North Dakota State University, PO Box #6050, Department #2620, Fargo, ND 58108, USA.
J Athl Train. 2012 Nov-Dec;47(6):643-7. doi: 10.4085/1062-6050-47.5.12.
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.
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).
Crossover study.
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.
Initial stimulation frequency did not affect TF (4 Hz = 16.2 ± 3.8 Hz, 14 Hz = 17.1 ± 5.0 Hz; t(19) = 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 (F(1,19) = 0.9, P = .36) but did differ over time (F(2,38) = 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).
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.
在电诱发痉挛模型中，刺激胫神经的初始频率为 4 Hz，以 2 Hz 的增量增加，直到短屈肌痉挛。痉挛发生的频率（即阈值频率[TF]）可能有很大差异。一个潜在的限制是，在 TF 之前进行多次亚阈刺激可能会引起疲劳，疲劳在操作上被定义为最大随意等长收缩（MVIC）力的降低，从而偏向 TF。
确定初始刺激频率为 4 Hz 或 14 Hz 时 TF 是否相似，以及刺激频率或随时间（痉挛前、痉挛后 1 分钟和痉挛后 5 分钟）的 MVIC 力是否不同。
交叉研究。
实验室。
20 名参与者（13 名男性：年龄=20.6±2.9 岁，身高=184.4±5.7 cm，体重=76.3±7.1 kg；7 名女性：年龄=20.4±3.5 岁，身高=166.6±6.0 cm，体重=62.4±10.0 kg），他们容易抽筋。
参与者进行 20 次练习 MVIC。休息 5 分钟后，记录三次 2 秒的 MVIC 并平均作为痉挛前的测量值。参与者以 4 Hz 或 14 Hz 进行刺激，从每个初始频率以 2 Hz 的增量增加频率，直到痉挛。痉挛后 1 分钟和 5 分钟再次评估 MVIC 力。
TF 和 MVIC 力。
初始刺激频率不影响 TF（4 Hz=16.2±3.8 Hz，14 Hz=17.1±5.0 Hz；t(19)=1.2，P=0.24）。两名参与者在以 14 Hz 初始刺激时 TF 不准确；他们在 4-Hz 条件下以 10 和 12 Hz 痉挛。初始频率之间的 MVIC 力没有差异（F(1,19)=0.9，P=0.36），但随时间而变化（F(2,38)=5.1，P=0.01）。痉挛后 1 分钟（25.1±10.1 N）的力低于痉挛前（28.7±7.8 N；P，0.05），但在痉挛后 5 分钟（26.7±8.9 N；P，0.05）恢复到基线。
首选的初始刺激频率可能为 4 Hz，因为它不会改变或高估 TF。痉挛后 1 分钟的 MVIC 力较低，这表明引起痉挛的是痉挛本身，而不是变化的电频率影响了力。如果要诱发多次痉挛，则在痉挛后应提供 1 到 5 分钟的恢复期。
