P. Crenna

A motor programme for the initiation of forward‐oriented movements in humans.

1. The EMG sequence activated before the initiation of a number of fast forward‐oriented voluntary movements was analysed quantitatively in normal subjects. 2. The sequence consisted of an initial inhibitory component directed to the soleus motor nucleus, followed by a second excitatory one directed to the tibialis anterior (TA). 3. The spectrum of functional utilization included motor tasks in which the prime movers are leg and thigh muscles (initiation of gait, rising on tip‐toes), thigh and trunk muscles (fast‐forward bending of the trunk, standing up) and upper‐limb muscles (forward throw or catch). 4. In a same motor task and across the different motor tasks, performed at various speeds, the latency of soleus inhibition and TA activation with respect to the onset of movement co‐varied according to a linear function, indicating a close temporal correlation between the two components. 5. In all the movements investigated, the earliest mechanical effect was a backward displacement of the centre of foot pressure in the sagittal plane. 6. Soleus inhibition alone and TA burst alone were each able to produce a backward displacement of the centre of foot pressure, but the effect was significantly slower after soleus inhibition. 7. The spatio‐temporal parameters of the sequence were modulated according to the pre‐existing postural conditions. For the gait initiation protocol, increasing initial forward leaning led to a decrease in the amplitude of soleus inhibition and the TA burst, and to a change in their relative time delays. Modulation was different on the two sides. We could define a postural boundary as the degree of forward leaning beyond which the full sequence is no longer called into action. 8. The spatio‐temporal parameters of the sequence were pre‐set according to the requirements of the forthcoming movement. In the gait initiation protocol, the amplitude and synchronization of the TA burst were directly correlated with velocity of movement, while the relative delay between soleus inhibition and TA activation was inversely correlated. Modulation on the two sides differed. We could define a velocity boundary as the velocity of movement below which the full sequence is no longer called into action. 9. We suggest that the EMG sequence described can be considered a motor programme that, through direct action on the position of the centre of foot pressure (the variable primarily controlled), will precisely adjust the configuration of forces external to the body, allowing the contraction of the prime mover(s) to interact appropriately with them for the production of a specific, forward‐oriented movement.

Quantitative comparison of five current protocols in gait analysis

Data collection and reduction procedures, coherently structured in protocols, are necessary in gait analysis to make kinematic and kinetic measurements clinically comprehensible. The current protocols differ considerably for the marker-set and for the biomechanical model implemented. Nevertheless, conventional gait variables are compared without full awareness of these differences. A comparison was made of five worldwide representative protocols by analysing kinematics and kinetics of the trunk, pelvis and lower limbs exactly over the same gait cycles. A single comprehensive arrangement of markers was defined by merging the corresponding five marker-sets. This resulted in 60 markers to be positioned either on the skin or on wands, and in 16 anatomical landmark calibrations to be performed with an instrumented pointer. Two healthy subjects and one patient who had a special two degrees of freedom knee prosthesis implanted were analysed. Data from up-right posture and at least three gait repetitions were collected. Five corresponding experts participated in the data collection and analysed independently the data according to their own procedures. All five protocols showed good intra-protocol repeatability. Joint flexion/extension showed good correlations and a small bias among protocols. Out-of-sagittal plane rotations revealed worse correlations, and in particular knee abduction/adduction had opposite trends. Joint moments compared well, despite the very different methods implemented. The abduction/adduction at the prosthetic knee, which was fully restrained, revealed an erroneous rotation as large as 30 degrees in one protocol. Higher correlations were observed between the protocols with similar biomechanical models, whereas little influence seems to be ascribed to the marker-set.

Locomotor Function in the Early Stage of Parkinson's Disease

The cardinal motor symptoms of Parkinsons disease (PD) have been widely investigated with particular reference to abnormalities of steady-state walking. The great majority of studies, however are related to severe forms of PD patients (phases of Hoehn and Yahr scale), where locomotor abnormalities are clearly manifested. Goal of the present study was to quantitatively describe locomotor symptoms in subjects with mild PD. Accordingly, a multitask protocol involving instrumental analysis of steady-state linear walking, initiation of gait, and turning while walking was applied to a group of patients with idiopathic PD in their early clinical stage (phases 1 and 2 of Hoehn and Yahr scale), as well as in age-matched elderly controls. Kinematic, kinetic, and myoelectric measures were obtained by optoelectronic motion analysis, force platform, and telemetric electromyography. Results in PD patients showed a tendency to bradykinetic gait, with reduction of walking speed and cadence. Impairments of gait initiation consisted in reduction of the backward shift of the center of pressure (CoP) and prolongation of the stepping phase. Alterations of the turning task were more consistent and included delayed reorientation of the head toward the new direction, altered head-upper trunk rotational strategy, and adoption of a greater number of steps to complete the turning. It is concluded that patients in the early stage of PD reveal mild alterations of steady-state linear walking and more significant anomalies in the transitional conditions, especially during changes in the travel direction. Quantitative analysis of nonstationary locomotor tasks might be a potentially useful starting point for further studies on the pathophysiology of PD.

Evidence of phase-dependent nociceptive reflexes during locomotion in man

In 10 healthy subjects freely walking along a straightline, the effects of painful sural nerve stimulation, applied in different phases of the step cycle, were investigated on two antagonistic muscles of the ipsilateral lower limb acting on the knee joint: vastus lateralis (VL) and biceps femoris caput breve (BF). A clear-cut modulation in the amplitude (area) of the net reflex responses was consistently observed in both the motor nuclei explored. The extensor muscle, VL, exhibited a long-latency (mean 122 ms) reflex response, which was maximally increased by stimuli applied toward the end of the swing and in the first half of the stance phase of the stride, whereas the response appeared to be gated during the transition from the foot-flat to forefoot-contact phase. A second facilitation period was brought about by stimuli delivered in the early swing. When the response occurred superimposed on the VL locomotor activity, suppression of the ongoing EMG preceded the reflex discharge. In the flexor, BF, the same stimulus elicited a short-latency (mean 57 ms) and a long-latency (mean 132 ms) reflex response. The former was maximal after stimulation around the toe-off phase and the latter was strikingly enhanced in the late swing, where it was preceded by suppression of the background locomotor EMG activity. Responses with intermediate features (latency 70 to 80 ms, duration 90 to 120 ms), probably resulting from the merging of the early and late components, might be evoked in addition, being greatest in the last swing and in the period preceding toe-off. The findings show that in man the reflex pattern evoked by a painful cutaneous stimulus during locomotion is determined by the phase of the step cycle during which the stimulus is delivered. A functional role in maintenance of postural balance during destabilizing withdrawal reactions is conceivable.

Impact of subthalamic nucleus stimulation on the initiation of gait in Parkinson's disease

The effects of subthalamic nucleus (STN) stimulation on the anticipatory postural actions associated with the initiation of gait were studied in ten patients with idiopathic Parkinson’s disease undergoing therapeutic deep brain stimulation. Kinematic, dynamic and electromyographic analysis was performed before and while subjects were starting gait in response to an external cue. Effects of STN stimulation on the standing posture preceding the go signal included significant improvement of the vertical alignment of the trunk and shank, decrease of the hip joint moment, backward shift of the center of pressure (CoP) and reduction of abnormal tonic and/or rhythmic activity in the thigh and leg muscles. Responses to bilateral STN stimulation were more consistent than those evoked by unilateral stimulation. Moreover, comparison between postural changes induced by STN stimulation applied prior to the gait initiation cue and during simple quiet standing revealed more significant responses in the former condition. Effects on the actual gait initiation process included shortening of the imbalance phase, larger backward/lateral displacement of CoP and more physiological expression of the underlying anticipatory muscular synergy. Additional changes were shortening of the unloading phase, shortening of the first-swing phase and increase in the length of the first step. Results demonstrate substantial influence of STN stimulation on functionally basic motor control mechanisms. In particular, the evidence of more significant responses upon attention-demanding conditions and the remarkable effects on postural programmes sub-serving feed-forward regulation of the onset of complex multijoint movements, suggests a consistent action on postural sub-systems relying on cognitive data processing and internal models of body mechanics.

Motor programmes for the termination of gait in humans: organisation and velocity-dependent adaptation

1 The organisation of the muscular activities responsible for the termination of gait, their modulation as a function of the rate of progression and the associated mechanical effects were investigated in normal adults, using EMG, force plate and kinematic recordings. In particular, the braking actions in reaction to a visual cue presented at the instant of heel‐strike were analysed quantitatively, with a focus on representative leg and thigh muscles of the weight‐supporting (stance) and oscillating (swing) limb, during walk‐and‐stop trials performed at three different velocities. 2 In the stance limb, the EMG associated with braking started approximately 150 ms after the stop signal and, on average, displayed a distal‐to‐proximal activation sequence that primarily involved the posterior muscle groups (soleus, SOL, and hamstring, HAM). With the exception of SOL, which showed a single EMG burst, EMG patterns consisted of two or three progressively larger components occurring reciprocally in antagonistic muscles. Increasing walking speed yielded a significant reduction of the activity in distal muscles, and a simultaneous increment in proximal muscles. The mechanical effect of the earlier braking actions, estimated from the backward‐directed wave of the horizontal ground reaction force, decreased in a velocity‐dependent manner. 3 In the swing limb the braking activities began approximately 330 ms after the stop signal and, on average, revealed a proximal‐to‐distal activation sequence with the extensor groups (quadriceps, QUAD, and SOL) playing a prominent role. They always consisted of single EMG bursts, largely co‐activated in the antagonist muscles. The onset latencies of the individual components showed a close correlation, and the spatio‐temporal parameters were always scaled in parallel. Unlike the stance limb, the mechanical braking action associated with the final contact of the swing limb increased with walking speed. 4 The results indicate that the muscle synergies responsible for the rapid termination of gait in response to a ground‐contact visual cue are produced by a relatively flexible set of motor commands modulated according to different velocity‐dependent strategies in the weight‐bearing limb, and by a single, fairly robust motor programme in the swing limb. Mechanical constraints related to the relative position of the centre of foot pressure and centre of body mass at the time the braking commands begin to affect external forces, may condition the difference between the two sides of the body.

Dynamics of the ankle joint analyzed through moment-angle loops during human walking: gender and age effects.

Aim of this study was to provide a non-invasive assessment of the dynamic properties of the ankle joint during human locomotion, with specific focus on the effects of gender and age. Accordingly, flexion-extension angles and moments, obtained through gait analysis, were used to generate moment-angle loops at the ankle joint in 120 healthy subjects walking at a same normalized speed. Four reproducible types of loops were identified: Typical Loops, Narrow, Large and Yielding loops. No significant changes in the slopes of the main loop phases were observed as a function of gender and age, with the exception of a relative increase in the slope of the descending phase in elderly males compared to adult females. As for the ergometric parameters, the peak ankle moment, work produced and net work along the cycle were slightly, but significantly affected, with progressively decrease in the following order: Adult Males, Adult Females, Elderly Males and Elderly Females. The evidence that only few of the quantitative aspects of moment-angle loops were affected suggests that the control strategy which regulates the biomechanical properties of the ankle joint during walking is rather robust and qualitatively consistent across genders and age.

Effect of L-dopa and Subthalamic Nucleus stimulation on arm and leg swing during gait in Parkinson's Disease

The effects of subthalamic nucleus (STN) stimulation and L-dopa administration on the arm and leg swing movements associated with overground walking were studied in a group of patients with idiopathic Parkinsons disease (PD). Ten patients undergoing deep brain stimulation and twenty controls were tested using 3D kinematic motion analysis. Parkinsonian patients under basal conditions walked more slowly and with reduced arm and leg swing compared to controls. Moreover, they displayed significant impairments of the normal interlimb coordination. Both STN stimulation and L-dopa increased the walking speed and the amplitude of arm and leg swing movements. Additional improvements of the coordination between upper and lower limb were documented by reductions of the phase-shift between arm and ipsilateral leg motion, with displacement toward the control range (perfect counterphase). STN stimulation alone and L-dopa alone produced similar effects on the variables analyzed. The combination of the two treatments, instead, yielded additive effects on the gait speed and a slight increase of the upper and lower limb range of motion, in the absence of further improvements in the inter-segmental coordination. Moreover, whereas the increased arm swing could be accounted by the sole adoption of a higher gait speed, both the increment of the leg movement amplitude and the decreased interlimb phase shift appeared to imply an additional effect, possibly related to the treatment. These results may suggest that differential supraspinal controls operate on the neural networks subserving upper and lower limb motion during human walking.

Coordination between upper- and lower-limb movements is different during overground and treadmill walking.

Locomotion studies employ either treadmill (TW) or overground walking (OW), considering that differences between them are negligible. The present study tests this notion by comparing coordination between upper- and lower-limb movements in healthy individuals during OW and TW at matched speeds. Results indicated that TW induced a higher cadence, which highly influenced interlimb coordination, in terms of frequency coupling and relative phase between arm and thigh motion. At low speed, the 2:1 pattern (double arm swing per stride) displayed lower incidence in TW compared to OW, and this was correlated with a lower sagittal acceleration at the shoulders, at twice the stride frequency, in the former condition. The low occurrence of the 2:1 coupling in TW, moreover, was correlated to a preferential adoption of a cadence exceeding 80% of the arm’s resonant frequency, whereas higher incidence of this pattern in OW involved a preferential cadence below the 80% threshold. Results indicated also that the relative phase between arm and ipsilateral thigh swinging was smaller in TW, in relation to an earlier occurrence of maximum thigh extension, shortened stance phase, and increased cadence. These findings suggest that arm–leg coordination is different in OW and TW, and that difference can be mainly ascribed to condition-specific setting of central mechanisms for scaling stride frequency, for controlling dynamic axial posture (sagittal shoulder acceleration), and, possibly, for maintaining inter-limb synchrony. Awareness of a different “motor set” in TW and OW is critical if data from the two paradigms are used in physiological and patho-physiological studies.

Enhanced catecholamine transporter binding in the locus coeruleus of patients with early Parkinson disease

BackgroundStudies in animals suggest that the noradrenergic system arising from the locus coeruleus (LC) and dopaminergic pathways mutually influence each other. Little is known however, about the functional state of the LC in patients with Parkinson disease (PD).MethodsWe retrospectively reviewed clinical and imaging data of 94 subjects with PD at an early clinical stage (Hoehn and Yahr stage 1-2) who underwent single photon computed tomography imaging with FP-CIT ([123I] N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl) tropane). FP-CIT binding values from the patients were compared with 15 healthy subjects: using both a voxel-based whole brain analysis and a volume of interest analysis of a priori defined brain regions.ResultsAverage FP-CIT binding in the putamen and caudate nucleus was significantly reduced in PD subjects (43% and 57% on average, respectively; p < 0.001). In contrast, subjects with PD showed an increased binding in the LC (166% on average; p < 0.001) in both analyses. LC-binding correlated negatively with striatal FP-CIT binding values (caudate: contralateral, ρ = -0.28, p < 0.01 and ipsilateral ρ = -0.26, p < 0.01; putamen: contralateral, ρ = -0.29, p < 0.01 and ipsilateral ρ = -0.29, p < 0.01).ConclusionsThese findings are consistent with an up-regulation of noradrenaline reuptake in the LC area of patients with early stage PD, compatible with enhanced noradrenaline release, and a compensating activity for degeneration of dopaminergic nigrostriatal projections.