Fatigue is defined as the reduction in capacity to perform the tasks and results from preceding physical exertion. Fatigue has been reported as one the main sources for reduction in productivity, poor quality and workers health and safety related issues. This research reviews a range of subjective and objective methods used in previous studies to measure physical fatigue and critically analyze their strengths and weaknesses. Then, various wearable sensor devices that allow for direct assessment of physiological parameters that change under the effects of fatigue are reviewed. The potential use of heart rate signals to monitor physical fatigue is discussed. Finally, a case study is conducted and heart rate signals are used to measure and detect physical fatigue.