The treadmill remains a necessary evil when completing run training allowing athletes to escape inclement weather to complete their workouts.  Thankfully, in Boulder we have few inclement days as we move through the Spring and Summer months allowing athletes to train outside.  Prior research has noted significant bio-mechanical differences in treadmill vs. ground running including athletes adopting a shorter stride length on the treadmill.  This reduction in stride length is accompanied by an increased in step frequency to maintain a given speed.  These changes will impact the rate and magnitude of loading across the leg during landing.  Recently, a Physical Therapy article examined the biomechanical impact of treadmill and over ground running on the knee and ankle structures. 

Willy and colleagues studied 18 healthy runners (9 female) who were running at least 10 km per week over the last 6 months and were free of injury over the previous 3 months (JOSPT. 2016).  Runners were analyzed in a Physical Therapy biomechanics laboratory while running on a treadmill and overground both at a previously self selected gait speed.  

Similar to prior research, runners selected a shorter stride length when using the treadmill compared to level ground.  The authors did not find differences in knee mechanics or loading between the two conditions.  Conversely, the authors noted greater achilles tendon loading and calf muscle contraction during treadmill running.  They attributed these changes to increased peak tendon forces during the treadmill run.  

This article was performed in healthy individuals but may have implications for those returning to running from achilles injury or those using the treadmill for the majority of their training runs.