| | Control of Balance Differs After Knee or Ankle Fatigue in Older WomenAbstract Bellew JW, Fenter PC. Control of balance differs after knee or ankle fatigue in older women. ObjectiveTo examine the effects of acute isokinetic knee or ankle fatigue on control of static and dynamic balance in older women. DesignPretest and posttest. SettingUniversity research laboratory. ParticipantsEighteen healthy, community-dwelling older women (age, 77±6y) with no history of falling. InterventionsMeasurements of static and dynamic balance control before and after isokinetically fatiguing the ankle plantar- and dorsiflexors or knee extensors and flexors in separate sessions. Main Outcome MeasuresPerformance on 3 clinical assessments of control of balance: modified Functional Reach Test (mFRT), Lower-Extremity Reach Test (LERT), and Single-Limb Stance Time Test (SLSTT). ResultsBalance declined in the mFRT after fatigue to each joint, with no significant difference in the magnitude of change between joints. Control of balance during the LERT decreased significantly only after knee fatigue, and control of balance during the SLSTT was significantly reduced only after ankle fatigue. ConclusionsBalance performance after acute isokinetic muscular fatigue to the knee or ankle is specific to the muscle groups fatigued and the balance tests used. MUSCULAR FATIGUE IS A REDUCTION in the force-generating capacity of muscle caused by recent activation and is considered a causative factor in declining control of balance.1, 2, 3, 4 Fatigability of skeletal muscle is characterized by the amount of time a given force or power output can be sustained or the extent that force or power output are reduced in a given time.5 Age-related changes in the neuromuscular system, motor unit remodeling, and the associated loss of strength and slowed contractile properties of skeletal muscle with aging increase fatigability in older adults.6, 7 Muscle fatigue is thought to alter afferent kinesthetic and proprioceptive feedback, which may manifest in a decreased ability to sense changes in postural stability.8, 9 This decreased awareness may compromise the maintenance of joint and bodily position, the coordination of voluntary movements, or the reaction to external stimuli.10 The incidence of falls in older adults is greater than in younger adults, and falls are the leading cause of accidental death in persons over 90 years of age.11, 12 Aging is associated with a decline in controlling postural sway and balance, particularly in an undisturbed, static stance.13 This decline may be exacerbated by acute muscular fatigue and may be a primary contributing factor to the increased incidence of falls among the elderly. The effect of acute lower-extremity muscular fatigue on control of balance has been reported by several groups with particular emphasis on static unilateral stance.1, 2, 14, 15 The available research on the relation between fatigue and balance has, however, focused on young, healthy subjects in the third and fourth decades. The effect of acute lower-extremity muscular fatigue on control of balance has not been examined in older adults. Therefore, the purpose of this study was to examine the effects of acute muscular fatigue of the ankle and knee musculature on static and dynamic balance in healthy older women. By this study, it may be possible to determine if control of balance in older adults declines after acute muscular fatigue and if ankle fatigue affects balance differently than knee fatigue. Methods  Eighteen healthy community-dwelling women without a history of falling were examined (mean ± standard deviation, age 77±6y; height, 1.6±8.1m; mass, 65.4±6.6kg). Exclusion criteria included uncontrolled hypertension, diagnosed osteoporosis, transient ischemic attacks, stroke, congestive heart failure, or visual or auditory compromise sufficient to prevent driving. After explanation of the study protocol, subjects agreed to participate by signing the consent form approved by the university institutional review board. Subjects were examined before and immediately after isokinetically inducing fatigue in the flexor and extensor muscles of the knee or ankle in two 30-minute sessions 1 week apart. The joint selected for fatiguing at the first session was balanced across subjects so that half began with the knee and half with the ankle. Control of balance was assessed in a randomized order by using a battery of clinical-based tests including the Single-Limb Stance Time Test (SLSTT), the modified Functional Reach Test (mFRT), and the Lower-Extremity Reach Test (LERT). Testing was conducted by using the self-reported dominant leg determined by which leg the subject would use to kick a ball, and all measures of balance were recorded by the lead author. Balance Assessment Dynamic balance control was assessed by using a modified version of the Functional and Lateral Reach Tests and the LERT. The reach tests, previously described by DeWaard16 and Duncan17 and colleagues, are defined as the maximal distance an individual can reach in the forward and lateral right and left directions while maintaining a fixed base of support on 2 feet. Because our subjects were healthy and did not have a history of falling, our modified version of the reach tests required subjects to perform the test while standing on the dominant leg only. Subjects stood with their dominant arm raised to shoulder height, finger tips extended as far as possible, and reached forward (modified functional reach forward), right (modified functional reach right), or left (modified functional reach left). To eliminate the effect of scapular protraction on functional reach, subjects were asked to push their arm and hand out as far as possible in the direction of reach before the test. Reach was recorded to the nearest 0.5cm as the difference between the starting position and the extended “reach” position by using the Rolyan Functional Reach Measuring Device.a Each subject performed 3 successive trials in each direction with a trial repeated if the subject lost balance, took a step, or raised the heel. The average of the 3 trials was used for analysis. Before testing, the intratester reliability of the lead author was determined. The LERT, a lower-extremity analog of the mFRT and previously described by Bellew et al,18 is an assessment tool that incorporates dynamic control of single-limb balance with lower-extremity neuromuscular control. To quantify lower-extremity reach, the Functional Training Gridb was used. Subjects stood on their self-reported dominant leg in the center of the grid designed as a series of concentric circles separated by 1cm and partitioned into colored sections resembling a dart board. While balancing on the dominant limb, subjects reached as far as possible with the opposite limb in the anterior direction and were required to maintain the position for a 2-second count while the examiner recorded the linear distance reached with the opposite leg. Subjects were permitted to use any body motion while reaching including knee flexion on the stance limb, extension of the arms for balance, or trunk extension and rotation. The maximal distance reached was measured to the nearest centimeter for 3 consecutive trials with the average of 3 trials used for data analysis. Before testing, the intratester reliability of the lead author was determined. Static balance control was assessed by using the SLSTT. The SLSTT quantifies the duration a subject can remain standing on the dominant limb with the arms by his/her side and eyes closed. Vellas et al13 reported that this test was the strongest predictor of injurious falls in healthy community-dwelling adults over the age of 60 years. Subjects stood barefooted inside a 45.7×50.8cm (18×20in) rectangular area marked by tape on a wooden platform. Timing began when the opposite foot was removed from the ground and the eyes closed. Timing ended with any of the following: the raised foot touched the ground, any part of the body was displaced outside the rectangular area, the arms were removed from the sides, the eyes were opened, the non–weight-bearing limb was braced on the stance limb, or the stance foot was displaced from its original position. The average of 3 trials was used for data analysis. Before testing, the intratester reliability of the lead author was determined. Fatigue Protocol Fatigue was induced in the sagittal plane movers of the knee and ankle by using an isokinetic dynamometerc at an angular velocity of 180°/s. Subjects used their self-reported dominant leg for all tests and were positioned according to manufacturer guidelines. At the knee, subjects performed repeated seated flexion and extension through a range from full knee extension to 100° of flexion. To fatigue the ankle, subjects performed repeated seated plantarflexion and dorsiflexion through full available range of motion. A fatigue protocol previously described by Yaggie and McGregor15 and Gribble and Hertel1 was used. The peak torque for each movement direction was determined during 5 maximal effort repetitions. After 2 minutes of rest, each subject performed repeated concentric and concentric repetitions until the torque output for both directions dropped below 50% of the calculated peak torque for 3 consecutive repetitions. Verbal encouragement was given throughout the testing. Balance testing was repeated immediately after the onset of muscular fatigue. Because all testing was conducted in the same room, time from fatigue to balance testing was less than 15 seconds. Statistical Analyses The analyses attempted to answer 2 questions: (1) did balance performance change after fatigue and, if yes, for both ankle and knee? and (2) Was the percentage change greater at 1 joint than the other? The means of the pre- and postfatigue trials and the calculated mean percentage change for balance at each joint were used for analyses.d The independent variables were joint (ankle or knee) and conditions (prefatigue, postfatigue), and the dependent variables were measures of balance (modified functional reach forward, modified functional reach right, modified functional reach left, SLSTT, LERT) and percent change in each test. Because the mFRT has 3 directions (forward, right, left), Bonferroni-adjusted paired samples t tests for 3 related measures were used to assess change from pre- to postfatigue conditions. Thus, α was set at P less than .017 (.05÷3) for the measures of mFRT. The level for significance remained P less than .05 for the SLSTT and LERT. Paired samples t tests were also used to assess differences in mean percentage change. Discussion In this investigation, control of static and dynamic balance was examined before and immediately after isokinetically fatiguing the knee flexors and extensors or ankle plantar- and dorsiflexors. Although control of balance on the mFRT declined in all 3 directions after fatigue of the knee and ankle, the magnitude of decline did not differ between the joints. In contrast, control of static balance during the SLSTT declined only after fatigue of the ankle, whereas control of dynamic balance during the LERT declined significantly only after fatigue of the knee. Although the magnitude of change in the LERT after ankle fatigue was greater than after fatigue at the knee, this failed to reach statistical significance, likely because of the inherent variability noted in the data. Despite the decline in control of balance on the mFRT after fatigue to the ankle and knee muscles, performance on the mFRT does not appear to differentiate between ankle or knee fatigue. However, the data of this investigation show that the SLSTT and LERT tests do and thus can be considered joint specific (ie, performance on a specific test is affected by which joint is fatigued). These findings hold significant clinical impact when selecting assessments for static and dynamic balance. Deficiency in balance control secondary to increased knee fatigability may remain latent if the testing of balance is performed by using the SLSTT. Similarly, the influence of ankle fatigability on balance may go undetected if the assessment is performed by using the LERT. These findings indicate the need for greater awareness of the joint specificity of clinical balance tests. The results of this investigation enhance the existing literature by being the first to examine the effect of acute isokinetic muscular fatigue on control of static and dynamic balance in older adults. Previous authors have reported an acute decline in balance control after fatigue of the leg muscles but only in younger subjects.2, 14, 15 Kwon et al2 were the first to investigate the relation between lower-extremity fatigue and control of balance in single-limb stance. These investigators isokinetically fatigued the ankle and knee musculature of 64 men and women ages 18 to 24 with a protocol nearly identical to that of this study. Their results showed a significantly greater decline in static single-limb balance after fatigue of the ankle as opposed to the knee. The results of the present study confirm those of Kwon regarding the significant decline in performance of the SLSTT after ankle fatigue. Similarly, Johnston et al14 investigated performance of single- and double-limb stance after simultaneous isokinetic fatigue of the ankle, hip, and knee musculature in 20 subjects ages 20 to 39. Their results showed a 2-fold decrease in balance performance in single- and double-limb stance after fatigue, but because their protocol simultaneously fatigued the muscle groups, it was impossible to differentiate the joint-specific effects of fatigue. However, the results from our study support Johnston because we too witnessed a reduction in balance postfatigue on all balance tests in our elderly subjects. The SLSTT was chosen as a measure of static balance control because previous studies in younger populations have often used this test,1, 2, 14, 15 and data have shown this to be a sensitive and significant predictor of injurious falls in older adults.13 Whipple et al19 reported that weakness of the ankle plantar- and dorsiflexors, but particularly the dorsiflexors, was a significant factor related to fall risk in older adults. Vellas et al13 reported a 2-fold increase in fall risk in subjects unable to maintain single-limb stance for at least 5 seconds. In our subjects, 8 (44% of all subjects) were unable to sustain 5 seconds of single-limb stance when assessing balance before fatiguing the ankle (9 when assessed before fatiguing the knee). After fatigue of the ankle, the number of subjects unable to maintain single-limb stance for at least 5 seconds rose to 14 (78%), whereas only 1 more (total of 10) was unable to meet the 5 seconds after knee fatigue. This further evidences the effect of ankle fatigue on control of single-limb stance. The LERT was selected as an assessment of dynamic balance because it requires control of single-limb balance and lower-extremity muscular strength and endurance.18 Likewise, when performing the test, most subjects flex the stance limb knee to increase their reach, thus increasing demand on the thigh musculature for proximal stability. The mFRT was also a logical choice to assess balance. The functional reach test is supported by DeWaard et al16 and Newton20 who reported this test’s ability to differentiate distinct components of balance control (ie, anterior and lateral stability and the ability to measure a subject’s limits of stability during functional reach). Control of balance is predicated on appropriate somatosensory input, including afferent input from the neuromuscular system, and the execution of appropriate musculoskeletal responses.2 Under normal conditions, changes in postural alignment result in peripheral changes in muscle tension and length, which in turn result in efferent adaptations to motor output effectively altering bodily position to prevent falling. A change in the ability to generate muscle tension secondary to fatigue, therefore, may underlie inefficient muscular responses to a disturbance in balance. There are several proposed mechanisms that may explain how fatigue results in decreased control of balance.2, 14, 15 Although it cannot be stated definitively, muscular fatigue around a joint may inhibit the joint’s proprioceptive muscular feedback system, thus affecting static posture.2, 14, 15 Additionally, a decrease in firing of the secondary endings in muscle spindles, as a result of increased joint temperature secondary to sustained exercise, may decrease the tonic response critical to balance.2 Researchers also postulate that muscle spindle desensitization, Golgi tendon desensitization, or ligamentous relaxation may occur when a muscle is fatigued.2, 14 Currently, it is unknown whether these proposed mechanisms are more pronounced or have a larger effect on control of balance in the elderly, but certainly the possibility exists and further exploration is necessary. Study Limitations This study may be limited in that healthy subjects with no history of falling were examined. To what degree acute fatigue would affect balance in frail older adults or those with a history of falling is unknown and worthy of study. Further investigation in this area may assist in identifying performance characteristics that may be amenable to rehabilitation or training interventions. With the increasing availability of computerized posturography in clinical settings, additional findings of the effect of acute fatigue on balance may be identified. Whether these computerized assessments of balance will show findings similar to those observed when using the clinical tests used in this study is a matter of conjecture but a viable question for future research. Conclusions The majority of research examining balance and fatigue has been conducted by using young, healthy subjects. Much less is available from older adults. Age-related changes in the neuromuscular system have been shown to yield deficits in skeletal muscle strength21 and endurance22 as well as deficits in balance23 and fatigability.4 This study finds that acute muscular fatigue results in decreased control of balance in healthy older women and that identification of this fatigue-induced decline in balance is test and joint specific. This investigation is the first of its kind reporting this joint specificity in fatigue and control of balance in older adults. Suppliers References 1. 1Gribble PA, Hertel J. Effect of lower-extremity muscle fatigue on postural control. Arch Phys Med Rehabil. 2004;85:589–592. Abstract | Full Text |
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23. 23Bellew JW. A correlation analysis between rate of force development of the quadriceps and postural sway in healthy older adults. J Geriatr Phys Ther. 2002;25:11–15. Program in Physical Therapy, Louisiana State University Health Sciences Center, Shreveport, LA.  Reprint requests to James W. Bellew, EdD, PT, 1501 Kings Hwy, Rm 310 SAHP, Shreveport, LA 71130-3932
Supported by the Louisiana State University Health Sciences Center (intramural small grants program). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. PII: S0003-9993(06)00976-2 doi:10.1016/j.apmr.2006.08.020 © 2006 The American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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