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Abstract
Objective—To test the efficacy of a community based 10 week exercise intervention to reduce fall risk factors in women with osteoporosis.
Methods—Static balance was measured by computerised dynamic posturography (Equitest), dynamic balance by timed figure of eight run, and knee extension strength by dynamometry. Subjects were randomised to exercise intervention (twice weekly Osteofit classes for 10 weeks) or control groups.
Results—The outcome in 79 participants (39 exercise, 40 control) who were available for measurement 10 weeks after baseline measurement is reported. After confounding factors had been controlled for, the exercise group did not make significant gains compared with their control counterparts, although there were consistent trends toward greater improvement in all three primary outcome measures. Relative to the change in control subjects, the exercise group improved by 2.3% in static balance, 1.9% in dynamic balance, and 13.9% in knee extension strength.
Conclusions—A 10 week community based physical activity intervention did not significantly reduce fall risk factors in women with osteoporosis. However, trends toward improvement in key independent risk factors for falling suggest that a study with greater power may show that these variables can be improved to a level that reaches statistical significance.
- osteoporosis
- balance
- strength
- fall risk
- exercise
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Take home message
Community based exercise classes can be safe for patients with osteoporosis, and such a programme produced trends toward increased knee extension strength, static balance, and dynamic balance in 65–75 year old women. However, the 10 week intervention did not achieve statistically significant changes in the fall risk profiles of the participants.
Osteoporotic fracture is a major health care problem world wide,1 and falls are the major precipitant of hip2, 3 and upper limb4 fractures. Certain fall risk factors such as impaired balance, abnormal gait patterns,5, 6 and muscle weakness7 respond favourably to physical activity.8–10
People with osteoporosis are often reluctant to join standard seniors exercise classes for fear of sustaining a low trauma fracture. Thus the Osteoporosis Program at BC Women's Hospital and Health Centre developed an exercise programme for people with osteoporosis. This programme began in 1997, and over 400 women have participated in it so far. To test its efficacy, we undertook a single blind, randomised controlled trial of a 10 week Osteofit exercise programme, in community dwelling women aged 65–75 years, who had osteoporosis confirmed by dual energy x ray absorptiometry.
Methods
SUBJECTS
Subjects were community dwelling women who were aged 65–75 and had osteoporosis diagnosed by dual energy x ray absorptiometry (Lunar Corp, Madison, Wisconsin, USA) at the total hip or lumbar spine or both—that is, bone mineral density T score at least 2.5 standard deviations below the young normal sex matched bone mineral density of the Lunar reference database.11 This group is described in more detail elsewhere (Carter N, et al. Quadriceps strength is a major determinant of static and dynamic balance as well as quality of life: a cross sectional study of 65–75 yr old community dwelling women with osteoporosis (submitted)).
After baseline measurements, 93 women were randomised to exercise intervention (n = 45) or control (n = 48) groups. Data reported are on the 79 women (39 control, 40 exercise) who were available for follow up 10 weeks after baseline measurement. The institutional review board approved the protocol, and all subjects gave written informed consent.
EXERCISE PROGRAMME: OSTEOFIT CLASSES
Osteofit is a community based exercise programme for people with osteoporosis; it aims to reduce the risk of falling and improve functional ability, and thereby enhance quality of life. The twice weekly exercise programme targets posture, balance, gait, coordination, and hip and trunk stabilisation. All instructors are registered by the BC recreation and parks association and certified by the BC Women's Hospital Osteoporosis programme. The classes for participants in this research study were typical of those in the Osteofit programme. The programme is outlined in more detail elsewhere (Carter et al. ‘Osteofit’—a community-based strength and balance training program improves dynamic balance and knee extension strength: a randomized, single-blind controlled trial in 65–75 yr-old women with osteoporosis (submitted)) and at the website http://www.osteofit.org.
The main workout consisted of strengthening and stretching exercises to combat poor posture, as well as exercises to improve balance and coordination. Exercises to improve functional ability included chair squats and getting up and down off the floor. Exercise repetitions were kept between eight and 16, and the weights were relatively light so that the participants did not work to fatigue with each set. Each subject kept a journal in which they recorded their participation and any illness or injury. Subjects assigned to the control group were asked to continue their daily routine activities.
DESCRIPTIVE DATA
At baseline and 10 weeks, participants attended our hospital based laboratory to complete questionnaires and undertake physical testing.
QUESTIONNAIRES
We evaluated general health with a questionnaire, and current physical activity with the seven day physical activity recall questionnaire.12
BALANCE, STRENGTH, AND ANTHROPOMETRY
An experienced neuroscientist clinician (AM) performed all static balance measurements using the Equitest computerised posturography platform (Neurocom International, Clackamas, Oregon, USA) to determine response to sensory perturbations (Sensory Organisation Test).13 This instrument provides numerous measures of sway, and we used the composite balance score as an indicator of static balance. The test-retest reliability of composite score for computerised posturography is 0.98 (Pearson r).
Dynamic balance was tested by a timed figure of eight running test around two cones placed 10 m apart.14, 15 The best attempt of two trials was recorded. The result was converted into velocity (m/s) to simplify interpretation of correlation and regression analysis. Positive correlation corresponds to improved dynamic balance.
The knee extension strength of the dominant leg was tested using Lord's strap assembly incorporating a strain gauge.16 Test-retest reliability in our laboratory for an age matched population (n = 8) is 0.92 (Pearson r). For analysis, knee extension strength is expressed per unit of height to compensate for the length of the lever arm; all data reported here are thus corrected.
STATISTICAL ANALYSES
Data were analysed using SPSS (Windows version 8.0). Descriptive data are reported for variables of interest (mean, SD, and 95% confidence interval (CI)). Unpaired t tests were used to compare baseline characteristics between groups and to assist in choosing covariates. Analysis of covariance was used to examine differences in percentage change between groups after controlling for confounding factors. Covariates were selected according to biological or statistical rationale. Multivariate analysis was used to search for confounding factors by adding independent variables to the model containing the “group” (exercise or control) variable and testing for a significant change in its coefficient (and therefore in the model adjusted R2). For variables to be used in the final model, they had to produce a significant change in the group variable coefficient. Therefore covariates differed for each of the dependent variables (table 1).
We also constructed three stepwise regression models to determine the most robust predictors of change in (a) composite posturography score, (b) figure of eight velocity (m/s), and (c) knee extension strength. Independent variables of interest were: baseline value (for posturography, figure of eight, and knee extension strength respectively), age (years), number of current medications, oestrogen use (years), tobacco use (yes/no), height (cm), weight (kg), current physical activity (hours), and Osteofit (yes/no). Variables were chosen on the basis of both theoretical and statistical (Pearson product-moment correlation) association with the outcome variables. Variables were entered into the model at p<0.10.
Results
Exercise and control groups did not differ in baseline for age, height, and weight (table 2). The control group reported fewer years of oestrogen use, fewer medications, and higher activity levels at baseline. Although the differences were not significant, variables were considered as potential covariates in the analyses.
Absolute (table 3) and percentage (fig 1) change for knee extension strength and static and dynamic balance for each group after controlling for confounding factors are summarised. Adjusted for covariates the exercise group improved in static balance by a mean (SE) 3.6 (1.7)% whereas the control group improved 1.3 (1.7)%. Similar non-significant trends were seen in dynamic balance (exercise group improved 6.9 (1.7)% and control 5.0 (1.7)%) and in knee extension strength (exercise group improved 13.9 (7.3)% and control decreased by 0.2 (7.3)%) (fig 1).
Participants reported no injuries from either measurement or the exercise intervention. Mean compliance with the exercise intervention as measured by instructor log was 78%, and the range was 44–100% of possible sessions attended.
STEPWISE REGRESSION
Table 4 shows models predicting change in static and dynamic balance and quadriceps strength. Baseline values explained a significant amount of the variance in each of the three regression models. Physical activity explained 10% of the variance in knee extension strength.
Discussion
This randomised controlled trial in 79 women with proven osteoporosis showed that a 10 week community based exercise intervention was safe in such women but that it did not promote statistically significant improvement in static balance, dynamic balance, or knee extension strength. Each of these three outcome variables is an independent risk factor for osteoporotic fracture.7 However, it is important to note that certain participants made substantial gains, and the mean increase in strength of almost 14% in knee extension strength is likely to be of biological significance, if not statistical significance, in this relatively small study. Furthermore, negative studies need to be reported to avoid publication bias and to help to define the dimensions of exercise that cause significant improvements in fall risk factors.
There is increasing demand for exercise studies to define clearly the dimensions of exercise needed to ameliorate health. This 10 week analysis indicates that such a short intervention may be of insufficient duration to substantially alter the fall risk profile in women with osteoporosis. This does not exclude the possibility that a longer intervention may achieve such a result.
We note several study limitations. Exercise intervention studies appeal to those who are healthy and motivated,17 and women who volunteered for this study were particularly fit for their age. This limits the population to which results can be generalised. Particularly frail women (in addition to having osteoporosis) may not be able to attend community based intervention.
We acknowledge that improving a fall risk factor profile does not guarantee fall reduction. There is a need for a larger study to evaluate the effect of this type of intervention in a high risk group that is powered to detect a treatment effect on falls, and ideally, injurious falls and fractures.18
The clinical implication of this study is that appropriately supervised community based exercise classes can be safe for patients with osteoporosis. However, 10 weeks appears to be too short to achieve statistically significant change in some important outcomes. Nevertheless, the trends we observed suggest that analysis of a longer intervention is warranted.
Covariates for each dependent variable in analysis of covariance models for the 10 week randomised controlled Osteofit exercise intervention study
Baseline characteristics in those completing the 10 week trial between exercise and control groups in the Osteofit randomised controlled trial
Absolute change in strength and dynamic and static balance over 10 weeks for exercise and control groups in the randomised controlled Osteofit study
Stepwise regression models for change in quadriceps strength (kg/cm), static posturography (Equitest), and dynamic balance (using the figure of eight test in m/s) including standardised β coefficients and adjusted R2
Percentage change over 10 weeks for exercise and control groups for figure of eight velocity, knee extension strength, and Equitest. Means are adjusted for covariates (see table 1). Bars are adjusted means and SE.
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Take home message
Community based exercise classes can be safe for patients with osteoporosis, and such a programme produced trends toward increased knee extension strength, static balance, and dynamic balance in 65–75 year old women. However, the 10 week intervention did not achieve statistically significant changes in the fall risk profiles of the participants.