Researchers are warning dog owners.

The most popular game to play with a dog is probably fetch. The aim is to throw something far away and get the dog to fetch it. However, it turns out that this could be dangerous for a dog and can cause it a lot of harm. A study has revealed that dogs make an unnatural shift in their body weight to carry things in their mouths, putting extra strain on their front legs. When fetch is played, and particularly heavy items are thrown, this can cause problems for the dog's legs and also affect their limbs and joints. Dogs usually divide their weight between their legs with the front two taking 60% and the back two taking 40% of the weight of their body. According to The Sun, Dr Bockstahler, a veterinary surgeon, said:

"This is comparable to a human holding a weight in his hand, who slightly tilts backwards and therefore shifts his body weight to his heels. The additional weight is physically burdensome for them.”

The study, which was published in the journal BMC Veterinary Research, found that dogs that carried items weighing half a kilogram shifted 66% of the weight onto their front legs, and increased it to 77% when they carried items up to 4kgs. Dr Bockstahler added:

"In animals with existing joint, tendon or muscle disorders, this could have a negative effect. Also in young, growing animals, this could have a negative effect, especially if the weights they are carrying are heavy. Training should be performed carefully. It does not mean retrieving work is bad, but it must be performed with the knowledge that it puts stress on the limbs.”

She did say that a tennis ball shouldn't cause any harm but not to exceed that weight when playing fetch.