The effects of training can be studied at various levels:

• Biochemical changes - Tissue level
• Systemic changes - Circulatory & Respiratory
• Other changes - Body composition, blood cholesterol and triglyceride levels, blood pressure and heat acclimatisation.

AEROBIC TRAINING CHANGES

1. Increased Myoglobin Content in skeletal muscle following training. Myoglobin is an oxygen binding pigment similar to haemoglobin. It stores oxygen in the muscle cell. Its most important function is aiding in the delivery of oxygen from the cell membrane to the mitochondria.

2. Improved Oxidation of Carbohydrate (Glycogen)
Training increases the capacity of skeletal muscle to break down glycogen in the presence of oxygen (oxidation) to carbon dioxide and water with ATP production. The capacity of the muscle to generate energy aerobically is improved due to two adaptations in the muscle cell following training:

• An Increase in Mitochondrial Density - The number, size and membrane surface area of skeletal muscle mitochondria.
• An Increase in Activity or Concentration of Krebs Cycle Enzymes - More ATP can be produced in the presence of oxygen.

3. Improved Oxidation of Fat - The breakdown (oxidation) of fat to carbon dioxide and water with ATP production is increased following training. As fat serves as a major fuel for endurance exercise this has definite advantages in increasing performance. At all submaximal workloads the trained person oxidizes more fat and less carbohydrate resulting in less glycogen depletion, less lactic acid accumulation and less muscular fatigue. An increased capacity to oxidize fat is related to:

• Increased intramuscular stores of triglycerides - The storage form of fat.
• An increased release of Free Fatty Acids from adipose tissue.
• Increased enzyme activity involved with activation, transport and breakdown of fatty acids.