Temperature, relative humidity and water absorption in ski boots

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1 Available online at Procedia Engineering 13 (2011) th Asia-Pacific Congress on Sports Technology (APCST) Temperature, relative humidity and water absorption in ski boots Patrick Hofer a, Michael Hasler a, Gulnara Fauland b, Thomas Bechtold b, Werner Nachbauer ac* a Centre of Technology of Ski and Alpine Sport, Innsbruck, Austria b Institute of Textile Chemistry/Physics, Innsbruck, Austria c Department of Sport Science, University of Innsbruck, Innsbruck, Austria Received 5 April 2011; revised 30 April 2011; accepted 2 May 2011 Abstract Besides mechanical properties the quality of ski boots is determined by their comfort characteristics. Boot climate is a major comfort measure, especially cold feet affect comfort. The purpose of the study was to determine the microclimate in ski boots during skiing. The boot climate was assessed by temperature, relative humidity and water absorption. Temperature and relative humidity were measured using 4 sensors placed on the foot above the metatarsophalangeal joints of the first and second toe, in the arch of the foot sole, on the dorsum of the foot above os cuneiforme II, and between liner and shell at the medial ankle. To determine the amount of absorbed water in liners and socks a precision balance was used. Two subjects were recorded during five skiing days. Two low and two high quality ski boots of two different boot producers were used for the tests. During all measurements the temperature inside the ski boot decreased when skiing at ambient temperature between -6.8 C and 6.0 C. The temperature at the toes dropped in four cases clearly below 20 C. High relative humidity values up to 93% and high water absorption in socks and liners up to 45.5 g were observed. The results indicate that the ski boot temperature was not affected by ski boots of low quality. It is recommended to reconsider the basic construction of liners in order to improve their moisture management. One possible improvement may be to construct the liner in a way that sweat and potentially melted snow are stored as far away as possible from the foot. In this case the outer layer of the liner should have a higher water uptake than the inner layer. In addition, highly hydrophobic sock materials should be selected in order to keep the socks dry and to avoid that the feet get wet Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of RMIT University Keywords: Ski boots; foot temperature; foot relative humidity * Corresponding author. Tel.: ; fax: address: werner.nachbauer@uibk.ac.at Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi: /j.proeng

2 Patrick Hofer et al. / Procedia Engineering 13 (2011) Introduction Besides mechanical properties the quality of ski boots is determined by their comfort characteristics. Comfort of ski boots is related to the correct fit of the boot and to the microclimate in the boot. Temperature is the most critical factor for assessing thermal wear comfort [1]. Temperature is determined by coldness, duration of the exposure to cold, level of physical activity, and moisture in the boot [2,3]. Ski boots possess quit good insulation properties. But water vapour transportation through the ski boot liner is in general hindered by laminated liner materials. However sweat or melted snow in the liner increase the thermal conductance and leads to insulation break downs [4,5,6]. Despite of the importance of the temperature management for feeling comfortable there are almost no data about the ski boot climate available. So the purpose of this study was to determine the microclimate in ski boots during skiing assessed by temperature, relative humidity and water absorption. Additionally, different kinds of ski boots were compared. 2. Methods Temperature and relative humidity were measured in the liner between skin and sock using 4 SHT15 sensors (Sensirion Inc., CH). These sensors have a thickness of 2.5 mm and a surface area of 0.37 cm². The 4 sensors were placed on the foot above the metatarsophalangeal joints of the first and second toe (toe sensor), in the arch of the foot sole (sole sensor), on the dorsum of the foot above os cuneiforme II (dorsum sensor), and between liner and shell above the medial ankle (shell sensor). The signals were stored using a 122 g data logger fixed at the lower leg. To determine the amount of water in liner and sock a precision balance (Kern 500, Kern & Sohn GmbH, DE) was used. The weight of liner and sock respectively was recorded before and after skiing as well as after drying. From the relative humidity and temperature the absolute humidity was calculated. Additionally, ambient temperature and ambient relative humidity were recorded in the middle part of the slope with a meteorological station. Two subjects were recorded without rest between 1.6 and 5.4 hours per day. The subjects used their own skiing cloth. The subjects wore socks of the same type (Speedmachine, Nordica Inc., IT) of the following composition: 18% wool, 40% acrylic, 40% polyamide, and 2% elastane. Two low (L1,L2) and two high quality ski boots (H1,H2) of two different boot producers (Head Inc., Austria and Tecnica Inc., Italy) were used for the tests. During recording the buckles of the boots were locked. The trials were carried out in ski resorts around Innsbruck, Austria from November 2009 to March All the procedures concerning participants were approved by the Institutional Review Board. The subjects were detailed informed regarding the objectives and conditions of the tests. Their consent to participate was confirmed by their signature. 3. Results Table 2 gives an overview of the collected data. During the tests ambient temperature ranged between -6.8 C and 6.0 C and ambient relative humidity between 36.0% and 69.5%. The mean of the minimal temperatures of the 6 measurements were 18.2 ± 3.4 C at the toe sensor, 28.6 ± 1.1 C at the dorsum sensor, 28.6 ± 1.7 C at the sole sensor, and 8.1 ± 3.5 C at the shell sensor. The temperature at the toes dropped in four cases clearly below 20 C and the differences between toes and the rest of the foot was in all tests above 5 C. The lowest temperatures were measured on the toe with 13.9 C, on the dorsum with 25.7 C, on the sole with 25.8 C, and between shell and liner with 5.2 C. Figure 1 shows exemplarily the temperature in the ski boots for subject 1 during wearing different ski boots. During these tests mean ambient temperature and humidity were 5.2 ± 0.6 C and 65 ± 1.1% for

3 46 Patrick Hofer et al. / Procedia Engineering 13 (2011) (H1) and 1.6 ± 0.4 C and 52 ± 1.1% for (L1). A similar temperature pattern for the different boots and activity was measured. At the beginning of each test the foot temperature showed the highest value and subsequently a clear decrease to the ambient temperature within circa 1 hour occurred. H1 L1 Fig. 1. Temperature in a high (H1) and a low quality ski boot (L1) during skiing. The relative humidity ranged from 50 to 93% at the toe, from 22 to 89% at the dorsum, from 30 to 91% at the sole, and from 16 to 87% between shell and liner at the ankle during the measurements. The mean values for the absolute humidity were 15.9 ± 1.2 g/m³ at the toe, 22.6 ± 0.7 g/m³ at the dorsum, 16.8 ± 1.5 g/m³ at the sole, and 5.2 ± 0.7 g/m³ at the shell sensor during the tests. The mean weight gains of the socks were 4.3 g and of the liner 26.3 g for an average test period of 4 h. Figure 2 shows exemplarily the relative humidity in the ski boots for subject 1 corresponding to the temperature values in Figure 1. The curves show an increase of all sensors. The slightly later increase of the relative humidity of the shell sensors is due to the temperature drop shown in Figure 1. Notable are the low dorsum sensor values in comparison to the other sensors. H1 L1 Fig. 2. Relative humidity in a high (H1) and a low quality ski boot (L1) during skiing.

4 Patrick Hofer et al. / Procedia Engineering 13 (2011) Figure 3 presents the absolute humidity in the H1 and L1 ski boots. The mean values during the tests were 14.0 ± 2.2 g/m³ (H1) and 12.0 ± 2.3 g/m³ (L1) at the toe, 23.3 ± 1.8 g/m³ and 18.8 ± 1.7 g/m³ at the dorsum, 14.5 ± 1.1 g/m³ and 12.4 ± 1.1 g/m³ at the sole, and 6.4 ± 0.8 g/m³ and 5.8 ± 0.7 g/m³ at the shell sensor, respectively. The socks were quite wet (H1 left 2 g/right 2 g after 5.4 h; L1 left 2 g/right 2.5 g after 4.1 h). On average the H1 liner absorbed 14.5 g of water and the L1 liner 7.5 g. H1 L1 Fig. 3. Absolute humidity in a high (H1) and a low quality ski boot (L1) during skiing. 4. Discussion During all measurements the temperature inside the ski boot decreased when skiing at ambient temperature between -6.8 C and 6.0 C. The temperature at the toes dropped in four cases clearly below 20 C and the differences between toes and the rest of the foot was in all tests above 5 C, both limiting values for causing discomfort and pain sensation [4]. Due to the absence of big foot muscles the foot is warmed mainly by blood flow. However, the blood flow is already significantly reduced at foot temperatures below 25 C [7,8]. This problem may be amplified in ski boots since bad fitting of the ski boot may reduce the blood flow additionally. Moreover, once the flow through the superficial veins of the lower leg has ceased, re-warming the foot does not produce superficial flow until the whole body is sufficiently warmed [7]. A relatively low level of cooling is sufficient to decrease muscle performance and increase injury risk [9]. In particular, an increase in knee injuries at low ambient temperatures for female skiers is reported [10]. For steering the skis fine movements of the foot are necessary. It is speculated that the motor control of the foot is affected by cooling. However, several other factors which may contribute to the increase of knee injuries by cooling are discussed. Cooling increased the latency of soleus H-reflex, which is an important mechanism in controlling motor behaviour of the lower leg [11]. The muscle fibre conduction velocity of knee muscles was slower with cooling [12]. The ability to maintain dynamic balance in females was reduced by cooling of the lower leg [13]. The results revealed high relative humidity values up to 93% and high water absorption in socks and liners up to 45.5 g during skiing. It is reported that high values of moisture reduce the thermal insulation of shoes [4,14,15] and ski boots [6]. So the measured decrease in temperature during skiing may be partially due to the increase of moisture in the ski boot. The source of moisture gain may be sweating. Also the penetration of snow with subsequent melting has to be taken into account. Further test protocol in the climate camber allowed to eliminate the possible effect of melted snow.

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6 Patrick Hofer et al. / Procedia Engineering 13 (2011) The results indicate that the ski boot temperature was not affected by ski boots of low quality. It seems that thermal resistance of the tested ski boots was about the same. This may be explained by the use of similar liner materials. The middle layer of the tested liners was made of polymer foam and the outer layer was a textile fabric with plastic coating. Differences in the liners were mainly found in the design, e.g. superficial material inserts mainly in the calf zone. 5. Conclusion Based on this study it looks important to prevent cooling of the feet especially of the toes during skiing. It is recommended to reconsider the basic construction of liners in order to improve their moisture management. One possible improvement may be to construct the liner in a way that sweat and potentially melted snow are stored as far away as possible from the foot. In this case the outer layer of the liner should have a higher water uptake than the inner layer. In addition, highly hydrophobic sock materials should be selected in order to keep the socks dry and to avoid that the feet get wet. An important aspect is also the overnight drying of the liners to avoid a reduction in thermal resistance. Acknowledgements This research was financially supported by the Interreg IV project Verletzungsprävention im alpinen Skilauf: Sicherheit als Erfolgsfaktor alpiner Regionen (SkiProTech) and the Austrian Research Promotion Agency FFG K-PROJECT Nr Sports Textiles. References [1] Senthilkumar P, Dasaradan BS. Comfort properties of Textiles. IE(I) Journal-TX 2007;88:3-4. [2] Gavin T. Clothing and Thermoregulation during Exercise. Sports Med 2003;33(13): [3] Rissanen S, Rintamäki H. Extremity Cooling and Re-warming Rates during Military Activities in Winter. In: RTO Human Factors and Medicine Panel (HFM). Symposium in Helsinki, Finland; April [4] Kuklane K. Protection of Feet in Cold Exposure. Ind. Health 2009;47: [5] Kuklane K, Holmer I, Giesbrecht G. Change of Foot Insulation at Various Sweating rates. Appl. Human Sci. 1999;18(5): [6] Heus R, Schols E, Kistemaker L. Frostbite in Ski Boots for Marines. In: Prevention of Cold Injuries RTO Human Factors and Medicine Panel (HFM). Specialists Meeting, Amsterdam; May [7] Kaufmann WC. The hand and foot in the cold. The Physician and Sportsmedicine 1983;11: [8] Allwood MJ, Burry HS. The effect of local temperature on blood flow in the human foot. J Physiology 1954;124: [9] Oksa J, Rintamaki H, Rissanen S. Muscle performance and electromyogram activity of the lower leg muscles with different levels of cold exposure. Eur J Appl Physiol Occup Physiol 1997;75: [10] Ruedl G, Fink C, Schranz A, Sommersacher R, Nachbauer W, Burtscher M. Impact of environmental factors on knee injuries in male and female recreational skiers. Scand J Med Sci Sports 2011; (in press) [11] Dewhurst S, Riches PE, Nimmo MA, De Vito G. Temperature dependence of soleus H-reflex and M wave in young and older women. Eur J Appl Physiol 2005;94: [12] Dewhurst S, Macaluso A, Gizzi L, Felici F, Farina D, De Vito G. Effects of altered muscle temperature on neuromuscular properties in young and older women. Eur J Appl Physiol 2010;108: [13] Piedrahita H, Oksa J, Rintamaki H, Malm C. Effect of local leg cooling on upper limb trajectories and muscle function and whole body dynamic balance. Eur J Appl Physiol 2009;105:

7 50 Patrick Hofer et al. / Procedia Engineering 13 (2011) [14] Kuklane K, Holmer I. Effect of Sweating on Insulation of Footwear. Int. J. of Occup. Safety and Ergonomics 1998;4(2): [15] Kuklane K, Gavhed D, Fredriksson K. A field study in dairy farms: thermal condition of feet. Int. J. Industrial Ergonomics 2001;27:

Frostbite in Ski Boots for Marines

Frostbite in Ski Boots for Marines Ronald Heus 1,2), Ed Schols 1) and Lyda Kistemaker 2) 1) TNO Science and Industry P.O. Box 6235, NL5600HE Eindhoven, The Netherlands 2) TNO Defence, Safety and Security, P.O. Box 23, NL3769ZG Soesterberg,