Negative splits are positive

What works for best performance in a long run or bike ride? Start hard and push it as far as you can, or start in a more comfortable speed and increase at the end?

It's the latter, when your mile (or km) times are getting faster as you go (negative splits), you are more likely to reach your best time. This is well known, and I have also tested it for myself on the treadmill. 

To the left is an example of negative splits on a recent training run.

Starting too hard is always a mistake, you cannot will yourself to keep it up to the end, your body is actually unable to respond. I am not going into the physiology of why, but I have enough experience to say that a too ambitious opening will fail to make a good time and it's not a lack of willpower.

When I did my half ironman earlier in the year, I was just focused on completing the course, not to reach a specific time or place. I managed the energy well, holding an even pace, and the final run ended up as my best performance for the day, I passed many competitors. At goal, I was tired, but not wiped out.

On some shorter races, I have pushed too hard early on, and had to walk at the end, even feeling faint. Starting hard always fail to deliver good results.

My best events, training and competition, have been when I am more controlled and start in a sustainable pace. If I feel ok halfway, I know I will last all the way. But of course, everything is within reason, you can't start too slow. It should feel fast, but like you could go forever. Remember, you can always increase the speed on the second half of the race, if you still have the energy.

For shorter races (and training), a proper warm up is essential. I have tested my warm up time on the treadmill, and it takes me up to 9 minutes to go from walking to competition speed. A few times when I was busy, I tried to hasten the warm up, but it can't be cut. I just can't run at competition speed without the full warm up.