Victoria Galea

POTENTIATION AND DEPRESSION OF THE M WAVE IN HUMAN BICEPS BRACHII

1. The effects of repeated excitation on the compound action potential, or M wave, of mammalian muscle fibres have been investigated in the human biceps brachii. 2. During continuous indirect stimulation at 10 and 20 Hz the mean voltage‐time area of the M wave doubled within the first minute, while the mean peak‐to‐peak amplitude increased by approximately half. The enlargement of the M wave was sustained during stimulation at 10 Hz but not at 20 Hz. Stimulation at 3 Hz caused a small increase which was significant for M wave amplitude only. 3. When the 20 Hz stimulation was performed under ischaemic conditions, the M wave first enlarged and then gradually declined. After 20 Hz stimulation was discontinued, the M wave increased in size; in the ischaemic experiments the release of the cuff produced a further, rapid augmentation. In both the ischaemic and non‐ischaemic experiments, the amplitudes and areas of the M waves during the recovery period became significantly larger than the resting values (range, 15‐60% at the endplate zone). 4. The mean muscle fibre impulse conduction velocity decreased to less than half the resting value during 20 Hz stimulation, with or without ischaemia, and then increased above the resting value during recovery. 5. On the basis of previous experiments in animals, the augmentation of the M wave was attributed to enhanced electrogenic Na(+)‐K+ pumping, and the biceps brachii appeared to be an excellent preparation for studying the time course of this enhancement.

Enhancing the ability of gait analyses to differentiate between groups: scaling gait data to body size

One goal of gait analysis is to distinguish clearly between a set of abnormal gait values measured from a patient referenced to a comparable population. However, the comparable population is often composed of individuals of various heights and weights, which increases inter-subject gait value variation which reduces the ability of a statistical test to identify a set of gait data outcomes with evaluative properties. Therefore, scaling gait data, based on subject leg length and mass, is commonly used to decrease the inter-subject variation but the efficacy of these methods is unknown. In this paper each of eight scaling strategies (none, ad hoc, dimensionless numbers, and five connected strategies based on similarity, dimensional analysis and muscle properties) were used to modify a set of gait data outcomes acquired from 10 individuals spanning a wide range of height (1.33-1.96 m) and mass (42.3-148.8 kg). These data were then examined to select that strategy and those scaling factors which maximally reduced inter-subject variation. The ad hoc, dimensionless numbers, and dynamic/mechanical/elastic (diameter of a limb (D) proportional to its length (L) to the 1.5 power; time proportional to L(2) D(-1)) scaling strategies reduced the global inter-subject gait data outcome variation to 44% of its un-scaled value. Considering ten commonly reported gait data outcomes (temporal and spatial (stride time, stride length, progression velocity), kinematic (angles in the sagittal and frontal planes, angles in the transverse plane), external kinetic (ground reaction force and moment), and internal kinetic (joint force, moment, and power)) these three scaling strategies provided the largest number of minimum inter-subject variations (10, 10, and 9, respectively). Reduced inter-subject variation in gait data outcomes increases the ability of a statistical tool to detect a difference between a patient and a comparable group. With a statistically significant difference a clinician can then decide if this patients gait pattern clinically deviates from that of the comparable group and an appropriate intervention warranted. The ad hoc, dimensionless numbers, and the dynamic/mechanical/elastic scaling strategies all reduce maximally the inter-subject variation in gait data outcomes.

Lower extremity kinematics of females with patellofemoral pain syndrome while stair stepping.

STUDY DESIGN Cross-sectional case-control design. BACKGROUND Although the etiology of patellofemoral pain syndrome (PFPS) is not completely understood, there is some evidence to suggest that hip position during weight-bearing activities contributes to the disorder. OBJECTIVE To compare the knee and hip motions (and their coordination) during stair stepping in female athletes with and without PFPS. METHODS Two groups of female recreational athletes, 1 group with PFPS (n = 10) and a control group without PFPS (n = 10), were tested. All participants ascended and descended stairs (condition) at 2 speeds (self-selected comfortable and taxing [defined as 20% faster than the comfortable speed]), while the knee and hip angles were measured with a magnetic-based kinematic data acquisition system. Angle-angle diagrams were used to examine the relationship between flexion/extension of the knee and flexion/extension, adduction/abduction, and internal/external rotation of the hip. The angle of the knee and the 3 angles of the hip at foot contact on the third step were compared between groups by means of 3-way analyses of variance (ANOVA), with repeated measures on speed and condition. RESULTS Group-by-speed interaction for knee angle was significant, with knee flexion being greater for the PFPS group for stair ascent and descent at a comfortable speed. Both the angle-angle diagrams and ANOVA demonstrated greater adduction and internal rotation of the hip in the individuals with PFPS compared to control participants during stair descent. CONCLUSION Compared to control participants, females with PFPS descend stairs with the knee in a more flexed position and have the hip in a more adducted and internally rotated position at foot contact during stair stepping at a comfortable speed.

Botulinum toxin as an adjunct to motor learning therapy and surgery for obstetrical brachial plexus injury

Following obstetrical brachial plexus injury, infants are unable to learn specific patterns of movement due to the disruption of neural pathways. Even with successful reinnervation (spontaneously or post surgical reconstruction), function can be suboptimal due to overactivity in antagonist muscles preventing movement of reinnervated muscles. Botulinum toxin type A (BTX‐A) was used to temporarily weaken antagonistic muscles early in the reinnervation process following brachial plexus injury, with the aim of facilitating functional improvement. A case series of eight children (five females, three males; mean age 12.5mo [SD 6.43]; range 5–22mo) with significant muscle imbalances but evidence of reinnervation were given BTX‐A injections into the triceps, pectoralis major, and/or latissimus dorsi muscles. After a single injection, all parents reported improvement in function. Active Movement Scale total score changed significantly between pre BTX‐A and 1 month (p=0.014), and 4 months (p=0.022) post BTX‐A injection. It is proposed that BTX‐A facilitated motor learning through improved voluntary relaxation of antagonist muscles while allowing increased activity in reinnervated muscles.

Depletion and sizes of motor units in spinal muscular atrophy

Motor unit number estimation (MUNE) was applied to the biceps brachii muscles of 13 young patients (age 5–24 years) with spinal muscular atrophy (SMA) and the results compared with those of healthy control subjects matched for age and gender. In the SMA patients, all motor unit (MU) estimates fell below the control range, and there was good correspondence between the values for the two arms in the same subject. No correlation could be found between the MUNEs and the severity of the weakness. This unexpected result was attributed to the presence of small and normal‐sized MUs in the muscles of patients, in addition to MUs that appeared to be considerably enlarged. The threefold mean increase in MU potential size was insufficient to compensate for the MU loss. In addition, the study confirmed that there are, on average, approximately 130 MUs in the healthy biceps brachii muscle.

Habitual physical activity levels are associated with biomechanical walking economy in children with cerebral palsy.

Maltais DB, Pierrynowski MR, Galea VA, Matsuzaka A, Bar-Or O: Habitual physical activity levels are associated with biomechanical walking economy in children with cerebral palsy. Am J Phys Med Rehabil 2005;84:36–45. Objective:To evaluate in children and adolescents with cerebral palsy the relationship between habitual physical activity and biomechanical treadmill walking economy and whether treadmill belt speed or walking time affect economy. Design:Physical activity was measured in 11 subjects (10.6–16.3 yrs) with mild cerebral palsy using a triaxial accelerometer. To determine biomechanical walking economy, subjects’ stride lengths and vertical sacral excursions were measured during each minute of three 3-min walks on a treadmill (at 60%, 75%, and 90% of individually determined fastest treadmill walking speed). Results:Biomechanical walking economy at 60%, 75%, and 90% of (their) fastest speed each explained about half of the intersubject variance in daily physical activity (movement counts). A similar relationship was found between these biomechanical walking economy variables and movement counts at or above the 80th and 90th percentile (total minutes per day, number of 5-min bouts per day). Walking economy was 23.9% higher when subjects walked at 90% than when they walked at 60% of their fastest walking speed. No other speed-related effects on economy were found, nor did time affect economy. Conclusions:Within this population, those with high biomechanical treadmill walking economy are the more habitually physically active. Treadmill belt speed, but not walking time, affects biomechanical walking economy.

Repeated treadmill walks affect physiologic responses in children with cerebral palsy.

PURPOSE To determine whether physiologic responses during treadmill walking in children with cerebral palsy (CP) are affected by repeated walking bouts on different days, and whether effects are different at different speeds. METHODS Three girls and five boys (9.2-15.7 yr, 23.3-64.4 kg) with mild CP received 12-15 min of treadmill walking practice and had their fastest walking speed (FWS) determined during an introductory visit. During each of three subsequent visits (day 1, day 2, day 3), subjects walked for 3 min at 60, 75, and 90% FWS. Resting physiologic measures were taken on day 1. RESULTS From day 1 to day 3, net ventilation ([OV0312]E), and net heart rate (HR) at 90% FWS decreased by 3.6 L.min-1 and 8 beats.min-1, respectively. There were no differences between day 1 and day 2 or day 1 and day 3 for any other physiologic variable at any speed. Day 3 was less than day 2 for net HR (60% FWS) and, independent of speed, net [OV0312]O2 (per kilogram of body mass and per stride) and net energy expenditure (kJ.min-1). Between-day reliability (R) of physiologic responses was > or = 0.95, except respiratory rate (R = 0.75). Intrasubject, between-day variability for the [OV0312]O2 measures was 7.6-12.9%. CONCLUSION Because there were no day 1 to day 3 reductions in metabolic variables, day 1 to day 3 reductions at 90% FWS in net HR may reflect decreased emotional stress over time and reductions in net [OV0312]E, an uncoupling of [OV0312]O2 and [OV0312]E. Despite between-day differences, reliable net physiologic and stable net metabolic variables may be collected in subjects with mild CP after one treadmill walking practice session.

Motion in Response to the Hypnotic Suggestion of Arm Rigidity: A Window on Underlying Mechanisms

Abstract Among hypnotized subjects passing a challenge suggestion of arm rigidity, how might patterns of motor activity (strategies) contribute to the illusion that the elbow cannot be bent? Kinematic analyses of upper limb and trunk were performed. Nonhypnotized subjects carefully enacted a set of prescribed strategies typifying responses possibly adopted by a hypnotized subject. Profile analysis showed striking heterogeneity of response in hypnotic subjects. Half of participants showed no perceivable strategy consistent with the hypothesis that subjects hallucinate the suggestion and so do not engage the motor periphery. Equally common were subtle oscillations or trembling of the arm implying that motion resembling difficulty in bending was initiated. This can be misperceived as unintentional and thus evidence of inability to bend. The lack of a motor strategy is more consistent with dissociated-control theory, whereas the trembling response is more consistent with social-cognitive and dissociated-experience theories.

Developing Biologically-Based Assessment Tools for Physical Therapy Management of Neck Pain

SYNOPSIS Neck pain is a common and episodic condition that is treated using a spectrum of interventions known to be moderately effective but is associated with a significant incidence of chronic pain. Recently, there has been increased focus on defining biological aspects of neck pain. Studies have indicated that neurophysiological, biomechanical, and motor control abnormalities are present and may be useful either in prognosis or classification. We review some of these findings in the context of our own work defining biological markers that may form the basis for clinical tests that can be used for prognosis, classification, or outcome evaluation in patients with neck pain. We have identified abnormalities in neurophysiology using quantitative sensory testing (vibration, touch, and current perception) and response to cold provocation that are related to neck disability. We have identified altered muscle biochemistry by measuring circulating muscle proteins in a lumbar surgery model and are now applying those methods to whiplash injury. We have incorporated capnography into treatment to address central physiological changes present in some patients by monitoring and training CO2 levels. We have developed an innovative new test, the Neck Walk Index, that captures abnormal control of head movement during slow gait as a means of differentiating patients with neck pain from either unaffected controls or individuals with other pathologies. We have used time-varying 3-dimensional joint orientation kinematics to assess deficits in motor control during an upper extremity reach task, the results showing that poor coordination and control of the shoulder girdle leads to shoulder guarding and inconsistencies in elbow joint movement. Despite some promising early results, future research is needed to determine how these measures help clinicians to diagnose, evaluate, and forecast future outcome for patients who present with neck pain. LEVEL OF EVIDENCE Diagnosis, level 5.

Speculations surrounding a spinal reflex

A method has been developed for measuring the Ia fibre input/motoneurone output relationship for the soleus H-reflex in healthy human volunteers. The shift in the relationship during weak toe extension, and in some subjects during weak plantar flexion, indicates the imposition of an inhibitory mechanism, presumably presynaptic. From these observations, and others previously made on long-loop reflexes, it is argued that the inhibitory mechanism may have evolved to suppress unwanted information from the periphery, not only during movement but in the resting state, and that this development was a necessary accompaniment of encephalisation.