## 4 Role of Musculoskeletal Models in Rehabilitation  
Along with investigating MSK disease state, and aetiology, MSK modelling and simulations can provide benefits relating to MSK rehabilitation. Rehabilitation is typically aimed at restoring muscle strength, joint stability, or joint loading to a typical or pre-injury state. Prescription of rehabilitation is  
Figure 4: Longitudinal changes in first and second peak hip joint contact forces in patients before, and 3 and 12 months following total hip arthroscopy [60]. typically based on general guidelines and are not highly tailored to individual patients. It is in this generic prescription where MSK modelling and simulations can enhance the rehabilitation pathway and decision making. By investigating MSK loading during various rehabilitation exercises and determining the load applied to specific tissues, exercise dosage can be tailored to achieve the optimal loading and inform rehabilitation progression [61; 62]. Previous research [63] in this area has provided insights into the magnitudes and locations of knee joint loading during different rehabilitation exercises (Figure 5). This information can be particularly useful to personalise the prescribed exercises based on injury location and rehabilitation stage. Utilising the disease biomarkers mentioned previously, the effectiveness of different rehabilitation programs can also be assessed in terms of restoration of typical joint loading or effect on a targeted biomarker. In addition to the investigation and refinement of current clinical guidelines, MSK modelling and simulations can be employed to, for instance, evaluate the effectiveness of new rehabilitation exercises to restore appropriate loading. For example, based on MSK modelling and simulations input, a ranking of exercise regimes was proposed to prevent femoral neck bone loss in females at risk of osteoporosis [64; 65]. Using MSK modelling and simulations, compensatory movement strategies to lower knee joint contact forces in patients with knee OA during stair climbing could be identified [57]. These insights may assist clinicians in providing guidelines for rehabilitation of patients to potentially avoid further progression and joint degeneration. This is even more clear in the field of gait retraining, where the therapist instructs the patient to modify their walking pattern in an attempt to alter the loading on a specific MSK tissue, typically cartilage. These retraining methods have been initially applied to patients with OA whereby specific kinematic gait features (e.g., toe position, trunk lean) are modified to reduce the moments around the knee [66; 67; 68; 69; 70; 71] or hip joint [72]. Similar to rehabilitation exercises, these gait retraining goals are based on generic guidelines and the effect on the MSK loading in the individual patient is typically not verified. Over the last decade, the optimisation of MSK modelling and simulation frameworks has driven the development of real-time feedback tools for gait retraining [73; 74; 75; 76]. These tools allow clinicians to monitor gait patterns and estimate joint moments in real-time to assess their adherence to the prescribed gait strategy but also to evaluate its effect on MSK loading. Although the testing of different gait strategies can be performed based on experimentally acquired data of the patient's gait, newly developed predictive simulations have been employed to test the effect of an imposed gait strategy on MSK loading without the need for repetitive and time consuming in-person patient assessments. The effect on various MSK tissues can then be investigated to determine if the gait strategy is a viable rehabilitation option. If further developed, this may provide not only optimised treatment planning and likely improved rehabilitation, but also significant time and cost savings for both the patient and clinician.