Changes in Postural Stability With Fatigue of Lower Extremity Frontal and Sagittal Plane Movers

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Changes in postural stability with fatigue of lowerextremity frontal and sagittal plane movers

Mahyar Salavati a, Mojgan Moghadam b,*, Ismaeil Ebrahimi c,Amir Massoud Arab a

aUniversity of Social Welfare and Rehabilitation Sciences, Tehran, Iran

bPhysical Therapy Department, Faculty of Rehabilitation Sciences, Iran University of Medical Sciences,

Mirdamad Blvd, Tehran, IrancIran University of Medical Sciences, Faculty of Rehabilitation Sciences, Tehran, Iran

Received 22 March 2006; received in revised form 4 June 2006; accepted 10 September 2006

Abstract

The purpose of this study was to quantify changes in postural stability with fatigue of the frontal and sagittal movers of the lower

extremities. There were four test sessions, with a randomized order assigned according to the muscles tested and the plane of motion. Subjects

were 20 healthy men (age: 22.6 2.4 years, height: 173.7 3.6 cm, weight: 63.3 7.9 kg). During each session, one set of muscle groups

was fatigued using isokinetic contractions: ankle plantar/dorsi flexors, ankle evertor/invertors, hip flexor/extensors or hip abductor/adductors.

The Biodex Stability System was used to assess anterior/posterior and medial/lateral stability before and after muscle fatigue. Repeated

measures ANOVAs revealed that fatigue was associated with a significant increase in all stability indices. Fatigue of the hip movers, whether

in the frontal or sagittal planes, led to greater increments in stability indices than fatigue of the ankle musculature. Fatigue of the frontal

movers resulted in greater increases in the medial/lateral stability index compared to fatigue of the sagittal movers. In conclusion, fatigue of

proximal lower extremity muscles affects postural stability and fatigue of the frontal movers is associated with postural instability in the

frontal plane.# 2006 Elsevier B.V. All rights reserved.

Keywords: Fatigue; Postural stability; Lower extremity

1. Introduction

The maintenance of balance is an essential requirement

for the performance of daily tasks and sporting activities

[1,2]. Several studies have examined how pathologic

conditions, aging and fatigue affect postural control

[316]. Muscular fatigue is a key factor argued to impairproprioception and postural control [515,17,18]. Recent

studies by Ochsendorf et al., Ramsdell et al., and Joyce et al.

indicated that isokinetic fatigue of the ankle plantar flexors

and dorsiflexors was associated with significant increases in

postural sway [1012]. Yaggie and McGregor found similar

results following fatigue of the ankle plantar flexors,

dorsiflexors, invertors and evertors [6]. Gribble and Hertel

examined the effects of isokinetic fatigue of hip and ankle

musculature on postural control during single leg stance.

There was an adverse effect of localized fatigue on postural

control maintenance and the effect was greater for fatigue ofthe sagittal or frontal plane movers of the hip compared to

the ankles [14,15].

Most studies have examined the effects of fatigue of the

ankle muscles andlittle attentionhas been paid to theability to

maintain postural stability with fatigue of the more proximal

muscles. Recent findings have shown that proprioceptive

inputs from the hip region are important for postural control

[19]. Nevertheless, there has been no previous attempt to

evaluate the effects of fatigue of muscles that move joints in

www.elsevier.com/locate/gaitpostGait & Posture 26 (2007) 214218

Institutional review board: The Institutional Review Board of

University of Social Welfare and Rehabilitation Sciences, Tehran, Iran

* Corresponding author. Tel.: +98 21 222 27124; fax: +98 21 224 18746.

E-mail address: [email protected] (M. Moghadam).

0966-6362/$ see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.gaitpost.2006.09.001
mailto:[email protected]://dx.doi.org/10.1016/j.gaitpost.2006.09.001http://dx.doi.org/10.1016/j.gaitpost.2006.09.001mailto:[email protected]


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different planes on the ability to maintain stability in those

planes. The purpose of this investigation is to compare

changes in postural stability following isokinetic fatigue of

frontal and sagittal movers, acting on either proximal or distal

segments of the lower extremities.

2. Methods

2.1. Subjects

Twenty healthy male college students (age: 22.6 2.4

years, height: 173.7 3.6 cm, weight: 63.3 7.9 kg)

volunteered to participate. Participants were excluded if

they had any history of lower extremity injury within the

past year, visual problems, dizziness and vertigo, any

deformity in lower extremities or spine, previous history of

surgery, neurological or systemic disorders. They were

also excluded if they had taken any sedative drug or

alcohol within the past 48 h or if they had professional

sports participation in the past 6 months [911]. Previous

studies showed that physical activity level and specificity

may influence balance ability and thus must be considered

in examining balance [20]. A sample of convenience of

eligible subjects gave informed consent to participate.

The Institutional Review Board of University of

Social Welfare and Rehabilitation Sciences approved

the study.

2.2. Testing procedure

A repeated measures design was used to test the primaryresearch question, which was the effect of fatigue of frontal

and sagittal movers acting on either hip or ankle on postural

stability. The dependent variable was postural stability, as

measured by overall, anteriorposterior, and mediallateral

stability indices (OSI, APSI and MLSI, respectively). The

independent variable was local muscle fatigue with four

levels: (1) distalsagittal (ankle plantardorsi flexors), (2)

distalfrontal (ankle evertorinvertors), (3) proximalsagit-

tal (hip flexorextensors), and (4) proximalfrontal (hip

abductoradductors).

There were four separate experimental sessions with a

break period of at least 48 h and a randomized order

assigned according to the muscles tested and the plane of

motion. During each session, postural stability was assessed

before and after completing an isokinetic fatigue protocol.

For all subjects, assessments and interventions were

performed with the dominant lower extremity.

2.3. Muscle fatigue

Distal segment and sagittal plane: Peak torque measure-

ments and fatigue protocols were performed using the

Biodex System III isokinetic dynamometer (Biodex Inc.,

Shirley, NY, USA). In order to determine the initial peak

torque (IPT) values two sets of concentric/concentric ankle

plantar/dorsiflexion movements were performed at 608/s and

1208/s, respectively. The first set was a familiarization task

and consisted of three submaximal and three maximal

contractions. In the second set, three trials of maximal effort

were performed with no rest. The highest peak torque of

three repetitions was recorded as IPT. After a 23 min rest,the fatigue protocol was initiated, during which subjects

performed continuous concentric/concentric plantar/dorsi-

flexion movements at 608/s and 1208/s, respectively. Fatigue

was judged to have occurred when the torque output in both

directions dropped below 50% IPT for three consecutive

movements [6,1012,14,15].

Distal segment and frontal plane: In order to induce

fatigue in the ankle invertors and evertors, a similar

procedure was performed for ankle eversion and inversion

with contraction speeds of 608 /s and 1208/s.

Proximal segment and sagittal plane: Flexors and

extensors of the hip joint were fatigued by performing a

similar fatigue protocol, at 608 /s and 908/s.

Proximal segment and frontal plane: To induce fatigue in

the hip abductors and adductors, a similar fatigue protocol

was performed at 608 /s and 908/s.

Verbal encouragement was given throughout all tests

and fatigue protocols using standard procedures [12,21].

Because there were different fatigabilities of the antag-

onistic muscle groups around the ankle and hip joints, we

used test speeds that we had found during our pilot studies

to cause fatigue in both muscle groups almost simulta-

neously.

After completing the fatigue protocols, subjects were

removed from the dynamometer and tested for posturalstability with a delay of no more than 60 s. This time interval

was based on the results of our pilot testing which showed no

recovery of fatigue within 24 min after the isokinetic

fatigue protocol. Recovery was defined as the return of peak

torque for two consecutive contractions above 80% IPT.

Schwendner et al. used a similar criterion to determine

fatigue recovery [21].

2.4. Postural stability assessment

In order to measure postural stability we used the

Biodex Stability System (Biodex Inc.). This system

consists of a circular movable platform interfaced with

computer software that enables the device to perform

objective measurements of stability indices. The platform

stability ranges from 18, with 1 representing the greatest

instability.

The Biodex Stability System was shown to be reliable in

several previous studies. Pincivero et al. reported intraclass

correlation coefficient (ICC) values of .6 (for stability level

8) to .95 (for stability level 2) in healthy subjects [22].

Schmitz and Arnold reported ICC values for dominant single

limb stance ranging from .8 to .43, using a decreasing

stability level from 8 to 2 over 30 s [23]. We confirmed

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reliability during our pilot study, with ICC values ranging

from .77 to .99.

For all trials, the platform was set and remained at stability

level 7. Subjects were asked to maintain single leg stance on

the platform with both arms folded across their chest. The

unsupported limb was held in a position of hip neutral

extension with partial abduction and 908 of knee flexion, so as

not to contact the test limb. To perform the dynamic balance

test, subjects were instructed to keep the moving platform aslevel as possible for 20 s, while they were barefoot and their

eyes were closed [8,9]. For each test a report was generated

providing values of OSI, APSI, and MLSI. These indicated

the variance of platform displacements from level in all

planes, the sagittal plane and frontal plane.

2.5. Statistics

To determine the effects of fatigue, fatigue segment and

fatigue plane on postural instability, separate 2 2 2

analyses of variance (ANOVAs) with repeated measures for

condition (pre-fatigue and post-fatigue), fatigue segment(distal and proximal) and fatigue plane (sagittal and frontal)

were conducted for OSI, APSI, and MLSI. The alpha level

was set at .05 for all analyses.

3. Results

The means and standard deviations for pre-fatigue and

post-fatigue measurements of all stability indices are

presented in Table 1. The results of the repeated measures

ANOVAs showed that fatigue had a significant effect on all

stability indices (OSI: F (1, 19) = 87.01, p = .00; APSI: F (1,

19) = 71.91, p = .00; MLSI: F (1, 19) = 39.23, p = .00). A

significant condition by segment interaction was also foundfor OSI (F (1, 19) = 24.11,p = . 00), APSI (F (1, 19) = 13.52,

p = . 00) and MLSI (F91, 19) = 6.63, p = . 01). Fatigue of the

hip mover muscles led to greater increments in stability

indices (deterioration in postural stability) compared to

fatigue of the ankle musculature (Fig. 1). There was also a

significant condition by plane interaction for MLSI (F (1,

19) = 4.71,p = .04). Fatigue of the frontal movers resulted in

a significantly greater increment in MLSI, compared to

fatigue of the sagittal movers (Fig. 2).

4. Discussion

The results of this study suggest that localized muscle

fatigue of the lower extremities reduces postural stability in

M. Salavati et al. / Gait & Posture 26 (2007) 214218216

Table 1

Means (standard deviations) of stability indices for four conditions of fatigue segments and planes

OSI APSI MLSI

Pre-fatigue Post-fatigue Pre-fatigue Post-fatigue Pre-fatigue Post-fatigue

Distal/sagittal 5.47(1.47) 6.89(1.90) 4.61(1.31) 5.98(1.83) 3.13(1.00) 3.52(1.04)

Distal/frontal 5.29(1.19) 6.58(1.66) 4.61(1.20) 5.58(1.50) 2.74(.61) 3.56(1.40)

Proximal/sagittal 5.41(1.39) 8.23(2.61) 4.25(1.16) 7.00(2.60) 3.42(1.30) 4.32(1.35)

Proximal/frontal 5.30(1.11) 8.73(2.53) 4.48(1.11) 7.17(1.97) 2.95(.84) 4.84(2.53)

Fig. 1. The condition segment interaction for: (A) mean APSI (F (1, 19)

= 13.52, p = .00) and (B) mean MLSI (F91, 19) = 6.63, p = .01).Fig. 2. The condition plane interaction for: (A) mean APSI (F (1, 19)

= .54, p = .46) and (B) mean MLSI (F (1, 19) = 4.71, p = .04).


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healthy young men. These findings are consistent with

Ochsendorf et al. Ramsdell et al., Joyce et al., Yaggie and

Mcgregor, and Gribble and Hertel [6,1012,14,15]. These

studies examined postural stability using static forceplates.

The additional knowledge that our data has contributed is

that localized muscle fatigue can also affect dynamic

postural stability as measured using a movable platform. It ispossible that the results reflect proprioceptive deficiencies

associated with muscle fatigue [17,18], increased muscle

reaction time or inappropriate efferent muscle responses

[18,24,25]. Although our results do not pinpoint which

aspects of the neuromuscular loop were affected by muscle

fatigue, we attempted to increase reliance on proprioceptive

feedback by instructing participants to perform the dynamic

balance tests without foot wear and with closed eyes [9].

Fatigue in proximal musculature of the lower extremity

was associated with the greater deterioration in postural

stability in either the sagittal or frontal planes. Although

these findings are consistent with those reported by Gribble

and Hertel, we found deterioration of postural stability in

both sagittal and frontal planes, following fatigue of the

ankle evertors and invertors. This was not observed in the

study of Gribble and Hertel [15] who reported that fatigue

of the ankle plantar flexors and dorsiflexors impaired

postural stability in the sagittal plane only. The different

findings may have occurred due to the use of different

measurement protocols. The dynamic balance tests used in

the present study may be more challenging and sensitive

test to detect small changes in postural stability, compared

to measuring center of pressure excursion velocity as

performed by Gribble and Hertel [14,15]. On the other

hand, Nyland et al. suggested that eccentric activation ofankle joint musculature might affect subtalar joint control

and proprioception. Muscle spindles of peroneal muscles

might also affect joint position sense at both the ankle and

subtalar joints [25].

It is possible that participants in the present study

employed a hip strategy to maintain stability, due to the

difficult and challenging conditions of dynamic balance test,

especially after fatigue induction. Shumway-Cook sug-

gested that stance on pliant surfaces caused an increased

reliance on a hip strategy [26]. Riemann et al. compared the

corrective actions of the ankle, knee, hip, and trunk during

single-leg stance on firm, foam, and multiaxial surfaces and

concluded that the ankle is of primary importance during

single-leg stance on firm, foam, and multiaxial surfaces,

with proximal joints having an increased role under more

challenging conditions [27]. Further kinematic analyses are

necessary to determine the effects of segmental muscle

fatigue on movement strategies used to maintain postural

stability.

Fatigue of the frontal movers of the lower extremities

reduced postural stability in frontal plane to a greater

extent than for the sagittal plane. The specific effects of

fatigue plane on the direction of postural stability

impairment may be due to the known directionally

sensitive activity of postural muscles [19]. However, such

an effect was not seen in the case of fatigue in sagittal plane

movers. This may be related to the single-leg stance as the

position of dynamic balance test in our study. In contrast to

the domination of sagittal plane control in double-leg

stance, it is hypothesized that the frontal plane is more

important during single-leg stance control. For single-legstance on a fixed surface, Hoogvliet et al. explained two

frontal plane strategies. The first was foot tilt due to the

movements of the subtalar joint. The second was similar to

the known hip strategy, except that it occured in the frontal

plane [27,28].

In conclusion, we have demonstrated that fatigue of

proximal musculature of the lower extremity has a greater

effect on postural stability than the more distal muscles. In

addition, fatigue of the frontal movers of the lower extremity

was associated with greater postural instability in the frontal

plane. In the real world, situations whereby local muscle

fatigue occurs after sports or daily activities might be

associated with disturbances in balance. Further investiga-

tions are needed to clarify the effects of local muscle fatigue

on postural stability in health and disease.

Acknowledgments

The authors would like to acknowledge Dr. Anoushirvan

Kazemnejad for statistical counseling, Dr. Kayvan Davat-

garan for his contribution to language editing and the

Research Committee of University of Social Welfare and

Rehabilitation Sciences, for ongoing support of their work.

The helpful comments and suggestions of the anonymousreviewers were greatly appreciated. Partially supported by

the University of Social Welfare and Rehabilitation

Sciences, Tehran, Iran.

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Changes in Postural Stability With Fatigue of Lower Extremity Frontal and Sagittal Plane Movers