The Scientific Basis of Aerobic Fitness Chapter 3

Overview of Energy Metabolism large nutrients digested into smaller, usable fuels – carbohydrates  glucose – fats (triglycerides)  fatty acids – proteins  amino acids blood delivers fuels to muscle which transforms them into ATP (adenosine triphosphate) ATP is the universal “currency” used by tissues for energy needs food + O 2  ATP + CO 2 + H 2 O + heat

Energy Systems: Fuels primary form is glucose transported to muscle (and other tissues) via blood stored in liver and muscle as glycogen ATP produced more quickly from CHO than from fats or proteins CHO stores can be depleted Carbohydrates

Energy Systems: Fuels stored in adipose tissue and in muscle muscle uses fatty acids for fuel produce ATP more slowly than CHO during rest, provides >½ the ATP, but little during intense exercise fat stores not depletable Fats (triglycerides)

Energy Systems: Fuels split into amino acids in gut, absorbed, and transported by blood 1º role is providing building blocks for metabolic functions and tissue building provides 5-15% of fuel for ATP production Proteins

Overview of Energy Metabolism muscles have small ATP storage capacity 3 energy systems produce ATP – aerobic – 1º system for endurance events – anaerobic – 1º system for speed events – “immediate” – 1º system for power events systems may work simultaneously – depends upon exercise intensity and duration

Interaction of Energy Systems Aerobic system takes 2-3 min to fully activate Anaerobic glycolysis takes ~5 s to fully activate Immediate system can provide ATP immediately

Glycolysis uses only CHO occurs in sarcoplasm (cytoplasm of a striated muscle fiber) first step is glucose transport into muscle after entry, 2 ATP are used (with glucose) glucose (C6) is split into two C3 molecules final product is pyruvate 4 ATP are synthesized pyruvate forms either lactate or enters mitochondria

Glucose Entry into Muscle blood [glucose] >>> cytosolic [glucose] glucose enters muscle via facilitated diffusion (i.e., glucose transporters) insulin and Ca 2+ stimulate glucose uptake phosphorylation of glucose (G-6-P) in muscle “traps” glucose

Metabolic Fate of Pyruvate lactate formation enters mitochondria (i.e. Kreb’s cycle) formation of Kreb’s cycle intermediates Pyruvate goes in one of three directions

Mitochondria not a bean shape, rather a long reticulum aerobic metabolism of CHO, fats, and proteins occur entirely in mitochondria all substrates formed into acetyl Coenzyme A before entering Kreb’s cycle

Anaerobic vs. Aerobic Energy Systems Anaerobic – ATP-CP : 10 sec. Or less – Glycolysis : Few minutes Aerobic – Krebs cycle – Electron Transport Chain 2 minutes +

100% % Capacity of Energy System 10 sec30 sec2 min5 min + Energy Transfer Systems and Exercise Aerobic Energy System Anaerobic Glycolysis ATP - CP

Exercise Energy Metabolism During Exercise At onset of exercise, three systems are used continuously, though contribution of the three systems change with time.

Anaerobic Conditioning Phosphate Pool – All out bursts of 5-10 seconds will significantly deplete the ATP-CP system. – Very little LA produced (< sec. Bursts) – Rest periods of 30 – 60 seconds will provide complete recovery ([ATP-CP] back to normal) – High intensity interval training Increases [ATP-CP] Facilitates neuromuscular adaptations to the RATE and PATTERN of the movement.

Anaerobic Conditioning Glycolysis / Lactic Acid System – ALL OUT effort beyond 10 seconds (usually 1 min.) – Very taxing on athlete (psychologically and physically) – Recover twice as long exercise bout 2-1 ratio – Results in “stacking” of LA  Increasingly high [LA] – Full recovery ([LA] back to baseline) may take hours. – ONLY occurs in muscles overloaded!

Aerobic Energy Production Steady state exercise beyond 3-4 minutes is powered mainly by Aerobic Glycolysis – Pyruvic Acid & Lipid/Protein fragments enter Kreb’s Cycle and ETC. Energy produced resynthesizes ATP. – As long as sufficient O 2 is available to meet energy needs, fatigue is minimal and exercise continues! – The intensity that elicits anaerobic metabolism is dependant on the person’s aerobic capacity

Glucose Pyruvic Acid (2) Energy H+H+ Lactic Acid (2) Acetyl Co-A (2) CO 2 & H + Krebs Cycle CO 2 H+H+ Energy ATP Mitochondria Inter Cellular Fluid To ETC Anaerobic Aerobic Fatty Acids Amino Acids

Krebs Cycle Energy ATP CO 2 H+H+ Electron Transport Chain ATP 2H + + O -- = H 2 O

Aerobic Capacity Ability of the Cardiovascular system to deliver oxygen rich blood to body tissues. Muscles ability to process and utilize oxygen to produce energy.

Evaluating Aerobic Capacity Measure – VO 2max via spirometry / graded exercise stress test Estimate – Sub-maximal graded exercise test – Step test Based on the fact that individuals with higher SV will recover faster Recovery HR will be lower in individuals w/ higher VO 2max

Heart Rate Response to Step Test

Factors That Effect Aerobic Conditioning Initial level of cardiovascular fitness Frequency of training Duration of training Intensity of training Specificity of training

Initial Fitness Level Lower initial fitness level allows more room for improvement Generally “average” individual can expect 5-25% improvement w/ 12 weeks of training Everyone has GENETIC Limit Some people are genetically more gifted and/or respond better to training

Frequency of Training Generally recommended: at least 3 X’s/week Training 4 or more days per week results in only small increases in VO 2max Weight control: 6 or 7 days/week recommended

Duration of Training 30 minutes of continuous exercise is recommended Discontinuous exercise of greater intensity has shown comparable results

Continuous vs. Discontinuous Exercise Continuous (Long Slow Distance) – 70-90% of HR max – Less taxing on individual Interval Training – Repetitive exercise intervals separated by rest intervals – Exercise Interval: 90% HR max – Rest interval: 3X’s as long as exercise (3:1 ratio)

Training Intensity Most critical factor in training May be expressed as: % of VO 2max Heart rate or % of maximum HR – METS – Rating of Perceived Exertion (RPE) – Calories per unit time

Training Intensity Threshold for aerobic improvement – At least 50-55% of VO 2max – 70%+ of age predicted max HR (220-age) – Often referred to as “conversational exercise” Overload will eventually become average activity – Must increase intensity / duration to continue improvement in CV endurance

ACSM Recommendations At least 3X’s per week 30 – 60 minutes Continuous, large muscle mass exercises Expend at least 300kcals per session 70% of age predicted max HR

Guidelines Start slowly – Much higher risk of injury before adaptation occurs Warm Up (50-60% Max HR) –  temp. of & blood flow to muscle – Gentle stretching Dress for the weather Cool Down – Increases LA removal – Decreases pooling of blood in veins – Gentle stretching

Why does blood lactate increase during heavy exercise? lactate appearance exceeds lactate removal evidence does not point to muscle hypoxia FT recruitment epinephrine release

Basal Metabolic Rate Your basal metabolic rate, or BMR, is the minimum calorific requirement needed to sustain life in a resting individual. It can be looked at as being the amount of energy (measured in calories) expended by the body to remain in bed asleep all day! BMR can be responsible for burning up to 70% of the total calories expended, but this figure varies due to different factors (see below). Calories are burned by bodily processes such as respiration, the pumping of blood around the body and maintenance of body temperature. Obviously the body will burn more calories on top of those burned due to BMR.

Components of Daily Energy Expenditure Segal KR et al. Am J Clin Nutr. 1984;40: Thermic effect of feeding Energy expenditure of physical activity Resting energy expenditure Sedentary Person (1800 kcal/d) Physically Active Person (2200 kcal/d) 8% 17% 75% 8% 60% 32% Slide Source:

Calorimetry gives energy needed for various levels of activity. Energy expenditures above basal: Eating, reading 0.4 Cal/kg-h Doing laundry 1.3 Cello playing 1.3 Walking slowly 2.0 Walking 4 mph 3.4 Swimming 2 mph 7.9 Crew race 16.0 Energy needed for activity

It takes energy just to stay alive. Basal metabolic rate, or BMR For warm-blooded animals, most energy used to maintain body temperature. Human BMR: 1.0 Cal/kg-h Example: m = 70 kg, 24 hour day Basal metabolism = 1.0 Cal/kg-h * 70 kg * 24 h/day =1680 Cal/day This doesn’t account for any activity. Basal metabolic rate

Figuring total caloric needs: One 75 kg person’s day Basal metabolism 1.0 Cal/kg-h * 24 h * 75 kg = 1800 Cal Reading, writing, talking, eating, 12.5 h 0.4 Cal/kg-h * 12.5 h * 75 kg = 375 Cal Walking slowly, 1 h 2.0 Cal/kg-h * 1 h * 75 kg = 150 Cal Playing cello, 1.25 h 1.3 Cal/kg-h * 1.25 h * 75 kg = 120 Cal Energy needed for digestion 2500 Cal consumed * 8% = 200 Cal Total needs: 2645 Cal

Solving for moderate exercise activity total daily energy expenditure (TDEE) Total daily energy expenditure

Harris-Benedict Note: 1 inch = 2.54 cm. 1 kilogram = 2.2 lbs. Example: You are female You are 30 yrs old You are 5' 6 " tall (167.6 cm) You weigh 120 lbs. (54.5 kilos) Your BMR = = 1339 calories/day Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) - (6.8 X age) Women: BMR = (9.6 X wt in kg) + (1.8 X ht in cm) - (4.7 X age)

Activity multiplier Sedentary = BMR X 1.2 (little or no exercise, desk job) Lightly active = BMR X (light exercise/sports 1-3 days/wk) Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk) Very active = BMR X (hard exercise/sports 6-7 days/wk) Extr. active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.) Example: Your BMR is 1339 calories per day Your activity level is moderately active (work out 3-4 times per week) Your activity factor is 1.55 Your TDEE = 1.55 X 1339 = 2075 calories/day Determine the energy cost: ______________________

Chapter 9 44

Reminders for Monday, September 21 st Quiz 3: Vo2 Max, Aerobic Field Tests (Chapter 2), and The Scientific Basis of Aerobic Fitness (Chapter 3) and lecture slides Meet at the football stadium for cardiorespiratory tests