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Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01. Published in final edited form as: Arthritis Rheumatol. 2015 December ; 67(12): 3166–3173. doi:10.1002/art.39336.
Muscle power is an independent determinant of pain and quality of life in knee osteoarthritis Kieran F. Reid, PhD, MPH1, Lori Lyn Price, MS2, William F. Harvey, MD, MSc3, Jeffrey B. Driban, PhD3, Cynthia Hau, MPH1, Roger A. Fielding, PhD1, and Chenchen Wang, MD, MSc3 1Nutrition,
Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
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2The
Institute for Clinical Research and Health Policy Studies, Tufts Clinical and Translational Science Institute Tufts Medical Center, Tufts University, Boston, MA, USA
3Center
for Integrative Medicine and Division of Rheumatology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA, USA
Abstract Objectives—We examined the relationships between lower extremity muscle strength, power and perceived disease severity in participants with knee osteoarthritis (OA). We hypothesized that dynamic leg extensor muscle power would be associated with pain and quality of life in knee OA.
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Methods—We used baseline data from a randomized controlled trial in 190 participants with knee OA (age: 60.2 ± 10.4 yrs; BMI: 32.7 ± 7.2 kg/m2). Knee pain was measured using the Western Ontario and McMaster Osteoarthritis Index and health-related quality of life using the Short Form 36 (SF-36). One-repetition maximum (1RM) strength was assessed using the bilateral leg press and peak muscle power was measured during 5 maximum voluntary velocity repetitions at 40% and 70% of 1RM. Results—In univariate analysis, greater muscle power was significantly associated with pain (r = -0.17, P < 0.02). It was also significantly and positively associated with SF-36 physical component scores (PCS) (r = 0.16, P < 0.05). After adjusting for multiple covariates, muscle power was a significant independent predictor of pain (P ≤ 0.05) and PCS (P ≤ 0.04). However, strength was not an independent determinant of pain or quality of life (P ≥ 0.06).
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Conclusions—Muscle power is an independent determinant of pain and quality of life in knee OA. Compared to strength, muscle power may be a more clinically important measure of muscle
Address for Correspondence: Kieran F. Reid, PhD, MPH. Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA. Phone: 617-556-3081. Fax: 617-556-3083. [email protected]. Conflict of Interests: The authors declare that they have no conflict of interest. Authors Contributions: All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Reid had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: Reid, Price, Harvey, Driban, Fielding, Wang Acquisition of data: Reid, Price, Harvey, Driban, Hau, Analysis and interpretation of data: Reid, Price, Harvey, Driban, Hau, Fielding, Wang Trial registration: ClinicalTrials.gov identifier: NCT01258985
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function within this population. New trials to systematically examine the impact of muscle power training interventions on disease severity in knee OA are particularly warranted. Keywords Knee Osteoarthritis; Muscle Power; Pain; Quality of Life Knee osteoarthritis (OA) causes pain, reduces quality of life, increases healthcare utilization and is a leading cause of long-term disability with advancing age.(1, 2) Despite the high prevalence and significant personal and economic impact of knee OA, the underlying etiology of this disease remains poorly understood.(3, 4) Greater knowledge of the physiological mechanisms underlying knee OA is particularly warranted and may accelerate the development of more effective preventive, therapeutic and rehabilitative interventions.
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As the lower extremity musculature modifies the loading environment at the knee, there has been much interest in the role of muscle parameters in knee OA. Muscle strength, the maximal force generating capacity of skeletal muscle, has been the focus of numerous investigations. However, studies examining muscle strength in the etiology of knee OA have presented inconsistent and controversial findings. For example, several cross-sectional studies of knee OA have shown that reduced muscle strength is associated with increased pain in some (5, 6) but not all studies.(7, 8) In addition, recent longitudinal evidence has demonstrated that baseline muscle strength did not predict the incidence or severity of subsequent knee OA in the Multicenter Osteoarthritis Study cohort over 2.5 years.(9) Similarly, changes in muscle strength were not related to the progression of knee OA over a 2.5 year period in symptomatic patients.(10) Moreover, Sharma et al.(11) suggested that greater muscle strength is associated with higher risk of knee OA progression in symptomatic patients with greater laxity in their knee. Taken together, these studies suggest that alternative, more definitive measures of muscle performance, should be examined in persons with knee OA.
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Skeletal muscle power is now recognized as a muscle parameter uniquely distinct from muscle strength, and is defined as the product of dynamic muscular force and muscle contraction velocity.(12, 13) Muscle power has been demonstrated to decline earlier and more precipitously than muscle strength across the adult life span.(12, 14) In addition, compared to muscle strength, lower extremity muscle power is a superior predictor of performance on functional movement tasks such as walking, rising from a chair, or climbing a flight of stairs among healthy and mobility-limited older adults.(12, 15, 16) Two small studies in knee OA patients have demonstrated that lower extremity power is more predictive of self-reported function than strength,(17) and muscle power is superior than strength in determining medial knee loading and adduction moments.(18) However, no study to date has comprehensively investigated lower extremity muscle power as a potential determinant of disease severity in knee OA or evaluated specific relationships between muscle power, knee pain and quality of life among individuals with symptomatic knee OA. Therefore, the purpose of this investigation was to examine the relationships between lower extremity muscle strength, muscle power, and perceived disease severity in a large study population with established knee OA. We hypothesized that dynamic leg extensor muscle Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
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power would be associated with knee pain and quality of life in participants with symptomatic knee OA.
Materials and Methods Study Design This study is a cross-sectional analysis performed on baseline data collected as part of a single-center, 52-week, randomized controlled comparative effectiveness trial of Tai Chi versus a Physical Therapy regimen in adults with knee OA.(19) Study Participants
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The study recruitment and enrollment criteria have been described previously in greater detail.(19) Briefly, recruitment of participants was conducted in the Greater Boston metropolitan area through advertisements in local print, social media, and from the rheumatology clinic patient database at Tufts Medical Center. Interested respondents received information about the study and answered a brief scripted survey to further determine their eligibility. After meeting the initial study eligibility criteria, all prospective participants attended the clinic for further examination by the study rheumatologist. Individuals were considered eligible if they were aged ≥ 40 years and met American College of Rheumatology criteria for symptomatic knee OA (pain on more than half the days of the past month during at least one of the following activities: walking, going up or down stairs, standing upright, or lying in bed at night)(20) and who have radiographic evidence of tibiofemoral or patellofemoral OA (defined as the presence of a definite osteophyte in the tibiofemoral compartment and/or the patellofemoral compartment, as assessed on standing anterior/posterior and lateral or sunrise views). All participants were required to have a Western Ontario and McMaster Osteoarthritis Index (WOMAC) pain subscale score ≥40 (visual analog version 3.1) on at least one of five questions (range 0 to 100 each, higher indicating more pain) at the baseline evaluation in order to participate. Study exclusion criteria included: 1) prior experience with Tai Chi or other similar types of complementary and alternative medicine, or prior experience with Physical Therapy programs for knee OA within the past year; 2) serious medical conditions including dementia, neurological disease, symptomatic heart or vascular disease (angina, peripheral vascular disease, congestive heart failure), severe hypertension, recent stroke, severe insulin-dependent diabetes mellitus, psychiatric disease, renal disease, liver disease, active cancer or anemia; 3) any intraarticular steroid injections or reconstructive surgery in the three months prior to baseline screening on the most severely affected knee (study knee); 4) any intra-articular hyaluronic acid injections in the six months prior to baseline screening; 5) a Mini-Mental Status examination score < 24;(21) or 6) inability to walk without a cane or other assistive device for the entire duration of the baseline assessments. Prior to enrollment, all participants signed an informed consent form. This study was approved by the Tufts Medical Center and Tufts University Health Sciences Institutional Review Board. Self-Reported Pain and Quality of life (Dependent variables) Knee Pain—Knee pain was measured using the WOMAC pain subscale, a validated, reliable, self-administered visual analogue scale specifically designed to evaluate knee and
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hip OA.(22) The pain subscale includes five items asking about pain at activity or rest within the previous 48 hours and has a score range of 0–500, with higher scores indicating more severe disease.
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Quality of Life—Quality of life was assessed using the Short Form-36 questionnaire (SF-36), a generic measure of health status with well-documented psychometric properties. (23, 24) The SF-36 consists of 36 questions related to eight dimensions of quality of life: limitations in physical activities because of health problems; limitations in social activities because of physical or emotional problems; limitations in usual role activities because of physical health problems; bodily pain; general mental health; limitations in usual role activities because of emotional problems; vitality; and general health perceptions. The questions are transformed into a point scale ranging from 0 to 100, with higher scores indicating better perceived health status. Scores on each of the eight domains were combined to obtain two aggregate scores: the physical component summary (PCS) score and the mental component summary (MCS) score. Lower extremity muscle strength, power and contraction velocity (Independent variables)
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Muscle Strength—Leg extensor muscle strength was quantitatively assessed using a computer-interfaced bilateral Keiser pneumatic leg press apparatus (Leg Press A420, Keiser Corporation, Fresno, CA) using the one-repetition maximum (1RM) technique. Maximal muscle strength was defined as the maximum load that could be moved throughout the full range of motion (ROM) while maintaining proper form.(25) Participants were seated with knees flexed to 90° and hips flexed to approximately 110°. Knee angle was measured using an electrogoniometer (ADInstruments, Colorado Springs, CO). Participants were instructed to perform several warm-up repetitions at minimal resistance to familiarize themselves with the apparatus. Previous studies from our laboratory have demonstrated that warm-up repetitions adequately prepare participants for testing without inducing fatigue.(25, 26) Each participant's ROM was determined during performance of a minimally loaded repetition prior to each test. An ultrasonic system measuring position, and therefore relative motion, aided examiners in establishing a subject's ROM by observing the excursion of a lighted bar on the output screen during performance of the measure with minimal resistance. Starting at a relatively low level, the examiner progressively increased the resistance after each successful repetition until the participant could no longer move the lever arm one time through their full ROM (optimally within 6–8 repetitions). Participants performed the concentric phase, maintained full extension, and performed the eccentric phase of each repetition over approximately 2, 1, and 2 s, respectively. To aid in accurate establishment of the 1RM, the subject's self-perceived level of exertion was also assessed after each successful repetition using the Borg scale.(27) If the subject's rating was ≤15, a rest period of 30–60 s was provided between repetitions. A rest period of 2 min was provided if the subject's rating was ≥15. Muscle Power and Contraction Velocity After measurement of the 1RM, assessment of leg extensor peak muscle power and peak contraction velocity was made after a 5 min rest period. Performance of this multiple attempt peak power test has been previously described and validated.(25) Briefly, each Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
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participant was instructed to complete a total of five repetitions each separated by 30 s as quickly as possible through their full ROM at 40% of the 1RM. External resistance was then raised to 70% of the 1RM and the participant was again instructed to extend their legs as quickly as possible through five repetitions. The highest measured power output and corresponding contraction velocity elicited at 40% and 70% of the 1RM was recorded as the respective measures of peak muscle power and peak contraction velocity. Covariates (Adjustment Variables) Measurement of height and weight were obtained during the initial clinic examination. Total number of medications was obtained via self-report using The Health Assessment Questionnaire (28). An index of depression symptomology was obtained using the Beck Depression inventory.(29)
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Statistical Analysis
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All data were first examined visually and statistically for normality of distribution and values are presented as means ± standard deviation (SD) unless otherwise stated. Significance level was set at P ≤ 0.05. Descriptive statistics were calculated and an independent samples t-test was used to determine baseline differences between males and females. Pearson correlation coefficients were used to assess the degree of association and potential for multicollinearity between variables. A priori, we identified five muscle performance parameters and a list of potential confounding variables. Five separate models were conducted to assess the influence of each of the muscle performance parameters (independent variables) on the dependent variables. The following covariates were chosen and used in all of the multivariable models: age, sex, race, height, weight, number of medications and depressive symptoms. These covariates were selected a priori because of their previously known associations with pain and/or muscle performance. Model assumptions and appropriateness were examined both graphically and analytically, and were adequately met. Because patellofemoral OA is associated with greater levels of lower extremity disability and knee pain, the multivariable regression analyses were also performed in a subset of study participants with radiographic definition of patellofemoral OA. Data were analyzed using SAS statistical software (Version 9.4).
Results
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A total of 1285 individuals completed the initial telephone prescreening questionnaire. From these, a total of 290 potential participants attended the clinic of the Clinical Research Center at Tufts Medical Center to further determine eligibility. Of these, 204 (71%) were eligible after baseline evaluation and randomized to the Tai Chi or a standard physical-therapy regimen. The major reason for ineligibility was the absence of radiographic evidence for knee OA. At baseline, 14 participants did not undergo leg extensor muscle strength and power testing for the following reasons: did not attend exercise testing laboratory (n = 8); felt unsafe (n = 3); refused to attempt test (n = 2); unable to comply with the testing protocol due to high level of abdominal obesity (n =1). Four participants who had a KellgrenLawrence score of zero met eligibility criteria because they had a definite osteophyte in the
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patellofemoral region. Therefore, this study reports data on a total of 190 participants. Baseline characteristics of the study sample are presented in Table 1. Table 2 displays the baseline measures of WOMAC pain, quality of life and measures of muscle performance for males and females. Compared to males, females had significantly higher levels of pain and significantly lower values for all measures of muscle performance evaluated.
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The univariate correlation coefficients between the dependent, independent and potential confounding variables are presented in Table 3. The correlation analyses revealed that WOMAC pain was significantly and inversely associated with all measures of muscle strength, peak muscle power and peak contraction velocity. For PCS, only peak muscle power at high external resistance (70% of 1RM) was significantly associated. No significant correlations were observed between MCS and any measure of muscle strength, power or contraction velocity. Table 4 presents the results of the multiple regression analyses. In separate regression models, peak muscle power evaluated at high external resistance (70% of 1RM), and peak contraction velocity measured at low external resistance (40% of 1RM) were significantly and independently associated with WOMAC pain after adjusting for multiple covariates (all P ≤ 0.05). Muscle strength was not significantly associated with WOMAC pain (P = 0.13). Peak muscle power evaluated at both low and high external resistances were significant independent predictors of PCS score (P = 0.04 and 0.003, respectively). The sensitivity analysis, taking into account presence of patellofemoral OA (n = 130), did not significantly change the overall findings (data not shown).
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Discussion This is the first study to identify relationships between muscle power, knee pain and quality of life in participants with symptomatic knee OA. The major finding of this investigation was that leg extensor muscle power was an independent determinant of knee pain and quality of life in knee OA. Peak muscle contraction velocity at low external resistance was also independently associated with knee pain. Importantly, we were unable to demonstrate that lower extremity muscle strength was a major determinant of disease severity. Our findings suggest that, compared to strength, muscle power is a more definitive measure of muscle performance and may have significant potential as a more influential parameter for understanding the interrelationships between muscle function and disease severity in knee OA.
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A notable observation from the current investigation is that the leg extensor muscle power, contraction velocity and strength levels exhibited in this knee OA population are low when compared to established reference levels from several populations of middle-aged and older adults without symptomatic knee OA.(26) Indeed, the muscle power values in the present study are equivalent to levels generated in a specific group of mobility-limited older adults with a mean age of ∼ 80 years.(26) This suggests that individuals with established knee OA have substantial and accelerated impairments in muscle power. However a direct
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comparison of the age-related differences in muscle power among participants with and without knee OA is needed to further verify this assertion.
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The results of the current investigation extend the findings of several smaller clinical studies that have specifically evaluated the relationships between muscle power and physical function in knee OA.(17, 30) In 39 patients who underwent total knee arthroplasty, compared to knee extensor strength, greater leg extensor muscle power was a superior predictor of performance in fast walking, repeated chair stand, and self-reported WOMAC function.(30) Similarly, in 40 participants with established knee OA, knee extension muscle power, measured isotonically using a dynamometer at low external resistances, was more predictive of WOMAC function than peak isometric muscle strength.(17) Isotonic knee extensor muscle power was also superior than muscle strength in determining medial knee loading and adduction moments during kinematic gait trials in 53 patients with clinical knee OA.(18) In the current study, we incorporated a dynamic, well-validated assessment of leg extensor muscle power within a large population of knee OA participants and demonstrated the novel clinical importance of muscle power as an independent predictor of pain and quality of life in these symptomatic patients.
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Taken together, and consistent with the present study findings, there is now significant emerging evidence implicating muscle power as a critical parameter in the etiology of knee OA pain. Consequently, training interventions specifically designed to target and improve muscle power, which may also reduce disease burden in knee OA, should be examined further. Our findings suggest that, compared to muscle power at low external resistance (40% of 1RM), muscle power generated at high external resistance (70% of 1RM) may be a marginally greater determinant of pain and quality of life in knee OA, Thus, muscle power training at higher external resistances should be examined in knee OA, since an intervention of high intensity power training may portend greater reductions in disease severity or comparatively greater improvements in physical functioning, compared to low resistance power training.(31) To date, two small pilot studies have successfully demonstrated the feasibility of low resistance power training (training performed at 40% of 1RM) for improving muscle power, pain and function in patients with knee OA.(32, 33) However, additional, larger-scale randomized controlled trials of resistance training interventions to improve lower extremity muscle power across a variety of training intensities, and their subsequent impact on pain, quality of life and functional outcomes in knee OA, are necessary.
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There may be several plausible physiological explanations for our overall findings. First, the lower extremity musculature plays an integral role in the stability, loading, proprioception and functional movement of the knee joint.(1, 30) As muscle power reflects the product of muscle force and speed of movement, and is a superior determinant of human locomotion and physical functioning when compared to strength, it is possible that dynamic knee stability may be greatly compromised by muscle power impairments, which contribute more to inadequate control of tibial translation during ambulation, leading to damage, and ultimately, knee pain. Similarly, compared to muscle strength deficits, muscle power impairments may also more critically limit the ability of the musculature to dissipate knee joint loads, thus increasing the risk of articular contact stress, which leads to pain. Second,
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lower limb muscles with impairments in maximal contractile velocity, rather than impairments in muscle force production, may fatigue more rapidly,(34, 35) leading to poor overall neuromuscular control, which could allow pathologic joint movement and painful loading of the articular structures.(36) Third, in the present study we incorporated a dynamic, closed kinetic chain assessment of leg extensor muscle power. The majority of prior studies in knee OA have evaluated muscle performance and disease severity outcomes using isokinetic dynamometry of the knee extensors, an assessment that restricts the evaluation of muscle force to a predetermined velocity.(30) Because important activities of daily living are typically closed kinetic chain tasks consisting of weight-bearing ambulation through various positions at variable velocities, such as walking or rising from a chair, our measure of dynamic leg extensor power represents a more functionally relevant assessment of muscle performance and, consistent with the overall findings from the current investigation, a more clinically important correlate of disease burden in knee OA.
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There are limitations associated with this investigation. The cross-sectional nature of the analysis precludes definitive casual inferences and information on the temporal relationships between knee pain, quality of life and muscle power. We also do not account for other individual differences such as knee alignment and that may account for additional variability in the relationships between disease severity and muscle performance. In addition, the influence of well-established risk factors for knee OA such as adipose mass and distribution, and other physiologic mechanisms that determine muscle performance, such as muscle mass and neural activation, were not specifically assessed in this investigation. Despite these limitations, our study provides important new clinically relevant findings that may accelerate the development of more effective therapeutic and rehabilitative interventions for individuals with knee OA.
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Conclusion This is the first study to comprehensively assess and demonstrate that lower extremity muscle power is an independent determinant of knee pain and quality of life in participants with established knee OA. Compared to traditional measurements of muscle strength, our findings emphasize that muscle power is a more clinically important measure of muscle performance in knee OA. Thus, resistance training interventions specifically designed to improve muscle power, and their associated impact on disease severity, should be systematically examined in persons with symptomatic knee OA.
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This study is supported by the National Institutes of Health (R01 AT00552, 1 K24 AT007323, UL1 RR025752, UL1TR000073 and UL1TR001064). The contents of this manuscript are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health. The investigators are solely responsible for the content of the manuscript and the decision to submit for publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This research was also based upon work supported by the U.S. Department of Agriculture, under agreement No. 58-1950-4-003. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. This research was also supported by the Boston Claude D. Pepper Older Americans Independence Center (1P30AG031679) and the Boston Rehabilitation Outcomes Center Grant (1R24HD065688-01A1).
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References
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1. Litwic A, Edwards MH, Dennison EM, Cooper C. Epidemiology and burden of osteoarthritis. British medical bulletin. 2013; 105:185–99. [PubMed: 23337796] 2. Felson DT, Lawrence RC, Hochberg MC, McAlindon T, Dieppe PA, Minor MA, et al. Osteoarthritis: new insights. Part 2: treatment approaches. Annals of internal medicine. 2000; 133(9):726–37. [PubMed: 11074906] 3. Brooks PM. Impact of osteoarthritis on individuals and society: how much disability? Social consequences and health economic implications. Current opinion in rheumatology. 2002; 14(5): 573–7. [PubMed: 12192258] 4. Brooks PM. The burden of musculoskeletal disease--a global perspective. Clinical rheumatology. 2006; 25(6):778–81. [PubMed: 16609823] 5. Hall MC, Mockett SP, Doherty M. Relative impact of radiographic osteoarthritis and pain on quadriceps strength, proprioception, static postural sway and lower limb function. Annals of the rheumatic diseases. 2006; 65(7):865–70. [PubMed: 16308342] 6. Madsen OR, Bliddal H, Egsmose C, Sylvest J. Isometric and isokinetic quadriceps strength in gonarthrosis; inter-relations between quadriceps strength, walking ability, radiology, subchondral bone density and pain. Clinical rheumatology. 1995; 14(3):308–14. [PubMed: 7641507] 7. Brandt KD, Heilman DK, Slemenda C, Katz BP, Mazzuca SA, Braunstein EM, et al. Quadriceps strength in women with radiographically progressive osteoarthritis of the knee and those with stable radiographic changes. The Journal of rheumatology. 1999; 26(11):2431–7. [PubMed: 10555906] 8. Steultjens MP, Dekker J, van Baar ME, Oostendorp RA, Bijlsma JW. Muscle strength, pain and disability in patients with osteoarthritis. Clinical rehabilitation. 2001; 15(3):331–41. [PubMed: 11386405] 9. Segal NA, Torner JC, Felson DT, Niu J, Sharma L, Lewis CE, et al. Knee extensor strength does not protect against incident knee symptoms at 30 months in the multicenter knee osteoarthritis (MOST) cohort. PM & R: the journal of injury, function, and rehabilitation. 2009; 1(5):459–65. 10. Amin S, Baker K, Niu J, Clancy M, Goggins J, Guermazi A, et al. Quadriceps strength and the risk of cartilage loss and symptom progression in knee osteoarthritis. Arthritis and rheumatism. 2009; 60(1):189–98. [PubMed: 19116936] 11. Sharma L, Dunlop DD, Cahue S, Song J, Hayes KW. Quadriceps strength and osteoarthritis progression in malaligned and lax knees. Annals of internal medicine. 2003; 138(8):613–9. [PubMed: 12693882] 12. Reid KF, Fielding RA. Skeletal muscle power: a critical determinant of physical functioning in older adults. Exerc Sport Sci Rev. 2012; 40(1):4–12. [PubMed: 22016147] 13. Bassey EJ, Fiatarone MA, O'Neill EF, Kelly M, Evans WJ, Lipsitz LA. Leg extensor power and functional performance in very old men and women. Clin Sci (Lond). 1992; 82(3):321–7. [PubMed: 1312417] 14. Metter EJ, Conwit R, Tobin J, Fozard JL. Age-associated loss of power and strength in the upper extremities in women and men. The journals of gerontology Series A, Biological sciences and medical sciences. 1997; 52(5):B267–76. 15. Bean JF, Leveille SG, Kiely DK, Bandinelli S, Guralnik JM, Ferrucci L. A comparison of leg power and leg strength within the InCHIANTI study: which influences mobility more? J Gerontol A Biol Sci Med Sci. 2003; 58(8):728–33. [PubMed: 12902531] 16. Foldvari M, Clark M, Laviolette LC, Bernstein MA, Kaliton D, Castaneda C, et al. Association of muscle power with functional status in community-dwelling elderly women. J Gerontol A Biol Sci Med Sci. 2000; 55(4):M192–9. [PubMed: 10811148] 17. Berger MJ, McKenzie CA, Chess DG, Goela A, Doherty TJ. Quadriceps neuromuscular function and self-reported functional ability in knee osteoarthritis. Journal of applied physiology. 2012; 113(2):255–62. [PubMed: 22604883] 18. Calder KM, Acker SM, Arora N, Beattie KA, Callaghan JP, Adachi JD, et al. Knee power is an important parameter in understanding medial knee joint load in knee osteoarthritis. Arthritis care & research. 2014; 66(5):687–94. [PubMed: 24920175]
Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
Reid et al.
Page 10
Author Manuscript Author Manuscript Author Manuscript Author Manuscript
19. Wang C, Iversen MD, McAlindon T, Harvey WF, Wong JB, Fielding RA, et al. Assessing the comparative effectiveness of Tai Chi versus physical therapy for knee osteoarthritis: design and rationale for a randomized trial. BMC complementary and alternative medicine. 2014; 14:333. [PubMed: 25199526] 20. Altman R, Asch E, Bloch D, Bole G, Borenstein D, Brandt K, et al. Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Arthritis and rheumatism. 1986; 29(8):1039–49. [PubMed: 3741515] 21. Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975; 12(3):189–98. [PubMed: 1202204] 22. Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. The Journal of rheumatology. 1988; 15(12):1833–40. [PubMed: 3068365] 23. Ware JE Jr, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Medical care. 1992; 30(6):473–83. [PubMed: 1593914] 24. McHorney CA, Ware JE Jr, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Medical care. 1993; 31(3):247–63. [PubMed: 8450681] 25. Callahan D, Phillips E, Carabello R, Frontera WR, Fielding RA. Assessment of lower extremity muscle power in functionally-limited elders. Aging Clin Exp Res. 2007; 19(3):194–9. [PubMed: 17607086] 26. Reid KF, Doros G, Clark DJ, Patten C, Carabello RJ, Cloutier GJ, et al. Muscle power failure in mobility-limited older adults: preserved single fiber function despite lower whole muscle size, quality and rate of neuromuscular activation. European journal of applied physiology. 2012; 112(6):2289–301. [PubMed: 22005960] 27. Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med. 1970; 2(2):92– 8. [PubMed: 5523831] 28. Bruce B, Fries JF. The Health Assessment Questionnaire (HAQ). Clinical and experimental rheumatology. 2005; 23(5 Suppl 39):S14–8. [PubMed: 16273780] 29. Beck AT, Ward CH, Mendelson M, Mock J, Erbaugh J. An inventory for measuring depression. Archives of general psychiatry. 1961; 4:561–71. [PubMed: 13688369] 30. Aalund PK, Larsen K, Hansen TB, Bandholm T. Normalized knee-extension strength or leg-press power after fast-track total knee arthroplasty: which measure is most closely associated with performance-based and self-reported function? Archives of physical medicine and rehabilitation. 2013; 94(2):384–90. [PubMed: 23085377] 31. Reid KF, Martin KI, Doros G, Clark DJ, Hau C, Patten C, et al. Comparative Effects of Light or Heavy Resistance Power Training for Improving Lower Extremity Power and Physical Performance in Mobility-Limited Older Adults. The journals of gerontology Series A, Biological sciences and medical sciences. 2014 32. Sayers SP, Gibson K, Cook CR. Effect of high-speed power training on muscle performance, function, and pain in older adults with knee osteoarthritis: a pilot investigation. Arthritis care & research. 2012; 64(1):46–53. [PubMed: 22012877] 33. Pelletier D, Gingras-Hill C, Boissy P. Power training in patients with knee osteoarthritis: a pilot study on feasibility and efficacy. Physiotherapy Canada Physiotherapie Canada. 2013; 65(2):176– 82. [PubMed: 24403682] 34. Petrella JK, Kim JS, Tuggle SC, Hall SR, Bamman MM. Age differences in knee extension power, contractile velocity, and fatigability. J Appl Physiol. 2005; 98(1):211–20. [PubMed: 15347625] 35. Pojednic RM, Clark DJ, Patten C, Reid K, Phillips EM, Fielding RA. The specific contributions of force and velocity to muscle power in older adults. Experimental gerontology. 2012; 47(8):608– 13. [PubMed: 22626972] 36. Segal NA, Glass NA. Is quadriceps muscle weakness a risk factor for incident or progressive knee osteoarthritis? The Physician and sportsmedicine. 2011; 39(4):44–50. [PubMed: 22293767]
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Table 1
Baseline Characteristics (n = 190)
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Variables
Mean ± SD
Age, yrs (min – max)
60.2 ± 10.4 (41 – 90)
Body Weight, kg
90.8 ± 21.0
Height, cm
166.4 ± 9.0
BMI, kg/m2
32.7 ± 7.2
Duration of pain, yrs
8.1 ± 9.2
Beck Depression Score
7.6 ± 8.8
Medications
4.4 ± 3.0
Conditions, n (%)
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Hypertension
93 (49.0)
Diabetes
34 (17.9)
Heart Disease
15 (7.9)
Kellgren-Lawrence Grade, n (%)* 0
4 (2.2)
1
10 (5.4)
2
70 (37.8)
3
65 (35.1)
4
36 (19.5)
Sex, n (%) Male
58 (30.5)
Female
132 (69.5)
Race, n (%)
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White
104 (54.7)
Black or African American
64 (33.7)
More than one race
8 (4.2)
Asian
5 (2.6)
American Indian or Alaskan native
4 (2.1)
Other/unknown
5 (2.6)
*
Kellgren-Lawrence grades were unavailable for 5 participants
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Table 2
Knee Pain, Quality of Life and Muscle Performance Characteristics (n = 190)
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Variables
Male (n = 58)
Female (n = 132)
P value
WOMAC pain
227.2 ± 91.2
261.6 ± 101.6
0.03
37.3 ± 8.6
36.7 ± 9.4
0.72
SF-36 physical component score SF-36 mental component score
52.8 ± 10.4
52.5 ± 8.7
0.86
1RM strength, newtons
1338.5 ± 389.0
835.6 ± 302.0
Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01. Published in final edited form as: Arthritis Rheumatol. 2015 December ; 67(12): 3166–3173. doi:10.1002/art.39336.
Muscle power is an independent determinant of pain and quality of life in knee osteoarthritis Kieran F. Reid, PhD, MPH1, Lori Lyn Price, MS2, William F. Harvey, MD, MSc3, Jeffrey B. Driban, PhD3, Cynthia Hau, MPH1, Roger A. Fielding, PhD1, and Chenchen Wang, MD, MSc3 1Nutrition,
Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
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2The
Institute for Clinical Research and Health Policy Studies, Tufts Clinical and Translational Science Institute Tufts Medical Center, Tufts University, Boston, MA, USA
3Center
for Integrative Medicine and Division of Rheumatology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA, USA
Abstract Objectives—We examined the relationships between lower extremity muscle strength, power and perceived disease severity in participants with knee osteoarthritis (OA). We hypothesized that dynamic leg extensor muscle power would be associated with pain and quality of life in knee OA.
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Methods—We used baseline data from a randomized controlled trial in 190 participants with knee OA (age: 60.2 ± 10.4 yrs; BMI: 32.7 ± 7.2 kg/m2). Knee pain was measured using the Western Ontario and McMaster Osteoarthritis Index and health-related quality of life using the Short Form 36 (SF-36). One-repetition maximum (1RM) strength was assessed using the bilateral leg press and peak muscle power was measured during 5 maximum voluntary velocity repetitions at 40% and 70% of 1RM. Results—In univariate analysis, greater muscle power was significantly associated with pain (r = -0.17, P < 0.02). It was also significantly and positively associated with SF-36 physical component scores (PCS) (r = 0.16, P < 0.05). After adjusting for multiple covariates, muscle power was a significant independent predictor of pain (P ≤ 0.05) and PCS (P ≤ 0.04). However, strength was not an independent determinant of pain or quality of life (P ≥ 0.06).
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Conclusions—Muscle power is an independent determinant of pain and quality of life in knee OA. Compared to strength, muscle power may be a more clinically important measure of muscle
Address for Correspondence: Kieran F. Reid, PhD, MPH. Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA. Phone: 617-556-3081. Fax: 617-556-3083. [email protected]. Conflict of Interests: The authors declare that they have no conflict of interest. Authors Contributions: All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Reid had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: Reid, Price, Harvey, Driban, Fielding, Wang Acquisition of data: Reid, Price, Harvey, Driban, Hau, Analysis and interpretation of data: Reid, Price, Harvey, Driban, Hau, Fielding, Wang Trial registration: ClinicalTrials.gov identifier: NCT01258985
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function within this population. New trials to systematically examine the impact of muscle power training interventions on disease severity in knee OA are particularly warranted. Keywords Knee Osteoarthritis; Muscle Power; Pain; Quality of Life Knee osteoarthritis (OA) causes pain, reduces quality of life, increases healthcare utilization and is a leading cause of long-term disability with advancing age.(1, 2) Despite the high prevalence and significant personal and economic impact of knee OA, the underlying etiology of this disease remains poorly understood.(3, 4) Greater knowledge of the physiological mechanisms underlying knee OA is particularly warranted and may accelerate the development of more effective preventive, therapeutic and rehabilitative interventions.
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As the lower extremity musculature modifies the loading environment at the knee, there has been much interest in the role of muscle parameters in knee OA. Muscle strength, the maximal force generating capacity of skeletal muscle, has been the focus of numerous investigations. However, studies examining muscle strength in the etiology of knee OA have presented inconsistent and controversial findings. For example, several cross-sectional studies of knee OA have shown that reduced muscle strength is associated with increased pain in some (5, 6) but not all studies.(7, 8) In addition, recent longitudinal evidence has demonstrated that baseline muscle strength did not predict the incidence or severity of subsequent knee OA in the Multicenter Osteoarthritis Study cohort over 2.5 years.(9) Similarly, changes in muscle strength were not related to the progression of knee OA over a 2.5 year period in symptomatic patients.(10) Moreover, Sharma et al.(11) suggested that greater muscle strength is associated with higher risk of knee OA progression in symptomatic patients with greater laxity in their knee. Taken together, these studies suggest that alternative, more definitive measures of muscle performance, should be examined in persons with knee OA.
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Skeletal muscle power is now recognized as a muscle parameter uniquely distinct from muscle strength, and is defined as the product of dynamic muscular force and muscle contraction velocity.(12, 13) Muscle power has been demonstrated to decline earlier and more precipitously than muscle strength across the adult life span.(12, 14) In addition, compared to muscle strength, lower extremity muscle power is a superior predictor of performance on functional movement tasks such as walking, rising from a chair, or climbing a flight of stairs among healthy and mobility-limited older adults.(12, 15, 16) Two small studies in knee OA patients have demonstrated that lower extremity power is more predictive of self-reported function than strength,(17) and muscle power is superior than strength in determining medial knee loading and adduction moments.(18) However, no study to date has comprehensively investigated lower extremity muscle power as a potential determinant of disease severity in knee OA or evaluated specific relationships between muscle power, knee pain and quality of life among individuals with symptomatic knee OA. Therefore, the purpose of this investigation was to examine the relationships between lower extremity muscle strength, muscle power, and perceived disease severity in a large study population with established knee OA. We hypothesized that dynamic leg extensor muscle Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
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power would be associated with knee pain and quality of life in participants with symptomatic knee OA.
Materials and Methods Study Design This study is a cross-sectional analysis performed on baseline data collected as part of a single-center, 52-week, randomized controlled comparative effectiveness trial of Tai Chi versus a Physical Therapy regimen in adults with knee OA.(19) Study Participants
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The study recruitment and enrollment criteria have been described previously in greater detail.(19) Briefly, recruitment of participants was conducted in the Greater Boston metropolitan area through advertisements in local print, social media, and from the rheumatology clinic patient database at Tufts Medical Center. Interested respondents received information about the study and answered a brief scripted survey to further determine their eligibility. After meeting the initial study eligibility criteria, all prospective participants attended the clinic for further examination by the study rheumatologist. Individuals were considered eligible if they were aged ≥ 40 years and met American College of Rheumatology criteria for symptomatic knee OA (pain on more than half the days of the past month during at least one of the following activities: walking, going up or down stairs, standing upright, or lying in bed at night)(20) and who have radiographic evidence of tibiofemoral or patellofemoral OA (defined as the presence of a definite osteophyte in the tibiofemoral compartment and/or the patellofemoral compartment, as assessed on standing anterior/posterior and lateral or sunrise views). All participants were required to have a Western Ontario and McMaster Osteoarthritis Index (WOMAC) pain subscale score ≥40 (visual analog version 3.1) on at least one of five questions (range 0 to 100 each, higher indicating more pain) at the baseline evaluation in order to participate. Study exclusion criteria included: 1) prior experience with Tai Chi or other similar types of complementary and alternative medicine, or prior experience with Physical Therapy programs for knee OA within the past year; 2) serious medical conditions including dementia, neurological disease, symptomatic heart or vascular disease (angina, peripheral vascular disease, congestive heart failure), severe hypertension, recent stroke, severe insulin-dependent diabetes mellitus, psychiatric disease, renal disease, liver disease, active cancer or anemia; 3) any intraarticular steroid injections or reconstructive surgery in the three months prior to baseline screening on the most severely affected knee (study knee); 4) any intra-articular hyaluronic acid injections in the six months prior to baseline screening; 5) a Mini-Mental Status examination score < 24;(21) or 6) inability to walk without a cane or other assistive device for the entire duration of the baseline assessments. Prior to enrollment, all participants signed an informed consent form. This study was approved by the Tufts Medical Center and Tufts University Health Sciences Institutional Review Board. Self-Reported Pain and Quality of life (Dependent variables) Knee Pain—Knee pain was measured using the WOMAC pain subscale, a validated, reliable, self-administered visual analogue scale specifically designed to evaluate knee and
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hip OA.(22) The pain subscale includes five items asking about pain at activity or rest within the previous 48 hours and has a score range of 0–500, with higher scores indicating more severe disease.
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Quality of Life—Quality of life was assessed using the Short Form-36 questionnaire (SF-36), a generic measure of health status with well-documented psychometric properties. (23, 24) The SF-36 consists of 36 questions related to eight dimensions of quality of life: limitations in physical activities because of health problems; limitations in social activities because of physical or emotional problems; limitations in usual role activities because of physical health problems; bodily pain; general mental health; limitations in usual role activities because of emotional problems; vitality; and general health perceptions. The questions are transformed into a point scale ranging from 0 to 100, with higher scores indicating better perceived health status. Scores on each of the eight domains were combined to obtain two aggregate scores: the physical component summary (PCS) score and the mental component summary (MCS) score. Lower extremity muscle strength, power and contraction velocity (Independent variables)
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Muscle Strength—Leg extensor muscle strength was quantitatively assessed using a computer-interfaced bilateral Keiser pneumatic leg press apparatus (Leg Press A420, Keiser Corporation, Fresno, CA) using the one-repetition maximum (1RM) technique. Maximal muscle strength was defined as the maximum load that could be moved throughout the full range of motion (ROM) while maintaining proper form.(25) Participants were seated with knees flexed to 90° and hips flexed to approximately 110°. Knee angle was measured using an electrogoniometer (ADInstruments, Colorado Springs, CO). Participants were instructed to perform several warm-up repetitions at minimal resistance to familiarize themselves with the apparatus. Previous studies from our laboratory have demonstrated that warm-up repetitions adequately prepare participants for testing without inducing fatigue.(25, 26) Each participant's ROM was determined during performance of a minimally loaded repetition prior to each test. An ultrasonic system measuring position, and therefore relative motion, aided examiners in establishing a subject's ROM by observing the excursion of a lighted bar on the output screen during performance of the measure with minimal resistance. Starting at a relatively low level, the examiner progressively increased the resistance after each successful repetition until the participant could no longer move the lever arm one time through their full ROM (optimally within 6–8 repetitions). Participants performed the concentric phase, maintained full extension, and performed the eccentric phase of each repetition over approximately 2, 1, and 2 s, respectively. To aid in accurate establishment of the 1RM, the subject's self-perceived level of exertion was also assessed after each successful repetition using the Borg scale.(27) If the subject's rating was ≤15, a rest period of 30–60 s was provided between repetitions. A rest period of 2 min was provided if the subject's rating was ≥15. Muscle Power and Contraction Velocity After measurement of the 1RM, assessment of leg extensor peak muscle power and peak contraction velocity was made after a 5 min rest period. Performance of this multiple attempt peak power test has been previously described and validated.(25) Briefly, each Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
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participant was instructed to complete a total of five repetitions each separated by 30 s as quickly as possible through their full ROM at 40% of the 1RM. External resistance was then raised to 70% of the 1RM and the participant was again instructed to extend their legs as quickly as possible through five repetitions. The highest measured power output and corresponding contraction velocity elicited at 40% and 70% of the 1RM was recorded as the respective measures of peak muscle power and peak contraction velocity. Covariates (Adjustment Variables) Measurement of height and weight were obtained during the initial clinic examination. Total number of medications was obtained via self-report using The Health Assessment Questionnaire (28). An index of depression symptomology was obtained using the Beck Depression inventory.(29)
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Statistical Analysis
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All data were first examined visually and statistically for normality of distribution and values are presented as means ± standard deviation (SD) unless otherwise stated. Significance level was set at P ≤ 0.05. Descriptive statistics were calculated and an independent samples t-test was used to determine baseline differences between males and females. Pearson correlation coefficients were used to assess the degree of association and potential for multicollinearity between variables. A priori, we identified five muscle performance parameters and a list of potential confounding variables. Five separate models were conducted to assess the influence of each of the muscle performance parameters (independent variables) on the dependent variables. The following covariates were chosen and used in all of the multivariable models: age, sex, race, height, weight, number of medications and depressive symptoms. These covariates were selected a priori because of their previously known associations with pain and/or muscle performance. Model assumptions and appropriateness were examined both graphically and analytically, and were adequately met. Because patellofemoral OA is associated with greater levels of lower extremity disability and knee pain, the multivariable regression analyses were also performed in a subset of study participants with radiographic definition of patellofemoral OA. Data were analyzed using SAS statistical software (Version 9.4).
Results
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A total of 1285 individuals completed the initial telephone prescreening questionnaire. From these, a total of 290 potential participants attended the clinic of the Clinical Research Center at Tufts Medical Center to further determine eligibility. Of these, 204 (71%) were eligible after baseline evaluation and randomized to the Tai Chi or a standard physical-therapy regimen. The major reason for ineligibility was the absence of radiographic evidence for knee OA. At baseline, 14 participants did not undergo leg extensor muscle strength and power testing for the following reasons: did not attend exercise testing laboratory (n = 8); felt unsafe (n = 3); refused to attempt test (n = 2); unable to comply with the testing protocol due to high level of abdominal obesity (n =1). Four participants who had a KellgrenLawrence score of zero met eligibility criteria because they had a definite osteophyte in the
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patellofemoral region. Therefore, this study reports data on a total of 190 participants. Baseline characteristics of the study sample are presented in Table 1. Table 2 displays the baseline measures of WOMAC pain, quality of life and measures of muscle performance for males and females. Compared to males, females had significantly higher levels of pain and significantly lower values for all measures of muscle performance evaluated.
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The univariate correlation coefficients between the dependent, independent and potential confounding variables are presented in Table 3. The correlation analyses revealed that WOMAC pain was significantly and inversely associated with all measures of muscle strength, peak muscle power and peak contraction velocity. For PCS, only peak muscle power at high external resistance (70% of 1RM) was significantly associated. No significant correlations were observed between MCS and any measure of muscle strength, power or contraction velocity. Table 4 presents the results of the multiple regression analyses. In separate regression models, peak muscle power evaluated at high external resistance (70% of 1RM), and peak contraction velocity measured at low external resistance (40% of 1RM) were significantly and independently associated with WOMAC pain after adjusting for multiple covariates (all P ≤ 0.05). Muscle strength was not significantly associated with WOMAC pain (P = 0.13). Peak muscle power evaluated at both low and high external resistances were significant independent predictors of PCS score (P = 0.04 and 0.003, respectively). The sensitivity analysis, taking into account presence of patellofemoral OA (n = 130), did not significantly change the overall findings (data not shown).
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Discussion This is the first study to identify relationships between muscle power, knee pain and quality of life in participants with symptomatic knee OA. The major finding of this investigation was that leg extensor muscle power was an independent determinant of knee pain and quality of life in knee OA. Peak muscle contraction velocity at low external resistance was also independently associated with knee pain. Importantly, we were unable to demonstrate that lower extremity muscle strength was a major determinant of disease severity. Our findings suggest that, compared to strength, muscle power is a more definitive measure of muscle performance and may have significant potential as a more influential parameter for understanding the interrelationships between muscle function and disease severity in knee OA.
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A notable observation from the current investigation is that the leg extensor muscle power, contraction velocity and strength levels exhibited in this knee OA population are low when compared to established reference levels from several populations of middle-aged and older adults without symptomatic knee OA.(26) Indeed, the muscle power values in the present study are equivalent to levels generated in a specific group of mobility-limited older adults with a mean age of ∼ 80 years.(26) This suggests that individuals with established knee OA have substantial and accelerated impairments in muscle power. However a direct
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comparison of the age-related differences in muscle power among participants with and without knee OA is needed to further verify this assertion.
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The results of the current investigation extend the findings of several smaller clinical studies that have specifically evaluated the relationships between muscle power and physical function in knee OA.(17, 30) In 39 patients who underwent total knee arthroplasty, compared to knee extensor strength, greater leg extensor muscle power was a superior predictor of performance in fast walking, repeated chair stand, and self-reported WOMAC function.(30) Similarly, in 40 participants with established knee OA, knee extension muscle power, measured isotonically using a dynamometer at low external resistances, was more predictive of WOMAC function than peak isometric muscle strength.(17) Isotonic knee extensor muscle power was also superior than muscle strength in determining medial knee loading and adduction moments during kinematic gait trials in 53 patients with clinical knee OA.(18) In the current study, we incorporated a dynamic, well-validated assessment of leg extensor muscle power within a large population of knee OA participants and demonstrated the novel clinical importance of muscle power as an independent predictor of pain and quality of life in these symptomatic patients.
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Taken together, and consistent with the present study findings, there is now significant emerging evidence implicating muscle power as a critical parameter in the etiology of knee OA pain. Consequently, training interventions specifically designed to target and improve muscle power, which may also reduce disease burden in knee OA, should be examined further. Our findings suggest that, compared to muscle power at low external resistance (40% of 1RM), muscle power generated at high external resistance (70% of 1RM) may be a marginally greater determinant of pain and quality of life in knee OA, Thus, muscle power training at higher external resistances should be examined in knee OA, since an intervention of high intensity power training may portend greater reductions in disease severity or comparatively greater improvements in physical functioning, compared to low resistance power training.(31) To date, two small pilot studies have successfully demonstrated the feasibility of low resistance power training (training performed at 40% of 1RM) for improving muscle power, pain and function in patients with knee OA.(32, 33) However, additional, larger-scale randomized controlled trials of resistance training interventions to improve lower extremity muscle power across a variety of training intensities, and their subsequent impact on pain, quality of life and functional outcomes in knee OA, are necessary.
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There may be several plausible physiological explanations for our overall findings. First, the lower extremity musculature plays an integral role in the stability, loading, proprioception and functional movement of the knee joint.(1, 30) As muscle power reflects the product of muscle force and speed of movement, and is a superior determinant of human locomotion and physical functioning when compared to strength, it is possible that dynamic knee stability may be greatly compromised by muscle power impairments, which contribute more to inadequate control of tibial translation during ambulation, leading to damage, and ultimately, knee pain. Similarly, compared to muscle strength deficits, muscle power impairments may also more critically limit the ability of the musculature to dissipate knee joint loads, thus increasing the risk of articular contact stress, which leads to pain. Second,
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lower limb muscles with impairments in maximal contractile velocity, rather than impairments in muscle force production, may fatigue more rapidly,(34, 35) leading to poor overall neuromuscular control, which could allow pathologic joint movement and painful loading of the articular structures.(36) Third, in the present study we incorporated a dynamic, closed kinetic chain assessment of leg extensor muscle power. The majority of prior studies in knee OA have evaluated muscle performance and disease severity outcomes using isokinetic dynamometry of the knee extensors, an assessment that restricts the evaluation of muscle force to a predetermined velocity.(30) Because important activities of daily living are typically closed kinetic chain tasks consisting of weight-bearing ambulation through various positions at variable velocities, such as walking or rising from a chair, our measure of dynamic leg extensor power represents a more functionally relevant assessment of muscle performance and, consistent with the overall findings from the current investigation, a more clinically important correlate of disease burden in knee OA.
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There are limitations associated with this investigation. The cross-sectional nature of the analysis precludes definitive casual inferences and information on the temporal relationships between knee pain, quality of life and muscle power. We also do not account for other individual differences such as knee alignment and that may account for additional variability in the relationships between disease severity and muscle performance. In addition, the influence of well-established risk factors for knee OA such as adipose mass and distribution, and other physiologic mechanisms that determine muscle performance, such as muscle mass and neural activation, were not specifically assessed in this investigation. Despite these limitations, our study provides important new clinically relevant findings that may accelerate the development of more effective therapeutic and rehabilitative interventions for individuals with knee OA.
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Conclusion This is the first study to comprehensively assess and demonstrate that lower extremity muscle power is an independent determinant of knee pain and quality of life in participants with established knee OA. Compared to traditional measurements of muscle strength, our findings emphasize that muscle power is a more clinically important measure of muscle performance in knee OA. Thus, resistance training interventions specifically designed to improve muscle power, and their associated impact on disease severity, should be systematically examined in persons with symptomatic knee OA.
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This study is supported by the National Institutes of Health (R01 AT00552, 1 K24 AT007323, UL1 RR025752, UL1TR000073 and UL1TR001064). The contents of this manuscript are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health. The investigators are solely responsible for the content of the manuscript and the decision to submit for publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This research was also based upon work supported by the U.S. Department of Agriculture, under agreement No. 58-1950-4-003. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. This research was also supported by the Boston Claude D. Pepper Older Americans Independence Center (1P30AG031679) and the Boston Rehabilitation Outcomes Center Grant (1R24HD065688-01A1).
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References
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1. Litwic A, Edwards MH, Dennison EM, Cooper C. Epidemiology and burden of osteoarthritis. British medical bulletin. 2013; 105:185–99. [PubMed: 23337796] 2. Felson DT, Lawrence RC, Hochberg MC, McAlindon T, Dieppe PA, Minor MA, et al. Osteoarthritis: new insights. Part 2: treatment approaches. Annals of internal medicine. 2000; 133(9):726–37. [PubMed: 11074906] 3. Brooks PM. Impact of osteoarthritis on individuals and society: how much disability? Social consequences and health economic implications. Current opinion in rheumatology. 2002; 14(5): 573–7. [PubMed: 12192258] 4. Brooks PM. The burden of musculoskeletal disease--a global perspective. Clinical rheumatology. 2006; 25(6):778–81. [PubMed: 16609823] 5. Hall MC, Mockett SP, Doherty M. Relative impact of radiographic osteoarthritis and pain on quadriceps strength, proprioception, static postural sway and lower limb function. Annals of the rheumatic diseases. 2006; 65(7):865–70. [PubMed: 16308342] 6. Madsen OR, Bliddal H, Egsmose C, Sylvest J. Isometric and isokinetic quadriceps strength in gonarthrosis; inter-relations between quadriceps strength, walking ability, radiology, subchondral bone density and pain. Clinical rheumatology. 1995; 14(3):308–14. [PubMed: 7641507] 7. Brandt KD, Heilman DK, Slemenda C, Katz BP, Mazzuca SA, Braunstein EM, et al. Quadriceps strength in women with radiographically progressive osteoarthritis of the knee and those with stable radiographic changes. The Journal of rheumatology. 1999; 26(11):2431–7. [PubMed: 10555906] 8. Steultjens MP, Dekker J, van Baar ME, Oostendorp RA, Bijlsma JW. Muscle strength, pain and disability in patients with osteoarthritis. Clinical rehabilitation. 2001; 15(3):331–41. [PubMed: 11386405] 9. Segal NA, Torner JC, Felson DT, Niu J, Sharma L, Lewis CE, et al. Knee extensor strength does not protect against incident knee symptoms at 30 months in the multicenter knee osteoarthritis (MOST) cohort. PM & R: the journal of injury, function, and rehabilitation. 2009; 1(5):459–65. 10. Amin S, Baker K, Niu J, Clancy M, Goggins J, Guermazi A, et al. Quadriceps strength and the risk of cartilage loss and symptom progression in knee osteoarthritis. Arthritis and rheumatism. 2009; 60(1):189–98. [PubMed: 19116936] 11. Sharma L, Dunlop DD, Cahue S, Song J, Hayes KW. Quadriceps strength and osteoarthritis progression in malaligned and lax knees. Annals of internal medicine. 2003; 138(8):613–9. [PubMed: 12693882] 12. Reid KF, Fielding RA. Skeletal muscle power: a critical determinant of physical functioning in older adults. Exerc Sport Sci Rev. 2012; 40(1):4–12. [PubMed: 22016147] 13. Bassey EJ, Fiatarone MA, O'Neill EF, Kelly M, Evans WJ, Lipsitz LA. Leg extensor power and functional performance in very old men and women. Clin Sci (Lond). 1992; 82(3):321–7. [PubMed: 1312417] 14. Metter EJ, Conwit R, Tobin J, Fozard JL. Age-associated loss of power and strength in the upper extremities in women and men. The journals of gerontology Series A, Biological sciences and medical sciences. 1997; 52(5):B267–76. 15. Bean JF, Leveille SG, Kiely DK, Bandinelli S, Guralnik JM, Ferrucci L. A comparison of leg power and leg strength within the InCHIANTI study: which influences mobility more? J Gerontol A Biol Sci Med Sci. 2003; 58(8):728–33. [PubMed: 12902531] 16. Foldvari M, Clark M, Laviolette LC, Bernstein MA, Kaliton D, Castaneda C, et al. Association of muscle power with functional status in community-dwelling elderly women. J Gerontol A Biol Sci Med Sci. 2000; 55(4):M192–9. [PubMed: 10811148] 17. Berger MJ, McKenzie CA, Chess DG, Goela A, Doherty TJ. Quadriceps neuromuscular function and self-reported functional ability in knee osteoarthritis. Journal of applied physiology. 2012; 113(2):255–62. [PubMed: 22604883] 18. Calder KM, Acker SM, Arora N, Beattie KA, Callaghan JP, Adachi JD, et al. Knee power is an important parameter in understanding medial knee joint load in knee osteoarthritis. Arthritis care & research. 2014; 66(5):687–94. [PubMed: 24920175]
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19. Wang C, Iversen MD, McAlindon T, Harvey WF, Wong JB, Fielding RA, et al. Assessing the comparative effectiveness of Tai Chi versus physical therapy for knee osteoarthritis: design and rationale for a randomized trial. BMC complementary and alternative medicine. 2014; 14:333. [PubMed: 25199526] 20. Altman R, Asch E, Bloch D, Bole G, Borenstein D, Brandt K, et al. Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Arthritis and rheumatism. 1986; 29(8):1039–49. [PubMed: 3741515] 21. Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975; 12(3):189–98. [PubMed: 1202204] 22. Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. The Journal of rheumatology. 1988; 15(12):1833–40. [PubMed: 3068365] 23. Ware JE Jr, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Medical care. 1992; 30(6):473–83. [PubMed: 1593914] 24. McHorney CA, Ware JE Jr, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Medical care. 1993; 31(3):247–63. [PubMed: 8450681] 25. Callahan D, Phillips E, Carabello R, Frontera WR, Fielding RA. Assessment of lower extremity muscle power in functionally-limited elders. Aging Clin Exp Res. 2007; 19(3):194–9. [PubMed: 17607086] 26. Reid KF, Doros G, Clark DJ, Patten C, Carabello RJ, Cloutier GJ, et al. Muscle power failure in mobility-limited older adults: preserved single fiber function despite lower whole muscle size, quality and rate of neuromuscular activation. European journal of applied physiology. 2012; 112(6):2289–301. [PubMed: 22005960] 27. Borg G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med. 1970; 2(2):92– 8. [PubMed: 5523831] 28. Bruce B, Fries JF. The Health Assessment Questionnaire (HAQ). Clinical and experimental rheumatology. 2005; 23(5 Suppl 39):S14–8. [PubMed: 16273780] 29. Beck AT, Ward CH, Mendelson M, Mock J, Erbaugh J. An inventory for measuring depression. Archives of general psychiatry. 1961; 4:561–71. [PubMed: 13688369] 30. Aalund PK, Larsen K, Hansen TB, Bandholm T. Normalized knee-extension strength or leg-press power after fast-track total knee arthroplasty: which measure is most closely associated with performance-based and self-reported function? Archives of physical medicine and rehabilitation. 2013; 94(2):384–90. [PubMed: 23085377] 31. Reid KF, Martin KI, Doros G, Clark DJ, Hau C, Patten C, et al. Comparative Effects of Light or Heavy Resistance Power Training for Improving Lower Extremity Power and Physical Performance in Mobility-Limited Older Adults. The journals of gerontology Series A, Biological sciences and medical sciences. 2014 32. Sayers SP, Gibson K, Cook CR. Effect of high-speed power training on muscle performance, function, and pain in older adults with knee osteoarthritis: a pilot investigation. Arthritis care & research. 2012; 64(1):46–53. [PubMed: 22012877] 33. Pelletier D, Gingras-Hill C, Boissy P. Power training in patients with knee osteoarthritis: a pilot study on feasibility and efficacy. Physiotherapy Canada Physiotherapie Canada. 2013; 65(2):176– 82. [PubMed: 24403682] 34. Petrella JK, Kim JS, Tuggle SC, Hall SR, Bamman MM. Age differences in knee extension power, contractile velocity, and fatigability. J Appl Physiol. 2005; 98(1):211–20. [PubMed: 15347625] 35. Pojednic RM, Clark DJ, Patten C, Reid K, Phillips EM, Fielding RA. The specific contributions of force and velocity to muscle power in older adults. Experimental gerontology. 2012; 47(8):608– 13. [PubMed: 22626972] 36. Segal NA, Glass NA. Is quadriceps muscle weakness a risk factor for incident or progressive knee osteoarthritis? The Physician and sportsmedicine. 2011; 39(4):44–50. [PubMed: 22293767]
Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
Reid et al.
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Table 1
Baseline Characteristics (n = 190)
Author Manuscript
Variables
Mean ± SD
Age, yrs (min – max)
60.2 ± 10.4 (41 – 90)
Body Weight, kg
90.8 ± 21.0
Height, cm
166.4 ± 9.0
BMI, kg/m2
32.7 ± 7.2
Duration of pain, yrs
8.1 ± 9.2
Beck Depression Score
7.6 ± 8.8
Medications
4.4 ± 3.0
Conditions, n (%)
Author Manuscript
Hypertension
93 (49.0)
Diabetes
34 (17.9)
Heart Disease
15 (7.9)
Kellgren-Lawrence Grade, n (%)* 0
4 (2.2)
1
10 (5.4)
2
70 (37.8)
3
65 (35.1)
4
36 (19.5)
Sex, n (%) Male
58 (30.5)
Female
132 (69.5)
Race, n (%)
Author Manuscript
White
104 (54.7)
Black or African American
64 (33.7)
More than one race
8 (4.2)
Asian
5 (2.6)
American Indian or Alaskan native
4 (2.1)
Other/unknown
5 (2.6)
*
Kellgren-Lawrence grades were unavailable for 5 participants
Author Manuscript Arthritis Rheumatol. Author manuscript; available in PMC 2016 December 01.
Reid et al.
Page 12
Table 2
Knee Pain, Quality of Life and Muscle Performance Characteristics (n = 190)
Author Manuscript
Variables
Male (n = 58)
Female (n = 132)
P value
WOMAC pain
227.2 ± 91.2
261.6 ± 101.6
0.03
37.3 ± 8.6
36.7 ± 9.4
0.72
SF-36 physical component score SF-36 mental component score
52.8 ± 10.4
52.5 ± 8.7
0.86
1RM strength, newtons
1338.5 ± 389.0
835.6 ± 302.0
