Walking is an extremely efficient way for humans to move around, which is one of the reasons it can be done for hours at a time without getting too tired. Running on the other hand requires a lot more energy than walking, effectively you are continuously jumping from one foot to the other. In fact, running consumes around 40 to 50% more kilojoules than walking the same distance which means in less time you can use up to twice as much energy (which is great is your looking to offset a few extra kilojoules). But if running isn’t your forte don’t be scared to intersperse short bouts of running with some walking in between to still use more energy but also give you a bit of a rest. This can also help you to gradually build up to longer runs.