Energy Expenditure at Rest Physical Activity Mc Ardle

Energy Expenditure at Rest & Physical Activity Mc. Ardle, Katch, & Katch Chapter 8

Energy Expenditure at Rest n Basal Metabolic Rate n n 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 n When RMR expressed per unit LBM, no n

Energy Expenditure at Rest n Influence of Body Size Differences in body size usually expressed in terms of body surface area (BSA). n From 20 -40, average values BMR are 38 kcal/m 2 per hour for men and 36 kcal/m 2 for women. n Lower BMR in women can be attributed to woman’s larger percent body fat & smaller muscle mass. n

Energy Expenditure at Rest n Estimate Resting Daily Energy Expenditure n n n Estimate kcal expenditure during rest by multiplying one’s surface area from nomogram by appropriate kcal expenditure/m 2 per hour by 24 hrs. Also possible to use Harris Bennedict formulas. Estimated values w/i ± 5% measured values.

Energy Expenditure at Rest Components of Total Daily Energy Expenditure n n Physical Activity: 15 -30% of TDEE Dietary Induced Thermogenesis (~10% TDEE) n n Thermic effect from processes of digesting, absorbing, & assimilating nutrients. Thermogenesis reaches maximum w/i 1 hr post Thermogenesis can vary 10%35% of ingested food energy Resting Metabolic Rate

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

Energy Expenditure in Physical Activity n Expression of Energy Expenditure Total (gross) – Resting energy expenditure (REE) = Net energy cost of the activity per se. n Recovery energy included in Total = exercise energy + recovery energy. n Utilization of 1 liter of O 2 generates about 5 kcal of energy. n Net O 2 cost of exercise = exercise VO 2 + recovery VO 2 – (resting VO 2 x time)

Energy Expenditure in Physical Activity n n 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.

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

Energy Expenditure in Physical Activity n Classification of Work Factors: n n Duration (min) and Intensity (VO 2 & k. Cal) A MET is a measure of activity intensity & represents an average person’s resting metabolism or VO 2 1 MET = 3. 5 ml kg 1 min-1

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

Economy & Efficiency of Energy Expenditure n n Mechanical Efficiency = Work Output ÷ Energy Input (expenditure). Work Output = Force x Distance n n kg m or ft lb. Three efficiency terms: 1. 2. 3. Gross Net Delta

Economy & Efficiency of Energy Expenditure Gross efficiency uses total oxygen uptake. Work Output Energy Expended n Net efficiency subtracts resting VO 2 from total. Work Output Energy Expended Above Rest n Delta efficiency computes relative energy cost of performing an additional increment n

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

n Energy Expenditure during Walking, Running, and Swimming Energy Expenditure during Walking n n 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.

n n n 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.

Energy Expenditure during Running n n 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 VO 2 more than shortening below optimum (and increasing stride frequency). Cost of running into headwind significantly

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

Energy Expenditure during Swimming n n 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.

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