A test of the effort equalization hypothesis in children with cerebral palsy who have an asymmetric gait

Healthy people can walk nearly effortlessly thanks to their instinctively adaptive gait patterns that tend to minimize metabolic energy consumption. However, the economy of gait is severely impaired in many neurological disorders such as stroke or cerebral palsy (CP). Moreover, self-selected asymmetry of impaired gait does not seem to unequivocally coincide with the minimal energy cost, suggesting the presence of other adaptive origins. Here, we used hemiparetic CP gait as a model to test the hypothesis that pathological asymmetric gait patterns are chosen to equalize the relative muscle efforts between the affected and unaffected limbs. We determined the relative muscle efforts for the ankle and knee extensors by relating extensor joint moments during gait to maximum moments obtained from all-out hopping reference test. During asymmetric CP gait, the unaffected limb generated greater ankle (1.36±0.15 vs 1.17±0.16 Nm/kg, p = 0.002) and knee (0.74±0.33 vs 0.44±0.19 Nm/kg, p = 0.007) extensor moments compared with the affected limb. Similarly, the maximum moment generation capacity was greater in the unaffected limb versus the affected limb (ankle extensors: 1.81±0.39 Nm/kg vs 1.51±0.34 Nm/kg, p = 0.033; knee extensors: 1.83±0.37 Nm/kg vs 1.34±0.38 Nm/kg, p = 0.021) in our force reference test. As a consequence, no differences were found in the relative efforts between unaffected and affected limb ankle extensors (77±12% vs 80±16%, p = 0.69) and knee extensors (41±17% vs 38±23%, p = 0.54). In conclusion, asymmetric CP gait resulted in similar relative muscle efforts between affected and unaffected limbs. The tendency for effort equalization may thus be an important driver of self-selected gait asymmetry patterns, and consequently advantageous for preventing fatigue of the weaker affected side musculature.

Change of Direction Biomechanics in a 180-Degree Pivot Turn and the Risk for Noncontact Knee Injuries in Youth Basketball and Floorball Players

BACKGROUND

Studies investigating biomechanical risk factors for knee injuries in sport-specific tasks are needed.

PURPOSE

To investigate the association between change of direction (COD) biomechanics in a 180-degree pivot turn and knee injury risk among youth team sport players.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

A total of 258 female and male basketball and floorball players (age range, 12-21 years) participated in the baseline COD test and follow-up. Complete data were obtained from 489 player-legs. Injuries, practice, and game exposure were registered for 12 months. The COD test consisted of a quick ball pass before and after a high-speed 180-degree pivot turn on the force plates. The following variables were analyzed: peak vertical ground-reaction force (N/kg); peak trunk lateral flexion angle (degree); peak knee flexion angle (degree); peak knee valgus angle (degree); peak knee flexion moment (N·m/kg); peak knee abduction moment (N·m/kg); and peak knee internal and external rotation moments (N·m/kg). Legs were analyzed separately and the mean of 3 trials was used in the analysis. Main outcome measure was a new acute noncontact knee injury.

RESULTS

A total of 18 new noncontact knee injuries were registered (0.3 injuries/1000 hours of exposure). Female players sustained 14 knee injuries and male players 4. A higher rate of knee injuries was observed in female players compared with male players (incidence rate ratio, 6.2; 95% CI, 2.1-21.7). Of all knee injuries, 8 were anterior cruciate ligament (ACL) injuries, all in female players. Female players displayed significantly larger peak knee valgus angles compared with male players (mean for female and male players, respectively: 13.9°± 9.4° and 2.0°± 8.5°). No significant associations between biomechanical variables and knee injury risk were found.

CONCLUSION

Female players were at increased risk of knee and ACL injury compared with male players. Female players performed the 180-degree pivot turn with significantly larger knee valgus compared with male players. However, none of the investigated variables was associated with knee injury risk in youth basketball and floorball players.

A 3D motion capture analysis of a giving-way ankle episode during a 180-degree pivot turn: A case report

Lateral ankle sprains are highly prevalent during sporting activities, as it accounts for approximately 60% of all athletic injuries. There is currently a paucity of research which provides kinetic and kinematic assessments of sprains and giving-way episodes of the ankle joint. The aim of this case study was to examine the kinetics and kinematics of the ankle and knee during a giving-way episode in a female ice hockey player during a 180-degree pivot turn, which was conducted in a 3D motion capture laboratory. Three trials were conducted on this participant (one accident trial, two control trials). Kinetic and kinematic analysis was conducted on the outside leg during a left 180-degree pivot turn (right leg). The plantarflexion angle of the giving-way trial was larger than the control trials from the point of initial contact until the end of the trial. Inversion was also 27-degrees greater 150 ms after initial contact in the giving-way trial and 26-degrees greater compared to control trials 1 and 2. Substantially greater plantarflexion, inversion and internal rotation angles of the ankle were observed during the giving-way trial compared to control trials. The maximum vertical and horizontal ground reaction forces, as well as ankle inversion and internal rotation moments, were lower for the giving-way trial in comparison to the control trials. Further research is needed to understand the influence of plantarflexion angle with a giving-way episode of the ankle. This study provides valuable kinetic and kinematic information regarding a giving-way episode of the ankle.

The gait is less stable in children with cerebral palsy in normal and dual-task gait compared to typically developed peers

There is limited evidence about gait stability and its alteration by concurrent motor and cognitive tasks in children with cerebral palsy (CP). We examined gait stability and how it is altered by constrained cognitive or motor task in CP and their typically developed (TD) controls. Gait kinematics were recorded using inertial-measurement units (IMU) from 18 patients with hemiplegia (13.5 ± 2.4 years), 12 with diplegia (13.0 ± 2.1 years), and 31 TD controls (13.5 ± 2.2 years) during unconstrained gait, and motor (carrying a tray) and cognitive (word naming) task constrained gait at preferred speed (~400 steps/task). Step duration, its standard deviation and refined-compound-multiscale entropy (RCME) were computed independently for vertical and resultant horizontal accelerations. Gait complexity was higher for patients with CP than TD in all tasks and directions (p < 0.001-0.01), being pronounced in vertical direction, cognitive task and for diplegic patients (p < 0.05-0.001). The gait complexity increased more (i.e. higher dual-task cost) from the unconstrained to the constrained gait in CP compared to TD (p < 0.05). Step duration was similar in all groups (p > 0.586), but its variation was higher in CP than TD (p < 0.001-0.05), and during the constrained than unconstrained gait in all groups (p < 0.01-0.001). The gait in children with CP was more complex and the dual-task cost was higher primarily for children with diplegic CP than TD during cognitive task, indicating that attentional load hinders their gait more. This raises the hypothesis that more attention and cortical resources are needed to compensate for the impaired gait in children with CP.

Can the Functional Movement Screen Method Identify Previously Injured Wushu Athletes?

The functional movement screen (FMS) is commonly used to evaluate sports injury risks, but no study has been reported for Wushu athletes. The aim of this study was to identify optimal FMS cut-off points for previously injured Wushu athletes and to examine the associations with other possible factors. In this study, a total of 84 Chinese Wushu athletes (15.1 ± 4.5 years old, 51% male) with a minimum of two years of professional training background in either Taiji, Changquan, or Nanquan were assessed by the FMS. Video recordings were used to confirm the scoring criteria, and previous injuries were assessed based on face-to-face interviews. An optimal cut-off of the FMS score was investigated by receiver operating characteristic curves with sensitivity and specificity. We found that FMS score of less than 16 (sensitivity = 80%, specificity = 56%) was related to an increased occurrence of injuries (odds ratio = 5.096, 95%CI: 1.679-15.465) for the current study sample. The training type and training levels were related with FMS scores. More than half of the athletes (58%) had FMS asymmetry and 21% of athletes reported pain while performing the FMS protocol. Future prospective studies are recommended to use FMS with cut-off of 16 points in Wushu athletes.

Deep learning approach for prediction of impact peak appearance at ground reaction force signal of running activity

Protruding impact peak is one of the features of vertical ground reaction force (GRF) that is related to injury risk while running. The present research is dedicated to predicting GRF impact peak appearance by setting a binary classification problem. Kinematic data, namely a number of raw signals in the sagittal plane, collected by the Vicon motion capture system (Oxford Metrics Group, UK) were employed as predictors. Therefore, the input data for the predictive model are presented as a multi-channel time series. Deep learning techniques, namely five convolutional neural network (CNN) models were applied to the binary classification analysis, based on a Multi-Layer Perceptron (MLP) classifier, support vector machine (SVM), logistic regression, k-nearest neighbors (kNN), and random forest algorithms. SVM, logistic regression, and random forest classifiers demonstrated performances that do not statistically significantly differ. The best classification accuracy achieved is 81.09% ± 2.58%. Due to good performance of the models, this study serves as groundwork for further application of deep learning approaches to predicting kinetic information based on this kind of input data.

Ankle and knee extensor muscle effort during locomotion in young and older athletes: Implications for understanding age-related locomotor decline

Age-related reduction in muscle force generation capacity is similarly evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. To better understand why ageing has the largest detrimental effect on ankle joint function during locomotion, we examined maximal ankle and knee extensor force development during a two-leg hopping test in older and young men, and used these forces as a reference to calculate relative operating efforts for the knee and ankle extensors as participants walked, ran and sprinted. We found that, across locomotion modes in both age groups, ankle extensors operated at a greater relative effort compared to knee extensors; however, slightly less pronounced differences between ankle and knee extensor muscle efforts were present among older men, mainly due to a reduction in the ankle extensor force generation during locomotion modes. We consider these findings as evidence that reduced ankle push-off function in older age is driven by a tendency to keep ankle extensor effort during locomotion lower than it would otherwise be, which, in turn, may be an important self-optimisation strategy to prevent locomotor-induced fatigue of ankle extensor muscles.

Effects of medially posted insoles on foot and lower limb mechanics across walking and running in overpronating men

Anti-pronation orthoses, like medially posted insoles (MPI), have traditionally been used to treat various of lower limb problems. Yet, we know surprisingly little about their effects on overall foot motion and lower limb mechanics across walking and running, which represent highly different loading conditions. To address this issue, multi-segment foot and lower limb mechanics was examined among 11 overpronating men with normal (NORM) and MPI insoles during walking (self-selected speed 1.70±0.19m/s vs 1.72±0.20m/s, respectively) and running (4.04±0.17m/s vs 4.10±0.13m/s, respectively). The kinematic results showed that MPI reduced the peak forefoot eversion movement in respect to both hindfoot and tibia across walking and running when compared to NORM (p<0.05-0.01). No differences were found in hindfoot eversion between conditions. The kinetic results showed no insole effects in walking, but during running MPI shifted center of pressure medially under the foot (p<0.01) leading to an increase in frontal plane moments at the hip (p<0.05) and knee (p<0.05) joints and a reduction at the ankle joint (p<0.05). These findings indicate that MPI primarily controlled the forefoot motion across walking and running. While kinetic response to MPI was more pronounced in running than walking, kinematic effects were essentially similar across both modes. This suggests that despite higher loads placed upon lower limb during running, there is no need to have a stiffer insoles to achieve similar reduction in the forefoot motion than in walking.

Predictors of lower extremity injuries in team sports (PROFITS-study): a study protocol

INTRODUCTION

Several intrinsic risk factors for lower extremity injuries have been proposed, including lack of proper knee and body control during landings and cutting manoeuvres, low muscular strength, reduced balance and increased ligament laxity, but there are still many unanswered questions. The overall aim of this research project is to investigate anatomical, biomechanical, neuromuscular, genetic and demographic risk factors for traumatic non-contact lower extremity injuries in young team sport athletes. Furthermore, the research project aims to develop clinically oriented screening tools for predicting future injury risk.

METHODS

Young female and male players (n=508) from nine basketball teams, nine floorball teams, three ice hockey teams, and one volleyball team accepted the invitation to participate in this four-and-half-year prospective follow-up study. The players entered the study either in 2011, 2012 or 2013, and gave blood samples, performed physical tests and completed the baseline questionnaires. Following the start of screening tests, the players will be followed for sports injuries through December 2015. The primary outcome is a traumatic non-contact lower extremity injury. The secondary outcomes are other sports-related injuries. Injury risk is examined on the basis of anatomical, biomechanical, neuromuscular, genetic and other baseline factors. Univariate and multivariate regression models will be used to investigate association between investigated parameters and injury risk.

Which muscles compromise human locomotor performance with age?

Ageing leads to a progressive decline in human locomotor performance. However, it is not known whether this decline results from reduced joint moment and power generation of all lower limb muscle groups or just some of them. To further our understanding of age-related locomotor decline, we compare the amounts of joint moments and powers generated by lower limb muscles during walking (self-selected), running (4 m s(-1)) and sprinting (maximal speed) among young, middle-aged and old adults. We find that age-related deficit in ankle plantarflexor moment and power generation becomes more severe as locomotion change from walking to running to sprinting. As a result, old adults generate more power at the knee and hip extensors than their younger counterparts when walking and running at the same speed. During maximal sprinting, young adults with faster top speeds demonstrate greater moments and powers from the ankle and hip joints, but interestingly, not from the knee joint when compared with the middle-aged and old adults. These findings indicate that propulsive deficit of ankle contributes most to the age-related locomotor decline. In addition, reduced muscular output from the hip rather than from knee limits the sprinting performance in older age.

Knee extensor and flexor dominant gait patterns increase the knee frontal plane moment during walking

High gait-induced knee frontal plane moment is linked with the development of knee osteoarthritis. Gait patterns across the normal population exhibit large inter-individual variabilities especially at the knee sagittal plane moment profile during loading response and terminal stance phase. However, the effects of different gait patterns on this moment remain unknown. Therefore, we examined whether different gait patterns are associated with atypically high knee frontal plane moments. Profiles of knee joint moments divided a sample of 24 subjects into three subgroups (11, 7, 6) through cluster analysis. Kinetics, kinematics, and spatio-temporal parameters were compared among clusters. Subjects who showed a typical sagittal plane moment pattern (n = 11) had 43% lower first peak of knee frontal plane moment compared to the cluster, which showed the dominance of the knee extensor moment during stance phase (n = 7, p < 0.01). In addition, a typical gait pattern cluster had 44% lower second peak knee frontal plane moment than the cluster, which showed the dominance of the knee flexor moment during the terminal stance phase (n = 6, p < 0.05). These findings indicate that different knee strategies driving gait considerably impact knee loading, suggesting that knee extensor and flexor dominant gait patterns demonstrate atypically high knee frontal plane moments. People in these subgroups may, therefore, be at higher risk of developing knee osteoarthritis.