Introduction. Increased joint resistance to imposed movement (“muscle hypertonia”) is a common finding in patients with an upper motor neuron syndrome, following stroke. Contributors to muscle hypertonia are of neural (increased reflex activity) and non-neural (altered visco-elastic properties) nature. Extracorporeal shock wave therapy (ESWT), a new noninvasive treatment modality, appears to be beneficial as hypertonia relieving therapy. However, clinical assessment such as the Ashworth test are unable to discriminate between underlying intrinsic and neural properties. Therefore, the effect of ESWT on the underlying neuromechanical components of muscle hypertonia remains unknown. The effect of ESWT on the contributors to joint resistance can be quantified using motorized ramp-and-hold movements and neuromuscular modeling of the musculoskeletal system of the ankle joint.

Methods. Patients with chronic muscle hypertonia (MAS > 1) were measured using ramp-and-hold rotations applied by a robotic manipulator, using slow (15 °/s) and fast (100 °/s) movement velocities. Ankle angle, torque and EMG of the tibialis anterior, soleus, gastrocnemius medialis and lateralis were measured and used to fit a neuromuscular model to the measured joint resistance. The neuromuscular model contains 15 optimizable parameters which represent the intrinsic and active muscle components. Outcome measures were the estimated model parameters, the range of motion (ROM), and modified Ashworth scale (MAS) of the ankle joint.

Results. No effect of ESWT treatment was observed on the estimated model parameters and the passive ROM. The MAS was significantly lower after ESWT treatment (Z = -2.121, p = 0.034). Movement velocity introduced changes in the estimated model parameters.

Conclusion. Conflicting results between the biomechanical assessment (estimated model parameters, ROM) and clinical assessment (Ashworth test), raises questions about the validity of the Ashworth test. Furthermore, since no effect was observed on the neuromuscular model parameters, no conclusion can be drawn on the effect of ESWT on the neural and non-neural contributors to ankle joint resistance in patients with chronic muscle hypertonia.