Peripheral nerve excitation and plantar flexion force elicited by electrical stimulation in males and females

Study Design: Two-group (gender) posttest only using a sample of convenienc e. Objectives: Our study examined the effect of gender on selected stimulus pr operties, perceived pain thresholds, and maximally tolerated level of contr action of the plantar flexor muscle group. Background: There is a dearth of literature regarding gender as a factor th at may influence the outcome following the application of neuromuscular ele ctrical stimulation. Data from other disciplines suggest that males and fem ales may not have similar tolerance to electrical stimulation. Methods and Measures: Eleven women (mean age, 28.3 years +/- 5.6 years) and 9 men (mean age, 33.2 years +/- 6 years) participated in a single session of electrical stimulation. A pair of 4.5 x 4.5 cm, self-adhesive, synthetic , polymer electrodes was placed over the medial and lateral heads of the ga strocsoleus muscle group. Electrical stimulation was provided by a battery- powered pulsatile stimulator generating a symmetric biphasic waveform, 200- mu second phase duration, and pulse rate of 50 pulses per second. During te sting, the subjects were seated on a specially constructed chair that incor porated a foot pedal attached to a piezoelectric force transducer to measur e plantar flexion force. Stimulation amplitude was increased slowly until 4 thresholds (sensory, motor, pain, and maximal pain) were sequentially achi eved. At each threshold, stimulus peak voltage, peak current, and phase cha rge used to elicit that threshold were recorded. Plantar flexion force was also recorded when stimulation was sufficient to achieve pain and maximal p ain thresholds. Results: The peak voltage, peak current, and phase charge needed to elicit the 4 thresholds did not differ between women and men at any threshold exam ined (2-factor ANOVA; Newman-Keuls post hoc tests). However, significantly higher stimulus peak voltage, peak current, and phase charge were recorded for each of the 4 thresholds (sensory, motor, pain, and maximal pain tolera nce) for both groups. The plantar flexion force elicited by electrical stim ulation was significantly lower in female subjects than in male subjects at both pain threshold and maximally tolerated stimulation levels. Conclusions: Gender can influence the magnitude of electrically induced pla ntar flexion contraction force. We hypothesize that females may require lon ger conditioning periods to achieve therapeutic levels of muscle contractio n.