Ronald Heus

Resultant clothing insulation: a function of body movement, posture, wind, clothing fit and ensemble thickness

Voor de modelvorming van de effecten van houding, beweging en wind is het belang van de kledinglagen veruit ondergeschikt aan dat van de ingesloten en aanhangende luchtlagen.

Clothing ventilation, vapour resistance and permeability index: changes due to posture, movement and wind

Veranderingen in de waterdampweerstand van kleding t.g.v. beweging en wind zijn af te leiden uit de verandering in warmteweerstand en een referentie meetwaarde.

Effects of temperature on electromyogram and muscle function

SummaryThe effects of 30 min of cooling (15°C water) and warming (40°C water) on arm muscle function were measured. A reference condition (24°C air) was included. Of nine young male subjects the maximal grip force (Fmax), the time to reach 66% ofFmax (rate of force buildup) and the maximal rhythmic grip frequency were determined, together with surface electromyographic activity (EMG) of a forearm muscle (flexor digitorum superficialis). The results showed that in contrast to warming, cooling resulted in a significant decrease of 20% in the FmaX and a significant 50% decrease in force build-up time and the maximal rhythmic grip frequency. The relationship between the root mean square value (rms) of the EMG and the static grip force did not change due to temperature changes. The median power frequency (MPF) in the power spectrum of the EMG signal decreased by 50% due to cooling but remained unchanged with heating. During a sustained contraction at 15% ofFmax (Fmax depending on the temperature) the increase in the rms value with contraction time was 90% larger in the warm condition and 80016 smaller in the cold condition compared to the increase in the reference condition. The MPF value remained constant during the warm and reference conditions but in the cold it started at a 50% lower value and increased with contraction time. Since the endurance time was not affected in the cold but 60% reduced in the warm, it was concluded that neither the rms nor the MPF reflected unambiguously the temperature related changes in functional performance of muscle strain with an equal relative load.

Physiological criteria for functioning of hands in the cold. A review

Hands are important instruments in daily life. Without hands man is hardly able to function independently. Proper functioning of the hands is determined by several physiological parameters. These physiological parameters in turn are influenced by environmental factors. In this view of the literature, physiological processes in manual dexterity are described and the influence of a cold environment on separate physiological processes is studied. In general, cold means loss of dexterity. For reasons of safety and performance, it is important to restrict the loss of manual dexterity. For this purpose, in this study minimum criteria are given for all separate physiological components. Most important minimum criteria are: a local skin temperature of 15 degrees C, a nerve temperature of 20 degrees C and a muscle temperature of 28 degrees C. Only during maximum dynamic work is a muscle temperature of 38 degrees C recommended. These temperatures are average values, and of course individual differences are evident.

Moisture accumulation in sleeping bags at - 7 degrees C and - 20 degrees C in relation to cover material and method of use.

Moisture accumulation in sleeping bags during extended periods of use is detrimental to thermal comfort of the sleeper, and in extreme cases may lead to sleep loss and hypothermia. As sub-zero temperatures were expected to affect vapour resistance of microporous membranes, the effect of using semipermeable and impermeable rain covers for sleeping bags on the accumulation of moisture in the bags during 6 days of use at − 7°C and 5 days at − 20°C were investigated. In addition, the routine of shaking off hoarfrost from the inside of the cover after the sleep period as a preventive measure for moisture accumulation was studied. Moisture accumulation (ranging from 92 to 800 grams) was found to be related to the vapour resistance of the materials used. The best semipermeable material gave the same moisture build-up as no cover at − 7°C, though build-up increased substantially at − 20°C. Shaking off the hoarfrost from the inside of the cover after each use was beneficial in preventing a high moisture build-up. It was concluded that semi-permeable cover materials reduce moisture accumulation in sleeping bags at moderate sub-zero temperatures, but in more extreme cold (− 20°C) the benefits are reduced in comparison to routinely shaking frost from impermeable covers. Compared to fixed impermeable covers, the benefits of all semi-permeable covers are large. For long-term use without drying facilities, the differences observed do favour the semi-permeable covers above impermeable ones, even when regularly removing the hoar frost from the inside in the latter.

Human energy expenditure when walking on a moving platform

Abstract The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (V˙O2, V˙CO2, V˙E and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m · s−1. Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J · kg−1 · m−1 vs 2.5 J · kg−1 · m−1, P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats · min−1 vs 103 beats · min−1, P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J · kg−1 · m−1 vs 2.7 J · kg−1 · m−1, P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform.

A method for assessing thermal comfort of shoes using a “sweating” foot

The conclusion is that our device for measuring water vapour absorption under different climatic conditions is very consistent, but in future we aim to connect the foot temperature simulation model with a measuring device in order to be able to measure the dynamic comfort of footwear.

Water vapour transport as determinant of comfort in evaluating shoes

Abstract Moisture disposal and thermal behaviour (shoe climate) over a number of hours is an important factor in shoe comfort, besides the fit of the shoes and energy (absorption). In most of shoe-testing laboratories these properties are frequently measured on materials, like leather linings and upper- or in-soles. Data for these materials can give an indication of the performance of the shoe, although differences can occur dependent on the shoe construction and the production methods used. At TNO, a test-method, the WSCR-method (Whole Shoe Comfort Rating), is set up where both the water vapour transport and thermal characteristics of complete shoes can be measured with the aid of an artificial foot. The method uses a flexible sock that is impermeable to water, but permeable to water vapour. This sock is placed into the shoe specimen, which is filled with water at a controlled temperature. The whole set-up is placed upon a balance (connected to a computer), in a laboratory (20°C and 65% relative humidity) or in a climatic chamber or box. The air speed is maintained at approximately 1 m/s. The Water Vapour Absorption, Water Vapour Permeability and Water Vapour Transport (WVT) are calculated from the measurements, as well as the average heat conductivity of the whole shoe. Five different trekking shoes were compared for (thermal) comfort. The results show that the shoe with the highest WVT-value have a 35% higher value than the shoe with the lowest value. For heat resistance, the same type of shoe had a 30% higher value than the lowest. The heat resistance and WVT values showed a significant negative correlation (−0.97; p

Maximal oxygen uptake during cycling is reduced in moving environments; consequences for motion-induced fatigue

In previous studies on physical fatigue during simulated ship movements, the apparent exhaustion of subjects after experimentation suggested that the traditional index of physical workload, oxygen consumption expressed as the percentage of peak oxygen consumption ([Vdot]O2-peak) measured in a separate graded exercise test (GXT), underestimates workload in a moving environment. In these studies, the GXT was carried out in a stationary environment, as is standard practice. To explain the underestimation, it was hypothesized that [Vdot]O2-peak might have been less if the GXT had been carried out in the moving environment. This paper reports on three experimental tests of this hypothesis, performed with a ship motion simulator and aboard a ship at sea. In all three experiments, [Vdot]O2-peak was indeed significantly reduced when the GXT was carried out in the moving environment. Theoretical reasons for this phenomenon are discussed and investigated, but a clear explanation is still lacking.

Positive pressure breathing during rest and exercise

The requirements to maintain a positive pressure with respiratory protection during heavy exercise and the effects on ventilation and feelings of discomfort were investigated. Eight male subjects participated, using the respirator system during rest and exercise at about 80% of their individual maximum power. A blower was used at maximum and medium capacity and at two pressure levels (3 and 15 mbar). Additionally, the mouth pressure was used as a feedback for the blower. The blower decreased the fraction of the breathing cycle with negative pressures from 50% (SD 4%) to 15% (SD 10%) during exercise. Negative pressures occurred at all settings of the blower during exercise. Thus, the currently available commercial blower systems do not supply a sufficient airflow to maintain a positive pressure during heavy exercise. Positive pressure breathing did not affect the ventilation and the circulation. But the oxygen consumption was higher with the blower and respirator than without.