Persons with a spinal cord injury (SCI) demonstrate strength deficits that can limit their functional ability to perform activities of daily living. For a specific lesion level, performance of functional activities is related to the level of muscle strength. Consequently, in clinical practice, we need reliable measures of muscle strength to determine mobility and self-care ability. Muscle-strength testing is used to document recovery or loss of motor function early in SCI, as well as measure improvements in strength in chronic SCI. We also need such measures for research purposes to determine the efficacy of clinical trials. Several methods are available for testing muscle strength of persons with SCI, such as handheld, handgrip, and isokinetic dynamometers. This article provides an overview of muscle-contraction definitions and testing methodologies and discusses the reliability of these testing methods and dynamometry devices.