Initial Electrical Stimulation Frequency and Cramp Threshold Frequency and Force

Abstract

Context In the electrically induced cramp model, the tibial nerve is stimulated at an initial frequency of 4 Hz with increases in 2-Hz increments until the flexor hallucis brevis cramps. The frequency at which cramping occurs (ie, threshold frequency [TF]) can vary considerably. A potential limitation is that multiple subthreshold stimulations before TF might induce fatigue, which is operationally defined as a decrease in maximal voluntary isometric contraction (MVIC) force, thereby biasing TF. Objective To determine if TF is similar when initially stimulated at 4 Hz or 14 Hz and if MVIC force is different among stimulation frequencies or over time (precramp, 1 minute postcramp, and 5 minutes postcramp). Design Crossover study. Setting Laboratory. Patients or Other Participants Twenty participants (13 males: age = 20.6 ± 2.9 years, height = 184.4 ± 5.7 cm, mass = 76.3 ± 7.1 kg; 7 females: age = 20.4 ± 3.5 years, height = 166.6 ± 6.0 cm, mass = 62.4 ± 10.0 kg) who were prone to cramps. Intervention(s) Participants performed 20 practice MVICs. After a 5-minute rest, three 2-second MVICs were recorded and averaged for the precramp measurement. Participants were stimulated at either 4 Hz or 14 Hz, and the frequency was increased in 2-Hz increments from each initial frequency until cramp. The MVIC force was reevaluated at 1 minute and 5 minutes postcramp. Main Outcome Measure(s) The TF and MVIC force. Results Initial stimulation frequency did not affect TF (4 Hz = 16.2 ± 3.8 Hz, 14 Hz = 17.1 ± 5.0 Hz; t19=1.2, P = .24). Two participants had inaccurate TFs when initially stimulated at 14 Hz; they cramped at 10 and 12 Hz in the 4-Hz condition. The MVIC force did not differ between initial frequencies (F1,19 = 0.9, P = .36) but did differ over time (F2,38 = 5.1, P = .01). Force was lower at 1 minute postcramp (25.1 ± 10.1 N) than at precramp (28.7 ± 7.8 N; P < .05) but returned to baseline at 5 minutes postcramp (26.7 ± 8.9 N; P > .05). Conclusions The preferred initial stimulation frequency might be 4 Hz because it did not alter or overestimate TF. The MVIC force was lower at 1 minute postcramp, suggesting the induced cramp rather than the varying electrical frequencies affected force. A 1- to 5-minute rest should be provided postcramp induction if multiple cramps are induced.

Significant and serious dehydration does not affect skeletal muscle cramp threshold frequency

“…If subjects performed MVIC incorrectly, a 1 min rest period was given and MVIC was reattempted. Researchers have reported high MVIC intratester reliability using this method (intraclass correlation coefficient (ICC) 3.3>0.81) 23. Following MVICs, subjects big toe and ankle were removed from the toe harness and foam block, respectively, and subjects were prepped for cramp induction.…”

Electrolyte beverage consumption alters electrically induced cramping threshold

“…A secondary finding of the present study was that pain was significantly lower in the EB compared with the PB condition, with each participant reporting less (six of nine) or similar (three of nine) pain after consumption of the EB. While significantly less pain was experienced in the EB than PB group, EB also received greater electrical stimulus frequency; therefore, the effect sizes reported for VPS likely underrepresent the true effect of EB on pain . Unlike pain, relative muscle activity did not significantly differ between conditions.…”

“…These durations were selected as they are believed to be similar to those that an athlete may adopt before competition or a conditioning session. During this time, a round 8‐mm (diameter) Ag‐AgCl stimulating electrode was placed over the tibial nerve slightly inferior to the medial malleolus, which sent a dispersing electrical stimulus to an 8‐cm 2 sponge electrode placed directly over the lateral malleus . To ensure proper placement of the electrode the tibial nerve was submaximally stimulated up to three times with an 80 V, 2 ms pulse to ensure strong flexion of the great toe (Grass S88, Astro‐Med Inc West Warwick, RI).…”

“…Participants who did not cramp after their 12th stimulation (30 Hz) were excluded from the study, as these participants were determined to not be cramp sensitive. Three criteria were required to be met for a muscle cramp to be confirmed: (1) the participant confirmed that they experienced an involuntary sustained contraction after the cessation of the stimulus, (2) the researcher used load cell data to confirm that involuntary contraction of the flexor hallucis brevis occurred, and (3) the EMG average root mean square for the 2 s after the cessation of the stimulation had to be greater than the mean plus 2 standard deviations of the raw baseline EMG measurement . Upon the initiation of a cramp, participants were given 10 s for the cramp to naturally dissipate.…”

“…During this time, a round 8-mm (diameter) Ag-AgCl stimulating electrode was placed over the tibial nerve slightly inferior to the medial malleolus, which sent a dispersing electrical stimulus to an 8-cm 2 sponge electrode placed directly over the lateral malleus. 19 To ensure proper placement of the electrode the tibial nerve was submaximally stimulated up to three times with an 80 V, 2 ms pulse to ensure strong flexion of the great toe (Grass S88, Astro-Med Inc West Warwick, RI). When positioning was confirmed, electrodes were anchored in place using medical and elastic tape.…”