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Whilst exercising at steady state a client has an RER of 0.91

and a VO2 of 1.32 litres per minute. What is the client's energy
usage rate from carbohydrates in grams per minute?

1 Answer

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The client's energy usage rate from carbohydrates is approximately 0.875 grams per minute.

The RER (respiratory exchange ratio) is the ratio of carbon dioxide produced to oxygen consumed during exercise. It provides an estimate of the type of fuel being metabolized. An RER of 0.91 indicates that the client is predominantly using fat as fuel.

To calculate the energy usage rate from carbohydrates in grams per minute, we first need to calculate the total energy expenditure (TEE) in kilocalories per minute. We can use the following formula:

TEE (kcal/min) = VO2 (L/min) x energy equivalent of oxygen (kcal/L)

The energy equivalent of oxygen is 5.0 kcal/L for carbohydrates. Therefore:

TEE = 1.32 x 5.0 = 6.6 kcal/min

Next, we need to calculate the proportion of TEE that comes from carbohydrates. Since the RER is 0.91, the proportion of energy expenditure from carbohydrates is:

Carbohydrate proportion = (1 - RER) / (1 - 0.7)

Where 0.7 is the RER value for fat metabolism. Plugging in the values:

Carbohydrate proportion = (1 - 0.91) / (1 - 0.7) = 0.53

Therefore, the energy usage rate from carbohydrates is:

Carbohydrate energy usage rate (kcal/min) = TEE x carbohydrate proportion = 6.6 x 0.53 = 3.5 kcal/min

Finally, we need to convert this to grams per minute by dividing by the energy density of carbohydrates, which is 4.0 kcal/g:

Carbohydrate usage rate (g/min) = 3.5 / 4.0 = 0.875 g/min

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