Does spinal excitability scale to the difficulty of the dual-task?

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• The soleus Hoffmann reflex (H-reflex) is a measure of spinal excitability.
• Previous research suggests H-reflex amplitude decreases with increased postural task difficulty.
• Dual-tasking involves performing a motor task concurrently with a cognitive task.

Purpose of the Study:

• To investigate if spinal excitability, assessed via soleus H-reflex, is modulated by the difficulty of a concurrent cognitive-motor dual-task.
• To compare spinal excitability during dual-tasking versus single-tasking balance challenges.

Main Methods:

• Twenty-two participants performed nine dual-task conditions combining three balance task difficulties with three visuo-motor task difficulties.
• Eight participants performed the balance tasks under single-task conditions.
• Soleus H-reflexes were measured throughout all trials using surface electromyography.

Main Results:

• Dual-task performance (accuracy, stabilometer control) declined significantly with increasing task difficulty (p < 0.05).
• No significant changes in soleus H-reflex amplitude were found across different dual-task difficulty levels (p = 0.483–0.758).
• In contrast, H-reflex amplitude decreased by approximately 25% during single-task balance performance from easy to hard conditions (p = 0.037).

Conclusions:

• Spinal excitability is not modulated by dual-task difficulty, unlike single-task balance challenges.
• When attentional resources are overloaded during dual-tasking, the ability to regulate spinal excitability for balance may be compromised.
• These findings challenge the assumption that spinal reflexes are consistently scaled with task demands under dual-task conditions.