Electrical train stimulation to assess exercise associated muscle cramp
Date of Award
Master of Science (Sports Science)
School of Exercise, Biomedical, and Health Sciences
Faculty of Computing, Health and Science
Muscle cramp is a forceful, involuntary contraction of skeletal muscle, but its underlying mechanisms are not well understood. Our limited understanding of muscle cramp may be due to its unreliable occurrence. Electrical train stimulation (ETS) has been reported to induce cramp in the small flexor muscles of the foot, and a relationship exists between the threshold frequency (TF) of ETS to induce cramp and muscle cramp susceptibility. The use of ETS to induce muscle cramp in the calf muscles however may be challenging, and the test-retest reliability of this method has not been examined in the calf muscles. Since athletes can experience muscle cramp in the calf muscles, in turn affecting their athletic performance, it is necessary to establish a method to assess calf muscle cramp. The first purpose of this study therefore was to determine the usefulness of the ETS application to the calf muscles, along with its reliability. Using a Compex 2 stimulator, ETS was applied to the calf muscles of both dominant and non-dominant legs in 10 men (33.5 ± 8.4 y) who reported experiencing cramp during training or competition. Each leg was treated separately in a counterbalanced order, with subjects in the supine position and legs supported by a bench that fixed the ankle at maximal plantarflexion. ETS consisted of 2 s (including 500 ms ramp time) of 300 μs square pulsed waves followed by 30 s rest. ETS commenced with two bouts of stimulation at 10 Hz during which the stimulation intensity was increased to the maximum tolerated, with values of 46.9 ± 6.5 and 45.4 ± 7.7 mA for the dominant and non-dominant legs, respectively. Subsequent stimulation trains increased by 3 Hz until cramp occurred, as confirmed by a spontaneous electromyograph (EMG) signal. The protocol was repeated 30 min after the first test, with the entire testing procedure repeated seven days later. Muscle cramp was induced in all subjects, but the TF varied amongst subjects (13-55 Hz). Mean TF value to induce muscle camp for the dominant leg was 25.0 ± 7.6 Hz for the first test and 23.7 ± 5.0 Hz for the second test. The non-dominant leg also showed similar values. Test-retest reliability, as indicated by the intraclass correlation coefficient (ICC), limits of agreement (LOA) and coefficient of variation (CV), were 0.94, 5.4 % and 9.2 %, respectively for the dominant leg, and 0.72, 9.8 % and 15.4 %, respectively for the non-dominant leg. These results show that ETS can induce muscle cramp in the calf muscles and that the TF of ETS was a reliable measure to assess the calf muscle cramp susceptibility. The second purpose of this thesis was to examine the influence of fatigue on the TF of ETS-induced muscle cramp in the calf muscles of 10 men (35.8 ± 9.2 y) who reported experiencing cramp during sporting activity. The previously described methods were used to assess muscle cramp in the calf muscles of the subject’s dominant leg with a stimulation intensity of 49.3 ± 4.9 mA before, immediately after, and 30 min after exercise. Exercise consisted of uphill treadmill walking, standing calf raises, skipping, drop jumps and cycling to fatigue, which was completed in 82.9 ± 2.0 min at an average heart rate of 141.7 ± 6.0 bpm. An isokinetic dynamometer was used to measure plantarflexor muscle torque of the dominant leg before and immediately after exercise, and following 30 mins of passive recovery. Blood and urine samples were obtained to assess electrolyte concentrations and hydration status before and immediately after exercise. Plantarflexor muscle torque decreased significantly (p < 0.05) approximately 20 % from the baseline (42.4 ± 17.1 Nm) immediately post exercise (34.6 ± 14.9 Nm), and was still significantly lower at 30 min post-exercise (37.4 ± 15.9 Nm). Serum (4.32 ± 0.35 vs 4.66 ± 0.38 mmol/L) and urine (56.3 ± 38.6 vs 87.2 ± 40.8 mmol/L) potassium concentrations, urine osmolality (551.1 ± 306.6 vs 683.9± 236.6 mmol/L), and urine specific gravity (1.014 ± 0.008 vs 1.022 ± 0.009) changed significantly from pre to post exercise, but serum osmolality, serum sodium and urine sodium concentrations remained unchanged. No significant changes in TF were evident before (23.2 ± 6.0 Hz), immediately after (22.6 ± 5.1 Hz) and 30 min post-exercise (25.3 ± 7.4 Hz). These results suggest that neither fatigue nor mild changes in hydration status affect the TF. Nevertheless, the duration of exercise used in this study might not have been sufficient to cause the physiological changes that may occur during training or racing. As muscle cramp can reliably be assessed by ETS, future investigations should use this method to uncover potential mechanisms related to muscle cramp, such as body temperature, hydration status and electrolyte concentrations.
LCSH Subject Headings
muscles - physiology
leg - physiology
muscle - contraction
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Pegoraro, R. V. (2010). Electrical train stimulation to assess exercise associated muscle cramp. Retrieved from http://ro.ecu.edu.au/theses/1845
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