Ergonomic posture breaks enhance solute transport in cartilage: a musculoskeletal–poroelastic modelling study

Prolonged sedentary behavior in modern workplaces is a recognized ergonomic risk factor linked to joint degeneration and impaired cartilage health. It has been known that Insulin-like growth factor 1 (IGF-1) plays an important role in maintaining chondrocyte activity and extracellular matrix turnover. This study presents a numerical model to investigate the influence of workplace ergonomic activities, especially repeated sit-to-stand (STS) cycles, on IGF-1 transport within cartilage. First, a musculoskeletal model was developed to quantify the knee joint reaction force and muscle loading induced by various ergonomic activities in accordance with WorkSafe Victoria’s posture-break guidelines. Then, interstitial fluid flow-induced advective transport of IGF-1 within cartilage is quantified by employing a poroelastic cartilage tissue model in conjunction with a cartilage contact model. The results demonstrate that STS activities can substantially enhance IGF-1 transport in cartilage. For instance, over a 5-hour period, an STS cycle with 10 min of sitting and 10 min of standing increased free, bound, and total IGF-1 uptake ratios by 15.8%, 9.6%, and 9.7%, respectively, compared with continuous sitting. Shorter STS cycle times yielded even greater improvements in IGF-1 uptake. Moreover, accurate representation of the contact gap proved critical, as neglecting it led to significant underestimation of solute transport.