Fixed muscle synergies and their potential to improve the intuitive control of myoelectric assistive technology for upper extremities.

BACKGROUND: Users of myoelectric controlled assistive technology (AT) for upper extremities experience difficulties in controlling this technology in daily life, partly because the control is non-intuitive. Making the control of myoelectric AT intuitive may resolve the experienced difficulties. The present paper was inspired by the suggestion that intuitive control may be achieved if the control of myoelectric AT is based on neuromotor control principles. A significant approach within neurocomputational motor control suggests that myosignals are produced via a limited number of fixed muscle synergies. To effectively employ this approach in myoelectric AT, it is required that a limited number of muscle synergies is systematically exploited, also when muscles are used differently as required in controlling myoelectric AT. Therefore, the present study examined the systematic exploitation of muscle synergies when muscles were used differently to complete point-to-point movements with and without a rod. METHODS: Healthy participants made multidirectional point-to-point movements with different end-effectors, i.e. with the index finger and with rods of different lengths. Myosignals were collected from 22 muscles in the arm, trunk, and back, and subsequently partitioned into muscle synergies per end-effector and for a pooled dataset including all end-effectors. The exploitation of these muscle synergies was assessed by evaluating the similarity of structure and explanatory ability of myosignals of per end-effector muscle synergies and the contribution of pooled muscle synergies across end-effectors. RESULTS: Per end-effector, 3-5 muscle synergies could explain 73.8-81.1% of myosignal variation, whereas 6-8 muscle synergies from the pooled dataset also captured this amount of myosignal variation. Subsequent analyses showed that gradually different muscle synergies-extracted from separate end-effectors-were exploited across end-effectors. In line with this result, the order of contribution of muscle synergies extracted from the pooled dataset gradually reversed across end-effectors. CONCLUSION: A limited number of muscle synergies was systematically exploited in the examined set of movements, indicating a potential for the fixed muscle synergy approach to improve the intuitive control of myoelectric AT. Given the gradual change in muscle synergy exploitation across end-effectors, future research should examine whether this potential can be extended to a larger range of movements and tasks.

The development of consistency and flexibility in manual pointing during middle childhood.

Goal-directed actions become truly functional and skilled when they are consistent yet flexible. In manual pointing, end-effector consistency is characterized by the end position of the index fingertip, whereas flexibility in movement execution is captured by the use of abundant arm-joint configurations not affecting the index finger end position. Because adults have been shown to exploit their system's flexibility in challenging conditions, we wondered whether during middle childhood children are already able to exploit motor flexibility when demanded by the situation. We had children aged 5-10 years and adults perform pointing movements in a nonchallenging and challenging condition. Results showed that end-effector errors and flexibility in movement execution decreased with age. Importantly, only the 9-10-year-olds and adults showed increased flexibility in the challenging condition. Thus, while consistency increases and flexibility decreases during mid-childhood development, from the age of nine children appear able to employ more flexibility with increasing task demands.

Superior return to sports rate after patellar tendon autograft over patellar tendon allograft in revision anterior cruciate ligament reconstruction.

PURPOSE: After revision anterior cruciate ligament reconstruction (ACLR), the rate of return to the pre-injury type of sport (RTS type) is low and graft choice might be an important factor. The aim of this study was to determine whether there is a difference in outcome after revision ACLR using a patellar tendon allograft compared to an ipsilateral patellar tendon autograft. It was hypothesized that the rate of RTS type using an ipsilateral patellar tendon autograft will be superior to using patellar tendon allograft. METHODS: The design is a retrospective cohort study. Inclusion criteria were patients who underwent revision ACLR with a minimum follow-up of 1 year after revision using a patellar allograft or ipsilateral autograft. Primary study parameter was rate of RTS type. Secondary study parameters were RTS level, subscores of the KOOS, the IKDCsubjective, the Tegner score and reasons for no RTS. RESULTS: Eighty-two patients participated in this study (36 allografts and 46 autografts). In patients with a minimum follow-up of 1 year, rate of RTS type was 51.4% for the patellar tendon allograft and 62.8% for the patellar tendon autograft group (n.s.). In patients with a minimum follow-up rate of 2 years, rate of RTS type was 43.3 versus 75.0%, respectively (p = 0.027). No differences in secondary study parameters were found. In patients with a minimum follow-up of 1 year, rate of RTS type was significantly higher (p = 0.025) for patients without anxiety compared to patients who were anxious to perform certain movements. CONCLUSION: After a minimum follow-up of 2 years, rate of RTS type is in favour of using an ipsilateral patellar tendon autograft when compared to using a patellar tendon allograft in patients undergoing revision ACLR; after a minimum follow-up of 1 year, no significant difference was found. In revision ACLR, the results of this study might influence graft choice in favour of autologous graft when the use of an allograft or autograft patellar tendon is considered. LEVEL OF EVIDENCE: III.

Innovative Video Feedback on Jump Landing Improves Landing Technique in Males.

Video feedback may be a powerful tool to change biomechanical landing patterns associated with anterior cruciate ligament (ACL) injury risk. This study investigated the effect of video feedback on drop vertical jump (DVJ) landing strategies in team sport athletes. 59 athletes were assigned to a video feedback (VI) or control (CTRL) group. A pretest, 2 training sessions and a posttest were conducted. In both training sessions, video feedback, consisting of a video of the athlete's contour superimposed onto an expert's contour performing the DVJ landing task, was provided to the VI group; the CTRL group did not receive feedback. Outcomes included: kinematics and kinetics at peak knee valgus/varus moment during pre- and posttest and percentage overlap of expert and athlete during the training sessions. At posttest, males in the VI group showed greater hip flexion angles (p=0.001) and range of motion (p<0.001), smaller vertical ground reaction force, and smaller ankle dorsiflexion moment (p<0.001) compared to pretest. At posttest, males in the VI group demonstrated smaller vertical ground reaction force (p=0.031) and ankle dorsiflexion moment (p=0.001) compared to males in the CTRL group. The VI group increased percentage overlap with the expert during training sessions and from start of the first to the end of the second training session (p<0.001). Overall, video feedback was effective to modify landing strategies favorably in males. While females imitated the expert model, their landing strategy did not change significantly. While Females may need additional (verbal) feedback to benefit from video feedback.

A Novel Mass-Spring-Damper Model Analysis to Identify Landing Deficits in Athletes Returning to Sport After Anterior Cruciate Ligament Reconstruction.

Schneider, DK, Gokeler, A, Otten, E, Ford, KR, Hewett, TE, Divine, JG, Colosimo, AJ, Heidt, RS, and Myer, GD. A Novel mass-spring-damper model analysis to identify landing deficits in athletes returning to sport after anterior cruciate ligament reconstruction. J Strength Cond Res 31(9): 2590-2598, 2017-A mass-spring-damper (MSD) model may serve as an extension of biomechanical data from 3-dimensional motion analysis and epidemiological data which helps to delineate populations at risk for anterior cruciate ligament (ACL) injuries. The purpose of this study was to evaluate such a model. Thirty-six ACL reconstruction (ACLR) group subjects and 67 controls (CTRL) completed single-leg drop landing and single-leg broad jump tasks. Landing ground reaction force data were collected and analyzed with an MSD model. Medians, interquartile ranges, and limb symmetry indices (LSIs) were calculated and comparisons were made within and between groups. During a single-leg drop landing, the ACLR group had a lower spring LSI than the CTRL group (p = 0.015) and landed with decreased stiffness in the involved limb relative to the uninvolved limb (p = 0.021). The ACLR group also had an increased damping LSI relative to the CTRL group (p = 0.045). The ACLR subjects landed with increased stiffness (p = 0.006) and decreased damping (p = 0.003) in their involved limbs compared to CTRL subjects' nondominant limbs. During a single-leg forward broad jump, the ACLR group had a greater spring LSI value than the CTRL group (p = 0.045). The CTRL group also recorded decreased damping values in their nondominant limbs compared with the involved limbs of the ACLR group (p = 0.046). Athletes who have undergone ACLR display different lower-limb dynamics than healthy controls, according to an MSD model. Quadriceps dominance and leg dominance are components of ACLR athletes' landing strategies and may be identified with an MSD model and addressed during rehabilitation.

Immersive virtual reality improves movement patterns in patients after ACL reconstruction: implications for enhanced criteria-based return-to-sport rehabilitation.

PURPOSE: The purpose of this study was to evaluate the influence of immersion in a virtual reality environment on knee biomechanics in patients after ACL reconstruction (ACLR). It was hypothesized that virtual reality techniques aimed to change attentional focus would influence altered knee flexion angle, knee extension moment and peak vertical ground reaction force (vGRF) in patients following ACLR. METHODS: Twenty athletes following ACLR and 20 healthy controls (CTRL) performed a step-down task in both a non-virtual reality environment and a virtual reality environment displaying a pedestrian traffic scene. A motion analysis system and force plates were used to measure kinematics and kinetics during a step-down task to analyse each single-leg landing. RESULTS: A significant main effect was found for environment for knee flexion excursion (P = n.s.). Significant interaction differences were found between environment and groups for vGRF (P = 0.004), knee moment (P < 0.001), knee angle at peak vGRF (P = 0.01) and knee flexion excursion (P = 0.03). There was larger effect of virtual reality environment on knee biomechanics in patients after ACLR compared with controls. CONCLUSION: Patients after ACLR immersed in virtual reality environment demonstrated knee joint biomechanics that approximate those of CTRL. The results of this study indicate that a realistic virtual reality scenario may distract patients after ACLR from conscious motor control. Application of clinically available technology may aid in current rehabilitation programmes to target altered movement patterns after ACLR. LEVEL OF EVIDENCE: Diagnostic study, Level III.

Quadriceps function following ACL reconstruction and rehabilitation: implications for optimisation of current practices.

PURPOSE: To determine the most effective practices for quadriceps strengthening after ACL reconstruction. METHODS: An electronic search has been performed for the literature appearing from January 1990 to January 2012. Inclusion criteria were articles written in English, German or Dutch with unilateral ACL-reconstructed patients older than 13 years, RCT rehabilitation programmes containing muscle strengthening, protocol described in detail and time frame of measurements reported. Quadriceps muscle strength and patient-reported outcomes were the endpoints. Included studies were assessed on their methodological quality using the CONSORT Checklist. RESULTS: From 645 identified studies, 10 met the inclusion criteria. Seven studies found an increase in quadriceps strength after intervention programmes regardless of type of training. An eccentric exercise programme showed significantly better values for isometric quadriceps strength compared to a concentric exercise programme. The Tegner activity scale showed a significant increase in activity level for all training programmes. The Cincinnati Knee Rating System showed significant improvements in particular for the neuromuscular training group. CONCLUSIONS: The evidence from this review indicates that eccentric training may be most effective to restore quadriceps strength, but full recovery may not be achieved with current rehabilitation practices. Neuromuscular training incorporating motor learning principles should be added to strengthening training to optimise outcome measurements. LEVEL OF EVIDENCE: II.

A Passive Polycentric Mechanism to Improve Active Mediolateral Balance in Prosthetic Walking.

Prosthetic legs are typically passive systems without active ankle control, restricting mediolateral balancing to a hip strategy. Resulting balance control impairments for persons with a lower extremity amputation may be mitigated by increasing hip strategy effectiveness, in which relatively small hip moments of force are adequate for mediolateral balancing. To increase hip strategy effectiveness we have developed a prosthetic leg prototype based on the Peaucellier mechanism, the Sideways Balance Mechanism (SBM). This polycentric mechanism adds a frontal plane degree of freedom, reducing mediolateral body displacements. Adding a passive joint alone introduces instability, in which mediolateral body rotation leads to CoM height loss, ultimately resulting in a fall. The SBM however provides stability typically absent by lengthening under rotation, thereby compensating for CoM height loss. By allowing for both foot rotation (in-/eversion), and increased mediolateral ground reaction force the SBM increases hip strategy effectiveness. We aimed to provide proof of principle that the SBM can improve active mediolateral balance control in prosthetic walking by increasing hip strategy effectiveness compared to a typical set-up. Comparison between a typical set-up and the SBM showed an increased mediolateral ground reaction force at equal hip moments of force for a 2D forwards dynamics computer simulation, and a reduced hip moment of force at equal mediolateral ground reaction force for a case study. Results validate increased hip strategy effectiveness of the SBM compared to a typical set-up, providing proof of principle that adding an SBM to a prosthetic set-up improves mediolateral balance control in prosthetic walking.

Establishing central sensitization inventory cut-off values in Dutch-speaking patients with chronic low back pain by unsupervised machine learning.

BACKGROUND: Human Assumed Central Sensitization (HACS) is involved in the development and maintenance of chronic low back pain (CLBP). The Central Sensitization Inventory (CSI) was developed to evaluate the presence of HACS, with a cut-off value of 40/100. However, various factors including pain conditions (e.g., CLBP), contexts, and gender may influence this cut-off value. Unsupervised clustering approaches can address these complexities by considering diverse factors and exploring possible HACS-related subgroups. Therefore, this study aimed to determine the cut-off values for a Dutch-speaking population with CLBP based on unsupervised machine learning. METHODS: Questionnaire data covering pain, physical, and psychological aspects were collected from patients with CLBP and aged-matched healthy controls (HC). Four clustering approaches were applied to identify HACS-related subgroups based on the questionnaire data and gender. The clustering performance was assessed using internal and external indicators. Subsequently, receiver operating characteristic (ROC) analysis was conducted on the best clustering results to determine the optimal cut-off values. RESULTS: The study included 63 HCs and 88 patients with CLBP. Hierarchical clustering yielded the best results, identifying three clusters: healthy group, CLBP with low HACS level, and CLBP with high HACS level groups. The cut-off value for the overall groups were 35 (sensitivity 0.76, specificity 0.76). CONCLUSION: This study found distinct patient subgroups. An overall CSI cut-off value of 35 was suggested. This study may provide new insights into identifying HACS-related patterns and contributes to establishing accurate cut-off values.

Relation between muscle activation pattern and pain: an explorative study in a bassists population.

OBJECTIVE: To explore the muscle activation patterns in relation to pain complaints in bassists studied during a musical task. This study was based on the assumption that pain complaints are caused by increased muscle activation during playing or relaxation and/or faster onset of fatigue of muscles. DESIGN: Cross-sectional study. SETTING: Nonclinical. PARTICIPANTS: Student bass guitarists (N=36) from conservatories in the Netherlands. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Bassists played a standard music piece for 30 minutes. Muscle activation levels and pain were recorded. Pain was registered with a Numeric Rating Scale (NRS 0-10). The muscle activation level of both the trapezius muscles and flexor carpi radialis was measured with sEMG: sEMG as the percentage of the maximal voluntary isometric contraction (%MVC) and the slope of the sEMG (slope of %MVC) were calculated. The %MVC as a function of time and the slope of %MVC were calculated during playing and for rest periods before and after playing. For statistic analysis, the Mann-Whitney U test and a multilevel multiregression analysis were used for comparing the sEMG data of bassists with and without pain. RESULTS: No significant differences in %MVC or the slope of %MVC were between the bassists with and without pain complaints. CONCLUSIONS: The results surprisingly indicate that pain complaints of bassists may not be associated with another muscle activation pattern. It is, therefore, not likely that pain is caused by increased muscle activation during playing and/or relaxation, nor by faster onset of fatigue.

Relationship between physical activity and central sensitization in chronic low back pain: Insights from machine learning.

BACKGROUND AND OBJECTIVES: Chronic low back pain (CLBP) is a leading cause of disability. The management guidelines for the management of CLBP often recommend optimizing physical activity (PA). Among a subsample of patients with CLBP, central sensitization (CS) is present. However, knowledge about the association between PA intensity patterns, CLBP, and CS is limited. The objective PA computed by conventional approaches (e.g. cut-points) may not be sensitive enough to explore this association. This study aimed to investigate PA intensity patterns in patients with CLBP and low or high CS (CLBP-, CLBP+, respectively) by using advanced unsupervised machine learning approach, Hidden semi-Markov model (HSMM). METHODS: Forty-two patients were included (23 CLBP-, 19 CLBP+). CS-related symptoms (e.g. fatigue, sensitivity to light, psychological features) were assessed by a CS Inventory. Patients wore a standard 3D-accelerometer for one week and PA was recorded. The conventional cut-points approach was used to compute the time accumulation and distribution of PA intensity levels in a day. For the two groups, two HSMMs were developed to measure the temporal organization of and transition between hidden states (PA intensity levels), based on the accelerometer vector magnitude. RESULTS: Based on the conventional cut-points approach, no significant differences were found between CLBP- and CLBP+ groups (p = 0.87). In contrast, HSMMs revealed significant differences between the two groups. For the 5 identified hidden states (rest, sedentary, light PA, light locomotion, and moderate-vigorous PA), the CLBP- group had a higher transition probability from rest, light PA, and moderate-vigorous PA states to the sedentary state (p < 0.001). In addition, the CBLP- group had a significantly shorter bout duration of the sedentary state (p < 0.001). The CLBP+ group exhibited longer durations of active (p < 0.001) and inactive states (p = 0.037) and had higher transition probabilities between active states (p < 0.001). CONCLUSIONS: HSMM discloses the temporal organization and transitions of PA intensity levels based on accelerometer data, yielding valuable and detailed clinical information. The results imply that patients with CLBP- and CLBP+ have different PA intensity patterns. CLBP+ patients may adopt the distress-endurance response pattern with a prolonged bout duration of activity engagement.

Concurrent validation of the Xsens IMU system of lower-body kinematics in jump-landing and change-of-direction tasks.

Inertial measurement units (IMUs) allow for measurements of kinematic movements outside the laboratory, persevering the athlete-environment relationship. To use IMUs in a sport-specific setting, it is necessary to validate sport-specific movements. The aim of this study was to assess the concurrent validity of the Xsens IMU system by comparing it to the Vicon optoelectronic motion system for lower-limb joint angle measurements during jump-landing and change-of-direction tasks. Ten recreational athletes performed four tasks; single-leg hop and landing, running double-leg vertical jump landing, single-leg deceleration and push off, and sidestep cut, while kinematics were recorded by 17 IMUs (Xsens Technologies B.V.) and eight motion capture cameras (Vicon Motion Systems, Ltd). Validity of lower-body joint kinematics was assessed using measures of agreement (cross-correlation: XCORR) and error (root mean square deviation and amplitude difference). Excellent agreement was found in the sagittal plane for all joints and tasks (XCORR > 0.92). Highly variable agreement was found for knee and ankle in transverse and frontal plane. Relatively high error rates were found in all joints. In conclusion, this study shows that the Xsens IMU system provides highly comparable waveforms of sagittal lower-body joint kinematics in sport-specific movements. Caution is advised interpreting frontal and transverse plane kinematics as between-system agreement highly varied.

Muscular and kinematic features in speed skaters indicate a task-specific dystonia.

OBJECTIVE: Skater's cramp is a movement disorder in speed skaters. We investigated whether affected skaters matched the disease profile of task-specific dystonia, specifically whether there was evidence of maladaptive muscle activity occurring simultaneously with aberrant movements (jerking). We further examined different skating intensities, positing no change would be more indicative of task-specific dystonia. METHODS: We analyzed video, kinematic and muscle activity in 14 affected skaters. We measured the angular velocity and electromyographic activity of normalized speed skating strokes using one dimensional statistical non-parametric mapping. Skaters were matched with comparably skilled controls, and filled out a bespoke clinical questionnaire. RESULTS: Skaters' impacted leg showed over-activation in the peroneus longus, tibialis anterior and gastrocnemius that coincided with higher foot movement compared to their healthy leg and controls. This pattern persisted regardless of skating intensity. Clinical features indicated it was task-specific and painless with common trigger factors including stress, equipment change, and falling. CONCLUSIONS: We showed aberrant muscular and kinematic activity in a movement disorder in speed skaters indicative of task-specific dystonia. SIGNIFICANCE: Understanding skater's cramp as a task-specific dystonia could reduce the damage that misdiagnosis and unsuccessful invasive operations have caused. Our quantitative method has value in testing future treatment efficacy.

Keeping your balance while balancing a cylinder: interaction between postural and voluntary goals.

The present study investigated whether postural responses are influenced by the stability constraint of a voluntary, manual task. We also examined how task constraint and first experience (the condition with which the participants started the experiment) influence the kinematic strategies used to simultaneously accomplish a postural response and a voluntary task. Twelve healthy, older adults were perturbed during standing, while holding a tray with a cylinder placed with the flat side down (low constraint, LC) or with the rolling, round side down (high constraint, HC). Central set changed according to the task constraint, as shown by a higher magnitude of both the gastrocnemius and tibialis anterior muscle activation bursts in the HC than in the LC condition. This increase in muscle activation was not reflected, however, in changes in the center of pressure or center of mass displacement. Task constraint influenced the peak shoulder flexion for the voluntary tray task but not the peak hip flexion for the postural task. In contrast, first experience influenced the peak hip flexion but not the peak shoulder flexion. These results suggest an interaction between two separate control mechanisms for automatic postural responses and voluntary stabilization tasks.

Proprioceptive deficits after ACL injury: are they clinically relevant?

OBJECTIVE: To establish the clinical relevance of proprioceptive deficits reported after anterior cruciate ligament (ACL) injury. MATERIAL AND METHODS: A literature search was done in electronic databases from January 1990 to June 2009. Inclusion criteria for studies were ACL deficient (ACL-D) and ACL reconstruction (ACL-R) articles written in English, Dutch or German and calculation of correlation(s) between proprioception tests and clinical outcome measures. Clinical outcome measures were muscle strength, laxity, hop test, balance, patient-reported outcome, objective knee score rating, patient satisfaction or return to sports. Studies included in the review were assessed on their methodological quality. RESULTS: In total 1161 studies were identified of which 24 met the inclusion criteria. Pooling of all data was not possible due to substantial differences in measurement techniques and data analysis. Most studies failed to perform reliability measurements of the test device used. In general, the correlation between proprioception and laxity, balance, hop tests and patient outcome was low. Four studies reported a moderate correlation between proprioception, strength, balance or hop test. CONCLUSION: There is limited evidence that proprioceptive deficits as detected by commonly used tests adversely affect function in ACL-D and ACL-R patients. Development of new tests to determine the relevant role of the sensorimotor system is needed. These tests should ideally be used as screening tests for primary and secondary prevention of ACL injury.

Concurrent validation of the Noraxon MyoMotion wearable inertial sensors in change-of-direction and jump-landing tasks.

Wearable inertial sensors (WIS) facilitate the preservation of the athlete-environment relationship by allowing measurement outside the laboratory. WIS systems should be validated for team sports movements before they are used in sports performance and injury prevention research. The aim of the present study was to investigate the concurrent validity of a wearable inertial sensor system in quantifying joint kinematics during team sport movements. Ten recreationally active participants performed change-of-direction (single-leg deceleration and sidestep cut) and jump-landing (single-leg hop, single-leg crossover hop, and double-leg vertical jump) tasks while motion was recorded by nine inertial sensors (Noraxon MyoMotion, Noraxon USA Inc.) and eight motion capture cameras (Vicon Motion Systems Ltd). Validity of lower-extremity joint kinematics was assessed using measures of agreement (cross-correlation: XCORR) and error (root mean square deviation; and amplitude difference). Excellent agreement (XCORR >0.88) was found for sagittal plane kinematics in all joints and tasks. Highly variable agreement was found for frontal and transverse plane kinematics at the hip and ankle. Errors were relatively high in all planes. In conclusion, the WIS system provides valid estimates of sagittal plane joint kinematics in team sport movements. However, researchers should correct for offsets when comparing absolute joint angles between systems.

Association between central sensitization and gait in chronic low back pain: Insights from a machine learning approach.

BACKGROUND: Central sensitization (CS) is often present in patients with chronic low back pain (CLBP). Gait impairments due to CLBP have been extensively reported; however, the association between CS and gait is unknown. The present study examined the association between CS and CLBP on gait during activities of daily living. METHOD: Forty-two patients with CLBP were included. CS was assessed through the Central Sensitization Inventory (CSI), and patients were divided in a low and high CS group (23 CLBP- and 19 CLBP+, respectively). Patients wore a tri-axial accelerometer device for one week. From the acceleration signals, gait cycles were extracted and 36 gait outcomes representing quantitative and qualitative characteristics of gait were calculated. A Random Forest was trained to classify CLBP- and CLBP + based on the gait outcomes. The maximum Youden index was computed to measure the diagnostic test's ability and SHapley Additive exPlanations (SHAP) indexed the gait outcomes' importance to the classification model. RESULTS: The Random Forest accurately (84.4%) classified the CLBP- and CLBP+. Youden index was 0.65, and SHAP revealed that the gait outcomes' important to the classification model were related to gait smoothness, stride frequency variability, stride length variability, stride regularity, predictability, and stability. CONCLUSIONS: CLBP- and CLBP + patients had different motor control strategies. Patients in the CLBP- group presented with a more "loose control", with higher gait smoothness and stability, while CLBP + patients presented with a "tight control", with a more regular, less variable, and more predictable gait pattern.

ACL injury prevention, more effective with a different way of motor learning?

PURPOSE: What happens to the transference of learning proper jump-landing technique in isolation when an individual is expected to perform at a competitive level yet tries to maintain proper jump-landing technique? This is the key question for researchers, physical therapists, athletic trainers and coaches involved in ACL injury prevention in athletes. The need for ACL injury prevention is clear, however, in spite of these ongoing initiatives and reported early successes, ACL injury rates and the associated gender disparity have not diminished. One problem could be the difficulties with the measurements of injury rates and the difficulties with the implementation of thorough large scale injury prevention programs. A second issue could be the transition from conscious awareness during training sessions on technique in the laboratory to unexpected and automatic movements during a training or game involves complicated motor control adaptations. The purpose of this paper is to highlight the issue of motor learning in relation to ACL injury prevention and to post suggestions for future research. CONCLUSION: ACL injury prevention programs addressing explicit rules regarding desired landing positions by emphasizing proper alignment of the hip, knee, and ankle are reported in the literature. This may very well be a sensible way, but the use of explicit strategies may be less suitable for the acquisition of the control of complex motor skills (Maxwell et al. J Sports Sci 18:111-120, 2000). Sufficient literature on motor learning and it variations point in that direction.

Frontal plane roll-over analysis of prosthetic feet.

In prosthetic walking mediolateral balance is compromised due to the lack of active ankle control, by moments of force, in the prosthetic limb. Active control is reduced to the hip strategy, and passive mechanical stability depends on the curvature of the prosthetic foot under load. Mediolateral roll-over curvatures of prosthetic feet are largely unknown. In this study we determined the mediolateral roll-over characteristics of various prosthetic feet and foot-shoe combinations. Characteristics were determined by means of an inverted pendulum-like apparatus. The relationship between the centre of pressure (CoP) and the shank angle was measured and converted to roll-over shape and effective radius of curvature. Further, hysteresis (i.e., lagging in CoP displacement due to material compliance or slip) at vertical shank angle was determined from the hysteresis curve. Passive mechanical stability varied widely, though all measured foot-shoe combinations were relatively compliant. Mediolateral motion of the CoP ranged between 4 mm and 40 mm, thereby remaining well within each foot's physical width. Derived roll-over radii of curvature are also small, with an average of 102 mm. Hysteresis ranges between 20% and 115% of total CoP displacement and becomes more pronounced when adding a shoe. This may be due to slipping of the foot core in its cosmetic cover, or the foot in the shoe. Slip may be disadvantageous for balance control by limiting mediolateral travel of the CoP. It may therefore be clinically relevant to eliminate mediolateral slip in prosthetic foot design.

Copers and Noncopers Use Different Landing Techniques to Limit Anterior Tibial Translation After Anterior Cruciate Ligament Reconstruction.

BACKGROUND: At 1 year after anterior cruciate ligament reconstruction (ACLR), two-thirds of patients manage to return to sports (copers), whereas one-third of patients do not return to sports (noncopers). Copers and noncopers have different muscle activation patterns, and noncopers may not be able to control dynamic anterior tibial translation (ATTd) as well as copers. PURPOSE/HYPOTHESIS: To investigate whether (1) there is a positive correlation between passive ATT (ATTp; ie, general joint laxity) and ATTd during jump landing, (2) whether ATTd is moderated by muscle activating patterns, and (3) whether there is a difference in moderating ATTd between copers and noncopers. We hypothesized that patients who have undergone ACLR compensate for ATTd by developing muscle strategies that are more effective in copers compared with noncopers. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 40 patients who underwent unilateral ACLR performed 10 single-leg hops for distance with both legs. Lower body kinematic and kinetic data were measured using a motion-capture system, and ATTd was determined with an embedded method. Muscle activity was measured using electromyographic signals. Bilateral ATTp was measured using a KT-1000 arthrometer. In addition, the Beighton score was obtained. RESULTS: There was no significant correlation between ATTp and ATTd in copers; however, there was a positive correlation between ATTp and ATTd in the operated knee of noncopers. There was a positive correlation between the Beighton score and ATTp as well as between the Beighton score and ATTd in both copers and noncopers in the operated knee. Copers showed a negative correlation between ATTd and gastrocnemius activity in their operated leg during landing. Noncopers showed a positive correlation between ATTd and knee flexion moment in their operated knee during landing. CONCLUSION: Copers used increased gastrocnemius activity to reduce ATTd, whereas noncopers moderated ATTd by generating a smaller knee flexion moment. CLINICAL RELEVANCE: This study showed that copers used different landing techniques than noncopers. Patients who returned to sports after ACLR had sufficient plantar flexor activation to limit ATTd.