Five good things about marathon running

• Regular running halves the risk of developing coronary heart disease

• Weight-bearing exercise protects against osteoporosis

• Respiratory system gets a good clear out

• Doesn't increase risk of arthritis

• Mental boost - exercise and achievement raise levels of feelgood hormone - endorphines

And five bad things

• May aggravate old injuries

• Dehydration can cause exhaustion

• Increased risk of muscle injury or stress fracture if you are wide-hipped, pigeon-toed, or knock-kneed

• Effort temporarily weakens immune system, so more likely to catch a cold after the race

• Overtraining can halt menstruation - raising the risk of osteoporosis in later life