BRINGING SCIENCE TO TREATMENT

Running from injury

Last year a landmark study revealed that vertical loading forces, long thought the scourge of injured distance and recreational runners, are likely not the causes of repeated injuries(1). Rather, Canadian researchers found that when evaluating kinetic variables in 65 healthy female runners, only peak braking force (PBF) was a significant predictor of repeated running injury (RRI)(1). Specifically, those with a PBF of .27 body weight (BW) had a nearly eight times greater chance of developing a subsequent injury than those with the lowest PBF. These same researchers at the University of British Columbia sought to determine if a therapeutic gait-retraining program could decrease the PBF in female recreational runners in order to decrease the chance of injury(2). They defined PBF “as the maximum posterior force observed from initial contact to 50% of stance.”

Using gait lab video analysis, they evaluated the kinematic parameters of 12 female recreational runners with a PBF of greater than .27 body weight prior to their participation in the gait-retraining.  As part of the study, each runner participated in a 15-week half marathon training program, completed online questionnaires, and attended gait retraining sessions in the gait lab. The retraining consisted of eight supervised treadmill running sessions at regular intervals during the study, using biofeedback to help train the runners to decrease the PBF.

The biofeedback gave the runners a visual representation of the PBF and each runner was instructed to keep the PBF as low as possible. Runners self selected strategies to lower the PBF. After 15 weeks the runners underwent repeated baseline tests, running as desired as in the initial test, but also being cued to run with their newly learned gait as well.

When compared to the natural running at baseline, the follow up natural running showed an average decrease of 15%  in the PBF. Step frequency increased 7% overall and step length decreased by 6% on average. The new gait showed an even further decrease of 18% of PBF when compared to baseline. The kinematics of the new amended running gait showed a 9% increase in the number of steps and an 8% shortening of stride length. The reduction of PBF in this cohort demonstrates clinical significance in that it reduces these runners’ risk of RRI by a factor of five(2). In addition, average vertical loading rates (AVLR) and instantaneous vertical loading rates (IVLR) were also reduced after the retraining program. This may have the added benefit of further reducing injury risk.

Clinical significance

The incidence of injury for the study subjects was extremely low, with only one participant complaining of shin splints during a training session. Otherwise, all completed all training sessions with nearly perfect adherence to the schedule. This alone is substantial since nearly half of all recreational runners experience some sort of running injury in the course of a year(2).

This preliminary study was exploratory in nature. With a small and specific sample size it is difficult to draw definitive conclusions. However, it’s notable that runners can be trained to decrease their PBF. Effectively, it appears that increasing cadence and decreasing stride length, more than adjusting the type of foot strike, foot strike angle, tibial shaft angle, or shoe wear, may decrease the risk of RRI. This is likely because the braking force during the first half of stance increases the further the foot lands away from the center of mass(3).

The investigators caution extrapolating too much from this initial study. However, it should heighten the clinician’s awareness of basic running kinematics when treating running related injuries. Rather than looking solely at the musculoskeletal system for dysfunction, a functional running evaluation should be included to assess stride length and cadence. Future research may discover that decreasing the incidence of injury may be as easy as running with a metronome.

References

  1. Scand J Med Sci Sports.2018 Oct;28(10):2164-2172
  2. JOSPT. 2019 March;49(3):136-43
  3. J Exp Biol.2015 Nov;218(Pt 21):3406-14

 

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