Background: Recovery from surgery has traditionally been measured using specific outcome measures, such as length of hospital stay. However, advances in technology have enabled the measurement of continuous, objective physical activity data in the perioperative period. The aim of this systematic review was to determine the relationship between length of hospital stay and physical activity data for patients undergoing surgery. Methods: A systematic search of EMBASE, Medline and the Cochrane Library, from inception until January 2017, was performed to identify all study designs that evaluated physical activity after surgery. Studies were included if a wearable sensor measured patient activity as an in-patient and the length of hospital stay was reported. Only English articles were included. Results: Six studies with a total of 343 participants were included in this review. All the studies were prospective observational studies. Each study used a different sensor, with the commonest being a tri-axial accelerometer, and multiple different physical activity outcome measures were used, thereby prohibiting meta-analysis. Four of the studies demonstrated a relationship between physical activity levels and length of hospital stay, while two studies did not show any significant relationship. Conclusion: The amount of physical activity performed post-operatively negatively correlates with the length of hospital stay. This suggests that objective physical activity data collected by body worn sensors may be capable of predicting functional recovery post-operatively.