In their February 2011 article, Effects of Step rate Manipulation on Joint Mechanics during Running, published in Medicine and Science in Sports and Exercise, Dr. Bryan Heidersheit and his colleagues at the University of Wisconsin-Madison examined what happens to joint loading and force production when a runner changes from their preferred cadence but maintains the same speed.
I was particularly interested in this as I routinely assess cadence or step rate on my athletes, especially if they're battling injury issues (in particular common knee issues like IT band syndrome or patella-femoral pain).
Here were the key findings of the study:
- Increasing a step rate may reduce energy absorption at the hip and knee which may be useful to individuals who are rehabbing from injuries to hips and knees
- A 5%-10% increase in step rate may reduce excessive hip motion which has been associated with onset of knee pain and ITB syndrome.
- It's clear that runners can modify their gait to reduce impact loading but what's less clear is how effective these strategies are in helping with injury recovery or in helping a comeback to running after the injury.
- Since this study was done on healthy (uninjured) runners, it's unclear whether injured runners would experience the same biomechanical changes to step rate manipulation.
- The step rate modification was conducted on a treadmill so it's unclear whether these results would be the same with over-ground running.
The study involved 45 healthy recreational runners who were averaging about 18.5 miles per week (range 15 - 28). All had been running for at least 3 months prior to the study. Each runner ran on a treadmill at a speed that they identified as their "typical moderate intensity run" and the researchers noted their preferred speed (average 6.5 mph, +/- 1.1 mph) and their preferred step rate (average 172.6, range +/- 8.8 steps per minute). The subjects were then asked to run at step rates that were 5% slower, 5% faster, 10% slower and 10% faster than their preferred rate while maintaining the same speed on the treadmill. Audible metronomes were used to help subjects maintain the appropriate step rate. Multiple high speed cameras as well as an instrumented treadmill were used to collect data on biomechanical characteristics and force absorption and production in each of the experimental conditions. Subjects were also asked to rate their level of perceived exertion for each running condition using the standard 15-point Borg scale.
The researchers discovered that there was a distinct correlation between stride rate and certain biomechanical characteristics and energy absorption and production patterns. "As step rate increased, step length was shorter, with less center of mass vertical excursion; the heel was placed horizontally closer to the center of mass at initial contact with a reduction in the braking impulse".
The interesting part is that when this happened, the rate of perceived exertion - or how hard the runners felt like they were working - only increased when step rate was increased by 10%. There was no significant difference with a 5% increase in step rate.
The energy absorbed at the ankle, knee and hip was also affected by changes in step rate. Increasing the step rate by 5% and 10% netted a 20% and 34% reduction (respectively) in energy absorption at the knee. The 10% increase in step rate also produced a 10% reduction in energy absorption at the hip.
Conversely, slowing the step rate by 5% or 10% resulted in an increase in force absorption at the knee as well as the hip.
Because subjects ran at their preferred speed for all conditions, the alterations in step rate were accompanied by proportional changes in step length. The authors noted, "many of the biomechanical changes we found when step rate increased are similar to those observed when running barefoot or with minimalist footwear".
The knee joint appeared to be the most sensitive to changes in step rate. With even a 5% increase in step rate, energy absorption at the knee was reduced by 20% and energy production was reduced by 18%. The challenge here is that shortening the stride length will require more loading cycles (more steps) to cover the same distance so it's unclear if the cumulative loading incurred by the lower extremity will be any different for a given distance of running.
The authors conclude with some worthwhile hypotheses and questions.
Making small alterations to a runner's step rate (increasing it by 5%) is one intervention to consider if a reduction in forces at the knee is a goal. This minor change in step rate will likely have a profound effect on forces absorbed and generated at the knee without making the runner feeling like the effort is much tougher.
IF someone's natural step rate is not ideal, then altering it is likely to achieve many favorable changes (foot strike pattern, posture, etc), and do so in a distinctly sub-conscious fashion. This is in contrast to many of the common "form coaching" tips instructing an athlete to strike the ground in a certain fashion or push off in a certain posture. Simply altering cadence may achieve a similar result without requiring conscious effort to alter posture or gait patterns.
Manipulation of step rate is probably just one option of many possible interventions though, so don't lose sight of the many pieces of the healthy runner puzzle - investigate other factors like strength, training volume, proprioception, flexibility, nutrition, etc. Running injuries are rarely the result of one factor and likewise are rarely resolved with only one intervention.
Alterations in step rate should be gradual and use of an audible metronome set to the proper cadence is helpful. Follow up with your athlete after any adjustment of this type to insure that the changes you've made give you the response you expected!
To your athletes ongoing success!
Medicine and Science in Sports and Exercise: February 2011 - Vol. 43, No.2, pp. 296-302.