Effect of ambient temperature on female endurance performance Julie Renberg a,b,n , Mariann Sandsund a , Øystein Nordrum Wiggen a , Randi Eidsmo Reinertsen a a SINTEF Technology and Society, Department of Health Research, P.O. Box 4760 Sluppen, NO-7465 Trondheim, Norway b Department of Biology, Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway article info Article history: Received 17 January 2014 Received in revised form 30 June 2014 Accepted 30 June 2014 Available online 4 July 2014 Keywords: Thermoregulation Cold Time to exhaustion Performance Female abstract Ambient temperature can affect physical performance, and an ambient temperature range of 4 °C to 11 °C is optimal for endurance performance in male athletes. The few similar studies of female athletes appear to have found differences in response to cold between the genders. This study investigated whether ambient temperature affects female endurance performance. Nine athletes performed six tests while running on a treadmill in a climatic chamber at different ambient temperatures: 20, 10, 1, 4, 9 and 14 °C and a wind speed of 5 m s 1 . The exercise protocol consisted of a 10-min warm-up, followed by four 5-min intervals at increasing intensities at 76%, 81%, 85%, and 89% of maximal oxygen consumption. This was followed by an incremental test to exhaustion. Although peak heart rate, body mass loss, and blood lactate concentration after the incremental test to exhaustion increased as the ambient temperature rose, no changes in time to exhaustion, running economy, running speed at lactate threshold or maximal oxygen consumption were found between the different ambient temperature conditions. Endurance performance during one hour of incremental exercise was not affected by ambient temperature in female endurance athletes. & 2014 Published by Elsevier Ltd. 1. Introduction Some winter sports athletes, such as cross-country skiers, are exposed to a wide range of ambient temperatures (T a ), which can be as high as 10 °C and as low as  20 °C during international competitive events. While solar radiation can increase the heat load on the body, rapid movement increases convective heat loss from the body. Wearing thin racing suits instead of traditional cold-weather clothing decreases protection against heat loss from the body. The effect of T a on performance has been widely studied in male subjects. These studies have found impaired endurance performance, measured as time to exhaustion (TTE), in cold (  20 °C and  15 °C) (Quirion et al., 1989; Sandsund et al., 1998) and warm (31 °C) (Rowland et al., 2008) environments compared to more neutral environments (20 °C, 23 °C and 19 °C respec- tively). A few studies have investigated performance in a wide variety of T a and have demonstrated that male athletes' optimal performance is achieved between  4 °C and 11 °C(Galloway and Maughan, 1997; Parkin et al., 1999; Sandsund et al., 2012; Sparks et al., 2005) . This temperature range can change according to the clothing worn, wind and relative humidity. Wearing standard cross-country skiing clothing in a gentle breeze, the temperature range for optimal performance for males is  4 °C to 1 °C (Sandsund et al., 2012). T a have been shown to have an effect not only on TTE, but also on performance-related physiological and metabolic responses, including running economy (Sandsund et al., 2012), running speed at lactate threshold (LT) (Sandsund et al., 2012) and maximal oxygen consumption (VO 2max )(Kruk et al., 1991; Oksa et al., 2004; Quirion et al., 1989). T a has a strong influence on skin temperature, and skin temperature is believed to indirectly reflect muscle temperature (Blomstrand et al., 1984; Oksa et al., 1997). Women have lower mean skin temperature (T skin ) than men when exposed to the same low T a (Stevens et al., 1987; Walsh and Graham, 1986). Dynamic muscular performance has been shown to be thermally dependent. For each 1 °C increase in muscle temperature, perfor- mance is improved by 2–5%; however if central temperature increases (i.e. hyperthermia), this positive relationship reverses and performance is impaired (Racinais and Oksa, 2010). A lower than optimum muscle temperature appears to reduce force and power (Ferretti et al., 1992), reducing muscle performance due to poorer coordination of working muscle groups (Oksa et al., 1997). Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jtherbio Journal of Thermal Biology http://dx.doi.org/10.1016/j.jtherbio.2014.06.009 0306-4565/& 2014 Published by Elsevier Ltd. n Corresponding author at: SINTEF Technology and Society, Department of Health Research, P.O. Box 4760 Sluppen, NO-7465 Trondheim, Norway. Tel.: þ47 911 54 489. E-mail addresses: Julie.Renberg@sintef.no (J. Renberg), Mariann.Sandsund@sintef.no (M. Sandsund), Oystein.Wiggen@sintef.no (Ø.N. Wiggen), Randi.E.Reinertsen@sintef.no (R.E. Reinertsen). Journal of Thermal Biology 45 (2014) 9–14