Today I trained using a new style of intervals that felt extremely effective, great heat-conditioning and really broke up the creeping-monotony of tempo, or the variety needed for Fartlek.
On an outdoor track and a sunny day with white fluffy rolling clouds you're in business. Okay, this isn't going to be all the time (especially here in Shanghai) but keep this technique in mind if such a day comes by. I'm claiming it as mine and calling it Nimbus Intervals.
Start with a 3-5 lap warm-up at a comfortable pace, then look to the sky. As the clouds roll across the sun you'll be running in and out of direct sunlight. When you enter a patch of shade, speed up to your quick pace and hold it for as long as you're out of the sun. Return to your comfortable pace when the shadow passes.
Days like this are characteristically blustery. Mix it up by sprinting every time you face into a gust of welcome breeze, or if you're growing exhausted drop down to 50% speed momentarily to soak it up.
Depending on how big the clouds are and how fast they're moving - you'll be running in and out of the sun at random intervals. Like Fartlek, this is a great way to train for speed changes from short bursts to sustained speed.
It also makes for good temperature conditioning training for sunny races. Of course beware that the direct sun can be strong and you'll need to take on extra liquids to compensate (not to mention adequate sun block). Cool down with a 3-5 lap gradual wind down and head to a nearby tree to stretch out.
Tip: Don't decide to run home from the track exhausted, run down a back alley, get side-swiped by a woman on a bike who's not looking where she's going, do a barrel roll and sprain your wrist... otherwise, like me, you'll be grumpy for a few days.