Electrical Muscle Stimulation Of Leg Extensors Does Not Enhance Drop Jump Performance

Abstract

Within the last years portable electric muscle stimulation (EMS) devices are offered on a commercial basis. They are advertised as simulating the muscular activation pattern of plyometric training programmes and, thus, improving the development of strength in stretch-shortening cycles, e. g. drop jumps. However, so far there is no experimental evidence for this claim. PURPOSE: Therefore, it was investigated if 4 weeks of EMS (Compex Medical Care®) of leg extensors (m. rectus femoris, m. gastrocnemius, m. soleus) might improve reactive strength during drop jumps. METHODS 34 healthy subjects (25 males, 9 females; age 19–27 yrs) took part in the study. They had no history of earlier resistance training of the lower limbs. After initial testing and stratification for jumping performance, subjects were randomly assigned to conventional drop jump training (DJ, n = 13; 6 series of 8 maximal drop jumps, dropping height: 28 cm during week 1 and progressively increased to 38 cm until week 4), EMS (n = 13; stimulation schedule analogous to DJ; maximal stimulation frequency: 150 Hz; amperage self-regulated to tolerated maximum), or to control conditions without change in physical activity (CO, n = 8). Supervised training was conducted twice per week, i. e. for a total of 8 sessions. Vertical jumping height (JH) and ground contact time (GCT) during drop jumps were measured before and after the intervention. The ratio JH/GCT was computed as a reactivity index (RI) and served as primary dependent variable. To control for transfer effects, after post-testing EMS and CO conducted an additional 2 week conventional drop jump training. RESULTS The largest increase in RI was recorded in DJ (11.3 ± 8.9%, p<0.001 compared with CO and EMS). The RI change in EMS was small (1.2 ± 2.6%) and did not differ significantly from CO (−1.3 ± 2.6%). Drop jump performance did not differ between EMS and CO after the transfer phase (6.4 ± 5.1% and 6.8 ± 2.7%, respectively; p = 0.85). CONCLUSIONS It can be concluded that 4 weeks leg extensor EMS do not lead to improvements in drop jump performance. Conventional drop jump training represents a more efficient training mode. Also, EMS does not facilitate larger training effects of the conventional training. Within a healthy young population, therefore, EMS cannot be recommended for the purpose of increasing reactive strength of the lower limbs.