Energy Expenditure at Rest & Physical Activity

1. Energy Expenditure at Rest & Physical Activity McArdle, Katch, & Katch Chapter 8

2. Energy Expenditure at Rest • Basal Metabolic Rate • BMR is rate of energy expenditure fasted, rested and supine conditions in thermoneutral environment. • Resting Metabolic Rate (RMR) is rate of energy expenditure when at rest but not basal (> BMR). • BMR proportional to BSA, after age 20  2% & 3% per decade in women and men, respectively • When RMR expressed per unit LBM, no difference • BMR represents largest fraction of TEE in sedentary

3. Energy Expenditure at Rest • Influence of Body Size • Differences in body size usually expressed in terms of body surface area (BSA). • From 20-40, average values BMR are 38 kcal/m2 per hour for men and 36 kcal/m2 for women. • Lower BMR in women can be attributed to woman’s larger percent body fat & smaller muscle mass.

4. Energy Expenditure at Rest • Estimate Resting Daily Energy Expenditure • Estimate kcal expenditure during rest by multiplying one’s surface area from nomogram by appropriate kcal expenditure/m2 per hour by 24 hrs. • Also possible to use Harris Bennedict formulas. • Estimated values w/i ± 5% measured values.

5. Energy Expenditure at Rest Components of Total Daily Energy Expenditure • Physical Activity: 15-30% of TDEE • Dietary Induced Thermogenesis (~10% TDEE) • Thermic effect from processes of digesting, absorbing, & assimilating nutrients. • Thermogenesis reaches maximum w/i1 hr post • Thermogenesis can vary 10%-35% of ingested food energy • Resting Metabolic Rate

6. Energy Expenditure at Rest • Factors affecting Total Daily Energy Expenditure • Climate. • RMR of people in tropic climate averages 5-10% higher. • RMR in extreme cold can triple. • Pregnancy.

7. Energy Expenditure in Physical Activity • Expression of Energy Expenditure • Total (gross) – Resting energy expenditure (REE) = Net energy cost of the activity per se. • Recovery energy included in Total = exercise energy + recovery energy. • Utilization of 1 liter of O2 generates about 5 kcal of energy. Net O2 cost of exercise = exercise VO2 + recovery VO2 – (resting VO2 x time)

8. Energy Expenditure in Physical Activity • Energy expended during weight-bearing activities increases proportional to body mass. • There is little relationship between body mass and energy expended during non-weight-bearing activities.

9. Energy Expenditure in Physical Activity • Average daily Total Energy Expenditure estimated to be 2900 – 3000 kCal for males, and 2200 kCal for females 15-50 y.o.a. • Great variability exists because of one’s physical activity; average person spends ___% day sedentary.

10. Energy Expenditure in Physical Activity • Classification of Work Factors: • Duration (min) and Intensity (VO2 & kCal) • A MET is a measure of activity intensity & represents an average person’s resting metabolism or VO2 1 MET = 3.5 mlkg-1min-1

11. Energy Expenditure in Physical Activity • Classification of Work • Intensity of Work often related to Heart Rate because of linear relationship to oxygen uptake.

12. Economy & Efficiency of Energy Expenditure • Mechanical Efficiency = Work Output ÷ Energy Input (expenditure). • Work Output = Force x Distance • kg  m or ft  lb. • Three efficiency terms: • Gross • Net • Delta

13. Economy & Efficiency of Energy Expenditure • Gross efficiency uses total oxygen uptake. Work Output Energy Expended • Net efficiency subtracts resting VO2 from total. Work Output Energy Expended Above Rest • Delta efficiency computes relative energy cost of performing an additional increment of work.

14. Energy Expenditure during Walking, Running, and Swimming • Economy is relationship between Energy output Energy input • Greater economy requires less oxygen uptake to perform a task. • Training adjustment that improves economy directly relates to improved exercise performance.

15. Energy Expenditure during Walking, Running, and Swimming • Energy Expenditure during Walking • Relationship between walking speed and oxygen uptake essentially linear between speeds of 3.0 and 5.0 kilometers per hour (1.9 to 3.1 mph). • At faster speeds, walking becomes less economical and relationship curves in upward direction.

16. Energy Expenditure during Walking, Running, and Swimming • Walking on snow and sand requires about twice the energy expenditure of walking on hard surfaces. • Energy cost is proportionally larger for larger people. • Hand-held weights increases energy cost of walking but may disproportionately elevate systolic blood pressure.

17. Energy Expenditure during Running • More economical to discontinue walking and begin to run or jog at speeds > 6.5 kmh (4 mph). • Net energy cost of running a given distance is independent of speed (pace). • Lengthening stride above the optimum length (and reducing stride frequency) increases VO2 more than shortening below optimum (and increasing stride frequency). • Cost of running into headwind significantly greater than the reduction with tailwind.

18. Energy Expenditure during Swimming • Energy expenditure to swim a given distance is about 4 times greater than to run same distance. • Energy must be expended to maintain buoyancy while generating horizontal motion and to overcome drag forces. • Total drag consists of: • Wave drag • Skin friction drag • Viscous pressure drag

19. Energy Expenditure during Swimming • Elite swimmers expend fewer calories to swim a given stroke at any velocity. • Women swim a given distance at lower energy cost than men because of greater buoyancy.

20. Illustration Reference • McArdle, William D., Frank I. Katch, and Victor L. Katch. 2006. Essentials of Exercise Physiology 3rd ed. Image Collection. Lippincott Williams & Wilkins.