Plantar flexor muscle weakness may cause stiff-knee gait

Area of Science:

• Biomechanics
• Gait Analysis
• Neuromuscular Function

Background:

• Stiff knee gait (SKG) is often linked to plantar flexor (PF) muscle weakness.
• Previous simulations suggest PF weakness contributes to SKG, but direct validation in humans is lacking.
• Understanding the isolated effect of PF weakness is crucial for gait rehabilitation.

Purpose of the Study:

• To investigate the impact of isolated plantar flexor muscle weakness on knee flexion velocity.
• To determine if induced PF weakness generates a stiff knee gait (SKG) pattern in healthy individuals.

Main Methods:

• Twenty healthy adults underwent a passive stretch protocol to reduce PF muscle strength by 33.1%.
• Three-dimensional gait analysis was performed before and after the intervention.
• Key parameters analyzed included peak knee flexion, range of motion, and timing during the gait cycle.

Main Results:

• Reduced PF strength significantly decreased knee flexion velocity at toe-off (p=0.008).
• Induced PF weakness led to a significant SKG pattern, characterized by reduced peak knee flexion (p=0.0001) and range of motion (p=0.006, p=0.002).
• These gait changes strongly correlated with decreased PF strength.

Conclusions:

• Plantar flexor weakness is a direct cause of stiff knee gait (SKG) by affecting key kinematic parameters.
• Therapeutic interventions that inadvertently weaken PF muscles may negatively influence SKG.
• This study provides empirical evidence linking isolated PF weakness to SKG development.