(Research Hub Theater) Improvement in Muscle Activation Latency Through Reactive Step Training in People with Parkinson’s Disease

Background and/or Objectives: Individuals with Parkinson’s Disease (PD) experience increased lower limb rigidity and fall risk due to inappropriate activation of muscles necessary for reactive stepping. A 2-week protective stepping training program using treadmill perturbations has previously demonstrated improvement in lower limb kinematics during reactive stepping, but the reasons are unknown. This study used surface electromyography (EMG) to investigate changes in muscle activation latency before and after training to understand potential contributions to improved step kinematics.

Design: Prospective Cohort Study

Setting: Gait and Balance Laboratory

Participants: 27 adults (age>65) diagnosed with PD at risk for falls.

Interventions: 6 protective stepping training sessions over 2 weeks. EMG was captured at 4 timepoints: baseline 1 (B1), baseline 2 (B2) two weeks later, post-intervention 1 (P1), and post-intervention 2 (P2) after a 2-month retention period.

Main Outcome Measures: Latency of activation in the medial gastrocnemius (MG) and tibialis anterior (TA) muscles during forward and backward reactive stepping.

Results: During backward reactive stepping, we observed small, consistent decreases (improvements) in agonist (TA) latency from B1 to P1 (mean=7.65ms, SE=3.58; p=.048) and from B2 to P1 (mean=4.25ms; SE=2.23; p=.074). This corresponds with significant kinematic changes of increased margin of stability, step length, and step latency. During forward reactive stepping, we observed consistent increases (improvements) in antagonist (TA) latency from B1 to P1 (mean=25.98ms; SE=6.83; p=.001) and B2 to P1 (mean=11.90ms, SE=5.43; p=.04). This corresponds with significant kinematic changes of increased step latency. No other statistically significant results were observed.

Conclusions: The small (~7-25ms) but consistent, and statistically significant changes in lower limb muscle onset latencies observed in people with PD after reactive balance training suggest possible neurophysiological training adjustments. However, given the small amplitude of latency changes, they may not explain the kinematic (i.e., step) changes observed through training. Further investigation should examine the amplitude of muscle activation and other potential contributory factors for improved stepping kinematics.