Fig. 2

Visualization of the studies assessing the muscle activity of the lower limbs muscles. Some of the works assessed only the activity of the muscles related to the ankle joint [29, 36–38, 46, 52], while other works also assessed the activity of more proximal muscles [19–21, 31, 32, 34, 35, 40, 42, 43, 65]. Between these studies, all the works measuring the total (biological plus exoskeletal) ankle work [19, 20, 33, 39–42] found that the total work was increased during the powered condition with respect to the unpowered one