Metabolic Calculations

Transcription

1 Metabolic Calculations Chapter 5 and Appendix D J.S. Blevins, Ph.D. ACSM PD, ES, RCEP Importance of Metabolic Calculations It is imperative that the exercise physiologist is able to interpret test results and estimate energy expenditure. Optimizing exercise protocols. Exercise prescription. Weight loss. Metabolic Topics Work, Energy, Power as they relate to calorimetry Expressions of oxygen uptake Concept of the MET Metabolic calculations Case studies 1

2 Work and Energy Work - Application of force through distance Work = Force x distance (i.e.kg x m) Force is constant W = 70 kg x 0.75 meters 52.5 kg m or 515 Joules Energy capacity to perform work 1 kcal = 4,186 J CHO = 5.05 kcal LO 2 Fat = 4.74 kcal LO 2 Each L of O 2 consumed = 5 kcal Power Power Amount of work per 6 unit time work/time (I.e. kgm/min; Watt) 1 W = 6 kgm min -1 Note = For cycle ergometry you must account for kg distance the flywheel moves the kg with one turn rev min -1 I.e. Monarch = 6 m rev -1 Power = (2 kg x 6 m rev -1 x 60 rev min -1 ) = 720 kgm min -1 or W Energy Expenditure Understanding energy expenditure is important for weight loss, work tasks, exercise prescription, etc. Calorie - basic unit of measure of energy expenditure Direct and Indirect Calorimetry can be used to estimate energy expenditure 2

3 Calorimetry Direct Calorimetry Indirect Calorimetry Metabolic Chamber (enclosed) Slide 8 Closed or Open Circuit Spirometry Indirect Calorimetry, Slide 11, Slide 10 Calorimetry Calorimetry 3

4 Calorimetry Indirect Calorimetry Calorimetry Indirect Calorimetry: Variables Obtained Oxygen consumption and carbon dioxide production (VO 2, VCO 2 ) Respiratory exchange ratio (RER or R)- Noninvasive method to estimate the relative contribution of fat and CHO to energy metabolism RQ during steady state conditions VCO 2 /VO 2 Calorie/ energy expenditure i.e. 1 liter of VO2 = ~ 5 kcals 4

5 Need a link In research and in practice, we use information obtained from open-circuit spirometry to give us estimates of energy expenditure, aerobic power, and fuel utilization. For example, we can use oxygen consumption measures to help us determine caloric expenditure during exercise. Expressions for O 2 uptake (VO 2 ) Absolute (L min -1 or ml min -1 ): Can be used in a form that will yield rate of energy expenditure (1 L of O 2 = 5 kcal) Relative (ml kg -1 min -1 ): used to compare individuals of different body size and to better quantify aerobic fitness level 5

6 MET Clinically, the MET or Metabolic equivalent is used to express energy expenditure and to prescribe exercise in clinical settings. 1 MET = 3.5 ml kg -1 min -1 For example 80 kg man working at 2.5 L min -1 2,500 ml min -1 / 80kg = ml kg -1 min ml kg -1 min -1 / 3.5 = 8.9 METs Practice with O 2 calculations Man weighing 176 lbs has pk O 2 uptake = 4.4 L min -1 What is his relative oxygen consumption? How many METs is this? A woman weighing 140 lbs has VO 2 pk = 36.7 ml kg -1 min -1 What is her absolute oxygen uptake? How many METs is this? How many METs would 70% of her peak capacity be equivalent to? How many calories per minute is she burning at her peak? How many calories per minute is she burning at 70%? Quiz Met Calc (3 points per question) Man weighing 200 lbs has pk O 2 uptake = 4.0 L min -1 What is his relative oxygen consumption? How many METs is this? A woman weighing 155 lbs has VO 2 pk = 32.1 ml kg -1 min -1 What is her absolute oxygen uptake? How many METs is this? What is the difference between indirect and direct calorimetry? 6

7 Estimation of Energy Expenditure We can estimate energy expenditure through American College of Sports Medicine SM Metabolic Equations Special considerations for these equations Need to assure that person is at steady state in order to use equations There is a variance in prediction Need to consider environmental considerations No rail-holding and make sure equipment is calibrated Gross Vs. Net O 2 cost ACSM Metabolic Calculations Can estimate energy expenditure if you have Vertical component Horizontal component Resting component Useful conversions (Memorize) Always convert lb to kg (lb/2.2) Centimeters = in x 2.54 Convert speed from mph to m/min (mi/h X 26.8) 1Watt = 6 kgm min -1 Remember equivalents Watts to kgm min -1 kcals (3,500 kcals = 1 lb of fat gain or loss) 1 L O 2 = 5 kcals For weight loss purposes, always account for resting metabolic rate, weekly physical activity and energy expenditure, and food intake Metabolic Calculations (S=Speed; G=Grade) Walking VO 2 = (0.1 S) + (1.8 S G) Treadmill and Outdoor Running VO 2 = (0.2 S) + (0.9 S G) Leg Ergometry VO 2 = 1.8 (W M -1 ) + 7 OR VO 2 = 1.8 (work rate)/(bm) Arm Ergometry VO 2 = (18 W M -1 ) Stepping VO 2 = (0.2 F) + ( H f)

8 Useful calculation tips to live by Write down all known s and do any necessary conversions first. Calculate each component separately, then complete the calculation I.e. vertical, horizontal, resting Make sure your answer agrees with the question in numerical and unit form (always provide units!!!) Walking ( mph) VO 2 = (0.1 S) + (1.8 S G) Horizontal Vertical Rest S= speed in m min -1 (convert if needed) G= grade in decimal form (i.e., 5% is 0.05); if 0% grade, then vertical=0 R= resting component NOTE: VO 2 is reported as ml kg -1 min -1 Walking Example A client is walking on a treadmill at 3mph up a 5% grade. What is his VO2? VO2 = (0.1 x S) + (1.8 x S x G) S = 3.5 mph x 26.8 = 93.8 m/min G = 5% =.05 VO2 = (0.1 x 93.8) + (1.8 x 93.8 x.05) VO2 = ml/kgmin 8

9 Running (>5.0mph) VO2= (0.2 S) + (0.9 S G) Horizontal Vertical Rest All variables are the same as for walking NOTE: VO 2 is reported as ml kg -1 min -1 Running Example A client is running at 9mph, 1% grade. What is his VO2? VO 2 = (0.2 S) + (0.9 S G) mph 26.8 = 241.2m/min VO 2 = (0.2x241.2)+(0.9x241.2x.01)+3.5 VO 2 = VO 2 = 53.9 ml kg -1 min -1 Leg Ergometry VO 2 = 1.8 (work rate)/(bm) BM = Body mass (weight) of subject in kg Work rate in kgm min -1, convert when necessary 1 W= 6 kgm min -1 kgm min -1 =R D f R= resistance in kg D= distance of the fly wheel 6m for Monark 3m for Tunturi f= frequency in rpm NOTE: VO 2 is reported as ml kg -1 min -1 9

10 Arm Ergometry VO 2 = 3 (work rate)/(bm) Find work rate the same as leg ergometry Major difference: D=2.4 for Monark arm ergometer NOTE: VO 2 is reported as ml kg -1 min -1 Arm Ergometer Example A 50 Kg client exercises on a Monark cycle ergometer pedaling at 50 rpm with the resistance at.5 Kgs. What is her VO2? VO 2 = 3 (work rate)/(bm) Work rate = 0.5kg x 2.4m x 50rpm Work rate = 60 kgm/min VO 2 ml kg -1 min -1 = 3 (60)/(50) VO 2 = 180/ VO 2 = VO 2 = 7.1 ml kg -1 min -1 Stepping Ergometry VO 2 = (0.2 f) + ( H f) f=stepping rate H=height of step in m NOTE: VO 2 is reported as ml kg -1 min -1 10

11 Step Example 70 kg person using 18 steps min -1, 25 cm step VO 2 = (0.2 x f)+(1.33 x 1.8 x H x f) +3.5 VO 2 = (0.2 x 18) + (1.33x1.8x0.25x18) VO 2 = VO 2 = 14.4 ml kg -1 min -1 or 4.1 METs Practice Calculation (from pg 311) A 71-year-old man weighing 180 lb walks on a motor-driven treadmill at 3.5 mph and a 15% grade. What is his gross MET level? More Practice Calculations A client weighs 155 lbs was determined to have a VO2 pk of 45 ml/kg/min. What is his oxygen consumption in absolute terms? In METs? How many kcals/min is he expending? More on pages

12 and Even More Practice Calculations A cardiac patient has just entered your cardiac rehabilitation program and has an exercise prescription to exercise 40 minutes at 6 METs, 4 days per week and the client weight 210 lbs. Calculate the following Treadmill grade for a speed of 2.5 mph Step rate for a 4 inch bench Resistance for a monarch bike at 50 rpm Total caloric expenditure for each workout session Indirect Calorimetry for Estimation of Fuel Utilization During Exercise CHO (glucose) C 6 H 12 O 6 Oxidation C 6 H 12 O 6 + 6O 2 6 CO H 2 O R = VCO 2 /VO 26 =6 VCO 2 / 6 VO 2 = 1.0 FAT (C 16 H 32 O 2 ) Oxidation C 16 H 32 O O 2 16 CO H 2 O R = VCO 2 /VO 26 = 16 VCO 2 / 23 VO 2 =