Recent research designed to improve outcome from total knee arthroplasty has included focus on strategies that increase the range of post-operative knee flexion. Patients with knee arthroplasty can now expect >100° of knee flexion following surgery, but it is not clear whether this improved range of motion facilitates outcome or whether patients take advantage of this range when completing daily functional activities. The aim of this study was to investigate the knee flexion angles used during daily functional activities that specifically required high degrees of knee flexion. It was hypothesised that patients with greater range of passive knee flexion would achieve higher degrees of knee flexion during functional activities.Motion analysis was used to assess the maximum knee flexion of 40 patients with total knee arthroplasty and 40 control participants as they performed maximum flexion squatting and lunging activities.Patients with knee arthroplasty used between 80.8 and 91.4° of knee flexion to complete these activities, which was 20 to 30% less than that used by the control participants. Patients with greater ranges of passive knee flexion had greater maximum knee flexion during functional activities. However, they used only between 68% and 77% of their full passive range when lunging and squatting.The development of rehabilitation strategies that aim to increase weightbearing knee flexion capacity may be warranted to improve functional performance following total knee arthroplasty.