Human muscle and spinal activation in response to body weight loading

Area of Science:

• Biomechanics and Motor Control
• Neuroscience
• Rehabilitation Engineering

Background:

• Independent human standing is fundamental for mobility.
• Restoring unsupported weight-bearing and gait remains a significant challenge in rehabilitation technology.
• Understanding muscle and spinal responses to gravitational loading is crucial for developing effective interventions.

Purpose of the Study:

• To investigate muscle and spinal activation patterns under different gravitational loads in healthy individuals.
• To identify critical body weight percentages and muscle activation thresholds for achieving standing.
• To provide data for developing spinal stimulation strategies to aid in restoring independent standing.

Main Methods:

• Surface electromyography (EMG) recorded muscle activity from 18 healthy participants.
• Participants were positioned at various body angles on a motorized plinth, simulating gravitational loads from 0% to 100% of total body weight (BW).
• Spinal activation maps were calculated from EMG data, focusing on lower lumbar and sacral segments.

Main Results:

• Group muscle activity significantly changed with body angle, with key muscles like vastus lateralis, soleus, and gastrocnemii activating at higher gravitational loads (60-100% BW).
• A critical loading threshold of approximately 87% BW was identified for increased muscle activation compared to the supine position.
• Significant differences in mean activation were observed in the L5 (fifth lumbar) and S1 (first sacral) spinal segments during weight-bearing.

Conclusions:

• Weight-bearing independent standing can potentially be achieved through targeted activation of specific superficial muscles.
• The findings suggest that 87% BW is a critical loading point for initiating substantial muscle activation.
• The identified pattern of muscle and spinal segment (L5-S1) activity provides a basis for developing spinal stimulation therapies for individuals with spinal cord injuries to restore standing and walking.