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Journal of Strength and Conditioning Research, 2005,© 2005 National Strength & Conditioning Association

, 9-15

THE EFFECTS OF SHORT-TERM UNILATERAL ANDBILATERAL LOWER-BODY RESISTANCE TRAINING ONMEASURES OF STRENGTH AND POWER

KEVIN W. MCCURDY, GEORGE A. LANGFORD, MIKE W. DOSCHER, LARRY P. WILEY,AND KIM G. MALLARD

Department of Kinesiology and Physical Education, Valdosta State University, Valdosta. Georgia 31698.

ABSTIIACT. McCurdy, K., G. Langford, M. Doscher, L. Wiley, andK. Mallard. The effects of short-term unilateral and bilaterallower-hody resistance training on measures of strength and pow-er. J. Strength Coiid. Res. 19(1):9-15. 2005.—The purpose of thisstudy was to compare the effects of ahort-term unilateral resis-tance training fUL) and bilateral resistance training (BL) withfree weights on several tests of unilateral and bilateral lower-body strength and power in men and women. Thirty-eight un-trained men and wonnen (mean body mass 78.3 ± 21.47 kg; age20.74 ± 2.6 years i completed the study. The groups trained 2days per week for 8 weeks with free weights and 2 days per weekfor .5 ofthe 8 weeks with plyometric drills. The resistance-train-ing program consisted ofa progression from 3 sets of 15 repeti-tions at 50% of the subject's predicted 1 repetition maximumIIRM) to 6 sets of 5 repetitions at 879f lRM. Training volumeand intensity were equal for each group. The free-weight squatwas used to measure unilateral and bilateral strength. Powerwas measured by the Magaria-Kalamen stair-climb test and theunilateral and bilateral vertical jump test. Analysis of covari-ance was used to analyze differences between men and womenand the interaction of group and gender. Pretest scores wereused as the covariate. The UL group improved more than theBL group on the unilateral vertical jump height (p = 0.001) andrelative power (p = 0.013). Afler adjusting for pretest differenc-es, the improved scores on all tests, except for the unilateralsquat, were similar between the men and the women. No sig-nificant interactions on all tests were found for the men or wom-en comparison between training groups. These results indicatethat UL and BL are equally effective for early phase improve-ment of unilateral and bilateral leg strength and power in un-trained men and women.

KEY WORDS, unilateral vertical jump, bilateral vertical jump,Margaria-Kalamen stair climb, unilateral squat, bilateral squat

INTRODUCTION

^ ^ '^ nilateral or partial unilateral supported exer-I —I cises (USE) such as lunges, step-ups, and uni-

T '~-l lateral squats are implemented in resistance-^ ^ ^ l ' ' ' ^ training programs as assistance exercises and(_ generally receive less emphasis than do coreexercises. Although USE are typically integrated intomost training programs, the emphasis of utilizationvaries, in part, because of the lack of scientific data todetermine the potential for these exercises to improvestrength and power. The exercises are typically used asa variation to hilateral supported exercises (BSE) such asthe bilateral squat.

The bilateral squat is typically implemented at the be-ginning of the resistance-training program to develop afoundation of strength for untrained subjects before usingUSE. However, many skills that rely on fundamental low-

er-body movements (running, throwing, hitting, kicking,vertical and horizontal leaps, and changing running di-rection) are performed entirely or predominantly in a uni-lateral weight-bearing phase. To most effectively improveperformance, resistance exercises should closely resemblethe mechanics and forces required to perform the neces-sary skills in a particular sport (1). Research data areneeded to determine if USE could he incorporated earlyin a resistance-training program to significantly improvestrength and explosive power.

Bilateral supported exercises have been extensivelyinvestigated to determine the efleets of lower-body train-ing on improved strength and power (4, 8, 13-16, 24).Staron et al. (24) investigated time course of muscularadaptations during the early phase (8 weeks of 16 train-ing sessions) of resistance training and found similar im-provements in muscle cross-sectional ar-ea and relativemaximal strength in the bilateral squat and leg press inmen and women. Currently, little research data revealthe efTects of USE on improved strength and power inmen and women. In a cross-sectional design of male andfemale subjects, Negrete and Brophy (19) found a signif-icant correlation between isokinetic single-1 eg squatstrength at 76 cm s ' in a weight-bearing stance and sin-gle-leg vertical jump height. The Linea isokinetic systemthat was used in this study measured the force during aconcentric phase in a standing position. This measuringsystem provided an external balance support during thesingle-leg stance, which could require different muscle re-cruitment when force is measured in a free-standing po-sition. Using electromyogram analysis, several research-ers have found that the hip abductors are recruited in asingle-leg stance (no external balance support) for frontalplane stabilization (7, 20, 23). in a group of college-agewomen, Cordova et al. (5) did not find a significant rela-tionship between isotonic or isokinetic single-leg pressstrength with rotary motion at 60" s ' and single-leg ver-tical jump reaction force after 5 weeks of training. Theresearcbers suggested that the strength improvement af-ter non-weight-bearing, closed-kinetic-chain training doesnot correlate with a cbange in force on a weight-bearing,closed-kinetic-chain movement.

Tbe effect of free-weight USE on weight-bearing uni-lateral and hilateral strengtb and power has yet to beinvestigated in men and women. Therefore, the purposeof this study was to compare the efTect of short-termtraining with BSE and USE on several measures of uni-lateral and bilateral strength and power in untrainedmen and women.

10 MrCuRiiY, LANGFORD, DOSCHER ET AL.

MKTHODS

Experimental Approach to the ProblemTo determine if training with USE would significantly in-crease strength and power similar to improvements aftertraining with BSE, 2 experimental groups were formed:unilateral resistance training (UL) and bilateral resis-tance training IBL). The UL group trained with USEwhereas the BL group trained with BSE. In this experi-mental design, BSE and USE were implemented aa coreexercises. After a pretest and 8 weeks of training, a post-test was conducted to determine early phase changes inunilateral and hilateral strength and power in untrainedsubjects. A distinct approach was to determine if BL im-proved unilateral strength and power and if UL improvedbilateral strength and power.

SubjectsTwenty-three men and 16 women between the ages of 18and 24 who were enrolled in an entry-level basic-instruc-tion weight-training course completed the study. All thesubjects who volunteered to participate were surveyed todetermine their training experience. The suhjects had notparticipated in lower-body resistance training within ayear hefore the study. All the subjects signed written in-formed consent forms that were reviewed by the Institu-tional Review Board of Valdosta State University to en-sure the subjects were knowledgeable ofthe norma! risksand procedures involved in the study. The class was ran-domly assigned to 2 groups for training: BL and UL.

TestingBefore baseline testing, the subjects were given a 2-week(4 training sessions) instructional period to learn propertechnique with loads that approached their 5 repetitionmaximum (5RM) for the unilateral and bilateral squat.Baseline tests for bilateral and unilateral strength andpower were measured during weeks 3 and 4. A rest periodwith a minimum of 48 hours was provided between eachday of testing. Before all tests, subjects were instructedto perform a 5-minute jog as a warm-up exercise andstretch to prevent injury due to testing. All warm-up setswere monitored and the protocol was posted in clear viewof the suhjects.

Bilateral power was measured with a countermove-ment vertical jump. Each subject was weighed withoutshoes and in minimal clothing before the vertical jumptest. Vertical jump height, average absolute power, andrelative power (average absolute power/mass) producedduring the jump were measured with contact timing matsinterfaced to a computer (Kinematic Measurement Sys-tem IKMSI Innervations, Windows 95/98/ME; Skye, Aus-tralia). Times were recorded in milliseconds and datawere transferred to a computer for analysis. The KMS,which uses total flight times to calculate average absolutepower and relative power, has been found to be sensitiveindicators of jumping performance with comparison ofpeak power (r ^ 0.88) and average power (r = 0.73) val-ues derived from a force plate (9). Each subject's highestjump of 3 trials and mass were used to calculate averageabsolute power by the following formula: [21.2 X jumpheight (cm)| + |(23 X subject mass (kg)I - 1,393 (9). Thetest-retest reliability of tbis method to determine powerin jumping has previously heen investigated for the uni-lateral vertical jump (r = 0.89) (21) and the bilateral ver-

tical jump (r = 0.95) (3) in untrained subjects. Subjectswere instructed to keep their arms on their hips duringthe vertical jumps to eliminate upper-hody momentum(21, 25).

During the strength assessment, each subject followedthe procedures while supervised by a researcher. All sub-jects were measured to attain a 90° angle between thefemur and the tibia while performing the squat test. Thesquat depth was marked and recorded by a measuringdevice designed to record the depth of the squat for eachrepetition to ensure that a 90° angle at the knee joint wasachieved (Figure 1). For all strength tests, the subjectscompleted a set of 5-10 repetitions with light weight onthe first set with a 1-minute rest period followed hy a setof 5 repetitions after adding 10-20% of weight. A 2- to 3-minute rest period was allowed between each successiveset. No more than 5 trials were allowed, including thewarm-up sets, to attain the 5RM. The 5RM test was usedto estimate the 1 repetition maximum (lRM), which wasdetermined by a lRM prediction chart (18).

The same 5RM protocol used during the bilateralsquat was followed to measure unilateral squat depth andstrength. Both strength tests were measured by the bar-bell free-weight squat. While performing the squat, sub-jects placed the top of their foot of the nondominant legon a support bar behind them to ensure the dominant legwas the only leg used to perform the squat (Figure 1).

Unilateral power was measured by the Margaria-Ka-lamen stair-climb test (M-K) and the unilateral verticaljump with a countermovement. All subjects were weighedwithout shoes and in minimal clothing. The M-K is char-acterized by a subject sprinting up a staircase of specifiedheight from a specific distance, stepping only on the third,sixth, and ninth steps, KMS contact timing mats wereplaced on steps 3 and 9. The time started at initial contactwith the third step and stopped at contact with the ninthstep. Subjects were instructed to complete the sprint upthe stairs with maximum velocity. The total power pro-duced during the test was calculated by the following for-mula: [Power (W) ^ weight (kg) X 9.8 ms ' X distance(m)/time (s)l (11).

Unilateral vertical jump height, average absolutepower, and relative power were measured witb the sameprotocol used during the bilateral vertical jump test withthe exception ofthe subjects jumping with the dominantleg only. To isolate the effectiveness ofthe dominant leg,the subjects were instructed to keep their uninvolved leginactive under their body (25, 29). .

Training ProtocolAfter the 2-week instructional period and 2-week testingperiod, both groups followed the resistance-training pro-grams 2 days per week for 8 weeks. Both BSE and USEwere implemented as core exercises to maximize strengthand power improvement. The core BSE consisted of bi-lateral squats and front squats, whereas the core USEconsisted of unilateral squats, lunges, and step-ups. TheUL group performed unilateral squats each session withlunges or step-ups, which were alternated each trainingsession. Training volumes and intensities, hased on sets,reps, and percentage of each subject's predicted 1 RM,were equal for both groups. Both programs excluded up-per-body exercises to eliminate the possibility of alteringthe results from potential improvement in upper-bodystrength or power. Both groups progressed from 3 sets of

UNILATERAL AND BILATERAL RESISTANCE TRAINING 11

FIGURE 1.

15 repetitions at 50^ of each subject's predicted lRM to6 sets of 5 repetitions at 87^/f through the 8 weeks oftraining. The UL group performed unilateral plyometrics2 days per week during weeks 3-8, whereas the BL groupperformed bilateral plyomtrics before tbe resistance-training session. Eacb group completed pogo jumps andcountermovement vertical leaps each session while pro-gressing from 3 sets of 5 to 3 sets of 15 from week 3 toweek 8. Tbe pogo jump was executed with minimal hipand knee flexion upon landing before rebounding verti-cally for maximum height without the use of the armswing, and the countermovement vertical leap was com-pleted with a one-half to three-quarters squat. Posttest-ing was conducted after the 8-week training period withthe same protocols as previously described for the base-line tests.

Statistical Analyses

Data were analyzed by 2 x 2 (gender x group) factorialanalysis of covariance. Homogeneity of regression as-sumptions were tested and confirmed before analysis.Posttest scores on all measures were treated as depen-dent variables, whereas pretest scores were used as thecovariate.

RESULTS

The results for the unilateral and hilateral strength weresimilar. Tbe analysis of posttest measures revealed nomain effect for group. After pretest score adjustments, theUL group performance on posttest trials was no difTerentthan that of the BL group. For tbe bilateral squat, nomain effect was found for gender. The posttest measuresfor men were not statistically different from those of wom-en. Although there was main effect for gender on the uni-lateral squat, the efTect size, revealing that the men'sscores were significantly higher than tbe women's scores,was small (partial X ^ 0.22). The interaction betweengroup and gender approached (p = 0.064) but did notreach significance. Men benefited no more from UL thanthey did from BL. Neither was there an advantage forwomen who trained with USE vs. BSE. The strengt,h re-sults are found in Table 1.

For the bilateral vertical jump test, no main efTect wasfound for training group or gender for vertical jumpheight, absolute power, and relative power. Unilateral re-sistance training was no different than double-leg train-ing, and no difference was found in the posttest scoresbetween the men and tbe women after adjusting for pre-

12 , LANGPORD, DOSCHER ET AL.

Table 1. Unilateral and bilateral strength—analysis of covariance posttest measures.f

Bilateral squat

Adjustedmean ± SE p value

Unilateral squatAdjusted

mean ± SE p value

Training groupULBL

(lenderMenW(imi>n

Ciender and groupUL menBL menUL womenBL women

217.16 ± 5.43224.86 ± 6.20

228.70 ± 6.67213.33 ± 8.33

216.60 ± 8.49240.80 ± 8.70217.73 ± 10.92208.93 ± 10.07

0.23

0.064

140.51 ± 3.64145.58 ± 4.37

154.37 ± 4.10131.72 ± 5.13

152.59156.15

5.595.63

128.43 ± 6.30135.01 ± 6.97

0.004*

''" Statistically significant ipt SE = standard error; UL

O.OS).unilateral resistance training; BL = bilateral resistance training.

Table 2. Bilateral vertical jump test—analysis of covariance posttest measures.!

Jump height (cm) Absolute power (W) Relative power (WkgAc^usted

mean ± SE p valueAdjusted

mean ± SE p valueAdjusted

mean ± SE p value

Training groupULBL

CrenderMenWomen

(lender and groupLIL menBL menUL womenBL women

33.7 ± 1.032.7 ± 1.1

34.1 ± 1.232.4 ± 1.4

34.3 ± 1.233.9 ± 1.933.0 ± 1.731.6 ± 1.8

0.2691115.9 ± 29.71087.8 ± 33.4

1070.2 ± 29.31133.4 ± 37.4

1095.1 ± 37.61045.4 ± 35.11136.6 ± 46.91130.1 -t 58.2

13.8 ± 0.313.3 ± 0.3

13.4 ± 0.413.7 ± 0.5

13.6 ± 0.413.2 ± 0.514.0 ± 0.613.4 ± 0.7

* Statistically significant (p < 0.05).t SE = standard error; UL = unilateral resistance training; BL = bilateral resistance training.

test difTerences. No interactions were hetween group andgender. Men benefited no more from UL than they didfrom BL. Neither was there an advantage for women whotrained with USE vs. BSE. The bilateral vertical jumpresults are reported in Table 2.

The unilateral vertical jump analysis revealed a maingroup effect for tbe unilateral vertical jump height (p ^0.001) and relative power (p = 0.013). The UL group im-proved significantly more than the BL group on theseunilateral variables. The effect sizes for tbe vertical jumpheight (partial X = 0.10) and relative power (partial X^ 0.17) were small. Although not significantly different,the UL group improved more than the BL group. No maineffects were found for gender on these variables. Men per-formed no differently than women. No interactions werehotweon group and gender. Men benefited no more fromUL than they did from BL. Neither was there an advan-tage for women who trained with USE vs. BSE. The uni-lateral vertical jump results are reported in Table 3.

No main effect was found for group or gender on theM-K. Unilateral resistance training was no difTerent thanBL, and men performed no differently than the womenon the posttest after adjusting for pretest differences.Also, no interaction was between group and gender. Men

did not benefit more from UL than they did from BL.There was also no advantage on the M-K for women whotrained with USE vs. BSE. The M-K results are reportedin Table 4.

The statistical power for the above analyses was quitelow. In none ofthe nonsignificant analyses did the powerexceed 0.25. This lack of power is primarily due to therelatively small n for each cell in the factorial design. Thislack of power combined with the relatively small effectsizes made it difficult to detect potential group differ-ences. I

DISCUSSION

Both training groups similarly improved in unilateral andbilateral squat strength. Tbese results were similar forthe men and women in this study. Worrell et al. (28)found significant strength gains in the unilateral seatedleg press and improvement in the number of step-up rep-etitions performed with the body weight plus 25% after 5weeks of an 8-in lateral step-up training program. Tbisprevious study investigated the effects of USE on a non-weight-bearing strength test and on a muscular-endur-ance step test. In our study, both groups trained and weretested with free-weight exercises. Because our subjects


Table 3. Unilateral vertical jump test—analysis of covariance posttest measures.f

Training groupULBL

GenderMenWomen

Gender and groupUL menBL menUL womenBL women

Jump height


0.001*18.9 ± 0.516.2 ± 0.5

<1.017.6 ± 0.617.5 ± 0.7

<1.019.1 ± 0.616.0 ± 0.918.6 ± 0.816.4 ± 0.9

Absolute power


<1.0771.7 ± 43.3751.7 ± 52.3

<1.0743.1 ± 46.5780.3 ± 57.4

<1.0739.8 ± 62.4746.3 ± 66.5803.7 ± 69.3757.0 ± 83.2

Relative

Adjustedmean ± SE

9.5 ± 0.28.8 ± 0.2

9.4 ± 0.29.0 ± 0.2

9.7 ± 0.29.1 ± 0.39.3 ± 0.38.6 ± 0.4

power

p value0.013*

0.170

<1.0

* Statistically significant ip < 0.05).t SE = standard error; UL - unilateral resistance training; BL = bilateral resistance training.

Table 4. Margaria-Kalamen stair climb—analysis of covari-ance posttest measures.t

Training groupULBL

GenderMenWomen

Gender and groupUL menBL menUL womenBL women

Power (W)


<1.0129.5 ± 2.7126.9 ± 3.4

<1.0124.9 ± 3.7131.5 ± 4.8

<1.0127.9 ± 4.6121.8 ± 4.7131.1 ± 5.1132.0 ± 6.5

* Statistically significant (p < 0.05).t SE - standard error; UL = unilateral resistance training;

BL = bilateral resistance training.

were untrained, we expected to find increased unilateralstrength after UL and increased bilateral strength afterBL because ofthe specificity ofthe training to the testingtechnique. Untrained subjects have a greater potential toimprove their strength (1), particularly when the strengthtest is performed with the same type of exercise used dur-ing training {12).

We also hypothesized that the UL would significantlyincrease the subjects' bilateral strength but questioned ifthe BSE group would significantly increase their unilat-eral strength. Hefzy et al. (10) found that 75% ofthe re-sistance is placed on the front leg during a lunge exercisewhen the knee is fiexed approximately 100" and suggest-ed that this exercise might be more beneficial than the 2-legged squat in strengthening the lower body. Althoughless total weight must be used to perform USE, the single-leg musculature could be working at a high relative in-tensity that is sufficient for improved strength. Further-more, during BSE (e.g., 2-legged squat), tho contralateralleg provides frontal plane stabilization, which potentiallyreduces the muscle-recruitment demands from the hipabductors that are active during the single-leg stance

(20). Rutherford and Jones (22) concluded that the im-provement in the ability to lill weights was duo to anincreased ability to coordinate other muscle groups in-volved in the movement used to stabilize the body. Wepredicted that the strength gained to produce hip andknee extension after BL may not be effectively used in aUSE strength test if the frontal plane stabilizor.>^ have notbeen adequately trained. The strength data in this studydo not support this speculation when training untrainedsubjects because no difference between the groups' im-provement were found on the unilateral squat. This is thefirst known study to determine that UL improved bilat-eral strength and that BL improved unilateral strength.USE and BSE were equally effective in improving unilat-eral and bilateral strength after short-term training inuntrained men and women. More research is needed todetermine if similar results are found with a longer train-ing period and with trained subjects. During the assess-ment of unilateral strength in trained athletes, strengthin the stabilizing muscles, such as hip abductors main-taining frontal plane stabilization, may be a greater fac-tor that determines squat strength.

After adjusting for pretest differences between themen and the women on the bilateral squat, no differenceswere found for strength gains. These data are consistentwith previous conclusions that percentage of strength im-provement is similar between men and women (24). How-ever, the men significantly improved more than the wom-en on the unilateral squat. The effect size was small (par-tial \^ ^ 0.22), indicating that this difference was notrobust. Recent studies have reported that difTerences inkinematics and muscle-group recruitment exist betweenmen and women during a unilateral squat and during tholanding phase on a single leg (17. 30). Women havo dem-onstrated difficulty in controlling the hip musculature byallowing more hip adduction, lower hip abductor activity,and more reliance on the knee extensors than do menduring tbe unilateral squat (17). This position places avalgus stress on the knee, which increases the potentialfor knee injuries. More research is needed to determineif strength gains are comparable between men and wom-en on the unilateral squat. Although heyond the scope ofthis study, improving unilateral strength may, in part,reduce the number of knee injuries in women.

14 MCCURDY, LANGFORD, DOSCHER ET AI..

The UL and BL groups performed both strength andplyometric exercises, which have been shown to be mosteHective to increase power performance (26, 27). Bothtraining groups similarly improved in the bilateral ver-tical jump height and absolute and relative power. Theimproved scores on the bilateral measures were similarfor the men and women. These data indicate that im-provement of power on bilateral tests is not compromisedin the early phase of a resistance-training program whenuntrained men or women train solely with USE.

The UL group significantly improved more (2.68 cm)than did the BL group in unilateral vertical jump height.Similar results were reported by Delcore et al. (6), whofound that unilateral plyometric training was better thanBL for increasing unilateral and bilateral vertical jumpperformance in female volleyball players. With the addi-tion of strength training, our study found similar resultsin the early phase of a resistance-training program forunilateral vertical jump height and relative power. Al-though absolute power was higher in the UL group, thelack of a significant dilTerence between groups is likelydue to the slight reduction in body mass in the UL group.In a simulation study ofthe effects of mechanical controland muscle strength on vertical jump performance, Bob-bert and Van Soest (2) concluded that athletes need topractice with their changed muscle properties to take fullbonofit of increased strength. As the BL group's strengthimproved during the training period, provided practicetime on the unilateral vertical jump could have improvedthe group's ahility to use their strength and power on theunilateral jump test. Although the UL group did not prac-tice the bilateral vertical jump, this gi'oup significantlyimproved on this test. Jumping practice could be imple-mented into the plyometric training drills in similar fu-ture research designs.

After adjusting the pretest differences on the unilat-eral vertical jump test, tbe improvement of jump heightand absolute and relative power were similar betweenmen and women. Although a significant difTerence wasnot found for the interaction of group and gender, themen in the UL group improved more than the men in theBL group for jump height (3.12 cm) and relative power(0.56 W kg '). The men in tbe BL group performed slight-ly bettor than the men in the UL group for absolute power(6.5 W). The women in the UL group improved more thanthe women in the BL group in jump height (2.23 cm),absolute power (46.7 W), and relative power (0.78W kg '). These results for the interaction between genderand group may have been significant with a larger sam-ple size, which is a limitation of the study.

After using pretest scores on the M-K as the covariate,no difi'crence existed between tbe UL and the BL groups'scores on the posttest. With this statistical analysis, theposttest scores for the men and women were also similar.No advantages were found for the men or women whocompleted UL or BL. The M-K was included in this studyas a unilateral task, whicb is executed by alternating 1foot in contact witb a step as the subject runs up thestairs. This test for unilateral power is more complex thanthe unilateral vertical jump test and requires a higherlevel of skill to perform. The short-term improvement ofstrength and power from the USE and BSE in this studyis likely due to neuromuscular adaptations. The neuro-muscular adaptations related to improved performance

on the M-K, which possibly occurred in this study, appearto be similar after UL and BL in men and women.

PRACTICAL APPLICATIONS |

This study found that the improved bilateral strengthand power measures were not significantly difTerent afterUL and BL in men and women. With the exception oftheunilateral squat, the improvements on all unilateral andhilateral tests were similar between men and women. Thesmall efTect size for the difference in the unilateral squatindicates that further investigation is warranted heforesuggesting that men improve more than women. The datain this study also indicate that USE may be more effectivethan BSE for improving unilateral vertical jumping per-formance. USE and BSE were equally efTective trainingprotocols to improve early phase performance on the M-K in men and women.

Given that untrained subjects participated in thisstudy, we expected to find improved strength and poweron the tests that were similar to the training treatment.The suhjects training with USE, when included and treat-ed in the training program as core exercises, were able toincrease bilateral strengtb and power in the early phaseof training equal to the subjects who trained with BSE.In untrained subjects, the bilateral squat is the exercisethat is typically included in the early phase of the train-ing program to quickly huild a foundation of strengtb be-fore integrating assistance exercises, such as USE. Ac-cording to our data, incorporating only USE early into thetraining program does not reduce short-term maximumbilateral strength and power gains in untrained men andwomen. The data also indicate tbat USE sbould receivepriority in the early phase ofthe resistance-training pro-gram designed to improve unilateral vertical jumpingperformance in untrained men and women. Future stud-ies should include resistance-trained athletes and a lon-ger training period to determine if similar results can befound. Differences in strength and power may appearwith a longer training period as potential improvementin hypertrophy contributes along with the neurologicaladaptations to the performance of these tests. Futurestudies should also be conducted to detennine the efTectof USE on other sport-specific skills. To improve func-tional strength and power, strength and conditioning spe-cialists need more data to determine the amount of em-phasis that sbould he placed on implementing USE intheir subjects' training programs.

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Address correspondence to Kevin McCurdy, kmccurdy®valdosta.edu.

the effects of short-term unilateral and bilateral … › ... · squat was followed to measure...

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