With preparation and common sense, you can avoid most - if not all - the potential health hazards of cycling

Safety awareness
Always wear a helmet and appropriate safety gear. Keep your bicycle in good repair. Make sure you are familiar with the road rules and follow them.

Dehydration 
The human body is mostly made up of water. Dehydration is serious and can be fatal. Avoid strenuous cycling on hot days, take plenty of liquids with you, and stop for frequent rest and drink breaks if you are doing a long ride.

Muscle injuries 
Muscles and tendons are more susceptible to injury when they are cold. Always warm up with a series of gentle stretches. When you first start riding, take it easy and aim for a slow and steady increase in heart rate.

Sunburn
Don't forget to regularly reapply your sunscreen. Even waterproof varieties can be washed off with constant sweating.

Source: goforyourlife.vic.gov.au