Papaioannou, A., Kennedy, C., Lee, J., Hewston, P., McArthur, C., Maharaj, S., Adachi, J., Boulos, P., Bobba, R., Rabinovich, A., McKenna, B., Palubiski, L., Mangin, D., Thabane, L., Marr, S., Kaasalainen, S., Tarride, J., Theou, O., Armstrong, D., Negm, A., Noseworthy, M., Rockwood, K., Dolovich, L., Alrob, H. A., Hladysh, G., Thompson, K., Ioannidis, G. (2026). Study protocol for a multiarm, randomized controlled trial to determine the effectiveness of community-based frailty rehabilitation to improve physical function in older adults: The OPTIMAL Fitness Trial. PLoS ONE. https://doi.org/10.1371/journal.pone.0343338