Oscar Pistorius lost his temper and began pumping iron furiously inside prison after learning that the state can appeal against his acquittal of murder and the shortness of his jail sentence for manslaughter.

A fellow inmate at the Kgosi Mampuru II (previously Pretoria Central) prison in South Africa, where Pistorius is serving his five-year manslaughter sentence, revealed how the news hit him.

"He got up and stomped. He went straight to the gym. He started lifting weights like it was going out of fashion. He is pissed off," the source said.

The reason behind Pistorius's meltdown may be that the appeal could rule out the chance of him being released early from jail.

Under the terms of the current sentence handed down, the runner will eligible in 2015 to serve part of his term at home.

But the appeal could change that, meaning Pistorius will be stuck behind bars far longer than he hoped.

The source told South Africa's The Times: "Who wouldn't be [angry]? He was definitely expecting to be out by August. Pistorius can barely console himself over the fact that he will be here for Christmas and New Year, instead of [partying] with his family and friends."

This week saw prosecutor Gerrie Nel argue successfully for an appeal, over the legal interpretation of the phrase "dolus eventualis" – that concerns intent by Pistorius in shooting dead his girlfriend Reeva Steenkamp.