Volitional Activity Research Articles

Functional Echomyography of the human denervated muscle: first results

In this study we followed with ultrasound three patients with permanent denervation to evaluate changes in morphology, thickness, contraction and vascularisation of muscles undergoing the home-based electrical stimulation program of the Rise2-Italy project. During a period of 1 year for the first subject, 6 months for the second subject and 3 months for the third subject we studied with ultrasound the denervated muscle comparing it (if possible) to the contralateral normal muscle. We evaluated: 1. Changes in morphology and sonographic structure of the pathologic muscle; 2. Muscular thickness in response to the electrical stimulation therapy; 3. Short-term modifications in muscle perfusion and arterial flow patterns after stimulation; 4. Contraction-relaxation kinetic induced by volitional activity or electrical stimulation. Morphology and ultrasonographic structure of the denervated muscles changed during the period of stimulation from a pattern typical of complete muscular atrophy to a pattern which might be considered “normal” when detected in an old patient. Thickness improved significantly more in the middle third than in the proximal and distal third of the denervated muscle, reaching in the last measurements of the first subject approximately the same thickness as the contralateral normal muscle. In all the measurements done within this study, arterial flow of the denervated muscle showed at rest a low-resistance pattern with Doppler Ultra Sound (US), and a pulsed pattern after electrical stimulation. The stimulation- induced pattern is similar to the trifasic high-resistance pattern of the normal muscle. Contraction- relaxation kinetic, measured by recording the muscular movements during electrical stimulation, showed an abnormal behaviour of the denervated muscle during the relaxation phase, which resulted to be significantly longer than in normal muscle (880 msec in the denervated muscle vs 240 msec in the contralateral normal one). The very high energy needed to stimulate the denervated muscles according to the Vienna home-based Functional Electrical Stimulation (h-b FES) strategy demonstrates that the explored muscles are denervated. This pilot study confirms the usefulness of Functional EchoMyography in the follow-up and the positive effects of h-b FES of denervated/reinnervating muscles.

P36-19 Effect of dorsal premotor cortex rTMS on volitional motor cortical activity studied by contingent negative variation and Bereitschaftspotential

P36-19 Effect of dorsal premotor cortex rTMS on volitional motor cortical activity studied by contingent negative variation and Bereitschaftspotential

P20-22 Modulation of interhemispheric inhibition by volitional motor activity: an ipsilateral silent period study

P20-22 Modulation of interhemispheric inhibition by volitional motor activity: an ipsilateral silent period study

Near‐Total Laryngectomy: An Alternative RLN Banking Procedure

Objectives: Laryngeal transplantation may become feasible in the next several years. A functional transplant will require separate reinnervation by nerves that are activated synchronously with laryngeal adductor and abductor functions, ideally by branches of the original recurrent laryngeal nerve. This report reviews the potential to preserve these nerve branches by use of the near-total, rather than total, laryngectomy procedure. Study Design: Case series Methods: A chart review was performed of patients for whom a near-total laryngectomy (NTL) was selected with the specific purpose of preserving intrinsic laryngeal muscles innervated by their native motor nerves. Anatomic features of the tumors that make this option available were delineated. Results: Three patients underwent NTL as treatment for malignancy involving the larynx. Each patient was relatively young and expressed an interest in pursuing a laryngeal transplant at a future date if such a procedure were offered. In each case the NTL was successful at controlling the tumor, and the patient was left with aspiration-free swallow and prosthesis-free alaryngeal voice. Ultrasound examination demonstrated persistent bidirectional movement of the remaining cricoarytenoid joint. Conclusions: The NTL procedure may be the ideal method for recurrent laryngeal nerve “banking” for possible future use in laryngeal transplantation. It preserves the original laryngeal neuromuscular units for both adduction and abduction, as will be required for a functional transplant. This procedure should be considered in all younger patients that require total laryngectomy. Near-total laryngectomy can often be used in cases where total laryngectomy is planned, as in these 3 cases. Robbins and Michaels found 46 of 64 (72%) total laryngectomy specimens oncologically could have had NTL (22) or less (24).5 Dumich et al. found 13 of 20 (65%) specimens could have had a near-total approach.6 There have been several reports that demonstrate that NTL in properly selected patients offers cancer control rates comparable to total laryngectomy.7-10 While NTL is not recommended for surgical salvage of radiation failures,10 it can be used following radiation for non-oncologic indications such as aspiration (e.g., Case 3). It can also be used as a “fall-back” option if there are unexpected intraoperative findings while performing a partial laryngectomy (e.g., Case 1). Although originally described for advanced (T3-T4) tumors of the glottis, supraglottis or pyriform sinus, other indications have been described such as base of tongue extension or anterior tracheal wall involvement11 (e.g., Case 2). NTL offers the advantage of tracheopharyngeal shunt speech without the need for a prosthesis. The location of speech production in the pharynx is similar to the original larynx, not more inferior as with a TEP. The remaining, innervated laryngeal muscles may also contribute to some modulation of voice quality. Ultrasound exam of the patients in this report showed continued volitional activity of these muscles more than 5 years post-operatively. But the biggest advantage, as highlighted in this report, is that an intact neuromuscular unit is maintained and thus allows the possibility of specific motor reinnervation of a future transplant. Other partial procedures, such as supracricoid laryngectomy, also maintain at least one neuromuscular unit and can be considered good “banking” procedures. The NTL is targeted at patients who would otherwise need a TL.

Neuromuscular responses in individuals with anterior cruciate ligament repair

Objective Knee surgery may alter the neuromuscular response to unexpected perturbations during functional, dynamic tasks. Long latency reflexes (LLR) follow a transcortical pathway and appear to be modifiable by task demands, potentially giving them a role in neuromuscular performance. We examined LLRs of the quadriceps and hamstrings in response to unexpected perturbations in individuals with a repaired anterior cruciate ligament (ACLR) during a weight-bearing task. We also investigated the anticipatory and volitional muscle activity that preceded and followed the LLR to quantify possible reflex adaptations associated with surgical repair. Methods Twelve females with ACLR and 12 healthy female controls performed a single leg squat maneuver, tracking a sinusoidal target. Random perturbations at the start of the flexion phase yielded tracking errors (“overshoot errors”) and triggered compensatory reflex activity. Results ACLR subjects demonstrated greater overshoot error and knee velocity during unexpected perturbations, increased LLR responses, and reduced absolute anticipatory, short-latency reflex, and voluntary quadriceps activity. Conclusions ACLR subjects showed impaired response to perturbation and a distinct EMG profile during a dynamic single leg weight-bearing task. Future research will determine the cause of neural adaptations in those with ACLR. Significance Neuromuscular adaptations may be a viable target for post-ACL injury rehabilitation interventions.

Assessing the accuracy and precision of musculoskeletal motion tracking using cine-PC MRI on a 3.0T platform

The rising cost of musculoskeletal pathology, disease, and injury creates a pressing need for accurate and reliable methods to quantify 3D musculoskeletal motion, fostering a renewed interest in this area over the past few years. To date, cine-phase contrast (PC) MRI remains the only technique capable of non-invasively tracking in vivo 3D musculoskeletal motion during volitional activity, but current scan times are long on the 1.5T MR platform (∼2.5 min or 75 movement cycles). With the clinical availability of higher field strength magnets (3.0T) that have increased signal-to-noise ratios, it is likely that scan times can be reduced while improving accuracy. Therefore, the purpose of this study is to validate cine-PC MRI on a 3.0T platform, in terms of accuracy, precision, and subject-repeatability, and to determine if scan time could be minimized. On the 3.0T platform it is possible to limit scan time to 2 min, with sub-millimeter accuracy (<0.33 mm/0.97°), excellent technique precision (<0.18°), and strong subject-repeatability (<0.73 mm/1.10°). This represents reduction in imaging time by 25% (42 s), a 50% improvement in accuracy, and a 72% improvement in technique precision over the original 1.5T platform. Scan time can be reduced to 1 min (30 movement cycles), but the improvements in accuracy are not as large.

Activity level, apoptosis, and development of cachexia in ApcMin/+ mice

Criteria for diagnosing cachexia in adults include unintentional loss in body weight, decreased strength, fatigue, anorexia, and low muscle mass. Cachexia is also associated with systemic inflammation, altered metabolism, and anemia. The Apc(Min/+) mouse is a model of cachexia directly related to intestinal tumor burden and subsequent chronic inflammation. These mice also demonstrate muscle weakness, fatigue, decreased volitional activity, and elevated circulating IL-6 levels. The purpose of this study was to determine the time course of changes in physical activity and their relationship to anemia, muscle apoptosis, and muscle mass and body mass loss during cachexia. A subset of male Apc(Min/+) mice were given access to voluntary activity wheels from 5 to 26 wk of age, while sedentary male Apc(Min/+) mice were housed in cages lacking wheels. At the study's end mice were stratified by cachectic symptoms. Severely cachectic mice had decreased wheel running performance at 15 wk of age, while anemia and body weight loss were not present until 18 wk of age. Severely cachectic mice had lower hemoglobin levels compared with mildly cachectic mice at 13, 18, and 22 wk of age. Severely cachectic mice also demonstrated threefold more BCL2-associated X protein (BAX) protein in the gastrocnemius muscle at 26 wk of age compared with mildly cachectic mice. In sedentary Apc(Min/+) mice at 26 wk of age anemia was present, and markers of apoptosis were induced in severely cachectic muscle. Proapoptotic protein expression was induced in both red and white portions of gastrocnemius muscle as well as in soleus muscle of severely cachectic mice compared with mildly cachectic mice. These data demonstrate that decrements in wheel running performance precede loss of body mass and that inherent muscle oxidative capacity is not protective against muscle apoptosis.

The design and testing of a novel mechanomyogram-driven switch controlled by small eyebrow movements

BackgroundIndividuals with severe physical disabilities and minimal motor behaviour may be unable to use conventional mechanical switches for access. These persons may benefit from access technologies that harness the volitional activity of muscles. In this study, we describe the design and demonstrate the performance of a binary switch controlled by mechanomyogram (MMG) signals recorded from the frontalis muscle during eyebrow movements.MethodsMuscle contractions, detected in real-time with a continuous wavelet transform algorithm, were used to control a binary switch for computer access. The automatic selection of scale-specific thresholds reduced the effect of artefact, such as eye blinks and head movement, on the performance of the switch. Switch performance was estimated by cued response-tests performed by eleven participants (one with severe physical disabilities).ResultsThe average sensitivity and specificity of the switch was 99.7 ± 0.4% and 99.9 ± 0.1%, respectively. The algorithm performance was robust against typical participant movement.ConclusionsThe results suggest that the frontalis muscle is a suitable site for controlling the MMG-driven switch. The high accuracies combined with the minimal requisite effort and training show that MMG is a promising binary control signal. Further investigation of the potential benefits of MMG-control for the target population is warranted.

White matter integrity associated with volitional motor activity

Variations of white matter integrity have been associated with interindividual differences in brain function. Still, little is known about the impact of white matter integrity on quantitative motor behaviour. Diffusion tensor imaging and continuous wrist actigraphy were measured on the same day in 12 individuals. Fractional anisotropy as measure of white matter integrity was correlated with the motor activity level. Positive correlations of fractional anisotropy and activity level were detected in the cingulum and the right superior longitudinal fasciculus underneath the precentral gyrus. Negative correlations were found in the left corticobulbar tract, in the right posterior corpus callosum and in the left superior longitudinal fasciculus. Volitional motor activity was associated with white matter integrity in motor relevant fiber tracts.

The Bereitschaftspotential in essential tremor

Essential tremor (ET) is an involuntary postural oscillation. It is unclear to which extent motor cortical activity in preparation of volitional movement is abnormal in ET. We measured the Bereitschaftspotential (BP) to address this question. Given the known influence of the cerebello-dentato-thalamo-cortical projection in the generation of the BP, patients were divided into two groups, defined by purely postural tremor (ET(PT)) or additional presence of intention tremor (ET(IT)) and compared to healthy controls. BP was recorded during self-paced rapid wrist extension movements. The late BP (500-0 ms before movement onset) was increased over the mid-frontal area in ET(PT), whereas it was reduced over the mid-parietal area in ET(IT) when compared to healthy controls. In addition, the late BP was reduced over a widespread centro-parietal area in ET(IT) compared to ET(PT). Findings suggest that presence vs. absence of cerebellar signs (intention tremor) in ET results in differential affection of volitional preparatory motor cortical activity. The BP increase in ET(PT) may indicate compensatory activity, whereas the widespread centro-parietal BP reduction in ET(IT) suggests dysfunction of the cerebello-dentato-thalamo-cortical projection. Reduction of the late BP amplitude may serve as a surrogate marker for dysfunction of the cerebello-dentato-thalamo-cortical projection in ET.

The instantaneous helical axis of the subtalar and talocrural joints: a non‐invasive in vivo dynamic study

BackgroundAn understanding of rear-foot (talocrural and subtalar joints) kinematics is critical for diagnosing foot pathologies, designing total ankle implants, treating rear-foot injuries and quantifying gait abnormalities. The majority of kinematic data available have been acquired through static cadaver work or passive in vivo studies. The applicability of these data to dynamic in vivo situations remains unknown. Thus, the purpose of this study was to fully quantify subtalar, talocrural and calcaneal-tibial in vivo kinematics in terms of the instantaneous helical axis (IHA) in twenty-five healthy ankles during a volitional activity that simulated single-leg toe-raises with partial-weight support, requiring active muscle control.MethodsSubjects were each placed supine in a 1.5 T MRI and asked to repeat this simulated toe-raise while a full sagittal-cine-phase contrast (dynamic) MRI dataset was acquired. From the cine-phase contrast velocity a full kinematic description for each joint was derived.ResultsNearly all motion quantified at the calcaneal-tibial joint was attributable to the talocrural joint. The subtalar IHA orientation and position were highly variable; whereas, the talocrural IHA orientation and position were extremely consistent.ConclusionThe talocrural was well described by the IHA and could be modeled as a fixed-hinge joint, whereas the subtalar could not be.

Dynamic in vivo 3-dimensional moment arms of the individual quadriceps components

The purpose of this study was to provide the first in vivo 3-dimensional (3D) measures of knee extensor moment arms, measured during dynamic volitional activity. The hypothesis was that the vastus lateralis (VL) and vastus medialis (VM) have significant off-axis moment arms compared to the central quadriceps components. After obtaining informed consent, three 3D dynamic cine phase contrast (PC) MRI sets ( x, y, z velocity and anatomic images) were acquired from 22 subjects during active knee flexion and extension. Using a sagittal-oblique and two coronal-oblique imaging planes, the origins and insertions of each quadriceps muscle were identified and tracked through each time frame by integrating the cine-PC velocity data. The moment arm (MA) and relative moment ( RM, defined as the cross product of the tendon line-of-action and a line connecting the line-of-action with the patellar center of mass) were calculated for each quadriceps component. The tendencies of the VM and VL to produce patellar tilt were evenly balanced. Interestingly, the magnitude of RM-P Spin for the VM and VL is approximately four times greater than the magnitude of RM-P Tilt for the same muscles suggesting that patellar spin may play a more important role in patellofemoral kinematics than previously thought. Thus, a force imbalance that leads to excessive lateral tilt, such as VM weakness in patellofemoral pain syndrome, would produce excessive negative spin (positive spin: superior patellar pole rotates laterally) and to a much greater degree. This would explain the increased negative spin found in recent studies of patellar maltracking. Assessing the contribution of each quadriceps component in three dimensions provides a more complete understanding of muscle functionality.

Modulation of preparatory volitional motor cortical activity by paired associative transcranial magnetic stimulation

Paired associative transcranial magnetic stimulation (PAS) has been shown to induce long-term potentiation (LTP)-like or long-term depression (LTD)-like change in excitability of human primary motor cortex (M1), as probed by motor evoked potential (MEP) amplitude. In contrast, little is known about PAS effects on volitional motor cortical activity. In 10 healthy subjects, movement related cortical potentials (MRCP) were recorded to index volitional motor cortical activity during preparation of simple thumb abduction (prime mover: abductor pollicis brevis, APB) or wrist extension movements (prime mover: extensor carpi radialis, ECR). PAS(LTP) increased, PAS(LTD) decreased, and PAS(control) did not change MEP(APB), while MEP(ECR), not targeted by PAS, remained unchanged in all PAS conditions. PAS(LTP) decreased MRCP negativity during the late Bereitschaftspotential (-500 to 0 ms before movement onset), only in the APB task, and predominantly over central scalp electrodes contralateral to the thumb movements. This effect correlated negatively with the PAS(LTP) induced increase in MEP(APB). PAS(LTD) and PAS(control) did not affect MRCP amplitude. Findings indicate a specific interference of PAS with preparatory volitional motor cortical activity, suggestive of a net result caused by increased M1 excitability and disrupted effective connectivity between premotor areas and M1.

High sucrose diet impact on voluntary wheel running prevents obesity in rats

Two important factors contributing to energy balance are caloric intake and physical activity. One form of volitional activity is voluntary wheel running (WR). The extent of WR diminishes with age and obesity. We examined the impact of a high fat (HF) (60% kcal, fat; 7% kcal, sucrose, 5.24 kcal/g) and a high sucrose (11% fat; 60% sucrose, 4.07kcal/g) diet on WR over 12 weeks compared with a chow diet (4% fat; 7% sucrose, 3.41kcal/g). The HF fed rats ate the most calories during the first week, with the high‐sucrose fed consuming more than controls, but less than HF fed rats. All rats consumed similar amounts of calories for the remaining 11 weeks, and overall cumulative caloric consumption was unchanged across groups. Only the HF fed rats became progressively obese. The rats in all groups ran progressively less over the 12 weeks with a 36% decrease in chow (p&lt;0.012), a 37% decrease in the HF (p&lt;0.032), and a 12.9% decrease in the high sucrose (p&lt;0.018). Those on the high‐sucrose diet had the smallest decrease in running (p&lt;0.035). In summary, voluntary WR declined progressively over 12 weeks on all diets, but decrease was least in the rats consuming the high‐sucrose diet. This higher level of physical activity may explain why these rats did not become obese, compared with the HF fed, despite consuming a similar amount of calories. Supported by Medical Research Service, Dept of Veterans Affairs and NIH AG026159.

Corticospinal involvement in volitional contractions

It is more than 25 years since Merton & Morton (1980) first demonstrated that it was possible to stimulate fast conducting corticospinal connections from motor cortex to spinal motoneurones in conscious humans. The initial stimulators used high-voltage electrical pulses that produced an uncomfortable twitch of scalp muscles under the stimulating electrodes. However, the advent of transcranial magnetic stimulation (TMS) made the procedure painless and it is now widely used to study motor cortical physiology. Despite its success, one thorny question remains: are the corticospinal connections activated by transcranial stimulation the same as those that are normally recruited in voluntary muscle contractions? It is undoubtedly true that the size of the response to a TMS pulse is modulated by volitional muscle contraction, but that does not mean that the outputs activated by the TMS pulse are the same as those used volitionally. So how do we tackle the question? One potential solution lies in the observation that stimulation at very low intensities, below the threshold for evoking a muscle twitch, can reduce ongoing volitional muscle activity. This is thought to occur by suppression of ongoing corticospinal excitation to motoneurones by activation of intracortical inhibitory circuits (Davey et al. 1994). The result means that TMS pulses can certainly affect volitionally produced activity in corticospinal fibres, but are these the same fibres as are activated by suprathreshold pulses? Unfortunately, the answer appeared to be no. The latency of electromyographic (EMG) suppression after a subthreshold TMS pulse had usually been found to be about 10 ms later than the onset of facilitation caused by a suprathreshold pulse. One explanation for the unusually long delay of this suppression was that in fact the TMS pulse was suppressing activity in slowly conducting corticospinal fibres, and that these, rather than the large diameter ones activated by suprathreshold pulses, were the source of volitional excitation to spinal motoneurones. However, as Butler et al. (2007) point out in this issue of The Journal of Physiology, there is one potential flaw in these measurements. They were all made in average recordings of rectified surface EMG activity. Determining the true onset of inhibition in such records is notoriously difficult because muscle action potentials recorded by the surface electrodes have a duration of about 5–10 ms (Widmer & Lund, 1989). Imagine it was possible to stop all the units firing at the same instant. Electrical activity would still continue for 5–10 ms as the final action potentials travelled down the muscle fibres, and it is this that complicates estimation of the onset of inhibition. In the present experiments, Butler et al. bypassed this problem by recording the activity of single motor units with needle electrodes, and constructing a peri-stimulus time histogram (PSTH) of discharge around the time of a TMS pulse to the motor cortex. This should give a true estimate of the difference in timing of facilitation evoked by a suprathreshold TMS pulse and inhibition produced by a subthreshold pulse. However, one last problem remained to be solved. A reliable measure of the onset of inhibition in a PSTH requires there to be a large number of counts in the baseline. Units discharge at around 10 Hz in the weak contractions that are needed to identify single motor units in human muscle. Thus, about 100 trials are needed to fill each 1 ms bin of the PSTHs used in these experiments. Since TMS pulses can be applied at about once every 5 s, this would take just under 10 min of recording. A good number of counts per bin to identify inhibition would be about 10, which would take some 1.5 h of experimenting. The solution to making the experiments tolerable for subjects is to manipulate the experimental conditions so that the onset of inhibition coincides with the expected time of firing of a unit. That way the number of counts per bin is high in the time interval of interest. This can be arranged by timing the TMS pulse with respect to the previous discharge of the unit such that the presumed onset of inhibition is about 100 ms later. With this arrangement, Butler et al. found that the difference in latency of TMS-evoked suppression was around 2 ms longer than facilitation when recordings were taken from the first dorsal interosseous muscle and 3 ms for the biceps brachii. Assuming an oligosynaptic (or even disynaptic) inhibition, this is compatible with inhibition of activity in the fast conducting fibres of the corticospinal tract. Thus, it appears that TMS is indeed likely to activate the same fast conducting corticospinal fibres as are used in volitional contractions. Perhaps more importantly, we now have a method of testing the extent of this contribution in different types of muscle contraction, from volitional finger and arm movements to walking and breathing.

Normative Three-Dimensional Patellofemoral and Tibiofemoral Kinematics: A Dynamic,in VivoStudy

In order to advance biomechanical modeling, knee joint implant design and clinical treatment of knee joint pathology, accurate in vivo kinematic data of the combined patellofemoral and tibiofemoral joint during volitional activity are critical. For example, one cause of the increased prevalence of anterior knee pain in the female population is hypothesized to be altered tibiofemoral kinematics, resulting in pathological patellofemoral kinematics. Thus, the objectives of this paper were to test the hypothesis that knee joint kinematics vary based on gender and to explore the correlation between the 3-D kinematics of the patellofemoral and tibiofemoral joints. In order to accomplish these goals, a large (n = 34) normative database of combined six degree of freedom patellofemoral and tibiofemoral kinematics, acquired noninvasively during volitional knee extension-flexion using fast-PC (dynamic) magnetic resonance imaging, was established. In this normative database, few correlations between tibiofemoral and patellofemoral kinematics were found. Specifically, tibial external rotation did not predict lateral patellar tilt, as has been stated in previous studies. In general, significant differences could not be found based on gender. Further investigation into these relationships in the presence of pathology is warranted.

When thoughts become action: An fMRI paradigm to study volitional brain activity in non-communicative brain injured patients

The assessment of voluntary behavior in non-communicative brain injured patients is often challenging due to the existence of profound motor impairment. In the absence of a full understanding of the neural correlates of consciousness, even a normal activation in response to passive sensory stimulation cannot be considered as proof of the presence of awareness in these patients. In contrast, predicted activation in response to the instruction to perform a mental imagery task would provide evidence of voluntary task-dependent brain activity, and hence of consciousness, in non-communicative patients. However, no data yet exist to indicate which imagery instructions would yield reliable single subject activation. The aim of the present study was to establish such a paradigm in healthy volunteers. Two exploratory experiments evaluated the reproducibility of individual brain activation elicited by four distinct mental imagery tasks. The two most robust mental imagery tasks were found to be spatial navigation and motor imagery. In a third experiment, where these two tasks were directly compared, differentiation of each task from one another and from rest periods was assessed blindly using a priori criteria and was correct for every volunteer. The spatial navigation and motor imagery tasks described here permit the identification of volitional brain activation at the single subject level, without a motor response. Volunteer as well as patient data [Owen, A.M., Coleman, M.R., Boly, M., Davis, M.H., Laureys, S., Pickard J.D., 2006. Detecting awareness in the vegetative state. Science 313, 1402] strongly suggest that this paradigm may provide a method for assessing the presence of volitional brain activity, and thus of consciousness, in non-communicative brain-injured patients.

The 3D patellar tendon moment arm: Quantified in vivo during volitional activity

The patellar tendon moment arm is a critical quantity in that it defines the quadriceps ability to generate a moment on the tibia. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the patellar tendon moment arm, measured non-invasively and in vivo during dynamic activity in a large normative population ( n=34) using a dynamic MRI technique (fast-PC MRI). The magnitude of the moment arm was defined as the shortest distance between the finite helical axis and the patellar tendon line of action. Using these data, the hypothesis that the patellar tendon moment arm is independent of gender was tested. In general, the moment arm increased from 20 to 50 mm during knee extension. There were significant differences ( P<0.05) in the moment arm between gender, but these differences were eliminated when the moment arm was scaled by the femoral epicondylar width. This study took a large step forward towards the ultimate goal of defining how pathology may alter joint dynamics through alteration in moment arms by establishing the first in vivo normative data base for the patellar tendon moment arm using non-invasive measures during volitional activity in a relatively large population ( n=34). The fact that the scaled moment arm was independent of gender may lend insights into impairments that tend to be gender specific, such as patellar maltracking. The next steps will be to quantify the patellar tendon moment arm in populations with specific pathologies.

Hip joint position modulates volitional knee extensor muscle activity after stroke

Evidence from animal and human models has demonstrated the importance of hip proprioceptors and vestibular inputs in modulating lower-extremity muscle activity through reflex pathways. Comprehension of the role of these sensory inputs following stroke may be important in understanding pathological muscle activity during functional activities. We therefore examined the influence of both hip and head/trunk position on volitional quadriceps activity in chronic stroke and control subjects. With the knee held at 60 degrees, maximal voluntary isometric quadriceps contractions were elicited with trunk orientation (head position) and hip angle systematically positioned at 0 degrees, 45 degrees, and 90 degrees. Integrated electromyographic activity from the quadriceps was compared between groups and conditions. Vasti activity in the stroke group was greater in a seated upright posture (hip flexed) than supine (hip neutral). Controlling for vestibular input, the stroke group demonstrated greater quadriceps activity (VL and RF) with a neutral hip compared to flexion. Such findings may have implications for understanding inappropriate muscle activity during walking after stroke, as hip extension occurs immediately prior to toe off, when inappropriate quadriceps activity is commonly observed.

Can supraspinal/central fatigue explain the lesser muscle endurance of men compared with women?

Several studies have shown that women can present with greater muscle endurance (less fatigability) compared with men ([3][1], [5][2], [10][3], [12][4]), although this is not always the case ([4][5], [8][6]). Most of these studies have focused on peripheral physiological mechanisms, mostly those