INTRODUCTION
The popularity of walking and running as fitness exercises has increased in recent years. Modifications are constantly being made to find the ideal intensity to maintain a fat burning zone. At various intensity levels of walking and running, each activity will use a specific percent of carbohydrates (CHO) and fats. Ultimately, the intensity of the exercise may decide the fuel source. CHO is primarily used during higher intensity exercise, whereas fats are the main contributors for low intensity, longer duration exercise. The longer the intensity is maintained at a steady state, the greater amount of stored fuel that is utilized with a shift toward increased expenditure of fat. Walking on an incline significantly increases the intensity, promotes fuel consumption, and changes the fuel source over walking on a flat surface. If the intensity during incline walking is comparable to the intensity during jogging, the metabolic effect of jogging could be achieved while walking with less susceptibility to injury. The purpose of this study was to determine the difference in metabolic demand and fuel utilization during walking and running at equivalent heart rate intensities.

METHODS
Eight (4 M, 4 F) moderately active college students randomly performed a 20-minute walk and a 20-minute run at an intensity equivalent to 70% of maximal heart rate on a motor-driven treadmill. Test order was randomly assigned. The walk was performed at 5.6 km/hr (3.5 mi/hr) with the incline adjusted to reach the same heart rate as recorded during running. During running, the treadmill remained level, and speed was adjusted to reach approximately the same heart rate as recorded during walking.

Pulmonary ventilation (V_E), VO₂, Kcal/min, and respiratory exchange ratio (R) were recorded from a computerized metabolic cart during the final 8 minutes of exercise, and the values were averaged for analysis. Percent fuel utilization was determined from steady-state R values. Heart rate was recorded from a Polar^TM heart rate monitor throughout the exercise.

RESULTS
There was no significant difference between walking and running at the same heart rate intensity for V_E, VO₂, Kcal/min, R, %CHO utilization, or %fat utilization (Table 1).

CONCLUSION
When exercising at equivalent intensities, there is no significant difference in the metabolic stress and fuel utilization between walking and running. The training benefit derived from walking should be the same as during running when metabolic and cardiac demands are approximately equal. The use of incline walking could reduce the potential of injury due to the higher impact during running. The major drawback is the requirement of an incline to achieve the same intensity during walking as during running.

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Table 1. Comparison between Walking and Running at the Same Heart Rate Intensity Varable Walking Mean Walking SD Running Mean Running SD t VE (L/min) 44.5 12.7 48.6 10.9 1.8 VO2 (L/min) 1.6 0.6 1.8 0.6 1.5 VO2 (ml/kg/min) 23.9 5.1 26.5 5.2 1.7 VCO2 (L/min) 1.5 0.5 1.6 0.5 1.3 Kcal/min 7.9 2.9 8.8 2.9 1.7 R (VCO2/VO2) 0.9 0.03 0.9 0.02 0.2 % CHO 71.2 9.8 70.0 8.2 0.2 % Fat 28.8 9.8 30.0 8.2 0.2

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