Overview and Basics of Exercise Physiology

1. Overview and Basics of Exercise Physiology Dianna Purvis MS, ACSM Sr. Scientist/Educator CHAMP HPRC

2. Topics to Cover • Background • Skeletal Muscle Fiber Types • Energy Systems • Physiological Responses to Exercise • Maximal Aerobic Capacity and Exercise Testing • Terms and Concepts Associated with Exercise

3. As a Nation…We Are Getting Fatter

4. Role of Physical Activity in Disease

5. Why Is This Important? • The importance of cardiorespiratory fitness (VO2 max) cannot be overemphasized • ↓cardiorespiratory fitness = ↑ morbidity & mortality all causes • Despite importance of high aerobic fitness, public health surveys show a high level of poor aerobic fitness in the US population

6. How Much Exercise? • Daily Aerobic Activity • 10,000 steps per day • 150 – 300 min/week (CDC) • ACSM guidelines • Strength exercises 2-3 times per week • Body weight • Resistance • Stretch daily • Consider yoga for flexibility and stress management

7. CDC/ACSM • http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html(CDC) • http://www.acsm.org(ACSM) • http://www.aafp.org/online/en/home/clinical/publichealth/aim/foryouroffice.html(AIM: Exercise Prescription Tools for Clinicians)

8. Skeletal Muscle

9. Skeletal Muscle Fiber Types • Slow-Twitch Type I • Fast-Twitch Type IIa Type IIx • Characterized by differences in morphology, histochemistry, enzyme activity, surface characteristics, and functional capacity • Distribution shows adaptive potential in response to neuronal activity, hormones, training/functional demands, and aging

10. Characteristics of Human Muscle Fiber Types

11. ATP Is GeneratedThrough 3 Energy Systems • ATP-PCr system • Glycolyticsystem • Oxidative system The process that facilitates muscular contraction is entirely dependent on body’s ability to provide & rapidly replenish ATP

12. Energy Systems for Exercise

13. 1. The ATP–PCr System

14. ATP-PCr Stores Deplete Rapidly

15. 2. The Glycolytic System • Requires 10-12 enzymatic reactions to break down glycogen to pyruvate or lactic acid, producing ATP • Occurs in the cytoplasm • Glycolysis does not require oxygen (anaerobic) • Without oxygen present, pyruvic acid produced by glycolysis becomes lactic acid • ATP-PCr and glycolysis provide the energy for ~2 min of all-out activity

16. Glycolysis

17. Conversion of Pyruvic Acid to Lactic Acid

18. Energy Sources for the Early Minutes of Intense Exercise The combined actions of the ATP-PCrand glycolytic systems allow muscles to generate force in the absence of oxygen; thus these two energy systems are the major energy contributors during the early minutes of high-intensity exercise…

19. 3. The Oxidative System • The oxidative system uses oxygen to generate energy from metabolic fuels (aerobic) • Oxidative production of ATP occurs in the mitochondria • Can yield much more energy (ATP) than anaerobic systems • The oxidative system is slow to turn on • Primary method of energy production during endurance events

20. Oxidative Metabolism

21. Common Pathways for the Metabolism of Fat, Carbohydrate, and Protein

22. Energy Transfer Systems and Exercise 100% % Capacity of Energy System Anaerobic Glycolysis Aerobic Energy System ATP - CP 10 sec 30 sec 2 min 5+ min Exercise Time

23. Glycolysis ß-Oxidation Aerobic and Anaerobic ATP Production Pyruvate Limited O2 Lactate Acetyl-CoA ATP Krebs Cycle FADH2 NADH+H+ H2O + ATP

24. Pulmonary & Cardiovascular System Changes with Onset of Exercise

25. Pulmonary Ventilation • Minute ventilation or VE (L/min) = Tidal volume (L/breathing) X Breathing rate (Breaths/min) • Measure of volume of air passing through pulmonary system:air expired/minute

26. Stroke Volume (SV) • Amount of blood ejected from heart with each beat (ml/beat)

27. Cardiac Output (CO) • Amount of blood ejected from heart each min (L/min) • CO = SV X HR • Rest: ~ 5 L/min • Exercise: ~10 to 25 L/min • Stroke Volume x Heart Rate • Fick Equation: VO2= CO X (a - v O2) • Primary Determinant = Heart rate

28. Maximal Oxygen Consumption (Aerobic Power or VO2 max) • Greatest amount of O2 a person can use during maximal physical exercise • Ability to take in, transport and deliver O2 to skeletal muscle for use by tissue • Expressed as liters (L) /min or ml/kg/min • Single most useful measurement to characterize the functional capacity of the oxygen transport system • Provides a quantitative measure of capacity for aerobic ATP resynthesis

29. Heart Rate and VO2max 100 90 80 70 % of Maximal Heart Rate 60 50 40 30 0 20 40 60 80 100 % of VO2max

30. Factors Affecting VO2max Intrinsic • Genetic • Gender • Body Composition • Muscle mass • Age • Pathologies Extrinsic • Training Status • Time of Day • Sleep Deprivation • Dietary Intake • Nutritional Status • Environment

31. Determinants of VO2max • Muscle Blood Flow • Capillary Density • O2 Diffusion • O2 Extraction • Hb-O2 Affinity • Muscle Fiber Profiles • Cardiac Output • Arterial Pressure • Hemoglobin • Ventilation • O2 Diffusion • Hb-O2 Affinity Peripheral Factors Central Factors

32. Requirements for VO2max Testing • Minimal Requirements • Work must involve large muscle groups • Rate of work must be measurable and reproducible • Test conditions should be standardized • Test should be tolerated by most people • Desirable Requirements • Motivation not a factor • Skill not required

33. Typical Ways to Measure VO2max • Treadmill (walking/running) • Cycle Ergometry • Arm Ergometry • Step Tests

34. Common Criteria Used to Document VO2 max • Primary Criteria • < 2.1 ml/kg/min increase with 2.5% grade increase often seen as a plateau in VO2 • Secondary Criteria • Blood lactate ≥ 8 mmol/L • RER ≥ 1.10 • ↑ in HR to 90% of age predicted max +/- 10 bpm • RPE ≥ 17

35. Aging, Training, and VO2max 70 Athletes Moderately Active 60 Sedentary 50 40 VO2max (ml/kg/min) 30 20 10 0 20 30 40 50 60 70 Age (yr)

36. Effect of Bed rest on VO2max 0 %Decline in VO2max 1.4 - 0.85 X Days; r = - 0.73 -10 % Decline in VO2max -20 -30 -40 0 10 20 30 40 Days of Bedrest Data from VA Convertino MSSE 1997

37. VO2max Classification for Men (ml/kg/min) Age (yrs) 20 - 29 30 - 39 40 - 49 50 - 59 60 - 69 Low <25 <23 <20 <18 <16 Fair 25 - 33 23 - 30 20 - 26 18 - 24 16 - 22 Average 34 - 42 31 - 38 27 - 35 25 - 33 23 - 30 Good 43 - 52 39 - 48 36 - 44 34 - 42 31 - 40 High 53+ 49+ 45+ 43+ 41+

38. VO2max Classification for Women (ml/kg/min) Age (yrs) 20 - 29 30 - 39 40 - 49 50 - 59 60 - 69 Low <24 <20 <17 <15 <13 Fair 24 - 30 20 - 27 17 - 23 15 - 20 13 - 17 Average 31 - 37 28 - 33 24 - 30 21 - 27 18 - 23 Good 38 - 48 34 - 44 31 - 41 28 - 37 24 - 34 High 49+ 45+ 42+ 38+ 35+

39. Terms and Concepts Associated with Exercise • Rating of Perceived Exertion • Training Heart Rate • Energy Expenditure • Thresholds and Exercise Domains • O2 Deficit and Excess Post-Exercise O2 Consumption

40. Approaches to Determining Training Heart Rate • Rating of Perceived Exertion • Training Heart Rate • 60 to 90% of Maximal HR • Max HR = 180 • 60% = 108 and 90% = 162 • 50 to 85% of Heart Rate Reserve • Max HR = 180 and Resting HR = 70 • HRR = 180 - 70 = 110 • 50% = 70 + 65 = 135; 85% = 94 + 70 = 164 • Plot HR vs. O2 Uptake or Exercise Intensity

41. 6 7 Very, very light 8 9 Very light 10 11 Fairly light Lactate Threshold 12 13 Somewhat hard 14 2.0 mM Lactate 15 H ard 2.5 mM Lactate 16 17 4 .0 mM Lactate Very hard 18 19 Very, very hard Rating of Perceived Exertion: RPE/Borg Scale

42. Estimating Maximal Heart Rate • OLD FORMULA: 220 – age • NEW FORMULA: 208 - 0.7 X age • New formula may be more accurate for older persons and is independent of gender and habitual physical activity • Estimated maximal heart rate may be 5 to 10% (10 to 20 bpm) > or < actual value.

43. Energy Expenditure • MET: Energy cost as a multiple of resting metabolic rate • 1 MET = energy cost at rest ~3.5 ml of O2/kg/min • 3 MET = 10.5 ml of O2 /kg/min • 6 MET = 21.0 ml of O2 /kg/min • 1 L/min of O2 is~ 5 kcal/L • VO2 (L/min) ~ 5 kcal/L = kcal/min • 1 MET = 0.0175 kcal/kg/min

44. Lactate/Lactic Acid • A product of glycolysis formed from reduction of pyruvate in recycling of NAD or when insufficient O2 is available for pyruvate to enter the Krebs Cycle • Extent of lactate formation depends on availability of both pyruvate and NAD • Blood lactate at rest is about 0.8 to 1.5 mM, but during intense exercise can be in excess of 18 mM

45. Intensity of exercise at which blood lactate concentration is 1 mM above baseline Production exceeds clearance Expressed as a function of VO2max, i.e., 65% of VO2max Can indicate potential for endurance exercise Lactate formation contributes to fatigue Impairs oxidative enzymes Lactate Threshold

46. 1.0 mM above baseline Lactate Threshold

47. Pyruvate:Lactate

48. Blood Lactate as a Function of Training Blood Lactate (mM) 25 50 75 100 Percent of VO2max

49. Ventilatory Threshold • Point at which pulmonary ventilation increases disproportionately with oxygen consumption during an increase in workload • At this exercise intensity, pulmonary ventilation no longer links tightly to oxygen demand at the cellular level

50. Lung Muscle RBC Ventilatory Threshold • During incremental exercise: • Increased acidosis (H+ concentration) • Buffered by bicarbonate (HCO3-) H+ + HCO3- H2CO3 H2O +CO2 • Marked by increased ventilation disproportionate to increase in workload