Reducing heat stress under thermal insulation in protective clothing: microclimate cooling by a 'physiological' method.

Heat stress caused by protective clothing limits work time. Performance improvement of a microclimate cooling method that enhances evaporative and to a minor extent convective heat loss was tested. Ten male volunteers in protective overalls completed a work-rest schedule (130 min; treadmill: 3 × 30 min, 3 km/h, 5% incline) with or without an additional air-diffusing garment (climatic chamber: 25°C, 50% RH, 0.2 m/s wind). Heat loss was supported by ventilating the garment with dry air (600 l/min, ≪5% RH, 25°C). Ventilation leads (M ± SD, n = 10, ventilated vs. non-ventilated) to substantial strain reduction (max. HR: 123 ± 12 b/min vs. 149 ± 24 b/min) by thermal relief (max. core temperature: 37.8 ± 0.3°C vs. 38.4 ± 0.4°C, max. mean skin temperature: 34.7 ± 0.8°C vs. 37.1 ± 0.3°C) and offers essential extensions in performance and work time under thermal insulation. PRACTITIONER SUMMARY: Heat stress caused by protective clothing limits work time. Performance can be improved by a microclimate cooling method that supports evaporative and to a minor extent convective heat loss. Sweat evaporation is the most effective thermoregulatory mechanism for heat dissipation and can be enhanced by insufflating dry air into clothing.

Performance, training and lifestyle parameters of marathon runners aged 20-80 years: results of the PACE-study.

Successful finishing of marathon requires regular endurance training and appropriate lifestyle. Thus, marathon running times and training data from large samples of physically active and fit elderly are ideal for the assessment of age-related performance. In the present study we analyzed 439 278 running times from result lists of 108 marathon competitions and data from a survey via internet questionnaire about training and behavioural factors of marathon finishers. Marathon times and 6 992 data sets from the internet questionnaire were separated into groups based on age and sex and analyzed by two-way ANOVA. Our main findings are that 1) there are virtually no relevant running time differences (p<0.01) in marathon finishers from 20 to 55 years and 2) the majority of middle-aged and elderly athletes have training histories of less than seven years of running. With the exception of marathon running times we did not encounter any significant gender related differences (p>0.01). The present findings strengthen the concept that considers aging as a biological process that can be considerably speeded up or slowed down by multiple lifestyle related factors.

Validation of a short-term memory test for the recognition of people and faces.

Memorising and processing faces is a short-term memory dependent task of utmost importance in the security domain, in which constant and high performance is a must. Especially in access or passport control-related tasks, the timely identification of performance decrements is essential, margins of error are narrow and inadequate performance may have grave consequences. However, conventional short-term memory tests frequently use abstract settings with little relevance to working situations. They may thus be unable to capture task-specific decrements. The aim of the study was to devise and validate a new test, better reflecting job specifics and employing appropriate stimuli. After 1.5 s (short) or 4.5 s (long) presentation, a set of seven portraits of faces had to be memorised for comparison with two control stimuli. Stimulus appearance followed 2 s (first item) and 8 s (second item) after set presentation. Twenty eight subjects (12 male, 16 female) were tested at seven different times of day, 3 h apart. Recognition rates were above 60% even for the least favourable condition. Recognition was significantly better in the 'long' condition (+10%) and for the first item (+18%). Recognition time showed significant differences (10%) between items. Minor effects of learning were found for response latencies only. Based on occupationally relevant metrics, the test displayed internal and external validity, consistency and suitability for further use in test/retest scenarios. In public security, especially where access to restricted areas is monitored, margins of error are narrow and operator performance must remain high and level. Appropriate schedules for personnel, based on valid test results, are required. However, task-specific data and performance tests, permitting the description of task specific decrements, are not available. Commonly used tests may be unsuitable due to undue abstraction and insufficient reference to real-world conditions. Thus, tests are required that account for task-specific conditions and neurophysiological characteristics.

Maximal manual stretcher carriage: performance and recovery of male and female ambulance workers.

The effects of a maximal duration stretcher carriage on heart rate (HR), lactate concentration, hand steadiness and hand-grip strength were studied up to 72 h post-exercise in 17 male and 15 female military ambulance personnel. Using both hands for transport, the participants walked on a treadmill ergometer at a speed of 4.5 km/h. Force measurements at the handlebars yielded mean loads of 245 N (25 kg) on each side. Each step on the treadmill induced additional force oscillations with peak forces up to 470 N corresponding to 130% (women) and 98% (men) of maximal voluntary contraction (MVC). In the males the maximal transport time was about twice the time in women (mean +/- SD: 184 +/- 51 s vs. 98 +/- 34 s). These differences had no significant effect on HR and lactate values. The same applies to hand steadiness, which showed only a transient deterioration immediately after exercise. In contrast to these parameters, substantial differences were seen in hand-grip strength recovery. Immediately after exercise, maximal hand-grip strength decreased by 150 N (25% MVC) in the males vs. 50 N (14%) in the females. Irrespective of gender, individuals with larger hand-grip strength and longer carriage durations (range 120 s-280 s) showed the slowest strength recoveries (up to 72 h) as compared to 1 h of recovery in participants with short transport durations (range 27 s-120 s). These findings suggest that the increasing number of eccentric strains during uninterrupted stretcher carriage induces cumulative muscle damages that may require some days for complete recovery.

Hand-grip strength of young men, women and highly trained female athletes.

Hand-grip strength has been identified as one limiting factor for manual lifting and carrying loads. To obtain epidemiologically relevant hand-grip strength data for pre-employment screening, we determined maximal isometric hand-grip strength in 1,654 healthy men and 533 healthy women aged 20-25 years. Moreover, to assess the potential margins for improvement in hand-grip strength of women by training, we studied 60 highly trained elite female athletes from sports known to require high hand-grip forces (judo, handball). Maximal isometric hand-grip force was recorded over 15 s using a handheld hand-grip ergometer. Biometric parameters included lean body mass (LBM) and hand dimensions. Mean maximal hand-grip strength showed the expected clear difference between men (541 N) and women (329 N). Less expected was the gender related distribution of hand-grip strength: 90% of females produced less force than 95% of males. Though female athletes were significantly stronger (444 N) than their untrained female counterparts, this value corresponded to only the 25th percentile of the male subjects. Hand-grip strength was linearly correlated with LBM. Furthermore, both relative hand-grip strength parameters (F (max)/body weight and F (max)/LBM) did not show any correlation to hand dimensions. The present findings show that the differences in hand-grip strength of men and women are larger than previously reported. An appreciable difference still remains when using lean body mass as reference. The results of female national elite athletes even indicate that the strength level attainable by extremely high training will rarely surpass the 50th percentile of untrained or not specifically trained men.

Physical performance, body weight and BMI of young adults in Germany 2000 - 2004: results of the physical-fitness-test study.

In westernized countries the sedentary lifestyle in conjunction with a hypercaloric diet has caused an increase in the number of obese adults. Moreover, recent studies suggest that the prevalence of overweight in children increased during the last decade. However, the literature has to be interpreted with some caution since the majority of epidemiological studies examining health, fitness, and obesity rely on self-reported data rather than measurements. A further limitation is that most studies examine either physical activity or nutrition, only few deal with both aspects simultaneously. In the present study we analyzed both aspects in more than 58,000 persons aged between 17 and 26 years. All of them were applicants for the German Bundeswehr, which accepts only volunteers with school leaving certificates and a body mass index (BMI) below 30 kg . m (-2). The admitted subjects performed a Physical-Fitness-Test (PFT) consisting of 5 simple sport tests (shuttle run, sit-ups, push-ups, standing jump, Cooper test). For 23 000 subjects additional measurements of body height and body weight as well as information about their education level were available. These data were combined with the PFT results. We found large deficits in the physical fitness of young adults: More than 37 % of the participants failed to pass the PFT, with failure rates of the male volunteers increasing significantly since 2001. While the female volunteers showed virtually constant body weight and BMI, the corresponding values of men increased monotonously between the age of 17 and 26 years. Physical fitness was positively, BMI negatively correlated with education level. The present findings suggest that body weight increases and fitness decreases in non-obese young adults in Germany. Despite the correlations between BMI and physical fitness the terms "overweight" and "physically unfit" should not be regarded as synonyms.

Recovery of hand grip strength and hand steadiness after exhausting manual stretcher carriage.

Rescue activities frequently require not only substantial and sustained hand-grip forces but also a subtle coordination of hand and finger muscles, e.g. when manipulating injection syringes after manual stretcher carriage. We investigated the recovery kinetics of manual coordination and muscle strength after exhausting stretcher carriage (4.5 km/h, load at each handle bar: 25 kg). Hand steadiness (frequency and duration of wall contacts when holding a metal pin into a small bore) and parameters of hand-grip strength were determined in 15 male volunteers before and immediately after the stretcher carriage. Measurements were repeated after 0.5, 1, 4 and 24 h of recovery. Mean carrying time was 215+/-87 s (SD), mean transport distance amounted to 264+/-104 m. During the carriage test, forces at the stretcher handles oscillated in the order of +/-50 N within each gait cycle. Immediately after exhaustion, hand steadiness was significantly deteriorated (threefold increase in frequency and duration of wall contacts), maximum and mean hand-grip force over 15 s were reduced by almost 20%. While the recovery of hand steadiness was complete by minute 30 after stretcher carriage, a significant reduction in maximum and mean hand-grip force by 12% could still be observed after 24 h. The present findings demonstrate that hand steadiness recovers much faster than maximum hand-grip strength after exhaustive manual stretcher carriage (less than 30 min vs. more than 24 h). Probably, muscle damage induced in particular by the eccentric components during stretcher transport seems to affect only the generation of large forces. By contrast, the generation and coordination of the much lower forces required for hand-steadiness appears to be impaired only during the short transient of metabolic recovery.

[Psychological results of mental performance in sleep deprivation]. / Psychologische Ergebnisse zur mentalen Leistungsfähigkeit bei Schlafdeprivation.

To quantify the effects of sleep periods that have different lengths of time during continuous operations (CONOPS) 2 independent groups of subjects performed several cognitive tasks for 3 days. The 72 h trial period contained three 60-min sleep periods for the 10 subjects of the experimental group and three sleep periods of 4 h each for the 14 subjects of the control group. With the exception of only one subtest the statistical analyses of the test results of the 2 groups show no significant differences in cognitive performance. It is suggested that high motivation is responsible for comparable performance of the subjects, which was essentially obtained by a monetary pay system for successful test performance.