I had always been active, fit and healthy. I could have a go at any sport I wanted without worrying about a bad back or any other injuries and if I ever wanted to let off some steam I could throw on a pair of running shoes without a second thought and pound the streets for a few miles.

But one evening in January 2008 that all changed. I started to cross a road, and I didn't make it to the other side. I was on a pedestrian crossing and the little man we all trust every day with our lives was green. Cars were stopped in the first two lanes of traffic, and there was no car in the third lane – until I got there. Suddenly there was definitely a car there, and it swept me off my feet.

I never saw the Renault Laguna that hit me. I didn't see the bumper that broke my legs and ripped my ligaments, I didn't see the bonnet I dented, or the windscreen I smashed with my head.

I just remember walking, flying through the air and then lying on cold, damp Tarmac, in the strangest, most intense and tingling pain I had ever felt.

I remember being amazed at how loud I could scream, and I was immediately surrounded by a buzzing crowd of kind commuters, holding my hands, putting me into the recovery position, phoning my poor mum.

The ambulance took me to an East London hospital – I was living in Hackney at the time as a student – and slowly the doctors started to put me back together.

I was desperate to get out and get home, but I couldn't leave until I proved I would be able to get myself around unaided. Although for most of the next few months I would be in a wheelchair, I had to be able to move myself short distances by foot – for example to the toilet and back.

By this stage I knew I had broken both my legs, but my biggest problem was ligament damage in both my knees. This is when the days, weeks and months of physiotherapy started.

I was fitted with braces on my legs which limited my movement, and had to get to grips with a Zimmer frame for a couple of days, trying my best not to put any weight through my sorry legs, and then crutches.

I was told to do very basic exercises three times a day – forget sit-ups, press-ups or lunges – all I had to do was manoeuvre myself to the edge of the bed with my legs over the edge and try and lift them from the knee, one at a time.

Sounds simple, doesn't it? But it was nearly impossible for the first couple of days, and with other tasks like rolling on to my side also proving to be an exhausting and time-consuming task, I just couldn't comprehend how I would ever be able to walk again. But, bit by bit, with lots of support from my family and physiotherapist, strength started to return.

After operations to fix my knees, I started physiotherapy in earnest. I went from having supermodel-skinny, wasted legs, to having a bit of muscle again.

The exercises changed week by week – standing on tip toe, side-stepping across a room, standing on one foot – and I diligently made sure I did them three times a day.

I went from a wheelchair, to crutches, to one crutch, and then all of a sudden, one day, I forgot to pick up my crutch and got half way to the kitchen before realising and yelling excitedly to my mum that I was walking unaided. By this point I had set myself a goal of the Bristol Half Marathon.

I wanted to be able to run again, I wanted to be able to say: this accident won't stop me doing anything, even if I have to try that bit harder than I would have had to before.

Seven months after the accident, I got on a treadmill and ran for the first time. It felt very strange, as if every muscle and joint in my lower body was waking up. They all hurt; they were all stiff.

That first year, I volunteered as a marshal at the half-marathon, feeling a few steps closer to my final goal.

I slowly built up the distances, my strength and fitness until in May 2009 I was in good enough shape to run the Bristol 10k – it was a great feeling and I felt well on the way to running those 13.1 miles last September.

Frustratingly, later that summer I developed a foot injury – a knock-on effect of my original injuries from the accident – which lasted for several months and ruled me out of the race.

I was forced to watch from the sidelines with tears in my eyes as my friends and boyfriend did it without me.

But earlier this year the pain in my foot subsided, and I was able to begin my running training again very tentatively.

Since March I have been slowly increasing my distances and speed, keeping to softer ground where I can to save my joints and running laps of the Downs, Stoke Park, Snuff Mills, Oldbury Court and Eastville Park.

So here I am – on the eve of the big race. I feel fighting fit, excited and ready for it, but also rather emotional every time I imagine the day.

It may not be an ascent of Everest, it may not be a full marathon, and I realise others have survived much worse traumas than me, but for me this has been the biggest challenge of my life and reaching the finish line means a lot.

At least once during every run I go out on at the moment, I envisage the final 100 metres of September 5. Head held high, I'm determined to power over the finish line with a smile on my face and commit that moment to memory – now I know that when life (or a Renault Laguna) knocks you down, you can get right back up and fight again.

You can read more about Emily's training in her blog, www.fromno bootstorunningshoes.blogspot.com.