Electrically elicited minimal visible tetanic contraction and its effect on abdominal muscles strength and endurance

The purpose of this study was to test if 3 h of electrically induced minimal visible tetanic contractions will enhance strength and endurance of the abdominal musculature. 16 males and 22 females were randomly assigned to a control (C) or experimental (E) group. The E group stimulation protocol included symmetric biphasic pulses, 200 μs phase duration, 50 pulses/s, and interrupted mode incorporating 3 s ramp up, 8 s contraction period and 5 s relaxation period. Two, 97 cm 2 surface electrodes were placed over the abdominal musculature and the subjects were required to stimulate 3 h daily, 5 days each week for 4 weeks. Trunk flexion force was measured during a series of 40 consecutive maximal volitional isometric contractions (MVIC) of the abdominals. Force data were recorded by a computerized dynamometer. Strength was determined by the highest of the 40 MVIC force measurements. Endurance was estimated by the force-time curve of 34 consecutive MVICs. The testing procedure of both groups was repeated after 2 and 4 weeks. Normalized MVIC data were subjected to ANOVA tests and revealed a significant increase in strength of the E over the C group (P = 0.05). There was a mean increase of 10.5 ± 0.16% and 14.0 ± 0.22% after 2 and 4 weeks of stimulation respectively. The C group did not gain strength. Each session's decrement of abdominal force in both groups, was statistically significant (P = 0.05) with a mean decline of 46.8 ± 14.2%. But the difference in force decline between groups or over the 4 weeks of stimulation was not significant. Subjects rated the perceived stimulation between comfortable to somewhat pleasant. We concluded that prolonged stimulation at minimal intensity can enhance abdominal strength and is well tolerated. Such protocol may be incorporated clinically when strengthening of the abdominals is indicated.