Reliability of Stationary Dynamometer Muscle Strength Testing in Community-Dwelling Older Adults

Transcription

1 1128 Reliability of Stationary Dynamometer Muscle Strength Testing in Community-Dwelling Older Adults Cheryl D. Ford-Smith, PT, MS, NCS, Jean F. Wyman, PhD, RN, R.K. Elswick Jr, PhD, Theresa Fernandez, MS, RN ABSTRACT. Ford-Smith CD, Wyman JF, Elswick RK Jr, Fernandez T. Reliability of stationary dynamometer muscle strength testing in community-dwelling older adults. Arch Phys Med Rehabil 2001;82: Objectives: To determine the 1-week test-retest reliability of stationary dynamometer scores in the measurement of muscle strength in older adults and to determine the reliability of composite scores obtained by combining right and left lower limb strength scores for each muscle group. Design: In separate sessions, 1 therapist performed repeated measurements of muscle force production. Setting: Outpatient physical therapy clinic of a large teaching hospital. Participants: A convenience sample of 25 volunteers aged 70 to 87 years residing independently in the community and who did not have significant health problems. Intervention: On 2 separate occasions, 1 week apart, bilateral isometric force measurements were obtained for the flexor and extensor muscle groups of the ankle, knee, and hip joints. Main Outcome Measures: For test-retest reliability of individual and composite scores, the intraclass correlation coefficients (ICCs) and 90% confidence intervals were determined. Results: The mean scores for ankle dorsiflexion, knee flexion and extension, and hip flexion exhibited excellent reliability with ICCs ranging from.90 to.76 for the individual lower limb scores and.91 to.84 for the composite scores. Scores for the remaining muscle groups exhibited good reliability with ICCs ranging from.74 to.71 for the composite scores. Conclusion: The stationary dynamometer is a reliable tool to use in determining lower limb muscle force production in elderly adults. Key Words: Elderly; Exercise; Leg; Rehabilitation; Reproducibility of results by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation THE STRENGTH of an individual can affect walking, balance, and the performance of activities of daily living. Therefore, it is important to have a reliable measure of strength From the School of Allied Health Professions, Department of Physical Therapy (Ford-Smith), School of Medicine (Elswick), School of Nursing (Fernandez), Medical College of Virginia, the Virginia Commonwealth University, Richmond, VA; and the School of Nursing, Center for Nursing Research of Elders, University of Minnesota, Minneapolis, MN (Wyman). Accepted in revised form October 9, Supported by the National Institute of Nursing Research (grant no. R01 NR02561). 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. Reprint requests to Cheryl D. Ford-Smith, PT, MS, NCS, Virginia Commonwealth University, Medical College of Virginia, Schl of Allied Health Professions, Dept of Physical Therapy, PO Box , Richmond, VA 23298, cfsmith@hsc.vcu.edu /01/ $35.00/0 doi: /apmr capabilities, particularly in the elderly. Strength the ability of a muscle to produce force changes in the elderly with normal aging, disuse, and disease effects, which can place them at higher risk for disability and falls. 1,2 Reliable strength scores obtained from essentially normal elderly individuals could be used as a guide in assessing pathology in aging adults with disability. A reliable strength measurement is also critical in evaluating outcomes associated with an exercise program. A variety of tools are being used to assess quantitatively both upper and lower limb strength. Studies have used isokinetic dynamometers to determine the strength capabilities of elderly individuals. 2-4 In general, these dynamometers are prohibitively expensive for routine clinical use and their size prohibits use outside of the clinical setting. Researchers have also reported on nontraditional methods for testing strength in older adults, but reliability has not been established for these instruments. 5,6 Hand-held dynamometers have gained popularity as a useful tool to measure muscle force production in the clinic, and these measurements have been found to correlate with isokinetic strength scores. 7,8 Bohannon 9 in 1986 examined the intrasession reliability of hand-held dynamometer measurements in the clinical setting. Thirty neurologically involved patients who ranged in age from 17 to 82 years were tested during their initial evaluation by a physical therapist. Therefore, scores were not analyzed over time (ie, on separate days). Eighteen muscle groups were tested, but not all 18 muscle groups were tested on each patient. Data analysis revealed high Pearson s correlation coefficients (r.84.99) when measurements were taken by 1 therapist with experience in the technique. However, it is important to note that Pearson s correlation coefficient only measures the strength of the relationship between 2 measures and does not indicate the level of agreement between them. Therefore, a high correlation does not necessarily mean the 2 tests agree or that the test has a high degree of reproducibility. 10 Also, the findings from Bohannon s study 9 cannot be generalized to the older population, given the large range of age groups and the use of subjects with neurologic involvement. Thus there is a need to establish test-retest reliability of the hand-held dynamometer in older adults without significant neurologic disease. Although advantages of the hand-held dynamometer are its portability and lack of attachments needed to measure upper and lower muscle groups, there is a major disadvantage. The reliability of the measurement depends on the strength of the examiner and his/her ability to maintain the testing position while holding against the resistance of a patient Depending on the strength of the examiner, he/she may not be able to measure the patient s maximum isometric strength. Consequently, isometric strength scores using a hand-held dynamometer may exhibit a great deal of variability. Reed et al 7 examined the relationship between hand-held isometric strength scores and isokinetic strength scores in 32 healthy elderly individuals 60 years and older. There was a strong association (r.72.85) between the 2 measurement approaches, but hand-held isometric scores were found to be

2 RELIABILITY OF STATIONARY DYNAMOMETER, Ford-Smith 1129 variable. Reed attributed this measurement variability to the lack of stability of the hand-held dynamometer and recommended the use of fixed instrumentation for clinical studies. A hand-held dynamometer that could be fixed in place could be used to assess quantitative changes in the physical performance of elderly individuals participating in strength training programs. This study sought to determine the 1-week test-retest reliability of stationary dynamometer scores in the measurement of lower extremity muscle strength in community-dwelling older adults. A second purpose was to determine the reliability of combining measurements taken from the right and left lower limbs into 1 composite score. The composite score would simplify the analysis, reporting, and interpretation of outcomes associated with exercise trials. METHODS Subjects A convenience sample of 25 volunteers (17 women, 8 men) participated in this study. Subjects had to be at least 70 years of age (range, 70 87yr; mean standard deviation [SD], yr) community-dwelling, mentally intact (Mini-Mental State Exam 14 scores 23), ambulatory without a quad cane or walker, and not have a hip or knee replacement. Subjects also had to be without progressive neurologic disorders, and severe cardiovascular or musculoskeletal disease. Most of the subjects were white (84%), college educated (68%), and walked without a straight cane (96%). One subject reported using a straight cane occasionally. More than half of the subjects reported walking a mile at least 3 times a week (68%). Eight subjects had reported falling once in the past year (32%) and 6 subjects had fallen twice (24%). Instrumentation Force was measured using the AccuForce II Digital Force Gage a attached to a portable steel frame designed by the Department of Biomedical Engineering at Virginia Commonwealth University, Medical College of Virginia Campus (fig 1). The frame was constructed with a moveable arm to adjust for limb length differences, a rotating disc to change dynamometer position, and a braking mechanism to hold the frame in place during an isometric contraction. The frame can accept up to 330kg of force with the brakes locked on a carpeted surface. The examiner can easily reposition the frame and dynamometer to allow for different muscle testing positions. Procedure All subjects signed an institutionally approved consent form and completed a comprehensive history and physical examination with a gerontologic nurse practitioner to determine if they met the inclusion criteria. Isometric force measurements were taken bilaterally for the flexor and extensor muscle groups of the ankle, knee, and hip joints. All subjects were tested on 2 separate occasions, 1 week apart, by the same physical therapist. Most subjects were tested at a similar time of day (eg, late morning or early afternoon). Each muscle group was tested for 3 trials. The therapist verbally reported each peak reading in kilograms to a research nurse who recorded it on a data collection form. Initially, all subjects were given verbal instructions in the motion they were to perform at a particular joint, then the therapist manually guided the joint through the motion. Subjects were then asked to perform the motion and push against the gauge pad as hard as they could when given the instruction: ready, push. Subjects performed an isometric contraction and Fig 1. AccuForce II Digital Force Gage attached to a portable steel frame with movable arm and rotating disc and braking mechanism. gradually increased their force over a 3-second count, and then were told to relax. The rest between trials was as long as it took to record the peak score from the digital readout and to reset the force gauge, approximately 30 seconds. Subjects were initially measured in the supine position for ankle plantarflexion, then moved to sitting for measurement of the remaining muscle groups. Muscle testing order was chosen based on gauge positioning, beginning with ankle plantarflexion, then knee extension, ankle dorsiflexion, knee flexion, hip extension, and hip flexion following the procedure described below. Ankle plantarflexion. Subjects were asked to lay supine on the treatment table with their ankles over the edge of the table. The ankle tested was passively placed in neutral position, and the force gauge pad was placed in contact with the plantar surface of the foot at the level of the metatarsal heads. All of the remaining muscle groups were tested with the subject seated on the end of the treatment table. The back was supported with a portable backboard (fig 2) that was held in place by weights. The subject was strapped to the treatment table at the waist and to the back board by a strap around the chest to promote upright posture. All subjects were instructed to keep their back straight, with hands placed in their lap throughout the testing. Ankle dorsiflexion. To measure the force produced during ankle dorsiflexion, the force gauge pad was adjusted to contact

3 1130 RELIABILITY OF STATIONARY DYNAMOMETER, Ford-Smith Knee extension. Quadriceps force was measured with the force gauge pad placed in contact with the skin overlying the anterior tibial shaft 2 inches proximal to the lateral malleolus. A 1-inch towel roll was used to provide padding to this area while the subject pushed against the gauge pad. Knee flexion. Hamstring force was measured with the force gauge pad placed in contact with the posterior leg 2 inches proximal to the lateral malleolus. Hip flexion. The hip flexors were measured with the force gauge pad placed in contact with the anterior thigh 2 inches from the proximal end of the patella. Data Analysis A peak force score was obtained for each trial and each muscle group. The mean of the peak force scores of the 3 trials for each muscle group were used in the data analysis. Means were calculated for each muscle group for both right and left limbs separately. The intraclass correlation coefficients (ICC, 3, 1) 15 and the 90% confidence intervals (CIs) were determined for the individual scores. The right and left lower limb scores were combined to determine a mean composite score for each muscle group. To determine the reliability of the composite scores for the knee, hip, and ankle flexion and extension variables, ICC (3, 1) 15 were estimated along with 90% CIs. The composite scores were analyzed separately for each muscle group to determine the mean test-retest peak scores by gender. Fig 2. Subject seated against portable backboard with waist and chest straps the dorsum of the foot over the shafts of the metatarsal bones. After placing the ankle in 10 of plantarflexion, the subject was asked to push up against the pad. Hip extension. Hip extension force was measured by lifting the leg off the table and placing the force gauge under the thigh so that the pad was just proximal to the popliteal fossa. The leg was passively lowered onto the pad and the command was given to push. Before the subject started pushing, the force gauge was set at zero. The knee extensors, knee flexors, and hip flexor muscle groups were measured with the subject s knee flexed to 90 as determined by a universal goniometer. RESULTS Table 1 presents the test and retest peak isometric force production scores for all subjects. The scores have been presented for each limb, as well as composite scores for both lower limbs. Dynamometer scores varied little between the right and left limbs during the test or retest sessions. Right and left quadriceps force production (knee extension) was the highest, with hamstring performance (knee flexion) exhibiting the lowest average force scores. Ankle dorsiflexion strength was weaker than ankle plantarflexion strength with scores ranging from kg to kg for plantarflexion and kg to kg for dorsiflexion. Subjects showed higher retest scores throughout a majority of muscle groups. Table 2 shows the ICCs for the individual mean right and left lower limb scores. The ICCs ranged from.61 to.90. The ICCs for the mean composite scores are presented in table 3; the ICCs ranged from.71 to.91. Using Fleiss s criteria, 16 the individual scores for right hip extension and left plantarflexion exhibited fair to good (ICC ) reliability at.69 and.61, respectively. The composite scores for hip extension and ankle plantarflexion also exhibited fair to good reliability with ICCs of.74 and.71, respectively. The mean scores for ankle dorsiflexion, knee flexion and extension, and hip flexion exhibited excellent (ICC.75) reliability, with ICCs ranging Table 1: Individual and Mean Test-Retest Peak Isometric Force Production Scores (kg) for Left and Right Limbs (n 25) Muscle Group Action Right Force Right Force (Retest) Left Force Left Force (Retest) Score Hip extension Hip flexion Knee extension Knee flexion Ankle plantarflexion Ankle dorsiflexion NOTE. Values are mean SD.

4 RELIABILITY OF STATIONARY DYNAMOMETER, Ford-Smith 1131 Table 2: Reliability ofright and Left Lower Limb Scores Lower Extremity Force ICCs 90% CI Plantarflexion: right mean Plantarflexion: left mean Dorsiflexion: right mean Dorsiflexion: left mean Hip extension: right mean Hip extension: left mean Hip flexion: right mean Hip flexion: left mean Knee extension: right mean Knee extension: left mean Knee flexion: right mean Knee flexion: left mean from.82 to.90 for the individual lower limb scores and.84 to.91 for the composite scores. Men exhibited greater force production capabilities than women in all muscle groups tested (table 4). DISCUSSION The results of this study have provided reliability estimates for individual and composite lower limb force production scores for older adults using a stationary hand-held dynamometer. Our strength scores were generally found to exhibit excellent reliability, however, the scores differed from that of other researchers. A review of the literature determined that measurement procedures, instrumentation, data analysis, and sample characteristics vary extensively. For example, Andrews et al 17 studied asymptomatic older adults to determine normative values for isometric force production using a hand-held dynamometer. They examined 8 upper limb and 5 lower limb muscle actions. All of their measurements were taken with the subjects in the supine position except for knee flexion and extension, which were measured in the sitting position. All of our measurements were taken in sitting except for ankle plantarflexion, which was measured in supine. Andrews 17 reported higher strength scores for ankle dorsiflexion and knee flexion and extension, whereas scores for hip flexion were lower than those obtained in this study. Bohannon 9 also examined subjects in the supine position, but used a wide range of ages and the subjects were neurologically impaired. Krebs et al 18 studied 120 community-dwelling older adults (mean age, 74.3yr) to determine if there was a relationship between lower limb strength and gait stability. They measured hip abduction and knee extension in sitting and hip extension in standing. Although the population was similar to ours, they reported lower strength scores in both hip and knee extension. Hip abduction was not measured in this study. Jette et al 19 used a hand-held dynamometer to obtain baseline and follow-up strength scores for 215 older adults who participated in a home-based resistance training program. They used the same testing procedures as Krebs, 18 thus reporting lower strength scores in hip and knee extension than generated by our subjects. In general, most subjects in our study showed higher strength scores during the retest session than during the first testing session. This could be because of familiarity with the test and the testing procedures during the second session. Frontera et al 2 found that mean peak torque scores for 45- to 78-year-old individuals were significantly higher for the second test than for the first test, suggesting that older adults may need 2 testing sessions to determine maximum force production scores. Men showed the capacity to produce more force than women in all muscle groups tested, which is consistent with the findings of other researchers. 20,21 Therefore, we found it necessary to report mean strength scores by gender. When both gender s strength scores are combined, it may limit the clinical usefulness of those scores. Our results agree with the findings of others that ankle dorsiflexion strength is less than ankle plantarflexion strength. 7 This difference is not surprising when considering that the cross-sectional area of the gastrocsoleus is greater than that of the anterior tibialis. Research has demonstrated a relationship between muscle cross-sectional area and force production. 22 The gastrocsoleus has a larger cross-sectional area, therefore it should produce more force. Also, limitations in dorsiflexion range of motion (ROM) could have hindered force production capabilities. All subjects moved into dorsiflexion from a position of 10 of plantarflexion. However, some subjects showed limited active ROM to neutral or 5 less than the neutral position when the force production was measured. Limited motion excursion could decrease the amount of force one can produce. As previously, noted dynamometer scores are influenced by the examiner If the examiner is unable to stabilize the hand-held dynamometer against the limb during a muscle contraction, then the magnitude of the strength measurement will be diminished. During a pilot study with 5 subjects, using a hand-held dynamometer, the examiner was unable to maintain the dynamometer position against the subject s limb. This occurred several times while measuring the large muscle groups, particularly with the male subjects. It was evident that there would be situations when the examiner would not be able to stabilize the limb and obtain maximum strength scores. Therefore, we elected to have a frame fabricated to stabilize the dynamometer during a maximum contraction. This worked well with a padded carpet placed under the frame. Subsequently, we have tested over 300 subjects, and have not had any situations in which the dynamometer could not be stabilized. A limitation of the frame is that it is portable within the clinical environment but would not be easily transported to other settings (eg, private home, fitness center) in the community because of its weight. However, elderly adults with pathology may not have the strength capabilities of community-dwelling older adults and may not need the additional stabilization the frame provides to obtain accurate strength scores. CONCLUSION The stationary dynamometer is a reliable tool to determine lower limb muscle force production in elderly adults. It is Table 3: Reliability of Dynamometer Scores ofright and Left Lower Limbs (n 25) Muscle Group Action ICCs 90% CI Hip extension Hip flexion Knee extension Knee flexion Ankle plantarflexion Ankle dorsiflexion

5 1132 RELIABILITY OF STATIONARY DYNAMOMETER, Ford-Smith Muscle Group Action Table 4: Mean Test-Retest Peak Isometric Force Production Scores (kg) for Each Gender Test Scores Men (n 8) Women (n 17) Retest Scores Test Scores Retest Scores Hip extension * Hip flexion Knee extension Knee flexion Ankle plantarflexion Ankle dorsiflexion NOTE. Values are mean SD. * n 16. inexpensive, portable, and accessible to a large number of clients. Combined lower limb scores exhibited excellent reliability, therefore using a composite score to analyze data and report outcomes would be advantageous. Further research is needed to compare the strength capabilities of older adults with pathology to our community-dwelling elderly. References 1. Hopp JF. Effects of age and resistance training on skeletal muscle: a review. Phys Ther 1993;73: Frontera WR, Hughes VA, Dallal GE, Evans WJ. Reliability of isokinetic muscle strength testing in 45- to 78-year-old men and women. Arch Phys Med Rehabil 1993;74: Wolfson L, Judge J, Whipple R, King M. Strength is a major factor in balance, gait, and the occurrence of falls. J Gerontol A Biol Sci Med Sci 1995;50: Rothstein JM, Lamb RL, Mayhew TP. Clinical uses of isokinetic measurements. Phys Ther 1987;67: Csuka M, McCarty DJ. Simple method for measurement of lower extremity muscle strength. Am J Med 1985;78: Fleming BE, Wilson DR, Pendergast DR. A portable, easily performed muscle power test and its association with falls by elderly persons. Arch Phys Med Rehabil 1991;72: Reed RL, Den Hartog R, Yochum K, Pearlmutter L, Ruttinger AC, Mooradian AD. A comparison of hand-held isometric strength measurement with isokinetic muscle strength measurement in the elderly. J Am Geriatr Soc 1993;41: Topp R, Mikesky AE. Reliability of isometric and isokinetic evaluations of ankle dorsi/plantar strength among older adults. Isokinet Exerc Sci 1994;4: Bohannon RW. Test-retest reliability of hand-held dynamometry during a single session of strength assessment. Phys Ther 1986; 66: Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986; 1: Wikholm JB, Bohannon RW. Hand-held dynamometer measurements: tester strength makes a difference. J Orthop Sports Phys Ther 1991;13: Byl NN, Richards S, Asturias J. Intrarater and interrater reliability of strength measurements of the biceps and deltoid using a hand held dynamometer. J Orthop Sports Phys Ther 1988;9: Stratford PW, Balsor BE. A comparison of make and break tests using a hand-held dynamometer and the kin-com. J Orthop Sports Phys Ther 1994;19: Folstein MF, Folstein SE, McHugh PR. Mini-mental state. A practical method of grading the cognitive state of patients for the clinician. J Psychiatr Res 1975;12: Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;36: Fleiss JL. The design and analysis of clinical experiments. New York: Wiley; p Andrews AW, Thomas MW, Bohannon RW. Normative values for isometric muscle force measurements obtained with hand-held dynamometers. Phys Ther 1996;76: Krebs DE, Jette AM, Assmann SF. Moderate exercise improves gait stability in disabled elders. Arch Phys Med Rehabil 1998;79: Jette AM, Lachman M, Giorgetti MM, Assmann SF, Harris BA, Levenson C, et al. Exercise it s never too late: the strong for life program. Am J Public Health 1999;89: Keating JL, Matyas TA. The influence of subject and test design on dynamometric measurements of extremity muscles. Phys Ther 1996;76: Rice CL, Cunningham DA, Paterson DH, Rechnitzer PA. Strength in an elderly population. Arch Phys Med Rehabil 1989;70: Bruce SA, Phillips, SK, Woledge RC. Interpreting the relation between force and cross-sectional area in human muscle. Med Sci Sports Exerc 1997;29: Supplier a. Ametek: Mansfield & Green Div, 8600 Somerset Dr, Largo, FL