a) Your resting oxygen consumption is 0.45 L/min and this value increases to 5.0

Question

a) Your resting oxygen consumption is 0.45 L/min and this value increases to 5.0 L/min after running at a speed of 8.5 mph on a treadmill at a grade of 1% for 15 minutes. Calculate your resting metabolic rate and your exercising metabolic rate if your respiratory exchange ratio was 0.75 at rest and 0.95 during your treadmill run. Use the table below to determine the kCal/LO2 for the RERs provided. (12 points) b) What is the likely cause for the change in RER from 0.75 to 0.95 (6 points). c) What might explain an RER above 1.0? (2 points) TABLE 5.1 Respiratory Exchange Ratio (RER) as a Function of Energy Derived From Various Fuel Mixtures % Kcal from Carbohydrates Fats RER (kcalL O) 0 16 100 84 67 49 32 16 0.71 0.75 4.74 0.80 4.80 0.85 0.90 4.92 0.95 1.00 4.69 51 68 84 100 4.86 4.99 5.05

Explanation / Answer

We know that calorie expenditure during exercise can be calculated by :

Oxygen consumed per minute [L/min] x ( Respiratory Exchange ration[RER] x Energy expenditure for that RER ) x Duration of exercise in minute

= 5.0 x ( 0.95 x 4.99 [ using the given chart] ) x 15

=355.54 Kcal/ 15 minute

= 23.70 Kcal /min

Same way At rest

0.45 x ( 0.75 x 4.74 ) Kcal/min

= 1.6 Kcal /min

So the answer is: Metabolic rate is (resting) = 1.6 Kcal/min, during exercise = 23.7 Kcal / min.

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b.)

We know that respiratory Exchange rate = CO2 production / O2 consumption. So during exercise carbon dioxide production is more than oxygen consumption. Now how is this?

During vigorous exercise the main utilized substrate for energy production is glucose. You can see from the chart that at an RER of 0.95, 84% of the energy comes from glucose metabolism. Now you know that the metabolism of glucose produces carbon dioxide. As the usage of carbohydrate ( glucose from 16% at resting state to 84% during exercise, from the given chart) increases during exercise than the Fat, carbon dioxide production rate increase sharply. So naturally, the RER which is a simple ratio of produced carbon dioxide and oxygen consumed increases during exercise.

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c.) Continuous strenuous exercise causes use of 100% carbohydrate for energy production--> as a result of this RER becomes 1.0 ( as well as respiratory quotient becomes 1.0). But there is lactic acid production in the muscle which is released into the blood--> blood buffers those lactic acid by releasing more carbon dioxide dissolved in the blood ---> so more carbon dioxide released ---> RER becomes more than 1.0

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