Human Energy Systems

NFSC 303

• You will not be required to do the mathematical conversions from one for of energy to another (p. 83-85 of textbook)

Energy Balance = “energy in” vs. “energy out”

Energy in:

Energy out:

How do we measure Calories?• Direct Calorimetry:

– In food: – In humans:

• Indirect Calorimetry:–

• Newer: IDEEA device– Intelligent Device for Energy Expenditure and

Activity– Records body motions every second for 24 hours.

Components of Energy Expenditure

• Energy to support basal metabolism: BEE

• Energy to support physical activity: TEE

• Energy to process food: TEF

Energy to Support Basal Metabolism

• BEE = Basal Energy Expenditure

• (Calculated from BMR = Basal Metabolic Rate)–

– Measured in standard state (no food/exercise for 12 hours; measurement taken right after waking, resting at a comfortable temperature)

– REE/RMR = Resting Energy Expenditure or Resting Metabolic Rate: similar numbers (not standard state)

• Primary factors affecting BMR/BEE:– –

• Other factors: growth, fever, ambient temp., pregnancy, smoking, disease, age, BSA, kcalorie intake–

To estimate BEE:1. Rough estimate: Body weight in pounds X 10

2. More accurate:

Men:

Women:

Example:

Energy to Support Physical Activity

• TEE = Thermic Effect of Exercise

Energy Needed to Process Food

• TEF = Thermic Effect of Food

BEEBEE

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Remember: Remember: BMR is BMR is measured 12 measured 12 hours after any hours after any physical physical exercise and in exercise and in a fasted state.a fasted state.

Wide difference in metabolic rates due to genetics...

• But within our individual range…

– lowest would be achieved via

– highest would be achieved with

Fueling Activity

• Exogenous fuels: from outside the body– dietary protein, CHO, and fat

• Endogenous Fuels: from within the body– – –

• importance increases in times of inadequate kcalories or CHO intake

Energy Metabolism:

All processes involved in the production, storage, and use of energy

• As macronutrients are broken down, E from the breakage of bonds is:– – –

ATP: Adenosine Triphosphate

• A-P~P~P• High-energy bonds

“store” energy• Cleaved to release E

for–

–

• A-P~P / P = ADP• A-P/ P = AMP• To regenerate ATP,

we need a source of P with high energy bonds:– ADP + P

– AMP + 2P

These high-energy bonds will come from:

Phosphocreatine: PCr

• High-E molecule - helps maintain a steady supply of ATP for short bursts of energy– – –

• To keep regenerating ATP:–

Metabolic Pathways

• Take place in the cytosol and mitochondria of the cell

• Anabolic Pathways: – – –

• Catabolic Pathways: – – –

• Anaerobic:

• Aerobic:

Overview of Pathways

Anaerobic Metabolism: Glycolysis•

•

• ONLY carbohydrate can do it.

Anaerobic Metabolism: Glycolysis

• Glucose (from glycogen) is “split” for E– It is only partially metabolized – will need oxygen to

metabolize it completely.

• Primary source of E during _____________ (when O2 availability is low)

• Takes place in the cytosol of the cell

Aerobic Metabolism: Krebs Cycle and Electron Transport

System (ETS)•

•

•

• Can metabolize fat, carbohydrate (finish the job) and some protein.

So to fuel activity, we need ATP.

ATP is generated by metabolizing our fuel sources: carbohydrate, fat, and some protein.

So how much of each fuel do we use during exercise? (What’s the fuel mix for a given exercise?)

Primary Exercise Fuels: CHO and FAT

• Carbohydrate from ______________

• Fat from ________________

Remember: only CHO can be burned when

oxygen availability is low

Fuel sources used during exercise Depend on:

• Intensity of activity

• Duration of activity

• Fitness level of the individual

• Macronutrient and kcalorie content of diet

• Fuel Sources:– Immediate – ATP/PCr system

– Anaerobic – O2 not required. •

•

• Glycolysis alone can support muscle contraction for ~ 30 seconds to 2 minutes.

– Aerobic – O2 required •

•

•

When Exercise Begins…

• O2 hasn’t gotten to muscles yet

• ATP/CP during first seconds

• Mostly Anaerobic for several minutes

• Then, aerobic (along with anaerobic) for the rest of exercise time.

Fuel sources used during exercise Depend on:

• Intensity of activity

• Duration of activity

• Fitness level of the individual

• Macronutrient and kcalorie content of diet

Exercise Intensity

• VO2Max

• THR range

• RPE

• Mild Intensity Exercise (walking)• • ____________________ are the predominant

fuel for ATP production (Krebs and ETS)• (~60% FA and 40% CHO)

• Moderate Intensity Exercise (ie. Jogging, aerobics)–

–

– Rely on – Therefore, more _________ is used

• (e.g. ~50% CHO/50% Fat)

– The longer the duration, the greater use of ___________ as fuel

– (for exercise lasting several hours, 60-70% energy can be supplied by fat).

• High Intensity Exercise (Strenuous, Intense)

– induces ________________state in muscle cell

–

– Glycolysis can’t be maintained… very intense

ex. only lasts seconds to minutes

Fuel sources used during exercise Depend on:

• Intensity of activity

• Duration of activity

• Fitness level of the individual

• Macronutrient and kcalorie content of diet

Exercise Duration

TIME

CHO

FAT

rest

Fuel sources used during exercise Depend on:

• Intensity of activity

• Duration of activity

• Fitness level of the individual

• Macronutrient and kcalorie content of diet

Fitness Status

• Increased fitness status:

• Increased: –

–

• Training Effects of Aerobic Exercise:

LDL (“bad”)cholesterol, HDL (“good”)cholesterol– strengthened heart, lungs– curbed appetite metabolic rate…

• Effects of Strength Training

LDL (“bad”) cholesterol constipation, diverticulosis, hemorrhoids, and poss.

Colon CA• speeds waste through colon

– stronger bones

Fuel sources used during exercise Depend on:

• Intensity of activity

• Duration of activity

• Fitness level of the individual

• Macronutrient and kcalorie content of

diet

Diet

• High fat diet –

• Lower fat, mod. prot, high CHO diet – –

Fatigue

• The inability to continue exercising at a desired level of intensity

• Inability to produce ATP to meet demands

• Other factors

• We’ll address fatigue in later sections.