Minimal detectable change of kinematic and spatiotemporal parameters in patients with chronic stroke across three sessions of gait analysis.

Three-dimensional gait analysis is the gold standard for gait-assessment in patients with stroke. This technique is commonly used to assess the effect of treatment on gait parameters. In clinical practice, three gait analyses are usually carried out (baseline, after treatment and follow-up), the objectives were to define the reproducibility and the Minimum Detectable Change (MDC) for gait parameters in stance and swing measured using 3D-gait analysis, and to assess changes in MDC across three repeated 3D-gait analyses. Three gait analyses (V1, V2 and V3) were performed at 7-day intervals in twenty-six patients with chronic stroke. Kinematic data (in the sagittal plane, during swing and stance) and spatiotemporal data were evaluated for the paretic limb. Reliability was tested using repeated measures ANOVA with a Tukey post hoc test, and the MDC values were calculated for each parameter. Only the range of hip motion during swing changed significantly between V1 and V2, but no other kinematic parameters changed. No significant differences were observed for the spatiotemporal parameters. MDC values were always higher during the V1vsV2 comparison for both kinematic and spatiotemporal parameters. This is the first study to evaluate the MDC for kinematic and spatiotemporal parameters during stance and swing. Reliability of kinematic and spatiotemporal data across sessions was very good over the three sessions. MDC values were the lowest between V2 and V3 for most parameters. Use of the MDC will allow clinicians to more accurately determine the effect of treatments.

Neuroendocrine and inflammatory responses to DHEA administration in young healthy women.

DHEA is reported to have beneficial effects for the elderly and for several pathologies because of its behavioral and anti-inflammatory properties. However, these properties have never been investigated in a young healthy population. The purpose of this double-blind, randomized study was therefore to investigate the effects of short-term DHEA administration (100 mg/day/4 weeks) on neuroendocrine (i.e., beta-endorphin and prolactin) and inflammatory (i.e., interleukin-6 and TNF-alpha) parameters in 10 young healthy female volunteers with regular sports practice. In parallel, the stress state was assessed with the Profile of Mood States (POMS) questionnaire. DHEA administration did not alter prolactin, interleukin-6 or TNF-alpha, and no significant change in tension, depression, anger, vigor, fatigue or confusion was noted. However, beta-endorphin levels increased significantly (p < 0.05) with the DHEA treatment. The results of this investigation indicate that short-term DHEA administration improves neuroendocrine modulation but does not affect the inflammatory status or psychological state in recreationally trained female athletes. Further studies are needed to determine the exact mechanisms and the responses of these parameters to DHEA administration at higher dosages and/or for longer durations, especially in response to physical/psychological stress.

Effect of oral glucocorticoid intake on autonomic cardiovascular control.

This study analyzed baroreflex sensitivity, heart rate and systolic blood pressure variabilities during an oral 1 week administration of prednisone. This study examined the hypothesis that prednisone might change both systolic blood pressure level and baroreflex sensitivity. Twelve physically active male subjects participated to a double-blind, randomized cross-over study consisting of two 1-week periods of treatment separated by a 4-week drug-free washout period: placebo (PLA) or prednisone (PRED). Trials were performed by each subject four times on the second (D2) and seventh (D7) day of each treatment period. ECG and blood pressure were continuously recorded to compute heart rate variability, systolic blood pressure variability and baroreflex sensitivity components with the smoothed pseudo Wigner Ville distribution and baroreflex analysis. Following D2 prednisone treatment, both HR (PLA: 60.8 ± 10.5 vs. PRED: 65.8 ± 9.1 beats min(-1), p = 0.008) and low frequency component of systolic blood pressure variability (D2: 3.09 ± 0.19 vs. D7: 2.34 ± 0.19, p < 0.041) increased whereas other components did not change. Over 7 days of treatment, LF-SBP amplitude increased (D2: 2.71 ± 0.89 vs. D7: 3.87 ± 0.6 mmHg, p = 0.037). A slight increase in both HR and LF-SBPV were observed suggesting a potential sympathetic cardiovascular stimulus. Although we found a significant effect of the 1-week prednisone treatment on heart rate and low frequency power of systolic blood pressure variability, we reported neither an increase in the systolic blood pressure level nor a decrease in the baroreflex sensitivity. Therefore, the fragility of our results cannot support a deleterious effect of 1-week administration of prednisone on the autonomic cardiovascular control which might be involved in cardiovascular diseases.

Comparative gait initiation kinematics between simulated unilateral and bilateral ankle hypomobility: Does bilateral constraint improve speed performance?

Improvement of motor performance in unilateral upper limb motor disability has been shown when utilizing inter-limb coupling strategies during physical rehabilitation. This suggests that 'default' bilateral central motor commands are facilitated. Here, we tested whether this bilateral motor control principle may be generalized to the lower limbs during gait initiation, which involves alternate bilateral actions. Disability was simulated by strapping to produce ankle hypomobility. Healthy adult subjects initiated gait at a self-paced speed with no ankle constraint (control), or with the stance, swing or bilateral ankles strapped. The duration of the anticipatory postural adjustments lengthened and the center of mass instantaneous progression velocity at foot-off decreased when the ankle was strapped. During the step execution phase, progression velocity at foot-contact was higher when both ankles were strapped compared to unilateral strapping of the stance ankle. These findings suggest that bilateral central motor commands are favored during walking tasks. Indeed, unilateral constraint of the stance ankle should compel the central nervous system to adapt specific commands to the constraint and normal sides whereas the 'default' bilateral motor commands would be utilized when both ankles are strapped leading to better kinematics performance. Bilateral in-phase upper limb coordination and bilateral alternating lower limb locomotor movements may share similar control mechanisms.

Time-course of prednisone effects on hormonal and inflammatory responses at rest and during resistance exercise.

Glucocorticoids are among the most commonly used drugs. They are widely administered for acute and chronic musculoskeletal pain, as well as for several other pain syndromes, although their therapeutic use is sometimes diverted for doping purposes. Their time-course effects on hormonal and inflammatory responses nevertheless remain poorly understood, both at rest and during exercise. We therefore studied the alterations induced by 1 week of prednisone treatment (60 mg daily) in recreationally trained male athletes after 2 days (i. e., acute) and 7 days (i. e., short-term). Hormonal (i. e., DHEA, DHEA-S, aldosterone, and testosterone) and pro- and anti-inflammatory markers (i. e., IL-6, IL-10, and IL-1ß) were investigated at rest and after resistance exercise. A significant decrease in DHEA and DHEA-S (p<0.01) without change in the DHEA/DHEA-S ratio, aldosterone, or testosterone was demonstrated after acute prednisone intake. A significant increment in IL-10 and a significant decrement in IL-6 (p<0.05) were also observed with prednisone both at rest and during exercise, without significant change in IL-1ß. Continued prednisone treatment led to another significant decrease in both DHEA and DHEA-S (p<0.05), whereas no change in the inflammatory markers was observed between days 2 and 7. Our data demonstrate that the anti-inflammatory effects of prednisone were maximal and stable from the beginning of treatment, both in rest and exercise conditions. However, hormonal concentrations continued to decline during short-term intake. Further studies are needed to determine the effects of hormonal time-course alterations with longer glucocorticoid treatment and the clinical consequences.

Therapeutic glucocorticoid administration alters the diurnal pattern of dehydroepiandrosterone.

Significant alteration in hypothalamic-pituitary-adrenal function has been demonstrated in patients after short-term glucocorticoid therapy, but its impact on the circadian rhythm of steroid hormones has never been investigated. This study examined the effects of short-term prednisone administration on the diurnal patterns of dehydroepiandrosterone (DHEA) and testosterone. Saliva samples were collected from 11 healthy, physically active, male volunteers for DHEA and testosterone analysis, as follows: every 4 h from 0800 to 2000 h on 2 control days without medication, and after 1 week of oral therapeutic prednisone treatment (60 mg daily) (days 0-3). Overall, a diurnal decline in the two steroid hormones was observed on the control days. After short-term glucocorticoid administration, DHEA concentrations were significantly decreased with a complete disappearance of the DHEA diurnal pattern, which lasted 2 days post-treatment. No glucocorticoid effect was observed for testosterone. The results indicate that short-term prednisone treatment affects the circadian pattern of saliva DHEA but not testosterone in healthy active volunteers. Further studies are necessary to determine whether this alteration in DHEA circadian pattern has clinical consequences in patients with chronic glucocorticoid therapy.

Effects of seat-thigh contact on kinematics performance in sit-to-stand and trunk flexion tasks.

It has been shown that thigh-seat contact-surface influences performance of isometric push-force with upper-limbs. The push-force performance is higher when subjects are seated with partial ischio-femoral / seat contact than when they are seated with full ischio-femoral contact. This was ascribed to greater pelvis and spine mobility induced by the short thigh-seat contact-surface. The present study tested the generalization of this hypothesis during movements involving body segment displacement, namely trunk flexion (TF) and sit-to-stand (STS) motor tasks. Both motor tasks were carried out in similar conditions to those implemented in the isometric push-force tasks, i.e. full ischio-femoral / seat contact (100-IFC) and short ischio-femoral contact (30-IFC, i.e. 30% of full ischio-femoral / seat contact). Results showed that kinematic performances (maximal antero-posterior and vertical center of mass velocity and maximal backward displacement of center of pressure) in both motor tasks were higher in 30-IFC than in 100-IFC. In the sit-to-stand task, time of seat-off is shorter in 30-IFC. As the subject's initial global posture was comparable across the experimental conditions, it can be discarded as a source of performance change. It is discussed that it is the enhanced pelvis mobility induced by the sitting condition which is responsible for the increase of motor performance in both trunk flexion and sit-to-stand tasks. Our results highlight the role of joint mobility in motor performance.

The diurnal patterns of cortisol and dehydroepiandrosterone in relation to intense aerobic exercise in recreationally trained soccer players.

Diurnal patterns of cortisol and dehydroepiandrosterone (DHEA) secretion, the two main peripheral secretory products of the hypothalamic-pituitary-adrenal neuroendocrine stress axis, have been well characterized in rest conditions but not in relation to physical exercise. The purpose of this investigation was therefore to determine the effects of an intense 90-min aerobic exercise on the waking diurnal cortisol and DHEA cycles on three separate days [without exercise, with morning exercise (10:00-11:30 h), and with afternoon exercise (14:00-15:30 h)] in nine recreationally trained soccer players. Saliva samples were collected at awakening, 30 min after awakening, and then every 2 h from 08:00 to 22:00 h. A burst of secretory activity was found for cortisol (p < 0.01) but not for DHEA after awakening. Overall, diurnal decline for both adrenal steroids was observed on resting and exercise days under all conditions. However, there was a significant increase in salivary cortisol concentrations on the morning-exercise and afternoon-exercise days at, respectively, 12:00 h (p < 0.05) and 16:00 h (p < 0.01), versus the other trials. This acute response to exercise was not evident for DHEA. The results of this investigation indicate that 90 min of intense aerobic exercise does not affect the circadian pattern of salivary adrenal steroids in recreationally trained athletes over a 16-h waking period, despite a transitory increase in post-exercise cortisol concentration. Further studies are necessary to determine whether these results are applicable to elite athletes or patients with cortisol or DHEA deficiency.

Sensorimotor integration during stance: processing time of active or passive addition or withdrawal of visual or haptic information.

Vision (V) and touch (T) help stabilize our standing body, but little is known on the time-interval necessary for the brain to process the sensory inflow (or its removal) and exploit the new information (or counteract its removal). We have estimated the latency of onset and the time-course of the changes in postural control mode following addition or withdrawal of sensory information and the effect of anticipation thereof. Ten subjects stood in tandem position. They wore LCD goggles that allowed or removed vision, or lightly touched (eyes-closed) with the index finger (haptic stimulation) a pad that could be suddenly lowered (passive task). In different sessions, sensory shifts were deliberately produced by opening (or closing) the eyes or touching the pad (or lifting the finger) (active task). We recorded eyelid movement and finger force (<1N), sway of center of foot pressure (CoP), electromyogram (EMG) of soleus, tibialis and peroneus muscle, bilaterally, and of extensor indicis. The latency of the CoP and EMG changes following the shifts were statistically estimated on the averaged traces of 50 repetitions per condition. Muscle activity and sway adaptively decreased in amplitude on adding stabilizing visual or haptic information. The time-interval from the sensory shift to decrease in EMG and sway was ∼0.5-2 s under both conditions. It was shorter for tibialis than peroneus or soleus and shorter for visual than haptic shift. CoP followed the tibialis by ∼0.2 s. Slightly shorter intervals were observed following active sensory shifts. Latencies of EMG and postural changes were the shortest on removal of both haptic and visual information. Subsequently, the time taken to reach the steady-state was ∼1-3 s under both active and passive tasks. A startle response at ∼100 ms could precede EMG changes. Reaction-time contractions in response to sensory shifts appeared at ∼200 ms, earlier than the adaptive changes. Changes in postural behavior require a finite amount of time from visual or haptic shift, much longer than reflexes or rapid voluntary responses, suggesting a time-consuming central integration process. This process is longer on addition than removal of haptic information, indicating a heavier computational load. These findings should be taken into account when considering problems of sensorimotor integration in elderly subjects or patients and when designing simulation models of human balance.

Influence of fear of falling on anticipatory postural control of medio-lateral stability during rapid leg flexion.

During leg flexion from erect posture, postural stability is organized in advance during "anticipatory postural adjustments" (APA). During these APA, inertial forces are generated that propel the centre of gravity (CoG) laterally towards stance leg side. This study examined how fear of falling (FoF) may influence this anticipatory postural control of medio-lateral (ML) stability. Ten young healthy participants performed a series of leg flexions at maximal velocity from low and high surface heights (6 and 66 cm above ground, respectively). In this latter condition with increased FoF, stance foot was placed at the lateral edge of the support surface to induce maximal postural threat. Results showed that the amplitude of ML inertial forces generated during APA decreased with FoF; this decrease was compensated by an increase in APA duration so that the CoG position at time of swing foot-off was located further towards stance leg side. With these changes in ML APA, the CoG was propelled in the same final (unipodal) position above stance foot as in condition with low FoF. These results contrast with those obtained in the literature during quiet standing which showed that FoF did not have any influence on the ML component of postural control. It is proposed that ML APA are modified with increased FoF, in such a way that the risk of a sideway fall induced by the large CoG motion is attenuated.

Control of mediolateral stability during rapid step initiation with preferred and non-preferred leg: is it symmetrical?

During voluntary stepping initiation, postural stability along the mediolateral direction is controlled via "anticipatory postural adjustment" (APA). This study tested the hypothesis that, in young healthy subjects, the biomechanical features of mediolateral APA depend on the leg that initiates stepping. Subjects (N=10) initiated a rapid single step with the preferred (P condition) and the non-preferred leg (NP condition) on a force-plate. Results showed that mediolateral APA duration (P=0.020) and amplitude were higher (as attested by the increase in maximal center-of-gravity velocity (P=0.003) and displacement (P<0.001) during APA), and that mediolateral stability was better (as attested by the attenuation in center-of-gravity velocity at time of swing-foot contact (P=0.007)) in P than in NP. These results support the view that stepping initiation in healthy subjects involves postural asymmetry. This statement may have relevant implications in clinical evaluation where postural asymmetry is generally considered as reflecting postural impairment.

Influence of sensory inputs and motor demands on the control of the centre of mass velocity during gait initiation in humans.

Human gait requires the simultaneous generation of goal-directed continuous movement (locomotion) and the maintenance of balance (postural control). In adults, the centre of mass (CoM) oscillates in the vertical plane while walking. During the single support phase of gait initiation, its vertical (vCoM) velocity increases as the CoM falls and is actively reversed prior to foot-contact. In this study we investigated whether this active control, which is thought to reflect balance control during gait initiation, is controlled by visual and somatosensory inputs (Experiment 1) and whether it is modified by a change in motor demands, two steps versus one step (Experiment 2). In all healthy adults, the vCoM velocity was braked, or controlled, by contraction of the soleus muscle of the stance leg. The elimination of visual input alone had no effect on braking, although its amplitude decreased when somatosensory inputs were disrupted (-47%), and further decreased when both visual and somatosensory inputs were disrupted (-83%). When subjects performed only one step, with no trailing of the stance foot, the vCoM velocity braking also decreased (-42%). These results suggest that active braking of the CoM fall during the transition to double support, an indicator of balance control, is influenced by both multisensory integration and the demands of the current motor program. The neural structures involved in this mechanism remain to be elucidated.

Effects of nigral stimulation on locomotion and postural stability in patients with Parkinson's disease.

The physiopathology of gait and balance disorders in Parkinson's disease patients is still poorly understood. Levodopa treatment and subthalamic nucleus (STN) stimulation improve step length and walking speed, with less effect on postural instability. These disorders have been linked to dysfunction of the descending basal ganglia outputs to brainstem structures. In this study, we evaluated the effects of stimulation of the substantia nigra pars reticulata (SNr), on locomotion and balance in Parkinson's disease patients. Biomechanical parameters and leg muscle activity were recorded during gait initiation in seven selected patients operated for bilateral STN stimulation, out of 204 stimulated patients, with one contact of each electrode located within the SNr. Step length, anteroposterior and vertical velocities of the centre of gravity were studied, with special reference to the subjects' ability to brake the centre of gravity fall before foot-contact, and compared to seven controls. In Parkinson's disease patients, five treatment conditions were tested: (i) no treatment, (ii) levodopa treatment, (iii) STN stimulation, (iv) SNr stimulation and (v) combined levodopa treatment and STN stimulation. The effects of these treatments on motor parkinsonian disability were assessed with the UPDRS III scale, separated into 'axial' (rising from chair, posture, postural stability and gait) and 'distal' scores. Whereas levodopa and/or STN stimulation improved 'axial' and 'distal' motor symptoms, SNr stimulation improved only the 'axial' symptoms. Compared to controls, untreated Parkinson's disease patients showed reduced step length and velocity, and poor braking just prior to foot-contact, with a decrease in both soleus (S) and anterior tibialis (AT) muscle activity. Step length and velocity significantly increased with levodopa treatment alone or in combination with STN stimulation in both natural and fast gait conditions, and with STN stimulation alone in the fast gait condition. Conversely, SNr stimulation had no significant effect on these measures in either condition. In the natural gait condition, no fall in the centre of gravity occurred as step length was low and active braking was unnecessary. In the fast gait condition, braking was improved with STN or SNr stimulation but not with levodopa treatment, with an increase in the stance leg S muscle activity. These results suggest that anteroposterior (length and velocity) and vertical (braking capacity) gait parameters are controlled by two distinct systems within the basal ganglia circuitry, representing respectively locomotion and balance. The SNr, a major basal ganglia output known to project to pontomesencephalic structures, is postulated as being particularly involved in balance control during gait.

Posture, dynamic stability, and voluntary movement.

This paper addresses the question of why voluntary movement, which induces a perturbation to balance, is possible without falling down. It proceeds from a joint biomechanical and physiological approach, and consists of three parts. The first one introduces some basic concepts that constitute a theoretical framework for experimental studies. The second part considers the various categories of "postural adjustments" (PAs) and presents major data on "anticipatory postural adjustments" (APA). The last part explores the concept of "posturokinetic capacity" (PKC) and its possible applications.

[Electromyographic study of stretch reflexes in the normal and prosthetic hip]. / Etude électromyographique des réflexes d'étirement intervenant au niveau de l'articulation coxo-fémorale normale et prothétique.

PURPOSE OF THE STUDY: Several studies have been devoted to the effect of proprioception on joint function. Modifications in feedback control from the cord have been observed in unstable joints due to capsule and ligament laxity. A few studies have examined the effect of knee and hip arthroplasty on proprioception, but none have established whether stretch reflexes affect function of a prosthetic joint. The purpose of the present study was to demonstrate the electromyographic characteristics of stretch reflexes of the normal hip joint and to compare them with those observed in the prosthetic hip. MATERIAL AND METHODS: Two groups of patients were studied. The first included eleven subjects free of neurological disorders whose studied limb was healthy. The second group included ten subjects with a total hip prosthesis who had undergone extensive capsulectomy during the arthroplasty. Voluntary muscle contraction was noted in each subject. In addition, electromyographic recordings were made to note response of the ipsilateral and contralateral quadriceps crural and tensor of the fascia lata during changes in joint position. Recordings were made with the subject in the supine position, the limb suspended, hip flexed at 45 degrees and knee extended. Three series of ten recordings were made in random order to measure the latency of muscle response to free fall of the limb, accelerated fall of the relaxed limb, and accelerated fall associated with calibrated contraction of the quadriceps. Mean latency of muscle response was calculated for each trial. RESULTS: In the conditions of this study, there was no statistically significant difference (p = 0.05) in the reflex time course between natural and prosthetic hips. DISCUSSION: Changes due to joint replacement and capsulectomy do not appear to affect the stretch reflexes of the hip joint.

Postural sway increase in low back pain subjects is not related to reduced spine range of motion.

This study questioned whether postural sway increase in low back pain subjects was related to impaired spine mobility, and especially to a decrease in the range of motion, which was assumed to represent structural spine stiffness. Ten low back pain subjects and ten healthy control subjects performed spine flexion-extension and spine side bending tests, and standing posturographic examination in different experimental conditions. Low back pain subjects showed increased postural sway along the antero-posterior axis and reduced side bending, i.e. posturographic and range of motion parameters varied in the opposite direction. Moreover, no correlation was found between these two types of parameters. Although significant, the slight decrease in spine side bending did not seem sufficiently great to disturb the low amplitude movements that maintain postural equilibrium. Hence, it was concluded that postural sway increase in low back pain is not related to a reduced spine range of motion, but might be linked to an increase in muscular active tension, which reduces dynamic mobility capacity.

Does respiration perturb body balance more in chronic low back pain subjects than in healthy subjects?

OBJECTIVE: To determine whether body balance is perturbed more in low back pain patients than in healthy subjects, under the concept of posturo-kinetic capacity. DESIGN: Comparison of posturographic and respiratory parameters between low back pain and healthy subjects. BACKGROUND: It has been demonstrated that respiratory movements constitute a perturbation to posture, compensated by movements of the spine and of the hips, and that low back pain is frequently associated with a loss of back mobility. METHOD: Ten low back pain patients and ten healthy subjects performed five posturographic tests under three different respiratory rate conditions: quiet breathing (spontaneous), slow breathing (0.1 Hz) and fast breathing (0.5 Hz). RESULTS: Intergroup comparison showed that the mean displacements of the center of pressure were greater for the low back pain group, especially along the antero-posterior axis, where respiratory perturbation is primarily exerted. Inter-condition comparison showed that in slow and fast breathing relatively to quiet breathing, the mean displacement of the center of pressure along the antero-posterior axis was significantly increased only for the low back pain group. CONCLUSION: According to the results, respiration presented a greater disturbing effect on body balance in low back pain subjects. RELEVANCE: This study provides information on the causes of the impaired body balance associated with chronic low back pain, which could be used to improve treatment strategy.

Are stance ankle plantar flexor muscles necessary to generate propulsive force during human gait initiation?

The study examined whether the generation of the forward propulsive force (PF) during gait initiation resulted mainly from the electromyogram activity of stance ankle plantar flexor muscles (APF) which 'push' on the ground as is generally claimed in the literature. Six unilateral above-knee amputees performed a specific gait initiation protocol, i.e. they were asked to walk as fast as possible from an upright posture. Data from a force platform were collected and processed to obtain gait parameters (centre of mass (CoM) acceleration, anteroposterior (A/P) progression velocity, step length, etc.). The results showed that the A/P CoM velocity at the time of foot-off differed depending on the state of the lower limb (sound or prosthetic limb) performing the step. However, the A/P velocity of the CoM reached at the time of foot contact was similar whatever the state of the lower limb initiating the gait. Thus, the absence of ankle and knee muscles did not affect the velocity of body progression, i.e. the generation of the PF in gait initiation. Furthermore, the comparable slopes of the A/P velocity between the stance sound limb and the stance prosthetic limb suggest that the organization of the motor synergy underlying the production of the PF remained the same and did not directly involve the APF. However, other mechanisms could explain PF generation. PF could be generated by the swing leg oscillation, by the trunk movement, or by other mechanisms such as the energy transfer and the exchange of gravity potential energy into kinetic energy.

In a complex sequential movement, what component of the motor program is improved with intensive practice, sequence timing or ensemble motor learning?

We investigated whether the higher maximum speed of complex athletic movements attained by experts compared with novices might solely be ascribed to the acquisition of a more efficient timing of the initiation of the simple movements that comprise complex sporting gestures. Six novices in fencing and five experts in fencing performed three experimental series: 7 trials of touche, 7 trials of lunge (control series) and 50 trials of lunge + touche (test series), where the touche and lunge were initiated with different chronological sequences imposed by the experimenter. The lunge and the touche can be assimilated to a fast forward step and to a pointing task, respectively. We compared the maximum speed of touche between the two groups, recorded by an accelerometer fixed to the hand guard of the foil, and the speed of the centre of mass obtained from a force plate. The speed of the centre of mass was not statistically different between the two groups in the control and in the test series. The maximum speed of touche was not statistically different between the two groups in the control series. In contrast, in the test series, the maximum speed of touche was higher in the fencers' than in novices' groups, while the timing of initiation of the lunge and the touche was similar. The results of the test series show that the higher maximum speed of touche of fencers compared with novices cannot solely be ascribed to the acquisition of a more efficient initiation timing in motor programming. In a complex fencing gesture, the higher maximum speed of touche following intensive practice is discussed with regard to the inhibition of negative effects linked to the "refractory period" associated with the initiation of two closely spaced motor programs.

In fencing, does intensive practice equally improve the speed performance of the touche when it is performed alone and in combination with the lunge?

Global movements are generally composed of several simple movements. In this study we tested the hypothesis that the effects of practice on the performance of a simple movement cannot be highlighted when it is performed alone but only when it is part of a global movement. For this purpose we examined the performance of the touche movement in fencing, in terms of maximal speed of the foil, when it is performed alone and in combination with the lunge. The touche can be assimilated to a pointing task towards a target while the lunge can be assimilated to a forward stepping movement. Four international class fencers and five novices were tested. The results show that 1) the performance in the isolated touche condition was comparable between the two test populations, 2) the performance was higher in the expert population compared to the novice population in the sequential touche + lunge condition, and 3) the velocity of the centre of mass at the time of the peak velocity of the touche was higher in the expert population than in the novice population in the sequential touche + lunge condition. In line with Bernstein's concepts on the effects of practice on motor control it is suggested that the experts exploit to advantage the forces developed during the lunge whereas the novices do not.