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.
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.
In the following project, we explored the relationships between age, vestibulopathy and stability control, in order to determine the age and vestibulopathy-related effects on stability control, and to establish if a relationship existed between static and dynamic stability task performance. The first study examined the response to repeated trip perturbations of healthy middle aged adults and vestibulopathy patients, the second examined feedforward adaptation of gait in young, middle aged and older adults to a sustained mechanical perturbation and the third examined the relationship between standing balance and recovery following a tripping perturbation in vestibulopathy patients. The results showed that vestibulopathy is related to a diminished ability to control and recover gait stability after an unexpected perturbation, and to a deficient reactive adaptation potential. With ageing, the ability to recalibrate locomotor commands to control stability is preserved, although this recalibration may be slower in old age compared to middle and young age. Given that a decline in vestibular function is seen with increasing age, we suggest that assessment of vestibular function may be necessary when investigating locomotor stability and falls risk in both research and clinical settings. Finally, despite static balance tasks and parameters being commonly used in clinical settings, we did not find a consistent relationship between static and dynamic stability task performance, indicating the importance of dynamic stability tests when assessing falls risk in clinical settings.
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.
As a treatment for end-stage elbow joint arthritis, total elbow replacement (TER) results in joint motions similar to the intact joint; however, bearing wear, excessive deformations and/or early fracture may necessitate early revision of failed implant components.
A finite element model of a TER assembly was developed based on measurements from a Coonrad-Morrey implant (Zimmer, Inc., Warsaw, IN) using nonlinear elasto-plastic UHMWPE material properties and a frictional penalty contact formulation. The loading scenario applied to the model includes a flexion-extension motion, a joint force reaction with variable magnitude and direction and a time varying varus-valgus (VV) moment with a maximum magnitude of 13 N.m, simulating a chair-rise scenario as an extreme loading condition. Model results were compared directly with corresponding experimental data. Experimental wear tests were performed on the abovementioned implants using a VIVO (AMTI, Watertown, MA) six degree-of-freedom (6-DOF) joint motion simulator apparatus. The worn TER bushings were scanned after the test using micro computed tomography (μCT) imaging techniques, and reconstructed as 3D models.
Contact pressure distributions on the humeral and ulnar bushings correlate with the sites of damage as represented by the μCT data and gross observation of clinical retrievals. The results demonstrate UHMWPE bushing damage due to different loading protocols. Numerical results demonstrate strong agreement with experimental data based on the location of deformation and creep on bushings and exhibit promising capabilities for predicting the damage and failure mechanisms of TER implants.
Since OpenSim uses motion capture data as input while solving inverse kinematic (IK), it is subjected to soft tissue artifact (STA) as the commonly used surface markers do not correctly represent the underlying rigid bones. The purpose of this study was to determine the effect of applying bone pin (BP) marker defined ranges of knee motion in OpenSim IK solutions. Participants completed successful jump lunges where they were asked to stand on their non-test limb and jump forward onto a force plate (AMTI OR 6-7-OP), land on their test limb and maintain balance for two seconds. Data were processed through OpenSim with generic knee joint constraints as well as constraints derived from BP kinematic data.
BP constrained results yielded a significantly more flexed, adducted and externally rotated knee. Significant differences were also observed for anterior/ posterior and distraction/ compression translations throughout the entire jump lunge while medial/lateral translations were only significant pre and 50 ms post contact. After contact, BP constraints produced a significantly greater flexor, abductor, and external rotator moment. With respect to translation forces, the BP solutions produced smaller posterior shear and greater medial shear and compressive forces at the knee joint.
Generic models available in the OpenSim repository contain knee joint ranges that are not physiologically realistic. Therefore, caution should be expressed when using the results from musculoskeletal modelling as STA and optimizations can introduce error in both the kinematics and kinetic solutions. This error is amplified during ballistic and high impact tasks such as jump landing.
Footwear plays a significant role in, and can influence children’s gait. Footwear type is especially important as a child grows and develops from a novice to an expert walker. Compared to barefoot walking, children generally have increased spatiotemporal (ST) gait parameters while walking with footwear. Gait variability has also shown to be affected by footwear. The degree of stiffness in footwear could have a large influence on children’s gait and variability. This study investigated effects of footwear stiffness on ST gait parameters and gait variability in novice walkers. Children with an average age of 33.3 ( 7.0) months participated in a single data collection. Heel and toe marker positions were acquired for one minute of walking per condition. Participants walked on the treadmill in three levels of footwear stiffness (rigid: hard-soled stiff shoe, semi-rigid: EVA sole athletic shoe, compliant: moccasin soft-sole shoe) and barefoot. ST gait parameters and gait variability were calculated for each condition using marker. and treadmill forces. ST parameters all increased in the rigid and semi-rigid footwear conditions compared to soft-sole and barefoot. Interestingly, there were no differences between barefoot and wearing a moccasin for any of the ST variables. There were no differences in SD and COV between any of the footwear conditions. The moccasin shoe promotes walking most similar to normal barefoot walking. Standard measures of variability failed to detect differences between footwear conditions. Further investigation into different measurements is necessary to parse out what effect footwear has on children’s gait variability.
The purpose of this study was to quantify adaptation to a new prosthesis in terms of mechanical work profiles. Currently, there is a lack of knowledge on how individuals adapt to a new prosthesis, with many studies investigating different prosthetic feet but not adaptation over time. Thus, there is a need for objective measures to quantify the process of adaptation. Mechanical power and work profiles are a prime subject for modern energy-storage-and-return type prostheses, as the amount of energy a prosthesis stores and returns (i.e., positive and negative work) during stance is directly related to how a user loads and unloads the limb. 22 individuals with unilateral, transtibial amputation were given a new prosthesis at their current mobility level (K3 or above) and wore it for a three-week adaptation period. Kinematic and kinetic measures were recorded from walking on overground force plates at 0, 1.5, and 3 weeks into the adaptation period. Positive and negative work done by the prosthesis and intact ankle-foot was calculated using a unified deformable segment model. Positive work from the prosthesis side increased by 6.1% and intact side by 5.7% after 3 weeks (p = .041, .036). No significant changes were seen in negative power from prosthesis or intact side (p = .115, .192). Analyzing work done by a prosthesis may be desirable for tracking a patient’s gait rehabilitation over time. Future work may analyze how mechanical work profiles relate to more traditional clinical measures.
Sensorimotor changes such as postural and gait instabilities can affect the functional performance of astronauts after gravitational transitions. When astronauts are trained before flight with supra-threshold noisy, stochastic vestibular stimulation (SVS), the central nervous system can be trained to reweight sensory information by using veridical information from other sensory inputs (such as vision and proprioception) for postural and gait control. This reweighting, in turn, can enhance functional performance in novel gravitational environments. However, the optimal maximum amplitude of stimulation has not yet been identified that can simulate the effect of deterioration in vestibular inputs for preflight training or for evaluating vestibular contribution in functional tests in general. Most studies have used arbitrary but fixed maximum current amplitudes from 3 to 5 mA in the mediolateral (ML) direction to disrupt balance function in both ML and anterior-posterior directions in healthy adults. The goal of this study was to determine the minimum SVS level that yields an equivalently degraded balance performance. Fourteen subjects stood on a compliant surface with their eyes closed and were instructed to maintain a stable upright stance. Measures of stability of the head, trunk, and whole body were quantified in the ML direction. Objective perceptual motion thresholds were estimated ahead of time by having subjects sit on a chair with their eyes closed and giving 1-Hz bipolar binaural sinusoidal electrical stimulation at various current amplitudes. Results from the balance task suggest that using stimulation amplitudes of 280% of motion-perceptual threshold (~2.2 mA on average) significantly degraded balance performance.
Running-related injuries are most often single-sided and are partially attributed to lower limb movement and loading asymmetries. For example, runners with tibial stress fractures demonstrate asymmetry in loading rate. Running is a dynamic athletic event in which runners often engage in both inclined and declined running with the goal of improving conditioning. Symmetry Angle (SA) is a commonly used, robust measure of determining symmetry. The purpose of this study was to compare peak vertical ground reaction force (VGRF) symmetry using the SA during uphill, level and downhill running on an instrumented treadmill.
Eleven healthy adults volunteered to participate in this study and running at 2.7 m/s at grades of 0°, 5.74° incline and 5.74° decline were analyzed. SA was computed using the peak VGRF values from both the limbs.
RESULTS AND DISCUSSION
No statistically significant differences in SA were observed between the three running conditions. (p=0.61) The unexpected uniformity in vertical GRF across uphill, level, and downhill running is consistent with the absence of changes in the peak magnitudes of the GRF observed previously. This suggests that neither moderate uphill or downhill running result in increases in peak GRF that may be considered injurious.
This was the first study that looked at kinetic symmetry using peak GRF in healthy recreational runners during the three running conditions. This study suggested that uphill and downhill running does not contribute to potential differences in interlimb symmetry and could be considered as a safe alternative to level running on a treadmill.