MOST people find running a half-marathon difficult, let alone attempting the full 42 kilometres.But try taking on a 100km race, with a few mountains in the mix.That's exactly what Warrnambool policeman, John Keats, did when he competed in the North Face 100 -- Australia's pinnacle of trail runs. The mammoth endurance race weaved its way through the Blue Mountains and this year attracted 350 competitors.Keats, 43, came 32nd in a time of 13 hours and 46 minutes."It was unbelievable, tougher than I ever imagined," he said. "I power-walked the last 11 kilometres. I had lost my running legs. It was full on."But despite the gruelling physical and mental challenge, Keats is already planning to line up for the North Face 100 next year.He said he learnt a lot from this year's event, held earlier this month."The killer was going downhill and the stairs (on the trail). I do a lot of uphill training but I've got to get my body used to that downward pressure."I'll go out to the biggest hill at Tower Hill and run up and down it for about two hours straight."Keats was holding third place in the first half of the Blue Mountains race. But his fortunes changed after passing through a checkpoint. He felt a dampness seep across his back."I went to have a drink out of my bladder (drink bottle) and there was nothing in it -- there was a leak."For two-and-half-hours I couldn't have anything to eat or drink, which was pretty tough. I had to run to the next checkpoint." Keats is no stranger to mega endurance runs. He won the Frankston to Portsea 55km ultra marathon earlier this year and has previously competed in 100km Oxfam runs in the Dandenongs.He is gearing up for the Melbourne Marathon, set for October, which he said should be a breeze."It's flat, no hills -- a lot different to the Blue Mountains. I'm really looking forward to it."