Human Movement Science 1 (1982) 139- 150 North-Holland Publishing Company

139

University of Illinois, USA

Ward, T. and .D. Grabiner, 1982. Chronic effects of electrical stimu- lation of muscle on the fractionated components of audio response time. Nluman Movement Science 1, 139- 150.

Six male volunteer subjects underwent five weeks ( I5 sessions ) of electrical stimulation (ES) of the triceps bra&ii muscle (medial head), participated in a pretest, and five weekly post-treatment performance tests of an elbow extension task. Response time (RSP) was electronically fractionated into the two components of reaction time (RT): premotor reaction time (PMT) and motor reaction time (MT): and movement time (MVT) for 45 degrees of elbow extension. Acceleration character- istics of the movement were quantified via a piezoelectric accelerometer mounted on a specially-built mechanism that allowed the desired motion in a transverse plane. Statistical analysis did not indicate significant treatment effects on the criterion measures, however, a significant linear trend for MT and significant linear and quadratic trends for MVT were indicated. Neuromuscular adaptation to the passage of electric current through nerve and muscle tissue was indicated by a significant quadratic trend and significant differences between all weekly accumulative (treatment) voltages. An unexpected significant negative correlation between PMT and MT was considered cause for further study. The particular technique of ES administration, although it produced consistant changes in RSP components (Ward and Grabiner 1981) was not as effective as methods described by other investigators for increased human performance.

The utilization of electrical stimulation (ES) is accepted as a mode of treatment for a spectrum of physiological conditions. ore than 2000 years ago the use of the torpedo fish, capable of generating and transmitting electric current, was prescribed as relief for ailments

* Mailing address: T. Ward, Biomechanics Research Laboratory, University of Illinois, 906 S. Goodwin, Urbana, IL 6 1801, USA.

0167.9457/82/0000-0000/$02.75 0 1982 North-

140 T. Ward, M.D. Grubiner / ES md neuromuscular function

ranging from arthritis to haemorrhoids ( cNea1 1977). primit:ve beginning, ES has grown into an area of study enc rehabilitation from spinal cord and peripheral nerve damage, orthotic engineering, healing of damaged bone tissue, reduction of pain, and improvement of rmal neuromusc r function (Vodovnik et a Vodovnik 197 1; ppenstahl 1980 albech and Strauss 1980; et al. 1965).

The purpose of this investigation was to quantify the chr of ES on the fractionated components of reaction time premotor reaction time (I? and motor reaction time changes in movement tim T) and acceleration characteristics of

onse task resulting m ES were also examined. F n a previous study

and Grabiner ( 1981) observed r ferential effects of PMT

ON

STIMULUS OFFl I I

EMG

A(XELERATlON

ELGCN (ad)

M-D

RSP

O-onset of movement r)T-reaction time

C-completion of movement PMT-premotor reaction

RSP-response time MT-motor reaction time

MD-motor duration MVT-movement time

Fig. 1. Stslized response time paradigm.

time

T. Wurd, M.D. Grubiner / ES und neuromusculur function 141

and motor duration, MD (the sum of the MT and VT latencies), occuring over a three-week treatment period. The greatest net changes for both parameters occurred after the initial week of stimulation. Concurrent with these changes were unexpected increases in the stimu- lation voltages necessary to elicit the criterion muscular response during treatment sessions. This apparent neuromuscular adaptation to both the passage of electrical current through nerve and contractile tissue and individual perception of current was analyzed in the present studv

Six male volunteer subjects (K= 24.33 yr, 180.76 cm, 79.08 kg) par- ticipated in the investigation which entailed six weekly :.performance tests and five weeks of ES occurring three times per week. Test data were collected on Mondays prior to each week’s first stimulation session. Stimulation followed a Monday/Wednesday/Friday schedule.

Identical testing procedures were followed during all testing sessions. The movement studied was a 45 degree elbow extension of the forearm in the horizontal plane. A specially built low-friction mechanism re- stricted all planar movement to the desired motion. The sitting subject’s right shoulder was flexed and medially rotated and the elbow flexed to 90 degrees so that both the arm and forearm were parallel to the transverse plane. The radio-ulnar joints were pronated so that the palmar surface of the hand was resting on the apparatus. The forearm was fully supported by the apparatus and attached to it with Velcro straps. The center of rotation for the elbow’ was coincident to the axis of rotation of the mechanism.

A Coulbourn modular component EMG system was programmed to deliver an audio stimulus and to fractionate and digitally display the

components. A foreperiod of one to three seconds occurred between a verbal “ready” signal and the stimulus. A digital counter, driven by a precision time base emitting pulses at 1 kHz started simultaneously with the stimulus. This counter continued until an increase in the resting medial head of the triceps brachii muscle terminat EMG was monitored with two silver-silver chloride electrodes (diameter = 8 mm, placed 30 fnm

apart). Standard electrode site preparation reduced electrode/skin im- pedance to less than 3 kilohms.

142 T. Ward, M.D. Grabiner / ES and neuromuscular function

The termination of P T initiated a second digital counter which continued count until movement of the mechanism/forearm unit occurred. sition of the arm was monitored via a potentiometer (elgon) inserted in the shaft of the mechanism and coincident with the axis of rotation. The voltage output of the as patched into a

arator and digital multimeter The comparator o that movement of less than one degree past the initial

position (accurate ) terminated counting by second counter, i vement had been initiate third digital counter remained on until the forearm had moved through

ortion of the program, and the outpu model 302A) mounted so that

s was tangential to the rotation of the mechanism. eleration curve was used in the

has been demonstrated that this part of the acceleration is the least affected by changes in other acceleration parameters and thus it was inferred that it is the most meaningful in terms of force production by the contractile component of muscle (

hree practice trials preceded fifteen recorded trials. The mean of the recorded trials for each variable was taken as the representative score for each subject.

Stimulation of the dial head of the triceps bra&ii muscle occurred three times per week. ch session consisted of 10 cycles of 30 seconds stimulation followed by 30 seconds of rest. The stimulator was a Teca

z. The magnitude of the stimula- lectrode applicat (diameter =

8 mm, placed 30mm apart), the stimulator, set at 1 was slowly turned up from zero volts until the subject indicated perception of the pulse. This was “sensory threshold” and this value was recorded. Voltage was increased further until a visible twitch below the stimulat- ing electrode was obtained. This value,

was the voltage used for repeated for each session.

“motor threshold” was also that session at 50 Hz. This

Fig. 2 depicts the changes in the criterion variables during the investiga- tion. -4 multiple regression approach for randomized blocks with re-

T. Wurd, M.D. Grubiner / ES md neuromuscular function 143

b 1 I I I

1 3 4 5 pretest

WEEKS OF TREATMENT

-premotor reaction time

-motor resciion time

0 -mcvement time

-positive duration (acceleration)

Fig. 2. Treatment effects on experimental variables.

peated measures and trend analysis was conducted (Pedhazur 1977; dhazur 1973). No significant treatment effects were

T or positive duration. e last measure of was, however, significantly slower than the initial measure (F d”= 6,29, p c 0.001). The inconsistency of this change in conjunction with the fact that it occurred during the final testing session, led the investigators to believe that it was the result of some residual variable(s) rather than a treatment effect.

Trend analysis revealed a significant linear trend for T (F= 9.128, df = 7,28, p = O.OOS), significant linear and quadratic trends for (F = 15.458 and 6.174, df = 7,28, p = 0.001 and 0.019, ” respect and, similarly, significant linear and quadratic trends for weekly accu-

voltage (F = 2028.875 and 57.954, df = 7,28, p ( 0.001, respec- ost hoc comparisons of the weekly group means of accumula-

144 T. Wurd, M.D. Grubiner / ES and neuronwscuhr function

Table 1 Mean sensory and motor thresholds for each treatment session.

Treatment Sensory threshold Motor threshold

1 3.0 8.0

2 6.0 22.0

3 6.0 21.0

4 2.0 7.5

5 3.8 15.5

6 5.0 20.0

7 8.5 27.0

8 7.0 28.0

9 9.0 36.0 10 6.0 29.0 11 6.0 24.0 12 12.0 40.0 13 5.0 28.0 14 9.0 31.0 15 12.0 52.0

tive voltage indicated that each week’s value was significantly higher than all preceding weeks. This is illustrated in fig. 3. The underlying rises in motor thresholds, which are responsible for the increases in accumulative voltage, are shown in table 1 and fig. 4. It should be noted that each subject’s accumulative voltage for each session was equal to the motor threshold for that session multiplied by the treatment time in minutes (five) added to the sum of all previous accumulative voltages.

’ ation of the zero-order correlations derived a significant negative relationship between

( r= -0.71, p c 0.001). This contradicts the findings of Botwinick and mpson (1966) who reported correlation coefficients for P ranging from - 0.10 to 0.24 (nonsignificant).

A significant negative correlation was found between MT and accu- mulative voltage (r = - 0.34, p C 0.05). A nonsignificant correlation was found between accumulative voltage and PMT (r = - 0.16). caruse of the unexpected correlation between PMT and MT and relationship between these variables and accumulative voltage a partial correlation coefficient between PMT and MT was calculated partialling out the effects of act mulative voltage. This coefficient for PMT and

T was calculated to be Accumulative voltage was also found to correlate significantly with VT (r= 0.45, p c 0.01) although the

19 t

T. Wurd, M.D. Grubiner / ES and neuromwcular function

1 2 3 4 5

WEEKS OF TREATMENT

145

Fig. 3. Weekly increases in accumulative voltage.

incongruous change in MVT during the final testing session may be responsible for the strength of the relationship. However, even though a significant relationship was observed between VT and positive dura- tion (r = 0.65, p c O.Ol), accumulative voltage was nonsignificantly related to positive duration ( r = 0.16).

It was of interest to compare the results obtained from the present group of subjects to those obtained in the initial study (

146 T. Ward, M.D. Grabiner / ES und neuromuscular function

35

Ij 4 30 v

2 25

$ 20

15

1234567 S 9 10 11 12 13 14 15

TREATMENT SESSIONS

O-sensory threshold

Fig. 4. Observed rises in sensory and motor thresholds. . -motor threshold

ig. 5 diagrams the comparison of net changes in P ivalent treatment eriods (three weeks). The most

striking simiiarrty is the increase in T following one week of ES. om this singularly close resemblance, the curves display a

de. The rate of change in the parameters and maximal et changes are not as great in the present study. This observation leads

to the postulation that individual responses to ES may encompass a considerable range. It does appear, though, that the RSP components

o manifest specific treatment effects in response to ES. The central component, T, seems to be adversly affected initially

by ES. This could be a res of changes in nerve conduction velocity. Using the techniques described by ood (1977), it may be possible to

etermine which fractionated component(s) of P T is affected by the treatment.

on inspection of the fractionated components it was ob- were primarily governed by decreases in iner (1981) suggested that observed de-

T. Wurd, M.D. Grabiner / ES und neuromuscular function 147

30

20

10

-3(

-4(

D -PMT,prasent study

-PMT,in.taal study

Q -MD,present study

-MD,init,al study

I I I I

I I I I

0 1 2 3

pretest

WEEKS t)F TREATMENT

Fig. 5. Comparison of results: initial and present studies.

D may have been related to histochemical and contractile nges of stimulated muscle related to functional shifts of

slow twitch motorneurons to those resembling fast twitch motorneurons reported by other investigators. This would be manifested by structural as well as contractile property changes. Structural changes produced by stimulation have been identified as occurring in the triadic junction, myofibrils and mitochondria (Ei erg and Gilai 1979). In considera- tion of the total elapsed time of however, the dominating parame-

148 T. Ward, M.D. Grabiner / ES and neuromuscular function

teh in MD changes, microstructures and organelles play only a minor role. It is the series elastic component (SEC) of contractile tissue that is the primary cause for the T latency in a given muscle (Komi 1979). During excitation-contraction-coupling the SEC must be lengthened to a minimal percentage of resting length before the force produced by the contractile element can be transmitted through musculoskeletal attach- ments.

The functional changes previously suggested by lting from ES would theoretically ac wever, concomitant changes in contraction speed as well

as other contractile properties were not presently observed, as ind VT and the positive duration of the acceleration curve. yed a significant correlation to accumulative voltage (Y = 0.45,

p c 0.0 1); however, positive duration was nonsignificantly correlated with accu ative voltage (r = 0.16). It is suggested, therefore, that in regard to changes may have been actuated by modifications to the SEC rather than a functional shift of slow twitch fibers to fast twitch fibers. T tenable in view of the relationships between accumulative volt age, and positive duration.

Another potential explanation for the reduction in MT is related to morphological alterations occurring in the muscle fibers such as the ones reported by Eisenberg and Gilai ( 1979). As indicated, ES may effect structural changes in the T-tubule system which is responsible for channeling surface depolarization to the interior of the cell. If these change. ‘YL ctich that the wave of dep rization propogated at a faster velocity it would result in decreased

actor that is related to MT is the surface conduction ve volved muscle fibers. It has been shown that muscle fiber diameter affects conduction velocity which is also influenced by the resting membrane potential of the cell (Chaplin et al. 1970). ES has been reported to decrease muscular atr y as well as to increase girth in healthy muscle (Johnson et al. 1977; ssey et al. 1965; Kotz 1973. As can be inferred from the rise in motor threshold (fig. 4), changes in the resting potential of the sarcoiemma occurred. Therefore, the utiliza- tion of ES may have been responsible for the observed decreases in MT through this mechanism. It is more likely er, that modification to the SEC was responsible for the decreas since it is the primary cause for the electromechanical delay in a given muscle (

The rise in accumulative voltage observed in the initial study (Ward

T. Ward, M.D. Grabiner / ES and neuromuscular function 149

and Grabiner 1981) was repeated in the present study. This was indicative of levels of accommodation occurring in afferents (sensory threshold), muscle tissue (motor threshola), and, perhaps, efferent fibers that may have been directly as well as indirectly stimulated. Adaptation to the passage of electrical current necessitating greater voltages to elicit the desired responses was indirectly observable. It should be noted in fig. 4 that there were decreases in the sensory and motor thresholds in all but one instance when there were 72 hours between sessions (Friday to Monday) rather than the normal 48 hours (Monday to Wednesday and Wednesday to Friday). This raises ques- tions as to the length of time that elicited changes in RSP components may be maintained after treatment has been terminated. otz ( 1977), for example, indicated increases in muscular strength that decayed only 10 percent after months of post-treatment.

The results of this investigation warrant the following conclusions. ES produced consistent changes in the central and peripheral compo- nents of RT and RSP (see fig. 5). These changes, however, are not as effective as those methods described by other authors (Fleury and Lagasse 1979; Boucher and Lagasse 1980; Kotz 1977).

The relationship between PMT and MT merits further examination. The discordant results between the present study and those of Botwinick and Thompson (1966) raise pertinent questions as to whether these variables are truly related to one another or whether ES manifests this relation. The possible interaction between ES and neuromuscular facili- tation upon the l&T components is another potential avenue of research Fleury alld Lagasse (1979) suggested potential gamma system involve- ment in changes elicited by functional electrical stimulation for a horizontal arm-sweep task.

Further experimentation is necessary to determine the specific de- scription of stimulation regimes, i.e., current mode, frequency, voltage, amperage, and length of treatment, to produce the desired functional neuromuscular results. Additionally, a variety of independent variables should be considered to further determine how i~ldividual response to specific treatment modes may be predicted. The information generated by research in this area is of importance both at the theoretical and applied strata of neuromuscular performance.

150 T. Ward M.D. Grabrner / ES and neuromuscular function

Botwinick, J. and L.W. Thompson, 1966. Premotor and motor components of reaction time. Journal of Experimental Psychology 7 1,9- 15.

and P.P. Lagasse, lY80. Effects of functional electrical stimulation (FES) on neuromuscular coordination mechanisms. Presented at the Fourth Annual Conference of the American Society of Biomechanics, Burlington, Vermont.

Chaplin, E.R., G.V,‘. Nell and SM. Walker, 1970. Excitation-contraction latencies in postnatal rat skeletal muscle fibers. Experimental Neurology 29, 142- 15 1.

Eisenberg, B.R. and A. Gilai, 1979. Structural changes in single muscle fibers after stimulation at a low frequency. Journal of General Physiology 74, l- 16.

Fleury, M. and P.P. Lagasse, 1979. Influence of functional electrical stimulation on premotor and motor reaction time. Perceptual and Motor Skills 48, 387-393.

Halbech, J.W. and D. Strauss, 1980. A comparison of electro-myo stimulation to isokinetic training in increasing power of the knee extensor mechanism. Journal of Qrthopaedic and Sports Physical Therapy 1, 20-24.

‘, 1980. Fractures: a shocking cure. Runner’s World 15, 38-41. P. Thurston and P.J. Ashcroft, 1977. The Russian technique of faradism in the

treatment of chondromalacia patellae. Physiotherapy Canada 29, 266-268. Kerlinger, F.N. and E.J. Pedhazur, 1973. Multiple regression in behavioral research. New York:

Holt, Rinehart and Winston. pp. 199-230.

Komi, P., 1979. Neuromuscular performance: factors influencing force and speed production. Scandinavian Journal of Sports Science 1,2- 15.

Kotz, I.M., 1977. Presented at the Canadian-Soviet Exchange Symposium on electrostimulation of skeletal muscle, Concordia University, Dec. 6- 15.

Massey, B., R.C. Nelson, B.C. Sharkey and T. Comden, 1965. Effects of high frequency electrical stimulation on the size and strength of skeletal muscle. Journal of Sports Medicine and Physical Fitness 5, 136- 144.

McNeal, D.R., 1977. ‘2000 years of electrical stimulation’. In: F.T. Hambrecht and J.B. Reswick (eds.), Functional electrical stimulation - applications in neural prothesis. New York: Marcel Dekkes. pp. 2-35.

Pedhazur, E.J., 1977. Coding subjects in repeated measures designs. Psychological Bulletin 84, 298-305.

Vodovnik, L., 1. Information processing in the central nervous system during electrical stimulation. dical and Biological Engineering 9, 675-682.

Vodovnik, L., W.J. Crochetiere and J.B. Reswick, 1967. Control of a skeletal joint by electrical stimulation of antagonists. Medical and Biological Engineering 5, 97-109.

Ward, T., n.d. Unpublished study. Ward, T. and M. Grabiner, 1981. Effects of electrical stimulation of muscle on the fractionated

components of response time. In press.

Wood, G., 1977. An electrophysiological model of human visual reaction time. Journal of Motor Behavior 9, 267-274.