The Clinical Effects of Cold Application on the Production of Electrically Induced Involuntary Muscle Contractions

Transcription

1 The Clinical Effects of Cold Application on the Production of Electrically Induced Involuntary Muscle Contractions Bonnie L. Van Lunen, Clayton Carroll, Kristen Gratias, and Doug Straley Context: Rehabilitation. Objective: To determine the effects of a 20-min ice treatment on pain tolerance and peak torque. Design: A factorial with repeated measures on 1 factor. Setting: Outpatient rehabilitation clinic. Participants: 20 men and 15 women. Intervention: The participants were randomly assigned to an experimental (ice bag) or control (no ice bag) group. Main Outcome Measures: Peak electrical-stimulation output intensity (ESOI) was recorded in mv, and isokinetic peak torque (IPT), in N m, every 4 min for 20 min. Results: ESOI and IPT increased over time. ESOI for the experimental condition was greater than for the control and within the experimental condition at 12, 16, and 20 min. No other differences were found for the IPT measures. There were no differences for ESOI and IPT between genders. Conclusions: Cryotherapy enables patients to tolerate greater output intensities but does not result in increased peak torque. Key Words: torque, cryotherapy, isometric Van Lunen BL, Carroll C, Gratias K, Straley D. The clinical effects of cold application on the production of electrically induced involuntary muscle contractions. J Sport Rehabil. 2003;12: Human Kinetics Publishers, Inc. To elicit the strength-training effects of neuromuscular electrical stimulation (NMES), it is necessary to achieve a strong tetanic muscle contraction. 1,2 The degree to which force is created by the electrically induced contraction is mainly related to the intensity of stimulation that is accepted by the patient. The higher the intensity of stimulation, the greater the number of muscle fibers recruited by the stimulus, therefore producing a training effect. 2-5 NMES treatment is thus often inefficient because patients with low pain thresholds might not reach an electrical-stimulation output intensity (ESOI) sufficient to create a strong muscle contraction. The effects of cryotherapy on involuntary muscle contractions have been studied experimentally, 6,7 but the results are controversial. Research has Van Lunen is with the Dept of Exercise Science, Physical Education and Recreation, Old Dominion University, Norfolk, VA Carroll is with the physician s assistant program, Trevecca Nazarene University, Nashville, TN Gratias is with the Athletic Dept, Princeton University, Princeton, NJ Straley is with the Athletic Dept, Manhattanville College, Purchase, NY

2 Cold Application and Induced Muscle Contractions 241 shown that there is an increased maximal involuntary contraction when a 2-minute ice massage is applied, 7 but there is no difference in the ability to tolerate current or produce higher torque values when a 30-minute ice treatment is applied. 6 No research has been done to evaluate the sequential effects of ice over time in reference to the ability to tolerate current or to produce torque. The purpose of this study was to examine the effects of cryotherapy on ESOI and isokinetic peak torque (IPT) throughout a 20- minute treatment. Methods A factorial design was used. Independent variables were test condition (ice bag, no ice), gender, and time (pretest and at 4, 8, 12, 16, and 20 minutes of application). The dependent variables were output intensity (milliamps) and peak torque (N m). Participants Thirty-eight participants, 20 men (age = 26 ± 5.6 years, height = ± 15.8 cm, mass = 86.0 ± 14.1 kg) and 18 women (23.9 ± 4.84 years, height = ± 8.6 cm, mass = 70.0 ± 12.0kg), volunteered to participate in this study. Participants had incurred no quadriceps injury within the past 12 months. Furthermore, all were asked to refrain from strenuous physical activity 24 hours before testing. Each participant gave written informed consent before participating. The institutional review board approved this study. Instrumentation A Forte CPS Series Electrical Stim Unit (Chattanooga Corp, Chattanooga, Tenn), was used to determine the ESOI tolerated by the participants. A Kin-Com Isokinetic Dynamometer (Chattanooga Corp) was used to determine the maximum torque of contraction produced by the participants. The IPT was measured in newton meters. Both data-gathering instruments were calibrated to the manufacturer s specifications before any testing of participants. Testing Procedures When participants arrived for the study, an anterior thigh skinfold was measured for each. 8 The midpoint, halfway between the anterior superior iliac spine and superior aspect of the patella, of the quadriceps muscle was marked on the thigh. A skinfold caliper was then used to measure the thickness at the marked position. The measurement was taken 3 times and the average of the 3 scores was calculated and used as the skinfold reading. The equation (skinfold reading)/2 was used to estimate the single thickness

3 242 Van Lunen et al of the thigh. The skinfold measures were 8.9 ± 3.3 for the men and 13.2 ± 3.2 mm for the women. The motor points of the vastus medialis and rectus femoris muscles were located on each participant s right leg using the Forte CPS Series electrical stimulator with a monopolar setup. A dispersive electrode was placed under the right hamstring, and gel was placed on the anterior thigh. The stimulating electrode (Neuroprobe) was moved over the muscle bellies of both the vastus medialis and the rectus femoris until the site of the most visible contraction was found over each muscle. These sites were marked as the motor points with a permanent marker to ensure accuracy of electrode placement. The skin over the approximate area of the motor points was shaved and cleansed with an alcohol swipe. The electrodes were then placed over the designated motor points, with one lead over the vastus medialis and the other over the rectus femoris. The participant was then seated on the Kin-Com chair with the backrest set at 80 above horizontal and the treatment leg in 60 of flexion. The axis of rotation of the Kin-Com was aligned with the knee joint. The lever arm was tightly strapped to the leg, 3 finger widths proximal to the lateral malleolus. A Velcro strap was placed over the anterior thigh, and a seat belt was pulled across the pelvis to increase stability. The speed of the Kin-Com was set at 0 per second to measure the isometric force. The Forte CPS Series electrical stimulator was used to induce a muscle contraction in the vastus medialis and rectus femoris muscles. Two singleuse, nonsterile, reusable, self-adhering, 2-in-diameter, pin-connector electrodes were placed in a bipolar setup on the motor points over the vastus medialis and rectus femoris. A frequency of 35 Hz combined with a pulse width of 200 µs was used to elicit the contraction. In order to familiarize the participants with the electrical stimulation, submaximal and maximal tolerance levels were determined by asking them to read from a list of verbal cues to describe their level of pain during muscle contraction. The verbal cues were as follows: I feel it, it is mild, it is moderate, it is strong, and shut it off. The verbal cue it is moderate was recorded as the submaximal reading, and the shut it off cue was recorded as the maximal tolerance level. The ESOI was then increased slowly until the participants reached their submaximal pain-tolerance level and signaled the examiner to stop. To determine the maximal tolerance level, the ESOI was again increased slowly until the participants reached their maximal pain tolerance and signaled for the NMES to be shut off. These 2 tests ended the familiarization session for the sensations of the NMES. After a 10-minute rest, the ESOI was again increased slowly until the participants reached their maximal pain tolerance. The maximal ESOI (ma) and the IPT output (newton meters) created by the involuntary muscle contraction were recorded as the pretest baseline. Stratified random assignment was used to place participants into 1 of 2 test groups: test group 1 (control: no ice application) or test group 2 (experimental: ice-bag application).

4 Cold Application and Induced Muscle Contractions 243 After the pretest baseline measurements, the participants remained seated on the Kin-Com, with the self-adhesive electrodes remaining in place, while receiving either ice-bag (test group 2) application or no ice application (test group 1). The ice bags consisted of two 1-gal plastic bags, each filled with 24 oz of crushed ice. The ice bags covered the entire length of the anterior aspect of the thigh. Both groups were tested for 20 minutes, but the participants who received ice had the 2 ice bags placed on the quadriceps, 1 over each electrode. During the 20-minute test, the ESOI was increased every 4 minutes until the participants reached their maximal pain tolerance and signaled the examiner to shut off the machine. The electrical stimulation remained off until the next test at the subsequent 4-minute mark. ESOI and IPT readings were taken and recorded at every 4-minute interval. Statistical Analyses Two separate factorial ANOVAs were performed, one for ESOI and one for IPT. We used the Tukey HSD method to determine which times differed significantly. A Pearson product moment correlation coefficient was calculated to examine the relationship between output intensity and peak torque at every 4-minute interval for experimental and control groups. The alpha level for all analyses was set a priori at P <.05. Results The means and standard deviations for ESOI and IPT are presented in Tables 1 and 2, respectively. IPT increased over time (F 5,170 = 8.73, P =.001), but no other differences were found. ESOI increased over time (F 5,170 = 53.41, P =.000). We found a difference between groups over time in relation to ESOI (F 5,170 = 14.28, P =.000; Figure 1), which significantly increased for the experimental group at 12, 16, and 20 minutes from the pretest measures. The experimental condition had a significantly greater ESOI than the control condition at 12, 16, and 20 minutes. There were no differences between genders for the measure of ESOI. Pearson product moment correlation coefficients between ESOI and IPT for the experimental and control groups at each 4-minute interval were strong and positive for the experimental condition, ranging from.83 to.91. Correlation coefficients for the control condition ranged from.69 to.72. Comments Noxious-level stimulation using NMES is painful but causes a strong muscle contraction. 2,3,5 Cryotherapy has a depressive effect on various physiological functions, for instance, decreasing nerve-conduction velocity, decreasing blood flow to the muscles, and decreasing metabolism. 9,10-12 What has remained unclear is the point at which cryotherapy potentially helps and

5 244 Van Lunen et al Table 1 Mean (± SD) Output Intensity (Milliamps) by Treatment Condition, Gender, and Time (min) Treatment Condition Experimental Control Men Women Men Women Time (n = 10) (n = 8) (n = 10) (n = 10) Pretest 65.1 ± ± ± ± ± ± ± ± ± ± ± ± ± 36.4* 50.0 ± 14.9* 65.4 ± ± ± 36.8* 51.9 ± 15.6* 65.8 ± ± ± 37.1* 55.3 ± 16.9* 68.0 ± ± 22.0 *Greater than pretest values (P <.05). Table 2 Mean (± SD) Peak Torque (N m) by Treatment Condition, Gender, and Time (min) Treatment Condition Experimental Control Men Women Men Women Time (n = 10) (n = 8) (n = 10) (n = 10) Pretest 83.0 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 33.3 then hinders an individual s ability to produce a strong involuntary muscle contraction. Our findings demonstrate that the application of cryotherapy causes an increase in tolerated ESOI but that it doesn t necessarily correspond to an increase in IPT. Both groups, however, significantly increased their peaktorque production over time. This might be because repeated exposure to

6 Cold Application and Induced Muscle Contractions 245 Figure 1 The output-intensity values for the experimental and control groups over time. *Greater than pretest values and corresponding control values (P <.05). NMES often enables individuals to increase their tolerance and increase the force produced, and this occurs between sessions, as well as between contractions in the same treatment session. 2 This increase in peak torque over time contradicts what has been demonstrated in previous research. 6 Use of long-term cryotherapy ( 30 minutes) has caused a decrease in strength measures for voluntary isometric contractions 13,14 and for involuntary isometric contractions. 6 Durst et al 6 demonstrated a decrease in peaktorque values for both an experimental group and a control group. This 30- minute ice treatment might have decreased the conduction of the pain-sensory fibers while cooling the intramuscular fibers, thereby decreasing nerve-conduction velocity. 6,9-11 The use of short-term cryotherapy and its effects on isometric contraction have also been evaluated. 7,12,15 This research supports the use of cryotherapy to increase ESOI with NMES. 7 Miller and Webers, 7 however, only evaluated 1 contraction posttreatment, so the effects of their research do not readily apply to the clinical setting because we often have patients complete more than 1 repetition in a therapy session. The effects of short-term cryotherapy on many sequential isometric contractions still need to be investigated. It is still undetermined why the men in the control group had such a large increase in peak torque and the women in the control group did not. The most likely explanation for lower muscle force in women is that the cross-sectional areas of muscle fibers are smaller in women and therefore

7 246 Van Lunen et al are unable to produce the same amount of force. 16 This still does not explain, however, why the men in the control group increased their peaktorque production. Possible explanations might involve another issue such as pain tolerance, in that the men might have had needed more experiences with the noxious stimulus in order to tolerate it at a higher level. From a physiological standpoint, NMES is the application of electrical stimulation to produce skeletal-muscle contractions as a result of the percutaneous stimulation of peripheral nerves. 2,3,5 Its use not only is successful in preventing muscle degeneration but also is just as effective as isometric exercise in preventing muscle atrophy in an immobilized joint. 17 The main mechanism that explains these training effects proposes that the muscle strengthening seen after NMES training results from a reversal of voluntary recruitment order, with a selective augmentation of type II (fatigable) muscle fibers. Because type II fibers have a higher specific force than that of type I (fatigue-resistant) muscle fibers, selective augmentation of type II muscle fibers will increase the overall strength of the muscle, 2,4,5,18,19 and therefore the use of NMES is beneficial. This supports the fact that using NMES for patients can have positive effects, especially if the patient has difficulty contracting a muscle or is immobilized for an extended period of time. Even though the use of NMES training has been shown to be successful in augmenting strength and reeducating muscle, a major limiting factor in its use has been the discomfort associated with electrically produced contractions. 2,3,5,7 For a patient with a low pain-threshold level, reaching a sufficient output-intensity level might be difficult, making the use of NMES treatment inefficient. 2,5,19 We did not find any difference in the amount of electrical stimulation that was tolerated between men and women. Some authors support this finding, 20 whereas others have reported that men can tolerate higher amounts of electrical stimulation. 21 Our study, however, supports the concept that patients who receive ice throughout a 20-minute treatment will be able to withstand higher levels of NMES. A limiting factor in our research methodology is the fact that the maximal voluntary isometric contraction of the muscle was not determined for each participant. Therefore, we are unable to determine whether the involuntary isometric peak torque approximated the value that the participants had for a voluntary isometric contraction. Nonetheless, all of the participants increased their peak-torque values over time and were even able to do this after completing a familiarization period. It might also be problematic to use output-intensity voltage as a means to determine whether patients can withstand higher levels of NMES and thus link it to a stronger contraction. The strength of an electrical-stimulation-elicited contraction depends on many factors such as electrode placement, skin condition, the type of waveform preferred by the patient, and others. 2,3,5 Our study demonstrates that cryotherapy allows individuals to tolerate higher-intensity NMES than NMES without it. This does not hold true,

8 Cold Application and Induced Muscle Contractions 247 however, for significant changes in peak-torque production. This addition of cryotherapy might have an effect on an individual s ability to handle pain and therefore enable that individual to tolerate a higher stimulus. It has been suggested that every therapy regimen be tailored to the coping style that an individual uses for pain. 18 For instance, researchers 22,23 have demonstrated that different individuals prefer various current waveforms and that this preference relates to comfort and therefore the ability to contract a muscle differently. If modalities help with individuals ability to cope with pain, they should be utilized if the outcome is achieved. Future research should investigate the effects of a combined voluntary isometric contraction with NMES and the application of various modalities. References 1. Currier DP, Mann R. Comparison of electrical stimulation with conventional isometric exercise. J Orthop Sports Phys Ther. 1984;5: Robinson AJ, Snyder-Mackler L. Clinical Electrophysiology: Electrotherapy and Electrophysiologic Testing. Baltimore, Md: Williams & Wilkins; Prentice WE. Therapeutic Modalities in Sports Medicine. Boston, Mass: McGraw- Hill; Rooney JG, Currier DP, Nitz AJ, Delitto A. Effect of variation in the burst and carrier frequency modes of neuromuscular electrical stimulation on pain perception of healthy subjects. Phys Ther. 1992;72: Starkey C. Therapeutic Modalities. Philadelphia, Pa: FA Davis Co; Durst JW, Gohdes DD, Ward WK, Workman K, Bryan JM. Effects of ice and recovery on maximal involuntary isometric torque production using electrical stimulation. J Orthop Sports Phys Ther. 1991;13: Miller CR, Webers RL. The effects of ice massage on an individual s pain tolerance level to electrical stimulation. J Orthop Sports Phys Ther. 1990;12: McArdle WD, Katch FI, Katch VL. Exercise Physiology: Energy, Nutrition, and Human Performance. Philadelphia, Pa: Lea & Febiger; Knight KL. Cryotherapy in Sport Injury Management. Champaign, Ill: Human Kinetics; Lehmann JF. Therapeutic Heat and Cold. Baltimore, Md: Williams & Wilkins; Michlovitz SL. Thermal Agents in Rehabilitation. Philadelphia, Pa: FA Davis; McGown HL. Effects of cold application on maximal isometric contraction. Phys Ther. 1967;47: Johnson J, Leider FE. Influence of cold bath on maximum handgrip strength. Percept Mot Skills. 1977;44: Oliver RA, Johnson DJ, Wheelhouse WW, Griffin PP. Isometric muscle contraction response during recovery from reduced intramuscular temperature. Arch Phys Med Rehabil. 1979;60:

9 248 Van Lunen et al 15. Burke DG, MacNeil SA, Holt LE, Mackinnon NC, Rasmussen RL. The effect of hot or cold water immersion on isometric strength training. J Strength Cond Res. 2000;14: Miller AE, MacDougall JD, Tarnopolsky MA, Sale DG. Gender differences in strength and muscle fiber characteristics. Eur J Appl Physiol. 1993;66: Erikson E, Haggmark T. Comparison: isometric muscle training and electric stimulation supplementing isometric muscle training in the recovery after knee ligament surgery. Am J Sports Med. 1982;7: Parker MG, Berhold M, Brown R, Hunter S, Smith MR, Runhling RO. Fatigue response in human quadriceps femoris muscle during high frequency electrical stimulation. J Orthop Sports Phys Ther. 1986;7: Delitto A, Strube MJ, Shulman AD, Minor SD, Rothstein JM. A study of discomfort with electrical stimulation. Phys Ther. 1992;72: Kramer JF. Comparison of voluntary and electrical stimulation induced torques at selected knee angles in male and female subjects. Physiother Can. 1987;39: Alon G, Kantor G, Smith GV. Peripheral nerve excitation and plantar flexion force elicited by electrical stimulation in males and females. J Orthop Sports Phys Ther. 1999;29: Bowman BR, Baker LL. Effects of waveform parameters on comfort during transcutaneous neuromuscular electrical stimulation. Ann Biomed Eng. 1985; 13: Delitto A, Rose SJ. Comparative comfort of three waveforms used in electrically eliciting quadriceps femoris contractions. Phys Ther. 1986;66: