Neuromuscular Control Strategies Research Articles

CLINICAL DECISION MAKING AND TREATMENT IN A RUNNER WITH HIP PAIN AND NEUROMUSCULAR CONTROL DYSFUNCTION: A CASE REPORT

The incidence of running related injuries remains high despite numerous efforts to understand the mechanical contributors to the etiology of these injuries. In light of continued running injury, theories of neuromuscular control, or movement patterns, have been suggested as possible contributors to running related injuries. However, the clinical decision making determining when altered neuromuscular control strategies may be affecting a runner's symptoms has not been described. Therefore, the purpose of this case report is to describe the clinical reasoning within the ICF framework for a runner with hip pain and neuromuscular control dysfunction. A 47-year-old, experienced, female runner presented with posterior hip pain and radiating posterior thigh pain limiting her ability to participate in running and threatened her goal to run in an upcoming marathon. Several features of her examination indicated soft tissue muscular irritation of the posterior hip complex related to impaired balance and control of the lower quarter during functional movement and running activities consistent with a neuromuscular control dysfunction. Her initial Focus on Therapeutic Outcomes (FOTO) score was 69 with predicted change score of +7. The subject was able to achieve her goals including a return to participation in her weekly running routine and competing in a marathon race. Objective examination features of range of motion, strength, and control of movement were all improved. Her reported function was greatly improved with a final FOTO score 98. The diagnosis and treatment of running related injuries remains a clinical challenge. This case report describes the examination and clinical reasoning in diagnosing neuromuscular control dysfunction and proposes a treatment progression to address this functional limitation. The decision making scheme is also structured to follow the International Classification of Functioning, Disability, and Health. 4.

Trunk muscle activation patterns during walking among persons with lower limb loss: Influences of walking speed

Persons with lower limb amputation (LLA) walk with altered trunk-pelvic motions. The underlying trunk muscle activation patterns associated with these motions may provide insight into neuromuscular control strategies post LLA and the increased incidence of low back pain (LBP). Eight males with unilateral LLA and ten able-bodied controls (CTR) walked over ground at 1.0 m/s, 1.3 m/s, 1.6 m/s, and self-selected speeds. Trunk muscle onsets/offsets were determined from electromyographic activity of bilateral thoracic (TES) and lumbar (LES) erector spinae. Trunk-pelvic kinematics were simultaneously recorded. There were no differences in TES onset times between groups; however, LLA demonstrated a second TES onset during mid-to-terminal swing (not seen in CTR), and activation for a larger percentage of the gait cycle. LLA (vs. CTR) demonstrated an earlier onset of LES and activation for a larger percentage of the gait cycle at most speeds. LLA walked with increased frontal plane trunk ROM, and a more in-phase inter-segmental coordination at all speeds. These data collectively suggest that trunk neuromuscular control strategies secondary to LLA are driven by functional needs to generate torque proximally to advance the affected limb during gait, though this strategy may have unintended deleterious consequences such as increasing LBP risk over time.

Muscle synergies are similar when typically developing children walk on a treadmill at different speeds and slopes

BackgroundThe aim of this study was to determine whether changes in synergies relate to changes in gait while walking on a treadmill at multiple speeds and slopes. The hypothesis was that significant changes in movement pattern would not be accompanied by significant changes in synergies, suggesting that synergies are not dependent on the mechanical constraints but are instead neurological in origin. MethodsSixteen typically developing children walked on a treadmill for nine combinations (stages) of different speeds and slopes while simultaneously collecting kinematics, kinetics, and surface electromyography (EMG) data. The kinematics for each stride were summarized using a modified version of the Gait Deviation Index that only includes the sagittal plane. The kinetics for each stride were summarized using a modified version of the Gait Deviation Index – Kinetic which includes sagittal plane moments and powers. Within each synergy group, the correlations of the synergies were calculated between the treadmill stages. ResultsWhile kinematics and kinetics were significantly altered at the highest slope compared to level ground when walking on a treadmill, synergies were similar across stages. ConclusionsThe high correlations between synergies across stages indicate that neuromuscular control strategies do not change as children walk at different speeds and slopes on a treadmill. However, the multiple significant differences in kinematics and kinetics between stages indicate real differences in movement pattern. This supports the theory that synergies are neurological in origin and not simply a response to the biomechanical task constraints.

Muscle synergy analysis in dart throwing.

This study aims to analyze muscle synergies in darts throwing movement to clarify how the central nervous system (CNS) controls muscle activation to produce complicated motion. Activities of 10 different muscles on upper limb were recorded through surface electromyography (EMG) electrodes from four participants with less experience of dart throwing. Subsequently, non-negative matrix factorization (NNMF) was applied to the collected EMG signals for muscle synergy analysis. Results showed that three muscle synergies could explain sufficiently the observed EMG data, with determination coefficient r2 = 0.91 ± 0.02 across four subjects. However, it was found that there was significant difference in terms of patterns of both muscle synergies and activation coefficients between participants, which might reflect different neuromuscular control strategies in dart throwing.

Muscle Fatigue Analysis of the Deltoid during Three Head-Related Static Isometric Contraction Tasks

This study aimed to investigate the fatiguing characteristics of muscle-tendon units (MTUs) within skeletal muscles during static isometric contraction tasks. The deltoid was selected as the target muscle and three head-related static isometric contraction tasks were designed to activate three heads of the deltoid in different modes. Nine male subjects participated in this study. Surface electromyography (SEMG) signals were collected synchronously from the three heads of the deltoid. The performances of five SEMG parameters, including root mean square (RMS), mean power frequency (MPF), the first coefficient of autoregressive model (ARC1), sample entropy (SE) and Higuchi’s fractal dimension (HFD), in quantification of fatigue, were evaluated in terms of sensitivity to variability ratio (SVR) and consistency firstly. Then, the HFD parameter was selected as the fatigue index for further muscle fatigue analysis. The experimental results demonstrated that the three deltoid heads presented different activation modes during three head-related fatiguing contractions. The fatiguing characteristics of the three heads were found to be task-dependent, and the heads kept in a relatively high activation level were more prone to fatigue. In addition, the differences in fatiguing rate between heads increased with the increase in load. The findings of this study can be helpful in better understanding the underlying neuromuscular control strategies of the central nervous system (CNS). Based on the results of this study, the CNS was thought to control the contraction of the deltoid by taking the three heads as functional units, but a certain synergy among heads might also exist to accomplish a contraction task.

Assessment of Upper Limb Motor Dysfunction for Children with Cerebral Palsy Based on Muscle Synergy Analysis

Muscle synergies are considered to be building blocks underlying motor behaviors. The goal of this study is to explore an objective and effective method to assess the upper limb motor dysfunction of cerebral palsy (CP) children from the aspect of muscle synergy analysis. Fourteen CP children and 10 typically developed (TD) children were recruited to perform three similar upper limb motion tasks related to the movements of elbow and shoulder joints, and surface electromyographic (sEMG) signals were recorded from 10 upper arm and shoulder muscles involved in the defined tasks. Non-negative matrix factorization algorithm was used to extract muscle synergies and the corresponding activation patterns during three similar tasks. For each subject in TD group, four muscle synergies were extracted in each task. Whereas, fewer mature synergies were recruited in CP group, and many abnormal synergy structures specific to CP group appeared. In view of neuromuscular control strategy differences, three synergy-related parameters were proposed and synergy structure similarity coefficient was found to have high ability in depicting the inter-subject similarity within task and the intra-subject similarity between tasks. Seven upper limb assessment (UPA) metrics, which were defined as the combinations of synergy structure similarity coefficients of three tasks, were proposed to assess the upper limb motor function of CP children. The experimental results demonstrated that these UPA metrics were able to assess upper limb motor function comprehensively and effectively. The proposed assessment method can serve as a promising approach to quantify the abnormality of muscle synergies, thus offering potential to derive a physiologically based quantitative index for assessing upper limb motor function in CP clinical diagnosis and rehabilitation.

The Alteration of Neuromuscular Control Strategies During Gait Initiation in Individuals with Chronic Ankle Instability

Background: Providing a clear picture of neuromuscular control mechanisms and deficits in patients with chronic ankle instability (CAI) requires further investigation. Gait initiation (GI) is a perfect task to evaluate concurrent open-loop (planned GI) and closed-loop (unplanned GI) neuromuscular control mechanisms in patients with CAI. Objectives: The current study aimed at evaluating neuromuscular control mechanisms via assessment of the center of pressure (COP) displacements during planned and unplanned GI in patients with CAI and healthy individuals. Methods: It was a case-control study. Twenty-two subjects with unilateral CAI and 22 healthy subjects stood on a force plate and initiated gait with maximal velocity under 2 conditions: i) planned (initiated gait after hearing the “all set” signal, when subjects felt ready to walk) and ii) unplanned (initiated gait “as soon as possible” after hearing acoustic signal). The COP parameters were assessed during the preparatory and the execution phase of GI. Results: The peak COP displacement toward swing leg decreased significantly, with P value = 0.003, in the preparatory phase of GI under planned and unplanned conditions in patients with CAI (0.028 ± 0.002) in comparison with the control group (0.038 ± 0.002). Forward velocity of the COP displacement increased in CAI patients (0.026 ± 0.003) compared with the control group (0.018 ± 0.002) in the execution phase of GI, with P value = 0.039. Conclusions: According to the findings of the current study, both open-loop and closed-loop neuromuscular control mechanisms altered in patients with CAI.

Characteristics of the Motor Units during Sternocleidomastoid Isometric Flexion among Patients with Mechanical Neck Disorder and Asymptomatic Individuals.

Mechanical neck disorder is a widespread and non-neurological musculoskeletal condition resulting from modern lifestyles. Presently, the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles and the characteristics of the short-term synchronization of the motor unit in patients with neck pain are ambiguous. This study therefore aims to clarify the fundamental electrophysiological properties of the motor units of the sternocleidomastoid muscles in patients with mechanical neck disorder and in asymptomatic individuals. We further investigated whether alterations in the degree of motor unit short-term synchronization occur. The surface electrophysiological signals of the bilateral sternal heads of the sternocleidomastoid muscles of twelve patients with mechanical neck disorder and asymptomatic individuals were detected at 25% of the maximum voluntary contraction during cervical isometric flexion and then decomposed into individual motor unit action potential trains. We found that the patients with mechanical neck disorder showed significantly higher initial and mean firing rates of the sternocleidomastoid muscles and displayed substantially lower motor unit short-term synchronization values compared with the asymptomatic subjects. Consequently, these convincing findings support the assertion that patients with mechanical neck disorder display altered neuromuscular control strategies, such as the reinforcement of motor unit recruitment firing rates in the sternocleidomastoid muscles. The motor units of these patients also revealed neural recruitment strategies with relatively poor efficiency when executing the required motor tasks.

Neuromuscular control strategies of the trunk antagonist muscles during the Biering-Sorensen test in individuals with recurrent low back pain and healthy subjects

OBJECTIVES To compare the activation pattern of the trunk antagonistic muscles and also the myoelectric manifestations of muscle fatigue between subjects with and without recurrent non-specific low back pain, during the fatigue provocation of the erector spinae. METHODS The study involved 19 subjects with recurrent low back pain with a non-specific cause (seven men, 12 women, 38.53 ± 8.12 years, 68.35 ± 18.12 kg, 1.66 ± 0.09 m), and 19 healthy subjects (seven men, 12 women, 40.42 ± 8.63 years, 69.57 ± 12.76 kg, 1.64 ± 0.07 m). The electromyographic signal of the internal oblique, lumbar multifidus, rectus abdominis and lumbar iliocostalis muscles, bilateral, were collected during Biering-Sorensen test execution. RESULTS The group with low back pain showed a lower co-contraction rate of the internal oblique/lumbar multifidus (p = 0.006) and lower activation amplitude of the internal oblique (p = 0.019), both on the right side when compared to the group without low back pain. No differences were observed between the groups for muscle fatigue indicators (p > 0.05). CONCLUSION When the erector spine muscle fatigue occurs - even when the groups were similar as to the ability of extensors muscles to resist fatigue - differences were found between subjects with and without low back pain regarding the recruitment pattern of the task antagonist muscle, because subjects with low back pain showed lesser activation and co-contraction in relation to the healthy group.

Lower extremity muscle activation onset times during the transition from double-leg stance to single-leg stance in anterior cruciate ligament reconstructed subjects

BackgroundPrevious studies mainly focused on muscles at the operated knee after anterior cruciate ligament reconstruction, less on muscles around other joints of the operated and non-operated leg. The aim of this study was to investigate muscle activation onset times during the transition from double-leg stance to single-leg stance in anterior cruciate ligament reconstructed subjects. MethodsLower extremity muscle activation onset times of both legs of 20 fully returned to sport anterior cruciate ligament reconstructed subjects and 20 non-injured control subjects were measured during the transition from double-leg stance to single-leg stance in eyes open and eyes closed conditions. Analysis of covariance (ANCOVA) was used to evaluate differences between groups and differences between legs within both groups, while controlling for peak center of pressure velocity. FindingsSignificantly delayed muscle activation onset times were found in the anterior cruciate ligament reconstructed group compared to the control group for gluteus maximus, gluteus medius, vastus medialis obliquus, medial hamstrings, lateral hamstrings and gastrocnemius in both eyes open and eyes closed conditions (P<.05). Within the anterior cruciate ligament reconstructed group, no significant different muscle activation onset times were found between the operated and non-operated leg (P>.05). InterpretationDespite completion of rehabilitation and full return to sport, the anterior cruciate ligament reconstructed group showed neuromuscular control deficits that were not limited to the operated knee joint. Clinicians should focus on relearning multi-segmental anticipatory neuromuscular control strategies after anterior cruciate ligament reconstruction.

Strategies for equilibrium maintenance during single leg standing on a wobble board

The aim of this study was to identify and compare movement strategies used to maintain balance while single leg standing on either a firm surface (FS) or on a wobble board (WB). In 17 healthy men, retroreflective markers were positioned on the xiphoid process and nondominant lateral malleolus to calculate trunk and contralateral-leg excursion (EXC) and velocity (VEL), and center of pressure (CoP) EXC and VEL during FS on a force platform. From the WB test, standing time (WBTIME) was determined and the board's angular EXC and VEL were calculated from four markers on the WB as surrogate measures for CoP dynamics. Electromyographic average rectified values (ARV) from eight leg and thigh muscles of the supporting limb were calculated for both tasks. WB ARV amplitudes were normalized with respect to the value of FS ARV and presented significantly higher peroneus longus and biceps femoris activity (p<0.05). WB standing time was correlated to trunk sagittal plane velocity (r=−0.73 at p=0.016) and excursion (r=−0.67 at p=0.03). CoP and WB angular movement measures were weakly and not significantly correlated between tasks. This lack of correlation indicates that WB balance maintenance requires movement beyond the ankle strategy as described for the FS task. WB standing likely demands different biomechanical and neuromuscular control strategies, which has immediate implications for the significance of WB tests in contrast to FS balance tests. Differences in control strategies will also have implications for the understanding of mechanisms for rehabilitation training using such devices.

17β-Estradiol Induced Effects on Anterior Cruciate Ligament Laxness and Neuromuscular Activation Patterns in Female Runners.

We investigate the effects of 17β-Estradiol across phases of menstrual cycle on the laxness of the anterior cruciate ligament (ACL) and the neuromuscular control patterns around the knee joint in female runners. Twelve healthy female runners who reported normal menstrual cycles for the previous 6 months were tested twice across one complete menstrual cycle for serum levels of 17β-estradiol, and knee joint laxity (KJL). Electromyographic (EMG) activity of the quadriceps and hamstrings muscles was also recorded during running on a treadmill. The changes in the EMG activity, KJL, and hormonal concentrations were recorded for each subject during the follicular and the ovulatory phases across the menstrual cycle. An observed increase in KJL in response to peak estradiol during the ovulatory phase was associated with increased preactivity of the hamstring muscle before foot impact (p<0.001). A consistent pattern was also observed in the firing of the quadriceps muscle recruitment pattern throughout the follicular phase associated with decreased hamstring recruitment pattern during weight acceptance phase of running (p=0.02). Additionally, a low ratio of medial to lateral quadriceps recruitment was associated with a significant reduction of the quadriceps to hamstring co-contraction ratio during the follicular phase. Changes in KJL during the menstrual cycle in response to 17β-estradiol fluctuations changes the neuromuscular control around the knee during running. Female runners utilize different neuromuscular control strategies during different phases of the menstrual cycle, which may contribute to increased ACL injury risk.

Muscle synergies and complexity of neuromuscular control during gait in cerebral palsy.

Individuals with cerebral palsy (CP) have impaired movement due to a brain injury near birth. Understanding how neuromuscular control is altered in CP can provide insight into pathological movement. We sought to determine if individuals with CP demonstrate reduced complexity of neuromuscular control during gait compared with unimpaired individuals and if changes in control are related to functional ability. Muscle synergies during gait were retrospectively analyzed for 633 individuals (age range 3.9-70y): 549 with CP (hemiplegia, n=122; diplegia, n=266; triplegia, n=73; quadriplegia, n=88) and 84 unimpaired individuals. Synergies were calculated using non-negative matrix factorization from surface electromyography collected during previous clinical gait analyses. Synergy complexity during gait was compared with diagnosis subtype, functional ability, and clinical examination measures. Fewer synergies were required to describe muscle activity during gait in individuals with CP compared with unimpaired individuals. Changes in synergies were related to functional impairment and clinical examination measures including selective motor control, strength, and spasticity. Individuals with CP use a simplified control strategy during gait compared with unimpaired individuals. These results were similar to synergies during walking among adult stroke survivors, suggesting similar neuromuscular control strategies between these clinical populations.

Effect Of Neuromuscular Fatigue On Emg Patterns In Subjects With Ankle Instability

Hip abductors and ankle evertors provide dynamic postural stability and muscle fatigue decreases their function, which could lead to lateral ankle sprains. Ankle instability (AI) patients exhibited different neuromuscular control strategies during functional activities compared to healthy subjects. PURPOSE: Examine the effect of fatigue and AI on muscle activity patterns during a forward-side jump. METHODS: 25 AI (23.3±1.9yrs, 176.5±10.5cm, 70.9±11.4kg) and 25 control subjects (23.7±2.5yrs, 175.0±10.8cm, 70.3±12.8kg) performed 5 forward-side jumps before and after fatiguing exercises while EMG signals were collected from the peroneus longus (PL) and gluteus medius (GM). Subjects ran on the treadmill for 5 min at between 5 and 6 mph. Next, subjects performed 20-sec lateral, and 20-vertical jumps. A max vertical jump was measured after each fatigue cycle. Subjects repeated three exercises until RPE reached 17 and the vertical jump fell below 80% of max jump height. Functional linear models (α=0.05) were used to evaluate differences between two conditions (pre- vs post-fatigue) in each group (AI vs control) for PL and GM activation. This analysis compared variables as polynomial functions rather than discrete values. Functions of each condition as well as 95% confidence interval (CI) bands were plotted to determine significant differences. RESULTS: Figure 1. Group by fatigue interactions were found at initial contact in PL and between 30-35% of stance in GM. Fatigue decreased EMG amplitude of PL between 15-50% in the control group and during 0-70% of stance in AI group. Decreased GM activation was found during 30-40% of stance in AI group, but not in control group. CONCLUSIONS: AI group showed greater pre- to post-fatigue reduction in PL and GM EMG amplitude than the control group. Greater deficits of PL and GM activity may infer a greater risk for injury.

Muscle synergy analysis for similar upper limb motion tasks.

Muscle synergy is considered as a vector specifying a pattern of relative muscle activation. The goal of this paper is to explore whether there exists similarities between muscle synergies in similar upper limb motion tasks. One center-out-center reaching task and two path movement tasks with regard to the elbow and shoulder joints were designed, and seven healthy adults were recruited in this study. Surface electromyographic (sEMG) signals were recorded from 10 upper arm and shoulder muscles, and muscle synergies were extracted using nonnegative matrix factorization algorithm. Although there existed individual differences among subjects, experimental results showed that the structures of muscle synergies extracted from these three similar tasks were similar on the ground of the values of Pearson's correlation coefficient was greater than 0.85. Through this finding, the neuromuscular control strategies of upper limb in similar tasks could be explained clearly, which also provided significant evidence to support the hypothesis of muscle synergies.

Patient-reported perception of difficulty as a clinical indicator of dysfunctional neuromuscular control during the prone hip extension test and active straight leg raise test

Two clinical tests used to assess for neuromuscular control deficits in patients with low back pain (LBP) are the prone hip extension (PHE) test and active straight leg raise (ASLR) test. For these tests, it has been suggested that patients be classified as “positive” if they demonstrate specific “abnormal” lumbopelvic motion patterns. For the ASLR test, the use of patient-reported perception of difficulty is also used to assess neuromuscular control. Thirty participants with LBP and 40 asymptomatic controls took part in this cross-sectional observational study. Participants performed both tests and were classified as “positive” or “negative” based on the presence or absence (respectively) of specific “abnormal” motion patterns. The participants also rated their perceived difficulty in performing the tests using a six-point scale. A two-way analysis of covariance (ANCOVA) was used to examine the effects of group (LBP/control) and examiner classification (positive/negative) on the perceived difficulty scores for each test. The LBP group perceived greater difficulty in performing both tests compared to the control group. Conversely, there was no significant difference in the perceived difficulties of the positive and negative examiner classifications for either test. Additional investigation is required to comment further on the relative usefulness of the perceived difficulty and observable motion patterns during these tests in assessing the neuromuscular control strategies of the lumbopelvic region, and their potential as a diagnostic tool or treatment outcome.

Neuromuscular control during stepping down in continuous gait in individuals with and without ankle instability

Ankle sprains are a common injury and those affected are at a risk of developing chronic ankle instability (CAI). Complications of an acute sprain include increased risk of re-injury and persistent disability; however, the exact link between ankle sprains and chronic instability has yet to be elucidated. The purpose of this study was to investigate neuromuscular control (including kinematics, kinetics and EMG) during stepping down from a curb, a common yet challenging daily activity, in persons with ankle instability (n = 11), those with a history of ankle sprain without persistent instability, called ankle sprain “copers” (CPRs) (n = 9) and uninjured controls (CTLs) (n = 13). A significant group difference was noted as the CPR group demonstrated increased tibialis anterior activity in both the preparatory (pre-touchdown) and reactive (post-touchdown) phases when compared to healthy and unstable groups (P < 0.05). It follows that the CPR group also demonstrated a significantly less plantar-flexed position at touchdown than the other two groups (P < 0.05). This is a more stable position to load the ankle and this strategy differed from that used by participants with CAI and uninjured CTLs. These findings provide insight into the neuromuscular control strategies of CPRs, which may allow them to more appropriately control ankle stability following sprains.

Extraction of basic movement from whole-body movement, based on gait variability

The aim of this study was to quantify the step-to-step variability (SSV) in speed-variant and speed-invariant movement components of the whole-body gait pattern during running. These separate aspects of variability can be used to gain insight into the neuromuscular control strategies that are engaged during running. Ten healthy, physically active, male recreational athletes performed five treadmill running trials at five different speeds (range: 1.3–4.9 m/sec). The whole-body movement was separated into principal movements (PM) using a principal component analysis. The PMs were split into two groups: a speed-variant group, where the range of motion (amplitude of PMs) changed with running speed; and a speed-invariant group, where the range of motion was constant across various speeds. The step-to-step variability (SSV) of the two groups was then quantified. The absolute SSV was the summed variability across all gait cycles, whereas the relative SSV was the summed variability divided by the magnitude of the movement. The absolute SSV of the speed-variant movements increased with running speed. By contrast, the relative SSV of the speed-variant group (as normalized to the PM amplitude) decreased asymptotically toward a minimal level as running speed increased. Both the absolute and relative SSV of the speed-invariant movements revealed a minimum at 3.1 m/sec. The whole-body gait pattern during running can be subdivided into speed-variant and speed-invariant movements. An interpretation of the SSV based on minimal intervention theory suggests that speed-variant movements are more tightly controlled, as evidenced by a lower degree of variability compared to the speed-invariant movements.

Associations between lower limb muscle activation strategies and resultant multi-planar knee kinetics during single leg landings

Anterior cruciate ligament injury prevention programs purportedly improve knee joint loading through beneficial modification of lower limb neuromuscular control strategies and joint biomechanics, but little is known about how these factors relate during single-legged landings. Thus, we examined the relationship between explicit lower limb muscular pre-activity patterns and knee joint biomechanics elicited during such landings. Randomized controlled trial. Thirty-five female athletes had 3D knee joint biomechanics and lower limb EMG data recorded during a series of single-leg landings. Regression analysis assessed the relationship between pre-activity of vastus lateralis, lateral hamstring and rectus femoris with peak knee flexion angle and moment, and external anterior tibial shear force. Vastus lateralis, lateral hamstring and vastus lateralis:lateral hasmtring co-contraction assessed the relationship with knee abduction angle and moment. Greater pre-activity of rectus femoris predicted increased peak anterior tibial shear force (R(2)=0.235, b=2.41 and P=0.003) and reduced knee flexion moment (R(2)=0.131, b=-0.591, and P=0.032), while greater lateral hamstring predicted decreased peak knee flexion angle (R(2)=0.113, b=8.96 and P=0.048). No EMG pre-activity parameters were predictors (P>0.05) for knee abduction angle and moment. Current outcomes suggest reducing reliance on quadriceps activation may be beneficial during single-legged landings. It also, however, may be required for adequate joint stability during such maneuvers. Further research is needed to determine if inadequate hamstring activation, rather than elevated quadriceps activation, leads to hazardous loading during single-legged landings.

Characteristics of human knee muscle coordination during isometric contractions in a standing posture: The effect of limb task

Different functional roles for the hands have been demonstrated, however leg control is not as well understood. The purpose of the present study was to evaluate bilateral knee neuromuscular control to determine if the limb receiving greater attention would have more well-tuned control compared to an unattended limb. Surface electrodes were placed on seven muscles of each limb, before standing on two force platforms. Visual feedback was given of the forces and moments of the “focus limb,” but not the “unattended limb.” Static isometric forces were matched with their focus limb, requiring their unattended limb to push in the opposite direction, using a combination of forward–backward–medial–lateral shear forces while muscle activity was collected bilaterally. There was a significant main effect for limb task (p=0.02), with the medial hamstrings being more specific (p=0.001) while performing the unattended limb and the lateral hamstring being more well-tuned (p=0.007) while performing the focus limb task. The focus limb’s medial and lateral gastrocnemius were principally active in the forwards direction, but only the unattended limb’s lateral gastrocnemius was active in the backwards direction. Findings suggest unique neuromuscular control strategies are used for the legs depending on limb task.