ORIGINAL ARTICLE

Yuko Taniguchi

Lateral specificity in resistance training:the effect of bilateral and unilateral training

Accepted: 27 August 1996

Abstract Maximal voluntary strength of simultaneousbilateral exertion has been shown to be small comparedto the sum of the unilateral exertions. Three experimentswere conducted to determine the effects of bilateral andunilateral resistance training on this bilateral deficit andto compare these in hands, arms, and legs. In each ex-periment, the subjects were divided into three groups:unilateral training group, bilateral training group, andcontrol group. The subjects of the training group per-formed maximal isometric handgrip training in experi-ment I, and maximal isokinetic arm and leg extensiontraining in experiments II and III. In each experiment,the subjects of the training group continued one of theseresistance training exercises three times a week, for 6weeks. The increase in handgrip strength of the bilateraltraining group produced in the bilateral condition [5.1(SEM 2.4)%, after 3 weeks, 6.4 (SEM 2.3) %, after 6weeks] was significantly greater compared with thecontrol group [)1.1 (SEM 1.0) %, after 3 weeks, )1.5(SEM 1.1) %, after 6 weeks. The increase in leg extensionpower of the bilateral training group produced in thebilateral condition [16.1 (SEM 9.6) %, after 3 weeks,24.1 (SEM 7.4) %, after 6 weeks] was significantlygreater compared with the unilateral training group[)5.0 (SEM 3.4) %, after 3 weeks, )3.4 (SEM 4.2) %,after 6 weeks] and the control group [)4.3 (SEM 2.5) %,after 3 weeks, 1.5 (SEM 5.5) %, after 6 weeks]. The in-crease in handgrip strength of the unilateral traininggroup produced in the unilateral condition [7.3 (SEM1.7) %, after 3 weeks] was significantly greater comparedwith the control group [)0.9 (SEM 1.8) %, after 3weeks]. The increase in arm extension power of theunilateral training group produced in the unilateralcondition [7.2 (SEM 1.8) %, after 6 weeks] was sig-nificantly greater compared with the bilateral traininggroup [)3.0 (SEM 2.3) %, after 6 weeks] and the control

group [)2.1 (SEM 2.6) %, after 6 weeks]. Bilateral in-dexes (BI) were shifted in a positive direction by bilateraltraining and tended to shift in a negative direction byunilateral training. With regard to the magnitude ofchange in BI, there were no significant differences amonghandgrip, arm extension, and leg extension training. It issuggested that there is lateral specificity in resistancetraining and that there is no difference among body partsin the modification of bilateral deficit by lateral training.

Key words Bilateral deficit · Resistance training ·Lateral specificity

Introduction

It has been shown many times that increases in volun-tary strength with training are largely specific to the typeof contraction (Dons et al. 1979; Fahey and Brown 1973;Kanehisa and Miyashita 1983a; Lindh 1979; Thor-stensson et al. 1976), angle of training (Bender andKaplan 1963; Gardner 1963; Lindh 1979; Meyers 1967;Raitsin 1974), velocity of contraction (Caiozzo et al.1981; Coyle et al. 1981; Kanehisa and Miyashita 1983a,b; Moffroid and Whipple 1970) and so on. All of theseexamples of specificity of training have been consideredto be attributable to neural adaptation (Sale 1986).

Many investigators have reported a reduction inmaximal voluntary strength induced by simultaneousbilateral exertion compared with unilateral exertion(Henry and Smith 1961; Howard and Enoka 1991; Kohet al. 1993; Oda and Moritani 1995; Ohtsuki 1981, 1983;Rube and Secher 1990; Schantz et al. 1989; Secher 1975;Secher et al. 1978, 1988; Vandervoort et al. 1984). Thisbilateral deficit has been suspected to be mediated byneural mechanisms such as interactions between thecerebral hemispheres or spinal reflexes and so on (Oht-suki 1983, 1994). If so, bilateral deficit could possibly beaffected specifically by training. The hypothesis would bethat bilateral force is increased but unilateral force is notchanged by bilateral training, so that the bilateral deficit

Eur J Appl Physiol (1997) 75: 144 – 150 Springer-Verlag 1997

Y. TaniguchiDepartment of Physical Education, International Budo University,841 Shinkan, Katsuura, Chiba 299-52, Japan

would be decreased. In the case of unilateral training,the opposite phenomena would occur.

Less attention appears to have been given to lateralspecificity (Archontides and Fazey 1993). Only Rubeand Secher (1990) have shown that two-leg trainingdecreased fatigue during two-leg tests, but not duringone-leg tests. Similarly, one-leg training decreased fati-gue during one-leg tests, but not during two-leg testseven though both legs were trained.

The effect of resistance training on this bilateral def-icit has been investigated only by cross-sectional studiesto compare the magnitude of the bilateral deficit be-tween the trained and the untrained (Howard and En-oka 1991; Schantz et al. 1989; Secher et al. 1988).

The main purpose of this study was to determine theeffects of unilateral and bilateral resistance training onthis bilateral deficit in the longitudinal aspect and toascertain whether the lateral specificity is found as aresult of resistance training.

The differing extent of the bilateral deficit has beenreported in the studies in which hands, arms, or legswere used (Henry and Smith 1961; Howard and Enoka1991; Koh et al. 1993; Oda and Moritani 1995; Ohtsuki1981, 1983; Rube and Secher 1990; Schantz et al. 1989;Secher 1975; Secher et al. 1978, 1988; Vandervoort et al.1984). Simultaneous extension of both legs is an unusualmovement that has been stated to be different to thenormal asynchronous motor pattern of human gait(Vandervoort et al. 1987). Bilateral muscle contractionsof the arms or hands, however, are more common ac-tivities (e.g. lifting and carrying loads). Differences inlevels of habitual activity among hands, arms, and legsmight be expected to generate differences in the effect oflateral training.

The second purpose of this study, therefore, was tocompare the modifications of bilateral deficit by lateraltraining in hands, arms, and legs.

Methods

Subjects

Three experiments that used handgrip (experiment I), arm exten-sion (experiment II), or leg extension training (experiment III) wereconducted to test the purpose of the study. In experiment I, 23 malestudents [mean age 20.6 (SEM 0.3) years, mean height 1.69 (SEM0.01) m, and mean body mass 66.6 (SEM 2.1) kg], in experiment II,4 female and 17 male students [mean age 20.3 (SEM 0.1) years,mean height 1.69 (SEM 0.02) m, and mean body mass 63.5 (SEM2.0) kg], in experiment III, 9 female and 9 male students [mean age21.2 (SEM 0.2) years, mean height 1.67 (SEM 0.02) m, and meanbody mass 63.8 (SEM 2.9) kg], participated giving a total of 13female and 49 male students in the study. This study was performedin accordance with the ethical standards laid down in the De-claration of Helsinki. All the subjects gave their informed consentfor participation in the study.

Apparatus

In experiment I, two Smedley dynamometers (Takei Scientific In-struments Co., Ltd.) were used to measure isometric handgrip

strength. Grip distance was adjusted to individual subject pre-ferences. The arm was kept extended straight downwards but didnot touch the body.

Isokinetic dynamometers, Chest Force and Kick Force (TakeiScientific Instruments Co., Ltd.) for measuring arm and leg exten-sion power (Saito et al. 1994) were used in experiments II and III.

The force bar or plate to which a force sensor (strain gauge) wasattached was moved away at a constant velocity in a straight lineon the guide rail. The moving velocity of the bar or plate wascontrolled by direct current motor resistance. The power that wasexerted by the subject was obtained as the product of the forceapplied to the bar or plate and the velocity of the bar or plate.

In the case of arm extension, the subject sat on a seat withhands grasping the bar and with the shoulder and elbow jointsflexed. The bar position was adjusted to the level of the subject’snipple. Immediately after a starting signal, the subject pushed thebar as fast as possible.

In the case of leg extension, the subject sat on a reclining seatwith her/his feet on the plate and hip, knee and ankle joints fullyflexed. The plate position was adjusted to 90° of the subject’s kneeangle. Immediately after a starting signal, the subject extended her/his legs as fast as possible.

To determine the arm or leg extension power, average powerwas calculated using the following equation:

P �

Xn

i�1

�F �i� � v�i��=n

where P is average power, F is force, v is velocity, and n is thenumber of samples that was collected every 5 ms in a singlemovement.

The validity and reproducibility of measurement procedureshad been established in a previous study (Saito et al. 1994) asfollows. Arm extension power had a high correlation coefficient (n= 34, r = 0.780, P < 0.001) with one-repetition maximum (1RM) ofa bench press. Leg extension power had a high correlation coeffi-cient (n = 30, r = 0.614, P < 0.001) with 1RM of a full squat. Therewas also a high correlation coefficient (n = 30, r = 0.717, P < 0.001)between leg extension power per unit of body mass and height ofvertical jumping. The results of reproducibility showed a highcorrelation coefficient between the first test and the second test (n =45, r = 0.944, P < 0.001 for arm extension power and n = 40, r =0.932, P < 0.001 for leg extension power).

Measurements

In experiment I, the subjects performed isometric handgrip strengthtests under the conditions of unilateral and bilateral exertions inrandom order with more than 5-min rests. In bilateral condition,the subjects held two Smedley dynamometers in both hands andexerted maximal isometric force simultaneously. Each conditionconsisted of two trials with 15–30 s rests in between. The maximalvalue was selected among the values marked in the two trials as themaximal strength for each subject in each condition.

In experiments II and III, the subjects performed isokinetic (80cm · s–1) arm or leg extension power tests under the conditions ofunilateral and bilateral exertions in random order with more than5-min rests. Each condition consisted of six trials with 15–30 s restsin between. The maximal value was selected among the valuesmarked in the six trials as the maximal power for each subject ineach condition.

After becoming fully familiarized with the apparatus and thereproducibility of measurement, all the subjects participated in theexperiment. In all three experiments, measurements were recordedbefore training, and 3 and 6 weeks after the beginning of training.

Training

In all the experiments, the posture of the subjects during trainingand the apparatus used were the same as those during measure-ment. In the experiment I, the unilateral training group performed

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3-s maximal isometric handgrip using each hand unilaterally fivesets a day. The bilateral training group performed 3-s maximalisometric handgrips using both hands bilaterally five times a day.The rest intervals between exercise tasks were 1 min. In the ex-periments II and III, the unilateral training group performed sixtimes maximal isokinetic (80 cm · s–1) arm or leg extension usingeach arm or leg unilaterally three sets a day. The bilateral traininggroup performed six times maximal arm or leg extension by botharms or legs bilaterally three sets a day. The rests between exercisetasks and sets were 15–30 s and 2–3 min, respectively. In all theexperiments, the training groups continued this resistance trainingthree times a week, for 6 weeks.

Data analysis

The data from each of the left unilateral, right unilateral, and bi-lateral tasks were used for calculation of the bilateral indexes (BI;Howard and Enoka 1991). The BI was computed as follows:

BI (%) = 100 [(left bilateral + right bilateral)/(left unilateral +right unilateral)] )100 in handgrip strength.

BI (%) = 100 [bilateral / (left unilateral + right unilateral)] )100in arm and leg extension power.

A BI greater than 0 indicated that the bilateral values weregreater than the unilateral values (bilateral facilitation), whereas aBI less than 0 indicated that the bilateral values were less than theunilateral values (bilateral deficit).

Statistical analysis

Two-way repeated-measures ANOVA and the least significantdifference (l.s.d.) method were used to determine the differenceamong the time courses of each group. One-way ANOVA andpost-hoc test (Fisher’s PLSD) were used to determine the differ-ences among groups at each time. The 0.05 level was chosen toindicate statistical significance for individual tests.

Results

The effect of bilateral and unilateral training on strengthor power

The values of strength or power in the bilateral andunilateral conditions before and after training are shown

in Tables 1–3. From these data, the ratios of improve-ment after training compared to before training in threegroups were calculated (Fig. 1). In the bilateral condi-tion, the effect of group on the ratio was significant[handgrip at 3 weeks: F (2, 20) = 4.336, P = 0.0273; at 6weeks: F (2, 20) = 4.984, P = 0.0175; leg extension at 3weeks: F (2, 15) = 3.901, P = 0.0432; at 6 weeks: F (2, 15)= 6.257, P = 0.0106]. It was revealed by the post-hoc testthat the ratios of improvement in the handgrip strengthand leg extension power of the bilateral training groupproduced in the bilateral condition were significantlylarger than the unilateral training group (Fig. 1, bottomleft) and control group (Fig. 1, top and bottom left). Nosignificant difference was found in arm extension powerin the bilateral condition.

In the unilateral condition, the effect of group on theratio was significant [handgrip at 3 weeks: F (2, 20) =5.327, P = 0.0140; arm extension at 6 weeks: F (2, 18) =5.510, P = 0.0136; leg extension at 6 weeks: F (2, 15) =4.075, P = 0.0386]. It was revealed using the post-hoctest that the ratio of improvement in the handgripstrength and arm extension power of the unilateraltraining group produced in the unilateral condition weresignificantly larger than in the bilateral training group(Fig. 1, middle right) and control group (Fig. 1, top andmiddle right). In the unilateral condition of leg extensionpower, no significant improvement was found in theunilateral training group, but was found in the bilateraltraining group (Fig. 1, bottom right).

The effect of bilateral and unilateral training on BI

The amounts of change in BI of each group are shown inTables 1–3. In experiment I, the effect of group [F (2, 20)= 3.529, P = 0.0487] was significant. It was revealed byanalysis using the l.s.d. method that the amount ofchange in BI of the bilateral training group was differentfrom BI of the unilateral training group (P = 0.0035)

Table 1 Change of handgrip strength of each training group during 6 week of isometric resistance training. BI Bilateral Indexes, seeMethods

Before After 3 weeks After 6 weeks

Bilateral training group (n = 7) mean SEM mean SEM mean SEMBilateral(R+L) (N) 895 41 937 32 951 39Unilateral(R+L) (N) 915 34 935 32 932 32BI(%) )2.2 2.3 0.2 1.0 1.8 0.8BI(after-before) (%) 2.3 2.5 4.0 2.2

Unilateral training group (n = 7)Bilateral(R+L) (N) 937 46 971 49 963 53Unilateral(R+L) (N) 919 50 983 48 959 63BI(%) 2.1 0.7 )1.3 1.3 0.9 1.4BI(after-before) (%) )3.4 1.7 )1.3 0.9

Control group (n = 9)Bilateral(R+L) (N) 961 26 949 23 946 29Unilateral(R+L) (N) 964 31 951 19 958 32BI(%) )0.1 1.7 )0.3 1.1 )1.0 1.9BI(after-before) (%) )0.2 1.8 )0.9 1.0

No significant difference between the values of each group before training

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and control group (P = 0.0330). In experiment II, al-though the time course of the unilateral training grouptended to be different from that of the bilateral traininggroup and the control group, there was no significanteffect of group. In experiment III, the effect of group[F (2, 15) = 3.711, P = 0.0490] was significant. It wasrevealed by analysis using the l.s.d. method that theamount of change in BI of the bilateral training groupwas different from BI of the unilateral training group(P = 0.0017) and control group (P = 0.0232).

The comparison between the changes of BI in variousbody parts

There was a significant effect of body part in BI beforetraining [F (2, 59) = 15.548, P < 0.0001]. The BI inhandgrip [mean 0 (SEM 0.01) n = 23] was significantlysmaller than BI in arm extension [)8.3 (SEM 0.02) n =21; P = 0.0006] and leg extension [)12.9 (SEM 0.02) n =18;P < 0.0001]. The BI in arm extension tended to be

smaller than leg extension though the difference was notsignificant (P = 0.0596).

In both bilateral and unilateral training, there wereno significant differences among the amounts of changeof BI by handgrip, arm extension, and leg extensiontraining (Tables 1–3).

Discussion

In the present study, it was shown that strength andpower produced in the bilateral condition were im-proved after bilateral resistance training and thatstrength and power produced in the unilateral conditionwere increased after unilateral resistance training, al-though there were a few exceptions. In the unilateralcondition of leg extension power, no significant im-provement was found in the unilateral training group,but some improvement was seen in the bilateral traininggroup. It was considered that one of the reasons for thiswas that subjects who had a greater trainability were

Table 3 Change of leg extension power of each training group during 6 week of isokinetic resistance training. Definitions as in Table 1

Before After 3 weeks After 6 weeks

Bilateral training group (n = 6) mean SEM mean SEM mean SEMBilateral (W) 885 177 1004 184 1058 182Unilateral(R+L) (W) 1063 176 1095 164 1160 185BI(%) )18.6 5.0 )10.3 4.9 )9.3 2.8BI(after-before) (%) 8.3 4.0 9.3 3.7

Unilateral training group (n = 6)Bilateral (W) 1029 114 986 121 1001 125Unilateral(R+L) (W) 1101 122 1069 131 1105 114BI(%) )6.5 2.4 )7.9 3.8 )10.4 4.4BI(after-before) (%) )1.4 2.1 )3.9 2.8

Control group (n = 6)Bilateral (W) 920 136 885 144 921 130Unilateral(R+L) (W) 1058 132 1019 140 1053 138BI(%) )13.7 3.7 )13.8 4.0 )12.2 4.1BI(after-before) (%) 0.0 2.7 1.5 4.5

No significant difference between the values of each group before training

Table 2 Change of arm extension power of each training group during 6 week of isokinetic resistance training. Definitions as for Table 1

Before After 3 weeks After 6 weeks

Bilateral training group (n = 8) mean SEM mean SEM mean SEMBilateral (W) 395 43 405 48 388 47Unilateral(R+L) (W) 428 41 438 48 413 37BI(%) )7.9 3.3 )7.9 3.1 )7.8 4.9BI(after-before) (%) 0.1 2.1 0.1 4.1

Unilateral training group (n = 6)Bilateral (W) 371 57 364 54 376 60Unilateral(R+L) (W) 395 53 388 47 420 53BI(%) )7.2 3.3 )7.3 7.6 )12.1 4.9BI(after-before) (%) )0.1 4.8 )5.0 2.1

Control group (n = 7)Bilateral (W) 382 37 379 14 373 24Unilateral(R+L) (W) 425 22 416 18 416 25BI(%) )9.6 1.9 )8.5 3.1 )10.4 1.8BI(after-before) (%) 1.1 2.6 )0.8 2.1

No significant difference between the values of each group before training

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included in the bilateral training group. However, themost important point was that even in this case BI wasshifted in a positive direction by bilateral resistancetraining and in a negative direction by unilateral re-sistance training as in the other cases. These patterns inresistance training of the upper and lower limbs were inagreement with the ‘‘strength training specificity’’ theory(Sale and MacDougall 1981).

The effect of resistance training on bilateral deficit hasbeen investigated only by cross-sectional studies tocompare the magnitude of bilateral deficit between thetrained and the untrained. Howard and Enoka (1991)have reported that whereas untrained subjects exhibiteda bilateral deficit, cyclists did not, and weight liftersproduced a bilateral facilitation. On the other hand, insome previous studies (Schantz et al. 1989; Secher et al.1988) it has been indicated that BI is not likely to be

affected by training. These studies would seem to beinconsistent with the present results. However, the ratiosdescribed in the study of Secher et al. (1988) were 80–81(BI )20 to )19) in the untrained, 86 (BI )14) in weight-lifters and 76 (BI )24) in cyclists. The bilateral / uni-lateral ratios described in the study of Schantz et al.(1989) were 0.86 (BI )14) in the untrained male groupand 0.92 (BI )8) in heavy-resistance trained male group.These values indicate that the magnitude of bilateraldeficit in weight-lifters and the heavy-resistance trainedsubjects who do bilateral leg extension regularly tends tobe less than that in the untrained. Furthermore, themagnitude of bilateral deficit in the cyclists who do al-ternating extension of two legs regularly tends to bemore than that in the untrained. Therefore, it is con-sidered that these facts are not inconsistent with theresults found in the present study.

In the present study, the averaged BI found inhandgrip before training ranged from )2.2 to 2.1. TheBI reported in previous studies in which handgrip wasused have ranged from 0 to )13.6 (Henry and Smith1961; Oda and Moritani 1995; Ohtsuki 1981). Of these

Fig. 1 Comparison between the ratios of changes of three groupsunder bilateral and unilateral conditions of each experiment. Valuesare means and SEM. Significant differences are indicated by*P < 0.05, **P < 0.01

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reports the study of Henry and Smith (1961) has usedthe same method of measurement as the present studyand showed results very similar to the present. Theyhave reported that maximal isometric handgrip strengthexerted by the dominant hand during simultaneous bi-lateral exertion decreased by 3% ()3 expressed in BI) incomparison with unilateral maximal strength but not bythe nondominant hand.

The averaged BI found in arm extension beforetraining ranged from )9.6 to )7.2. Since the types ofmovement used were different from the present study adirect comparison cannot be made, but there are a fewstudies in which arm extension has been used. Ohtsuki(1983) has reported a bilateral deficit for right and leftelbow extension in maximal isometric conditions (BI)24.6 and )18.8). On the other hand, Secher et al. (1988)have reported that two-arm extension strength was si-milar to the sum of the strengths of the right and leftarms. The results of present study were placed in themiddle of these studies.

In leg extension, the averaged BI before trainingranged from )18.6 to )6.5. There have been some stu-dies on bilateral deficit in which leg extension was used.These studies have reported that BI in isometric con-traction were from )25 to )2 (Rube and Secher 1990;Schantz et al. 1989; Secher et al. 1978, 1988) and from)48.8 to )2.5 in isokinetic contraction (Coyle et al. 1981;Vandervoort et al. 1984). The present study was withinthe range of these previous studies.

Consequently, it was considered that BI found in thepresent study were valid, and that the magnitude of thebilateral deficit changed over a wide range according tothe limbs involved. The bilateral deficit found in the legsthat were usually used with an asynchronous motorpattern was larger than the bilateral deficit found in thehands and arms that were used more frequently withbilateral contraction.

Although the amount of change of BI in the bilateraltraining group by leg extension training tended to belarger than those by handgrip and arm extension train-ing, these differences were not significant similar to thosefound in the unilateral training groups. Therefore therewere no clear differences among the hands, arms, andlegs in the modification of bilateral deficit by lateraltraining. It was considered that although the initial va-lues of BI in various parts of the body were affected bythe pattern of habitual use, the magnitudes of mod-ifications of bilateral deficit in various parts of the bodywere almost the same if the amount of training per-formed was similar.

It has been suspected that there may be at least threepossible mechanisms subserving the bilateral deficit; di-vision of attention, reciprocal inhibition and interhemi-spheric inhibition (Ohtsuki 1994). It is assumed thatthese neural mechanisms may also be related to thechange of BI as a result of bilateral and unilateral re-sistance training. However, the mechanisms of bilateraldeficit themselves have been discussed and are still un-clear. Therefore, further investigation using the methods

of electroencephalography and electromyography arenecessary to examine the mechanisms that are re-sponsible for the lateral specificity of resistance training.

It was concluded that BI were shifted in a positivedirection by bilateral resistance training and in a nega-tive direction by unilateral resistance training and thatthere was no clear difference among body parts in themodification of bilateral deficit by lateral training.

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