|Ladies that lunch|
Rest and recovery is as much a part of training as the runs themselves - rest is essential as it's during this downtime your body repairs and strengthens itself. The two primary physical aspects of rest are replenishment of depleted glycogen and fluid supplies and the repair of damaged tissues. Without sufficient recovery time, your body will continue to breakdown and resulting in an increased chance of injury and subsequent decreased performance which is counter productive to what you're trying to achieve.
Recovery starts from the moment you finish training - so in order to help your body repair spend time warming down and stretching (things which are often neglected). Next focus on the rehydration and refuel process (see this post for details). An entire rest day should be built into your training schedule - I always have one full day of no training per week to maximize recovery. Depending on your schedule this may mean you have days with two training sessions (like me). This is preferable to not having a whole day off as optmised repair takes time.
My rest days are spent doing just that, resting! There is often a tendency for people to want to fit some sort of training into their off days but this only minimizes the impact of what you're trying to achieve. Today for example, the girls when for a swim whereas I sat in the Jacuzzi! Exercise forces blood into your muscles which is what you want to avoid when resting - your muscles can better repair when they aren't being stretched. The only exception I make to this rule is Yoga, because that doesn't raise the heartbeat and therefore doesn't force blood into your muscles. Yoga is also great for easing stiffness and is great for targeting any particular problem areas. My back was feeling stiff this morning so I did a 30 min session before going out which seems to have done the trick.
Don't feel guilty on off days - make the most of them, you've earned it!