Ignoring the many pathological conditions that could cause such symptoms, such discomfort is common both before one achieves proper fitness, or in unfamiliar conditions such as excessive dust or unusually dry or cold air.

Pumping cold air over the mucous membrane of the pharynx, trachea, and bronchi - during a run in bracing weather, say - may well cause irritation. If the condition is benign then, as one becomes fitter, part of the bodily adaptation to the exercise is to adjust the rate at which your respiratory epithelium secretes mucus in reaction to irritation and to prevent drying out. Either too much or too little mucus can be harmful. In due course your respiratory tract becomes less sensitive to cold air.

The pain in the thorax and abdomen may also be partially caused by respiratory muscle cramps, or painful stretching of some connective and lung tissue.

As one becomes fitter, part of the adaptation is to reduce the amount of air required for a given level of exertion by relaxing the upper respiratory tract, increasing haemoglobin levels in the blood, improving the supply of oxygen and reducing over-breathing.

Jon Richfield, Somerset West, South Africa