Abstract
The integrity of the corticomotor pathway is paramount in the optimal functioning of skeletal muscle. However, variability of neurophysiological assessment via peripheral nerve and transcranial magnetic stimulation can render interpretation difficult. Seldom evidence exists regarding the reliability of such measurements in the leg extensors, which have important locomotive and functional roles. This study aimed to assess the test-retest reliability of peripheral, corticospinal and intracortical responses in the vastus medialis. Transcranial magnetic and direct current electrical nerve stimulation were delivered to sixteen healthy young adults (8M and 8F) on two separate occasions. The Hoffmann reflex, maximal compound wave, motor evoked potential, corticospinal silent period, intracortical facilitation, and short-interval intracortical inhibition were recorded from the vastus medialis at rest, and during controlled submaximal voluntary contraction. Relative reliability was quantified using intra-class correlation coefficient (ICC2,1). Absolute reliability was quantified using standard error of measurement (SEm) and minimal detectable change (MDC). Corticospinal silent period, corticospinal silent period/motor evoked potential ratio, active motor evoked potential, maximal Hoffman reflex, and passive short-interval intracortical inhibition demonstrated “good to excellent” relative reliability (ICC ≥ 0.643). Intracortical facilitation demonstrated the lowest relative reliability (ICC = 0.420–0.908). Corticospinal silent period displayed the lowest absolute reliability (SEm ≤ 18.68%). Good reliability of the maximal compound wave, Hoffman reflex, motor evoked potential, and corticospinal silent period allow for reliable neurological evaluation of peripheral and corticospinal pathways in the vastus medialis. Future research should investigate reliability of the intracortical (short-interval intracortical inhibition and intracortical facilitation) measures by using different paired-pulse stimulus parameters. These findings hold important implications for neurophysiological assessment conducted in the leg extensor group.
Highlights
The integrity of the human motor system is essential in the development of muscular force, power and overall physical function
We aim to assess peripheral (H-reflex and M-wave), corticospinal (MEP and corticospinal silent period (CSP)) and intracortical (SICI and intracortical facilitation (ICF)) measures evoked from peripheral nerve and transcranial magnetic stimulation (TMS)
The findings demonstrated that the spinal reflex afferent and efferent pathways can be reliably measured in the vastus medialis (VM)
Summary
The integrity of the human motor system is essential in the development of muscular force, power and overall physical function. The musculature of the lower limbs play an important role in functional and performance tasks, locomotion and knee joint integrity (Avramidis et al, 2003; Peeler and Anderson, 2007). We investigated the lower-limb muscle VM for two reasons; (1) the VM generates the most consistent H-reflex response compared to the VL and rectus femoris (Kameyama et al, 1989) and (2) the VM plays an important role in the function and injury prevention of the knee. The VM has a crucial influence on gait performance and motor control of the knee (Avramidis et al, 2003), and its weakness is viewed as a contributing factor to patellofemoral joint dysfunction (Peeler and Anderson, 2007). The VM tends to atrophy to a greater extent than the other quadriceps muscles during disuse (Appell, 1990)
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