Monitoring the metabolic cost or oxygen consumption associated with rest and exercise is crucial to understanding the impact of disease or physical training on the health of individuals. Traditionally, measuring the skeletal muscle oxygen cost associated with exercise/muscle contractions can be rather expensive or invasive (i.e., muscle biopsies). More recently, specific protocols designed around the use of near-infrared spectroscopy (NIRS) have been shown to provide a quick, non-invasive easy to use tool to measure skeletal muscle oxygen consumption (mVO 2 ). However, the data and results from NIRS devices are often misunderstood. Thus, the primary purpose of this sourcebook update is to provide several experimental protocols students can utilize to improve their understanding of NIRS technology, learn how to analyze results from NIRS devices as well as better understand how muscle contraction intensity and type (isometric, concentric or eccentric) influence the oxygen cost of muscle contractions.