The use of physical methods to assess how work is being performed is crucial to the work of many ergonomists. The physical methods included in this section can be used to obtain essential surveillance data for the management of injury risks in the workforce. It is generally accepted that many musculoskeletal injuries begin with the worker experiencing discomfort. If ignored, the risk factors responsible for the discomfort eventually will lead to an increase in the severity of symptoms, and what began as mild discomfort will gradually become more intense and will be experienced as aches and pains. If left unchecked, the aches and pains that signal some cumulative trauma eventually may result in an actual musculoskeletal injury, such as tendonitis, tenosynovitis, or serious nerve-compression injury like carpal tunnel syndrome. Sensations of discomfort are the body’s early warning signs that some attribute of the worker’s job should be changed. Discomfort will also adversely affect work performance, either by decreasing the quantity of work, decreasing the quality of work through increased error rates, or both. Reducing the levels of discomfort actually decreases the risk of an injury occurring. Consequently, changes in levels of discomfort can also be used to gauge the success of the design of an ergonomic product or the implementation of an ergonomic program intervention.