Fatiga y Control Postural Dinamico

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Journal of Sport Rehabilitation,2009, 18, 240-257

2009 Human Kinetics, Inc.

The Effects of Gender and Fatigueon Dynamic Postural Control

Phillip A. Gribble, Richard H. Robinson, Jay Hertel,and Craig R. Denegar

Context: Decits in static postural control related to atigue have been investigatedpreviously, but there is little evidence to link atigue to perormance measures o

dynamic postural control. Objective: To investigate the eects o atigue and gender

on perormance measures o the Star Excursion Balance Test (SEBT). Design:

Mixed-model design. Setting: Research laboratory.Participants: 16 healthy young

adults. Intervention: Subjects perormed the SEBT beore and ater 4 dierent

atiguing conditions.Main Outcome Measures: The normalized reach distances and

sagittal-plane kinematics o the knee and hip were recorded. Results: Fatigue pro-

duced decits in normalized reach distances and decreased knee fexion in all 3 reach-

ing directions. Overall, women were able to reach arther than men while simultane-

ously demonstrating a greater amount o knee fexion. Conclusions: Genderdierences were observed during perormance o the SEBT, with women demonstrat-

ing greater reach distances and knee fexion, and atigue amplied these dierences.

Keywords: kinematics, Star Excursion Balance Test, balance

Fatigue is believed to increase muscle-spindle discharge, subsequently alter-ing aerent inormation into the central nervous system and infuencing jointawareness.1,2 Aerent inormation is a critical portion o the eedback loops thathelp create and maintain postural control. Previous studies have examined the

negative eect atigue has on measures o static postural control.311 However,there has been little investigation o the infuence o atigue on dynamic measureso postural control.12 Dynamic postural-control tasks require a greater degree ocoordinated movement patterns using contributions rom multiple joints,13 but ithas not been established whether atigue alters these tasks or the contributing jointpatterns negatively.

Dynamic postural control can be assessed as the center o mass is controlledwhile ones base o support is moving.13 In addition, as we examined in this study,dynamic postural control during perormance o a voluntary task might involvecompleting a movement that translates the bodys center o gravity without com-


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Gender, Fatigue, and Dynamic Postural Control 241

promising its base o support.13 There have been numerous tests developed toassess dynamic postural control in the geriatric population1416 but very ew teststhat assess the dynamic balance capabilities o the athletic population. The Star

Excursion Balance Test (SEBT) is one such test. It assesses maximum reach with1 leg while maintaining a base o support with the other leg.1719 The reliabilityand clinical applicability o the SEBT have been established.12,1820 A previousstudy demonstrated that males are able to perorm this task better, demonstratinglarger reach distances than emales.21 However, when the reach distances werenormalized to the leg length o the stance limb, no signicant gender dierenceswere observed.

One technique or examining biomechanical contributions to a task is the useo kinematics to quantiy movement patterns. Previous investigations havereported gender dierences in knee-fexion angle and quadriceps activation during

unctional tasks.2224 Although there have been limited comparisons o genderduring perormance o the SEBT,21 we could nd no investigations reported in theliterature involving SEBT perormance that examined kinematic pattern dier-ences in hip and knee fexion between males and emales. In addition, there areew data that show the eects o neuromuscular atigue on joint angle during theperormance o this dynamic postural task.12

There are neuromuscular and biomechanical dierences between genders atthe knee during unctional tasks such as landing and cutting, with males demon-strating a larger amount o knee fexion than emales.22,24,25 Although this genderdierence in knee fexion is established in other selected tasks, it is not knownwhether there are similar dierences throughout the lower extremity during adynamic postural-control task such as the SEBT and how muscle atigue couldproduce dierences in neuromuscular control during the reaching task betweenmales and emales.

Thereore, the purpose o this study was to examine the eects o gender andatigue o the sagittal-plane movers in the lower extremity on kinematic measuresand dynamic postural control as measured with reach distance during perormanceo the SEBT. By systematically atiguing sagittal-plane movers o the ankle, knee,and hip, dierences in reaching strategies between male and emale subjects were

examined beore and ater atigue. We hypothesized that (1) increased reach dis-tance during the SEBT would occur simultaneously with increased knee fexiono the stance limb beore and ater atigue, (2) reach distance and knee fexionwould decrease ater the atiguing condition, (3) men would demonstrate greaterreach distance and knee fexion than women beore and ater atigue, and (4) theintroduction o atigue would ampliy the gender dierences described in hypoth-esis 3.

Methods

Participants

Sixteen physically active subjects (8 men: age 22 5 2 45 years height 1 81


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signed a university-approved inormed-consent orm. All subjects had no historyo injury to the lower extremity or vestibular disorders and had been ree rommild head injury or the previous 6 months. Subjects were right-limb dominant,

with limb dominance dened as the limb with which they preerred to kick aball.

Procedures

Subjects reported to the laboratory or 5 testing sessions at least 1 week apart,during which they perormed the SEBT beore and ater a atiguing condition ora control, no-atigue condition. The 5 testing conditions were isokinetic ankleatigue, isokinetic knee atigue, isokinetic hip atigue, a lunging task, and control(no atigue). The order o the 5 testing sessions was counterbalanced. Reach dis-

tance during the SEBT was measured while sagittal-plane kinematics o the stanceleg were recorded. During each session, subjects completed the protocol usingboth the right and let legs; the order o stance leg was also counterbalanced. Atercompleting the test with one leg, subjects sat quietly or 30 minutes beore begin-ning the same protocol or the opposite leg.

During the initial session, leg length was measured with the subject lyingsupine on a plinth with a standard tape measure rom the anterior superior iliac tothe distal end o the medial malleolus. This measurement was used to calculate thedependent variable or normalized reach distance.

Instrumentation

An isokinetic dynamometer (Biodex, Inc, Shirley, NY) was used to induce atiguein the sagittal-plane movers o the hip, knee, and ankle. A metronome was used toprovide the rhythm o movement or perormance o lunges. Subjects wore anadjustable weight vest (All Pro Exercise Products, Inc, Longboat, FL) carrying10% o their body weight while perorming the lunging task. Kinematic data oankle-, knee-, and hip-joint positions were collected using a digital video camera(Panasonic Digital Palmcorder, Panasonic Electronics, Denver, CO) sampled at

30 rames per second. Joint angles in the sagittal plane were calculated using theSMART video-analysis system (ECI-Sotware, Inc, Boston, MA).

Star Excursion Balance Test

The Star Excursion Balance Test (SEBT) was perormed with the subjects stand-ing in the middle o a grid ormed by 8 lines on the foor made with athletic tapeextending out at 45 rom each other17 (Figure 1). The SEBT consists o 8 reach-ing directions corresponding to the grid lines. Because o the constraints relatedto the timing o postatigue measures and the act that we were mainly con-

cerned with sagittal-plane kinematics o the stance leg, only 3 o the 8 reachingdirectionsanterior (Figure 1[a]), medial (Figure 1[b]), and posterior (Figure1[c]) o the SEBT were perormed during the preatigue and postatigue con


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Subjects were instructed to reach with their leg as ar as possible along the

line, make a light touch on the line, and return the reaching leg back to the centerwhile maintaining a single-leg stance with the other leg in the center o the grid(Figure 1) They were instructed to make a light touch on the ground with the most

Figure 1 Reaching in the (a) anterior, (b) medial, and (c) posterior directions o the StarExcursion Balance Test.


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Reach distances were recorded by placing a mark on a measuring tape securedto the foor corresponding to the touchdown points o each subject. The investiga-tor recorded the reaching distance as the distance rom the center o the grid to the

point o maximum excursion o the reaching leg. A trial was discarded andrepeated i the investigator thought the subject used the reaching leg or a substan-tial amount o support at any time, removed his or her oot rom the center o thegrid, or was unable to maintain balance on the support leg throughout the trial.

Subjects participated in 5 separate testing sessions and on each testing dayperormed the reaching trials in each o the 3 selected directions o the SEBTbeore and ater the designated condition. For each o the 4 testing sessions inwhich atigue was induced, the designated atigue protocol was completedbetween the pretrial and posttrial. On the control, nonatiguing, day, subjects wereallowed 5 minutes o quiet sitting between the pretest and posttest trials. At the

beginning o each testing session, they were allowed to practice reaching in the 3directions 6 times to minimize any learning eect.18 Subjects were aorded 5minutes o rest between the practice trials and the pretest trials. The pretest trialsconsisted o 3 consecutive reaches in each o the anterior, medial, and posteriordirections, with the directions randomized. Ater the 4 atigue-condition sessions,posttesting commenced within 15 seconds o when the designated level o atiguewas achieved. The order o reach direction or the posttesting trials ollowed thesame randomized order as the pretest or each testing session.

Kinematic AnalysisA digital video camera was positioned on a tripod 8 m rom the center o the SEBTgrid. Markers were placed on the acromion o the scapula, greater trochanter o theemur, lateral knee-joint line, and lateral malleolus. Subjects perormed the testwith the lateral side o the stance leg acing the camera. The single-camera setupallowed quantication o the amount o sagittal-plane motion in degrees at the kneeand hip or all 3 reaching directions without subjects having to reposition theirstance leg or each reaching direction.26

Raw data were processed with Video Wave III video-processing sotware(MGI Sotware Corp, Ontario, Canada). The SMART system calculated kine-

matic data or hip fexion and extension and knee fexion and extension at themaximum reach distance, designated as touchdown o the reaching leg.26

Fatigue

Three o the atiguing conditions were perormed on the isokinetic dynamometer,set or concentricconcentric unction. Sagittal-plane movement patterns at theankle (plantar fexion and dorsifexion), knee (fexion and extension), and hip(fexion and extension) were used. Patient positioning ollowed guidelines setorth by the manuacturer.

Subjects perormed 5 continuous maximum trials at 60/s or the designatedmovement pattern to determine peak torque. Ater a 2-minute rest, they repeatedh 60/ i l il d i d d b l


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point o origin and the target reaching distance, equal to their individual leg length.Lunges were perormed at the rate o 1 lunge every 2 seconds. A lunge cycle wasdened as having the subject reach toward the target, achieve approximately 90

o hip and knee fexion in the lunging leg while maintaining an upright trunk, andreturn the reaching leg back to the point o origin.

Subjects were given ample practice time to ensure proper execution o thelunging task. They were given 2 minutes to rest between practice trials and testtrials. Fatigue was induced by having them perorm the task a maximum numbero times until they could not complete it with proper orm or were unable to meetthe required rhythm or 2 repetitions in a row.27 Throughout the task, subjectsreceived verbal cues to ensure proper technique and verbal encouragement to con-tinue the task until atigued.

The th testing session was used to establish baseline data and involved the

control condition. During this session, no atiguing task was implemented. Instead,the subjects sat quietly or 5 minutes between the pretest and posttest peror-mances o the SEBT.

Statistical Analysis

The means o reach distance and maximum joint-fexion angles rom the 3 trialso each perormance o the SEBT were calculated and used or statistical analysis.Reach distances were divided by leg length and multiplied by 100 to calculate adependent variable that represents reach distance as a percentage o leg length

(MAXD).21 Because o the inherent dierences in movement patterns between the3 reaching directions, there were no direct comparisons made, and each was ana-lyzed separately. For each reaching direction, 3 separate 5 2 2 2 ANOVAswere perormed or normalized reach distance, knee-fexion angle, and hip-fexion angle with within actors o condition (control, ankle, knee, hip, and lungeatigue), side (let and right), and time (preatigue and postatigue) and a betweenactor o gender (male and emale). Tukeys post hoc testing was perormed toidentiy specic dierences in the presence o a signicant interaction. The levelo signicance was set a priori at .05 or all analyses. All statistical analyses wereperormed using SPSS 10.0 (SPSS, Inc, Chicago, IL).

Results

For the 5 pretest sessions, ICC values were calculated or the dependent variablesin each reaching direction. ICC values or MAXD ranged rom .941 to .951, orknee fexion rom .876 to .935, and or hip fexion rom .927 to .964. This indi-cates high reliability o the pretest measures across the 5 testing sessions or all 3reaching directions.

For all reported statistically signicant interactions, there were also signi-

cant main eects. In the presence o a signicant interaction, the interaction ismore meaningul and attention is given to the interaction rather than the main h b h l i i h ld h b


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The actor o side was included in our research design, and we did test theright and let sides. We do not mention this actor in our results because in noinstance did it contribute as a signicant independent variable. Because we did not

report nonsignicant ndings, side is not mentioned. We eel that the volume othe results precludes us rom reporting all the nonsignicant ndings.

Anterior Direction

MAXD. For the anterior reaching direction, atigue created a decrease in MAXDor both genders compared with the control day; however, among the men, theknee atigue condition produced a signicantly greater decline in MAXD (.043)than in the other conditions (gender-by-condition-by-time interaction: F4,56 =3.52, P = .012; Figure 2).

Kinematics. Kinematically, a signicant gender-by-condition interaction (F4,56= 2.54, P = .05) demonstrated that women used more knee fexion than men during3 o the atigue conditions (ankle, knee, and lunge), with the largest disparitybetween genders or knee fexion or the lunge atigue condition (7.96; Figure 3).Similarly, women used more hip fexion (29.10 4.24) than men (11.434.24) during the reaching task (Gender: F1,14 = 8.68, P = .01).

Medial Direction

MAXD.For the medial reaching direction, all 4 atigue conditions created prepost decreases in MAXD (condition-by-time interaction: F4,56 = 7.04, P < .001)

and knee fexion (condition-by-time: F4,56 = 4.69, P = .002) compared with thecontrol day (Figure 4). However, women reached signicantly arther ater atigue(0.882 0.021) than men (0.847 0.021; gender-by-time: F1,14 = 5.81, P = .03;Figure 5[a]).

Kinematics. Beore atigue, the women used a larger amount o knee fexion(72.36 2.58) than the men (67.72 2.59; gender-by-time: F1,14 = 7.16, P =.018; Figure 5[b]). In addition, the women experienced a smaller pretest-to-posttest decline in knee fexion (1.54) than the men (4.16; Figure 5[b]).

Posterior Direction

MAXD. For the posterior reaching direction, women produced larger MAXDvalues than men at the preatigue and postatigue sessions, and womens MAXDwas less aected by atigue than the mens (gender-by-time: F1,14 = 6.67, P =.022; Figure 6[a]). Fatigue at the ankle, knee, and lunge exercises created signi-cant prepost decreases in MAXD (condition-by-time: F4,56 = 5.82, P = .001;Figure 7[a]).

Kinematics. Women used a signicantly larger degree o knee fexion ateratigue (60.36 3.03) than the men (54.56 3.03; gender-by-time: F1,14 =8 375 P 012 Fi 6[b]) I dditi kl ( 2 93) d l ti ( 3 95)


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Comments

The results o this study show that atigue in the lower extremity adversely aectsdynamic postural control as assessed with the SEBT. In addition, gender infu-

enced perormance o the dierent reaching directions o the SEBT. When exam-ining the relationships between joint-angle positions and MAXD, the infuenceson perormance center most signicantly on the knee with noticeable contribu

Figure 2 Gender Condition Time interactions or reach distance as a percentageo leg length (MAXD) in the anterior direction or (a) men and (b) women. *P < .05. Withthe men, the lunge atigue condition created a signicant decline in MAXD ater atigue.


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Effects of Gender

Although previous data have shown ew dierences across gender or normalizedreach distances during perormance o the SEBT,21 there has been no investigationinto gender dierences in reaching strategies that might be used during thesetasks. It appears that the ideal reaching pattern to produce the maximum reach inthe anterior direction involves as much knee and hip fexion as possible and thatany infuence o gender on MAXD is infuenced by sagittal-plane positioning othe knee and hip. Electromyographic activity o the vastus medialis oblique andvastus lateralis in the stance limb has been shown to be greater in the anterior

direction than during any o the other reaching directions o the SEBT.28 Ourresults indicated that women achieved a greater amount o knee and hip fexionthan men. Perhaps the women are able to recruit the medialis oblique and vastuslateralis more eciently, allowing or better control o the knee in the sagittalplane during this task.

Perormance in the medial and posterior reaching direction also appears to besignicantly infuenced by the position o the knee in the sagittal plane. Womenwere able to produce signicantly larger MAXD values while simultaneously pro-ducing greater knee-fexion angles in this reaching direction. Although these anal-yses were examined individually, it might be concluded that women perorm

better at this task partially because o their ability to create a greater degree oknee fexion.

Figure 3 Gender Condition interactions or knee fexion in the anterior reachingdirection. *P < .05. Women used more knee fexion than the men during the lunge, knee,and ankle atigue conditions.


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H l25 d i i l ll d k f i d i

Figure 4 Condition Time interactions or (a) reach distance as a percentage o leglength (MAXD) and (b) knee fexion in the medial reach direction. *P < .05. For both de-pendent variables, the lunge, knee, ankle, and hip atigue conditions created a signicantdecline ater atigue compared with the no-atigue condition.


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Although the 3 reaching directions involve tasks requiring unique movementpatterns and are considered inherently dierent, men demonstrated smaller knee-fexion angles in the 3 reaching directions than women Perhaps the issue that is

Figure 5 Gender Time interactions or (a) reach distance as a percentage o leglength (MAXD) and (b) knee fexion in the medial reaching direction. *P < .05, time di-erence. +P < .05, group dierence.


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Figure 6 GenderTime interaction or (a) reach distance as a percentage o leg length(MAXD) and (b) knee fexion in the posterior reaching direction. *P < .05, time dierence.+P < .05, group dierence.


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Figure 7 Condition Time interaction or (a) reach distance as a percentage o leglength (MAXD) and (b) knee fexion in the posterior reaching direction. *P < .05. For

MAXD, the ankle, knee, and lunge atigue conditions created a signicant decline ateratigue. For knee fexion, the ankle and lunge atigue conditions created a signicant de-cline ater atigue


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various unctional measures to determine whether the speed o the task and asso-ciated interaction with the environment dictates perormance between genders.

Constraints-behavior theory, infuenced by the interaction o task, organis-

mic, and environmental constraints, might be useul in examining these dier-ences.29 In this experiment, task and environmental constraints were the same ormen and women, suggesting that the observed dierences must be organismic.Organismic constraints can be categorized as structural and unctional. From astructural perspective, women might have gained an advantage by maintainingtheir center o mass lower because o wider hips.30,31

From a unctional perspective, Zeller et al30 ound that during single-legsquats, emales demonstrated greater ankle dorsifexion and pronation, hip adduc-tion, fexion, and external rotation and less trunk lateral fexion than males. Theyattribute the dierences to emales starting in and maintaining a more valgus

position o the knee, which would create a wider pelvic base and lower the centero mass, creating better stability, potentially infuencing the joint position through-out the extremity.

Van Wegen et al31 have demonstrated dierences in static postural controlbetween elderly and younger populations as measured through time-to-boundaryvalues. This method o assessing postural control, which examines the temporalsaety margins o postural sway, has not been compared between genders orduring the SEBT; however, it might be that the decisions to employ knee fexionto complete the task refect ones ability to eciently challenge the temporalsaety margins o the boundaries o the base o support. Eective management othe interaction o the demands o the task and the environmental constraints isperhaps maniested as increased knee fexion. Future studies should quantiytime-to-boundary values to determine the degree to which these margins mightinfuence a dynamic postural-control task.

Effects of Fatigue

For men and women, atigue had a negative infuence on knee fexion thatadversely aects MAXD. The ankle and lunge atigue tasks infuenced knee-fexion-angle changes while simultaneously reducing MAXD. Although theinduced atigue conditions were designed to infuence muscle groups about spe-cic joints, those infuences do not seem to be constrained to the targeted joints,as observed rom the kinematic changes in the knee and hip.

In our study, MAXD and knee fexion experienced simultaneous decits withthe knee-atigue protocol. Electromyographic activity o the vastus medialisoblique and vastus lateralis in the stance limb has been shown to be greater in theanterior direction than during any o the other reaching directions o the SEBT.28With atigue, the vastus medialis oblique and vastus lateralis might have lost theability to eectively contract to help maintain dynamic postural control during

this task. We did not quantiy this, but the potential alteration in muscle activationater atigue could have infuenced the knee and hip angles, subsequently contrib-uting to a decrease in MAXD In addition the women appeared more resistant to


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quadriceps. Future studies should use EMG to urther quantiy these observeddierences across genders related to atigue.

It has been suggested that emales are more resistant to atigue at lower

intensities.31,32 In all 3 reaching directions, women perormed better, and thegender dierences were amplied by atigue, suggesting that the men were moreadversely aected by atigue. The human movement system seems to have a sig-nicant energy-minimization bias that, in certain tasks, must be overcome i per-ormance is to be maximized.33 The SEBT creates a problem o conficting goalso maintaining balance and maximizing reach distance. Having to perorm thetask under atigued conditions might have shited the infuence toward energyminimization, evidenced by a reduction in reach distance. Although the SEBT isa challenging task, perhaps its metabolic demand is low enough that women areless resistant to altered perormance in a state o atigue and do not need to mini-

mize their energy or the task, allowing them to still use selected movement strate-gies more eciently than men.

Limitations

The kinematic analyses in our study only reported sagittal-plane movements.There are multiple combinations o multiplanar movement that might be occur-ring during all 3 reaching tasks that we were unable to quantiy in this project.Rotation at the hips and trunk that was not quantied in this study might have

infuenced the perormance o the task. Future investigations should involve moresophisticated means o kinematic analysis to help describe the contributions omotion outside the sagittal plane.

We chose to report our data related to the eects o atigue on the selectedtask using a prepost variable (time) and the examination o the 5 separate atigu-ing tasks (condition). An alternative approach to these relationships would havebeen to present delta scores to represent the change in atigue over time in placeo the raw pretest and posttest scores. Although that approach could have provideda simpler design, we elt that it was important to retain the pretest comparisons sothat the additional purpose o examining the infuences o gender beore atigue

could be achieved. In addition, there is evidence to suggest that the use o deltascores in an ANOVA model is associated with a weaker level o reliability thanusing raw scores.34,35 Also, the ICC values or our reach distance and kinematicdependent variables during the pretest assessments when comparing the 5 sepa-rate testing days ranged rom .876 to .964, indicating that reliability o the pretestmeasures was strong, which we elt allowed us to use prepost raw scores orcomparison.

A ew enorced task constraints might have infuenced the subjects peror-mance. The participants were required to keep their hands on their hips and theirheels in contact with the foor. This might have altered their reaching strategy, but

we elt that it was more important to standardize the instructions or perormancein an attempt to minimize error because o excessive accessory motions at uncon-


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subject produces when asked to provide maximum eort and sustain that levelduring a atiguing condition. In an eort to control this, the same investigatorprovided the same verbal cues and encouragement to all subjects throughout all

the tasks.

Conclusion

In conclusion, gender and atigue appear to infuence dynamic postural control asmeasured with the SEBT. Women perormed better on the task than men, and oneo the explanations or this nding is the increased knee fexion exhibited by thewomen at the point o maximum reach distance. This biomechanical dierencebetween men and women was amplied under atiguing conditions to the lower

extremity as reach distances and knee fexion decreased in both groups withatigue, but the decline was larger among the men. Future investigation into theneuromuscular contributions to the biomechanical dierences resulting romatigue in the lower extremities between genders should continue to examine therelationship o the knee during perormance and by what mechanism atigue infu-ences the level o neuromuscular control inherent to men and women. Whenselecting appropriate rehabilitation tasks, clinicians should be aware that this taskmight be more challenging or men than women, as evidenced by the greater nor-malized reaching distances o the women. In addition, the SEBT might be anappropriate rehabilitation task or patients with sagittal-plane knee-motion de-

cits because it relies on and challenges sagittal-plane knee movement. Finally,clinicians should be aware that atigue can infuence dynamic postural control anduse this to their advantage when ormulating rehabilitation or the lower extrem-ity, while taking steps to minimize atigue i optimal perormance on the task isdesired.

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Fatiga y Control Postural Dinamico

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