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chapter 4

chapter 4. Energy Costs of Physical Activity. Ways to Measure Energy Expenditure. Direct calorimetry: transfer of body heat to water Indirect calorimetry: measure VO 2 uptake Convert VO 2 to kilocalories: use caloric equivalent of O 2 (4.7-5.0 kcal . L –1 ). Measuring Oxygen Uptake.

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chapter 4

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  1. chapter4 Energy Costsof Physical Activity

  2. Ways to MeasureEnergy Expenditure Direct calorimetry: transfer of body heat to water Indirect calorimetry: measure VO2 uptake Convert VO2 to kilocalories: use caloric equivalent of O2 (4.7-5.0 kcal . L–1) . .

  3. Measuring Oxygen Uptake Closed-circuit system: Breathe 100% O2. Open-circuit system:Breathe room air. Measure timed volume of exhaled air.Measure O2 and CO2 content.Calculate VO2 by standard procedures. .

  4. Ways to ExpressEnergy Expenditure . • VO2: L · min–1 • Kcal · min–1VO2 (L · min–1) x kcal · L–1 • VO2: ml · kg–1 · min–1 • METsVO2 (ml · kg–1 · min–1)/3.5 ml · kg–1 · min–1 • Kcal · kg–1 · hr–1 . . .

  5. Estimating the Energy Costof Activities • Estimates have a standard deviation of about 7% to 9%. • Estimates represent the steady-state cost of the activity. • Total O2 cost = net cost of activity + 3.5 ml · kg–1 · min–1.

  6. Estimating the Oxygen Costof Walking Good for speeds from 1.9 to 3.7 mi · hr–1 (50 to 100 m · min–1) VO2 = [horizontal component] + [vertical (grade) component] + rest. .

  7. What Is the Oxygen Uptakeof a 176 Lb (80 Kg) Person Walkingat 3 mi · hr–1 on a 10% Grade? Given: 1 mi · hr–1 = 26.8 m · min–1; 1 L O2 = 5 kcal; 1,000 ml = 1 L 3 mi · hr–1 = 80 m · min–1; fractional 10% grade = 0.10 (continued)

  8. What Is the Oxygen Uptakeof a 176 Lb (80 Kg) Person Walkingat 3 mi · hr–1 on a 10% Grade? (continued) . VO2 = [8 ml · kg–1 · min–1 ] + [14.4 ml · kg–1 · min–1 ] + 3.5 ml · kg–1 · min–1 VO2 = 25.9 ml · kg–1 · min–1. .

  9. Estimating the Oxygen Costof Running . VO2 = [horizontal component] + [vertical (grade) component] + rest.

  10. What Is the Oxygen Uptakefor Running at 6 mi · hr–1 (161 m · min–1)? Note that the vertical component is 0 because the grade is 0. VO2 = [32.2 ml · kg–1 · min–1] + 3.5 ml · kg–1 · min–1 VO2 = 35.7 ml · kg–1 · min–1. . . (continued)

  11. What Is the Oxygen Uptake for Running at 6 mi · hr–1 (161 m · min–1)? (continued) How many METs is that? 35.7 ml · kg–1 · min–1/3.5 ml · kg–1 · min–1 = 10.2 METs.

  12. Oxygen Cost of Cycle Ergometry . VO2 (ml · kg–1 · min–1) = work + unloaded cycling + rest. VO2 (ml · kg–1 · min–1) = [1.8 ml · kgm–1 x work rate (kgm · min–1)]/kg + 3.5 ml · kg–1 · min–1 + 3.5 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = [1.8 ml · kgm–1 x work rate (kgm · min–1)]/kg + 7 ml · kg–1 · min–1. In watts (W), where 1 W = approximately 6 kgm: VO2 (ml · kg–1 · min–1) = [10.8 ml · W–1 x work rate (W)]/kg + 7 ml · kg–1 · min–1. . . .

  13. . What Is the VO2 of a 198 lb (90 kg) Person Working at 600 kgm · min–1? . VO2 (ml · kg–1 · min–1) = [1.8 ml · kgm–1 x 600 kgm · min–1]/90 kg + 7 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = 12 ml · kg–1 · min–1 + 7 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = 19 ml · kg–1 · min–1. . .

  14. Does the Same Work Rate Require a Greater Relative Effort by a 132 lb (60 kg) Person? VO2 (ml · kg–1 · min–1) = [1.8 ml · kgm–1 x 600 kgm · min–1]/60 kg + 7 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = 18 ml · kg–1 · min–1 + 7 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = 25 ml · kg–1 · min–1. . . .

  15. Oxygen Cost of Arm Cycle Ergometry . VO2 (ml · kg–1 · min–1) = work + rest. VO2 (ml · kg–1 · min–1) = [3 ml · kgm–1 x work rate (kgm · min–1)]/kg + 3.5 ml · kg–1 · min–1. In watts (W), where 1 W = approximately 6 kgm: VO2 (ml · kg–1 · min–1) = [18 ml · W–1 x work rate (W)]/kg + 3.5 ml · kg–1 · min–1. . .

  16. . What Is the VO2 for a 110 lb (50 kg) Person Working at 25 W on an Arm Ergometer? . VO2 (ml · kg–1 · min–1) = [18 ml · W–1 x 25 W]/50 kg + 3.5 ml · kg–1 · min–1. VO2 (ml · kg–1 · min–1) = 9 + 3.5 ml · kg–1 · min–1 = 12.5ml · kg–1 · min–1. .

  17. Oxygen Cost of Stepping . VO2 = [stepping back and forth] + [stepping up and down] + rest. VO2 = [0.2 ml · kg–1 · min–1 x step rate] + [1.8 ml · kgm–1 x 1.33 x height (m) x step rate] + 3.5 ml · kg–1 · min–1. .

  18. What Is the Oxygen Cost for Stepping at 30 steps · min–1on an 8 in. Step? Given: 1 in. = 2.54 cm or 0.0254 m, so 8 in. = 0.2 m. VO2 = [0.2 ml · kg–1 · min–1 x step rate] + [1.8 ml · kgm–1 x 1.33 x height (m) x step rate] + 3.5 ml · kg–1 · min–1. VO2 = [0.2 ml · kg–1 · min–1 x 30] + [1.8 ml · kgm–1 x 1.33 x 0.2 m x 30] + 3.5 ml · kg–1 · min–1. VO2 = [6 ml · kg–1 · min–1] + [14.36 ml · kg–1 · min–1] + 3.5 ml · kg–1 · min–1. VO2 = 23.9 ml · kg–1 · min–1. . . . .

  19. . What Is the Step Rate Needed to Achieve a VO2 of 30 ml · kg–1 · min–1 on an 8 in. Step? 30.0 = [0.2 x rate] + [1.8 x 1.33 x 0.2 x rate] + 3.5. 26.5 = 0.2 x rate + 0.4788 x rate. 26.5 = 0.6788 x rate. Rate = 26.5 / 0.6788 = 39 steps · min–1.

  20. Is the Energy Cost of Walking andRunning a Mile the Same? First determine the costs of each activity, given the information below. • Gross cost includes resting energy expenditure. • Net cost includes the cost of the activity alone. • Resting energy expenditure = 1 kcal · kg–1 · hr–1. For a 160 lb (72.6 kg) person, resting energy expenditure is 1.2 kcal · min–1.

  21. Gross Versus Net Cost of Walking Consider a 160 lb (72.6 kg) person who walks at 3 mi · hr–1 (4.8 km · hr–1 ) for 20 min: • Gross (total) cost per mile = 79 kcal. • Net cost = gross cost – cost of rest for 20 min (24 kcal). • Net cost = 55 kcal · min–1.

  22. Gross Versus Net Cost of Jogging or Running Consider a 160 lb (72.6 kg) person who jogs at 6 mi · hr–1 (9.7 km · hr–1 ) for 10 min: • Gross (total) cost per mile = 123 kcal. • Net cost = gross cost – cost of rest for 10 min (12 kcal). • Net cost = 111 kcal · min–1.

  23. Net Caloric Cost per Milefor a 160 lb (72.6 kg) Person

  24. Estimated Net Energy Cost of 30 min of Exercise at 70% HRR or VO2R . Body weight (lb)

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