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A Useful Technique for Measurement of Back Strength in Osteoporotic and Elderly Patients
A Useful Technique for Measurement of Back Strength in Osteoporotic and Elderly Patients
PAUL J. LIMBURG, B.A., Mayo Medical School; MEHRSHEED SINAKI, M.D., Department ofPhysical Medicine and Rehabilitation; JOHN W. ROGERS, B.S., Mayo Medical School; PATRICK E. CASKEY, B.S.M.E., BRYAN K. PIERSKALLA, B.S.E.T., Section ofEngineering Development
Improvement ofback extensor strength (BES) can be used as a therapeutic method for patients with chronic back pain and osteoporosis. The method of evaluation must be reliable and accurate without compromising the condition of the patient. We report the development of a back isometric dynamometer (BID-2000) designed specifically by two ofus to address these concerns in elderly patients with osteopenia or osteoporosis. As the demographics of the general population change, increasing numbers of patients will need the type of monitoring that the BID-2000 provides. Aging has been shown to cause a reduction in the number of functional muscle motor units. To examine this effect on BES, we tested 50 normal, healthy women who were 30 to 79 years old. Proper testing of BES in patients with fragile vertebrae should include isometric measurement in the prone position, maneuverability of the device to allow comfortable positioning of the patient, and simplicity of technique to minimize repetitious performance of maximal contraction. The BID-2000 incorporates each of these features and also provides meaningful results inexpensively. The device offers a safe, reliable (coefficient of variation = 2.33%), and valid (}' = 0.001) method of evaluation. The results ofour study demonstrated moderate, steady reduction ofBES with increasing age and with each successive decade.
Kyphotic postural change is the most physically disfiguring and psychologically damaging effect of osteoporosis. 1 The incidence of osteoporosis can be substantially decreased only by early detection and subsequent intervention in the high-risk patient population. Disproportionate weakness in back extensor musculature relative to body weight or flexor strength considerably increases the possibility of compressing vertebrae in the fragile osteoporotic spine. Recogni-
tion and improvement of decreased back extensor strength (BES) enhance the ability to maintain proper vertical alignment.f A review of the literature shows various analytic techniques and devices designed to determine BES in diverse subject igroups.f" The current study introduces a new back isometric dynamometer (BID-2000), designed by two of us (M.S. and P.E.C.), which offers specific advantages for the measurement of BES in patients with osteopenia or osteoporosis. Its design allows pain-free testing of the patient and proAddress reprint requests to Dr. Mehrsheed Sinaki, Department ofPhysical Medicine and Rehabilitation, Mayo Clinic, vides results to the clinician simply and inexpensively. In the past, commercial and researchRochester, MN 55905. Mayo Clin Proc 66:39-44, 1991
39
40
BACK STRENGTH IN ELDERLY PATIENTS
oriented devices used to assess BES have not been applicable to patients with osteopenia or osteoporosis. Such devices did not make allowances for the fragile spine with reference to exertional pain and fracture risk, both of which discredit the recording of supposed maximal effort. The geriatric population has an increased risk for debilitating postural changes because of several factors, the two most apparent being a greater prevalence of osteoporosis and involutional loss of functional muscle motor units.P-'? The effects of generalized muscle reduction on BES have, to our knowledge, not been reported. Using the BID-2000 with normal, healthy female volunteers, we established baseline values for BES by successive decades from ages 30 to 79 years. Analysis of the data would reveal any change in BES with advancing age.
METHODS
Technique ofAssessment.-The BID-2000 is a strain-gauge dynamometer that measures isometric BES. During assessment, subjects lie prone with the hips and knees in the neutral position and the arms fully extended at the elbows, pointing caudally (similar to the position used earlier by Nachemson and Lindh"). No immobilizing straps are necessary with proper placement of the padded transducer head. Its upper edge is aligned with the superior borders of the scapulae across the midline. The design prohibits any fluctuation in the level of the fulcrum (at the pelvis), which could occur if restraining straps were used (Fig. 1). During the measurements, subjects raise their hands from the table to prevent unwanted contribution of upper extremity musculature to the upward force generated by the trunk against the transducer head. Direct contact between the pelvis and the table must be maintained throughout the determinations. The extensor muscles are contracted for 5 seconds, with no initial upward jerking motions directed at the transducer. The force generated during exertion is processed by an electronic measuring device and converted to a digital display (in either pounds or kilograms). The patient is allowed one
Mayo Clin Proc, January 1991, Vol 66
Fig. 1. Diagram showing positioning of subject for measurement of back extensor strength with strain-gauge back isometric dynamometer (BID-2000).
warm-up trial, which is followed by three successive maximal effort trials separated by 1-minute resting periods. BES values are considered acceptable if the result ofthe final trial does not exceed the preceding efforts by more than 5%. The maximal force achieved is then recorded, with adherence to the foregoing standardized guidelines. Reproducibility of Technique.-Thirteen healthy subjects (eight female and five male) in good physical condition were studied to evaluate the reproducibility of results with the BID-2000. For inclusion of a subject in the study, physical health had to be judged as good on the basis of interviews and physical examinations. Subjects could have no recent history (within the past 5 years) of back pain or injury to the spine. Measurements consisted of three sessions on the BID-2000 completed within a 1-month period (Table 1). Interexaminer error was eliminated by having the same evaluator perform the three measurements on each subject. The 1-month time frame prevented the possibility ofinaccuracies arising from strengthening effects of either the procedure itself or changes in a subject's level of physical activity. The coefficient of variation with the BID-2000 was 2.33%, a significant improvement over a similar isometric dynamometer described in an earlier publication.H The previous dynamometer was determined to be unacceptable for use with the fragile spine of subjects with osteopenia or osteoporosis. Several subjects tested were unable to exert a maximal effort because of pain
Mayo CUn Proc, January 1991, Vol 66
experienced during placement of or exertion against the rigid transducer head of the device. Modifications on the BID~2000 added maneuverability and cushioning to the measuring unit. Validity of Technique.-Sixty-five normal subjects underwent assessment ofBES with the BID-2000 and an additional evaluation with an isometric function of the IsoStation B-200, a commercially available device. 12 Results with the two techniques had a correlation of 0.38 (P = 0.001) (Fig. 2). RESULTS Among 50 healthy women selected randomly from subgroups determined by age (10 women in each of the following categories-30 to 39, 40 to 49, 50 to 59, 60 to 69, and 70 to 79 years), BES decreased with increasing age (Fig. 3). The mean values for height, weight, and BES in each subgroup are shown in Table 2. No subject experienced back pain or complained of any difficulties that may have influenced the interpretation of maximal effort.
BACK STRENGTH IN ELDERLY PATIENTS
41
Table I.-Reproducibility of Measurements of Back Extensor Strength With the BID-2000 in 13 Healthy Subjects* Trial 1 (date)
Trial 2 (date)
Trial 3 (date)
1
5053 (2/12/87)
50 (2/16/87)
(3/2/87)
2
80 (3/3/87)
77 (3/10/87)
78 (3/13/87)
3
73 (2/12/87)
80 (2/16/87)
73 (3/2/87)
4
70 (2/12/87)
69 (2/16/87)
71 (3/2/87)
5
90 (2/12/87)
91 (2/16/87)
93 (3/2/87)
6
70 (2/16/87)
75 (2/18/87)
77 (3/3/87)
7
69 (2/16/87)
71 (2/18/87)
69 (3/3/87)
8
46 (2/12/87)
41 (2/18/87)
43 (3/10/87)
9
118 (3/3/87)
120 (3/10/87)
122 (3/13/87)
10
163 (2/16/87)
164 (2/18/87)
164 (3/3/87)
Subject
DISCUSSION 11 182 181 182 (2/24/87) (3/3/87) (2/16/87) The BID-2000 method is ideal for measurement 12 156 155 158 ofBES, the desired factor for study in osteopenia (4/5/87) (4/15/87) (3/31/87) and osteoporosis. Because subjects are in the 13 183 185 182 prone position during measurement, BES can be (3/3/87) (2/16/87) (2/24/87) determined without contributions from the lower extremity musculature (in contrast to some other *Subjects 1 through 8 = female; subjects 9 through 13 = measuring devices).13.14 The BID-2000 method male. Measurements are shown in pounds. BID = back isometric dynamometer. also removes the influence of trunk weight on extensor strength. Thus, with this technique, one factor that may result in inaccurate record- cious means of management. Nonloading exering of BES is eliminated. In a quantitative cises have not been proved to be effective for preassessment of back strength, Langrana and as- venting involutional bone loss in postmenopausal sociates'" reported similar results with isomet- (estrogen-deficient) women," but other modest ric and isokinetic testing. This finding allows exercise programs have modified the rate of dethe more desirable isometric method (with lim- crease of bone mineral density.8,16-18 ited motion of the vertebrae) to be used in paImprovement ofBES with extension exercises tients with a compromised spine. has become the preferred physiotherapeutic Application to Patients With Osteopenia option for managing patients with osteopenia or Osteoporosis.-In patients with decreased and osteoporosis in that the relative risk of bone mineral density, pharmacologic, nutrition- damaging the fragile spine is less than with al, and physiotherapeutic aspects of manage- flexion exercises.19 The applicability of the BIDment are important. Physiotherapy is the least 2000 device in the treatment of these patients intrusive and should be emphasized as an effica- centers on its provision of an objective means for
42
Mayo elin Proc, January 1991, Vol 66
BACK STRENGTH IN ELDERLY PATIENTS
• •• • •• • • • • ." • • • ·'i • "--, • --..... • • • • •• • • •• • +
..,... ...
120 110
~
100
I
lD
90
C
0
80
~.o tn,
70
+=
0,;::
!!l
s:
60 50
j en W
40
P=0.OO1 Y = 0.44(x)
30
lD
20
10
n=65 r=0.38
40
50
70
60
80
90
100
110
33.41
120
130
BES with BI0-2000, Ib Fig. 2. Correlation of values obtained with isometric evaluation of back extensor strength (BES) by IsoStation B-200 and BID-2000 in 65 normal subjects. BID = back isometric dynamometer.
monitoring compliance. Therapeutic exercise programs are, by necessity, prolonged; thus, even the most well-intentioned patient may stray from the prescribed protocol. An additional hazard that should not be overlooked is the
•
100 .0
-...
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C>
..;1 •
80
c:
-... • Q)
tn 0 tn
c:
Q)
60
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co
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~
possibility of straining the spine through repeated evaluation of back strength. We have found that the design ofthe BID-2000 appreciably reduces the risk of iatrogenic injury but still provides reliable data for follow-up.
20
m
•
•••
•
• • •
n=50 r=-0.63
I.
0
30
35
40
45
50
55
60
65
70
75
80
Age, yr Fig. 3. Reduction of back extensor strength with increasing age in 50 healthy women.
BACK STRENGTH IN ELDERLY PATIENTS
Mayo Clin Proc, January 1991, Vol 66
43
evaluation ofBES; (2) most fragile skeletons can be safely tested with the BID-2000; (3) the low coefficient of variation of the BID-2000 indicates Height (cm) Weight (kg) BES (lb) that it can be used effectively to detect changes Age (yr) in BES that result from aging, inactivity, or 30-39 158-170.5 52-86 51-97 (35) (164.2) (64.6) (79.6) other factors; and (4) normal, healthy female subjects have a general decline inBES with 40-49 152-171.8 41-72 38-92 (44) (161.7) (58.4) (63.9) increasing age. 50-59 156-170 52-70 40-76 As the elderly population expands, it will (57) (162.2) (59.8) (60.2) require an increasing proportion of the available 60-69 145-168 50-73 28-89 medical care. Currently, approximately 25 mil(65) (160.3) (61.5) (59.0) lion people in the United States are older than 65 70-79 150-170 47-83 18-59 years, and this number will increase to approxi(74) (157.8) (62.8) (38.7) mately 55 million by the year 2030. 23. The asso*Data are shown as range (mean). BES = back extensor ciated increase in the number of patients at risk strength; BID = back isometric dynamometer. for developing kyphosis will necessitate a safe, reliable method for evaluation of BES, such as Application to Patients With Chronic that provided by the BID-2000. Back Pain.-For the minority of patients afflicted with back pain who have chronic symp- ACKNOWLEDGMENT toms, exercise therapy is beneficial.20 Many We thank Sandra K. Fitzgerald for secretarial different types of exercise programs are avail- assistance with the submitted manuscript. able,20.21 but the use of extension exercises is currently favored.t' In a study of patients seeking hospitalization because of back discomfort, Addison and Schultz'" found that the strength of REFERENCES 1. Sinaki M, Grubbs NC: Back strengthening exercises: the extensors was substantially less than that of quantitative evaluation of their efficacy for women the back flexors. This finding supports current aged 40 to 65 years. Arch Phys Med Rehabil 70:1620, 1989 theories for treatment but does not confirm 2. Sinaki M: Beneficial musculoskeletal effects ofphysiwhether the weakness is primary or secondary cal activity in the older woman. Geriatr Med Today to the development of back pain. 8:53-72, November 1989 3. Parnianpour M, Nordin M, Kahanovitz N, Frankel V: Although the exact mechanism by which exer1988 Volvo award in biomechanics: the triaxial coucise provides relief from back pain is unknown, pling of torque generation of trunk muscles during this method of management deserves a trial isometric exertions and the effect of fatiguing isomertial movements on the motor output and movement before intervention with narcotics or a surgical patterns. Spine 13:982-992,1988 procedure. Compliance with the program must 4. Nachemson A, Lindh M: Measurement of abdominal be assessed objectively. Although it primarily and back muscle strength with and without low back provides comfortable evaluation of BES despite pain. Scand J Rehabil Med 1:60-65, 1969 5. Chaffin DB: Ergonomics guide for the assessment of the presence of back pain, the BID·2000 also can human static strength. Am Ind Hyg Assoc J 36:505be useful for motivating patients to exert a truly 511,1975 maximal effort through a visual display of the 6. Kumar S, Chaffin DB, Redfern M: Isometric and isokinetic back and arm lifting strengths: device and BES and the option of an auditory signal (bell) measurement. J Biomech 21:35-44,1988 that is triggered when subjects exceed a prepro7. Smidt GL, Blanpied PR, Anderson MA, White RW: grammed strength. Comparison of clinical and objective methods of asTable 2.-Height, Weight, and Back Extensor Strength (as Measured by the BID·2000) in 50 Healthy Women, Stratified by Age*
CONCLUSION The important findings of this study are that (1) the BID-2000 is a safe and reliable apparatus for
8.
sessing trunk muscle strength-an experimental approach. Spine 12:1020-1024, 1987 Smith EL Jr, Reddan W, Smith PE: Physical activity and calcium modalities for bone mineral increase in aged women. Med Sci Sports Exerc 13:60-64, 1981
44
9.
10.
11.
12. 13. 14. 15.
16.
Mayo Clin Proc, January 1991, Vol 66
BACK STRENGTH IN ELDERLY PATIENTS
McComas AJ, Fawcett PRW, Campbell MJ, Sica REP: Electrophysiological estimation ofthe number ofmotor units within a human muscle. J Neurol Neurosurg Psychiatry 34:121-131, 1971 Gutmann E: Age changes in the neuro-muscular system and aspects of rehabilitation medicine. In Neurophysiologic Aspects of Rehabilitation Medicine. Edited by AA Buerger, JS Tobis. Springfield, Illinois, Charles C Thomas, Publisher, 1976, pp 42-61 Sinaki M, McPhee MC, Hodgson SF, Merritt JM, Offord KP: Relationship between bone mineral density of spine and strength of back extensors in healthy postmenopausal women. MayoClinProc 61:116-122, 1986 B-200 User's Manual. Revision 2.0. Hillsborough, North Carolina, Isotechnologies, Inc., June 1988 Langrana NA, Lee CK, Alexander H, Mayott CW: Quantitative assessment of back strength using isokinetic testing. Spine 9:287-290, 1984 Langrana NA, Lee CK: Isokinetic evaluation of trunk muscles. Spine 9:171-175,1984 Sinaki M, Wahner HW, Offord KP, Hodgson SF: Efficacy of nonloading exercises in prevention of vertebral bone loss in postmenopausal women: a controlled trial. Mayo Clin Proc 64:762-769,1989 Aloia JF, Cohn SH, Ostuni JA, Cane R, Ellis K: Prevention ofinvolutional bone loss by exercise. Ann Intern Med 89:356-358, 1978
17.
18.
19. 20.
21. 22. 23.
Krelner B, Toft B, Pors Nielsen S, Tandevold E: Physical exercise as prophylaxis against involutional vertebral bone loss: a controlled trial. Clin Sci 64:541-546, 1983 Brewer V, Meyer BM, Keele MS, Upton SJ, Hagan RD: Role of exercise in prevention of involutional bone loss. Med Sci Sports Exerc 15:445-449, 1983 Sinaki M, Mikkelsen BA: Postmenopausal spinal osteoporosis: flexion versus extension exercises. Arch Phys Med Rehabil 65:593-596, 1984 Lichter RL, Hewson JK, Radke SJ, Blum M: Treatment of chronic low-back pain: a community-based comprehensive return-to-work physical rehabilitation program. Clin Orthop 190:115-123,1984 Lee CK: The use of exercise and muscle testing in the rehabilitation of spinal disorders. CUn Sports Med 5:271-276, April 1986 Addison R, Schultz A: Trunk strengths in patients seeking hospitalization for chronic low-back disorders. Spine 5:539-544, 1980 Office of Human Development Services: Need for Long-Term Care: Information and Issues; A Chartbook of the Federal Council on the Aging. Publication No. OHDS 81-20704. Washington, DC, US Government Printing Office, 1981, pp 1-25; 39-55
PAUL J. LIMBURG, B.A., Mayo Medical School; MEHRSHEED SINAKI, M.D., Department ofPhysical Medicine and Rehabilitation; JOHN W. ROGERS, B.S., Mayo Medical School; PATRICK E. CASKEY, B.S.M.E., BRYAN K. PIERSKALLA, B.S.E.T., Section ofEngineering Development
Improvement ofback extensor strength (BES) can be used as a therapeutic method for patients with chronic back pain and osteoporosis. The method of evaluation must be reliable and accurate without compromising the condition of the patient. We report the development of a back isometric dynamometer (BID-2000) designed specifically by two ofus to address these concerns in elderly patients with osteopenia or osteoporosis. As the demographics of the general population change, increasing numbers of patients will need the type of monitoring that the BID-2000 provides. Aging has been shown to cause a reduction in the number of functional muscle motor units. To examine this effect on BES, we tested 50 normal, healthy women who were 30 to 79 years old. Proper testing of BES in patients with fragile vertebrae should include isometric measurement in the prone position, maneuverability of the device to allow comfortable positioning of the patient, and simplicity of technique to minimize repetitious performance of maximal contraction. The BID-2000 incorporates each of these features and also provides meaningful results inexpensively. The device offers a safe, reliable (coefficient of variation = 2.33%), and valid (}' = 0.001) method of evaluation. The results ofour study demonstrated moderate, steady reduction ofBES with increasing age and with each successive decade.
Kyphotic postural change is the most physically disfiguring and psychologically damaging effect of osteoporosis. 1 The incidence of osteoporosis can be substantially decreased only by early detection and subsequent intervention in the high-risk patient population. Disproportionate weakness in back extensor musculature relative to body weight or flexor strength considerably increases the possibility of compressing vertebrae in the fragile osteoporotic spine. Recogni-
tion and improvement of decreased back extensor strength (BES) enhance the ability to maintain proper vertical alignment.f A review of the literature shows various analytic techniques and devices designed to determine BES in diverse subject igroups.f" The current study introduces a new back isometric dynamometer (BID-2000), designed by two of us (M.S. and P.E.C.), which offers specific advantages for the measurement of BES in patients with osteopenia or osteoporosis. Its design allows pain-free testing of the patient and proAddress reprint requests to Dr. Mehrsheed Sinaki, Department ofPhysical Medicine and Rehabilitation, Mayo Clinic, vides results to the clinician simply and inexpensively. In the past, commercial and researchRochester, MN 55905. Mayo Clin Proc 66:39-44, 1991
39
40
BACK STRENGTH IN ELDERLY PATIENTS
oriented devices used to assess BES have not been applicable to patients with osteopenia or osteoporosis. Such devices did not make allowances for the fragile spine with reference to exertional pain and fracture risk, both of which discredit the recording of supposed maximal effort. The geriatric population has an increased risk for debilitating postural changes because of several factors, the two most apparent being a greater prevalence of osteoporosis and involutional loss of functional muscle motor units.P-'? The effects of generalized muscle reduction on BES have, to our knowledge, not been reported. Using the BID-2000 with normal, healthy female volunteers, we established baseline values for BES by successive decades from ages 30 to 79 years. Analysis of the data would reveal any change in BES with advancing age.
METHODS
Technique ofAssessment.-The BID-2000 is a strain-gauge dynamometer that measures isometric BES. During assessment, subjects lie prone with the hips and knees in the neutral position and the arms fully extended at the elbows, pointing caudally (similar to the position used earlier by Nachemson and Lindh"). No immobilizing straps are necessary with proper placement of the padded transducer head. Its upper edge is aligned with the superior borders of the scapulae across the midline. The design prohibits any fluctuation in the level of the fulcrum (at the pelvis), which could occur if restraining straps were used (Fig. 1). During the measurements, subjects raise their hands from the table to prevent unwanted contribution of upper extremity musculature to the upward force generated by the trunk against the transducer head. Direct contact between the pelvis and the table must be maintained throughout the determinations. The extensor muscles are contracted for 5 seconds, with no initial upward jerking motions directed at the transducer. The force generated during exertion is processed by an electronic measuring device and converted to a digital display (in either pounds or kilograms). The patient is allowed one
Mayo Clin Proc, January 1991, Vol 66
Fig. 1. Diagram showing positioning of subject for measurement of back extensor strength with strain-gauge back isometric dynamometer (BID-2000).
warm-up trial, which is followed by three successive maximal effort trials separated by 1-minute resting periods. BES values are considered acceptable if the result ofthe final trial does not exceed the preceding efforts by more than 5%. The maximal force achieved is then recorded, with adherence to the foregoing standardized guidelines. Reproducibility of Technique.-Thirteen healthy subjects (eight female and five male) in good physical condition were studied to evaluate the reproducibility of results with the BID-2000. For inclusion of a subject in the study, physical health had to be judged as good on the basis of interviews and physical examinations. Subjects could have no recent history (within the past 5 years) of back pain or injury to the spine. Measurements consisted of three sessions on the BID-2000 completed within a 1-month period (Table 1). Interexaminer error was eliminated by having the same evaluator perform the three measurements on each subject. The 1-month time frame prevented the possibility ofinaccuracies arising from strengthening effects of either the procedure itself or changes in a subject's level of physical activity. The coefficient of variation with the BID-2000 was 2.33%, a significant improvement over a similar isometric dynamometer described in an earlier publication.H The previous dynamometer was determined to be unacceptable for use with the fragile spine of subjects with osteopenia or osteoporosis. Several subjects tested were unable to exert a maximal effort because of pain
Mayo CUn Proc, January 1991, Vol 66
experienced during placement of or exertion against the rigid transducer head of the device. Modifications on the BID~2000 added maneuverability and cushioning to the measuring unit. Validity of Technique.-Sixty-five normal subjects underwent assessment ofBES with the BID-2000 and an additional evaluation with an isometric function of the IsoStation B-200, a commercially available device. 12 Results with the two techniques had a correlation of 0.38 (P = 0.001) (Fig. 2). RESULTS Among 50 healthy women selected randomly from subgroups determined by age (10 women in each of the following categories-30 to 39, 40 to 49, 50 to 59, 60 to 69, and 70 to 79 years), BES decreased with increasing age (Fig. 3). The mean values for height, weight, and BES in each subgroup are shown in Table 2. No subject experienced back pain or complained of any difficulties that may have influenced the interpretation of maximal effort.
BACK STRENGTH IN ELDERLY PATIENTS
41
Table I.-Reproducibility of Measurements of Back Extensor Strength With the BID-2000 in 13 Healthy Subjects* Trial 1 (date)
Trial 2 (date)
Trial 3 (date)
1
5053 (2/12/87)
50 (2/16/87)
(3/2/87)
2
80 (3/3/87)
77 (3/10/87)
78 (3/13/87)
3
73 (2/12/87)
80 (2/16/87)
73 (3/2/87)
4
70 (2/12/87)
69 (2/16/87)
71 (3/2/87)
5
90 (2/12/87)
91 (2/16/87)
93 (3/2/87)
6
70 (2/16/87)
75 (2/18/87)
77 (3/3/87)
7
69 (2/16/87)
71 (2/18/87)
69 (3/3/87)
8
46 (2/12/87)
41 (2/18/87)
43 (3/10/87)
9
118 (3/3/87)
120 (3/10/87)
122 (3/13/87)
10
163 (2/16/87)
164 (2/18/87)
164 (3/3/87)
Subject
DISCUSSION 11 182 181 182 (2/24/87) (3/3/87) (2/16/87) The BID-2000 method is ideal for measurement 12 156 155 158 ofBES, the desired factor for study in osteopenia (4/5/87) (4/15/87) (3/31/87) and osteoporosis. Because subjects are in the 13 183 185 182 prone position during measurement, BES can be (3/3/87) (2/16/87) (2/24/87) determined without contributions from the lower extremity musculature (in contrast to some other *Subjects 1 through 8 = female; subjects 9 through 13 = measuring devices).13.14 The BID-2000 method male. Measurements are shown in pounds. BID = back isometric dynamometer. also removes the influence of trunk weight on extensor strength. Thus, with this technique, one factor that may result in inaccurate record- cious means of management. Nonloading exering of BES is eliminated. In a quantitative cises have not been proved to be effective for preassessment of back strength, Langrana and as- venting involutional bone loss in postmenopausal sociates'" reported similar results with isomet- (estrogen-deficient) women," but other modest ric and isokinetic testing. This finding allows exercise programs have modified the rate of dethe more desirable isometric method (with lim- crease of bone mineral density.8,16-18 ited motion of the vertebrae) to be used in paImprovement ofBES with extension exercises tients with a compromised spine. has become the preferred physiotherapeutic Application to Patients With Osteopenia option for managing patients with osteopenia or Osteoporosis.-In patients with decreased and osteoporosis in that the relative risk of bone mineral density, pharmacologic, nutrition- damaging the fragile spine is less than with al, and physiotherapeutic aspects of manage- flexion exercises.19 The applicability of the BIDment are important. Physiotherapy is the least 2000 device in the treatment of these patients intrusive and should be emphasized as an effica- centers on its provision of an objective means for
42
Mayo elin Proc, January 1991, Vol 66
BACK STRENGTH IN ELDERLY PATIENTS
• •• • •• • • • • ." • • • ·'i • "--, • --..... • • • • •• • • •• • +
..,... ...
120 110
~
100
I
lD
90
C
0
80
~.o tn,
70
+=
0,;::
!!l
s:
60 50
j en W
40
P=0.OO1 Y = 0.44(x)
30
lD
20
10
n=65 r=0.38
40
50
70
60
80
90
100
110
33.41
120
130
BES with BI0-2000, Ib Fig. 2. Correlation of values obtained with isometric evaluation of back extensor strength (BES) by IsoStation B-200 and BID-2000 in 65 normal subjects. BID = back isometric dynamometer.
monitoring compliance. Therapeutic exercise programs are, by necessity, prolonged; thus, even the most well-intentioned patient may stray from the prescribed protocol. An additional hazard that should not be overlooked is the
•
100 .0
-...
.r:.
C>
..;1 •
80
c:
-... • Q)
tn 0 tn
c:
Q)
60
0
co
••
40
x Q)
~
possibility of straining the spine through repeated evaluation of back strength. We have found that the design ofthe BID-2000 appreciably reduces the risk of iatrogenic injury but still provides reliable data for follow-up.
20
m
•
•••
•
• • •
n=50 r=-0.63
I.
0
30
35
40
45
50
55
60
65
70
75
80
Age, yr Fig. 3. Reduction of back extensor strength with increasing age in 50 healthy women.
BACK STRENGTH IN ELDERLY PATIENTS
Mayo Clin Proc, January 1991, Vol 66
43
evaluation ofBES; (2) most fragile skeletons can be safely tested with the BID-2000; (3) the low coefficient of variation of the BID-2000 indicates Height (cm) Weight (kg) BES (lb) that it can be used effectively to detect changes Age (yr) in BES that result from aging, inactivity, or 30-39 158-170.5 52-86 51-97 (35) (164.2) (64.6) (79.6) other factors; and (4) normal, healthy female subjects have a general decline inBES with 40-49 152-171.8 41-72 38-92 (44) (161.7) (58.4) (63.9) increasing age. 50-59 156-170 52-70 40-76 As the elderly population expands, it will (57) (162.2) (59.8) (60.2) require an increasing proportion of the available 60-69 145-168 50-73 28-89 medical care. Currently, approximately 25 mil(65) (160.3) (61.5) (59.0) lion people in the United States are older than 65 70-79 150-170 47-83 18-59 years, and this number will increase to approxi(74) (157.8) (62.8) (38.7) mately 55 million by the year 2030. 23. The asso*Data are shown as range (mean). BES = back extensor ciated increase in the number of patients at risk strength; BID = back isometric dynamometer. for developing kyphosis will necessitate a safe, reliable method for evaluation of BES, such as Application to Patients With Chronic that provided by the BID-2000. Back Pain.-For the minority of patients afflicted with back pain who have chronic symp- ACKNOWLEDGMENT toms, exercise therapy is beneficial.20 Many We thank Sandra K. Fitzgerald for secretarial different types of exercise programs are avail- assistance with the submitted manuscript. able,20.21 but the use of extension exercises is currently favored.t' In a study of patients seeking hospitalization because of back discomfort, Addison and Schultz'" found that the strength of REFERENCES 1. Sinaki M, Grubbs NC: Back strengthening exercises: the extensors was substantially less than that of quantitative evaluation of their efficacy for women the back flexors. This finding supports current aged 40 to 65 years. Arch Phys Med Rehabil 70:1620, 1989 theories for treatment but does not confirm 2. Sinaki M: Beneficial musculoskeletal effects ofphysiwhether the weakness is primary or secondary cal activity in the older woman. Geriatr Med Today to the development of back pain. 8:53-72, November 1989 3. Parnianpour M, Nordin M, Kahanovitz N, Frankel V: Although the exact mechanism by which exer1988 Volvo award in biomechanics: the triaxial coucise provides relief from back pain is unknown, pling of torque generation of trunk muscles during this method of management deserves a trial isometric exertions and the effect of fatiguing isomertial movements on the motor output and movement before intervention with narcotics or a surgical patterns. Spine 13:982-992,1988 procedure. Compliance with the program must 4. Nachemson A, Lindh M: Measurement of abdominal be assessed objectively. Although it primarily and back muscle strength with and without low back provides comfortable evaluation of BES despite pain. Scand J Rehabil Med 1:60-65, 1969 5. Chaffin DB: Ergonomics guide for the assessment of the presence of back pain, the BID·2000 also can human static strength. Am Ind Hyg Assoc J 36:505be useful for motivating patients to exert a truly 511,1975 maximal effort through a visual display of the 6. Kumar S, Chaffin DB, Redfern M: Isometric and isokinetic back and arm lifting strengths: device and BES and the option of an auditory signal (bell) measurement. J Biomech 21:35-44,1988 that is triggered when subjects exceed a prepro7. Smidt GL, Blanpied PR, Anderson MA, White RW: grammed strength. Comparison of clinical and objective methods of asTable 2.-Height, Weight, and Back Extensor Strength (as Measured by the BID·2000) in 50 Healthy Women, Stratified by Age*
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