While the day-to-day physical work has bulked him up, he also suffers from joint pains and a cough, owing to the cold, damp and dusty environment underground.

But experts are warning of the dangers of prolonged use, such as the risk of shin splints and joint pains.

Symptoms include high fever, joint pains and nausea, but in severe cases, it can lead to internal bleeding, liver enlargement, circulatory shutdown and death.