It's oh so tempting to go hurtling off at the start of a race. You feel great because you rested a few days before the race, had a good night's sleep after a proper meal and no alcohol (well maybe!), your adrenaline is flowing and you are surrounded by competitive runners you want to beat! You rationalise that if you run hard while you're feeling good, you'll get "time in the bank" for the inevitable fade towards the end. If you run the second half of a race slower than the first half this is called a positive split.
A negative split is when you run the second half of a race faster than the first half. It usually produces better race times and less fatigue. Most world records over distances greater than 800m were set with negative splits. Leading coaches think negative splits are good for both elite and recreational runners to aim for. It takes a couple of miles to warm up thoroughly during a race, for your joints to become fully mobile and your muscles well perfused with blood and in peak condition. If you run the first half of a 10k too fast you'll be making excessive demands on muscles and joints before they are working at their optimum and the consequent fatigue is more pronounced.
Most of us mere mortals struggle to finish a marathon or even a half marathon faster than at the start. But a 10k is a great distance to aim for a negative split.
Set yourself a realistic target finish time and during training runs, practise increasing your pace during the last few miles. A negative split doesn't mean flying the second half five minutes faster but 30 - 45 seconds would be a good goal.
I recently ran a flat-ish two lap 10k. I'd run it before so was familiar with the route. My pb for a 10k is 49:12 but that was a long time ago and I usually struggle to get near 50 mins. So I planned on 8:10 min/miles for the first lap and 8 min/miles for the second lap, which would give me a finish time of 50 mins. It worked well, I managed to hold steady for the first 5k at the planned pace, and had energy left for the second lap. I felt good overtaking people regularly during the last few km and ran the second half 40 seconds faster than the first, finishing in a 'good for me' time of 49:20. Instead of feeling lousy for the last 3k and 'hanging on', I only felt sick for the last few hundred metres!