A promising approach to effectively reduce cramp susceptibility in human muscles: a randomized, controlled clinical trial

Abstract

Background: To investigate if the cramp threshold frequency (CTF) can be altered by electrical muscle stimulation in a shortened position.

Methods: A total of 15 healthy male sport students were randomly allocated to an intervention (IG, n = 10) and a non-treatment control group (CG, n = 5). Calf muscles of both legs in the IG were stimulated equally twice a week over 6 weeks. The protocol was 3×5 s on, 10 s off, 150 µs impulse width, 30 Hz above the individual CTF, and was at 85% of the maximal tolerated stimulation energy. One leg was stimulated in a shortened position, inducing muscle cramps (CT), while the opposite leg was fixated in a neutral position at the ankle, hindering muscle cramps (nCT). CTF tests were performed prior to the first and 96 h after the 6(th) (3 w) and 12(th) (6 w) training session.

Results: After 3 w, the CTF had significantly (p<0.001) increased in CT calves from 23.3±5.7 Hz to 33.3±6.9 Hz, while it remained unchanged in nCT (pre: 23.6±5.7 Hz, mid: 22.3±3.5 Hz) and in both legs of the CG (pre: 21.8±3.2 Hz, mid: 22.0±2.7 Hz). Only CT saw further insignificant increases in the CTF. The applied stimulation energy (mA² • µs) positively correlated with the effect on the CTF (r = 0.92; p<0.001).

Conclusions: The present study may be useful for developing new non-pharmacological strategies to reduce cramp susceptibility.

Trial registry: German Clinical Trials Register DRKS00005312.

Figure 1. CONSORT flow chart, depicting the passage of participants through the four different stages of the present trial: enrollment, allocation to the intervention (IG) and control group (CG), follow-up, and analysis.

Figure 2. Cramp threshold frequencies (CTF) of calf muscles (m. gastrocnemius medialis) measured at pre-, mid- (3 weeks), and post- (6 weeks) tests following an electrical muscle stimulation protocol that was applied in a shortened (circles) or a neutral position (squares).

Further, CTF values of the non-trained legs of the control group (diamonds) are displayed. Vertical bars represent 0.95 confidence intervals. *  =  sign. different from pre values (p<0.001), #  =  sign. difference between groups (p<0.001).