Which energy system shall I use to chase down this toe rag?

Natalie in her P.Js!

Apparently she warned the attacker that she would catch him, as she put on her running shoes, and he found it very amusing that a 5 foot 4 inch slip of a girl thought that she was capable of this. So what was he thinking as he laughed and ran away? Well he probably predicted a short sprint of maybe 10 - 15 seconds by which time he would be away and Natalie would have given up. What he didn't bargain for was the fact that Natalie has an incredibly well trained anaerobic lactic system that meant she could run at a faster speed than him once the time of the effort went on for more than two minutes. She knew this but he probably doesn't know what an anaerobic lactic system is! (I'm guessing of course!)

We have three energy systems: Alactic, anaerobic lactic and aerobic.

The alactic system is the B of the Bang. It is a chemical reaction that occurs as we get up to do anything quickly. I reckon this guy probably has developed his quite well if he makes a habit of breaking into people's property and then running off quickly. To develop this system you need to train by working hard for a maximum of 10 seconds and then have plenty of rest, maybe ten minutes depending on how well trained you are, between efforts.

The anaerobic lactic energy system becomes more dominant if the exercise is intense or fast and it lasts for up to 3 minutes. It depends how intense the exercise is as to when your body starts struggling to get enough oxygen in to remove the waste products (acidosis) that start to build up once you cross over your lactate threshold. My guess is that Natalie would have had a far higher lactate threshold than this guy. In other words she could operate aerobically at a high intensity for longer without tipping over her lactate threshold. Apparently the chase lasted for around 4 minutes. No wonder he collapsed on the floor outside W H Smith whilst she stood over him and told him he should have listened to her! He will have got to the stage where there was so much lactic acid in his muscles and blood that he will have felt like he was running through treacle and may well have felt sick, so had to slow down and stop. Natalie, on the other hand, after four minutes of hard running was probably feeling like she was just getting into her rhythm as her body is trained to operate just under that threshold until the later stages of an endurance race. This system is typically trained by interval training or repetition work. A type of training that Natalie has done for years.

Natalie isn't the only female endurance runner who has found success in chasing down criminals. Last year PC Kelly Morgan, who has a runbritain handicap score of 6.2, chased down a teenager who had been causing trouble outside a house in South Wales. Kelly, who is 5 foot 5 and was in training for the Volkswagen Prague Marathon, chased the teenager through woods until he turned round and told her he was giving up because he was very tired! Mmmm...another case of an untrained anaerobic lactate system me thinks!

I caught up with PC Dave Mitchinson who, like Natalie and Kelly is diminuitive but has great speed-endurance. Dave is currently in 38th position on the runbritain Grand Prix after running the Bristol 10k in 30:35. The only chase he has ever lost was when the criminal was on a bike. In this ipadio interview he tells us what typically happens during and after the chase.