Methods: In a randomized controlled trial, 177 participants with knee OA conducted a high-intensity (70%-80% of the Repetition Maximum (1RM)) or low-intensity (40%-50% 1RM) RT program 3 times a week for 12 weeks. Measures of clinical outcomes and serum samples were collected at the start of RT (pre-intervention), after 3 months at the end of RT (post-intervention), and 6 months after RT (follow-up). As a reflection of systemic inflammation (CRP), synovitis (CRPM, C3M), bone turnover (OC, CTX-I), cartilage turnover (PRO-C2, C2M, huARGS), muscle turnover (PRO-C3, PRO-C6), and cell behaviour (col10neo) a total of eleven serum biomarkers were analysed. With the exception of CRP, which was determined with an immunoturbidimetric assay, ELISA assays were used to quantify serum levels of the other 10 serum biomarkers. The primary outcome measures are the changes in serum biomarker levels. Other outcome measures include upper leg muscle strength, performance-based tests, and self-reported outcomes on pain and activity limitations.
Results: High-intensity RT resulted in greater improvements in muscle strength compared to low-intensity RT when measured by the estimated 1RM. No significant differences between groups were found for upper leg muscle strength (Nm/kg) when measured with an isokinetic dynamometer. Both groups showed similar improvements in pain and physical functioning. Although there is no difference between groups in clinical outcomes, except for the estimated 1RM, we expect that participants in the high-intensity RT group are more likely to have enhanced serum levels of catabolic biomarkers than participants in the low-intensity RT group. Since both the high-intensity RT group and low-intensity RT group improved over time, we expect that changes in serum biomarker levels are associated with overall improvements in clinical outcomes. Almost all participants had normal CRP values (<10 mg/L) at baseline. No significant differences between the intensity RT groups in CRP levels at baseline, at 3 months, and 6 months were found. In both groups, there was no evidence that RT influenced CRP serum levels.
Conclusions: The work to date on CRP serum levels suggests that RT did not influence CRP levels. This result may be explained by the high percentage of participants with normal CRP levels (<10 mg/L). We are currently in the process of analyzing the remaining 10 neo-epitope biomarkers. We expect that our remaining 10 assays have the potential to measure changes in serum biomarker levels in response to RT. This will be the first study to investigate the effects of high-intensity versus low-intensity RT on musculoskeletal tissue turnover in individuals with knee OA. With this, we aim to determine whether high-intensity RT can improve upper leg muscle strength and physical performance without worsening systemic inflammation or causing adverse effects on musculoskeletal knee OA-related tissues.