Hypohydration alters pre-frontal cortex haemodynamics, but does not impair motor learning.

It is unknown how hypohydration influences fine motor performance training and motor learning. Here, 30 participants (aged 19-46 years) were randomly assigned to a hypohydration (HYPO) or control (CON) group (both n = 15). Moderate hypohydration (~ 2.4% loss in body mass) was produced in HYPO via active dehydration before a 46 min fluid restricted rest period was undertaken. The conclusion of rest coincided with when CON attended the facilities. Both groups undertook a discrete sequence production task consisting of 6 training blocks, and returned ~ 300 min later to complete a delayed retention and transfer test while euhydrated. Bilateral pre-frontal cortex (PFC) haemodynamics were assessed using functional near-infrared spectroscopy throughout training and delayed learning assessments. Response time improved across training (P < 0.01) and was similar between the groups (both P = 0.22). Analysis of training PFC haemodynamics revealed a significant group by block interaction for oxygenated (O2Hb; P < 0.01), but not deoxygenated haemoglobin (P = 0.77). In training block 1, bilateral O2Hb was higher in HYPO (P = 0.02), while bilateral O2Hb increased in CON between blocks 2-3 and 5-6 (both P ≤ 0.03). During the delayed retention and transfer test, no group differences or interactions were found in response time, response error, or PFC haemodynamics (all P ≥ 0.27). Moderate hypohydration does increase PFC activation during motor skill learning, however, this appears to be transient and of little consequence to training or delayed retention or transfer performance.

Effects of muscle strengthening and cardiovascular fitness activities for poliomyelitis survivors: A systematic review and meta-analysis.

OBJECTIVE: To evaluate and assess the effectiveness of muscle strengthening and cardiovascular interventions in improving outcomes in poliomyelitis (polio) survivors. DATA SOURCES: A systematic literature search was conducted in Medline, PubMed, CINAHL, PsychINFO, Web of Science, and Google Scholar for experimental and observational studies. Study selection and extraction: Screening, data-extraction, risk of bias and quality assessment were carried out independently by the authors. The quality appraisal and risk of bias were assessed using the Downs and Black Checklist. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement was followed to increase clarity of reporting. DATA SYNTHESIS: A total of 21 studies that met all the inclusion criteria were subjected to statistical analyses according to intervention (muscle strengthening or cardiovascular fitness). A random-effects meta-analysis showed a statistically significant effect for the exercise interventions favouring improvement in outcomes according to the International Classification of Functioning, Disability and Health (ICF). CONCLUSION: This review provides further insight into the effects associated with muscle strengthening and cardiovascular interventions among polio survivors, and helps to further identify the current state of research in this area. Future research is needed, focusing on individualized approaches to exercise with polio survivors and specific exercise prescription recommendations, based on established frameworks, such as the ICF.

Thirst perception exacerbates objective mental fatigue.

Thirst is represented within the anterior cingulate and insular cortices, and may share some common neuroanatomical structures that are implicated with the regulation of mental fatigue. This novel study investigated whether thirst might modulate the subjective, behavioural, or neurophysiological representations of mental fatigue. In a crossover design, thirst was monitored in 15 males during 60 min of cycling in normothermic conditions. Participants either consumed water to the dictates of their thirst (sated), or fluid was withheld and replaced with periodic salt water mouth rinses (thirst). Following either satiety or thirst, a 60 min modified Stroop task was completed to evoke mental fatigue. Prefrontal cortex (PFC) haemodynamics were monitored throughout the prolonged task, and subjective perceptions of fatigue were reported through a visual analogue scale. Behavioural performance was quantified as the total number of Stroop task iterations completed in the mentally fatiguing task, and by collating response time and accuracy into the inverse efficiency score (IES) for each 5 min interval throughout the task. During thirst, fewer iterations were completed and poorer IES performance was evident toward the latter portion of the mentally fatiguing task. Compensatory elevations in PFC oxyhaemoglobin were produced in each condition, however, differed temporally, and were premature during thirst. A diminished capacity to sustain cognitive performance is likely the product of an inability to preserve the distribution of resources within the prefrontal cortex, due to heightened activation about thirst regulatory centres. These data provide novel insight into the relationship between thirst and mental fatigue, and suggest that drinking to the dictates of thirst may be a pertinent strategy to sustain prolonged cognitive performance.

The effect of active hypohydration on cognitive function: A systematic review and meta-analysis.

Hypohydration is generally considered to have a negative effect on cognitive function, despite several studies reporting comparable findings between hydration states. Recommendations to avoid moderate dehydration (≥ 2% loss in body mass) are commonly made to athletes, on the provision that this deficit may impair optimal cognitive performance. To determine whether cognitive function is impaired by hypohydration, and investigate the existence of the proposed critical water deficit of ≥2% loss in body mass purported to diminish cognitive performance, we conducted a systematic search of the literature and examined appropriate studies by meta-analysis. Overall, cognitive performance was not found to be impaired by hypohydration (g = -0.177; 95% CI = -0.532-0.179; P = .331). Nor were the underlying cognitive domains (complex attention, executive function, learning and memory) impaired (all P > .236), independent of the incurred fluid loss (less than or >2% loss in body mass), although results were not always homogenous (I2 ranging between 0% and 93%). Collectively, these results suggest that hypohydration may not compromise cognitive function, nor any of the investigated subdomains to a greater extent than if euhydration had been maintained. Furthermore, recommendations to avoid moderate hypohydration on the basis of maintaining optimal cognitive function are not substantiated by this meta-analysis.