Thibault Deschamps

On Discontinuities in Motor Learning: A Longitudinal Study of Complex Skill Acquisition on a Ski-Simulator

Abstract The qualitative behavioral reorganizations that occurred during the acquisition of a complex motor skill were examined. Five novice participants practiced for 39 sessions of ten 1-min trials on a modified version of the ski-simulator. Analyses focused on the motion of the apparatus platform, modeled as a self-sustained oscillator. At the beginning of the experiment, all participants adopted a behavior that could be modeled with a highly nonlinear stiffness function and a Rayleigh damping function. The behavior in the final part of the experiment was captured by a qualitatively different model, with a linear stiffness function and a van der Pol damping behavior. The transition from the initial to the final model was gradual and was marked in most cases by an abrupt increase of oscillation frequency. During the transition stage, the 2 damping behaviors seemed alternately exploited within each trial. The results are discussed in the framework of the dynamical systems approach to motor coordination and learning, considering motor skill acquisition as a phase transition.

Postural control and cognitive decline in older adults: Position versus velocity implicit motor strategy

The present study explored the impact of cognitive decline on postural control strategies in older adults with and without cognitive decline from mild cognitive impairment (MCI) to mild-to-moderate Alzheimer disease (MMAD). We hypothesized that the cognitive decline affected the postural control leading to higher bounding limits of COP velocity dynamics. Based on a cross-sectional design, 175 non-faller older adults were recruited in Angers University Hospital, France, including 50 cognitively healthy individuals [CHI] (mean age 76.42 ± 4.84 years; 30% women), 64 age- and body mass index-matched participants with MCI (mean age 77.51 ± 6.32 years; 39% women), and 61 age- and body mass index-matched participants with MMAD (mean age 78.44 ± 3.97 years; 62% women). For all data collection of postural sway, the participants were asked to maintain quiet stance on force platform. The postural test consisted of two trials of quiet stance, with eyes open and with eyes closed. The COP parameters were mean and standard deviation (SD) of position, velocity and average absolute maximal velocity (AAMV) in antero-posterior and medio-lateral directions. Overall, the analysis concerning all COP parameters revealed a significant main effect of cognitive status on velocity-based variables, with post hoc comparisons evidencing that SD velocity and AAMV increased with cognitive impairment. The current findings suggest an active control (or corrective process) of COP velocity dynamics for CHI, whereas MCI and MMAD are affected by COP movements.

Gait disturbances as specific predictive markers of the first fall onset in elderly people: a two-year prospective observational study

Falls are common in the elderly, and potentially result in injury and disability. Thus, preventing falls as soon as possible in older adults is a public health priority, yet there is no specific marker that is predictive of the first fall onset. We hypothesized that gait features should be the most relevant variables for predicting the first fall. Clinical baseline characteristics (e.g., gender, cognitive function) were assessed in 259 home-dwelling people aged 66 to 75 that had never fallen. Likewise, global kinetic behavior of gait was recorded from 22 variables in 1036 walking tests with an accelerometric gait analysis system. Afterward, monthly telephone monitoring reported the date of the first fall over 24 months. A principal components analysis was used to assess the relationship between gait variables and fall status in four groups: non-fallers, fallers from 0 to 6 months, fallers from 6 to 12 months and fallers from 12 to 24 months. The association of significant principal components (PC) with an increased risk of first fall was then evaluated using the area under the Receiver Operator Characteristic Curve (ROC). No effect of clinical confounding variables was shown as a function of groups. An eigenvalue decomposition of the correlation matrix identified a large statistical PC1 (termed “Global kinetics of gait pattern”), which accounted for 36.7% of total variance. Principal component loadings also revealed a PC2 (12.6% of total variance), related to the “Global gait regularity.” Subsequent ANOVAs showed that only PC1 discriminated the fall status during the first 6 months, while PC2 discriminated the first fall onset between 6 and 12 months. After one year, any PC was associated with falls. These results were bolstered by the ROC analyses, showing good predictive models of the first fall during the first six months or from 6 to 12 months. Overall, these findings suggest that the performance of a standardized walking test at least once a year is essential for fall prevention.

Postural Sway, Falls, and Cognitive Status: A Cross-Sectional Study among Older Adults

BACKGROUND Cognitive impairment-related changes in postural sway increase fall risk among older adults. Better understanding this association could be helpful for fall prevention. OBJECTIVE To examine the center-of-pressure (COP) velocity association with cognitive status and history of falls, in cognitively healthy individuals (CHI), patients with mild cognitive impairment (MCI), and with mild-to-moderate Alzheimers disease (MMAD). METHODS Six hundred and eleven older community-dwellers (77.2 ± 7.9 years; 51.8% men) were separated into CHI, MCI, and MMAD participants. By computing the average absolute maximal velocity (AAMV), the bounding limits of COP velocity dynamics were determined while participants were asked to maintain quiet stance on a force platform with eyes open or with eyes closed. Age, gender, history of falls, body mass index, medications, handgrip strength, Timed Up & Go score were used as covariates. RESULTS The multivariate ANCOVA, with AAMV in eyes open and eyes closed conditions as dependent variables, showed that the highest AAMVs that bound the COP velocity dynamics of postural sway were associated with cognitive impairment (p = 0.048) (i.e., lowest limits in CHI and MCI as compared with MMAD) and falls (p = 0.033) (i.e., highest limits in fallers). CONCLUSIONS These findings identified the bounding limits of COP velocity as a hallmark feature of cognitive impairment-related changes in postural sway, in particular for MMAD. This point is of special interest for clinical balance assessment and fall prevention in MMAD patients in order to plan long-term targeted fall-prevention programs.

Postural control as a function of time-of-day: influence of a prior strenuous running exercise or demanding sustained-attention task

BackgroundThe current experiment investigated the impact of two potential confounding variables on the postural balance in young participants: the induced-experimental activity prior to the static postural measurements and the well-documented time-of-day effects. We mainly hypothesized that an exhaustive exercise and a high attention-demanding task should result in alterations of postural control.MethodsTen participants performed three experimental sessions (differentiated by the activity – none, cognitive or physical – prior of the assessment of postural stability), separated by one day at least. Each session included postural balance assessments around 8 a.m., 12.00 p.m. and 5 p.m. ± 30 min. The physical and cognitive activities were performed only before the 12 o’clock assessment. The postural tests consisted of four conditions of quiet stance: stance on a firm surface with eyes open; stance on a firm surface with eyes closed; stance on a foam surface with eyes open and stance on a foam surface with eyes closed. Postural performance was assessed by various center of pressure (COP) parameters.ResultsOverall, the COP findings indicated activity-related postural impairment, with an increase in body sway in the most difficult conditions (with foam surface), especially when postural measurements are recorded just after the running exercise (physical session) or the psychomotor vigilance test (cognitive session).ConclusionsEven if no specific influence of time-of-day on static postural control is demonstrated, our results clearly suggest that the activities prior to balance tests could be a potential confounding variable to be taken into account and controlled when assessing clinical postural balance.

Effects of a six-month intradialytic physical ACTIvity program and adequate NUTritional support on protein-energy wasting, physical functioning and quality of life in chronic hemodialysis patients: ACTINUT study protocol for a randomised controlled trial

BackgroundProtein-energy wasting (PEW) is common in hemodialysis patients and is a powerful predictor of morbidity and mortality. Although much progress has been made in recent years in identifying the causes and pathogenesis of PEW in hemodialysis patients, actual management by nutritional interventions is not always able to correct PEW. Some investigators suggest that physical exercise may increase the anabolic effects of nutritional interventions, and therefore may have a potential to reverse PEW. The aim of this study is to investigate the effect of intra-dialytic progressive exercise training and adequate nutritional supplementation on markers of PEW, functional capacities and quality of life of adult hemodialysis patients.Methods and designFifty end-stage renal disease patients undergoing hemodialysis, who meet the diagnostic criteria for PEW, will be randomly allocated into an exercise or control group for 6 months. The exercise consists of a progressive submaximal individualized cycling exertion using an adapted cycle ergometer, during the three weekly dialysis sessions. Biological markers of nutrition (albumin, prealbumin) will be followed monthly and all patients will be assessed for body composition, walk function, muscle strength, postural stability and quality of life at baseline and during the eighth week (t+2), the sixteenth week (t+4) and the twenty-fourth week (t+6) of the 6-month adapted rehabilitation program.DiscussionThe successful completion of this current trial may give precious clues in understanding PEW and encourage nephrologists to extend prescription of exercise programs as well as therapeutic and as preventive interventions in this high-risk population.Trial registrationThe protocol for this study was registered with the France Clinical Trials Registry NCT01813851.

Persistent coordination patterns in a complex task after 10 years delay: subtitle: how validate the old saying "once you have learned how to ride a bicycle, you never forget!".

Motor learning studies have for a long time focused on performance variables (in terms of speed or accuracy) in assessing learning, transfer and retention of motor skills. We argue, however, that learning essentially resides in changes in coordination variables (in terms of qualitative organization of behavior) and that relevant tests for assessing the effectiveness of learning and retention should consider these variables. The aim of this experiment was to test the retention of a complex motor skill, after a long-term delay. Ten years ago, five participants were involved in an experiment during which they practiced for 39 sessions of ten 1-min trials on a ski-simulator. All participants volunteered for a retention test, ten years after, for one session of ten 1-min trials. Analyses focused on the oscillations of the platform of the simulator. Performance was assessed in terms of amplitude and frequency. Coordination was accounted for by an analysis of dynamical properties of the motion of the platform, and especially the nature of the damping function that was exploited for sustaining the limit cycle dynamics. Results showed a significant decrement in performance variables. In contrast, all participants adopted from the first trial onwards the coordination mode they learned 10years ago. These results confirm the strong persistence of coordination modes, once acquired and stabilized in the behavioral repertoire. They also support the importance of coordination variables for a valid assessment of learning and retention.

The effects of required amplitude and practice on frequency stability and efficiency in a cyclical task.

From an ecological point of view, motor learning emerges from the interplay of constraints on action, which shape behaviour towards the optimal solution, and practice, conceived as an active exploration of the workspace, to search this optimal solution. In the experiment reported here, we studied this interplay for a cyclical task performed on a ski-simulator. Our aim was to assess the respective effects of amplitude and practice on frequency variability and efficiency. On the basis of previous empirical findings, amplitude was expected, beyond a critical value, to constrain and stabilize the frequency of the movement. Three groups of participants practised during four sessions at three different amplitudes (15, 22.5 and 30 cm). The results showed that participants moving at large amplitude displayed more stable and more consistent frequencies. Nevertheless, there was no interaction effect between target amplitude and practice. On the other hand, movement economy and harmonicity increased with practice, but were not affected by amplitude. Finally, the results of transfer tests showed that the effects of large amplitude on frequency variability were not resistant to a subsequent decrease in target amplitude. These results suggest that constraints and practice act independently on motor behaviour, and that a high constraint could be detrimental to the development of effective search strategies.

Implicit postural control strategies in older hemodialysis patients: An objective hallmark feature for clinical balance assessment

Elderly patients with end stage renal diseases (ESRD) undergoing hemodialyis (HD) present poorer physical function and higher accident falls than healthy elderly population. Therefore, the aim of this study was to examine the HD-related changes in postural sway in ESRD patients, as an objective hallmark of their functional abilities. We hypothesized that the ESRD symptoms (i.e. uremic syndrome) and the HD therapy affected the postural control, evidenced by higher bounding limits of center-of-pressure (COP) velocity dynamics. Fifty-five participants, including 28 HD patients and 27 age, body mass index and gender-matched healthy participants HS (70.42 ± 13.69 years; 23.46 ± 4.67 kg/m(2); 35.7% women vs. 73.62 ± 6.59 years; 25.09 ± 3.54 kg/m(2); 37% women), were asked to maintain quiet stance on force platform, with eyes open and eyes closed. COP parameters were mean and standard deviation (SD) of position, velocity and average absolute maximal velocity (AAMV) in antero-posterior and medio-lateral directions. The results revealed a significant main effect of group on velocity-based variables, highlighting that mean velocity, SD velocity and AAMV (p<0.01) were higher for HD as compared to HS. These findings identified the bounding limits of COP velocity as an objective hallmark feature of HD-related changes in postural sway. The clinical assessment of this active control of COP velocity dynamics could be useful to examine the effects of targeted intradialytic exercise programs on functional performances and for early detection of increased fall risk in HD patients.

Influence of an exhausting muscle exercise on bimanual coordination stability and attentional demands.

The present study investigated the influence of a bilateral exhaustive exercise on the stability of bimanual anti-phase coordination pattern and attentional demands. Eight subjects performed the anti-phase coordination pattern in two sessions: an Exhausting Session and a Control Session. During the Exhausting Session, subjects performed the bimanual coordination after exhaustion of forearms muscles (i.e. endurance time test). For the Control Session, no endurance time test was previously designed before the performance of anti-phase coordination. Within these experimental sessions, two levels of load (loaded and unload) and two frequencies (1.75 and 2.25 Hz) were also manipulated during the bimanual task. Attentional demands associated with performing the anti-phase coordination pattern was measured via a probe reaction time task (RT). The results showed that relative phase variability was higher for the fastest frequency after the exhaustive exercise. Moreover, as a result of the previous muscle exercise, the observed phase coupling was less accurate. No significant effect was found concerning the attentional demands as assessed through RT. The present findings suggest that the muscle exhaustion affects bimanual performance at a more peripheral level.