Search

Objectives: Sleep is essential for recovery and performance in elite athletes. While it is generally assumed that exercise benefits sleep, high training load may jeopardize sleep and hence limit adequate recovery. To examine this, the current study assessed objective sleep quantity and sleep stage distributions in elite athletes and calculated their association with perceived training load.Design: Mixed-methods.Methods: Perceived training load, actigraphy and one-channel EEG recordings were collected among 98 elite athletes during 7 consecutive days of regular training.Results: Actigraphy revealed total sleep durations of 7:50±1:08h, sleep onset latencies of 13±15min, wake after sleep onset of 33±17min and sleep efficiencies of 88±5%. Distribution of sleep stages indicated 51±9% light sleep, 21±8% deep sleep, and 27±7% REM sleep. On average, perceived training load was 5.40±2.50 (scale 1-10), showing large daily variability. Mixed-effects models revealed no alteration in sleep quantity or sleep stage distributions as a function of day-to-day variation in preceding training load (all p's>.05).Conclusions: Results indicate healthy sleep durations, but elevated wake after sleep onset, suggesting a potential need for sleep optimization. Large proportions of deep sleep potentially reflect an elevated recovery need. With sleep quantity and sleep stage distributions remaining irresponsive to variations in perceived training load, it is questionable whether athletes' current sleep provides sufficient recovery after strenuous exercise. [ABSTRACT FROM AUTHOR]

This paper investigates the flow-blocking ability of a novel valve-mode magneto-rheological (MR) device to determine whether it can be used to replace the existing electro-mechanical solenoid valves that are used to control the semi-active spring characteristics in a four-state, semi-active vehicle suspension system (called the 4S4 system). MR fluids exhibit a reversible behavior that is controlled by changing the intensity of an externally applied magnetic field, allowing a change in the effective viscosity of the fluid. A mathematical model of the proposed flow-blocking valve has been developed using a combination of the quasi-Newtonian fluid model and the Bingham plastic model. This model has been modified with suitable parameters and is used to predict the blocking characteristics of the MR valve. An experimental setup has been developed with a prototype triple-pass valve mode MR fluid channel. The experimental results demonstrate that the MR valve designed and developed in this study is capable of generating a significantly high-pressure drop at very low flow rates, effectively blocking flow for practical use in the 4S4 system. [ABSTRACT FROM AUTHOR]

Objective: Sleep disturbances such as nocturnal awakenings frequently occur in demented elderly persons and can contribute to depression, cognitive impairment, and caregiver burden. Recognizing sleep disturbances at an early stage of the disease progress is a first prerequisite of intervention and monitoring of progress. This study aimed to investigate the reliability of subjective sleep reports in early- and moderate-stage Alzheimer dementia (AD), by investigating whether they differ from matched healthy normal comparison groups with respect to the discrepancy of subjective and objective sleep estimates. Measurements: Subjective sleep was assessed using the Pittsburgh Sleep Quality Index, the Sleep Disorders Questionnaire, and the Athens Insomnia Scale. Objective sleep was estimated using actigraphy. Results: As compared with the normal comparison group (N = 26), AD patients (TV = 55) complained less of insomnia, while their objective sleep estimates indicated, in fact, more disturbed sleep, including a longer sleep onset latency and a lower sleep efficiency. Regression analyses aimed at predicting actigraphic sleep parameter estimates from their subjective counterparts showed significant predictive value of only very few subjective sleep parameters. Subjective reports of both patients and the normal comparison group had significant value in predicting actigraphic indices of total sleep time and bedtime. In addition, subjective reports of the normal comparison group, but not of patients, were of value to predict actigraphic indices of sleep onset latency, average sleep bout duration, and sleep efficiency. Conclusion: The results show that the value of sleep questionnaires is limited in early- and moderate-stage AD. Actigraphy may be essential to ensure that sleep problems do not go undetected and untreated. (Am J Geriatr Psychiatry 2012; 20:460-467) [ABSTRACT FROM AUTHOR]