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Biomedical subjects

L Snyder-Mackler

Publications and source records attributed to L Snyder-Mackler.

At least 19 recordsLinked to original sources
PubMed2005

Elucidation of a potentially destabilizing control strategy in ACL deficient non-copers.

PURPOSE: The purpose was to differentiate the dynamic knee stabilization strategies of potential copers (individuals who have the potential to compensate for the absence of an ACL without episodes of giving way after return to pre-injury activities) and non-copers (those who have knee instability following ACL rupture with return to pre-injury activities). METHODS: Twenty subjects with ACL rupture were assigned to potential coper (n=10) and non-coper (n=10) groups via a screening examination. Ten active people without lower extremity injury were also tested. Knee angle, tibial position and muscle activity data were collected while subjects stood in unilateral stance on a platform that moved horizontally in an anterior direction. Analysis included the preparation for platform movement; and monosynaptic, intermediate reflex and voluntary response intervals after platform movement. RESULTS: Non-copers showed greater knee flexion than uninjured subjects, and had a posterior tibial position and altered hamstring recruitment compared to the other groups. Potential copers demonstrated greater medial quadriceps activity while maintaining knee kinematics similar to uninjured subjects. Both potential copers and non-copers had greater co-contraction between medial hamstrings and quadriceps than uninjured subjects. All excitatory muscle activation occurred in the intermediate reflex interval. DISCUSSION AND CONCLUSIONS: Non-copers displayed aberrant muscle recruitment that may contribute to knee instability. Potential copers maintained normal tibial position using a strategy that permits quadriceps activation without excessive anterior tibial translation. Muscle recruitment in the intermediate reflex interval suggests neuromuscular training may influence the strategies.

Adaptation, Physiological↗
PubMed2005

Evidence for differential control of tibial position in perturbed unilateral stance after acute ACL rupture.

Functional outcomes in anterior cruciate ligament-deficient "potential copers" and "non-copers" may be related to their knee stabilization strategies. Therefore, the purpose of this study was to differentiate dynamic knee stabilization strategies of potential copers and non-copers through analysis of sagittal plane knee angle and tibia position during disturbed and undisturbed unilateral standing. Ten uninjured potential coper and non-coper subjects stood in unilateral stance on a platform that translated anteriorly, posteriorly and laterally. Knee angle and tibia position with reference to the femur were calculated before and after platform movement. During perturbation trials, potential copers maintained kinematics that were similar to uninjured subjects across conditions. Conversely, non-copers stood with greater knee flexion than uninjured subjects and a tibia position that was more posterior than the other groups. Both non-copers and potential copers demonstrated small changes in tibia position following platform movement, but direction of movement was not similar. The similarities between the knee kinematics of potential copers and uninjured subjects suggest that potential copers compensated well from their injury by utilizing analogous dynamic knee stabilization strategies. In comparison to the other groups, by keeping the knee in greater flexion and the tibia in a more posterior position, non-copers appear to constrain the tibia in response to a challenging task, which is consistent with a "stiffening strategy". Based on the poor functional outcomes of non-copers, a stiffening strategy does not lead to dynamic knee stability, and the strategy may increase compressive forces which could contribute to or exacerbate articular cartilage degeneration.

Acute Disease↗
PubMed2001

Dynamic stability in the anterior cruciate ligament deficient knee.

Some individuals can stabilize their knees following anterior cruciate ligament rupture even during activities involving cutting and pivoting (copers), others have instability with daily activities (non-copers). Movement and muscle activation patterns of 11 copers, ten non-copers and ten uninjured subjects were studied during walking and jogging. Results indicate that distinct gait adaptations appeared primarily in the non-copers. Copers used joint ranges of motion, moments and muscle activation patterns similar to uninjured subjects. Non-copers reduced their knee motion, and external knee flexion moments that correlated well with quadriceps strength. Non-copers also achieved peak hamstring activity later in the weight acceptance phase and used a strategy involving more generalized co-contraction. Both copers and non-copers had high levels of quadriceps femoris muscle activity. The reduced knee moment in the involved limbs of the non-copers did not represent "quadriceps avoidance" but rather represented a strategy of general co-contraction with a greater relative contribution from the hamstring muscles.

Adult↗
PubMed2001

Biomechanical evidence supporting a differential response to acute ACL injury.

OBJECTIVE: To describe movement patterns in people with complete anterior cruciate ligament rupture objectively identified as good candidates for non-operative management of the injury. DESIGN: Involved side kinematics and kinetics were compared to the uninvolved side and to uninjured subjects. BACKGROUND: High-level athletes with anterior cruciate ligament rupture and poor dynamic stability (non-copers) have movement alterations, including less knee flexion and a decreased internal knee extensor moment during loading response, that are not seen in those with excellent knee stability (copers). Our screening exam can identify people with good rehabilitation potential for non-operative management of anterior cruciate ligament injury (potential copers), but the movement strategies of these individuals are unknown. METHODS: Sagittal plane kinematics and kinetics during the stance phase of walking and jogging were collected from 11 subjects who had an acute anterior cruciate ligament rupture and met the criteria of the screening exam, and were compared to 10 uninjured subjects, who we studied previously. Variables were those in which non-copers differed from uninjured subjects. RESULTS: The potential copers flexed their involved knee less than uninjured subjects and their uninvolved side during walking. Potential copers, compared to uninjured subjects, also had a lower vertical ground reaction force during loading response, a lower knee support moment, and an increased ankle support moment during walking. In jogging, the involved knee angle at initial contact was more extended compared to uninjured subjects, and the amount of knee flexion was less than the uninvolved side. No differences in kinetics were present during jogging. CONCLUSIONS: This study provides evidence that the potential copers identified by the screening examination have movement patterns that are consistent with people who have more knee stability than non-copers. RELEVANCE: Although potential copers have developed some characteristics of a successful stabilization strategy, the presence of kinematic alterations indicates that they may benefit from training programs designed to enhance dynamic knee stability.

Activities of Daily Living↗
PubMed2001

Characterization of the human quadriceps muscle in active elders.

OBJECTIVE: To compare muscle activation deficits and muscle physiology in older versus younger adults. DESIGN: A maximal volitional isometric contraction of the quadriceps muscle with burst-superimposition was used to assess strength and activation. In addition, force-frequency testing during fresh, fatigue, and recovery conditions and electrically elicited fatigue testing were performed. SETTING: Muscle performance laboratory. PATIENTS: Healthy, active young (age range, 20-28 yr) and older (age range, 66-83 yr) subjects. MAIN OUTCOME MEASURES: Torque production, activation of the quadriceps, F50 values from the force-frequency relationships (frequency at which 50% of the maximum normalized force is produced), and the average amount of fatigue. RESULTS: Older subjects were weaker (574.4 +/- 156 N) than younger subjects (900.9 +/- 295 N) and had significantly greater deficits in central activation in the quadriceps muscles (elderly = 95.5% activation; younger = 98.1% activation). The force-frequency curves for the elderly were to the left of the younger subjects for all 3 testing conditions. Aged muscles fatigued to the same extent as younger muscle (young = 49.8% +/- 2.6%, elderly = 51.1% +/- 2.8%). CONCLUSIONS: These results can be used to modify high-intensity strength training protocols designed to optimize sustainable strength gains in the elderly during rehabilitation.

Adult↗
PubMed2001

The use of electrical stimulation to increase quadriceps femoris muscle force in an elderly patient following a total knee arthroplasty.

BACKGROUND AND PURPOSE: Persistent residual quadriceps femoris muscle force deficits after total knee arthroplasty (TKA) are commonly reported and can prevent patients from returning quickly and fully to functional activities. Neuromuscular electrical stimulation offers a potentially more effective means of increasing muscle force than current rehabilitation protocols. CASE DESCRIPTION: The patient was a 66-year-old man. Neuromuscular electrical stimulation for increasing quadriceps femoris muscle force was initiated 3 weeks after TKA for 11 sessions to supplement stretching exercises and a high-intensity volitional strengthening program. OUTCOME: The patient's isometric quadriceps femoris muscle force increased from 50% (involved/uninvolved) at 3 weeks after surgery to 86% at 8 weeks after surgery. A concurrent increase in his uninvolved quadriceps femoris muscle force concealed the patient's true increase in his involved quadriceps femoris muscle force in a side-to-side comparison. The patient's final involved quadriceps femoris muscle force (10 weeks after surgery) was 93% of the initial uninvolved quadriceps femoris muscle force. DISCUSSION: Our patient was able to return to independent activities of daily living and recreational activities, with force gains that surpassed those reported in the literature.

Aged↗
PubMed2001

Dynamic knee stability: current theory and implications for clinicians and scientists.

We will discuss the mechanisms by which dynamic knee stability may be achieved and relate this to issues that interest clinicians and scientists concerned with dynamic knee stability. Emphasis is placed on the neurophysiologic evidence and theory related to neuromuscular control. Specific topics discussed include the ensemble firing of peripheral mechanoreceptors, the potential for muscle stiffness modulation via force and length feedback, postural control synergies, motor programs, and the neural control of gait. Factors related to answering the difficult question of whether or not knee ligament injuries can be prevented during athletic activities are discussed. Prevention programs that train athletes to perform their sport skills in a safe fashion are put forth as the most promising prospect for injury prevention. Methods of assessing neuromuscular function are reviewed critically and the need for future research in this area is emphasized. We conclude with a brief review of the literature regarding neuromuscular training programs.

Anterior Cruciate Ligament Injuries↗
PubMed2001

Maximum voluntary activation in nonfatigued and fatigued muscle of young and elderly individuals.

BACKGROUND AND PURPOSE: Researchers studying central activation of muscles in elderly subjects (> or = 65 years of age) have investigated activation in only the nonfatigued state. This study examined the ability of young and elderly people to activate their quadriceps femoris muscles voluntarily under both fatigued and nonfatigued conditions to determine the effect of central activation failure on age-related loss of force. SUBJECTS AND METHODS: Twenty young subjects (11 men, 9 women; mean age = 22.67 years, SD = 4.14, range = 18-32 years) and 17 elderly subjects (8 men, 9 women; mean age = 71.5 years, SD = 5.85, range = 65-84 years) participated in this study. Subjects were seated on a dynamometer and stabilized. Central activation was quantified, based on the change in force produced by a 100-Hz, 12-pulse electrical train that was delivered during a 3- to 5-second isometric maximum voluntary contraction (MVC) of the quadriceps femoris muscle. Next, subjects performed 25 MVCs (a 5-second contraction with 2 seconds of rest) to fatigue the muscle. During the last MVC, central activation was measured again. RESULTS: In the nonfatigued state, elderly subjects had lower central activation than younger subjects. In the fatigued state, this difference became larger. DISCUSSION AND CONCLUSION: Central activation of the quadriceps femoris muscle in elderly subjects was reduced in both the fatigued and nonfatigued states when compared with young subjects. Some part of age-related weakness, therefore, may be attributed to failure of central activation in both the fatigued and nonfatigued states.

Adult↗
PubMed2000

Dynamic stability after ACL injury: who can hop?

Single-leg hops are used clinically to assess knee function in patients following anterior cruciate ligament (ACL) rupture and reconstruction. Researchers study ACL-deficient individuals in order to identify movement strategies in the absence of a major knee stabilizer, thereby providing information to clinicians regarding treatment options. Single-leg hops represent an activity which places higher demands on the knee than walking or jogging. Hops are thought by some to represent demands that are more comparable to those found during high level sports. Therefore hopping might provide more information about knee stability during dynamic activities than less strenuous activities. This paper reflects one component of a larger study involving comparisons of joint motions and muscle activity patterns in uninjured individuals (n=10) and two groups of athletes who had complete ACL ruptures; one group had substantial knee instability (noncopers, n=10), and the other had no signs of knee instability (copers, n=11). In this paper we report the findings from the single-leg hop activity. The results indicate that coper subjects move in a manner nearly identical to uninjured persons. Kinetic data suggest that copers stabilize their knees with greater contributions from the ankle extensor muscles. Muscle activity data demonstrate that there is no reduction in quadriceps femoris activity in the coper subjects. In the group of ten subjects with knee instability (noncopers) who participated in the overall study involving walking, jogging, hopping, and a step activity only four were willing to hop. Work in our laboratory has established that when high level athletes rupture their ACL, the majority of them cannot return to high level sports. The small number of noncopers in this study who were willing to hop supports our previous findings. Those noncopers who did hop displayed reduced knee range of motion and external knee flexion moments, a movement strategy remarkably similar to that found during other activities. Neither the copers nor the noncopers showed evidence that quadriceps activation was diminished.

Adult↗
PubMed2000

A decision-making scheme for returning patients to high-level activity with nonoperative treatment after anterior cruciate ligament rupture.

This report describes the development and current use of decision-making criteria for returning patients to high-level physical activity with nonoperative management of anterior cruciate ligament ruptures, and presents the results of treatment for patients who met our criteria as candidates for nonoperative rehabilitation and attempted to return to high-level physical activity with nonoperative management. The screening examination consists of four one-legged hop tests, the incidence of knee giving-way, a self-report functional survey, and a self-report global knee function rating. We screened 93 consecutive patients with acute unilateral anterior cruciate ligament rupture, classifying them as either candidates (n = 39, 42%) or noncandidates (n = 54, 58%) for nonoperative management. Of the 39 rehabilitation candidates 28 chose nonoperative management and returned to preinjury activity levels, 22 of whom (79%) returned to preinjury activity levels without further episodes of instability or a reduction in functional status. No patient sustained additional articular or meniscal damage as a result of rehabilitation or return to activity. The decision-making scheme described in this study shows promise in determining who can safely postpone surgical reconstruction and temporarily return to physically demanding activities. Continued study to refine and further validate the decision-making scheme is recommended.

Adolescent↗
PubMed2000

Failure of voluntary activation of the quadriceps femoris muscle after patellar contusion.

STUDY DESIGN: Descriptive study of phenomenon. OBJECTIVES: To determine the extent of failure of voluntary activation of the quadriceps femoris muscle in patients early after patellar contusion. BACKGROUND: Pain and effusion are related to the presence of quadriceps inhibition. We hypothesized that patients with patellar contusions would be unable to fully recruit their quadriceps muscles and that the activation deficit would be associated with self-report measures of function. METHODS AND MEASURES: Sixteen patients who had sustained a unilateral patellar contusion fewer than 4 months prior to testing participated in the study (7 men, 9 women; mean age = 30.0 +/- 11.6). Subjects completed a self-report questionnaire to assess knee function and performed an isometric burst superimposition test on the involved and uninvolved quadriceps at 60 degrees of knee flexion. The subjects were assigned to 2 groups according to the presence (n = 5) or absence (n = 11) of quadriceps inhibition. RESULTS: Sixty-nine percent of the subjects tested were able to fully activate their quadriceps. Both groups had a decreased knee extensor force on the involved side compared to the uninvolved, but the group with inhibition had a lower side-to-side percentage of knee extensor force (mean = 65.5% +/- 18.9) than those without inhibition (mean = 85.5% +/- 16.4). CONCLUSION: Early after patellar contusion, approximately one-third of the patients demonstrated quadriceps inhibition. According to our working hypothesis, the majority of the patients tested should have demonstrated inhibition. Quadriceps inhibition was not associated with the activities of daily living, sports activity, or global rating scales in this study. Decreased volitional quadriceps force production (the hallmark of inhibition) was the only variable that discriminated patients with patellar contusion who had inhibition from those who did not.

Adult↗
PubMed2000

Proposed practice guidelines for nonoperative anterior cruciate ligament rehabilitation of physically active individuals.

Nonoperative management of anterior cruciate ligament (ACL) rupture has not been a successful option for those who participate in high-level physical activity. However, there are instances when patients may want to attempt to return to physically demanding activities with nonoperative rehabilitation for an ACL injury. The purpose of this commentary is to describe guidelines for nonoperative management of physically active individuals with ACL injuries who wish to return to preinjury levels of physical activity. The guidelines are based on the results of 2 clinical studies that improved the overall success of nonoperative management of physically active individuals with ACL ruptures. A decision-making process for selecting appropriate candidates for nonoperative management (rehabilitation candidates) is described. Individuals are classified as rehabilitation candidates if they have no concomitant ligament or mensical damage associated with the ACL injury, have a unilateral ACL injury, and meet all 4 of the following criteria: (1) timed hop test score of 80% or more of the uninjured limb, (2) Knee Outcome Survey Activities of Daily Living Scale score of 80% or more, (3) global rating of knee function of 60% or more, and (4) no more than 1 episode of giving way since the incident injury to the time of testing. Individuals meeting the criteria of a rehabilitation candidate undergo an intensive rehabilitation program before returning to high-level activity. The rehabilitation program consisting of lower extremity muscle strength training, cardiovascular endurance training, agility and sport-specific skill training, and a training program using balance perturbations is described.

Anterior Cruciate Ligament Injuries↗
PubMed2000

The efficacy of perturbation training in nonoperative anterior cruciate ligament rehabilitation programs for physical active individuals.

BACKGROUND AND PURPOSE: Treatment techniques involving perturbations of support surfaces may induce compensatory muscle activity that could improve knee stability and increase the likelihood of returning patients to high-level physical activity. The purpose of this study was to determine the efficacy of augmenting standard nonoperative anterior cruciate ligament (ACL) rehabilitation programs with a perturbation training program. SUBJECTS: Twenty-six patients with acute ACL injury or ruptures of ACL grafts participated in the study. Subjects had to have a unilateral ACL injury, be free of concomitant multiple ligament or meniscal damage requiring surgical repair, and pass a screening examination designed to identify patients who had the potential to return to high-level physical activity with nonoperative treatments. Subjects also had to be regular participants in level I activities (eg, soccer, football, basketball) or level II activities (eg, racquet sports, skiing, construction work). METHODS: Subjects were randomly assigned to either a group that received a standard rehabilitation program (standard group) or a group that received the standard program augmented with a perturbation training program (perturbation group). Treatment outcome was determined from scores on the Knee Outcome Survey's Activities of Daily Living Scale (ADLS) and Sports Activity Scale, a global rating of knee function, scores on a series of single-limb hop tests, measurements of maximum isometric quadriceps femoris muscle force output, and the group frequency of unsuccessful rehabilitation. Unsuccessful rehabilitation was defined as the occurrence of an episode of giving way of the knee or failure to maintain the functional status of a rehabilitation candidate on retesting. RESULTS: More subjects had unsuccessful rehabilitation in the standard group compared with the perturbation group. There was a within-group x time interaction for the ADLS, global rating of knee function, and crossover hop test scores. These scores decreased from posttraining to the 6-month follow-up for the standard group. CONCLUSION AND DISCUSSION: Although both the standard program and the perturbation training program may allow subjects to return to high-level physical activity, the perturbation training program appears to reduce the risk of continued episodes of giving way of the knee during athletic participation and allows subjects to maintain their functional status for longer periods.

Activities of Daily Living↗
PubMed1999

Laxity, instability, and functional outcome after ACL injury: copers versus noncopers.

PURPOSE: The purpose of this study was to determine the relationship among laxity, quadriceps strength, instability, and function in subjects with complete rupture of the anterior cruciate ligament (ACL) who compensate well for the injury (copers) and those who require surgical stabilization (noncopers). METHODS: Forty-five patients with unilateral ACL rupture (confirmed via arthroscopy or magnetic resonance imaging (MRI) and arthrometer measurements) participated in this study. Subjects were divided into two groups: copers (N = 12), and subacute noncopers (N = 18) and chronic noncopers (N = 15). All copers had returned to all preinjury activity (including index sport) without limitation. Maximum manual anterior tibiofemoral laxity measurements, quadriceps femoris muscle strength measurements, and a series of hop tests were performed. Lysholm Scale, Knee Outcome Survey (KOS), global rating of knee function, and the International Knee Documentation Committee (IKDC) form were completed. RESULTS: There was no significant difference in laxity between copers (X = 5.5+/-2.7 mm) and noncopers (chronic, X = 5.1+/-2.8 mm and subacute, X = 4.2+/-2.2 mm) or in IKDC scores among the groups. The copers, however, scored significantly better than the chronic and subacute ACL-deficient subsets on all other measures. Measurements of laxity were not correlated to any functional outcome measure or to episodes of instability. CONCLUSIONS: Copers were not different in any meaningful way from the noncopers before injury, had equal or greater side-to-side laxity differences, and functioned normally. A battery of tests was identified that accurately discriminated noncopers from copers even early after injury. Thus, measurements of laxity alone are insufficient for determining functional status after ACL injury.

Activities of Daily Living↗