Electrical Muscle Stimulation and Isometric Exercise Effects on Selected Quadriceps Parameters*

Transcription

1 /86/ $02.00/0 THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copyright by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association Electrical Muscle Stimulation and Isometric Exercise Effects on Selected Quadriceps Parameters* H. D. HARTSELL, PhD The purpose of the study was to compare the effects of 1) monopolar (MI) and bipolar (BI) electrical muscle stimulation (EMS) concurrent with isometric exercise, and 2) EMS (MI and BI) concurrent with isometric exercise to isometric exercise (I) alone on girth, dynamic strength, muscular power, and muscular endurance of the right quadriceps muscle. All three experimental groups completed a 6-week program of training on the right lower limb which was isometrically restrained at -30 knee extension. Additionally, the MI and BI groups received low frequency (65 Hz) EMS. A control group (C) was involved in pre- and post-testing sessions only. Results indicated that 1) EMS concurrent with isometric exercise was more effective in improving quadriceps strength over a group that did no training, but was no more effective than isometric exercise alone; 2) the two EMS techniques yielded similar results for healthy innervated muscle; 3) dynamic strength was minimally increased by EMS; 4) power was positively increased more by the monopolar technique; and 5) endurance was positively increased more by the bipolar technique. It was concluded that while the two techniques of EMS concurrent with isometric exercise have the potential to positively increase selected physiological parameters in healthy innervated muscle, the greatest benefits will be noted for the weaker muscle. Recently the surge of interest and research in electrical muscle stimulation (EMS) has provided a variety of viewpoints as to the benefits that EMS may lend to the areas of sports and rehabilitation. To date, most research on tetanizing EMS has focused on the strengthening effects of low and medium frequency current^.^-^ Frequently, these studies compare different techniques of immobilization and EMS, various conditions of pathological insult and EMS, or the effects of EMS at the tissue level as illustrated through biopsy analy- sis.4~5~7~8 However, quantitative and qualitative cross-comparisons remain difficult as a consequence of the wide variation in, and discrepant reporting of, equipment specifications with techniques of electrode application, experimental protocol, and the physiological status of human muscle studied. In addition to omitting details on current fre- quency, many investigators fail to report specifications of equipment ~tilized.~,~-~ Variables such 'All work was performed at the University of Alberta, Edmonton, Alberta. as pulse width and wave form are required if the reader is to be permitted an unbiased opportunity toward interpretation of the results. Others overlook any explanation as to the electrode placement used, or decide to utilize a personally devised method without rationale as to why it differs from the'conventional norm^.^-^ The bipolar and monopolar methods as well as electrode plate size, and whether or not a reversal of charge occurred are again important if the reader is to objectively evaluate the results. The EMS protocol differs dramatically among investigators. Some fail to specify a pr~tocol.~~'~ Others use the established 10:50:10 protocol of the Soviets.487s8 In addition, a 5-6 sec contraction followed by a 5-sec rest has been used as well as a 6-sec contraction followed by a 10-sec rest, repeated 6 time^.^.^ For the protocols differing from the researched 10:50:10 protocol, no justification can be found.10s1 ' Various physiological states of human muscle and EMS have been investigated. One can find studies utilizing healthy muscle, anterior cruciate ligament repairs, or other post-injury cases ,19

2 204 HARTSELL JOSPT Vol. 8, No. 4 Studies employing many combinations of current types, protocols, and states of muscular health have yielded a variety of conclusions. These include: 1) EMS is more effective in improving muscular strength than no training, 2) EMS alone is more effective than isometric exercise alone, 3) EMS concurrent with isometric exercise is more effective than isometric exercise alone, and 4) EMS with or without isometric exercise is as effective but no more effective than isometric exercise alone in improving muscular Strength.3.4, The purposes of the present study were to compare two techniques of EMS concurrent with isometric exercise using the standardized 10:50:10 format, and secondly to compare the effects of EMS concurrent with isometric exercise to that of isometric exercise alone, using healthy innervated human quadriceps muscle. The physiological parameters studied were girth, dynamic strength, muscular power, and muscular endurance. PROTOCOL Twenty-one male student volunteers ranging in age from 18 to 35 years participated. None had a recent history of significant lower limb pathology. A Cybex It@ (Cybex, Division of Lumex, Inc., Ronkonkoma, NY ) isokinetic exercise unit was used to record the isometric strength of the right quadriceps muscle at 60' knee flexion. From the average score of the three trials given per subject, a stratified random design was used to place the subjects into one of four groups: control group (C) (N = 5), isometric exercise (I) (N = 4), monopolar EMS concurrent with isometric exercise (MI) (N = 6), and bipolar EMS concurrent with isometric exercise (BI) (N = 6). For all groups the right quadriceps muscle was tested and trained. The control group (C) participated in pre- and post-testing sessions only. The total treatment regime for the three experimental groups involved a period of 6 weeks, exclusive of the pre- and post-testing sessions. During the 6-week training period all subjects were requested to limit participation in physical activity which deviated from their stated norm and to maintain a weekly activity sheet. -testing duplicated pre-testing in format and consisted of girth and isokinetic measurements. The girths were taken with the subject supine, relaxed, and legs extended. Circumferential girth in cm was measured at the midbelly of the vastus medialis (MVM), and again at the midquadriceps (MQ). For the isokinetic measurements, a Cybex II unit calibrated prior to each session was employed. Subjects were stabilized by means of a strap across the pelvis, a shoulder harness, and straps across the distal one-third of the anterior thighs and they were maintained in 75' hip flexion against a backrest. The hip was positioned in neutral abduction/adduction and the knee joint center of the right lower extremity was aligned with the rotational axis of the Cybex input shaft. The subject performed a maximal voluntary contraction until instructed to stop. With the exception of muscular endurance, a maximum of three practice trials was permitted prior to each of the following tests: a) Dynamic strength (DS): measured by having the subject contract throughout an active range of motion (ROM) from -90 to O0 knee extension. A maximum rotational test velocity of 30 /sec was used. Three consecutive maximal effort contractions in both directions of flexion and extension were permitted. The average of the maximum extension peaks was calculated and taken as the measurement value, recorded in f4 Ibs. b) Muscular power (MP): measured by having the subject contract throughout?n active ROM from -90' to O0 knee extension. A maximum rotational test velocity of 180 /sec was used. Three consecutive maximal effort contractions in both directions of flexion and extension were permitted. The average of the maximum extension peaks was calculated and taken as the measurement value, recorded in ft Ibs. c) Muscular endurance (ME): measured by having the subject contract throughout an active ROM from -90' to O0 knee extension and continue repetitions until peak torque reached 50% of the initial maximum value for the quadriceps. ME was recorded in sec. A maximal rotational test velocity of 180 /sec was used. Training sessions were conducted by the author and verbal commands during the sessions were consistent for all subjects. The training sessions were conducted daily using the 10:50:10 format, 5 dayslweek. The subject lay supine on a plinth and was permitted to grasp the sides of the plinth. The right knee was flexed over a standard knee flexion board and maintained in 20-30' flexion. A restraining strap was placed across the pelvis at the level of the anterior superior iliac spine (ASIS), and secondly just proximal to the

3 JOSPT October 1986 EMS TECHNIQUES AN1 3 ISOMETRIC EXERCISE 205 ankle joint but permitting full dorsiflexion. Once in position, group I was instructed to "extend" at the knee joint with a maximal effort quadriceps contraction that lasted for a duration of 10 sec. The ankle was fully dorsiflexed. A 50-sec rest period followed and the procedure was repeated until 10 consecutive contractions had been performed. The MI and BI groups followed a similar format, concurrently with the addition of EMS. The conventional electrode plate and sponge pad preparation was utilized. For the MI group, the active electrode plate (6 x 8 cm) and sponge pad (7 x 9 cm) were placed over the motor point of the vastus medialis (VM) while the dispersive electrode plate (8.5 x 11.5 cm) and sponge pad (9.5 x 12.5 cm) were placed over the femoral nerve in the femoral triangle. For the 81 group, the active electrode plate (6 x 8 cm) and sponge pad (7 x 9 cm) were placed over the distal aspect of VM while the dispersive electrode plate (6 x 8 cm) and sponge pad (7 x 9 cm) were placed over the proximal aspect of VM. The EMS was administered using a low frequency muscle stimulator which delivered a square wave farm, pulse frequency of 65 Hz, and an individual pulse time of 2.0 msec. Prior to eacw training session the maximum current intensity was located for each subject. Concurrent with the electrical current, the EMS subject was instructed to extend at the knee jont with a maximal effort quadriceps contraction. The combination of voluntary and involuntary contraction was maintained for a duration of 10 sec. A 50-sec rest period followed and the protocol was repeated until 10 consecutive contractions had been performed. Current intensity was subjectively increased during a voluntary contraction. The statistical analysis used was a 2-factor (treatment by occasion) MANOVA, with the occasion factor being treated as the repeated measure. Main treatment effects, post hoc Helmert contrasts and nonorthogonal pair-wise contrasts were calculated on the variables taken simultaneously and, second, taken individually. Following this, the main occasion effects were calculated simultaneously. Interaction effects for all groups were calculated simultaneously and all possible pairs of groups were reported. Where significance was observed the interaction effects were calculated on individual variables. Throughout the analysis, the p = 0.05 level of significance was used. RESULTS Table 1 displays group means and standard deviations for all variables on occasion. A significant treatment effect (p < 0.01) was observed when all groups were contrasted simultaneously for the main group effects (Table 2). All Helmert contrasts for group effects were statistically significant (p < 0.01). Thus, a general treatment effect was observed when the vector of averaged means for groups I, MI, and BI was contrasted to the mean vector for group C. A significant treatment effect (p < 0.01) was observed when the means vector for group I was contrasted to the vector of averaged means for groups MI and BI. A final contrast of the means vector for groups MI and BI was also significant (p < 0.01). All pairwise contrasts of the group means vectors were statistically significant (p < 0.01). Individual variable effects for means group effects (Table 3) illustrated significant treatment effects (p < 0.01). An analysis of individual variable effects on occasion demonstrated that MQ was the only nonsignificant (p > 0.05) variable and that the MVM (cm) MQ (cm) DS (ft-lbs) MP (ft-lbs) ME (sec) TABLE 1 Treatment means for groups x variable TABLE 2 Mean group effects averaged over occasion MVM MQ DS MP ME (cm) (cm) (ft-lbs) (ft-lbs) (sec) C MI BI

4 TABLE 3 Mean group effects and mean occasion effects for individual variables Mean group effect (p) Mean occasion effect (p, F-ratios* MVM <0.01 = MQ <0.01 > DS co.01 < MP <0.01 < ME <0.01 < * Critical F = 4.35, p TABLE 4 lnteraction effects lnteractlon effect (p) =0.03 C: l >0.05 C:MI >0.05 C:BI <0.01 1:MI >0.05 1:BI =0.30 MI:BI <0.01. MVM MQ DS MP TABLE 5 lnteraction effects on individual variables Group C vs l C vs MI C vs BI I vs MI I vs BI MI vs BI C vs l C vs MI C vs BI I vs MI I vs BI M vs BI lnteraction effect I DI greatest F-ratios occurred for variables MP and ME (Table 3). When all variables were taken simultaneously (Table 4), a significant overall interaction effect (p = 0.03) was observed but the pre- and posttraining interaction effects between group pairs on all variables taken simultaneously did vary. lnteraction effects were calculated on the individual variables and when all groups were taken simultaneously (Table 5), the interaction effects for variables MVM, MQ, and DS were nonsignificant (p > 0.05). taken simultaneously on variable MI and secondly variable BI were 'SELL JOSPT Vol. 8, No. 4 observed to be significant (p = 0.01) for the interaction effect. Group pair interaction effects were significant for only certain pairs. For both measurements of girth, a treatment effect (p < 0.01) was observed for all Helmert contrasts. At MVM, group BI showed the greatest improvement (0.92 cm) with training while group MI increased an average of 0.05 cm and group I demonstrated little change. At MQ, group BI demonstrated the greatest average change (2.1 2 cm) with training but also displayed the lowest pretraining measures. On variable MQ, groups I and MI showed average decrements of 0.63 and 0.20 cm, respectively. For DS, a significant treatment effect (p < 0.01) was observed for all Helmert contrasts. Group I showed the greatest change ( ft-lbs) with training despite having the highest pre-training values. Groups MI and BI changed the least (5.0 and ft-lbs, respectively). For MP, no significant differences (p > 0.05) between group C and the average of groups I, MI, and BI were observed. All remaining Helmert contrasts were significant (p < 0.01) and significant treatment effects (p I 0.02) were observed between all pairs of means for groups contrasted. Group BI recorded the greatest average change (13.33 ft-lbs) with training but alsofad the lowest pre-training measurements. Group MI improved an average of ft-lbs. However, the change with training for group BI was not enough to increase the training effect to the average levels for group MI and BI. For ME, a treatment effect (p < 0.01) was observed when the mean of group I was contrasted to the averaged mean for the EMS groups. Nonsignificance (p > 0.05) was observed for the remaining Helrnert contrasts. Significant pair-wise contrasts were noted for groups C:l, C:BI, I:MI, and I: BI. Group BI increased an average of 5.40 sec with training even though characterized as having the highest average pre-training measure. Group MI increased an average of 4.08 sec as a result of training. DISCUSSION In support of previous re~earch,~~~~~ the present study indicated that EMS concurrent with isometric exercise improves quadriceps strength beyond performance levels of untrained individuals. However, EMS concurrent with isometric exercise is as effective as, but no more effective than, iso-

5 JOSPT October 1986 EMS TECHNIQUES AND ISOMETRIC EXERCISE metric exercise alone in incrementing strength of healthy, innervated muscle. The concept of the weaker the muscle initially, the greater are the strength gains after an EMS training program was verified generally across all variables (excluding DS) by group BI, characterized as having the lowest average pre-training scores and greatest increments. These findings support previous studies done by Eriksson and Haggmark5, Godfrey et al7, and Johnson et al8 who utilized post-trauma patients with varied states of weakened muscle subjected to protocols of EMS. Physiologically, the cross-sectional area of a muscle increases with exercise as a result of increased myofibrillar density and a reduction in the amount of sarcoplasm in the contractile complex". Since an EMS induced muscle contraction most closely approximates a voluntary contraction1', similar rationale for girth increments with EMS and isometric exercise may be indicated. Concurrent with the physiological changes is an increased quality of contraction, a reported EMS effe~t,"-'~.'~ which is dependent upon the number of contracting fibers. Bipolar EMS produces a direct and even distribution of current throughout thestimulated muscle.4." As a result, the physiological changes of increased myofibrillar density and reduction of sarcoplasmic reticulum" may occur throughout the course of the muscle, creating possible girth increments. Monopolar EMS produces an indirect stimulation of a muscle group as a whole, and specifically to the muscle whose motor point is ~timulated.~~" Consequently, girth changes may be expected after a training program of EMS concurrent with isometric exercise, and greater gains should be noted in states of weaker muscle as evidenced by group 61, characterized by the lowest average pre-training values. -training increments were observed for the training groups on all isokinetic measures. Significant overall interaction effects were observed for measures of MP and ME, although interaction effects between groups I, MI, and BI were lacking for variables MP and ME, reinforcing the concept that EMS concurrent with isometric exercise is as effective but no more effective than isometric exercise alone in healthy subjects. Changes in DS for the EMS groups were contrary to expectation. For all the groups taken simultaneously, a significant pre- and post-training effect was observed, but further analysis did not reveal a significant interaction effect between the groups. Beneficial results for the EMS groups were expected due to previous st~dies~~'~~'~ reporting either a maintenance of strength increments after an isometric exercise program or OtherS5.8. u. 12 reporting strength increments after an EMS program. The present study combined voluntary and involuntary exercise. MP and ME increments were noted after training for the EMS groups; consequently, increments in DS were expected. KotslO." stated that optimal strength increments occurred after treatment sessions (the present study maintained a minimum of 30 sessions) and second, that EMS was capable of recruiting more motor units beyond that which an individual is capable of voluntarily recruiting. The rationale for the lack of DS increments for the EMS groups may be that the subjects subconsciously relied on the current for the little "extra effort" toward a maximal contraction. Once the absence of the current was accepted, the EMS subjects increased their voluntary effort to approach maximum, as evidenced by the following post-tests of MP and ME. In theory, the monopolar technique may have a greater potential to develop DS. Though the increments were small for the EMS groups, the monopolar EMS group showed greater improvement even though maintaining a higher initial level of strength. Monopolar EMS affects superficial and deep muscles supplied by the nerve ~timulated~.~." and since DS involves the quadriceps group as a harmonious working unit, the more muscles involved, the greater should be the potential for strength increments. ~lthough previous studies have not reported power and endurance as affected by EMS, several viewpoints may be given in support of the variables MP and ME as being the only significant variables. All training groups showed increments in MP, but the EMS groups demonstrated the greatest changes with training. The monopolar group improved an average of 11.26% and the bipolar group an average of 15.78%. Power increments for the EMS groups were significant when individually compared to group C. This result did not remain as such for group I. Thus, the EMS techniques were more effective than isometric exercise alone toward increasing MP when contrasted to an untrained group. Changes in the EMS groups were not significant to definitively conclude which technique was more effective toward improving MP, possibly an indication of a

6 208 HARTSELL JOSPT Vol. 8, No. 4 low frequency stimulator utilized on healthy, innervated muscle. Based on the physiological principles of the EMS techniques, greater increments may be anticipated with use of the monopolar technique. Power should increase as more muscles are recruited and the monopolar technique stimulates superficial and deep muscles To reiterate, the greater changes on MP for the weaker muscle are expected as a result of the physiological effects of EMS inclusive of increased motor unit recruitment, improved peripheral nerve fibers and the angle of pull being more efficient effects, and capillary blood flo~.'~.'~ K o ~ s ~ for ~ VM. ~ as ~ full extension is approached, endurance stated that the most suitable frequency to cause may be enhanced through use of the bipolar techmaximal power of a muscle was a rhythmical nique. stimulation of Hz and, second, that optimal power increments were produced after a CONCLUSION minimum of sessions. The present study included both of these factors. The order of re- Although EMS concurrent with isometric exercruitment changes from the norm of slow twitch cise positively affects human muscle, either techfiber to fast twitch fiber, to that of fast twitch nique is limited in the resultant effectiveness on fibers innervated by large motoneurons recruited healthy innervated muscle through utilization of a first by EMS.'O-" Power predominantly involves low frequency stimulator. The greatest changes the action of fast twitch fibers.' Kots1O." also to be achieved occurred for weaker muscle. Thus, stated the rationale to be the result of the fast it is being suggested that the greatest potential twitch and slow twitch fiber ratio remaining the use for either EMS technique is in the rehabilitasame, but that the quality of recruitment tended tion of weakened or traumatized muscle. The to be influential toward activating more of the fast selection of EMS technique will be dependent twitch fibers. Finally, a certain amount of CNS upon the temporary or long-term goals of any inhibition is normally present during a muscle rehabilitation program. contraction1 and the subsequent recruitment of all motor units in a muscle becomes impossible, REFERENCES thus dampening the eventual power output. A decrease in the CNS inhibition would facilitate motor unit recruitment and enhance power.' With the use of EMS, the CNS does not give input but voluntary contraction increases which would imply a change in the PNS." Both EMS techniques affected ME increments significantly over an untrained group whereas group I was nonsignificant when contrasted to group C. The gains may be indicative of the lower initial measures, and the physiological effects of EMS concurrent with isometric e~ercise.~ Due to lack of statistical significance between groups MI and ME, a conclusion as to which EMS technique enhances ME more is lacking. Considering initial levels of performance and improvements with training, bipolar EMS was observed to provide the weatest - effects toward improving - ME. EMS known to improve the endurance capacity of muscle. Second, the bipolar technique focused on VM. As a subject performs the endurance test, fatigue results causing the lower limb to fail while attempting the last few degrees to full extension of the knee joint. The final 30' to full extension requires a 60% increase in quadriceps force without fatigue The VM works throughout the full range of knee joint motion but as a result of the fiber alignment, a low angle of insertion of the distal 1. Astrand P-0. Rodahl K: Textbook of Work Physiology. New York: McGraw-Hill Book Co Bouman HD, Shaffer KJ: Physiological basis of electrical stimulation of human muscle and its clinical application. Phys Ther Rev 37: Currier DP, Lehman J. Lightfoot P: Electrical stimulation in exercise of the quadriceps femoris muscle. Phys Ther 59: , Curwin S. Stanish WD. Valiant G: Clinical applications and biochemical effects of high frequency electrical stimulation. CATA J 7: Eriksson E. Haggmark T: Comparison of isometric muscle training and electrical stimulation supplementing isometric muscle training in the recovery after knee ligament surgery. Am J Sports Med 7: Garret TR. Laughman RK. Youdas JW: Strengthening brought about by a new Canadian muscle stimulator: a preliminary study. Phys Ther 60: Godfrey CM. Jayawardena H, Quance TA, Welsh P: Comparison of electro-stimulation and isometric exercise in strengthening the quadriceps muscle. Physiother Canada 31 : , Johnson DH. Thurston P. Ashcroft PJ: The Russian technique of faradism in the treatment of chondromalacia patella. Physiother Canada 29: ,1977 increases capillary blood flow and motor unit recruitment, improves tissue oxygenation, and removes metabolic waste product^,'^.'^ factors of muscle function. Eur J ~ p p ~ 9. Komi PV. Viitasalo JT, Rauramaa R. Vikko V: Effect of isometric strength training on mechanical, electrical and metabolic aspects Physiol 40: lo. Kots Y: The training of muscular power by methods of electrical

7 JOSPT October 1986 EMS TECHNIQUES AND stimulation. State Central lnstitute of Physical Culture, Moscow, Kots Y: Electro-stimulation. State Central Institute of Physical Culture. Moscow, Licht S: Therapeutic Electricity and Ultraviolet Radiation, Ed 2. New Haven, CT: Elizabeth Licht Publishing Co., Lieb FJ, Perry J: An electromyographic study under isometric contractions. J Bone Joint Surg (Am) 53: , Lieb FJ. Perry J: Quadriceps function: an anatomical and mechanical study using amputated Ilmbs. J Bone Jolnt Surg (Am) 50: Muller EA, Quanbury A. Basmajian JV: Surface electrical stimulation of the lower limb. Arch Phys Med Rehabil 51 : , 1970 ISOMETRIC EXERCISE Rozier CK, Elder JD, Brown M: vention of atrophy by isometric exercise of a casted leg. J Sports Med Phys Fitness 19: , Scott PM: Clayton's Electrotherapy and Actinotherapy, Ed 7. Great Britain: Balliere Tindall and Cassell Shriber WJ: A Manual of Electrotherapy, Ed 4. Philadelphia: Lea and Febiger, Taylor AW. Katz IM, Lavoie M: The effects of faradic stimulation on skeletal muscle fibre area. Can J Appl Sports Sci 3:185, 1978