Because no scientific formula exists that accurately maps out the appropriate combination, frequency and prescribed duration of different activities for cross training, designing a cross-training program is both an art and a science.
Based on clinical studies, most people will plateau in their exercise programs somewhere between their sixth and eighth week. At a minimum, exercisers should change their routines during that time frame.
During those six to eight weeks, exercisers should have at least two different alternating activities. They can alternate within the same workout or vary their routine every other day.
This way, they still work their legs but give them a break from the high impact of running. Runners also benefit from engaging their upper bodies and conditioning the muscles that normally are not used while running. Another example is group cycling enthusiasts who may do well to alternate a weight-bearing exercise, such as jogging, elliptical exercise or stairclimbing.