Sports Science

An Assessment of a novel approach for determining the player kinematics in elite rugby union players

Rugby is intrinsically an impact sport which results in concussions being a frequent injury within the game. Repeated concussion is linked to early-onset dementia and depression, and the rules for limiting repeated concussion are an ongoing controversy. Therefore a greater understanding of the dynamics of head impacts in rugby and the mechanism of concussion is required. Accordingly, this study focuses on assessing the use of Model Based Image Matching (MBIM) and multi-camera view video for measuring six degree of freedom head kinematics during an impact event in rugby union. The matching is performed on video evidence using 3-D animation software Poser 4. The surroundings are built in the virtual environment based on the real dimensions of the sport field. A skeleton model is then used to fit the player’s anthropometry for each video frame thus allowing player kinematics to be measured. The results from this initial study suggest that the MBIM method can be applied to head impact cases in rugby union. The head kinematics results from this case are similar to those reported in literature. The MBIM method should be applied to a number of head impact cases to establish thresholds for concussion injuries in rugby. The data gained from the MBIM method can allow for more reliable kinematic data to be inputted into finite element analysis and rigid body simulations of concussion impacts. This can allow multi-axis force measurements to be measured within the brain and neck. This can ultimately lead to an improvement in concussion injury prevention and management.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Sports Science

The Effect of a Raised Surface on Frontal Plane Knee Loading and Muscle Activation During a Sidecut in Recreational Female Softball Players

Collegiate softball has become increasingly popular since the passage of Title IX. As with any sport, injuries are a common occurrence. Interestingly, the base runner is at the highest risk of injury, and rounding the base, specifically, has resulted in approximately 187 game-day injuries. Rounding the base involves planting the right foot on a raised surface and cutting to the left, a dynamic movement often associated with noncontact ACL injuries. Frontal plane loading and unbalanced quadriceps-to-hamstring co-contraction indices (Q:H CCI) have been associated with increasing the likelihood of noncontact ACL injuries occurring. Neuromuscular abnormalities pre- and post-contact have also been suggested to increase the risk of injury. To date, no study has analyzed the effect of rounding a base on noncontact ACL injury risk factors in softball players. Nine recreationally active females completed two base conditions. The first simulated rounding a base with no base on the force platform (NB), and the second simulated rounding a base with a base on the force platform (WB). Three-dimensional motion capture, one force platform, and electromyography were utilized. Results indicated the WB condition reduced the risk of noncontact ACL injury by decreasing frontal plane loading. Movement patterns at the ankle and abnormal foot strikes may provide a better explanation for why noncontact ACL injuries occur while rounding first base. Post-contact Q:H CCI was significantly greater than pre-contact, indicating significantly greater quadriceps activity post-contact. Neuromuscular training could potentially reduce the load applied to the ACL and decrease the risk of injury.
Listed In: Biomechanics, Sports Science

Muscle and tendon adaptation in young and older adult athletes: A combined longitudinal and cross sectional investigation

This study examined triceps surae muscle strength and tendon stiffness in young adult elite sprinters and jumpers over one season, in order to detect potential discordance between muscle and tendon adaptation due to training. Furthermore, we examined the effect of habitual training on triceps surae muscle-tendon unit (MTU) mechanical properties in young and older athletes, using a cross-sectional design. Eleven healthy younger elite sprinters and jumpers, 12 master athletes, 12 recreationally active young controls and one young elite athlete, 10 months after unilateral Achilles tendon reconstruction participated. All young athletes underwent regular measurements over one season. Triceps surae muscle strength and tendon stiffness of both legs were analysed using dynamometry and ultrasonography synchronously. Within one season, similar patterns of relative changes in muscle strength and tendon stiffness were seen in the young elite athletes. For the tendon reconstruction athlete, the affected leg showed no increases in muscle strength or tendon stiffness over one season, and remarkably lower muscle strength but similar tendon stiffness compared to the non-affected leg. Healthy young elite athletes showed higher muscle strength and tendon stiffness than both other subject groups, with no differences between young controls and master athletes. Our results provide evidence for training-induced concordant adaptation of muscle and tendon over one season within healthy young elite athletes. Achilles tendon rupture and reconstruction may be a major risk factor for irreversible discordance within the triceps surae MTU. Finally, habitual athletics training over the lifespan may effectively counteract age-related decreases in muscle strength and tendon stiffness.
Listed In: Biomechanics, Sports Science

Bilateral assessment of cartilage with UTE-T2* quantitative MRI and associations with knee center of rotation following anterior cruciate ligament reconstruction

Purpose: Anterior cruciate ligament (ACL) tear greatly increases the risk of knee osteoarthritis (OA), even when patients undergo ACL reconstruction surgery (ACLR). Changes to walking kinematics following ACLR have been suggested to play a role in this degenerative path to post-traumatic OA by shifting the location of repetitive joint contact loads that occur during walking to regions of cartilage not conditioned for altered loads. Recent work has shown that changes to the average knee center of rotation during walking (KCOR) between 2 and 4 years after ACLR are associated with long term changes in patient reported outcomes at 8 years. Changes to KCOR result in changes to contact patterns between the femur and the tibial plateau. However, it is unknown if changes to this kinematic measure are reflected by changes to cartilage as early as 2 years after surgery. Ultrashort TE-enhanced T2* (UTE-T2*) mapping has been shown to be sensitive to subsurface changes occurring in deep articular cartilage early after ACL injury and over 2 years after ACLR that were not detectable by standard morphological MRI. Thus, the purpose of this study was to test the hypothesis that side to side differences in KCOR correlate with side to side differences in UTE-T2* quantitative MRI (qMRI) in the central weight bearing regions of the medial and lateral tibial plateaus at 2 years following ACLR. Methods: Thirty-five human participants (18F, Age: 33.8±10.5 yrs, BMI: 24.1±3.3) with a history of unilateral ACL reconstruction (2.19±0.22 yrs post-surgery) and no other history of serious lower limb injury received bilateral examinations on a 3T MRI scanner. UTE-T2* maps were calculated via mono-exponential fitting on a series of T2*-weighted MR images acquired at eight TEs (32μs -16 ms, non-uniform echo spacing) using a radial out 3D cones acquisition. All subjects completed bilateral gait analysis. Medial-lateral (ML) and anterior-posterior (AP) coordinates of average KCOR during stance of walking were calculated for both knees. Side to side differences in KCOR were tested for correlations with side to side differences in mean full thickness UTE-T2* quantitative values in the central weight bearing regions of the medial and lateral tibial plateau using Pearson correlation coefficients. Results: There was a distribution in UTE-T2* values, with some subjects having higher UTE-T2* and some lower in the ACLR knee relative to the contralateral knee. A significant correlation (R=0.407, p=0.015, Figure 1A) was observed between UTE-T2* and the ML KCOR with a more lateral KCOR corresponding to higher values of UTE-T2* for the medial tibia. Similarly, for the lateral tibia, a lower UTE-T2* was correlated with a more posterior KCOR (R=0.363, p=0.032, Figure 1B). Significant correlations were not observed for UTE-T2* in the lateral tibia with the ML position of KCOR or for UTE-T2* in the medial tibia with the AP position of KCOR. Conclusions: The results of this study support the hypothesis that side to side differences in mean full thickness UTE-T2* qMRI correlate with side to side differences in knee kinematics at 2 years after ACLR. The finding that a more lateral KCOR in the ACLR knee correlates with UTE T2* values in the medial tibia that were higher than the contralateral side suggests that this kinematic change, which has been previously shown to result in more relative motion between the femur and tibia in the medial compartment, could be affecting subsurface matrix integrity, inducing changes detectable by UTE-T2* mapping. Additionally, the finding that a more posterior KCOR in the ACLR knee correlated with UTE-T2* values in the lateral tibia that were lower than the contralateral knee further suggests that the UTE-T2* metric may reflect early changes in cartilage health. When interpreted within the context of prior work showing that a posterior shift in KCOR from 2 to 4 years post-surgery correlated with improved clinical outcomes at 8 years, the observed lower UTE-T2* with a more posterior KCOR, which is reflective of improved quadriceps recruitment, suggests positive cartilage matrix properties. In spite of the limitations of this cross-sectional and exploratory study, and the difficulty accounting for changes in the contralateral knee, these results support future studies of the relationship between UTE-T2* and KCOR to provide new insight into predicting the risk for OA after ACLR.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research, Sports Science


Analysis of lower limb biomechanics during jumping and landing tasks are often used to assess lower limb injury risk in research and applied practice within professional team sports. However, there are limited instances of these movements being incorporated into research focusing on Achilles tendinopathy development. PURPOSE: To investigate whether differences existed in lower limb motion and moments during jumping and landing between individuals who develop Achilles tendinopathy and those who remain injury free. METHODS: Male professional Rugby Union players without lower limb injury (n = 43) were compared to players who sustained Achilles tendinopathy (n = 8). Five single-leg drop vertical jumps per leg were performed at the start of their pre-season training. Motion of the lower limbs were recorded synchronously with ground reaction force. RESULTS: Players who sustained Achilles tendinopathy demonstrated significantly increased rear-foot inversion-eversion range of motion (p = 0.03), a reduction in dorsi-plantarflexion range of motion (p = 0.01) and knee flexion-extension range of motion (p = 0.03). Peak dorsiflexion velocity (p = 0.02) and peak knee flexion velocity were also reduced in those with Achilles tendinopathy (p = 0.03). No differences in hip joint kinematics were observed. Controls displayed slightly larger peak plantarflexion moments; however this difference was not statistically significant (p = 0.15, g = 0.60). CONCLUSIONS: The findings indicated that players who subsequently developed Achilles tendinopathy displayed an altered single leg landing strategy when compared to players who did not sustain injury; with motion of the ankle joint and rear-foot most influenced.

Listed In: Biomechanics, Sports Science


Accelerometers have become extremely popular in the measurement of stride frequency as well as other related stride variables with current sensors capable of recording both accelerations and electromyography. The purpose of this preliminary investigation was to assess the estimation of stride frequency during running using a single tri-axial accelerometer compared to a commonly used infrared device the OptojumpTM system. Five healthy participants wore a Delsys Trigno tri-axial accelerometer attached to the right anterior shin and participants repeatedly ran at a submaximal pace through a four metre section of OptojumpTM. Stride frequency was calculated as stride time divided by one. For the OptojumpTM, stride time was the sum of contact and flight times from two consecutive steps. For the accelerometer, stride time was calculated as the time between two consecutive foot contacts on the right side. Foot contact was identified by local maxima in the Y (medial-lateral) acceleration trace. Estimates of stride frequency were compared using paired samples t- tests, intraclass correlation coefficients (ICCs) and Bland and Altman 95% limits of agreement (LOA) with significance set at p < 0.05. The mean difference between estimates was 0.01 Hz (95% LOA: -0.05-0.07 Hz) with single and average ICCs for stride frequency of 0.93 and 0.96 respectively. The results suggest that an accelerometer attached to the shin can accurately estimate stride frequency in running. Discrepancies in stride frequencies can be partially explained by differences in device sampling rates i.e. 137.15 Hz versus 1,000 Hz
Listed In: Biomechanics, Gait, Sports Science

Ankle Sprain Copers Demonstrate Unique Lower Extremity Neuromechanics Compared to Healthy Controls and Chronic Ankle Instability Subjects

Chronic ankle instability (CAI) patients show various sensorimotor deficits, which may be related to the chronic nature of instability. Ultimately, an intervention should focus on deficits which may perpetuate the problem, but an understanding of successful sensorimotor function may best come from those who sprained their ankles with no problematics outcome (copers). PURPOSE: To examine sagittal ankle angles, moments, tibialis anterior and medial gastrocnemius EMG activation during a single-leg maximal vertical side-cutting jump task. METHODS: 66 subjects (M=42, F=24; 22.2±2 yrs, 173.8±8 cm, 71.4±11 kg) consisted of 22 CAI (77.1±15.3% FAAM ADL, 62.5±20.4% FAAM Sports, 4.1±2.8 sprains), 22 Copers (100% FAAM ADL & Sports, 2.0±1.1 sprains), and 22 healthy controls. Subjects performed 10 jumps, consisting of a max vertical jump, landing on a force plate, and transitioning immediately to a side-cutting jump, while the dependent variables were collected during stance. Functional linear models (α=.05) were used to detect mean difference between groups. If functions and associated 95% confidence intervals did not cross the zero, then significant differences existed. RESULTS: Figure 1 shows that copers and AI exhibited up to 2.5° less dorsiflexion angle during 30-75% of stance, relative to controls. While copers exhibited similar neuromechanics to controls in sagittal ankle moment, tibialis anterior and medial gastrocnemius EMG activation, those with CAI demonstrated up to 0.5 Nm/kg less plantarflexion moment, 2.5% less tibialis anterior and 47% less medial gastrocnemius EMG activation. CONCLUSION: Copers show neuromechanics similar to healthy controls at times, and similar to those with CAI at others. Reduced plantarflexion moment and medial gastrocnemius EMG activation suggest that those with CAI may rely more on static stabilizers (e.g., bones) than dynamic stabilizers (e.g., muscles), which could increase impact loads on tibiotalar cartilage surface.

Listed In: Biomechanics, Sports Science

Matching participants for triceps surae muscle-tendon unit mechanical properties eliminates age-related differences in drop jump performance

In the current study, we aimed to determine if differences in drop jump height or motor task execution strategy between young and middle-aged adults exist, when triceps surae MTU capacities (muscle strength and tendon stiffness) were matched. The triceps surae MTU biomechanical properties of 29 middle-aged and 26 younger adults were assessed during isometric voluntary ankle plantarflexion contractions of the dominant leg using a custom-made dynamometer and ultrasonography simultaneously. The 12 young adults with the lowest triceps surae muscle strength and the 12 middle-aged adults with the greatest muscle strength then completed a series of drop jumps from different heights. Ground contact time, average vertical ground reaction force, average mechanical power and jumping height were recorded. Younger and middle-aged adults attained comparable jumping heights independent of the drop jump height. There were significant age effects on ground contact time and average vertical ground reaction force during ground contact phase, with the middle-aged adults showing higher ground contact times but lower forces, leading to a significant age effect on mechanical power. Significant correlations were found between triceps surae MTU capacities and drop jump height. The results of the current study demonstrate that when triceps surae MTU capacities are matched, young and middle-aged adults show comparable performance of a jumping task, despite having different motor strategies. Finally, the results suggest that neuromuscular factors other than maximum isometric strength and tendon stiffness may influence motor task execution strategy during jumping.
Listed In: Biomechanics, Sports Science

Effects of an 8-week cadence gait training program on knee loading in individuals following ACL reconstruction

While normalization of gait is a primary goal of early rehabilitation, between limb asymmetries in knee extensor moment can persist 6-24 months later and previous literature assessing gait interventions is limited. The purpose of this study was to assess the influence of subject-specific cadence gait training program on knee loading mechanics following ACLr. Nine individuals completed an 8-week cadence training program (20min, 3x/week; Table1) and nine sex- and surgery-matched individuals served as controls. All eighteen participants received standard physical therapy and were tested at 1 and 3 months post-op. Kinematic and kinetic data were collected during walking at a self-selected speed. Repeated measures ANOVAs were used for comparisons; significance α≤0.05. Main effects of limb and time were observed: knee ROM (kROM;p<0.001;p=0.044;Fig.1) and knee extensor moment (kEXT;p=0.003;p=0.002) in the cadence and control groups, respectively. No main effects of group for kROM (p=0.136) or kEXT (p=0.229) were found. A trend toward a significant group x time x limb interaction was observed in kEXT (p=0.092), but not kROM (p=0.412). Post-hoc analyses of kEXT (Fig.2) revealed a significant time x limb interaction for the cadence group (p=0.053) but not the control group (p=0.884). In the cadence group, the time x limb interaction was driven by a 131% increase in kEXT in the surgical limb versus a 42% increase in the non-surgical limb between T1 and T2. Consistent with previous findings, these pilot data show promising results as the cadence intervention resulted in improvements in sagittal plane knee loading compared to controls.

Listed In: Biomechanics, Gait, Orthopedic Research, Physical Therapy, Sports Science


While the popularity of triathlon is increasing, the underlying biomechanics of the various bicycling positions and saddle types are not yet understood. PURPOSE: To determine how bicycle rider position and saddle type (road vs. triathlon) affect the bicycle-rider interface forces (BRIFs) at a standardized power and cadence. METHODS: A stationary cycling ergometer was modified to include force transducers at the saddle, bottom bracket, and stem. Anatomical measurements were made in order to fine-tune rider fit on the ergometer. 9 subjects completed riding trials in all combinations of road position, road saddle, triathlon position, and triathlon saddle. Riding trials were 6 minutes, at a standardized power output of 2 Watts per kilogram (W/kg) and 90 Revolutions per Minute (RPM). RESULTS: Analysis was broken into three categories: Road Saddle, Road Position (RR) vs. Triathlon Saddle, Road Position (TR), Road Saddle, Triathlon Position (RT) vs. Triathlon Saddle, Triathlon Position (TT), and Road Saddle, Road Position vs. Triathlon Saddle, Triathlon Position. Surprisingly, there were no significant differences in saddle vertical forces between either body positions or saddle type. However, there were significant differences at the handlebar; 8.4% more body weight supported at the handlebar in the triathlon position compared to the road position while using a triathlon saddle. CONCLUSION: Across cycling positions, there is a significant change in saddle and stem vertical forces. However, within a cycling position, saddle type does not change the amount of vertical force seen at the saddle.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science