step frequency and patellafemoral joint forces
More evidence is accumulating that alterations in cadence may affect joint loading, particularly at the knee.
Rachel Lenhart and her colleagues at the University of Wisconsin-Madison evaluated 30 healthy recreational runners (average age 33) who were currently pain-free and running at least 15 miles a week for the past 3 months. The objective of the study was to assess changes in muscle and joint loading in relation to changes in running cadence (step frequency). The hypothesis was that increasing step frequency would result in a reduction in patellafemoral joint force due partly to a change in the posture of the knee during the loading phase of gait.
All subjects were first tested to determine their self-selected step rate and pace on a treadmill. They were then tested at that same speed, using a metronome to help them alter their cadence by 10% faster and also by 10% slower than their preferred cadence. Motion analysis was performed using high speed cameras and the specialized treadmill recorded ground reaction forces while surface electrodes recorded muscle activity.
The results were consistent with previous studies, and confirmed the author’s hypothesis that changes in step frequency affect muscle and tendon loading as well as joint loading at the knee. Specifically, when the subjects ran at the same speed on the treadmill but with a faster step frequency (110% of their self-selected cadence), there was a statistically significant reduction in patellofemoral joint force, as well as patellar tendon force. Conversely, when they ran that same speed with a slower step frequency (90% of self-selected cadence) the forces were significantly higher.
Since excessive patellofemoral force has been suspected to be involved in patellofemoral pain syndrome, it might be worthwhile to assess cadence and consider gradual adjustments to a slightly faster cadence in an attempt to reduce these forces. However, changes in cadence should be gradual as previous studies by UWM researcher Dr. Bryan Heidersheit published in the February 2011 issue of MSSE (read my summary here) found that alterations of cadence of 10% were accompanied by an increase in perceived exertion, whereas alterations of 5% were not.
Limitations of this study are similar to previous studies in that the research was done on athletes who are uninjured, and the measurements were done while running on a treadmill rather than over ground. In addition, other factors such as strength, flexibility, training volume, proprioception etc., that may contribute to or prevent injury were not included in this study. Of interest in this regard is a recent study published in the June 2013 issue of MSSE (read my summary here) that identifies hip weakness as a significant factor in contributing to patellofemoral pain in runners.
In summary, as you evaluate your athletes, try to take a step back and evaluate the BIG picture. It’s rare that one thing alone causes an injury and even rarer that one intervention will solve it. Assess your athletes strength, flexibility, cadence, and do a thorough review of their training history in order to identify areas in need of adjustment. Make your changes gradual and monitor your athletes to make sure that any changes you make move them in the right direction.
To your athletes ongoing success!Coach Janet Hamilton, MA, RCEP, CSCS