energy systems of human body

1. Energy Systems of the Human
Body
Understanding How the Body Fuels
Physical Activity

2. Introduction to Energy in the
Human Body
• The human body requires energy to perform
all physiological functions, from breathing and
thinking to moving and digesting. This energy
comes from food, primarily in the form of
carbohydrates, fats, and proteins. These
macronutrients are converted into ATP, the
energy currency of the body.

3. ATP – The Energy Currency
• ATP (Adenosine Triphosphate) is the molecule
that stores and provides energy for cellular
processes. Energy is released when a
phosphate group is removed from ATP,
forming ADP (Adenosine Diphosphate). Cells
regenerate ATP through various metabolic
pathways to sustain activity.

4. The Three Energy Systems
• The body utilizes three main energy systems
to regenerate ATP:
• 1. ATP-PC (Phosphagen) System – short bursts
of energy, no oxygen required.
• 2. Anaerobic Glycolysis – moderate duration
and intensity, no oxygen required.
• 3. Aerobic System – long-duration, lower-
intensity activities, oxygen required.
• These systems work together, with dominance
depending on the intensity and duration of

5. ATP-PC (Phosphagen) System
• • Duration: 0–10 seconds
• • Fuel Source: Creatine phosphate stored in
muscles
• • Characteristics: Immediate energy, no
oxygen required, quick depletion
• • Example Activities: Sprinting, high jump,
shot put
• This system is the fastest at regenerating ATP
but has limited capacity.

6. Anaerobic Glycolysis (Lactic Acid
System)
• • Duration: 10 seconds to 2 minutes
• • Fuel Source: Glucose (from blood or
glycogen)
• • Characteristics: Moderate-speed ATP
production, no oxygen required, lactic acid
produced
• • Example Activities: 400m sprint, circuit
training
• This system provides energy quickly but leads
to muscle fatigue due to lactic acid

7. Aerobic (Oxidative) System
• • Duration: Over 2 minutes
• • Fuel Sources: Carbohydrates, fats, and
proteins (in extreme cases)
• • Characteristics: Slowest ATP production, but
sustainable over time, oxygen required
• • Example Activities: Long-distance running,
cycling, swimming
• This system is efficient for prolonged activities
and supports recovery.

8. Energy System Interactions
• All three energy systems function
simultaneously during activity, but their
contribution varies by intensity and duration:
• • High-intensity, short-duration: ATP-PC
dominates
• • Moderate-intensity, medium-duration:
Anaerobic Glycolysis dominates
• • Low-intensity, long-duration: Aerobic System
dominates
• This dynamic response ensures the body can

9. Comparison of Energy Systems
• ATP-PC System: 0–10 sec | Fuel: Creatine
Phosphate | No oxygen | By-product: Creatine
• Anaerobic Glycolysis: 10 sec–2 min | Fuel:
Glucose | No oxygen | By-product: Lactic Acid
• Aerobic System: 2 min+ | Fuel: Carbs, Fats |
Oxygen required | By-products: CO₂, H₂O

10. Application in Sports
• Understanding energy systems is crucial for
optimizing athletic performance:
• • Power athletes (e.g., sprinters, weightlifters)
benefit from ATP-PC training.
• • Anaerobic system is vital for sports with
repeated sprints (e.g., soccer, basketball).
• • Endurance athletes (e.g., marathoners,
triathletes) rely on the aerobic system.
• Training programs should match energy
system demands of the sport.

11. References
• • American College of Sports Medicine.
ACSM's Guidelines for Exercise Testing and
Prescription.
• • McArdle, W.D., Katch, F.I., & Katch, V.L.
Exercise Physiology: Nutrition, Energy, and
Human Performance.
• • Human Kinetics. Essentials of Strength
Training and Conditioning.