For other training programs visit the Runners World website. Durden's chart is arranged in suggested miles. The most important days in this schedule aren't the hard days, but the easy ones in between. Easy days are very critical because they allow the body to recover from and adapt to the hard training done during the rest of the week. If you did not have the easy days between the hard ones, the training would break you down rather than make you stronger.
Easy days are also a good day for cross training.
Riding a bike, brisk walking, swimming and weight training are all beneficial activities for marathoners in training. Another key component to training for a marathon is the long runs. These runs are essential and should be done every week. If you have to skip a run don't let it be on your long day. The long runs allow your body to adapt to the stresses of running the long distance of a marathon.