Objective: To review electromyographic and kinematic patterns in patients with runner’s dystonia (RD).

Background: RD is a task-specific focal limb dystonia, preferentially involving the lower extremities in long distance runners during the act of running. To date there have been no studies describing EMG patterns or kinematics in RD.

Methods: 12 patients with RD were evaluated in the NIH biomechanics laboratory. Mean age was 56.3 years, with a mean disease duration of 4.9 years. The affected leg was on the left in 7 patients, the right in 4 patients, and bilateral in 1 patient. Surface EMG electrodes were placed over four leg muscles: tibialis anterior, gastrocnemius, quadriceps, and hamstrings. EMG was evaluated qualitatively in terms of timing and duration relative to the gait cycle, and for the presence of co-contracting muscles. Kinematic data was obtained with an infrared motion capture system and processed with Visual3D software.

Results: Abnormal EMG activity by individual muscles was highly variable. The most common pattern among all muscles was early activation. Continuous activity and co-contraction were more common in affected limbs, but affected and unaffected sides were not significantly different. In walking, step length significantly predicted gait speed in both affected (β=1.70*) and unaffected limbs (β=1.13*). However in running, only the affected limb (β=2.51*) was predictive of gait speed. Combining EMG with kinematics allowed us to distinguish between dystonic and compensatory activity as well as between RD and non-dystonic mimics. *(p<.03).

Conclusions: This study identifies EMG abnormalities in the lower limbs of patients with RD, similar to those reported for the upper extremity in writer’s cramp: mistiming of activation, failure of activation, and co-contraction of agonist/antagonist muscles. These features were present in both affected and unaffected limbs. Abnormalities in the unaffected limb may represent compensatory activation needed to maintain bipedal gait. We also demonstrate task-specificity in RD. Gait speed was significantly predicted by step length in both limbs while walking, yet in running, only the affected limb was predictive of gait speed. Lastly we highlight the value of examining patients with RD in a biomechanics laboratory. A combined approach of clinical assessment, EMG, and kinematics may reliably distinguish dystonic from compensatory activity and RD from non-dystonic mimics.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/electromyographic-and-kinematic-patterns-in-runners-dystonia/