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REGIONAL SWEAT RATES OF THE ARMS AND HANDS IN MALE SQUASH PLAYERS Caroline Smith, Vincent Ventenat and George Havenith Human Thermal Environments Laboratory, Loughborough University, UK Centre de Recherché DECATHLON, Lille, France Contact person:
[email protected] INTRODUCTION A number of studies have been conducted on regional sweat rates. However, data vary considerably. A problem with much of the work conducted in this field is that sweat rates are related to the thermal state of the body. The use of different thermal states during these studies means that many of the results are not directly comparable. Data have tended to show great individual variation in regional sweat rates. Another issue is that much of the research has only measured sweat rates in a single location of each body region, consequently providing data that is specific to only a limited area of skin. This is mainly a result of the use of ventilated capsules as the predominant method of sweat collection, which only measure an area of 2-3 cm2. To obtain more detailed information regarding regional sweat rates, an absorbent method of sweat collection has been developed which allows the simultaneous measurement of large areas of the body. The aim of this experiment was to quantify regional sweat rates on the arms and hands of male squash players, and to gather baseline physiological data which can be used to aid in the design and development of racket sports equipment. METHODS Ten male subjects (age: 38 ±13 years, height: 176 ±6.3 cm, weight: 77.6 ±6.3 kg) who were regular squash players, attended the Human Thermal Environments Laboratory for two sessions. The first was a measurement session, during which arm and hand dimensions were taken for the calculation of absorbent pads. The second was an experimental session which was conducted in a glass backed squash court at an ambient temperature of 26.1±1.8°C and relative humidity of 67±6% to simulate summer conditions and induce thermal sweating. Following the measurement session, two sets of absorbent pads were produced for each subject. These were weighed inside labelled airtight bags, in which they were stored until testing. A total of 8 pads were used, covering the anterior and posterior upper and lower arm. Cotton gloves were used for sweat collection on the hands, with latex gloves placed over them to prevent the evaporation of sweat during the test periods. To limit the migration of sweat between zones of the glove small incisions were made across the base of each finger. On arrival to the experimental session subjects were provided with shorts and t-shirt and then weighed. Infra red images of the nude, dried, skin were taken prior to testing, before and after each pad application, and immediately after testing to monitor skin temperature. Resting heart rate and aural canal temperature were taken before subjects warmed up, with heart rate monitored throughout the experiment at 15 second intervals. The subject played squash for a total of 60 minutes against another player who was not being tested. The subject could drink water freely during the experiment to prevent dehydration, with volumes recorded. The target heart rate of the subject during the testing was 140-160 beats per minute (bpm), which was set to the control workload. Sweat samples were taken at 25 min and 50 min during the experiment, for a duration of 10 min. The subjects removed the shirt and towelled the skin dry immediately prior to pad application, to ensure only sweat produced during the sample period was collected. Pads were applied and held in place using a stretch zip t-shirt. All of the pads had an impermeable backing to prevent evaporation. Cotton gloves were applied to the hands 285
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and latex gloves were placed over the top. Immediately following the sample period the pads were returned to their airtight bags and sealed. The cotton gloves were cut along the borders of the palm, back of the hand, and the fingers, before being placed in individual airtight bags. Between the two sample periods, pre-weighed wristbands and absorbent pads were applied to each wrist on the subject. Following the 60-min squash session, the weight and aural canal temperature of the subject were recorded. On completion of the experimentation all pads were reweighed inside their airtight bags. The surface area of each pad was calculated from the dry weight of each pad and the weight per unit of surface area of a piece of control material. The sweat rate was calculated in grams per meter square per hour (g.m-2.h-1) using the weight change of the pad, the pad surface area, and the length of time the pad was applied to the skin. RESULTS The data indicate large variation in both individual regional sweat rates and gross sweat loss. For example, sweat rates for the back of the right hand varied from 160 to 940 g.m-2.h-1 between subjects, whilst those for the right posterior lower arm range from 184 to 989 g.m-2.h1 . This large variation in sweat rate can be seen across all of the regions which were tested. Individual gross sweat loss ranged from 278 to 997 g.m-2.h-1. Figure 1 illustrates the median sweat rates for the arms and hands during both sample periods, in addition to the wristbands which were worn between the two samples. Sweat rates were higher on the arms than the hands, however the wrists showed the highest values.
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Figure 1. Median sweat rates (g.m-2.h-1) and interquartile range for the arms and hands during a 60-min squash session, with the wristbands applied between samples.
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Sweating Figure 2 shows the skin temperature of nude, dry skin during the experiment. An increase in skin temperature can be observed following the application of pads, followed by a decrease once the pads had been removed. The increase in skin temperature following the second sample period was smaller than that following the first sample period. 35
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Figure 2. Skin temperature (°C) of the arms and hands during the 60 minute squash session. DISCUSSION Any method used in the collection of sweat will itself interfere with the sweat rate to some degree. For absorbent use, two factors may cause opposing effects: an increase in skin humidity may be expected during sampling periods using the absorbent method, acting to lower the regional sweat rate due to hidromeiosis. Conversely, an increase in skin temperature may occur, as observed in the results, serving to artificially increase the regional sweat rate. These factors were minimised during testing due to pad application time not exceeding 10 minutes, although an increase in skin temperature, particularly for the first sample period, was observed following sample periods. Data showed large variation in individual sweat rates, however the patterns across regions were quite consistent. All subjects were physically active, which implies there will be some degree of acclimatisation with regards to their sweat rate. Sweat rates were observed to be highest on the lower anterior and posterior arm, followed by the back of the hand. Regions showing the lowest sweat rates were the anterior and posterior upper arm, followed by the thumb, and finally the fingers and palm. The regions showing the highest sweat rates showed median values of 643 g.m-2.h-1 and 567 g.m-2.h-1for the anterior lower and posterior lower arm respectively. The regions showing the lowest sweat rates provided values of 179 g.m-2.h-1 for finger 2 (middle finger) and 192 g.m-2.h-1 for finger 4 (little finger). Sweat rates were slightly lower in the second sampling period, however a decrease in heart rate was observed indicating a reduction in the intensity of exercise. High sweat rates on the wrist bands, which were worn with no other pads in place at that time, indicated there was a migration of sweat down the arm, in addition to the sweat produced at the wrist itself. This finding has an
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important role in the design of racket sports equipment, in particular grip design, and shows the relevance of the use of sweat absorbing wristbands in preventing sweat from the arm reaching the hand. REFERENCES Cotter, J. D., Patterson, M. J., and Taylor, N. A. S., 1995. The topography of eccrine sweating in humans during exercise. Eur. J. Appl. Physiol., 71, 549-554 Havenith, G., 2001. An individual model of human thermoregulation for the simulation of heat stress response. J. Appl. Physiol., 90, 1943-1954 Nadel, E. R., Bullard, R. W., and Stolwijk, J. A. J., 1971. Importance of skin temperature in the regulation of sweat. J. Appl. Physiol., 31(1), 80-87 Weiner, J. S., 1945. The regional distribution of sweating. J. Appl. Physiol., 104, 32-40
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