Immediate crossover fatigue after unilateral submaximal eccentric contractions of the knee flexors involves peripheral alterations and increased global perceived fatigue.

After a unilateral muscle exercise, the performance of the non-exercised contralateral limb muscle can be also impaired. This crossover fatigue phenomenon is still debated in the literature and very few studies have investigated the influence of eccentric contractions. This study was designed to assess neuromuscular adaptations involved in the crossover fatigue of the non-exercised contralateral knee flexor muscles. Seventeen healthy young men performed a unilateral submaximal eccentric exercise of the right knee flexors until a 20% reduction in maximal voluntary isometric contraction torque was attained in the exercised limb. Before (PRE), immediately after exercise cessation (POST) and 24 hours later (POST24), neuromuscular function and perceived muscle soreness were measured in both the exercised limb and non-exercised limb. In addition, global perceived fatigue was assessed at each measurement time. At POST, significant reductions in maximal voluntary isometric contraction were observed in the exercised limb (-28.1%, p < 0.001) and in the non-exercised limb (-8.5%, p < 0.05), evidencing crossover fatigue. At POST, voluntary activation decreased in the exercised limb only (-6.0%, p < 0.001), while electrically evoked potentiated doublet torque was impaired in both the exercised limb and the non-exercised limb (-11.6%, p = 0.001). In addition, global perceived fatigue significantly increased at POST (p < 0.001). At POST24, all measured variables returned to PRE values, except for perceived muscle soreness scores exhibiting greater values than PRE (p < 0.05). A possible cumulative interaction between peripheral alterations and global perceived fatigue may account for the immediate crossover fatigue observed in the non-exercised limb.

Effect of a sex stereotype on cortical activity during a self-paced exercise: A motor-related cortical potential approach.

Recent research has shown that inducing a negative stereotype toward women does not always decrease the subsequent motor performance of women, but can increase it, especially during endurance tasks. The mechanisms involved are nonetheless still poorly understood. The main aim of the present study was to investigate the effect of a negative stereotype toward women on men's and women's performance during an endurance task, and to analyze the neuropsychological mechanisms involved through motor-related cortical potentials and motivation toward men/women. Thirty-four participants were assigned to a negative stereotype toward women condition and a nullified-stereotype condition and performed 80 self-paced intermittent isometric elbow contractions at a moderate perceived intensity. Results showed that women performed better when assigned to the negative stereotype toward women condition, they were more motivated to outperform men, and their MRCP amplitudes were higher in this same condition over the prefrontal cortex (i.e., FP1 and FP2). Concerning men, they also performed better when the negative stereotype toward women was induced. However, no effect emerged on motivation toward women and MRCP amplitudes. This study showed that inducing a negative stereotype during an endurance task led to a performance increase in women, which is contrary to the stereotype threat theory, strengthening the idea of a task-dependency effect when inducing a negative stereotype. This performance improvement observed in women may be caused by increased motivation to outperform men and a planning of the upcoming movement. Concerning men, more research is needed to clarify the mechanisms involved in such performance improvement.

Co-contraction around the knee and the ankle joints during post-stroke gait.

BACKGROUND: Impairments resulting from hemiparetic stroke lead to persistent difficulties with walking. Abnormal co-contraction patterns of lower limb muscles might be a compensatory mechanism to deal with its resulting gait impairments. AIM: The aim of this study was to assess muscle co-contraction obtained from muscle moments in chronic hemiparetic patients presenting a stiff-knee gait (SKG) during walking. DESIGN: Cross-sectional study. SETTING: Clinical movement analysis laboratory in a health center and a community hospital. POPULATION: Twelve hemiparetic patients 6 months' post-stroke (mean±SD age 49.3±12.5) walking with a SKG and twelve healthy adults (mean±SD age 23.5±7.7). METHODS: Hemiparetic patients walked at their natural gait speed while healthy adults walked at their natural and slow gait speed. Spatiotemporal, kinetic and kinematic gait parameters were determined for both lower limbs. Co-Contraction Index at the knee and the ankle was calculated from muscle moments estimated using an EMG-driven model during the first (DS1) and second (DS2) double support and the single support (SS) phases and the swing phase (SW). RESULTS: The results revealed that chronic stroke patients have reduced ankle co-contraction and increased knee co-contraction during DS1 phase, increased ankle co-contraction during DS2 phase and increased knee co-contraction during SW phase on the paretic side. On the non-paretic side, muscle co-contraction was higher at the knee during SS phase. CONCLUSIONS: Increased co-contraction during walking in both the paretic and the non-paretic side, in patients with hemiparesis exhibiting a SKG, might be an adaptive strategy to increase walking stability, as it may be related to spasticity, but also could result in a high metabolic cost. CLINICAL REHABILITATION IMPACT: The information obtained in this study may be used to support rehabilitation programs focusing on the selectivity of movement control such as strength or power training.

Recommendations for the Use of Serious Games in Neurodegenerative Disorders: 2016 Delphi Panel.

The use of Serious Games (SG) in the health domain is expanding. In the field of neurodegenerative disorders (ND) such as Alzheimer's disease, SG are currently employed both to support and improve the assessment of different functional and cognitive abilities, and to provide alternative solutions for patients' treatment, stimulation, and rehabilitation. As the field is quite young, recommendations on the use of SG in people with ND are still rare. In 2014 we proposed some initial recommendations (Robert et al., 2014). The aim of the present work was to update them, thanks to opinions gathered by experts in the field during an expert Delphi panel. Results confirmed that SG are adapted to elderly people with mild cognitive impairment (MCI) and dementia, and can be employed for several purposes, including assessment, stimulation, and improving wellbeing, with some differences depending on the population (e.g., physical stimulation may be better suited for people with MCI). SG are more adapted for use with trained caregivers (both at home and in clinical settings), with a frequency ranging from 2 to 4 times a week. Importantly, the target of SG, their frequency of use and the context in which they are played depend on the SG typology (e.g., Exergame, cognitive game), and should be personalized with the help of a clinician.

Changes in Gait Variability From First Steps to Adulthood: Normative Data for the Gait Variability Index.

The process of learning to walk is ongoing throughout childhood. The Gait Variability Index (GVI; A. Gouelle et al., 2013) has been proposed to quantify the variability of spatiotemporal parameters (STP) during gait. The authors' aim was to evaluate the GVI and STP of healthy children and teenagers to (a) determine changes in the GVI with age and to derive normal values in children and (b) to evaluate the influence of STP on the GVI. A total of 140 typically developing children from 1 to 17 years old were categorized into 7 groups of 20 based on age. Spatiotemporal gait parameters were recorded using an electronic walkway. GVI increased and STP changed with age. In the children-teenagers group, the GVI was positively related to step length, speed, and negatively to cadence. Following normalization by lower limb length, correlations were no longer significant. In contrast, raw base of support was not correlated with the GVI but normalized base of support was. A multiple linear regression showed that only age had a direct impact on the GVI, indicating that gait continues to change after 6-7 years. These changes were only demonstrated by the GVI, highlighting its usefulness for the evaluation of gait in young populations.

Interpersonal distance modeling during fighting activities.

The aim of this article is to elaborate a general framework for modeling dual opposition activities, or more generally, dual interaction. The main hypothesis is that opposition behavior can be measured directly from a global variable and that the relative distance between the two subjects can be this parameter. Moreover, this parameter should be considered as multidimensional parameter depending not only on the dynamics of the subjects but also on the "internal" parameters of the subjects, such as sociological and/or emotional states. Standard and simple mechanical formalization will be used to model this multifactorial distance. To illustrate such a general modeling methodology, this model was compared with actual data from an opposition activity like Japanese fencing (kendo). This model captures not only coupled coordination, but more generally interaction in two-subject activities.

Path integration: is there a difference between athletes and non-athletes?

The ability to estimate distance walked when blindfolded is associated with the vestibular, proprioceptive and (loco-)motor systems. In this study, we examined subjects' ability to walk when blindfolded to a previously seen target. We examined whether there is a difference of performance in path integration between athletes and non-athletes. Two groups of healthy volunteers took part in this experiment: 21 athletes and 20 non-athletes. Subjects were asked to walk at three different velocities (slow, normal, fast) to a target (10 m in front of them) that they had seen before being blindfolded. Increase in velocity was associated with a decrease in the distance walked for both groups. Both groups were accurate at normal velocities. Athletes were also accurate at fast velocities whereas non-athletes undershot the target. In both groups, accuracy considerably decreased at slow velocities. It seems that our perceptual system can adapt to different velocities (normal, fast) but is most strongly disrupted at low velocity. When attempting to modify walking velocity, step length is also modified, playing a determining role in the estimation of distance.