Background: Estimating joint contact forces (JCFs) is crucial for understanding osteoarthritis progression and optimising implant designs. However, existing musculoskeletal modelling approaches show variability in estimating JCFs during squatting. Reductions in muscle strength within specific groups are commonly observed due to factors such as ageing, certain physiological conditions or surgeries. Aims and Objectives: This study aims to assess the impact of reducing lower-limb muscle group strength on JCFs during squatting. Materials and Methods: Marker trajectories, ground reaction forces and in vivo knee JCFs (KJCFs) during squatting were obtained from an open-source dataset. The standard OpenSim pipeline of scaling, inverse kinematics, static optimisation and joint reaction analysis was used to quantify JCFs by reducing muscle group strengths (quadriceps, hamstrings, calf, knee-crossing and hip-crossing muscles). Results: The simulations revealed changes in knee and hip JCFs compared to the nominal model due to the reduction in muscle group strength. The research also found noticeable disparities between estimated and measured joint forces, even after a reduction in muscle strength of the musculoskeletal model. Conclusion: These findings underscore the challenges in accurately estimating JCFs and enhance our understanding of the intricate relationship between muscle group strength and JCFs during squatting. This research revealed that strengthening hip muscles can lower peak KJCFs without significantly increasing hip JCFs, while also guiding targeted rehabilitation and informing patient-specific implant design to improve joint health.