Exercise and the muscles and digestion

Muscle is tissue that can contract; skeletal muscles do the work in exercise. There are fast-twitch and slow-twitch fibres.

Hypertrophy: regular training enlarges muscle fibres (diameter and length) and raises their protein, glycogen and enzymes.

Aerobic changes: more myoglobin, more energy from oxidising glycogen, more use of fat. Anaerobic changes: better tolerance of lactic acid and changes in fibre types and blood flow. Endurance training increases capillaries per fibre.

Stronger muscles work with less effort, lactic acid builds up later, and strength, flexibility and endurance increase.

Digestion: exercise improves blood flow to the digestive organs, raises metabolism slightly, prevents constipation by speeding food through the large intestine, and strengthens internal organs against digestive disease.