I have long suggested that the number one biomechanical risk factors for an overuse running injury and determinate of running economy is joint moments. That is generally affected by variations in joint axes positions. The loads in the tissues and how hard a muscle has to work is determined by the joint moments. Different ways of running will affect those joint moments in different runners differently, due to the individual variation in joint axes positions (see this discussion). Joint moments are also going to be affected by other things, such as speed:
Comparisons of increases in knee and ankle joint moments following an increase in running speed from 8 to 12 to 16 kilometers per hour
Jesper Petersen, Rasmus O. Nielsen, Sten Rasmussen, Henrik Sørensen
Clinical Biomechanics; Published Online: September 14, 2014
Knowledge regarding knee and ankle joint load across a range of running speeds is important, if running related injuries are to be prevented. The purpose of the present study was to test the hypothesis that peak plantar flexion moment increases relatively more than peak knee extension moment when running speed is increased.
Kinematic and ground reaction force data were collected from 33 recreational runners during steady-state running at three different speeds: 7.96 km · h−1 (SD 0.18), 11.92 km · h−1 (SD 0.25) and 15.91 km · h−1 (SD 0.36). Peak plantar flexion moment and peak knee extension moment were calculated using a standard three-dimensional inverse dynamics approach.
There was a significant interaction between the joint location and running speed (P = 0.03): When running speed increased from 7.96 to 15.91 km · h−1, mean peak plantar flexion moment increased by 0.74 N · m · kg−1 (95%CI: 0.64;0.85) which was more than the 0.52 N · m · kg−1 (95%CI: 0.42;0.63) increase in mean peak knee extension moment.
A greater increase in biomechanical load occurs for the plantar flexors of the ankle joint than for the extensors of the knee joint when running speed increases. This may indicate that at an excessive running speed, the structures at the posterior part of the lower leg and underneath the foot are relatively more vulnerable to injury compared with the structures at the anterior part of the knee. As a considerable load reduction is achieved, a decrease in running speed may benefit rearfoot striking recreational runners experiencing pain in the posterior lower leg or underneath the foot.
Not surprisingly, they found an increase in both the knee extension moment and the plantarflexion moment with increased speed, but the plantarflexion moment increased a greater amount, hence the authors commenting:
It is indicated that as running speed increases, the plantar flexors of the ankle joint are burdened to a greater extent than the extensors of the knee joint. This could lead to the assumption that at an excessive pace, the structures at the posterior part of the lower leg and underneath the foot are more vulnerable to injury compared with the structures at the anterior part of the knee.
Nothing I can see is an issue in this study except for perhaps the minor issues of:
- the subjects were asymptomatic and the results may or may not be the same for those with Achilles or knee problems, though I see no reason why they would not be
- it was NOT done on a treadmill (good) which does make it more difficult to achieve the desired speeds and multiple trials with feedback would have been needed to achieve this; some information on this was provided in the paper, but more detail would have been helpful to be more comfortable with this issue
- the order of running speeds was not randomized (the authors did acknowledge this, citing the reasons of practicality for the targeting the desired speeds)
What was really neat about the above study is that it does fit in quite neatly with this study that tried to divide injuries into volume or pace related injuries. That study found that the pace related injuries were Achilles tendinopathy, gastrocnemius injuries and plantar fasciitis. The above study goes some way in explaining why …. don’t you love it when a plan comes together!
Probably the only thing I would be tempted to disagree with is the statement: “a decrease in running speed may benefit rearfoot striking recreational runners experiencing pain in the posterior lower leg or underneath the foot.” Yes, a decrease in running speed would decrease the load in those structures, but what runner would want to do that? and surely a better approach before trying that would be to implement other load reduction strategies first.
As always, I go where the evidence takes me until convinced otherwise…and if you have an injury, run slower (but not further).
Petersen, J., Nielsen, R., Rasmussen, S., & Sørensen, H. (2014). Comparisons of increases in knee and ankle joint moments following an increase in running speed from 8 to 12 to 16km·h−1 Clinical Biomechanics DOI: 10.1016/j.clinbiomech.2014.09.003