The article discusses research being done on muscle blood flow and blood flow. It references the study "Positron Emission Tomography Detects Greater Blood Flow and Less Blood Flow Heterogeneity in the Exercising Skeletal Muscles of Old Compared With Young Men During Fatiguing Contractions," by T. Rudroff et al. in the 2014 issue of "The Journal of Physiology." The researchers examined blood perfusion, muscle mass and contraction, and adenosine triphosphate (ATP).