MODEL RELEASED. Cramp. View of a female physiotherapist treating a rugby player for calf cramp. Cramp is a painful spasm in a muscle caused by excessive and prolonged contraction of the muscle fibres. It often occurs toward the end of a rugby game because of a build-up of lactic acid & other chemicals (caused by increased muscular activity) and small areas of muscle fibre damage. Cramps can also occur due to repetitive movements. Profuse sweating through exercise causes loss of sodium salts which disrupts muscle cell activity and may cause cramp. Stretching and massaging the muscle relieves the problem. Photographed in Pontefract, West Yorkshire, England.