Copyright © 2006 Lippincott Williams & Wilkins. Energy Expenditure During Rest and Physical Activity Chapter 8

Copyright © 2006 Lippincott Williams & Wilkins. Objectives Define basal metabolic rate, indicating factors that affect it Explain the effect of body weight on the energy cost of different forms of physical activity Identify factors that contribute to the total daily energy expenditure Outline different classification systems for rating the strenuousness of physical activity

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Describe two means to predict resting daily energy expenditure Explain the concept of exercise efficiency and exercise economy List factors that affect the energy cost of walking and running Identify factors that contribute to the lower exercise economy of swimming compared with running

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Energy Expenditure at Rest

Copyright © 2006 Lippincott Williams & Wilkins. Basal Metabolic Rate (BMR) The minimum energy required to sustain the body’s functions in the waking state

Copyright © 2006 Lippincott Williams & Wilkins. Basal Metabolic Rate (BMR) (cont’d) Is assessed by measurement of under the following standardized conditions –12 hours postabsorptive –No undue muscular exertion for at least 12 hours prior to measurement –Measured after the person has been lying quietly for 30 to 60 minutes in a dimly lit, temperature-controlled room

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Dietary-Induced Thermogenesis (DIT) Consuming food increases energy metabolism as a result of the following energy-requiring processes –Digestion of nutrients –Absorption of nutrients –Assimilation of nutrients The magnitude of DIT ranges from 10 to 35% of the ingested food

Copyright © 2006 Lippincott Williams & Wilkins. Energy Expenditure During Physical Activity

Copyright © 2006 Lippincott Williams & Wilkins. Thermic Effect of Physical Activity Profoundly affects total daily energy expenditure (TDEE) Accounts for ~15 to 30% of TDEE

Copyright © 2006 Lippincott Williams & Wilkins. Thermic Effect of Physical Activity (cont’d) Gross energy expenditure: The total energy expenditure for a given (exercise) time period Net energy expenditure: The energy expenditure solely attributed to physical activity after subtracting out the resting energy expenditure

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Effect of Body Mass Body size plays an important role in exercise energy requirements Energy expended during weight-bearing exercise increases directly with the body mass transported

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Metabolic Equivalent (MET) One MET represents an adult’s average, seated, resting oxygen consumption or energy expenditure –1 MET ~ 250 ml/min –1 MET = 3.5 ml/(kgmin)

Copyright © 2006 Lippincott Williams & Wilkins. Metabolic Equivalent (MET) (cont’d) The MET provides a convenient way to rate exercise intensity with respect to a resting baseline –2 MET = 7.0 ml/(kgmin) –10 MET = 35.0 ml/(kgmin)

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Heart Rate to Estimate Energy Expenditure HR and relate linearly throughout a broad range of aerobic exercise intensities Thus, HR may provide an estimate of (and energy expenditure) during physical activity However, factors other than influence HR response to exercise

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Energy Expenditure During Walking, Running, and Swimming

Copyright © 2006 Lippincott Williams & Wilkins. Factors Affecting Endurance Performance Aerobic power ( ) Efficiency of energy use Economy of movement

Copyright © 2006 Lippincott Williams & Wilkins. Efficiency Mechanical efficiency (ME): indicates the percentage of the total chemical energy expended that contributes to the external work output ME (%) = Work Output / Energy Expended100

Copyright © 2006 Lippincott Williams & Wilkins. Efficiency (cont’d) Expressions of ME –Gross mechanical efficiency –Net mechanical efficiency –Delta efficiency

Copyright © 2006 Lippincott Williams & Wilkins. Efficiency (cont’d) Factors influencing ME –Work rate –Movement speed –Extrinsic factors –Muscle fiber type –Fitness level –Body composition –Technique

Copyright © 2006 Lippincott Williams & Wilkins. Economy of Movement Reflects the relationship between energy input and output For example, at a given submaximum speed of running, cycling, or swimming, an individual with greater movement economy will consume less oxygen

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Stride Length, Frequency, and Running Speed Running speed can increase in 3 ways –Increase stride frequency –Increase stride length –Increase both stride length and frequency

Copyright © 2006 Lippincott Williams & Wilkins. Did You Know? Children are less economical runners than adults and require 20 to 30% more oxygen per unit of body mass to run at a given speed

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Did You Know? Swimming requires about four times more energy to swim a given distance compared to running

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Energy Cost of Drag Three components comprise the total drag force that impedes a swimmer’s forward movement –Wave drag –Skin friction drag –Viscous pressure drag

Copyright © 2006 Lippincott Williams & Wilkins. Effects of Buoyancy: Men vs. Women Women, on average, are more buoyant than men due to their greater fat mass The increased buoyancy translates to greater swimming economy The potential hydrodynamic benefit enjoyed by women becomes noteworthy during longer distances, when swimming economy takes on added importance