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