Photoperiod Impact on a Sailor's Sleep-Wake Rhythm and Core Body Temperature in Polar Environment.

INTRODUCTION: Studies have reported circadian desynchronizations and sleep disruptions in onshore populations in the Arctic during the polar day. Although the Arctic region is becoming more accessible by sea and evidence is growing to implicate the importance of fatigue in sailing accidents, no study related to circadian disruptions has focused on sailors. The aim of this study was to observe, during a 155-d polar sailing trip between Greenland and Russia, the evolution of the sleep-wake rhythm and core body temperature (Tc) in a sailor. METHODS: During the expedition, an electronic sleep diary was recorded daily and a continuous measurement of Tc using telemetric pills was performed every 10 d (recording depending on transit time, ≈24 h). Ephemerides were manually determined day by day using global positioning system position and revealed 3 phases (phase 1: decrease of night duration; phase 2: polar day; phase 3: increase of night duration). RESULTS: A significant difference (P<0.05) was observed in daily sleep time between phase 2 (7.6±2.5 h) and phase 3 (8±2 h). The period of Tc rhythm changed during the expedition (phase 1: 24.2±0.5 h; phase 2: 25±0.3 h; phase 3: 24±0.6 h). Dissociation between Tc rhythm and sleep occurred during phase 2. CONCLUSIONS: Our study observed that during a polar sailing expedition, many circadian disruptions appeared as free-running rhythms or dissociation between sleep and Tc rhythm. Future studies will evaluate effects of these disruptions and their probable association with accident risks.

Neural substrates of reduced walking activity after supratentorial stroke: A voxel-based lesion symptom mapping study.

BACKGROUND: Most stroke patients exhibit low levels of walking activity, a key component of secondary stroke prevention. The predictors of walking activity may be multifactorial and are thus far partially understood. We aimed to study the neuroanatomic correlates of low levels of daily walking activity following hemispheric stroke. METHODS: In this cross-sectional study, 33 community-dwelling stroke survivors (age: 63.9 ±â€¯12.9 years; % female: 36.4%; NIHSS at admission: 3.3 ±â€¯4.0) were prospectively recruited at least 3 months after a first ever, unilateral, supratentorial stroke confirmed by brain magnetic resonance imaging. Walking activity was measured by daily step counts (steps∙day-1), recorded using an Actigraph GT3x+ triaxial accelerometer over 7 consecutive days. Voxel-based lesion-symptom mapping was performed to identify brain areas associated with walking activity following stroke. RESULTS: Participants presented 4491.9 ±â€¯2473.7 steps∙day-1. Lower levels of walking activity were related to lesions of the posterior part of the putamen, of the posterior limb of the internal capsule and of the anterior part of the corona radiata. No cortical region was associated with walking activity. CONCLUSIONS: Our preliminary results identify subcortical neuroanatomical correlates for reduced walking activity following stroke. If confirmed, these results could serve as a rationale for the development of targeted rehabilitative strategy to improve mobility after stroke.

Consensus statement on placebo effects in sports and exercise: The need for conceptual clarity, methodological rigour, and the elucidation of neurobiological mechanisms.

In June 2017 a group of experts in anthropology, biology, kinesiology, neuroscience, physiology, and psychology convened in Canterbury, UK, to address questions relating to the placebo effect in sport and exercise. The event was supported exclusively by Quality Related (QR) funding from the Higher Education Funding Council for England (HEFCE). The funder did not influence the content or conclusions of the group. No competing interests were declared by any delegate. During the meeting and in follow-up correspondence, all delegates agreed the need to communicate the outcomes of the meeting via a brief consensus statement. The two specific aims of this statement are to encourage researchers in sport and exercise science to 1. Where possible, adopt research methods that more effectively elucidate the role of the brain in mediating the effects of treatments and interventions. 2. Where possible, adopt methods that factor for and/or quantify placebo effects that could explain a percentage of inter-individual variability in response to treatments and intervention.

Cognitive performance and self-reported sleepiness are modulated by time-of-day during a mountain ultramarathon.

Ninety-two runners completed the study during a 168 km mountain ultramarathon (MUM). Sleepiness, self-reported sleep duration, and cognitive performance were assessed the day before the race and up to eight checkpoints during the race. Sleepiness was assessed using the Karolinska Sleepiness Scale. Cognitive performance was also assessed using the Digital Symbol Substitution Task (DSST). Runner reported 23.40 ± 22.20 minutes of sleep (mean ± SD) during the race (race time: 29.38 to 46.20 hours). Sleepiness and cognitive performance decrements increased across this race, and this was modulated by time-of-day with higher sleepiness and greater performance decrements occurring during the early morning hours. Runners who slept on the course prior to testing had poorer cognitive performance, which may suggest that naps on the course were taken due to extreme exertion. This study provides evidence that cognitive performance deficits and sleepiness in MUM are sensitive to time into race and time-of-day.

Exploring the Metabolic and Perceptual Correlates of Self-Selected Walking Speed under Constrained and Un-Constrained Conditions.

Mechanisms underpinning self-selected walking speed (SSWS) are poorly understood. The present study investigated the extent to which SSWS is related to metabolism, energy cost, and/or perceptual parameters during both normal and artificially constrained walking. Fourteen participants with no pathology affecting gait were tested under standard conditions. Subjects walked on a motorized treadmill at speeds derived from their SSWS as a continuous protocol. RPE scores (CR10) and expired air to calculate energy cost (J.kg-1.m-1) and carbohydrate (CHO) oxidation rate (J.kg-1.min-1) were collected during minutes 3-4 at each speed. Eight individuals were re-tested under the same conditions within one week with a hip and knee-brace to immobilize their right leg. Deflection in RPE scores (CR10) and CHO oxidation rate (J.kg-1.min-1) were not related to SSWS (five and three people had deflections in the defined range of SSWS in constrained and unconstrained conditions, respectively) (p > 0.05). Constrained walking elicited a higher energy cost (J.kg-1.m-1) and slower SSWS (p < 0.05) versus normal walking. RPE (CR10) was not significantly different between walking conditions or at SSWS (p > 0.05). SSWS did not occur at a minimum energy cost (J.kg-1.m-1) in either condition, however, the size of the minimum energy cost to SSWS disparity was the same (Froude {Fr} = 0.09) in both conditions (p = 0.36). Perceptions of exertion can modify walking patterns and therefore SSWS and metabolism/ energy cost are not directly related. Strategies which minimize perceived exertion may enable faster walking in people with altered gait as our findings indicate they should self-optimize to the same extent under different conditions.

Upper limb movement analysis during gait in multiple sclerosis patients.

PURPOSE: Gait disorders in multiple sclerosis (MS) are well studied; however, no previous study has described upper limb movements during gait. However, upper limb movements have an important role during locomotion and can be altered in MS patients due to direct MS lesions or mechanisms of compensation. The aim of this study was to describe the arm movements during gait in a population of MS patients with low disability compared with a healthy control group. METHODS: In this observational study we analyzed the arm movements during gait in 52 outpatients (mean age: 39.7±9.6years, female: 40%) with relapsing-remitting MS with low disability (mean EDSS: 2±1) and 25 healthy age-matched controls using a 3-dimension gait analysis. RESULTS: MS patients walked slower, with increased mean elbow flexion and decreased amplitude of elbow flexion (ROM) compared to the control group, whereas shoulder and hand movements were similar to controls. These differences were not explained by age or disability. CONCLUSION: Upper limb alterations in movement during gait in MS patients with low disability can be characterized by an increase in mean elbow flexion and a decrease in amplitude (ROM) for elbow flexion/extension. This upper limb movement pattern should be considered as a new component of gait disorders in MS and may reflect subtle motor deficits or the use of compensatory mechanisms.

Stride time variability as a marker for higher level of gait control in multiple sclerosis: its association with fear of falling.

Fear of falling (FOF) and gait disorders represent both prevalent symptoms in patients with multiple sclerosis (MS); however, the association between FOF and higher level of gait control (HLGC) has not been studied in MS. This study aims to assess the association between FOF and HLGC in patients with MS. HLGC was assessed by stride time variability (STV) during single and dual-tasks (forward counting, backward counting, categorical verbal fluency and literal verbal fluency) and FOF was quantified by the falls efficacy scale-international (FES-I). Seventy-one patients (age: 39.27 ± 9.77 years; 63 % female) were included in this cross-sectional study (Expanded Disability Status Scale (median): 2.00) with a low prevalence of FOF (FES-I: 21.52 ± 8.37). The mean gait speed was 1.19 ± 0.23 m/s with a STV of 2.35 ± 1.68 % during single walking task. STV during single task and the dual tasks of forward counting and backward counting were associated with the FES-I in the univariable linear regression models (p ≤ 0.001), but only STV while backward counting (ß: 0.42, [0.18;0.66]) was associated with FOF in the multivariable model (adjusted for age, gender, previous fall, Expanded Disability Status Scale and gait speed). These findings indicate that FOF is associated with STV while backward counting, a marker of HLGC in relationship with working memory in a MS population including a majority of low disabled patients.

Gait variability in multiple sclerosis: a better falls predictor than EDSS in patients with low disability.

This longitudinal study aims to compare the role of stride time variability (STV) and EDSS for predicting falls in 50 patients with multiple sclerosis with low disability. 21.7 % developed falls (follow-up: 22 months). STV (IRR: 1.73, 95 % CI: 1.23-2.41, p = 0.001) and EDSS (IRR: 2.29, 95 % CI: 1.35-3.90, p = 0.002) were associated with the number of falls. Adding STV to EDSS improves the predictive power of the model from 21 to 26 %, but not adding EDSS to STV.