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Regional activation within vastus medialis and lateralis in clinical and experimental pain

University of British Columbia

The possibility to preferentially activate the distal region of the vastus medialis (VM) has been debated for a long time in physiotherapy for its potential relevance for patellofemoral pain (PFP). However, there is little experimental evidence that quadriceps muscle activation can be modulated regionally, either in voluntary tasks or in the presence of pain. This thesis examined whether the human neuromuscular system can preferentially control regions within the quadriceps muscle, and if pain results in regional modulation of quadriceps muscle activation. Methods: Regional activation within the VM (Chapters 2 to 5) and vastus lateralis (VL; Chapters 4 and 5) was investigated using high-density surface electromyography. To investigate whether the human spinal cord has the neuromuscular circuitry to selectively recruit motor units located in different muscle regions, regional stretch reflexes were elicited by applying mechanical stimuli along the VM insertion on the patella (Chapter 2). The possibility to regionally activate the VM in dynamic voluntary contractions was studied (Chapter 3). Principal component analysis was used to identify differences in regional activation patterns between 36 females with PFP and 20 age- and sex-matched controls (Chapter 4). Finally, the effect of location-specific acute nociceptive input on muscle activation within VM and VL was studied (Chapter 5). Results: Regionalized stretch reflexes provided evidence that the human spinal cord has the neuromuscular circuitry to selectively modulate the activation of regions within the VM. Redistribution between VM and VL and within the VM was observed in controls when comparing concentric and eccentric contractions. In the same task, less redistribution was observed in females with PFP, especially those with higher maximal knee extension strength. Region-specific adaptations of VM activation were observed in response to localized nociceptive input. Discussion: This dissertation provides evidence for regional activation between quadriceps heads and within the VM in reflex and voluntary contractions. Regional modulation of quadriceps muscle activation was observed in PFP and with experimental pain. This thesis highlights the role of regional activation within the quadriceps muscle in health and pain, and provides support for current theories on how the human nervous system adapts to pain.

Text

2020-05-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/65130

Rehabilitation Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/