Muscle strength is defined herein as the maximum voluntary force or torque brought to bear on the environment under a given set of test conditions. Granting that some authorities eschew the term "strength" in favor of the more generic word "performance" or the phrase "force control," I will use the more traditional term strength. The concept of muscle strength will not be limited, as it sometimes is, to the context of a single isometric maximal voluntary contraction.
This review will focus on issues and practical options relevant to measuring muscle strength in the geriatric population. Although the issues and options are not unique to these individuals, the tendency of strength to decrease with age1-4 makes them particularly relevant to this group.
MUSCLE STRENGTH TESTING ISSUES
Why measure muscle strength?
The body and its various segments, as well as objects encountered by the body within the environment, have mass. If an individual is to accelerate or decelerate these masses, forces must be generated. Skeletal muscles are the means by which accelerative and decelerative forces are produced. Although maximum force is seldom required in everyday life, a sufficient force must be generated if a task is to be completed successfully. An individual with a high force-producing capacity (strength) is less likely to be thwarted by more demanding activities (eg, opening a tight jar lid). Other things being equal, the greater force-generating capacity of stronger individuals will render them less functionally limited by a pathology (eg, stroke) that results in impaired strength. It also will provide them with a reserve that will enable them to persist longer at submaximal activities. These realities render strength important and worth measuring.
A wealth of correlational research also provides support for measuring muscle strength. Muscle strength has been shown to correlate concurrently with overall functional performance as well as with performance at specific functional activities such as walking, climbing steps, and attaining a standing position (Fig 1).5-17 Muscle strength also has been found to correlate with important nonfunctional variables. Among these variables are nutritional status and bone mineral density.18-21 Moreover, muscle strength is a predictor of such diverse outcomes as postoperative complications,22-24 functional decline,25,26 and survival.27-29
Why measure strength quantitatively?
Undoubtedly, manual muscle testing is the procedure used most often by clinicians to measure muscle strength. Since it requires no equipment, it can be applied quickly and easily in any setting. The widespread use and advantages of manual muscle testing notwithstanding, its subjectivity and insensitivity limit its value relative to quantitative options.
Manual muscle testing is demonstrably subjective. This subjectivity does not pose much of a problem during the testing of weaker muscles whose scores are based on the presence of a contraction or the amount of joint excursion, either with gravity eliminated or against gravity. Once the tester has to apply and grade resistance, however, subjectivity becomes problematic. While testers are clearly able to modulate their forces, they are limited in their ability to apply consistent forces30(Fig 2). In addition, there are differences in the maximal forces they are able to apply.31
The subjectivity of manual muscle testing renders it insensitive, particularly at the higher grades. More than 50 years ago, Beasley32 demonstrated that 20% to 25% differences in strength were not discernible by testers using manual muscle testing. He also noted that children, whose strength was only 50% of normal, were misjudged as having normal strength. Since the publication of Beasley's work, numerous other investigators33-38 have documented the insensitivity and limited responsiveness of manual muscle testing compared with various quantitative alternatives.
PRACTICAL OPTIONS FOR MEASURING STRENGTH QUANTITATIVELY
Quantitative strength testing options are those that yield measurements in real numbers. To be practical they must be rapidly applicable in a variety of settings. Three quantitative options are excluded from this review because they lack such practicality: weights, fixed dynamometry, and isokinetic dynamometry. Determining strength (eg, a one-repetition maximum) using weights involves trial and error and possibly the transportation of weights. The setup time is prohibitive for both fixed and isokinetic dynamometers. Moreover, isokinetic dynamometers are very difficult to move from place to place. Three options without these limitations follow.
Hand-grip dynamometry refers to the use of instrumentation to measure the grasping strength of the hand (Fig 3). Modified sphygmomanometers or similar devices can be used to measure grip strength, but they should probably be avoided since they measure pressure, which is influenced by the area over which force is applied.39 The Jamar is apparently the most widely employed dynamometer,40 but the use of others has been described regularly in the literature.
Several methods for measuring grip strength have been described. Since elbow and shoulder position, as well as the width of the grasp, can affect the force measured,41-44 it is important that the procedure be conducted consistently. The American Society of Hand Therapists suggested use of the Jamar dynamometer in its second (most narrow) handle position, with the subject seated, the shoulder adducted and in neutral rotation, the elbow flexed to 90°, and the forearm and wrist in neutral.45 When a consistent technique is used, grip dynamometry is highly reliable.46,47 Hand-grip dynamometry is obviously limited to the measurement of a single task (ie, hand grasp). It can be used, however, to characterize overall muscle strength (particularly of the tested upper extremity).48 The internal consistency of muscle strength measures justifies such a generalization.49
Several investigators47,50-54 have presented normative values for grip strength obtained with a dynamometer. These studies are listed in Table 1. The normative values that I use to make judgments about impairments—those of Mathiowetz et al50—are presented in Table 2.
Hand-held dynamometry involves the use of a dynamometer that is held by a tester and applied to the tested segment of a patient's body (Fig 4). A modified sphygmomanometer can be used, but it is not recommended for the same reasons as noted earlier in the section on hand-grip dynamometry.55 Several models of hand-held dynamometers are marketed commercially. Dynamometers incorporating load cells are more expensive than those relying on springs, but they probably retain their accuracy better over time.56
Many factors influence the measurements obtained with hand-held dynamometers. Procedures must be incorporated to account for these factors. At a minimum, I suggest the use of make tests rather than break tests; the forces associated with make tests are lower and not influenced by spasticity.57,58 Moreover, I suggest that the individuals tested be asked to come to maximum force over a period of 1 to 2 seconds and that they continue with their maximum effort for no more than 3 to 4 seconds. Testing should be conducted with the joint in the middle half of its range and the effect of gravity eliminated or lessened. The tester must have sufficient strength to hold the dynamometer steady while the tested individual pushes against it. If the tester is not strong enough, valid and reliable measurements will not be obtained59 unless supplementary stabilization is employed. Belts have been used effectively to this end.60,61 Testers of adequate strength who employ consistent methods can obtain valid and reliable measurements using hand-held dynamometry.62-64
Although not so prevalent as for hand-grip dynamometry, normative values for hand-held dynamometry have been published.65-71 These studies are summarized in Table 3. For judgments regarding impairments in extremity strength, I recommend the values presented in Table 4.
Muscle strength also can be tested functionally; that is, it can be measured by quantifying the time or repetitions associated with specific bodily maneuvers. These functional tests use the weight of the body or various body segments for resistance.
Although there are many functional strength tests, the sit-to-stand test (chair-stand test) is probably used most often with older individuals. All sit-to-stand tests employ a chair (preferably armless) of standard height. Ideally the chair should have a hard or firm surface and be stabilized against a wall. Tested individuals stand up and sit down as quickly as they can without the use of their upper extremities; some instructions call for the arms to be folded in front of the chest (Fig 5).72 Performance is either quantified on the basis of the number of repetitions completed in a given period of time (ie, 10 or 30 seconds)73-76 or the time required to perform a given number of repetitions (usually 5 or 10).72,77-79
The sit-to-stand test has been shown to possess both convergent construct and discriminant validity. The former is supported by the correlation between sit-to-stand performance and knee extension force73,74 and leg press force.76 The latter is shown by the lower sit-to-stand performance among individuals who are older, who have lower habitual activity levels, and who report a higher need for assistance with activities of daily living.72,76,77 Reliability coefficients reported for different versions of the test vary. Measurements of the time for a single chair stand (intraclass correlation coefficient [ICC] = .25)78 lack reliability compared with measurements of the time for five or more repetitions (reliability coefficients ≥ .67).78-80 Jones et al76 reported test-retest reliability coefficients of .77 to .95 for the number of chair stands performed in 30 seconds.
Many older individuals are unable to perform one or more repetitions of the sit-to-stand maneuver. In the study by Guralnik et al,72 more than 25% of the men and 30% of the women over 80 years of age were unable to perform five chair stands. For those able to perform the requisite number of repetitions or to continue for the allotted time, however, reference values have been published. Csuka and McCarty77 published regression equations for predicting normal performance for 10 stand-ups. For women the predicted time in seconds was 7.6 + .17 · age; for men the predicted time in seconds was 4.9 + .19 · age. Guralnik et al72 reported mean and median times for five stand-ups to be 13.2 and 12.6 seconds, respectively, for males and 14.4 and 13.7 seconds, respectively, for females 71 to 79 years. For individuals age 80 years or more they documented mean and median times of 15.0 and 14.0 seconds, respectively, for males and 16.1 and 15.0 seconds, respectively, for females. Table 5 presents normative values reported by Rikli and Jones81 for the number of sit-to-stands performed in 30 seconds.
Other functional tests
Several functional tests other than the sit-to-stand test have been described in some detail in the literature. These include other lower extremity tests such as step-ups and standing toe-raises as well as tests of upper body and trunk strength.
Amundsen and Graves described a procedure for quantifying lower extremity strength on the basis of patients' "ability to step up onto and off of platforms of progressively increasing height (10.2, 20.3, 30.5, and 40.6 cm)."82(p25) Overall, patients' ability correlated significantly with their peak knee extension torque (normalized against body weight) of the left (r = .72) and right (r = .59). Others have described step tests, but the tests they describe have either been used with young individuals or to characterize other aspects of motor performance (eg, endurance or agility).83 Lundsford and Perry84 described a "heel-rise" test to quantify ankle plantar flexion strength. For 203 individuals age 20 to 59 years they documented the number of unilateral heel-rises performed. The average number of repetitions completed was 27.9 (range, 6 to 70). The lower limit of the 99% confidence interval was 25 repetitions.
Although used primarily with younger individuals,85-87 pull-ups, push-ups, and sit-ups can be employed with some older individuals.88 The validity of push-ups has been established by the correlation of push-up and bench-press performance.85 Normative values obtained from a sample of older Canadian men and women are available for the push-ups and sit-ups.88 The number of push-ups completed in 60 seconds was 6.1 ± 4.6 for men 65 to 69 years and 3.7 ± 3.6 for men 70 to 75 years; the number completed was 4.3 ± 5.5 for women 65 to 69 years and 3.3 ± 3.4 for women 70 to 75 years. The number of sit-ups completed in 60 seconds was 8.7 ± 6.1 for men 65 to 69 years and 7.2 ± 6.8 for men 70 to 75 years; the number completed was 4.0 ± 5.8 for women 65 to 69 years and 4.0 ± 5.6 for women 70 to 75 years.
There are numerous quantitative alternatives to manual muscle testing for quantifying muscle strength. Although all of these alternatives merit broader application, circumstances will determine the best choice for specific situations.
1. Christ CB, Boileau RA, Slaughter MH, Stillman RJ, Cameron JA, Massey BH. Maximal voluntary isometric force production characteristics of six muscle
groups in women aged 25 to 74 years. Am J Hum Biol.
2. Bemben MG, Massey BH, Bemben DA, Misner JE, Boileau RA. Isometric muscle
force production as a function of age in healthy 20- to 74-year-old men. Med Sci Sports Exerc.
3. Lindle RS, Metter EJ, Lynch NA, et al. Age and gender comparisons of muscle
strength in 654 women and men aged 20-93 years. J Appl Physiol.
4. Sunnerhagen KS, Hedberg M, Henning G-B, Cider A, Svantesson U. Muscle
performance in an urban population sample of 40- to 79-year-old men and women. Scand J Rehabil Med.
5. Bohannon RW. Determinants of gown donning performance soon after stroke. Eur Phys Med Rehabil.
6. Bohannon RW, Walsh S. Association of paretic lower extremity muscle
strength and balance with stair climbing ability in patients with stroke. J Stroke Cerebrovasc Dis.
7. Bohannon RW, Hull D, Palmeri DL. Muscle
strength impairments and gait performance deficits in kidney transplant candidates. Am J Kidney Dis.
8. Hughes MA, Myers BS, Schenkman ML. The role of strength in rising from a chair in the functionally impaired elderly. J Biomech.
9. Schenkman M, Hughes MA, Samsa G. The relative importance of strength and balance in chair rise by functionally impaired older individuals. J Am Geriatr Soc.
10. Lankhorst GJ, Van de Stadt RJ, Van der Korst JK. The relationships of functional capacity, pain, and isometric and isokinetic torque in osteoarthritis of the knee. Scand J Rehabil Med.
11. Vliet Vlieland TPM, Van der Wijk TP, Jolie IMM, Zwinderman AH, Hazes JMW. Determinants of hand function in patients with rheumatoid arthritis. J Rheumatol.
12. Slavin MD, Jette DU, Andres PL, Munsat TL. Lower extremity muscle
force measures and functional ambulation in patients with amyotrophic lateral sclerosis. Arch Phys Med Rehabil.
13. Cunningham DA, Paterson DH, Himann JE, Rechnitzer PA. Determinants of independence in the elderly. Can J Appl Physiol.
14. Rantanen T, Guralnik JM, Izmirlian G, et al. Association of muscle
strength with maximum walking speed in disabled older women. Am J Phys Med Rehabil.
15. Chang RW, Dunlop D, Gibbs J, Hughes S. The determinants of walking velocity in the elderly. Arthritis Rheum.
16. Buchner DM, Larson EB, Wagner EH, Koepsell TD, DeLateur BJ. Evidence for a non-linear relationship between leg strength and gait speed. Age Ageing.
17. Salem GJ, Wang M-Y, Young JT, Marion M, Greendale GA. Knee strength and lower- and higher-intensity functional performance in older adults. Med Sci Sports Exerc.
18. Martin S, Neale G, Elia M. Factors affecting maximal momentary grip strength. Hum Nutr Clin Nutr.
19. Windsor JA, Hill GL. Grip strength: a measure of the proportion of protein loss in surgical patients. Br J Surg.
20. Sinaki M, Fitzpatrick LA, Ritchie CK, Montesano A, Wahner HW. Site-specificity of bone mineral density and muscle
strength in women. Am J Phys Med Rehabil.
21. Tan J, Cubukcu S, Sepici V. Relationship between bone mineral density of the proximal femur and strength of hip muscles in postmenopausal women. Am J Phys Med Rehabil.
22. Davies CWT, Jones DM, Shearer JR. Hand-grip—a simple test for morbidity after fracture of the neck of femur. J R Soc Med.
23. Guo C-B, Zhang W, Ma D-A, Zhang K-H, Huang J-Q. Hand grip strength: an indicator of nutritional state and the mix of postoperative complications in patients with oral and maxillofacial cancers. Br J Oral Maxillofac Surg.
24. LeCorneau KA, McKiernan J, Kapadia SA, Neuberger JM. A prospective randomized study of preoperative nutritional supplementation in patients awaiting orthoptic liver transplantation. Transplantation.
25. Ishizaki T, Watanabe S, Suzuki T, Shibata H, Haga H. Predictors for functional decline among nondisabled older Japanese living in community during a 3-year follow-up. J Am Geriatr Soc.
26. Rantanen T, Guralnik JM, Foley D, et al. Midlife hand grip strength as a predictor of old age disability. JAMA.
27. Callahan LF, Pincus T, Huston JW. Measures of activity and damage in rheumatoid arthritis: depiction of changes and prediction of mortality over five years. Arthritis Care Res.
28. Fujita Y, Nakamura Y, Hiraoka J, et al. Physical-strength tests and mortality among visitors to health-promotion centers in Japan. J Clin Epidemiol.
29. Laukkanen P, Heikkinen E, Kauppinen M. Muscle
strength and mobility as predictors of survival in 75-84-year-old people. Age Ageing.
30. Knepler C, Bohannon RW. Subjectivity of forces associated with manual-muscle
test grades of 3+, 4−, and 4. Percept Mot Skills.
31. Mulroy SJ, Lassen KD, Chambers SH, Perry J. The ability of male and female clinicians to effectively test knee extension strength using manual muscle
testing. J Orthop Sports Phys Ther.
32. Beasley WC. Influence of method on estimates of normal knee extensor force among normal and postpolio children. Phys Ther Rev.
33. Aitkens S, Lord J, Bernauer E, Fowler WM, Lieberman JS, Berck P. Relationship of manual muscle
testing to objective strength measurements. Muscle Nerve.
34. Schwartz S, Cohen ME, Herbison GJ, Shah A. Relationship between two measures of upper extremity strength: manual muscle
test compared to hand-held myometry. Arch Phys Med Rehabil.
35. Andres PL, Skerry LM, Thorneli B, Portney LG, Finison LJ, Munsat TL. A comparison of three measures of disease progression in ALS. J Neurol Sci.
36. Anderson H, Jakobsen J. A comparative study of isokinetic dynamometry and manual muscle
testing of ankle dorsal and plantar flexors and knee extensors and flexors. Eur Neurol.
37. Dvir Z. Grade 4 in manual muscle
testing: the problem with submaximal strength assessment. Clin Rehabil.
38. Bohannon RW. Measuring knee extensor muscle
strength. Am J Phys Med Rehabil.
39. Lusardi M, Bohannon RW. Handgrip strength: comparability of measurements obtained with a Jamar dynamometer and modified sphygmomanometer. J Hand Ther.
40. Smith RO, Benge MW. Pinch and grasp strength: standardization of terminology and protocol. Am J Occup Ther.
41. Su C-Y, Lin J-H, Chien T-H, Cheng K-F, Sung Y-T. Grip strength: relationship to shoulder position in normal subjects. Kaohsiung J Med Sci.
42. Balogun JA, Akomolafe CT, Amusa LO. Grip strength: effects of testing posture and elbow position. Arch Phys Med Rehabil.
43. Mathiowetz V, Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg.
44. Harkonen R, Piirtomaa M, Alaranta H. Grip strength and hand position of the dynamometer in 204 Finnish adults. J Hand Surg.
45. Fess EW. Grip strength. In: JS Casanova, ed. Clinical Assessment Recommendations.
2nd ed. Chicago, IL: American Society of Hand Therapists; 1992:41-45.
46. Mathiowetz V, Weber K, Volland G, Kashman N. Reliability and validity of grip and pinch strength evaluations. J Hand Surg.
47. Peolsson A, Hedlund R, Oberg B. Intra- and inter-tester reliability and reference values for hand strength. J Rehabil Med.
48. Bohannon RW. Hand-grip dynamometry provides a valid indication of upper extremity strength impairment in home care patients. J Hand Ther.
49. Bohannon RW, Andrews AW. Characterization of isometric limb muscle
strength of older adults. J Aging Phys Activity.
50. Mathiowetz V, Kashman N, Volland G, Weber K, Dowe M. Grip and pinch strength: normative data for adults. Arch Phys Med Rehabil.
51. Oberg T, Oberg U, Karsznia A. Handgrip and fingerpinch strength. Physiother Theory Pract.
52. Thorngren K-G, Werner CO. Normal grip strength. Acta Orthop Scand.
53. Crosby CA, Wehbe MA, Mawr B. Hand strength: normative values. J Hand Surg.
54. Bassey EJ, Harries UJ. Normal values for handgrip strength in 920 men and women aged over 65 years, and longitudinal changes over 4 years in 620 survivors. Clin Sci.
55. Bohannon RW, Lusardi MM. Modified sphygmomanometer versus strain gauge hand-held dynamometer. Arch Phys Med Rehabil.
56. Bohannon RW, Andrews AW. Accuracy of spring and strain gauge hand-held dynamometers. J Orthop Sports Phys Ther.
57. Bohannon RW. Make versus break tests of elbow flexion force using a hand-held dynamometer. Phys Ther.
58. Bohannon RW. Make versus break tests for measuring elbow flexor muscle
force with a hand-held dynamometer in patients with stroke. Physiother Can.
59. Wikholm JB, Bohannon RW. Hand-held dynamometer measurements: tester strength makes a difference. J Orthop Sports Phys Ther.
60. Desrosiers J, Rochette A, Payette H, Gregoire L, Boutier V, Lazowski D-A. Upper extremity isometric strength measurement
using the belt-resisted method: reliability study with healthy elderly people. Can J Rehabil.
61. Kramer JF, Vaz MD, Vandervoort AA. Reliability of isometric hip abductor torques during examiner- and belt-resisted tests. J Gerontol.
62. Bohannon RW, Wikholm JB. Measurements of knee extension force obtained by two examiners of substantially different experience with a hand-held dynamometer. Isokinetic Exerc Sci.
63. Bohannon RW. Hand-held versus isokinetic dynamometer for measurement
of static knee extension torques. Clin Phys Physiol Med.
64. Bohannon RW, Andrews AW. Inter-rater reliability of hand-held dynamometry. Phys Ther.
65. Bohannon RW. Upper extremity strength and strength relationships among young women. J Orthop Sports Phys Ther.
66. van der Ploeg RJO, Fidler V, Oosterhuis HJGH. Hand-held myometry: reference values. J Neurol Neurosurg Psychiatry.
67. Backman E, Johansson V, Hager B, Sjoblom P, Henriksson KG. Isometric muscle
strength and muscular endurance in normal persons aged between 17 and 70 years. Scand J Rehabil Med.
68. Andrews AW, Thomas MW, Bohannon RW. Normative values for isometric muscle
force measurements obtained with hand-held dynamometers. Phys Ther.
69. Bohannon RW. Reference values for extremity muscle
strength obtained by hand-held dynamometry from adults aged 20-79 years. Arch Phys Med Rehabil.
70. Phillips BA, Lo SK, Mastaglia FL. Muscle
force measured using "break" testing with a hand-held myometer in normal subjects aged 20-69 years. Arch Phys Med Rehabil.
71. Beenakker EAC, van der Hoeven JH, Fock JM, Maurits NM. Reference values of maximum isometric force obtained in 270 children aged 4-16 years by hand-held dynamometry. Neuromuscul Disord.
72. Guralnik JM, Simonsick EM, Ferrucci L, et al. A short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission. J Gerontol.
73. Bohannon RW, Smith J, Hull D, Palmeri D, Barnhard R. Deficits in lower extremity muscle
and gait performance among renal transplant candidates. Arch Phys Med Rehabil.
74. Bohannon RW. Alternatives for measuring knee extension strength of the elderly at home. Clin Rehabil.
75. Rikli RE, Jones CJ. Development and validation of a functional fitness test for community-residing older adults. J Aging Phys Activity.
76. Jones CJ, Rikli RE, Beam WC. A 30-s chair stand test as a measure of lower body strength in community-residing older adults. Res Q Exerc Sci.
77. Csuka M, McCarty DJ. Simple method for measurement
of lower extremity muscle
strength. Am J Med.
78. Jette AM, Jette DU, Ng J, Plotkin DJ, Bach MA. Are performance-based measures sufficiently reliable for use in multicenter trials? J Gerontol.
79. Netz Y, Argov E. Assessment of functional fitness among independent older adults: a preliminary report. Percept Mot Skills.
80. Newcomer KL, Krug HE, Mahowald ML. Validity and reliability of the timed tests for patients with rheumatoid arthritis and other chronic diseases. J Rheumatol.
81. Rikli RE, Jones CJ. Functional fitness normative scores for community-residing older adults, ages 60-94. J Aging Phys Activity.
82. Amundsen LR, Graves JM. Testing knee extensor muscles of survivors of poliomyelitis. J Hum Muscle Performance.
83. Ross M. Test-retest reliability of the lateral step-up test in young adult healthy subjects. J Orthop Sports Phys Ther.
84. Lunsford BR, Perry J. The standing heel-rise test for ankle plantar flexion: criterion for normal. Phys Ther.
85. Mayhew JL, Ball TE, Arnold MD, Bowen JC. Push-ups as a measure of upper body strength. J Appl Sport Sci Res.
86. LaChance PF, Hortobagyi T. Influence of cadence on muscular performance during push-up and pull-up exercise. J Strength Conditioning Res.
87. Nelson JK, Yoon SH, Nelson KR. A field test for upper body strength and endurance. Res Q Exerc Sport.
88. McCulloch RG, Clark DJ, Pike I, Slobodian YM. Gender specific trends in fitness and anthropometric parameters in a selected Saskatchewan sample, aged 65-75 years. Can J Aging.