Sudden exertion in the unfit is the biggest risk. Unaccustomed strain on a heart that is diseased, subject to irregular rhythms or otherwise damaged may result in abrupt failure. Doctors recommend a gradual exercise programme to build up fitness.
Mr Cook was reportedly diagnosed with high blood pressure six months ago. If the problem was long standing and had gone undetected, it may have caused lasting damage to the heart.
His former wife, Margaret, described him as "an adventurous man who liked to push himself to the limit". That is fine for someone who keeps in trim with regular trips to the gym to maintain fitness. But it should sound warning bells for anyone who leads a high-stress, sedentary life as the effects of a sudden physical load imposed on the heart can be disastrous.
Heart disease is the most common cause of premature death in the United Kingdom.