The tackle height law in rugby union has been an area of concern for many years. It is currently set at the line of the ball carrier’s shoulder. The goal of this study is to use Model-Based Image-Matching (MBIM) and human volunteer tackles in a marker-based 3D motion analysis laboratory to examine the severity of a legal tackle to the shoulder/chest of the ball carrier (with no head contact) and the effect of tackles above and below the chest on ball carrier inertial head kinematics, respectively. From the real-world tackles, the estimated ball carrier peak resultant change in head angular velocity was 30.4 rad/s (23.1 rad/s, 14.0 rad/s and 21.8 rad/s in the coronal, sagittal and transverse direction, respectively). In the staged tackles, the median peak resultant head linear and angular acceleration and change in head angular velocity values for tackles above the chest were greater than for below the chest. The results support the proposition of lowering the current tackle height law. Due to the real-world tackle (MBIM), the ball carrier head kinematics indicated a greater than 75% chance of sustaining a concussion, based on the literature. This was the case even though no contact was made with the ball carrier’s head. Therefore, repeatedly engaging in this type of legal tackle may be detrimental for long-term brain health. However, by lowering the tackle height law to below the chest, ball carrier inertial head kinematics can be reduced significantly, thus reducing the repetitive loading placed on the brain.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science

ACL injury mechanisms are commonly determined from evidence gathered during highly controlled lab-based activities. However, many non-contact ACL ruptures occur following a reaction to an external stimulus, when athletes are unable to pre-plan their movement strategy1. The purpose of this study was to determine if unanticipated drop-jump landing altered lower-limb biomechanics. Ten participants performed two counter-balanced single-leg drop-jump landing conditions (anticipated and unanticipated). Unanticipated landings were conducted by randomly displaying either a left or right arrow immediately following jump takeoff. The visual cue was triggered by the participant making contact with a force platform, set at a threshold of 10N. Three-dimensional kinematic and kinetic data for the ankle, knee and hip were time-normalized over the jumping and landing phase and with-in participant averaged over the successful trials. Paired sample t-tests, using Statistical Parametric Mapping, evaluated between condition differences over the jumping and landing phases (α = 0.05). Participants landed with significantly greater hip abduction (p=0.004) during the unanticipated condition over the entire landing phase (0-100%). Participants also landed with significantly less hip external rotation (p=0.048) over the final 17% of the landing phase. Although no differences were identified at the knee joint, participants landed with greater hip abduction and less external rotation when the movement was unaticipated. Given that proximal factors play a contributing role towards controling knee mechanics, the altered hip position could be a compensatory strategy to limit knee abduction and reduce ACL injury risk during unanticipated tasks2. 1. Olsen et al. AJSM 2004;32(4):1002-1012 2. Powers JOSPT 2010;40(2):42-51
Listed In: Biomechanics

When performing high knee flexion movements (>120º), thigh-calf (TC) and heel-gluteal (HG) structures come into contact and transmit force between segments. Previous work has only assessed the effect of these forces on net external knee joint forces and moments in the sagittal plane. Therefore, the purpose of this study was to quantify the effect of incorporating the 3D location and orientation of TC and HG force vectors on external forces and moments acting on the knee. Sixteen participants (8 M/F) completed five repetitions of six high-flexion movements. Kinematics, kinetics, and pressure distribution (of TC and HG contact) were measured from the right lower limb. Inverse dynamics were calculated with and without TC and HG force, to determine the change in magnitude. During high knee flexion movements, there was a significant reduction in AP forces (~50%) and F/E moments (~27%) as a result of considering contact between lower limb segments. Novel to this study was the ability to account for the 3D force vector and CoF location of TC and HG by tracking the motion of the pressure mat allowing the effect on frontal plane moments to be determined. There was a significant increase in the Ab/Ad moment (~60% in two movements) which is a known risk factor for knee osteoarthritis development. These results will improve the biofidelity of future high flexion musculoskeletal models of the knee. Future work is required to determine if findings from this young and healthy population translates to occupational or individuals that habitually kneel.
Listed In: Biomechanics

Frontal plane mechanics have been associated with running-related injuries such as patellofemoral pain. Strengthening and gait retraining programs aimed at reducing hip adduction during running have been shown to be effective at alleviating symptoms, however evidence of their effect on running kinematics is equivocal. It is possible that such programs exert their benefits through altering kinetics rather than kinematics in the frontal plane during running. Further, the contributions of the ankle to frontal plane mechanics have not been well studied. PURPOSE: To determine if hip and ankle strength are associated with frontal plane kinetics in female runners. METHODS: 64 healthy women running at least 16km per week participated in this study. Isometric hip abduction and ankle inversion strength were measured using a handheld dynamometer. 3D gait analysis was conducted as participants ran on an instrumented treadmill at 2.7 m/s. Participants were ranked in order of isometric strength of both the hip and ankle, and divided into tertiles of high, medium and low strength. 2-way MANOVA was used to determine the relationship between strength and peak moment, positive work and negative work in the frontal plane of the hip and the ankle. Tukey post-hoc tests were conducted where applicable (α=0.05). RESULTS: There was no significant interaction effect, or main effect of hip strength. There was a significant main effect of ankle strength on frontal plane kinetics (p=0.024). Specifically, the strong ankle group compared to the weak ankle group had significantly greater magnitude of peak ankle inversion moment (0.95(0.32) vs 0.68(0.22) Nm/kg, p=0.033), hip abduction moment (-2.78(1.02) vs -1.88(0.24) Nm/kg, p=0.002) and hip frontal plane positive work (0.27(0.19) vs. 0.13(0.03) W/kg, p=0.006). CONCLUSION: Isometric ankle but not hip strength is associated with kinetics in the frontal plane during running in females. Thus ankle strength should not be overlooked in clinical evaluation and treatment of runners.
Listed In: Biomechanics, Gait, Physical Therapy, Sports Science

Lateral ankle sprains, caused by rapid ankle inversion, and noncontact anterior cruciate ligament (ACL) knee injuries, caused by excessive knee loading, are among the most common lower extremity injuries that occur during dynamic tasks, such as cutting. Ankle braces are commonly used to prevent lateral ankle sprains by reducing ankle inversion. There is limited and conflicting research about how an ankle brace affects other joints, such as the knee, during cutting movements. It is also not known if sex differences exist during a cutting task when an ankle brace is present. The purpose of this study was to determine the effects of an Ultra Zoom® hinged ankle brace and sex on ankle and knee biomechancis during a cutting maneuver. Eighteen recreationally active adults completed sidestep cutting trials with and without an Ultra Zoom® ankle brace. Three-dimensional ankle and knee kinematics and GRF were collected. Separate 2×2 (sex × brace) repeated measures ANOVAs were used. Results indicated the brace reduced frontal plane ankle kinematics and had no effect on knee kinematics. Additionally, females demonstrated decreased knee flexion compared to males. An ankle brace during a cutting maneuver restricted frontal plane ankle movement. Furthermore, the only significant changes in knee mechanics were due to sex differences, which has been well documented. These findings indicate that the use of an Ultra Zoom® hinge brace is suitable for sports, reduces the risk of lateral ankle injuries, and does not alter knee mechanics, and therefore may not increase the risk of ACL injury.
Listed In: Biomechanics, Sports Science