Initial development of skill with a reversed bicycle and a case series of experienced riders.

Riding a bicycle is considered a durable skill that cannot be forgotten. Here, novice participants practiced riding a reversed bicycle, in which a reversing gear inverted the handlebar's rotation. Although learning to ride the reversed bicycle was possible, it was slow, highly variable, implicit, and followed an S-shape pattern. In the initial learning phase, failed attempts to ride the normal bicycle indicated strong interference between the two bicycle skills. While additional practice decreased this interference effect, a subset of learners could not ride either bicycle after eight sessions of practice. Experienced riders who performed extensive practice could switch bicycles without failed attempts and exhibited similar performance (i.e., similar handlebar oscillations) on both bicycles. However, their performance on the normal bicycle was worse than that of the novice bicycle riders at baseline. In conclusion, "unlearning" of the normal bicycle skill precedes the initial learning of the reversed bicycle skill, and a signature of such unlearning is still present following extensive practice.

Perceptual Inhibition Is Not a Specific Component of the Sensory Integration Process Necessary for a Rapid Voluntary Step Initiation in Healthy Older Adults.

OBJECTIVES: We investigated whether performing step initiation during a proprioceptive perturbation would require greater perceptual or motor inhibitory control in older adults. METHOD: Fifty-two healthy adults (young: n = 26, mean age 22.5 years vs. older: n = 26, mean age 70.1 years) performed a stepping reaction time task, with different inhibition requirements (i.e., perceptual vs. motor inhibitory conflict), with two proprioceptive configurations: with and without application of Achilles tendon vibrations. RESULTS: Beyond a systematically greater stepping reaction time in older adults (p < .01), no difference was found between the perceptual versus motor inhibitory conflict resolution, regardless of age and proprioceptive configuration. Furthermore, slower reaction time was observed for young participants in the presence of Achilles tendon vibrations unlike older adults, who showed the same reactive stepping performance with or without vibrations (p < .05). DISCUSSION: These findings show that perceptual inhibition cannot be considered as specifically involved in the central processing of proprioceptive signals, at least not in active older adults. Rather than motor system malfunctioning or a reduced amount of proprioceptive afference, we propose that cortical-proprioceptive processing in older adults remains as effective as in young adults, regardless of the high attentional requirements for step responses.

Can Methodological Considerations Challenge the Dissociation of the Perceptual and Motor Inhibitory Processes?

Using an original conflict task paradigm, Nassauer and Halperin (2003) argued that inhibition ability can be classified into two distinct perceptual and motor inhibitory processes. The current study examined the robustness of this paradigm by raising two major methodological points: the amount of information that needs to be processed and the task order (fixed vs. random). Sixty young adults performed the original or modified tasks. Overall, a decrease in the amount of information had the effect of removing the stimulus conflict on some subtests. Therefore, no more inhibition performance could be assessed. Even if the findings can be interpreted as a change in response-related complexity that relates reaction time performance to the informational processing load, the discrepancies in terms of the amount of information originally designed are necessary to induce inhibitory conflicts. Additionally, unlike previous recommendations, the fixed task order initially adopted cannot be considered an essential methodological requirement.

Examination of reactive motor responses to Achilles tendon vibrations during an inhibitory stepping reaction time task.

Inhibition is known to influence balance, step initiation and gait control. A specific subcomponent of inhibition, the perceptual inhibition process, has been suggested to be specifically involved in the integration of proprioceptive information that is necessary for efficient postural responses. This study aimed to investigate the inhibition requirements of planning and executing a choice step initiation task in young adults following experimental perturbation of proprioceptive information using Achilles tendon vibrations. We developed an inhibitory stepping reaction time task in which participants had to step in response to visual arrows that manipulated specific perceptual or motor inhibition according to two proprioceptive configurations: without or with application of vibrations. Performance of twenty-eight participants (mean age 21 years) showed that Achilles tendon vibrations induced an increase in attentional demands (higher reaction time and longer motor responses). Further, this increase in attentional demands did not affect specifically the different inhibitory processes tested in this reactive stepping task. It suggests that attentional demands associated with the vibratory perturbation to postural control do not lead to a shift from automatic to more attentional inhibition processes, at least in young adults.

Altered force-generating capacity is well-perceived regardless of the pain presence.

An inability to perceive changes in action capabilities may result in increased risk of injury and/or reduced performance. We investigated whether the perception of ability to perform a maximal single-leg hop was updated when the actual ability to perform the task was reduced due to experimentally altered force-generating capacity and associated pain. Twenty-five healthy volunteers performed a series of maximal isometric voluntary knee extensions (MVC), performance estimates and actual performances of a maximal single-leg hop. The motor tasks were completed for each leg, before (t0_pre), and immediately (t0_post), 48 hr (t+48hr) and 1 month (t+1month) after, a neuromuscular electrical stimulation (NMES) protocol was used to decrease the force generating capacity of the quadriceps muscle of 1 leg. MVC torque decreased by ∼30% after the NMES protocol for the stimulated leg at t0_post and t+48hr (p < .001). This reduction was associated with a significant decrease in estimation of performance and actual performance of the maximal single-leg hop at t0_post and t+48hr for the test leg (p < .001). The reduction in performance ability was associated with low-level pain immediately after NMES, and moderate pain and an increase in the belief that everyday motor tasks would be harmful 48 hours after NMES. Participants accurately estimated their performance capabilities during each testing period. This study provides a critical step toward understanding the potential for decreased force-generating capacity and muscle pain to modify the relationship between motor performance and perceived abilities.

Motor Adaptations to Pain during a Bilateral Plantarflexion Task: Does the Cost of Using the Non-Painful Limb Matter?

During a force-matched bilateral task, when pain is induced in one limb, a shift of load to the non-painful leg is classically observed. This study aimed to test the hypothesis that this adaptation to pain depends on the mechanical efficiency of the non-painful leg. We studied a bilateral plantarflexion task that allowed flexibility in the relative force produced with each leg, but constrained the sum of forces from both legs to match a target. We manipulated the mechanical efficiency of the non-painful leg by imposing scaling factors: 1, 0.75, or 0.25 to decrease mechanical efficiency (Decreased efficiency experiment: 18 participants); and 1, 1.33 or 4 to increase mechanical efficiency (Increased efficiency experiment: 17 participants). Participants performed multiple sets of three submaximal bilateral isometric plantarflexions with each scaling factor during two conditions (Baseline and Pain). Pain was induced by injection of hypertonic saline into the soleus. Force was equally distributed between legs during the Baseline contractions (laterality index was close to 1; Decreased efficiency experiment: 1.16±0.33; Increased efficiency experiment: 1.11±0.32), with no significant effect of Scaling factor. The laterality index was affected by Pain such that the painful leg contributed less than the non-painful leg to the total force (Decreased efficiency experiment: 0.90±0.41, P<0.001; Increased efficiency experiment: 0.75±0.32, P<0.001), regardless of the efficiency (scaling factor) of the non-painful leg. When compared to the force produced during Baseline of the corresponding scaling condition, a decrease in force produced by the painful leg was observed for all conditions, except for scaling 0.25. This decrease in force was correlated with a decrease in drive to the soleus muscle. These data highlight that regardless of the overall mechanical cost, the nervous system appears to prefer to alter force sharing between limbs such that force produced by the painful leg is reduced relative to the non-painful leg.

Combining intra-dialytic exercise and nutritional supplementation in malnourished older haemodialysis patients: Towards better quality of life and autonomy.

Protein-energy wasting (PEW), defined as a loss of body protein mass and fuel reserves, is a powerful predictor of adverse outcomes in haemodialysis (HD) patients. Robust arguments suggest that intra-dialytic exercise, combined with oral/parenteral nutrition, enhances the effect of nutritional interventions in HD patients. This pilot randomized controlled trial investigated the feasibility and the effects of a 6 month intra-dialytic cycling program combined to a nutritional support on PEW, physical functioning (gait, balance, muscle strength) and quality of life (QoL) in older HD patients (mean age 69.7 ± 14.2 years).Twenty-one patients fulfilling diagnostic criteria of PEW were randomly assigned to Nutrition-Exercise group (GN-Ex , n = 10) or Nutrition group (GN , n = 11). Both groups received nutritional supplements in order to reach recommended protein and energy intake goals. In addition GN-Ex completed a cycling program. No significant difference between groups was found in the number of patients having reached remission of PEW. Likewise, no change was observed in serum-albumin, -prealbumin, C-reactive protein, body mass index, lean- and fat-tissue index, or quadriceps force. Interestingly, we found positive effects of exercise on physical function and QoL for the GN-Ex , as evidenced by a significant improvement in the 6-min walk test (+22%), the absence of decline in balance (unlike the GN ), and a noteworthy increase in QoL (+53%). Combining intra-dialytic exercise and nutrition in HD patients is feasible, and well accepted, improves physical function and QoL but it appears not to have the potential to reverse PEW.

The effect of hemodialysis session on postural strategies in older end-stage renal disease patients.

Patients suffering from end-stage renal disease experience multiple disabilities, such as muscle wasting, weakness, higher postural sway, and fall rates compared with healthy population, which has a negative effect on physical functioning and autonomy. The vital treatment of hemodialysis is recognized to induce important post-hemodialysis fatigue, hypotension, cramps, and headache due to the rapid fluid redistribution, among others. Nevertheless, even the well-known negative effect of aforementioned consequences of hemodialysis treatment, its effect on physical function, especially postural balance, is unclear. Thus, this study hypothesized the adverse effect of hemodialysis treatment on postural sway in 12 end-stage renal disease patients (mean age 63.3 ± 11 years) through the analysis of center-of-pressure (COP) trajectories recorded before and immediately after hemodialysis session. Evident postural alterations were observed at post-hemodialysis balance assessment for COP position-based (Fs < 7.7, P < 0.02) and COP velocity-based variables (Fs > 2.33, P < 0.05), without changes in complexity of COP time series in anteroposterior and mediolateral directions. These results suggest that period after hemodialysis treatment is particularly unsafe, as evidenced by important disability in postural control, and highlight the importance of the medical support and falls-related prevention strategies of these older frail patients after hemodialysis treatment.

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.

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.

BACKGROUND: Protein-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 DESIGN: Fifty 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. DISCUSSION: The 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 REGISTRATION: The protocol for this study was registered with the France Clinical Trials Registry NCT01813851.

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

BACKGROUND: The 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. METHODS: Ten 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. RESULTS: Overall, 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). CONCLUSIONS: Even 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.