Arm swing helps to increase vertical jump height (VJH), in part by a greater hip joint muscle work. The force–velocity relationship has been put forward to explain the increase in hip joint work. Nevertheless, the efficacy ratio, muscle shortening length, and active state might be parameters that affect the effective energy and then VJH. The purpose of this study was to evaluate the influence of arm swing on effective energy in vertical jumping. Eight subjects performed maximal squat jumps with (SJarm) and without arm swing (SJ). A simulation model of the musculo-skeletal system was applied. For subjects and simulation, VJH was about 20% higher during SJarm. In subjects, this was explained by the shoulder joint work (34%) and an increase of L5-S1 joint work (66%). In simulated jump, effective energy increase during SJarm (+80.74 J) was related to an improvement of the total muscle work and not to the efficacy ratio. The increase in total muscle work was due to anterior deltoid work and to greater erector spinae, biceps femoris, and gluteus work. The greater muscle works were explained by a slower shortening velocity for all the muscles and by a greater shortening length and active state for the biceps femoris.