Intracortical inhibition, corticospinal excitability and voluntary activation in people with and without patellofemoral pain

The aims of this study were to investigate the intra-rater reliability of peripheral nerve stimulation (PNS) and transcranial magnetic stimulation (TMS) in people with and without patellofemoral pain (PFP) and to compare nervous system function between these groups, using a case-control design. We sought people with and without PFP to participate in PNS and TMS testing to calculate maximal compound motor action potential, maximal force, voluntary activation (VA), active motor threshold (AMT), corticospinal excitability (CSE), silent period, and short-interval intracortical inhibition. People with PFP also rated their current pain and function. Single-measure intraclass correlation coefficients with 95% confidence intervals were used to determine intra-rater reliability, with standard error of measurement and minimum detectable change calculated. Between-group differences in PNS and TMS variables were determined using Student's two-tailed, independent samples t-tests or Mann-Whitney U-tests. Twenty-seven people without and 23 people with PFP completed PNS and TMS testing. For intra-rater reliability, 18 people without and 17 people with PFP returned for a second testing session, and intraclass correlation coefficient values ranged from good to excellent (0.62-0.96). People with PFP demonstrated significantly lower VA (P < 0.0001), higher AMT (P = 0.014) and lower CSE (P = 0.018). In conclusion, both PNS and TMS demonstrate acceptable intra-rater reliability in people with and without PFP. Elevated AMT and reduced CSE indicate that people with PFP might have a hypoexcitable motor cortex-corticospinal pathway, and lower VA indicates reduced recruitment of high-threshold motor units. These findings indicate that a neurophysiological mechanism might underpin the poor prognosis of PFP.