Clinical Science (1992) 82, 321-327 (Printed in Great Britain)
32 I
Leg extensor power and functional performance in very old men and women E. Joan BASSEY*, Maria A. FIATARONEt$$,Evelyn F. O’NEILL$, Margaret KELLY$, William J.EVANSt and Lewis A. LlPSlTZ$$ “Department of Physiology and Pharmacology, Medical School, University of Nottingham, Nottingham, U.K., US. Department of Agriculture, Human Nutrition Research Centre on Aging at Tufts University, Boston, Massachusetts, U.S.A., $Hebrew Rehabilitation Centre for Aged, Boston, Massachusetts, U.S.A., and §Division on Aging, Harvard Medical School, Boston, Massachusetts, U.S.A.
t
(Received I 3 May/ I 7 October I99 I ; accepted 29 October I99 I )
1. Residents of a chronic care hospital (13 men of mean age 88.5+6 SD years and 13 women of mean age 86.5t-6 SD years) who had multiple pathologies were assessed for leg extensor capability in several ways. 2. A custom-built rig was used to assess leg extensor power, that is, maximal power output over less than 1 s in a single extension of one leg. Performance measures were obtained by timing chair rises (from a standard chair 0.43 m high), stair climbing (four risers, total height 0.635 m) and a walk (6.1 m). For each measurement the best of several trials were recorded as definitive. 3. Leg extensor power was significantly correlated with all performance measures, but the performance measures were not related to each other except for chair rising and walking speed. 4. Women had significantly less extensor power than men, but their power explained more of the variance in performance, e.g. power accounted for 86% of the variance in walking speed. 5. There was no relation within the group between age and any of the variables measured. 6. Measurement of leg extensor power in frail elderly people may prove useful in focusing effective rehabilitation programmes.
INTRODUCTION Leg extensor power is needed for many basic activities in daily life, such as walking or rising from a seated position [l-51. The ability to do these things easily is taken for granted by healthy young people, but it is threatened in old age by various impairments which probably include lack of muscle power. Recently, a rig has been developed which allows safe and convenient measurement of the power available in a single extension of one leg [6]. This rig can be used with all age groups and levels of physical capability. The time period of this
measurement is brief, less than 1 s, so it depends upon the resources which can be commanded by the nervous system from within the muscle cells rather than circulatory or respiratory factors. Power output measured in this way should correlate well with short-term performance measures, for instance speed of stair-climbing [7] or chair rising. It may also be related to speeds of walking over short distances in old people, since leg extension provides forward momentum. For some people these ordinary activities tax the resources of the muscles close to their limit [S]. The aim of the study was to find out to what extent power output measured in the rig predicted performance in old people.
METHODS Subjects These were 26 ambulatory residents of the Hebrew Rehabilitation Centre for Aged (HRCA), a long-term care institution. Those who were recruited were able to follow directions and to walk across the room with an assistive device if necessary. Most of the subjects had already taken part in previous studies [S]. This study was approved by the Human Investigations Review Committee of HRCA and Tufts University. All subjects gave their verbal informed consent. The physical and clinical characteristics of the subjects are shown in Table 1 and 2, respectively. Skeletal size of the body was assessed as demi-span [9] as well as height because of the prevalence of kyphosis [lo].All subjects were on prescribed medications, all had a history of falls, many had multiple health problems and half spent most of their time in a wheelchair (five men and eight women). One woman had Parkinson’s disease which was moderately well controlled with Sinemet (carbidopa/levodopa, four times daily). Mental competence was assessed formally on a four-point scale [ll] within 2 weeks of the other measurements. Eleven subjects were normal, nine had mild impairment
Key words: aged, exercise, muscle power, walking. Abbreviation: HRCA, Hebrew Rehabilitation Centre for Aged. Correspondence: Dr Joan Bassey, Department of Physiology and Pharmacology,Medical School, University of Nottingham, Nottingham NG7 2UH, U.K.
E. J. Bassey e t al.
322
Table I. Physical characteristics of subjects. Values are means ~ S E M .Statistical significance (Student's t-test): compared with men.
Men Women
n
Age (years)
Weight (kg)
Height (m)
Demi-span (m)
13 13
88-1 1.6 86t 1.5
64.7 t 2.7 54.7 i 2.8*
1.58k0.03 I .50 +0.03*
0.75 k0.02 0.70 k0.02*
Table 2. Clinical characteristics of subjects. Values are absolute prevalences (there were no significant differences between men and women in any o f these disease groups: many had more than one disease). Men (n = 13) Diabetes Hypertension Heart disease* Parkinson's Neurological diseaset Cervical arthritis Syncope Musculo-skeletal disease: Cancer Other (history of gastrointestinal bleed, incontinence o f urine) No. of medications per patient (mean k SD)
*P (0.05
4 7
II 0 6 3 I1 4 2 7 5.2*2.4
Women (n = 13)
4 6
7 I
8 I 12
8 I 7 5.2k2.1
*Chronic heart failure, angina, myocardial ischaemia, crescendo angina, valvular disease, cardiomyopathy, arrhythmia, bradytachy syndrome or pacemaker. t Seizure disorder, cerebrovascular disease, autonomic disorder, neuromuscular disorder, peripheral neuropathy, labyrinthine disorder. :Chronic arthritis with chronic pain o r deformity, skeletal deformity.
and six had moderate impairment; none was severely impaired. There was no sex difference in this distribution.
Leg extensor power The measurement of leg extensor power requires that the subject, in a seated position with folded arms, gives a maximal push to a large foot pedal. The equipment consists of a rig with an adjustable seat, facing the pedals which are connected through a chain to a flywheel. An opto-switch detects the flywheel speed and a recorder displays the outcome in W. The final (maximal) speed of the flywheel after a pedal push is used to calculate the average power. The details of the calculations and the calibration of the system have been described previously [6]. The seat is adjusted on runners for each individual, to allow the leg to reach full extension exactly at the end of the pedal travel which is 0.165 m. The seat has no arms and a low back (0.15 m), so the forces generated in the leg are contained between the buttocks and the sole of the foot. A fixed eccentric plate in the linkage between the pedal cranks and the chain alters the mechanical advantage of the push progressively as the flywheel
accelerates. The time taken for one pedal push varies with the power of the individual (values range from 0.25 to 0.75 s). After a practice push, maximal efforts were required. Strong verbal encouragement was given and at least five trials were allowed, up to a maximum of nine if the subiect was still showing- improvements. The highest recorded power output was taken as the definitive measurement. Both left and right legs were measured separately, with the order randomized. The measurement was repeated on 18 subjects about 1 week later at the same time of day.
Performance measurements (chair rising, stair climbing and walking 6.1 m) Subjects were asked to perform as fast as they could and to repeat the performance after a short rest. The tests were done in the order listed above. The time taken was recorded with a stop watch to the nearest 0.01 s. Since these subjects did not have the muscle power to move rapidly, no danger arose from the development of high momentum. Subjects had performed these tests in previous studies and were therefore familiar with them 181. Chair rising. The chair had arms and was square in design with a level seat 0.43 m from the floor. Subjects were required to sit in the chair with their back supported and to fold their arms. Then, on a word of command from the investigator, they were required to rise from the chair to a full standing position as rapidly as possible. The investigator made a subjective judgement about whether a full stance had been reached, based on familiarity with the subiect and their cauabilities obtained before the formal test was conducted. Some were unable to rise and were therefore allowed to use the arms of the chair and to have their walking frame in position in front of them for balance once they were standing up. The best time out of three tries was taken as the definitive measurement. This test is similar to one for younger, healthier people which requires a number of consecutive chair rises [ 121. Stair climbing. The stairs were 0.635 m high (four risers of 0.15 m), 1.0 m wide, with sturdy banister rails on each side and around the top platform. The horizontal distance was 1.22 m. From a standing start with arms at their sides, subjects walked up as rapidly as possible using the banisters for balance if necessary. They turned around on the top platform and walked down in their own time. Walking. Subjects were asked to walk a level 6.1 m course using their normal method of locomotion. First, they were asked to walk at their normal speed and then as fast as possible. For many the normal speed was as fast as L
A
Leg extensor p o w e r and performance in t h e
they could go. The best speed achieved was used for the analysis.
Analysis Results were expressed, unless otherwise stated, as mean sf^^^ or for skewed distributions as medians finterquartile range. Comparisons between groups were made by using Student’s r-test or Mann-Whitney U-tests, and correlations between variables were assessed by using Pearson’s product moment r or Spearman’s p. If a probability level of 5% was found, it was accepted that the findings were significant. The coefficient of variation on re-test was calculated according to the method of Healy [13], which is suitable for duplicate measures [coefficient of variation = SD of paired differences divided by the square root of 2 (expressed as OO/ of gross mean on first occasion)].
RESULTS All 26 subjects (13 women and 13 men), ranging in age from 80 to 99 years, were measured for walking speed and leg extensor power. Three women were unable to climb the stairs and one man could not rise from his chair. Men were significantly taller, larger and heavier as expected, but there was no sex difference in age, prevalence of disease (Table 2) nor in the numbers who used a walking frame.
Height and demi-span Skeletal size, measured as demi-span, was significantly related, as expected, to height, sex, weight and leg extensor power, but it was not related to age, stride length, any of the performance measures or to the ratio of leg power to body mass. The predicted height (derived from the demi-span measurement and equations previously described [9])was significantly and variably greater than the measured height (the maximum difference was 15 cm and mean differences zk SD were 6.9 cm k 5.3 for the men and 7.7 cm f4.30 for the women). This predicted height was not significantly different from reported adult heights in a sub-group of 16 subjects who were confident that they remembered their young adult height. The predicted
323
old
height was therefore used to derive a body mass index (weight in kg divided by height in m2).The values ranged from 19 to 28 kg/rn2 (mean values k SD were 24.0 k 2.76 for the men and 22.4 k 3.02 for the women).
Leg extensor power Both legs were assessed, except in one of the men who had had a hip replacement within the last 6 months. There was no order effect. The difference between the legs was more than 10% in two-thirds of the group so further analysis employed the highest value from either leg, that is ‘best leg’, or else the highest value for each leg was taken and the two added together, that is ‘both legs’. Reliability within the test was assessed by comparing the best with the second best performance. The differences were small, for example for the right leg on the first day the median difference was 2.0 W (interquartile range = 0.9-4.5 W). Correlation coefficients for re-test ( n = 18) were high (right leg, r = 0.85; left leg, r = 0.94; best leg, r = 0.91; both legs, r = 0.93). The coefficient of variation on re-test was about 16% whether the data from the right, left, best or both legs were used. There was no difference between men and women in this variation nor was it affected by the mental competence of the subject. Results from the first day of measurement have been used when possible (since this was also the day on which performance measurements were made). In six subjects satisfactory measurement of leg extensor power was obtained only on the second day. The data are also expressed as a ratio of power to body mass. The group mean results for men and women separately are given in Table 3. The men were about twice as powerful as the women; the difference was less marked when power was expressed in proportion to body weight, but it remained significant. There was no relation with age within the group. Those with neurological disease (including the one woman with Parkinson’s disease) had significantly poorer leg extensor power for body mass than the others (Student’s t-test for unpaired means, P
32 I
Leg extensor power and functional performance in very old men and women E. Joan BASSEY*, Maria A. FIATARONEt$$,Evelyn F. O’NEILL$, Margaret KELLY$, William J.EVANSt and Lewis A. LlPSlTZ$$ “Department of Physiology and Pharmacology, Medical School, University of Nottingham, Nottingham, U.K., US. Department of Agriculture, Human Nutrition Research Centre on Aging at Tufts University, Boston, Massachusetts, U.S.A., $Hebrew Rehabilitation Centre for Aged, Boston, Massachusetts, U.S.A., and §Division on Aging, Harvard Medical School, Boston, Massachusetts, U.S.A.
t
(Received I 3 May/ I 7 October I99 I ; accepted 29 October I99 I )
1. Residents of a chronic care hospital (13 men of mean age 88.5+6 SD years and 13 women of mean age 86.5t-6 SD years) who had multiple pathologies were assessed for leg extensor capability in several ways. 2. A custom-built rig was used to assess leg extensor power, that is, maximal power output over less than 1 s in a single extension of one leg. Performance measures were obtained by timing chair rises (from a standard chair 0.43 m high), stair climbing (four risers, total height 0.635 m) and a walk (6.1 m). For each measurement the best of several trials were recorded as definitive. 3. Leg extensor power was significantly correlated with all performance measures, but the performance measures were not related to each other except for chair rising and walking speed. 4. Women had significantly less extensor power than men, but their power explained more of the variance in performance, e.g. power accounted for 86% of the variance in walking speed. 5. There was no relation within the group between age and any of the variables measured. 6. Measurement of leg extensor power in frail elderly people may prove useful in focusing effective rehabilitation programmes.
INTRODUCTION Leg extensor power is needed for many basic activities in daily life, such as walking or rising from a seated position [l-51. The ability to do these things easily is taken for granted by healthy young people, but it is threatened in old age by various impairments which probably include lack of muscle power. Recently, a rig has been developed which allows safe and convenient measurement of the power available in a single extension of one leg [6]. This rig can be used with all age groups and levels of physical capability. The time period of this
measurement is brief, less than 1 s, so it depends upon the resources which can be commanded by the nervous system from within the muscle cells rather than circulatory or respiratory factors. Power output measured in this way should correlate well with short-term performance measures, for instance speed of stair-climbing [7] or chair rising. It may also be related to speeds of walking over short distances in old people, since leg extension provides forward momentum. For some people these ordinary activities tax the resources of the muscles close to their limit [S]. The aim of the study was to find out to what extent power output measured in the rig predicted performance in old people.
METHODS Subjects These were 26 ambulatory residents of the Hebrew Rehabilitation Centre for Aged (HRCA), a long-term care institution. Those who were recruited were able to follow directions and to walk across the room with an assistive device if necessary. Most of the subjects had already taken part in previous studies [S]. This study was approved by the Human Investigations Review Committee of HRCA and Tufts University. All subjects gave their verbal informed consent. The physical and clinical characteristics of the subjects are shown in Table 1 and 2, respectively. Skeletal size of the body was assessed as demi-span [9] as well as height because of the prevalence of kyphosis [lo].All subjects were on prescribed medications, all had a history of falls, many had multiple health problems and half spent most of their time in a wheelchair (five men and eight women). One woman had Parkinson’s disease which was moderately well controlled with Sinemet (carbidopa/levodopa, four times daily). Mental competence was assessed formally on a four-point scale [ll] within 2 weeks of the other measurements. Eleven subjects were normal, nine had mild impairment
Key words: aged, exercise, muscle power, walking. Abbreviation: HRCA, Hebrew Rehabilitation Centre for Aged. Correspondence: Dr Joan Bassey, Department of Physiology and Pharmacology,Medical School, University of Nottingham, Nottingham NG7 2UH, U.K.
E. J. Bassey e t al.
322
Table I. Physical characteristics of subjects. Values are means ~ S E M .Statistical significance (Student's t-test): compared with men.
Men Women
n
Age (years)
Weight (kg)
Height (m)
Demi-span (m)
13 13
88-1 1.6 86t 1.5
64.7 t 2.7 54.7 i 2.8*
1.58k0.03 I .50 +0.03*
0.75 k0.02 0.70 k0.02*
Table 2. Clinical characteristics of subjects. Values are absolute prevalences (there were no significant differences between men and women in any o f these disease groups: many had more than one disease). Men (n = 13) Diabetes Hypertension Heart disease* Parkinson's Neurological diseaset Cervical arthritis Syncope Musculo-skeletal disease: Cancer Other (history of gastrointestinal bleed, incontinence o f urine) No. of medications per patient (mean k SD)
*P (0.05
4 7
II 0 6 3 I1 4 2 7 5.2*2.4
Women (n = 13)
4 6
7 I
8 I 12
8 I 7 5.2k2.1
*Chronic heart failure, angina, myocardial ischaemia, crescendo angina, valvular disease, cardiomyopathy, arrhythmia, bradytachy syndrome or pacemaker. t Seizure disorder, cerebrovascular disease, autonomic disorder, neuromuscular disorder, peripheral neuropathy, labyrinthine disorder. :Chronic arthritis with chronic pain o r deformity, skeletal deformity.
and six had moderate impairment; none was severely impaired. There was no sex difference in this distribution.
Leg extensor power The measurement of leg extensor power requires that the subject, in a seated position with folded arms, gives a maximal push to a large foot pedal. The equipment consists of a rig with an adjustable seat, facing the pedals which are connected through a chain to a flywheel. An opto-switch detects the flywheel speed and a recorder displays the outcome in W. The final (maximal) speed of the flywheel after a pedal push is used to calculate the average power. The details of the calculations and the calibration of the system have been described previously [6]. The seat is adjusted on runners for each individual, to allow the leg to reach full extension exactly at the end of the pedal travel which is 0.165 m. The seat has no arms and a low back (0.15 m), so the forces generated in the leg are contained between the buttocks and the sole of the foot. A fixed eccentric plate in the linkage between the pedal cranks and the chain alters the mechanical advantage of the push progressively as the flywheel
accelerates. The time taken for one pedal push varies with the power of the individual (values range from 0.25 to 0.75 s). After a practice push, maximal efforts were required. Strong verbal encouragement was given and at least five trials were allowed, up to a maximum of nine if the subiect was still showing- improvements. The highest recorded power output was taken as the definitive measurement. Both left and right legs were measured separately, with the order randomized. The measurement was repeated on 18 subjects about 1 week later at the same time of day.
Performance measurements (chair rising, stair climbing and walking 6.1 m) Subjects were asked to perform as fast as they could and to repeat the performance after a short rest. The tests were done in the order listed above. The time taken was recorded with a stop watch to the nearest 0.01 s. Since these subjects did not have the muscle power to move rapidly, no danger arose from the development of high momentum. Subjects had performed these tests in previous studies and were therefore familiar with them 181. Chair rising. The chair had arms and was square in design with a level seat 0.43 m from the floor. Subjects were required to sit in the chair with their back supported and to fold their arms. Then, on a word of command from the investigator, they were required to rise from the chair to a full standing position as rapidly as possible. The investigator made a subjective judgement about whether a full stance had been reached, based on familiarity with the subiect and their cauabilities obtained before the formal test was conducted. Some were unable to rise and were therefore allowed to use the arms of the chair and to have their walking frame in position in front of them for balance once they were standing up. The best time out of three tries was taken as the definitive measurement. This test is similar to one for younger, healthier people which requires a number of consecutive chair rises [ 121. Stair climbing. The stairs were 0.635 m high (four risers of 0.15 m), 1.0 m wide, with sturdy banister rails on each side and around the top platform. The horizontal distance was 1.22 m. From a standing start with arms at their sides, subjects walked up as rapidly as possible using the banisters for balance if necessary. They turned around on the top platform and walked down in their own time. Walking. Subjects were asked to walk a level 6.1 m course using their normal method of locomotion. First, they were asked to walk at their normal speed and then as fast as possible. For many the normal speed was as fast as L
A
Leg extensor p o w e r and performance in t h e
they could go. The best speed achieved was used for the analysis.
Analysis Results were expressed, unless otherwise stated, as mean sf^^^ or for skewed distributions as medians finterquartile range. Comparisons between groups were made by using Student’s r-test or Mann-Whitney U-tests, and correlations between variables were assessed by using Pearson’s product moment r or Spearman’s p. If a probability level of 5% was found, it was accepted that the findings were significant. The coefficient of variation on re-test was calculated according to the method of Healy [13], which is suitable for duplicate measures [coefficient of variation = SD of paired differences divided by the square root of 2 (expressed as OO/ of gross mean on first occasion)].
RESULTS All 26 subjects (13 women and 13 men), ranging in age from 80 to 99 years, were measured for walking speed and leg extensor power. Three women were unable to climb the stairs and one man could not rise from his chair. Men were significantly taller, larger and heavier as expected, but there was no sex difference in age, prevalence of disease (Table 2) nor in the numbers who used a walking frame.
Height and demi-span Skeletal size, measured as demi-span, was significantly related, as expected, to height, sex, weight and leg extensor power, but it was not related to age, stride length, any of the performance measures or to the ratio of leg power to body mass. The predicted height (derived from the demi-span measurement and equations previously described [9])was significantly and variably greater than the measured height (the maximum difference was 15 cm and mean differences zk SD were 6.9 cm k 5.3 for the men and 7.7 cm f4.30 for the women). This predicted height was not significantly different from reported adult heights in a sub-group of 16 subjects who were confident that they remembered their young adult height. The predicted
323
old
height was therefore used to derive a body mass index (weight in kg divided by height in m2).The values ranged from 19 to 28 kg/rn2 (mean values k SD were 24.0 k 2.76 for the men and 22.4 k 3.02 for the women).
Leg extensor power Both legs were assessed, except in one of the men who had had a hip replacement within the last 6 months. There was no order effect. The difference between the legs was more than 10% in two-thirds of the group so further analysis employed the highest value from either leg, that is ‘best leg’, or else the highest value for each leg was taken and the two added together, that is ‘both legs’. Reliability within the test was assessed by comparing the best with the second best performance. The differences were small, for example for the right leg on the first day the median difference was 2.0 W (interquartile range = 0.9-4.5 W). Correlation coefficients for re-test ( n = 18) were high (right leg, r = 0.85; left leg, r = 0.94; best leg, r = 0.91; both legs, r = 0.93). The coefficient of variation on re-test was about 16% whether the data from the right, left, best or both legs were used. There was no difference between men and women in this variation nor was it affected by the mental competence of the subject. Results from the first day of measurement have been used when possible (since this was also the day on which performance measurements were made). In six subjects satisfactory measurement of leg extensor power was obtained only on the second day. The data are also expressed as a ratio of power to body mass. The group mean results for men and women separately are given in Table 3. The men were about twice as powerful as the women; the difference was less marked when power was expressed in proportion to body weight, but it remained significant. There was no relation with age within the group. Those with neurological disease (including the one woman with Parkinson’s disease) had significantly poorer leg extensor power for body mass than the others (Student’s t-test for unpaired means, P
