Werin, MB, Maenhout, AG, Icket, J, Jacxsens, N, Kempkes, E, and Cools, AM. Does the activity in scapular muscles during plyometric exercises change when the kinetic chain is challenged?—An EMG study. J Strength Cond Res 36(7): 1793–1800, 2022—Plyometric exercises for the shoulder are used in rehabilitation and in workout regime when the sport demands high speed power training. The aim of this clinical laboratory electromyography (EMG) study was to determine whether scapular muscle performance differs during plyometric shoulder exercises when changing the demand on the kinetic chain. Thirty healthy overhead athletes, with a mean age of 22.7 years (±2.2), performed 6 exercises, with both a low and a high demand on the kinetic chain, in prone, side and standing in positions. The EMG activity of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) on the tested side and bilateral of gluteus maximus (GM) and abdominal oblique externus (OE) was registered with wireless surface EMG. Intermuscular muscle ratios UT/SA, UT/MT, and UT/LT were also calculated. The level of significance set for the study was alpha = 0.05. The muscle ratio UT/SA was significantly lower (p < 0.05) when high demand on the kinetic chain compared with low. SA muscle activity showed significantly (<0.001) higher values in the prone position with high demand on the kinetic chain compared with low. All 3 trapezius muscle parts had significantly higher values (p < 0.001) in the prone compared with side and standing positions. The GM and OE showed significantly higher (p ≤ 0.01) activity in positions more demanding for the kinetic chain. When composing a strengthening or a rehabilitation program for athletes, the knowledge of how scapular and trunk muscles interact can be used to amplify the strengthening effect.