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Initial electrical stimulation frequency and cramp threshold frequency and force.
Kevin C Miller1, Kenneth L Knight
1North Dakota State University, PO Box #6050, Department #2620, Fargo, ND 58108, USA. kevin.c.miller@ndsu.edu
Journal of Athletic Training
|November 28, 2012
Summary
The initial stimulation frequency (4 Hz vs. 14 Hz) did not significantly alter the threshold frequency (TF) for electrically induced cramps. Maximal voluntary isometric contraction (MVIC) force decreased post-cramp but recovered within 5 minutes.
Area of Science:
- Neuromuscular physiology
- Exercise science
- Biomedical engineering
Background:
- Electrically induced cramps use tibial nerve stimulation to determine threshold frequency (TF).
- Fatigue from subthreshold stimulations may bias TF measurements.
- Maximal voluntary isometric contraction (MVIC) force assesses muscle fatigue.
Purpose of the Study:
- To compare TF when initial stimulation is 4 Hz versus 14 Hz.
- To assess MVIC force differences across stimulation frequencies and over time post-cramp.
Main Methods:
- Crossover study design in a laboratory setting.
- Twenty participants prone to cramps were recruited.
- MVIC force measured pre-stimulation, and at 1 and 5 minutes post-cramp, following stimulation at 4 Hz or 14 Hz increments until cramp.
Main Results:
- Initial stimulation frequency did not significantly affect TF (4 Hz: 16.2 ± 3.8 Hz; 14 Hz: 17.1 ± 5.0 Hz).
- MVIC force did not differ between initial frequencies but decreased at 1 minute post-cramp (25.1 ± 10.1 N) versus precramp (28.7 ± 7.8 N).
- MVIC force returned to baseline levels by 5 minutes post-cramp.
Conclusions:
- A 4 Hz initial stimulation frequency is preferred as it does not alter or overestimate TF.
- Reduced MVIC force post-cramp is likely due to the cramp itself, not varying electrical frequencies.
- A 1-5 minute rest period is recommended after cramp induction if multiple cramps are induced.
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