When such small incidents can suddenly open up a void beneath an international athlete, it is no wonder they tend to be a cautious bunch. But Sergeant Kelly Holmes, of the No 1 Household Division Army Youth Team, adopts a markedly different approach to life.
Earlier this year, during an exercise with other Army instructors, Britain's Commonwealth 1500 metres champion was asked to canoe down the white-water rapids at the Holme Pierrepont national water-sports centre. As it happens, she has a particular fear of water - "my biggest nightmare is about drowning" - but that was not the overriding factor for her.
"If the lads were going to do it, I was going to do it," she says. "I couldn't let myself down." She set off, eventually capsized, and hung on to her canoe as she was dragged through the churning water. "I thought I was going to die," she says. "After a while I had to let go of the canoe and hang on to one of the slalom poles on the course. My legs were dangling down, and I thought I was going to get them broken."
When she eventually got to dry land, thankfully unharmed, she had the consolation of discovering that several of the lads had not, in the event, put themselves at risk in the same way. One up to Sgt Holmes.
The 800m field she beat at the Crystal Palace grand prix on Friday - accelerating down an outside lane as if she was on a motorway - was the best to have been assembled so far this season. Only two days earlier, Holmes had competed for the Army in an inter-services match, running the 800m, a leg of the 400m relay (in 52.7sec) and - at half an hour's notice - the 3,000m. One up to Sgt Holmes.
Holmes, demonstrably, is not your average, coddled athlete. This season she has built upon the form which brought her Commonwealth gold and European silver last season, and as the World Championships loom next month, she is shaping up as one of the most outstanding female middle-distance talents this country has produced since Ann Packer. Medals in Gothenburg look like a probability rather than a possibility, although she must first negotiate this weekend's AAA Championships and trials at Birmingham, where she hopes to double up at both 800m and 1500m.
If Holmes has an extra spring in her step this season, it is because she has been able to resolve the potential split in her life between the demands of athletics and the Army. She has now switched from being a physical training instructor at Aldershot to a posting at Mill Hill, where she acts in more of a public relations capacity, helping to take groups of young people on adventure training or assault courses to give them an idea of what Army life involves.
Army recruiting offices carry posters of a soldier who is so perfect for the job that she could almost have been specially invented. "I'm female, I'm black, and I'm an international athlete," she says. "I think I'm a good role model."
Crucially, she is now given more time to train properly, and has recently moved to Seven-oaks so she can be closer to the man who has coached her since she was 12 years old, Dave Arnold.
"The new job was a weight off my mind," she says. "If I couldn't have got something sorted out I think I would have had to leave, because there is so much at stake for me. The next two years are going to be the important ones.
"Everything is coming together at the moment. I think I have had it for three years, but it is only now that it is coming through, because this is the first year I have been able to train properly. I did a lot of gym work last year, but no real quality work on the track. If I could get a Commonwealth title and European silver with that, I'm hoping to do even more now."
The palpable commitment - the stand-up-and-be-counted attitude - is something Holmes has displayed since she first began training with Arnold at the age of 12, after her mother had taken her down to the local track in Tonbridge.
"Even at that age, she used to think the world had come to an end if she lost," Arnold recalls. "You have to watch a person like that. You have to take care that they don't get into things they can't cope with."
There seems little in prospect now which falls into that category for Holmes. The white-water experience, however, is not something she is keen to repeat. In future, she will stick to tamer pursuits. Rock climbing. Abseiling. That sort of thing.