challenging dynamic tasks whilst adequately stabilizing the knee joint and maintaining their postural balance. Nevertheless, the interaction between knee protective mechanisms (such as knee unloading and knee stabilisation) and postural balance strategies has not yet been comprehensively analyzed. Thus, the aim of this study was to investigate landing balance strategies in ACLR athletes at time of RTS. Twenty-one athletes with a unilateral ACLR were tested at the time of RTS while performing a single leg hop for distance on both limbs. Three balance mechanisms that influence the GRF during the landing phase (foot placement, center of pressure (CoP) excursion, counter-rotation of segments) were investigated and compared between the ACL injured and uninjured limb. Interactions between knee protective mechanisms and postural balance strategies were tested using a statistical parametric mapping regression analysis. Results show that CoP excursions in the injured limb increased, as well as ankle joint moment contribution to anterior-posterior (A-P) GRF. Besides, patients presenting reduced knee joint contribution to A-P GRF had to compensate with higher hip joint contribution in order to maintain postural balance. In conclusion, ACLR athletes who at RTS still protect their reconstructed knee are forced to employ compensatory postural balance strategies. Therefore, there is a persistent trade-off between knee protection and postural balance at the moment of RTS.

Whole-body dynamic stability in side cutting: Implications for markers of lower limb injury risk and change of direction performance.

Control of the centre of mass (CoM) whilst minimising the use of unnecessary movements is imperative for successful performance of dynamic sports tasks, and may indicate the condition of whole-body dynamic stability. The aims of this study were to express movement strategies that represent whole-body dynamic stability, and to explore their association with potentially injurious joint mechanics and side cutting performance. Twenty recreational soccer players completed 45° unanticipated side cutting. Five distinct whole-body dynamic stability movement strategies were identified, based on factors that influence the medial ground reaction force (GRF) vector during ground contact in the side cutting manoeuvre. Using Statistical Parametric Mapping, the movement strategies were linearly regressed against selected performance outcomes and peak knee abduction moment (peak KAM). Significant relationships were found between each movement strategy and at least one selected performance outcome or peak KAM. Our results suggest excessive medial GRFs were generated through sagittal plane movement strategies, and despite being beneficial for performance aspects, poor sagittal plane efficiency may destabilise control of the CoM. Frontal plane hip acceleration is the key non-sagittal plane movement strategy used in a corrective capacity to moderate excessive medial forces. However, whilst this movement strategy offered a way to retrieve control of the CoM, mitigating reduced whole-body dynamic stability, it also coincided with increased peak KAM. Overall, whole-body dynamic stability movement strategies helped explain the delicate interplay between the mechanics of changing direction and undesirable joint moments, providing insights that might support development of future intervention strategies.

How reliable are knee kinematics and kinetics during side-cutting manoeuvres?

INTRODUCTION: Side-cutting tasks are commonly used in dynamic assessment of ACL injury risk, but only limited information is available concerning the reliability of knee loading parameters. The aim of this study was to investigate the reliability of side-cutting data with additional focus on modelling approaches and task execution variables. METHODS: Each subject (n=8) attended six testing sessions conducted by two observers. Kinematic and kinetic data of 45° side-cutting tasks was collected. Inter-trial, inter-session, inter-observer variability and observer/trial ratios were calculated at every time-point of normalised stance, for data derived from two modelling approaches. Variation in task execution variables was regressed against that of temporal profiles of relevant knee data using one-dimensional statistical parametric mapping. RESULTS: Variability in knee kinematics was consistently low across the time-series waveform (≤5°), but knee kinetic variability was high (31.8, 24.1 and 16.9 Nm for sagittal, frontal and transverse planes, respectively) in the weight acceptance phase of the side-cutting task. Calculations conveyed consistently moderate-to-good measurement reliability. Inverse kinematic modelling reduced the variability in sagittal (∼6 Nm) and frontal planes (∼10 Nm) compared to direct kinematic modelling. Variation in task execution variables did not explain any knee data variability. CONCLUSION: Side-cutting data appears to be reliably measured, however high knee moment variability exhibited in all planes, particularly in the early stance phase, suggests cautious interpretation towards ACL injury mechanics. Such variability may be inherent to the dynamic nature of the side-cutting task or experimental issues not yet known.

Test-retest reliability and sensitivity of the Concept2 Dyno dynamometer: practical applications.

Strength assessment is often part of the objective periodical observation of teams, squads, or large groups of athletes. Equipment that provides assessment that is mobile and is easy to use will reduce the impact on the athletes' training and competitive calendar. However, any equipment used must be reliable to allow accurate monitoring of performance. The aim of this study was to examine the reliability of the Concept2 Dyno dynamometer. Forty-six competitive athletes (males: n = 36, age 23.3 ± 6.8 years, height 1.80 ± 0.09 m, body mass 82.3 ± 15.6 kg; females, n = 10, age 20.7 ± 1.4 years, height 1.65 ± 0.09 m, body mass 62.7 ± 11.8 kg), with a strength training background of more than 2 years, performed a familiarization session and 3 experimental sessions with 1 week intervening each. Each experimental session consisted of 3 maximal efforts of seated chest press (CPress), seated row (SRow), and seated leg press (LPress) exercises. Reliability was assessed examining systematic bias, intraclass correlation coefficient, coefficient of variation (CV), and 95% limits of agreement (95% LoA) between sessions. No systematic bias was found for any of the exercises. Intraclass correlation coefficients were high (0.89-0.98) with relatively low CV (6.2-4.3%). Finally, 95% LoA indicated that subsequent testing could underestimate by a factor of 0.87 or overestimate by a factor of 1.17, on average. These results indicate that Concept2 Dyno dynamometer is reliable and can be used in the field to efficiently monitor strength performance. Coaches and researchers should use "analytical goals" to help decide as to the use of Concept2 Dyno for their purposes.