Increased force variability in chronic stroke: contributions of force modulation below 1 Hz

Area of Science:

• Neuroscience
• Motor Control
• Rehabilitation Science

Background:

• Increased force variability is a key indicator of arm motor impairment after stroke.
• Force variability in healthy individuals is linked to force modulation below 1 Hz.
• The relationship between post-stroke force variability and low-frequency force modulation remains unclear.

Purpose of the Study:

• To compare force modulation below 1 Hz in individuals with chronic stroke and age-matched healthy controls.
• To investigate if altered low-frequency force modulation contributes to increased force variability post-stroke.

Main Methods:

• Participants (N=26) performed isometric grip tasks at submaximal force levels.
• Force variability was quantified using the coefficient of variation.
• Force modulation below 1 Hz was analyzed using power spectrum density with high resolution (0.07 Hz).

Main Results:

• Stroke survivors exhibited greater force variability than healthy controls, and their paretic hand showed more variability than the non-paretic hand.
• Force modulation below 1 Hz differed significantly between stroke survivors and controls, and between paretic and non-paretic hands.
• Specifically, the paretic hand showed increased power around 0.2 Hz and decreased power around 0.6 Hz compared to controls and the non-paretic hand.
• Force variability was strongly predicted by modulation at specific frequencies below 1 Hz (R² = 0.80).

Conclusions:

• The modulation of force below 1 Hz is significantly altered in individuals with stroke.
• These specific low-frequency force modulations are associated with increased force variability post-stroke.
• Analyzing force modulation below 1 Hz offers valuable insights into motor control changes following stroke and potential therapeutic targets.