Hip and knee osteoarthritis are common, progressive degenerative joint diseases that significantly impact mobility and quality of life. With an increasing prevalence in aging populations, total joint replacement (TJR) remains the gold standard surgical treatment for end-stage disease. While joint replacement effectively reduces pain, post-operative functional recovery remains highly variable, influenced by preoperative function, comorbidities, muscle strength, and rehabilitation strategies. This chapter explores the predictors of functional outcomes following total hip replacement (THR) and total knee replacement (TKR), highlighting the role of muscle strength, BMI, and preoperative health status in determining long-term success. We examine the impact of prehabilitation on optimising preoperative strength and function, along with supporting postoperative physiotherapy and resistance training in accelerating recovery. Understanding patient motivations, barriers to exercise, and the role of outcome measures such as patient-reported outcome measures (PROMs), performance-based assessments, and radiographic evaluations in assessing post-TJR recovery is necessary for optimising rehabilitation protocols, improving long-term function, and maximising the benefits of joint replacement surgery.