Background: The clinical characteristics of sarcopenia, including low muscular strength, are commonly seen among people with multiple myeloma. A scoping review was conducted to explore the role of exercise as a potential countermeasure for sarcopenia in this population. Our objectives were to (1) describe the design and findings of the studies and (2) identify the outcomes used in exercise-related studies to characterize sarcopenia. Methods: A systematic search (to March 2025) was conducted for published studies involving exercise or physical activity for individuals with multiple myeloma using key databases (MEDLINE, Embase, CINAHL, Scopus). Results: Of 971 articles reviewed, 12 articles were included, involving 967 total participants and 624 with multiple myeloma. All 12 studies included a measure for muscle physical performance, 9 studies included measures for muscular strength, and 7 studies included measures for muscle quantity/quality. Five studies reported a significant improvement from exercise for measures of muscular strength, four studies reported a significant benefit for physical performance, and three studies reported a benefit in muscle quantity. Few studies included outcomes that met all the international criteria recommended to characterize sarcopenia. Conclusions: Further multicentre research trials are needed to better understand whether and how exercise may be helpful for people with multiple myeloma, especially in the context of sarcopenia.