By Emily Delzel
Backward running involves lower patellofemoral joint compression forces than forward running and is a viable strategy for rehabilitation of patellofemoral pain syndrome in runners, allowing them to continue exercise without increasing these forces, according to UK research e-published in April in the Journal of Biomechanics.
Previous trials of backward and forward running and their effect on patellofemoral joint compression forces (PFJCF) have shown lower PFJCF for backward running than forward running, but in these studies participants ran slower backward than forward. Investigators from Cardiff University in Wales studied the effects of backward and forward running at the same speeds. Participants completed three trials each of backward and forward running.
Running speeds between the two conditions were almost identical
(3 ± 0.2 m/s), but PFJCF and peak knee moment were significantly lower for backward versus forward running and peak hip flexor moments were significantly higher in forward running.
Lead author Paulien Roos, PhD, Cardiff Academic Fellow in the Arthritis Research UK Biomechanics and Bioengineering Centre, noted, “Changes in PFJCF between forward and backward running were not due to running speed, but to a strategy change that took place, from predominantly telescopic in forward running to predominantly pendular in backward running.”
Pendular movement is typically observed in walking, while telescopic motion, which involves a large compression and passive recoil of the stance limb, is seen in forward running. Pendular movement requires high hip flexor moments rather than high knee extensor moments to generate push off.
Roos and her colleagues also found a correlation between center of pressure (COP) location at foot strike and PFJCF, with reduced PFJCF if the COP was closer to the forefoot at foot strike.
“This means that a forefoot strike running style would have lower compressive forces at the patellofemoral joint than a heel strike running style,” she said. “The initial foot contact was important in defining the PFJCF and suggests there is an opportunity to investigate various running styles for therapeutic application.”
In an earlier analysis of the same study group, presented by Roos et al in 2011 at the 23rd International Society of Biomechanics Congress in Brussels, Belgium, the investigators assessed whether the reduced PFJCF seen with backward running was due to kinetics or kinematics. Peak knee moment was significantly higher in forward running than backward running, while knee angle at peak knee moment did not differ significantly between the two conditions. This indicates that kinetics, or moments, and not kinematics, or knee angle, lead to the reduced compressive forces seen in backward running, Roos said.
“Our study demonstrates that it is sensible to have an in-depth analysis of exercises used in therapy that includes kinematics and kinetics and relates those to each other. There is a need for movement science and movement therapy to meet more often,” she said.
Richard Willy, PT, PhD, OCS, assistant professor of physical therapy at Ohio University, Athens, who reviewed the study for Lower Extremity Review, noted that applying these findings to clinical practice should be done with caution.
“Incorrect implementation of either backward running or changing one’s strike pattern alone may increase injury risk,” Willy said. “Due to the increased plantarflexion moments, forefoot running may be associated with an increased risk of overuse injuries to the plantar flexors. In contrast, backwards running presumably increases the stress on the hip musculature.”
He noted, however, that performing moderate amounts of backward running in conjunction with moderate amounts of forward running with a reduced heel strike may allow for continued running in individuals with patellofemoral pain while mitigating the risk of sustaining overuse injuries associated with either running technique in isolation.
Roos PE, Barton N, van Deursen RW. Patellofemoral joint compression forces in backward and forward running. J Biomech 2012 Apr 14. [Epub ahead of print]
Roos PE, Button K, Barton N, van Deursen RW. Patellofemoral joint compression forces in backward running. Presented at the 23rd International Society of Biomechanics Congress, Brussels, Belgium, July 2011.