. The Canadian field-naturalist. Natural history. BMR Running Speed (m ⢠s'1) Figure 1. Post-absorptive basal metabolic rate (BMR; W ⢠kg1) and metabolic rate in one Arctic Fox running on a treadmill at three different speeds in January (solid squares) and in July (open squares) (n = the number of experiments). The equations describing the relation- ships between metabolic rate and running speeds are: Metabolic rate in January = â v + (n = 9; r = ); Metabolic rate in July = ⢠v + (n = 20;r = ). 210- n=8 n=6 n=6 195- 180- 165- 150- 135- 120- 105n rest 90 "- s
. The Canadian field-naturalist. Natural history. BMR Running Speed (m ⢠s'1) Figure 1. Post-absorptive basal metabolic rate (BMR; W ⢠kg1) and metabolic rate in one Arctic Fox running on a treadmill at three different speeds in January (solid squares) and in July (open squares) (n = the number of experiments). The equations describing the relation- ships between metabolic rate and running speeds are: Metabolic rate in January = â v + (n = 9; r = ); Metabolic rate in July = ⢠v + (n = 20;r = ). 210- n=8 n=6 n=6 195- 180- 165- 150- 135- 120- 105n rest 90 "- s: 75- ^-rV/â^- â'âiâ'âiâ<- âiââ âiââ âi Running Speed (m ⢠s"1) Figure 2. Post-absorptive mean heart rate (bpm) in one Arctic Fox running on a treadmill at three different speeds in July (n = the number of experiments). ning was about 15% lower in January compared to July (Table 2). HR, which was measured only in July, increased with running speed (Figure 2). There was a significant positive linear relationship between HR and metabolic rate at increasing running speeds (Figure 3). The equation describing the relationship between the two variables is: [7] Metabolic rate = + ⢠HR (n = 19; r2 = ; p< ), where metabolic rate is in W ⢠kg"1 and HR is beats -min1. Starvation for 11 days induced a reduction in meta- bolic rate during running, with up to 11% lower values in January and 14% in July (Table la). Starvation for 11 days decreased the net cost of running from post- absorptive values by up to 13% in January, and 17% in July (Table 2). HR measured in July decreased after 11 days starvation by up to 27% at different running speeds (Table la).. 120 140 160 180 200 220 Heart rate (beats min'1) Conventionally, the net cost of running is expressed as the energy needed for moving 1 kg a distance of 1 m, also referred to as the efficiency of locomotion (Dewasmes et al. 1980; Fuglei and 0ritsland 1999a). In the post-abso
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