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Sock Material and Warm-Up Effects on Foot Temperature during Treadmill Running Tej M. Patel, 1 Nicholas J. Oestreich, 2 Mitchell L. Post, 2 Brandon J. Ross, 1 Alyssa C. Schmidt, 2 Brent T. Shelton, 3 Julie E. Smith, 4 Travis L. Stinson, 2 Nickolas Van Roekel, 1 Rachel M. Barkley, 1 David S. Senchina 5 1 Biochemistry, Cell, and Molecular Biology Program; 2 College of Business & Public Administration; 3 College of Education; 4 College of Pharmacy & Health Sciences; 5 Biology Department, Drake University, Des Moines, IA, 50311 ABSTRACT: Manufacturers market a variety of athletic socks to runners with varying claims of comfort and ergogenic properties. This study (approved by Drake IRB ID 2009-10088) investigated how foot temperature during running was modulated by different socks. Additionally, the influence of a short warm-up period prior to data collection was investigated. Sixteen male subjects (21.3 1.4 yrs) completed four 10-minute running trials at self-selected but constant speeds in four different socks: cotton, synthetic, a cotton/synthetic blend, and a combination of the blend sock plus a calf compression sleeve. Eight subjects performed a 5-minute warm-up at approximately 75% of their trial treadmill speed and eight did not warm up whatsoever. Foot temperature was recorded for the 10 minutes during running and 5 minutes immediately after. Heart rate and subjective ratings of perceived comfort and heat were recorded throughout. There were no significant differences in foot temperature across socks during or after running. Subjects perceived their feet as being warmer in the cotton and blend socks compared to the synthetic sock or the blend sock plus the sleeve. There were no differences in comfort perception across trials. Expectedly, there was a trial order effect for subjects who didn’t warm up such that foot temperature was higher in later trials compared to earlier trials. These results suggest that (a) socks of differing materials may transfer heat similarly, (b) wearing a calf compression sleeve influences perceptions of foot temperature, and (c) subjects’ perceptions of foot temperature may not coincide with actual temperature. INTRODUCTION: • The ability of a sock to dissipate foot heat generated during running may impact on performance in long-distance events and foot health over weeks of training. • Since 70% of sweat production occurs on the upper foot (and hence the bulk of evaporative cooling; [5]), it is the best location for measuring foot temperature. • The few studies available suggest that cotton content of a sock is unrelated to its heat transfer properties (1) and that, under previous experimental conditions, foot temperature is not influenced by cotton vs. synthetic socks (1,2,4). • Because these studies were limited in their scope, the purpose of our investigation was to examine the influence of sock material under more rigorous conditions with co-factors such as warm-up or presence of a compression sleeve. METHODS: Procedures were pre-approved by the Drake University Institutional Review Board (ID 2009-10088) . Sixteen males (21.3 1.4 yrs; stature = 181.9 1.6 cm, 73.8 2.4 kg) who could exercise in size 11.5 shoe, could run for 30 min, and have no precluding medical conditions participated. Subjects visited the lab for one experimental session involving four 10-min treadmill runs (Sole, Inc.) spaced by sitting 10-min rest periods. Trial order was counterbalanced and subjects had to run the same self-selected speed for all 4 trials (average 7.4 0.3 mph). Flexible thermistors (thermometers; YSI, Inc.) were attached to the upper right foot, lateral side midway across the arch using electrical tape, one against the skin and one at the same site between the sock and the shoe (Figure 1). Temperature was recorded from both sites during the 10-min run and the first 5-min of sitting rest. All subjects ran in a pair of Asics GT 2110 running shoes throughout the session (Figure 2b) This shoe has a mass of 411.2 g, as compared to the runners’ own average running shoe mass of 363.1 8.9g. Runners wore the same shoes under 4 different sock conditions (Table 1): cotton, blend, blend + compression sleeve , and synthetic. Heart rate was recorded throughout but no significant changes were documented and the data is not shown. Subjects’ self-rated perceptions of comfort and stability were assessed independently via 10-cm visual analogue scale (3) where subjects placed a mark along the scale where they perceived foot temperature or comfort, accordingly (see Table 2 for more explanation). Subjects were allowed water ad libitum. RESULTS: Tables 2 and 3—The change in foot temperature during running and rest was not significantly different between the different sock regimens in either the warm-up or the no warm- up groups (all p 0.504). However, there was a significant trial order effect in the no warm-up group for change in skin temp 0-10 min (p=0.033); expectedly, the effect was such that the change in foot temperature decreased with increasing trial number. Tables 4 and 5—There were significant differences in subject s’ perceptions of foot heat by sock regimen in the warm-up group (p=0.051) but not in the no warm-up group (p=0.101). Subjects in the warm-up group perceived their feet as being cooler when wearing the blend + sleeve as compared to wearing the blend alone (p=0.034) or the cotton (p=0.026). There was also a trend for subjects to perceive their feet as being significantly cooler when wearing the synthetic sock as compared to the cotton (p=0.058) or blend alone (p=0.076). Similar effects, though not significant, were seen in the no warm-up group. There were no differences in comfort ratings by sock for either the warm-up group (p=0.789) or the no warm-up group (p=0.669) (Tables 4 and 5). DISCUSSION: • Sock type was not a significant factor in running-induced changes in foot temperature (Tables 2 and 3). For a 10- minute run, the sock’s composition is not likely to impact on actual foot temperature. Whether this holds true for longer runs (more typically seen in runners) remains to be shown. • Despite the lack of difference in actual foot temperature across trials, subjects in the warm-up group perceived the blend + sleeve combination and synthetic sock as reducing foot temperature more than the blend alone or cotton (Table 3). Other researchers have similarly reported that actual foot temperature and subjects’ perception of foot temperature may not coincide (4). Since we did not see differences in comfort ratings, other factors must be influencing these results. REFERENCES: (1)Hennig EM, Sterzing T, Brauner T, Kroiher J (2010). http://www.staffs.ac.uk/isb-fw/ISBFootwear.Abstracts05/Foot22.Hennig.SockConstruction.pdf (2)Herring KM and Richie DH (1993). Journal of the American Podiatric Association 83(9): 515-522. (3)Mills K, Blanch P, Vicenzio B (2010). Medicine & Science in Sports & Exercise 42(10): 1966- 1971. (4)Purvis AJ and Tunstall H (2004). Ergonomics 47(15): 1657-1668. (5)Taylor NA, Caldwell JN, Mekjavic IB (2006). Aviation, Space, and Environmental Medicine 77(10): 1020-1027. Sock Type Manufacturer Composition Cotton S.A. Gear (TSA, Inc.) 100% cotton Blend Adidas Climalite (Adidas, Inc.) 53% polyester, 37% cotton, 8% olefin, 1% natural latex, 1% spandex Synthetic Heatgear (Under Armour, Inc.) 98% polyester, 2% spandex Calf Compression Sleeve Zoot Active (Zoot, Inc.) 70% polypropylyene, 30% spandex Table 1—Type and composition of socks used in this study. Figure 2 (left to right)— (a) Socks used including cotton (top), blend (middle), and synthetic (bottom) with sleeve shown rightmost. (b) Subject with compression sleeve. (c) Asics GT-2110 running shoe. Cotton Blend Blend + Sleeve Synthetic Skin, 0-10 min 2.06 0.33 2.23 0.33 2.68 0.32 2.14 0.32 Sock, 0-10 min 1.95 0.39 2.35 0.38 3.15 0.38 2.84 0.6=38 Skin, 10-15 min -0.33 0.25 -0.07 0.25 -0.41 0.24 -0.4 0.24 Sock, 10-15 min 0.37 0.15 0.33 0.14 0.11 0.14 0.15 0.14 Cotton Blend Blend + Sleeve Synthetic Skin, 0-10 min 2.19 0.3 2.53 0.29 2.44 0.3 1.91 0.27 Sock, 0-10 min 2.25 0.38 2.88 0.37 3.09 0.39 2.35 0.35 Skin, 10-15 min -0.05 0.17 -0.26 0.16 -0.04 0.17 0.12 0.16 Sock, 10-15 min 0.67 0.17 0.4 0.17 0.5 0.18 0.6 0.16 Tables 2 (above) and 3 (below)—Foot temperature change (expressed as C, mean standard error) at both skin and sock thermometer sites. Data for the warm-up group is shown in Table 2 (above) and data for the no warm-up group is shown in Table 3 (below). Cotton Blend Blend + Sleeve Synthetic Comfort 4.0 1.4 4.2 1.3 5.0 1.3 5.7 1.3 Heat 5.9 0.7 5.8 0.6 3.7 0.6 4.0 0.6 Cotton Blend Blend + Sleeve Synthetic Comfort 6.2 0.9 4.7 0.8 5.4 0.9 5.7 0.8 Heat 5.9 0.6 5.9 0.6 4.3 0.6 3.8 0.6 Tables 4 (above) and 5 (below)—Subjects’ perceptions of comfort and heat and assessed via a 10-cm visual analogue scale. A “0” indicates most uncomfortable/hot imaginable and a “10” indicates most comfortable/cool imaginable. Values are mean standard error. Data from the warm-up group is shown in Table 4 (above) and from the no warm-up group in Table 5 (below). Figure 1—Thermometer set-up (left to right). (a) “Skin thermometer” placed on the dorsal surface of the right foot arch, slightly lateral. (b) “Sock thermometer” placed next to the skin thermometer. (c) Both attached thermometers plus shoe.
