Strength training elicits benefits both in performance and on a psychological level in women, such as increased muscle strength and improved self-esteem. Whole-body electromyostimulation (WB-EMS) could be a training strategy for enhancing muscular strength. The aim of this study was to assess the acute effects of a single session of WB-EMS superimposed over classic resistance training on isometric strength, endurance strength and flexibility. Furthermore, the safety of the protocol was assessed by monitoring the levels of creatine kinase (CK) 48 h after the training protocol was completed. Sixteen active women (aged 22.06 ± 1.88) were randomly assigned to an experimental group (EG) (n = 8) and a control group (CG) (n = 8). The EG performed four sets of 12 repetitions of three strength exercises with superimposed WB-EMS, while the CG performed the same protocol without WB-EMS. RM-ANOVA showed a significant time*group interaction on posterior kinetic chain extensors’ mean and peak strength in the EG (F(1,14) = 10.036; p = 0.007; and F(1,14) = 20.719; p < 0.001; respectively). A significant time*group interaction was found in the sit and reach test for the EG (F(1,14) = 10.362; p = 0.006). Finally, ANOVA performed on the CK levels showed no significant difference between the groups (F(1,14) = 0.715; p = 0.412). WB-EMS training led to an immediate improvement in strength performance and flexibility, and this protocol was shown to be safe in terms of CK levels, 48 h after completing the training protocol.