NHS Choices has developed a 5-week podcast series called Strength and Flex to complement Couch to 5K.
Narrated by the lovely Laura (of C25K fame), the five-level plan takes you through a series of equipment-free exercises to strengthen your legs, core muscles and upper body.
You can download it here:
Frequently asked question - What can I do on rest days?
What do you do on a rest day?
What do you do on your 'rest' days?
what do you do on rest day
How many rest days do you take? 
