Speed Up, Slow Down

If walking or running is part of your training and you want to spice things up a bit you could speed up and slow down again. Of course in sports science this is a training method with the name of an Ikea chair: Fartlek. 

It's Swedish for "speed play" and a type of interval training. It helps you get better at aerobic exercise because you push your limit and slow it down again but you do it at random times. Usually interval training has set periods of hard work and then recovery but in Fartlek it's more random. You might walk for a bit, sprint a bit, then just a gentle jog to recover and then do it all again. It's good for you to challenge your top end ability as it trains different energy systems and will get you better at running further and faster. (It's basically an excuse for why you've sat down at the bus stop while out on your Coach to 5K.) 

Make sure you warm up properly before you start pretending you're a cheetah for 10 seconds as you don't want anything to go twang.

A more in-depth article.