ATHLETICS:THURSDAY WAS my first day off in about six weeks, and I finally got to fulfil a long-overdue appointment at the new mountain bike trails in Ballyhoura. It was worth the wait – it was about as much fun as I've ever had on a bike.

That is, until the last descent home when my front wheel hit a small rock, sending me flying over the handlebars and crashing into the dirt path, the bike landing directly on top of me and the big chain ring neatly piercing the back of my right calf muscle. Ouch!

In the spirit of Tom Simpson, they put me back on my bike and I rode the rest of the way home laughing off the crash and thinking the only thing really hurt was my pride.

It seemed that way, too, until yesterday morning when I went for a run, and all of a sudden that same right calf muscle seized up, as if someone stabbed it with a dagger. It stopped me in my tracks and there was no chance of going on.

It’s probably killed my chances of running next month’s Dingle Marathon, but imagine I had been training for something serious?

That’s the thing about running – or indeed jumping or throwing: an injury can creep up without warning, and no matter what the cause it’s very quickly a case of game over. In any other sport you might get away with it. In athletics, one small tear, one little strain, one dull ache and months or even years of training can be wasted in an instant.

It doesn’t even have to be a physical injury. A minor head cold may only throw the body off just a few percentage points, but it’s enough to throw the performance off considerably – particularly if the event is measured in centimetres or fractions of a second.

Truth is, no other sport walks a thinner line between peak athletic performance and sudden debilitating injury.

There were several reminders of this at last weekend’s national track and field championships in Santry. For the majority of Ireland’s elite athletes, it was the last showcase for selection for the World Championships, which begin in Berlin a week from today. Inevitably, some failed to make the finish line. Others failed to even make the start line – and sometimes you have to wonder what they did to deserve such disappointment.

Martin Fagan, for instance, has surely endured more than his fair share of injuries already. In January of last year, Fagan ran through a double stress fracture of his sacrum to secure the qualifying time for the Olympic marathon in Beijing. After several months of rehab, he got himself fit again just in time for Beijing. Then, in arguably the most important race of his life, his left Achilles’ tendon gave way, eventually forcing him to drop out about three miles from the finish. No one drops out of an Olympic marathon unless they absolutely have to. Just ask Paula Radcliffe.

It was a crushing experience for Fagan, but he quickly turned his thoughts to the European Cross Country in Brussels and the promise of some redemption. Just before halfway in that race, while in pole position, Fagan tripped and fell – and ended up in 24th place. At his best he would surely have medalled.

Evidence of that came a few months later when he beat John Treacy’s national half-marathon record, running 60 minutes 57 seconds. You do the maths on that and figure out Fagan’s marathon potential.

Then, in April, in his first track race of the year, Fagan ran the B standard for Berlin over 10,000 metres, clocking 27:58.48. Things were looking good. The plan was to run an autumn marathon, probably New York, but he wanted to keep his options open for Berlin, and so he came to Santry last weekend to run the 10,000 metres.

A little after halfway, while in pole position, his left Achilles’ gave way. Again. Fagan left the track in a wheelchair and it may be some time before he gets fit. Again.

No wonder he feels a little fed up with the sport, but Fagan is a rare and wonderful talent, and we can only hope he sticks with it.

For others, just making the start line in Santry was a step too far. Maria McCambridge had also run a B standard for Berlin in the marathon, but a gluteus muscle strain knocked her training off course, and she won’t make that start line either.

With Fagan and herself both out, Ireland will have no representative in any distance running race in Berlin beyond the 5,000 metres. Yet again Alistair Cragg is left flying the flag.

Other athletes coming off injury, and with qualifying marks for Berlin, probably could have made it if they wanted to, but previous experience of competing half-fit was enough to convince them otherwise.

For Joanne Cuddihy, who still boasts vast untapped potential over 400 metres, that was the wise decision. Cuddihy went to Beijing last summer with a calf muscle strain, and while she probably shouldn’t have raced, she’d come too far not to.

Rather than rush her comeback for Berlin, Cuddihy is to spend the next year working and training at the Australian Institute of Sport. If she can stay injury-free, 2010 promises headlines.

It was a pity, too, that neither Paul Hession nor Derval O’Rourke got to run their finals in Santry last weekend – but at least they weren’t injured. Hession had a head cold and withdrew from the 100 metres, while O’Rourke picked up a chest infection running in Stockholm a few days before and withdrew from the 100 metre hurdles.

Both will be on the plane to Berlin next week – back, we’re told, to full health, but it remains to be seen if their peak performance has been thrown off.

But the athlete I feel most sorry for right now is Mary Cullen. This time last year Cullen was preparing to watch the Beijing Olympics from her training base in Providence, Rhode Island. She’d qualified for the 2007 World Championships in Osaka, but was already experiencing a pain in her right shin. That was later diagnosed as a stress fracture, requiring a six-week break. With Beijing looming, she headed for some warm-weather training in Florida. On one of her morning runs she tripped and fell on the footpath. A few days later the pain in her pelvis was severe, and later diagnosed as a bilateral stress fracture of the sacrum – one of the worst running injuries of all.

So she watched Beijing on television, knowing she should be there. That inspired her to throw all her efforts into a comeback for the World Championships in Berlin.

In December, she finished fourth at the European Cross Country – having done much of the early running. In March, a few weeks after breaking Sonia O’Sullivan’s national record over 3,000 metres, Cullen won bronze at the European Indoors in Turin. Suddenly Berlin couldn’t come around quick enough.

By the end of April, having enjoyed a few weeks’ training in her native Sligo, Cullen suffered a recurrence of the stress fracture. On top of that, she got a minor illness. A double-whammy, just when she thought her fortunes had finally turned kind.

Once again she’ll watch a major championships knowing she should be there, knowing every athlete is one hamstring pull away from oblivion.