# Week 4: Exercise physiology Lab Flashcards

What are the clinical applications of indirect calorimetry?

Assess functional capacity (VO2 max or symptom limited capacity.

Assess submaximal responses: metabolic efficiency

Diagnostic - e.g cause of dyspnea

Prognostic - identify risk of adverse effect/suitability for surgery

Evaluate impact on intervention - exercise programme

Exercise prescription

Nutritional - energy expenditure

Occupational assessment - deep sea divers

Metabolic cost of activity - economy and efficiency in terms of oxygen usage.

What is the metabolic threshold?

The point at which metabolic demands of exercise can no longer be met aerobically and an increase in anaerobic metabolism occurs. Reflected by an increase in blood lactate concentration and fatigue onset. Mirrored by changes in the ventilatory response.

Also referred to as the lactate threshold, ventilatory threshold or anaerobic threshold.

What is indirect calorimetry measuring?

Quantifies gas exchange to estimate the energy expenditure of an individual.

Based on the respiration equation

Glucose + 6 O2 —-> 6CO2 + 6H2O and heat

Therefore measuring oxygen consumption can be used in a ratio to estimate heat production hence metabolic rate.

Assumes that pulmonary oxygen uptake is equal to oxygen uptake by tissues.

What is metabolic rate?

The rate of energy production by the body.

How does oxygen consumption relate to energy?

1L of oxygen consumption is equal to burning 5 kilocalories

What are the limitations of indirect calorimetry?

Oxygen consumption is only proportional to energy production in aerobic respiration - this will be limited to a certain level of activity reached at varying intensities in different tissues.

How does direct calorimetry work?

Chamber

Surrounded by a tank of a known volume of water

Give a known volume of oxygen into the tank and get the person to exercise

Measure the change in temperature of the water, use this to calculate the energy

What is closed circuit indirect calorimetry?

Breath from a known volume of oxygen, measure the change in volume of oxygen and energy expenditure is measured

What is open circuit indirect calorimetry?

Individual breaths from ambient air and expired air is analysed for carbon dioxide.

Use a ratio to calculate the oxygen consumption, then the energy expenditure.

How do you calculate the volume of oxygen consumed in calorimetry?

The changes in oxygen fractions

The changed in carbon dioxide fraction

The respiratory rate

Changes in baormetric pressure

Room temperautre

What is total energy expenditure?

The amount of hear used by humans body for daily functioning.

Includes basal energy expenditure or resting metabolic rate

Diet-induced thermogenesis

Active energy expenditure (exercise)

What equations can estimate the resting metabolic rate?

What do they require?

Harris Benedict Equation - sex, age, height and weight

Miffline-St Jeor - sex, weight height and age

What is the Harris-Benedict equation?

Male

66.5 +(13.8*body mass in Kg) + (5.0*height in cm)- 6.75* age in years

Female

655.1 + (9.6* body mass in Kg) + (1.84 * height in cm) - 4.6756 * age in years)

Calculates resting metabolic rate

What is the Mifflin St-Jeor equation?

Calculates resting metabolic rate

Male = 5 + (10xweight kg) + (6.25xheight in cm) - (5 x age in years)

Women = (10xweight kg) + ( 6.25 x height cm) - (5* age in yrs) - 161

How can we calcute energy expenditure by oxygen consumption?

VO2max (L.min-1) * (60*24) * 4.8kcal.min-1

Must be awake in supine, 10 hours after a meal, no physical activity within 8 hours, no strenuous exercise in last 24 hours, state of mental relaxation, ambient suitable temperature (Standard conditions)

Why are different equation have different outcomes for basal metabolic rate?

Developed by testing on different populations

Indirect measurements have inherent measures e.g incorrect use of equipment/calibration

Based on different research results

What makes up total energy expenditure?

resting metabolic rate - 60-70%

Diet induced thermogenesis - 6-10%

Physical activity - 20-30%

What factors influence total energy expenditure?

Age - decrease as age (loss of skeletal muscle)

Sex - higher in males (more lean)

Lean body mass

Hormones

Genetics

Temperature

Pregnancy etc

What clincal features increase resting metabolic rate?

Inflammation

Obesity

Physical agitation

Stress

Metabolic acidosis

Hyperventilation

Hyperthermia

Hyperthyroidism

What clinical features decrease resting metabolic rate?

Coma/deep sleep

Heavy sedation

Hypothermia

Gluconeogenesis

Metabolic alkalosis

Starvation

Sarcopenia