Changes in respiratory exchange ratio (RER). White circles with the dotted line indicate summer data (n = 17, mean ± S.E), and black squares with the solid line indicate winter data (n = 17, mean ± S.E). In winter, RER was significantly greater over the course of the experiment than it was in summer. In addition, RER was significantly lower during cold exposure in winter than it was during that same period in summer. *P < 0.05, **P < 0.01 when summer and winter values were compared.