Limitations and strengths
SECONDARY, RECRUITMENT, KNEE OSTEOARTHRITIS
The main limitation of this study is that we did not conduct a feasibility and pilot study before we initiated the trial, thus we had not estimated recruitment rate beforehand. The main reasons for the slow recruitment rate were lack of time to recruit in the primary health care and that only one person recruited participants. Multi-center studies and adequate resources used on the recruitment process should be emphasized to successfully conduct similar RCTs. We decided to terminate the trial early and chose to do that when the COVID-19 pandemic hit Norway in March 2020. The estimates for our outcomes had wide CIs, and with a larger data set, the results may have been different. The clinically important difference for the KOOS QoL with 10 points might not be correct as it has been suggested to be 8 points for “somewhat better” and 15.6 points for a great deal better [The strength of this study is that we have included relatively young study participants from primary and secondary care and conducted the study in clinical practice. We analyzed data with a mixed-effect linear model that includes participants regardless of one missing follow-up, and includes both fixed and random factors. This study was designed at a time point when user involvement was not a mandatory part of trials, however, the strength exercise program was developed collaboration with specialists in sport physical therapy with high competence in treating patients with knee osteoarthritis. Furthermore, according to the systematic review by Luan et al. [