The purpose of this study was to identify gait asymmetries during the mid-stance phase of gait among subjects with knee instability (''non-copers'') after acute anterior cruciate ligament (ACL) rupture. Twenty-one non-copers with acute, isolated ACL injury ambulated at their intentional walking speed as kinetic, kinematic, and electromyographic (EMG) data were collected bilaterally. Lower extremity movement patterns and muscle activity were analyzed during the midstance and weight acceptance phases of stance. When compared to the uninjured limb, subjects exhibited lower sagittal plane knee excursions and peak knee angles, and higher muscle cocontraction on the injured limb. There was a lower knee flexion moment at peak knee extension, a trend for the knee contribution to the total support moment to be lower, and a higher ankle contribution to the total support moment on the injured limb. There were differences in the magnitude of muscle activity which included higher hamstring activity and lower soleus activity on the injured limb. Changes in quadriceps, soleus, and hamstring muscle activity on the injured limb were identified during weight acceptance that had not previously been reported, while hip compensation for a lower knee contribution to the total support moment has been described. Non-copers consistently stabilize their knee with a stiffening strategy involving less knee motion and higher muscle contraction. The variable combination of muscle adaptations that produce joint stiffness, and the ability of both the ankle and the hip to compensate for lower knee control indicate the non-coper neuromuscular system may be more malleable than previously believed. ß

Background-A treatment algorithm and screening examination to guide patient management and prospectively determine potential for highly active individuals to succeed with non-operative care after anterior cruciate ligament (ACL) rupture.

Female athletes involved in jumping and cutting sports injure their anterior cruciate ligaments (ACL) 4-6 times more frequently than their male counterparts in comparable sports. Neuromuscular factors, including quadriceps dominance, has been incriminated as contributing to the higher rates of injury in women. Currently, the most effective form of intervention developed to reduce female ACL injury rates has been neuromuscular training. The purpose of this study was to (1) identify gender based muscle activity patterns during disturbed walking that may contribute to ACL injury, and (2) determine if a novel training program could positively influence patterns among healthy female athletes utilizing a disturbed gait paradigm. Twenty healthy athletes (female=10, male=10) were tested. All subjects participated in five trials during which a platform translated horizontally in a lateral direction at heel contact before and after completing ten sessions of a perturbation training program. Electromyographic (EMG) data from the vastus lateralis, medial and lateral hamstrings, and medial gastrocnemius were collected. Trials were analyzed for the muscle onset, termination of activity, peak amplitude, time to peak amplitude, and integrated EMG activity. Muscle cocontraction, the simultaneous activation of antagonistic muscles (lateral hamstrings-vastus lateralis, and medial gastrocnemius-vastus lateralis), was calculated as indicators of active knee stiffness in preparation for heel strike, during weight acceptance and midstance. Prior to training, women had significantly higher peak quadriceps activity and higher integrated quadriceps activity during midstance than men. Both medial and lateral hamstring integrals during midstance increased from pre to posttraining. Onset times to peak activities for hamstrings and quadriceps were similar before training except for medial hamstring time to peak which occurred after heel strike in most women. Time to peak medial hamstring activity moved from after to just before heel strike after training. Women had higher medial gastrocnemius-vastus lateralis cocontraction indices in the preparatory and weight acceptance phases of gait than men after training. Prior to training, the athletic women in our sample demonstrated characteristic quadriceps dominance and decreased active knee stiffness when compared to male athletes. Modulation of activity and timing of ACL agonist musculature (hamstrings and gastrocnemius) from before to after training resulted in normal quadriceps-hamstring balance and increased active stiffness. These alterations in ACL agonist muscle activation patterns may reduce the risk of biomechanical strain injury among a high risk population.

Background and Purpose. Dynamic knee stabilization strategies of people who successfully compensate for the absence of an anterior cruciate ligament (ACL) ("copers") are different from those of people who do not compensate well for the injury ("noncopers"). Early after injury, certain patients ("potential copers") can increase the likelihood of successfully compensating for the injury by participating in 10 sessions of perturbation training. The purpose of this study was to determine how perturbation training alters muscle co-contraction and knee kinematics in potential copers. Subjects. Seventeen individuals with acute, unilateral ACL rupture who were categorized as potential copers and 17 subjects without injuries who were matched by age, sex, and activity level were recruited for this study. Methods. Motion analysis and electromyographic data were collected as subjects walked across a stationary or moving platform (horizontal translation) before and after perturbation training. Results. Before training, potential copers had higher co-contraction indexes and lower peak knee flexion angles than subjects without injuries. After training, potential copers' movement patterns more closely resembled those of subjects without injuries (ie, they showed reduced co-contraction indexes and increased peak knee flexion angles during stance). Discussion and Conclusion. Perturbation training reduced quadriceps femoris-hamstring muscle and quadriceps femoris-gastrocnemius muscle co-contractions and normalized knee kinematics in individuals with ACL rupture who were classified as potential copers. Findings from this study provide evidence for a mechanism by which perturbation training acts as an effective intervention for promoting coordinated muscle activity in a select population of people with ACL rupture. [Chmielewski TL, Hurd WJ, Rudolph KS, et al. Perturbation training improves knee kinematics and reduces muscle co-contraction after complete unilateral anterior cruciate ligament injuries. Phys Ther. 2005;85:740 -754.]

Objective-To evaluate upper-extremity symmetry during wheelchair propulsion across multiple terrain surfaces. Design-Case series.Setting-A biomechanics laboratory and the community. Participants-Manual wheelchair users (N=12). Interventions-Not applicable.Main Outcome Measures-Symmetry indexes for the propulsion moment, total force, tangential force, fractional effective force, time-to-peak propulsion moment, work, length of push cycle, and power during wheelchair propulsion over outdoor and indoor community conditions, and in conditions.Results-Upper-extremity asymmetry was present within each condition. There were no differences in the magnitude of asymmetry when comparing laboratory with indoor community conditions. Outdoor community wheelchair propulsion asymmetry was significantly greater than asymmetry measured during laboratory conditions. Conclusions-Investigators should be aware that manual wheelchair propulsion is an asymmetrical act, which may influence interpretation when data is collected from a single limb or averaged for both limbs. The greater asymmetry identified during outdoor versus laboratory conditions the emphasizes need to evaluate wheelchair biomechanics in the user's natural environment. KeywordsBiomechanics; Rehabilitation; Upper extremity; Wheelchairs THE BILATERAL NATURE of wheelchair propulsion places both upper extremities at risk for overuse injury. Upper-extremity pain 1-3 and overuse injury [4][5][6] are common in manual wheelchair users. Limb pain is frequently associated with activities of daily living 2,3,7 and is hypothesized to be a consequence of repetitive wheeling (eg, manually propelling a wheelchair) and upper-extremity weight bearing activities. The novel mode of ambulation © 2008 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Reprint requests to Kai-Nan An, PhD, Guggenheim Bldg 1-28, Rochester, MN 55905, an.kainan@mayo.edu.. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. and potential deleterious impact on function has consequently made wheelchair propulsion the focus of many biomechanic investigations. NIH Public AccessMeasurement of propulsion force is now possible with instrumented wheelchair rims. The technology is, however, expensive. Often investigators are able to purchase only 1 instrumented rim, limiting studies to evaluation of 1 extremity. Investigators who have collected bilateral upper-extremity kinetic data during wheelchair propulsion subsequently averaged the data for both limbs [8][9][10] or have selected only 1 limb for analysis. 11 This suggests that side-to-side differences during wheelchair propulsion are not meaningful. However, in a study of pushrim propulsion patterns, Boninger et al 12 alanalyzed left and right upper extremities separately and reported that several subjects had different propulsion pa...