Comparisons of maximal phosphofructokinase (PFK) activity (a), glucose (Glu) content (b), and free fatty acid (FFA) content (c) in the myocardium of Eurasian Tree Sparrows (Passer montanus) between high altitude (3230 m) and low altitude (80 m) areas. The statistical results are shown in Table 1. The asterisk represents a significant difference (P < 0.05) between groups