Low back injuries and low back pain are often caused by improper task execution, overuse or lack of guidance and training. Our current understanding of dose-response relationships between risk factors that contribute to these injuries remains unclear. Enhanced monitoring of risk factors contributing to injuries could provide more complete exposure-response information. It is difficult to continuously monitor workers and their exposures to ergonomic risk factors using existing technologies. This paper presents a practical approach to advance continuous measurements of common risk factors by quantifying the weight of an object during lifting and carrying, lift frequency and lift duration during manual material handling (MMH). We estimate these parameters based on the ground reaction forces (GRF) and considering trunk dynamics. The results show that by considering trunk dynamics and applying simple signal processing techniques, we can precisely estimate these risk parameters. These parameters can then be used to estimate injury risk of workers. The developed methodology is designed for real-time continuous monitoring applications and sets the foundation for future development of in-field monitoring of workers with wearable sensors.