One of the items of most interest in this weekend's V8 Supercars is how Greg Murphy manages to muscle his big V8 round the Hamilton circuit at 250km/h without full use of his legs.

In fact, the racing will be helping him regain the use of his calf after his recent back injury.

New Zealand's most successful V8 Supercars racer so far, Murphy is back on the horse after getting the all clear to go racing again at the Hamilton ITM400 round of the series.

Three weeks ago, Murphy had surgery to repair a blown disc in his back, sustained in a massive shunt with Jonathon Webb at the opening round of the championship in Adelaide. He had initially damaged the disc in a 2010 accident but felt nothing after the qualifying crash with Webb or after the first two races at the non-points scoring round at Melbourne two weeks later.


However, during the last race Murphy noticed his left leg was feeling a bit tingly and he had an ache in his thigh.

Even after getting out of the car, he still felt some discomfort and over the next few days, the pain moved around and eventually the calf muscle gave out. After a conversation with his surgeon and an MRI scan, it was decided he needed an operation.

"That [rupturing a disc] is what happens when you instantaneously put 45G of force through your spine. I'm lucky it was only one that went but it was the one I had injured before," said Murphy.

While he's not worried about the repair to the disc itself holding up to the rigours of thundering around a street circuit and banging off various kerbs, there is the incision and its repair to be considered.

"That part of the surgery should be fine. I'll just get the trainer to strap it well up and make sure it's well covered and it'll all be good.

"It's come together really well and repaired itself nicely. There's still a bit of water and fluid in there but it's not causing any discomfort."

As most sports people will know, a herniated (or ruptured) disc is not the best of injuries to sustain when legs are an important part of your sport.

When a disc herniates, the cushion that sits between the spinal vertebrae is pushed outside its normal position, or may even rupture. When a disc bulges out from between the vertebrae, the spinal nerves and spinal cord can become pinched, causing the message to get a little garbled between brain and legs.

"The biggest thing is getting the communication from the brain to the nerve to respond 100 per cent again. It's probably only about 60 per cent at the moment.

"It doesn't affect me in the race car when I'm pushing the pedals. That part of it is fine but the strange part is that I can't do a calf raise. When I'm sitting in the seat and my back, bum and thighs are supported I can put pressure on the pedals, no problem."

A good analogy is riding a bicycle where you have to push down on the ball of your foot to turn the pedal. At the moment it's an exercise Murphy can't do, but when his back has something to push against, everything works fine using his thigh.

"I had a similar problem in 2010 and I was a bit worried that it would really affect my driving and I wouldn't be able to push the pedals properly. However, as soon as I got in the car, I found that it helped re-train the nerve by putting pressure on the pedal," said Murphy.