I just read an interesting study comparing the footstrike of marathon runners at different stages of the race. Of 286 random runners studied, less than 88 percent were rear footstriking within the first 7 miles. By the 20 mile mark this number increased to over 90 percent. Factors influencing this breakdown can be attributed to muscular fatigue, which can be linked to training. Muscular imbalances can also play a role. Your take home message: address the firing patterns of proper form through the use of drills and make sure your training program is adequately preparing you for the muscle fatigue that you’ll; experience on race day.
Your cadence can also determine how long you are able to hang onto an optimal footstrike as well as help you conserve energy.