The Impact Of Remote And Localized Knee Pain On Maximal Strength Of Knee Extensors In College-aged Individuals.

Previous research has shown conflicting results on whether external application of pain alters maximal strength. These results may be due to the differing location, type, and intensity of applied pain. PURPOSE: The purpose of this study was to determine if electrical pain applied to the contracting or contralateral knee joint, to mimic osteoarthritis pain, altered maximal strength. METHODS: Twenty-two participants (Females = 9, Males = 12, N/A = 1) completed five visits (2 familiarization and 3 experimental) separated by 48 hours. Participants performed 4 maximal voluntary knee extensions—two with and two without the application of an electrical stimulus that elicited a pain rating of 4 out of 10. The site of pain application either the ipsilateral or contralateral knee, was randomly assigned between visits. Motor unit recruitment was determined using twitch-interpolation and voluntary activation was determined using surface EMG from the vastus lateralis. RESULTS: MVC was reduced when pain was applied to the knee, regardless of pain location (200.0 ± 69.7 Nm vs. 193.7 ± 67.7; p = 0.004 for main effect), motor unit recruitment (78.2 ± 13.6% vs. 75.8 ± 11.9%; p = 0.03 for main effect), and EMG RMS (0.256 ± 0.138 mV vs. 0.226 ± 0.112 mV; 92.0 ± 17.3% of no pain condition; p = 0.0003 for main effect) decreased significantly following application of knee pain, regardless of application site indicating a decrease in neural drive to the muscle when pain was present. CONCLUSIONS: The results of the research indicate that with the presence of external knee pain, there was a significant decrease in force output regardless of the pain being in the contralateral or ipsilateral knee. This indicates that both the localized and distal pain stimulus impacted measures indicative of increasing central fatigue and shows that a decrease in central drive is the main factor resulting in the force decline with the presence of pain.