Fuel Sources & Exercise Metabolism

Table3.7 Major characteristics of the human energy systemsATP-PCr Lactic

AcidOxygen Oxygen

Main energy source ATP, PCr CHO CHO Fat

Intensity level Highest High Lower Lowest

Rate of ATP Production

Highest High Lower Lowest

Power Highest High Lower Lowest

ATP Capacity Lowest Low High Highest

Endurance Capacity Lowest Low High Highest

O2 Needed No No Yes Yes

Track Event 100 m 200-800 m 5,000 m Ultra

Time 1-10 s 30-120 s >5 min hours

Table 3.8 Percentage contribution of anaerobic and aerobic energy sources during different time periods of maximal work

Time 10 sec

1 min

2 min

4 min

10 min

30 min

50 min

130 min

AnaerobicAerobic

8515

7030

5050

3070

1585

590

298

199

Energy Stores In the Average ManMass (lb)

Energy (kJ)

Energy (kcal)

Rx Time (Min)

Liver Glycogen

0.22 1,600 400 20

Muscle Glycogen

0.88 6,400 1,600 80

Blood Glucose

0.022 160 40 2

Fat 23 390,000 93,000 4,900

Protein 18.75 142,000 34,000 1,800

Some Possible Causes of Fatigue During Exercise

• Increased formation of depressant neurotransmitters– Increased serotonin levels

• Decreased levels of energy substrates– Phosphocreatine– Muscle glycogen– Blood-sugar level– Branched-chain amino acids

Fatigue Sites Cont’d• Disturbed intracellular environment

– Impaired calcium recycling• Disturbed acid-base balance

– Increased H+ due to lactic acid• Decreased oxygen transport

– Decreased blood volume due to dehydration• Increased core temperature

– Decreased cooling due to dehydration• Disturbed electrolyte balance

– Increased or decreased concentration due to sweat losses and H2O replacement