The Scientific Basis of Aerobic Fitness Chapter 3.

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 + O2 ATP + CO2 + H2O + 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

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%

% C

apacity of Energy S

ystem

10 sec 30 sec 2 min 5 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 (< 10-15 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 O2 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+

Lactic Acid (2)

Acetyl Co-A (2)

CO2 & H+

Krebs

CycleCO2

H+

Energy ATP

ATP

Mitochondria

Inter Cellular Fluid

To ETC

Anaerobic

AerobicFatty Acids Amino Acids

Krebs

Cycle

Energy ATP

CO2

H+

Electron Transport

Chain

ATP

2H+ + O-- = H2O

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 – VO2max via spirometry / graded exercise stress

testEstimate

– 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 VO2max

Heart Rate Response to Step Test

20

40

60

80

100

120

140

160

180

Rest BeginExercise

1 min 2 min EndExercise

1 min 2min

Sedentary

Trained

Elite Athlete

Factors That Effect Aerobic Conditioning

Initial level of cardiovascular fitnessFrequency of trainingDuration of trainingIntensity of trainingSpecificity 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 LimitSome people are genetically more gifted

and/or respond better to training

Frequency of TrainingGenerally recommended: at least 3

X’s/weekTraining 4 or more days per week

results in only small increases in VO2max

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 trainingMay be expressed as:

% of VO2max

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 VO2max

– 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 week30 – 60 minutesContinuous, large muscle mass

exercisesExpend at least 300kcals per session70% 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;40:995-1000.

Thermic effect of feeding

Energy expenditure of physical activity

Resting energy expenditure

Sedentary Person (1800 kcal/d)

Physically Active Person

(2200 kcal/d)

8%8% 17%17%

75%75%

8%8%

60%60%

32%32%

Slide Source: www.obesityonline.org

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 usedto maintain body temperature.

•Human BMR: 1.0 Cal/kg-hExample: 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 metabolism1.0 Cal/kg-h * 24 h * 75 kg = 1800 Cal

Reading, writing, talking, eating, 12.5 h0.4 Cal/kg-h * 12.5 h * 75 kg = 375 Cal

Walking slowly, 1 h2.0 Cal/kg-h * 1 h * 75 kg = 150 Cal

Playing cello, 1.25 h1.3 Cal/kg-h * 1.25 h * 75 kg = 120 Cal

Energy needed for digestion2500 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 femaleYou are 30 yrs oldYou are 5' 6 " tall (167.6 cm)You weigh 120 lbs. (54.5 kilos)Your BMR = 655 + 523 + 302 - 141 = 1339 calories/day

Men: BMR = 66 + (13.7 X wt in kg) + (5 X ht in cm) - (6.8 X age)Women: BMR = 655 + (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 1.375 (light exercise/sports 1-3 days/wk)Mod. active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)Very active = BMR X 1.725 (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 dayYour activity level is moderately active (work out 3-4 times per week)Your activity factor is 1.55Your TDEE = 1.55 X 1339 = 2075 calories/day

Determine the energy cost: ______________________

Chapter 9

44

Reminders for Monday, September 21st

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