Individualized Technique Feedback for Instant Technique Improvements and Knee Abduction Moment Reductions - A New Approach for 'Sidestepping' ACL Injuries?

Background: Sidestep cutting technique is highly individual and has been shown to influence knee joint loading. However, studies assessing whether individualized technique feedback improves technique and ACL injury-relevant knee joint loads instantly in a sport-specific task are lacking. Purpose: To determine the instant effects of individualized augmented technique feedback and instructions on technique and the peak external knee abduction moment (pKAM) in a handball-specific sidestep cut. Additionally, to determine the effects of technique modifications on the resultant ground reaction force and its frontal plane moment arm to the knee joint center. Study Design: Controlled laboratory cohort study. Methods: Three-dimensional biomechanics of 48 adolescent female handball players were recorded during a handball-specific sidestep cut. Following baseline cuts to each side, leg-specific visual and verbal technique feedback on foot strike angle, knee valgus motion, or vertical impact velocity using a hierarchically organized structure accounting for the variables' association with performance was provided. Subsequently, sidestep cuts were performed again while verbal instructions were provided to guide technique modifications. Combined effects of feedback and instructions on technique and pKAM as well as on the resultant ground reaction force and its frontal plane moment arm to the knee joint center were assessed. Results: On average, each targeted technique variable improved following feedback and instructions, leading to instant reductions in pKAM of 13.4% to 17.1%. High inter-individual differences in response to feedback-instruction combinations were observed. These differences were evident in both the adherence to instructions and the impact on pKAM and its components. Conclusion: Most players were able to instantly adapt their technique and decrease ACL injury-relevant knee joint loads through individualized augmented technique feedback, thereby potentially reducing the risk of injury. More research is needed to assess the retention of these adaptations and move towards on-field technique assessments using low-cost equipment. Level of Evidence: Level 3.

Lateral Ankle Joint Injuries in Indoor and Court Sports: A Systematic Video Analysis of 445 Nonconsecutive Case Series.

BACKGROUND: Lateral ankle sprains are one of the most common injuries in indoor and court sports. Self-reports and case studies have indicated that these injuries occur via both contact and noncontact injury mechanisms typically because of excessive inversion in combination with plantarflexion and adduction of the foot. Video-based documentation of the injury mechanism exists, but the number of cases reported in the literature is limited. PURPOSE: To retrieve and systematically analyze a large number of video-recorded lateral ankle injuries from indoor and court sports, as well as describe the injury mechanism, injury motion, and injury pattern across different sports. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 445 unique video-recorded lateral ankle sprain injuries were retrieved from indoor and court sports of broadcasted levels of competition. The videos were independently analyzed by 2 different reviewers. Outcomes included classification of the injury mechanism according to the International Olympic Committee consensus guidelines, primary and secondary motions of ankle joint distortion, and documentation of the fixation point (fulcrum) around which the foot rotates. RESULTS: Overall, 298 (67%) injuries were direct contact, 113 (25%) were noncontact, and 32 (7%) were indirect contact incidents. Direct contact injuries were especially prevalent in basketball (76%), handball (80%), and volleyball (85%), while noncontact injuries dominated in tennis and badminton (96% vs 95% across both). Inversion (65%) and internal rotation (33%) were the primary distortion motions, with the lateral forefoot (53%) and lateral midfoot (40%) serving as the main fulcrums. Landing on another player's foot was the leading cause of injury (n = 246; 55%), primarily characterized by inversion (79%) around a midfoot fulcrum (54%). The noncontact and indirect landings on floor (n = 144; 33%) were primarily characterized by a distortion around a forefoot fulcrum (69%). CONCLUSION: Two of 3 ankle sprains from online video platforms were direct contact injuries, with most involving landing on another player's foot. The distortion motion seems to be related to the injury mechanism and the fixation point between the foot and the floor. The injury mechanisms varied greatly between sports, and future studies should clearly differentiate and investigate the specific injury mechanisms.

How Approaching Angle, Bottleneck Width and Walking Speed Affect the Use of a Bottleneck by Individuals.

Understanding pedestrian dynamics at bottlenecks and how pedestrians interact with their environment-particularly how they use and move in the space available to them-is of safety importance, since bottlenecks are a key point for pedestrian flow. We performed a series of experiments in which participants walked through a bottleneck individually for varying combinations of approaching angle, bottleneck width and walking speed, to investigate the dependence of the movement on safety-relevant influencing factors. Trajectories as well as 3D motion data were recorded for every participant. This paper shows that (1) the maximum amplitude of shoulder rotation is mainly determined by the ratio of the bottleneck width to the shoulder width of the participant, while the direction is determined by the starting angle and the foot position; (2) the 'critical point' is not invariant to the starting angle and walking speed; (3) differences between the maximum and minimum speed values arise mainly from the distribution of deceleration patterns; and (4) the position of crossing shifts by 1.75 cm/10 cm, increasing the bottleneck width in the direction of origin.

A biomechanical report of an acute lateral ankle sprain during a handball-specific cutting movement.

Biomechanical measurements of accidental ankle sprain injuries are rare but make important contributions to a more detailed understanding of the injury mechanism. In this case study, we present the kinematics and kinetics of a lateral ankle sprain of a female athlete performing handball-specific fake-and-cut manoeuvres. Three-dimensional kinematics and kinetics were recorded and six previously performed trials were used as reference. Plantarflexion, inversion, and internal rotation angles were substantially larger than the reference trials and peaked between 190 and 200 ms after initial ground contact. We observed a highly increased inversion and internal rotation moment. However, compared to the non-injury trials the data also revealed a reduction in the second dorsiflexion moment peak. Ground reaction forces were lower throughout the injury trial. Other parameters at initial ground contact including ankle and hip position, step length, and the traction coefficient indicate that a preparatory maladjustment occurred. This study adds valuable contributions to the understanding of lateral ankle sprains by building upon previously published reports and considering the shoe-surface interaction as an important factor for injury.

The effect of footwear outsole material on slip resistance on dry and contaminated surfaces with geometrically controlled outsoles.

Previous studies have compared slip resistance of commercially available footwear, however, often lacking the ability to isolate factors such as material and surface properties, or/and geometry. The aim of this study was to compare slip resistance of geometrically identical shoes with varying outsole materials. Three left Ecco Xpedition III shoes were constructed out of three different outsole materials: polyurethane (PU), thermoplastic polyurethane (TPU) and vulcanised rubber (RU). The shoes were tested for dynamic coefficient of friction (DCOF) on a steel and a tile surface, without contamination and with glycerine and canola oil as contaminants. The shoes were significantly (p < 0.001) different from each other across all surface/contaminant conditions/combinations, with the PU having a significantly 61-125% (p < 0.001) higher DCOF on contaminated surfaces compared to the RU outsole.Practitioner summary: Previous research has suggested the importance of studying individual parameters separately of footwear in relation to slip resistance. In this study, we managed to construct geometrically identical shoes and compare the slip resistance between three different outsole materials. We found that the polyurethane outsole was the least slippery choice of material for this specific footwear model on contaminated surfaces.

Unanticipated fake-and-cut maneuvers do not increase knee abduction moments in sport-specific tasks: Implication for ACL injury prevention and risk screening.

Non-contact anterior cruciate ligament injuries typically occur during cutting maneuvers and are associated with high peak knee abduction moments (KAM) within early stance. To screen athletes for injury risk or quantify the efficacy of prevention programs, it may be necessary to design tasks that mimic game situations. Thus, this study compared KAMs and ranking consistency of female handball players in three sport-specific fake-and-cut tasks of increasing complexity. The biomechanics of female handball players (n = 51, mean ± SD: 66.9 ± 7.8 kg, 1.74 ± 0.06 m, 19.2 ± 3.4 years) were recorded with a 3D motion capture system and force plates during three standardized fake-and-cut tasks. Task 1 was designed as a simple pre-planned cut, task 2 included catching a ball before a pre-planned cut in front of a static defender, and task 3 was designed as an unanticipated cut with three dynamic defenders involved. Inverse dynamics were used to calculate peak KAM within the first 100 ms of stance. KAM was decomposed into the frontal plane knee joint moment arm and resultant ground reaction force. RANOVAs (α ≤ 0.05) were used to reveal differences in the KAM magnitudes, moment arm, and resultant ground reaction force for the three tasks. Spearman's rank correlations were calculated to test the ranking consistency of the athletes' KAMs. There was a significant task main effect on KAM (p = 0.02; η p 2 = 0.13). The KAM in the two complex tasks was significantly higher (task 2: 1.73 Nm/kg; task 3: 1.64 Nm/kg) than the KAM in the simplest task (task 1: 1.52 Nm/kg). The ranking of the peak KAM was consistent regardless of the task complexity. Comparing tasks 1 and 2, an increase in KAM resulted from an increased frontal plane moment arm. Comparing tasks 1 and 3, higher KAM in task 3 resulted from an interplay between both moment arm and the resultant ground reaction force. In contrast to previous studies, unanticipated cutting maneuvers did not produce the highest KAMs. These findings indicate that the players have developed an automated sport-specific cutting technique that is utilized in both pre-planned and unanticipated fake-and-cut tasks.

Athletes with high knee abduction moments show increased vertical center of mass excursions and knee valgus angles across sport-specific fake-and-cut tasks of different complexities.

Young female handball players represent a high-risk population for anterior cruciate ligament (ACL) injuries. While the external knee abduction moment (KAM) is known to be a risk factor, it is unclear how cutting technique affects KAMs in sport-specific cutting maneuvers. Further, the effect of added game specificity (e.g., catching a ball or faking defenders) on KAMs and cutting technique remains unknown. Therefore, this study aimed: (i) to test if athletes grouped into different clusters of peak KAMs produced during three sport-specific fake-and-cut tasks of different complexities differ in cutting technique, and (ii) to test whether technique variables change with task complexity. Fifty-one female handball players (67.0 ± 7.7 kg, 1.70 ± 0.06 m, 19.2 ± 3.4 years) were recruited. Athletes performed at least five successful handball-specific sidestep cuts of three different complexities ranging from simple pre-planned fake-and-cut maneuvers to catching a ball and performing an unanticipated fake-and-cut maneuver with dynamic defenders. A k-means cluster algorithm with squared Euclidean distance metric was applied to the KAMs of all three tasks. The optimal cluster number of k optimal = 2 was calculated using the average silhouette width. Statistical differences in technique variables between the two clusters and the tasks were analyzed using repeated-measures ANOVAs (task complexity) with nested groupings (clusters). KAMs differed by 64.5%, on average, between clusters. When pooling all tasks, athletes with high KAMs showed 3.4° more knee valgus, 16.9% higher downward and 8.4% higher resultant velocity at initial ground contact, and 20.5% higher vertical ground reaction forces at peak KAM. Unlike most other variables, knee valgus angle was not affected by task complexity, likely due to it being part of inherent movement strategies and partly determined by anatomy. Since the high KAM cluster showed higher vertical center of mass excursions and knee valgus angles in all tasks, it is likely that this is part of an automated motor program developed over the players' careers. Based on these results, reducing knee valgus and downward velocity bears the potential to mitigate knee joint loading and therefore ACL injury risk.

The influence of shaft stiffness on joint kinematics and kinetics during hiking.

Hiking boots provide an interface for walking in challenging environments, typically equipped with a shaft to provide ankle joint stability in rough terrains. Currently it is unclear if the ankle joint is stabilized to an extent that protects against ankle injuries, and if so, to what degree this added ankle stability sacrifices ankle mobility and hence decreases efficient gait propulsion. The aim of the present study was to compare the effect of shaft construction and stiffness on lower extremity kinematics and kinetics during level and step-down walking to simulate hiking conditions. Thirteen healthy males walked in one low-cut and three shafted commercially available hiking shoes with varying shaft stiffness. Lower extremity kinematics and ground reaction forces were recorded simultaneously. During level walking, ankle plantar-dorsiflexion range of motion was significantly reduced for the stiffest shaft hiking shoe compared to the low-cut shoe. A reduction in the muscle contribution to ankle joint work was found for all shafted shoes compared to the low-cut shoe. The reduced ankle joint work for the shafted shoes conversely increased eccentric knee joint work. Kinematic and kinetic differences between shoes diminished during box step-down walking. The present study shows that shaft height and stiffness can influence ankle joint range of motion, and ankle and knee joint work, with the high-shaft shoes redistributing load from the ankle to the knee joint. This may have implications for gait efficiency and increase the risk of knee joint loading or injuries.

Does the Spraino low-friction shoe patch prevent lateral ankle sprain injury in indoor sports? A pilot randomised controlled trial with 510 participants with previous ankle injuries.

BACKGROUND: Lateral ankle sprains are common in indoor sports. High shoe-surface friction is considered a risk factor for non-contact lateral ankle sprains. Spraino is a novel low-friction patch that can be attached to the outside of sports shoes to minimise friction at the lateral edge, which could mitigate the risk of such injury. We aimed to determine preliminary effectiveness (incidence rate and severity) and safety (harms) of Spraino to prevent lateral ankle sprains among indoor sport athletes. METHODS: In this exploratory, parallel-group, two-arm pilot randomised controlled trial, 510 subelite indoor sport athletes with a previous lateral ankle sprain were randomly allocated (1:1) to Spraino or 'do-as-usual'. Allocation was concealed and the trial was outcome assessor blinded. Match and training exposure, number of injuries and associated time loss were captured weekly via text messages. Information on harms, fear-of-injury and ankle pain was also documented. RESULTS: 480 participants completed the trial. They reported a total of 151 lateral ankle sprains, of which 96 were categorised as non-contact, and 50 as severe. All outcomes favoured Spraino with incidence rate ratios of 0.87 (95% CI 0.62 to 1.23) for all lateral ankle sprains; 0.64 (95% CI 0.42 to 0.98) for non-contact lateral ankle sprains; and 0.47 (95% CI 0.25 to 0.88) for severe lateral ankle sprains. Time loss per injury was also lower in the Spraino group (1.8 vs 2.8 weeks, p=0.014). Six participants reported minor harms because of Spraino. CONCLUSION: Compared with usual care, athletes allocated to Spraino had a lower risk of lateral ankle sprains and less time loss, with only few reported minor harms. TRIAL REGISTRATION NUMBER: NCT03311490.

Application of Inertial Motion Unit-Based Kinematics to Assess the Effect of Boot Modifications on Ski Jump Landings-A Methodological Study.

Biomechanical studies of winter sports are challenging due to environmental conditions which cannot be mimicked in a laboratory. In this study, a methodological approach was developed merging 2D video recordings with sensor-based motion capture to investigate ski jump landings. A reference measurement was carried out in a laboratory, and subsequently, the method was exemplified in a field study by assessing the effect of a ski boot modification on landing kinematics. Landings of four expert skiers were filmed under field conditions in the jump plane, and full body kinematics were measured with an inertial motion unit (IMU) -based motion capture suit. This exemplary study revealed that the combination of video and IMU data is viable. However, only one skier was able to make use of the added boot flexibility, likely due to an extended training time with the modified boot. In this case, maximum knee flexion changed by 36° and maximum ankle flexion by 13°, whereas the other three skiers changed only marginally. The results confirm that 2D video merged with IMU data are suitable for jump analyses in winter sports, and that the modified boot will allow for alterations in landing technique provided that enough time for training is given.

Three-dimensional kinematics of shoulder function in stroke patients: Inter- and intra-rater reliability.

BACKGROUND: It is important to monitor progress during rehabilitation of stroke patients. To that end, clinical function tests may be supported by three-dimensional kinematic measures. The aim of this study was to evaluate the inter- and intra-rater reliability of three-dimensional kinematic measures of shoulder movements in stroke patients with reduced shoulder function. METHODS: Seventeen patients were tested in three sessions by two trained raters. Three-dimensional motion capture was performed of the more affected upper extremity and the trunk. Measures of movements of the scapula and humerus related to the trunk, the trunk related to the laboratory, the forearm related to the humerus, and temporospatial measures were obtained during two reach tasks from the Wolf Motor Function Test, ReachLow and ReachHigh. Inter- and intra-rater reliability was quantified with intraclass correlation coefficients (ICC). FINDINGS: In general, range of movements of scapula, shoulder, trunk and elbow and movement time and reach length showed high inter-rater reliability (ICC∞ 0.84-0.98) and intra-rater reliability (ICC∞ 0.75-1.00), A minimum of five trials per task were required to achieve reliable ICC estimates. INTERPRETATION: Selected three-dimensional kinematic measures can be used reliably to evaluate specific movements of the shoulder in stroke patients with reduced shoulder function.

Prediction of running-induced Achilles tendinopathy with pain sensitivity - a 1-year prospective study.

Background and aims Achilles tendinopathy is common among runners, but the etiology remains unclear. High mechanical pain sensitivity may be a predictor of increased risk of developing Achilles tendinopathy in this group. The purpose of this study was to investigate whether local pain sensitivity could predict the development of Achilles tendinopathy in recreational male runners. The overall hypothesis was that high pain sensitivity would be related to a higher risk of developing Achilles tendinopathy among recreational male runners. Methods Ninety-nine recreational male runners were recruited and followed prospectively for 1 year. At baseline and after 500 km of running the pressure pain threshold (PPT) was assessed at the infraspinatus and at the Achilles tendon (AT-PPT). Based on the AT-PPT at baseline, a median split was used to divide the runners into two groups. The high pain sensitivity groups was defined as runners displaying a pain pressure threshold below 441 kPa on the Achilles tendon, while the low pain sensitivity group was defined as runners displaying a pain pressure threshold above 441 kPa on the Achilles tendon, respectively. Subsequently, the cumulative risk difference between the two groups was assessed by using the pseudo-observation method. Results High pain sensitivity runners sustained 5%-point (95% CI: -0.18 to 0.08) more Achilles tendinopathy episodes during the first 1,500 km. No significant group differences in risk were found at 100, 250, 500, 1,000 and 1,500 km of running. Conclusions No significant association was found between mechanical pain sensitivity in the Achilles tendon and the risk of developing Achilles tendinopathy. However, the risk difference indicated a association between a high mechanical pain sensitivity and an increased risk of developing Achilles tendinopathy. It is plausible that changes in pain sensitivity were masked by unmeasured covariates, such as the differences in progression/regression of training volume and running speed between the two groups. This study was limited in size, which limited the possibility to account for covariates, such as differences in progression/regression of running speed between runners. With the limitations in mind, future studies should control the training volume, speed and running shoes in the design or account for it in the analysis. Implications Pain sensitivity of the Achilles tendon seems not to be related to an increased risk of developing Achilles pain in relation to running.

Predictors of falls in recreational snowboard jumping: An observational study.

PURPOSE: Jumping is popular in the sport of snowboarding. Epidemiological research has shown an increased risk of injury associated with this activity. Falls are common when jumping and although there is a logical connection between falling and injury occurrence, thus far little attention has been given to factors involved in the jumping-fall relationship. The current study aimed to add to the current knowledge base by identifying predictors of falling during intentional snowboard jumping within terrain park facilities. METHODS: Seven hundred and four jumps were video recorded and qualitatively coded using a custom template of predetermined parameters related to manoeuvre choice, landing technique and jump success. RESULTS: Falling was common within the sample population at a rate of one fall for every five jump attempts. Landings made on the flat or knuckle of the snow jump as well as incorrect board positioning at landing were found to be significant predictors of falling. Additionally the choice of manoeuvre was found to influence the risk of falls, with spinning jumps associated with a greater fall risk when compared to non spinning jumps. No clear relationship was identified between jump length measures and falling risk. CONCLUSION: It is likely that jumping will remain popular in snowboarding and thus research efforts should focus on minimising the risk of injury associated with this skill. Reducing the overall incidence of falling, identified in the current study to be high, is a potential area for improvement. The potential for fall risk reduction through technique and decision making changes provides justification for further research in this area.

Pedobarography as a clinical tool in the management of diabetic feet in New Zealand: a feasibility study.

BACKGROUND: The peripheral complications of diabetes mellitus remain a significant risk to lower-limb morbidity. In New Zealand, risk of diabetes, comorbidity and lower-limb amputation are highly-differential between demographic groups, particularly ethnicity. There is growing and convincing evidence that the use of pedobarography - or plantar pressure measurement - can usefully inform diabetic foot care, particularly with respect to the prevention of re-ulceration among high-risk patients. METHODS: For the current feasibility study, we embedded pedobarographic measurements into three unique diabetic foot clinic settings in the New Zealand context, and collected pedobarographic data from n = 38 patients with diabetes using a platform-based (Novel Emed) and/or in-shoe-based system (Novel Pedar). Our aim was to assess the feasibility of incorporating pedobarographic testing into the clinical care of diabetic feet in New Zealand. RESULTS AND CONCLUSIONS: We observed a high response rate and positive self-reported experience from participants. As part of our engagement with participants, we observed a high degree of lower-limb morbidity, including current ulceration and chronic foot deformities. The median time for pedobarographic testing (including study introduction and consenting) was 25 min. Despite working with a high-risk population, there were no adverse events in this study. In terms of application of pedobarography as a clinical tool in the New Zealand context, the current feasibility study leads us to believe that there are two avenues that deserve further investigation: a) the use of pedobarography to inform the design and effectiveness of offloading devices among high-risk diabetic patients; and b) the use of pedobarography as a means to increase offloading footwear and/or orthoses compliance among high-risk diabetic patients. Both of these objectives deserve further examination in New Zealand via clinical trial.

Medial shoe-ground pressure and specific running injuries: A 1-year prospective cohort study.

OBJECTIVES: Achilles tendinitis, plantar fasciopathy and medial tibial stress syndrome injuries (APM-injuries) account for approximately 25% of the total number of running injuries amongst recreational runners. Reports on the association between static foot pronation and APM-injuries are contradictory. Possibly, dynamic measures of pronation may display a stronger relationship with the risk of APM-injuries. Therefore, the purpose of the present study was to investigate if running distance until the first APM-injury was dependent on the foot balance during stance phase in recreational male runners. DESIGN: Prospective cohort study. METHODS: Foot balance for both feet was measured during treadmill running at the fastest possible 5000-m running pace in 79 healthy recreational male runners. Foot balance was calculated by dividing the average of medial pressure with the average of lateral pressure. Foot balance was categorized into those which presented a higher lateral shod pressure (LP) than medial pressure, and those which presented a higher medial shod pressure (MP) than lateral pressure during the stance phase. A time-to-event model was used to compare differences in incidence between foot balance groups. RESULTS: Compared with the LP-group (n=59), the proportion of APM-injuries was greater in the MP-group (n=99) after 1500km of running, resulting in a cumulative risk difference of 16%-points (95% CI=3%-point; 28%-point, p=0.011). CONCLUSIONS: Runners displaying a more medial pressure during stance phase at baseline sustained a greater amount of APM-injuries compared to those displaying a lateral shod pressure during stance phase. Prospective studies including a greater amount of runners are needed to confirm this relationship.

Sensory Feedback in Interlimb Coordination: Contralateral Afferent Contribution to the Short-Latency Crossed Response during Human Walking.

A constant coordination between the left and right leg is required to maintain stability during human locomotion, especially in a variable environment. The neural mechanisms underlying this interlimb coordination are not yet known. In animals, interneurons located within the spinal cord allow direct communication between the two sides without the need for the involvement of higher centers. These may also exist in humans since sensory feedback elicited by tibial nerve stimulation on one side (ipsilateral) can affect the muscles activation in the opposite side (contralateral), provoking short-latency crossed responses (SLCRs). The current study investigated whether contralateral afferent feedback contributes to the mechanism controlling the SLCR in human gastrocnemius muscle. Surface electromyogram, kinematic and kinetic data were recorded from subjects during normal walking and hybrid walking (with the legs moving in opposite directions). An inverse dynamics model was applied to estimate the gastrocnemius muscle proprioceptors' firing rate. During normal walking, a significant correlation was observed between the magnitude of SLCRs and the estimated muscle spindle secondary afferent activity (P = 0.04). Moreover, estimated spindle secondary afferent and Golgi tendon organ activity were significantly different (P ≤ 0.01) when opposite responses have been observed, that is during normal (facilitation) and hybrid walking (inhibition) conditions. Contralateral sensory feedback, specifically spindle secondary afferents, likely plays a significant role in generating the SLCR. This observation has important implications for our understanding of what future research should be focusing on to optimize locomotor recovery in patient populations.

The effect of crossed reflex responses on dynamic stability during locomotion.

In recent studies, we demonstrated that a neural pathway within the human spinal cord allows direct communication between muscles located in the opposing limb. Short-latency crossed responses (SLCRs) are elicited in the contralateral triceps surae at an onset of 40-69 ms following electrical stimulation of the ipsilateral tibial nerve (iTN). The SLCRs are significantly affected by lesions of the central nervous system where the patients are unable to attain normal walking symmetry. The aim of this study was to elucidate the functionality of SLCRs by investigating their effects on the center of pressure (CoP) and pressure distribution. SLCRs were elicited by iTN stimulation at the end of the ipsilateral swing phase while the participants (n = 8) walked on a treadmill. CoP location and pressure distribution on the sole of the contralateral foot were recorded using instrumented insoles inserted bilaterally in the participant's shoes. The SLCR induced a significant displacement of the CoP toward the medial and anterior direction, associated with a significant increase in pressure at the level of the first metatarsal head. The SLCR contributed to dynamic stability, accelerating the propulsion phase of the contralateral leg and thus preparing for a faster step in the event that the ipsilateral leg is not able to support body weight. The results presented here provide new insight into the functionality of SLCRs, introducing the perspective that training these reflexes, as shown successfully for other reflex pathways, would increase dynamic stability in patients with impaired locomotion.

Potential interaction of experimental knee pain and laterally wedged insoles for knee off-loading during walking.

BACKGROUND: Laterally wedged insoles are one of the gait modifications potentially slowing down progression of medial knee osteoarthritis. Clinical studies have, however, found large individual differences in the biomechanical effect and an insufficient pain reduction. To clarify if and how pain mediates mechanical changes during gait the current study investigated how acute experimental knee pain changes the mechanical effect of laterally wedged insoles in healthy subjects during walking. METHODS: 3D gait analysis was carried out for twelve healthy individuals. The study followed a cross-over design and data were collected with both a neutral and a 10-degree laterally wedged insole with experimental pain induced by hypertonic and isotonic saline injections into the infrapatellar fat pad. Peak knee adduction moment was the primary outcome. A repeated ANOVA (analysis of variance) was used to evaluate the relationship between the factors wedge, condition and test number. FINDINGS: Wedges significantly reduced peak knee adduction moment but experimental knee pain did only marginally affect its magnitude in either condition. While frontal plane mechanics were relatively unaffected by pain, the sagittal plane knee extension moment increased with laterally wedging (P=0.008), whereas late knee flexion moment was reduced by experimental knee pain (P=0.04). INTERPRETATION: The effect of laterally wedged insoles in attenuating knee adduction moment during walking is independent of experimental knee pain. The present study provides evidence that subjects with experimental knee pain reduce knee loading by reducing extension moment, whereas lateral wedges have the opposite effect and increase the extension moment.

Motor modules of human locomotion: influence of EMG averaging, concatenation, and number of step cycles.

Locomotion can be investigated by factorization of electromyographic (EMG) signals, e.g., with non-negative matrix factorization (NMF). This approach is a convenient concise representation of muscle activities as distributed in motor modules, activated in specific gait phases. For applying NMF, the EMG signals are analyzed either as single trials, or as averaged EMG, or as concatenated EMG (data structure). The aim of this study is to investigate the influence of the data structure on the extracted motor modules. Twelve healthy men walked at their preferred speed on a treadmill while surface EMG signals were recorded for 60s from 10 lower limb muscles. Motor modules representing relative weightings of synergistic muscle activations were extracted by NMF from 40 step cycles separately (EMGSNG), from averaging 2, 3, 5, 10, 20, and 40 consecutive cycles (EMGAVR), and from the concatenation of the same sets of consecutive cycles (EMGCNC). Five motor modules were sufficient to reconstruct the original EMG datasets (reconstruction quality >90%), regardless of the type of data structure used. However, EMGCNC was associated with a slightly reduced reconstruction quality with respect to EMGAVR. Most motor modules were similar when extracted from different data structures (similarity >0.85). However, the quality of the reconstructed 40-step EMGCNC datasets when using the muscle weightings from EMGAVR was low (reconstruction quality ~40%). On the other hand, the use of weightings from EMGCNC for reconstructing this long period of locomotion provided higher quality, especially using 20 concatenated steps (reconstruction quality ~80%). Although EMGSNG and EMGAVR showed a higher reconstruction quality for short signal intervals, these data structures did not account for step-to-step variability. The results of this study provide practical guidelines on the methodological aspects of synergistic muscle activation extraction from EMG during locomotion.