^aDepartment of Health and Physical Education, The University of Tokyo

^bDepartment of Rehabilitation, Kouseinenkin Hospital, Tokyo

　

In this cross-sectional study we investigated the association of walking characteristics with bone mineral density (BMD) in elderly women to examine the relationships between mobility, balance, body sway, and osteoporosis. Participants were 109 elderly Japanese women aged 62-89 years, ambulatory and voluntarily enrolled in the Fall Prevention Program. For each participant, bone mineral density in the femur and speed of sound, transmission index and osteo-sono index (OSI) in the calcaneus were estimated using a dual-energy x-ray absorptiometry (DEXA) and quantitative ultrasound (QUS) instrument, and they were grouped (osteoporosis, osteopenia, or normal) according to their BMD level.

Measurements were performed in the right femur and heel. We also examined waist girth, hip girth, 10-m walking speed, maximal step length, 40-cm step, one-legged balance time with eyes open, and postural sway. There were no significant differences in 40-cm step, body sway, and one-legged balance time among the groups.

In contrast, maximal step length, 10-m walking speed, total step during the 10m walk, and mean stride length during the 10-m walk were significantly associated with the higher BMD group (normal) (p<0.05). There were significant correlations between walking test parameters and femoral neck BMD (10-m walking speed: r=-0.23, total step: r=-0.24, mean stride length: r=0.24, maximal step length: r=0.19) and OSI (10-m walking speed: r=0.25, total step during 10-m walk: r=-0.18, mean stride length during 10-m walk: r=0.19, maximal step length: r=0.31).

Our results suggest that short maximal step length and slow 10-m walking speed are impaired with osteoporosis in elderly women. Femoral neck BMD and calcaneal OSI are correlated with these mobility parameters. Thus, the characteristics of this simple walker's test could be a useful instrument in the diagnosis of osteoporotic women.

　

Key Words : Walking Speed, Osteoporosis, Elderly Women

　

●Correspondence address : Department of Physical and Health Education, The University of Tokyo, Hyuntae PARK, Hongoh 7-3-1, Bunkyo-ku, Tokyo, Japan, TEL/FAX +81-3-5841-2796, E-mail : tonypark@p.u-tokyo.ac.jp

　

Bone loss and the consequent increase in the risk of fracture are a major health concern for postmenopausal and elderly women. Approximately 1.5 million fractures occurring annually in the United States are attributable to osteoporosis ^1）. According to recent studies, a certain amount of exercise inhibits bone deterioration as it helps maintain, or decrease the loss of, bone mass ^2-3）.

Walking is currently the most frequently reported form of physical activity and has been found to promote better adherence than more intensive exercise; it requires no special skills or facilities and is achievable by virtually all age groups with little risk of injury. For these reasons walking is a particularly suitable form of exercise for the elderly. Furthermore, brisk walking has been reported to have a beneficial effect on bone quality ^4-5）. Walking is accompanied by a gravitational load, and it may be the impact of walking which helps prevent the decalcification of bone ^6）. Walking ability and gait changes in normal adults are associated with falls, functional disability, nursing home placement, and death ^7-9）. Moreover, measurements of walking ability are predictors of hip fracture, and both low bone mineral density (BMD) and poor or abnormal gait are risk factors for hip fracture ^10-12）. Much research has focused on the relationships between gait characteristics and falls. However, the interrelationships between osteoporosis and walking characteristics are not well known. To explore how osteoporosis and walking characteristics are related, we developed a safe and easy method to measure the walker's characteristics and investigate these associations. This study presents a cross-sectional study of 109 women aged 62-89 years, and examines the relationship between walking characteristics and BMD. The aim was to investigate whether or not changes in walking characteristics correlate with osteoporosis (higher BMD versus low BMD) by determining the association of 40-cm step, 10-m walking speed, and maximal step length to BMD in elderly women. Moreover, we were particularly interested in the association between dynamic and static balance ability and osteoporosis.

　

One hundred and nine elderly Japanese women, who had participated regularly in the Fall Prevention Program at the Department of Orthopedics and Rehabilitation, Koseinenkin Hospital, Tokyo, were investigated. This program provides examination, exercise and health education with the aim of improving walking ability and preventing falls and osteoporosis. Each woman underwent a medical history review and a physical test. Weight and height were each measured using scales and stadiometer, and body mass index (BMI) was calculated by dividing weight by squared height. Waist girth and hip girth were measured in a standing position.

　

BMD was assessed by dual-energy X-ray absorptiometry using Hologic-1000 densitometers (Waltham, Massachusetts, USA). Standard protocols provided by the manufacturer were used to examine the BMD of the right femoral neck and results were expressed as BMD in grams per square centimeter. Quantitative ultrasound (QUS) measurements of the right calcaneus were performed using an AOS-100 (Aloka, Tokyo, Japan). Bone synthesis evaluation was performed by measurement of the osteo-sono index (OSI). The OSI was calculated by the equation [OSI= TI×SOS²], where TI represents the transmission index and SOS the speed of sound, SOS is the ultra sound velocity through the heel and may be related to BMD in the calcaneus and TI is a value is proposed to be related to the frequency-dependent attenuation, or BUA, and may be related bone strength at the same site ^13）

　

10-m walking speed was measured by timing the subjects as they walked across a 10 m stretch of firm, uncarpeted, unwaxed wood floor. The total length of the marked walkway course was 15m, allowing for 2.5m acceleration and deceleration zones. Tape was attached along the walkways for the subjects to maintain a straight course. The subjects performed two trials, and the best time was selected. Maximal step length was the length they stepped forward. After deciding which leg to use as the support leg, the subjects were instructed to extend the opposite foot from the start line as far as possible. Once the leg was extended to a maximum, the opposite leg was stepped forward and the feet were brought together. The test began anew when they jumped. The 40-cm step test was measured by scoring (1 = good, 2 = fair, 3 = poor) the subjects as they stepped up and down across the step box. The subjects were instructed to stand about 30 cm away from a 40-cm high step box. They stepped forward up and down across the box comfortably two times.

　

The one-legged balance test was measured by recording how long the subjects could maintain a standing position on one leg with their eyes open. After deciding which leg to use as the support leg, the subjects were instructed to assume a normal, relaxed standing position, bare-foot and with arms at the sides, and stand quietly. They performed this for a maximum duration of 30 seconds. The task was immediately stopped in the case of the lifted leg touching the other leg or touching the floor.

　

Subjects stood bare-foot, with feet 30° apart, straight knees, arms along the body and hands held to the side, upright in the middle of the platform. The position of the feet was adjusted to project the subject's gravity line both through the center of foot pressure and the platform center. The center of pressure was measured for 30 seconds using a stabilometer G-5500 (Anima, Tokyo, Japan), under eyes opened and closed conditions. In both conditions, the subjects were instructed to be motionless during the whole recording period. In the eyes open test the subjects were viewing an eye-level target at a distance of approximately 1.5m in front of them. Data were sampled at 10 Hz during recording periods. Center of pressure was calculated as the product of anteroposterior and lateral sway. In this study, total locus length was used for comparing postural sway.

　

To determine differences in characteristics between groups, the chi-square test and the non-parametric Kruskal-Wallis test were performed. For the parametric data, one-way analysis of variance was performed. Significant interactions were examined (Tukey's test) to determine the difference among groups. To assess the relationships between the variables of mobility and osteoporosis, partial correlational analyses of the data were used Logistic regression models were used to determine odds ratios (OR) and 95% confidence intervals (CI) for osteoporosis and quartiles of walking speed. The significance level of 0.05 was set for all models.

　

According to our datas, the mean ages of the women were 73.2 (osteoporosis group), 71.4 (osteopenia group), and 69.5 (normal group) years, while their mean weight was 47.7, 53.5, and 60.6 kg respectively. Weight and BMI were significantly lower in osteoporotic women than in either the osteopenic or the normal groups. Moreover, the mean value of weight was significantly lower than the normal or the osteopenic women, but BMI was not significantly different between osteopenic and normal women. Mean waist and hip ratio did not differ significantly. Women with higher BMD had longer maximal step length compared with osteoporotic women. There were no significant differences in the 40 cm step test score among the groups. In 10 m walking speed, total step and mean stride length during the 10 m walk better performance was associated with the normal group. The mean values for postural stability and balance parameters did not reveal any association among the groups.

There were significant correlations between bone density and walking characteristics (positive correlation: 10-m walking speed mean stride length and maximal step length: negative: total step) as Table 2 and Figure 1 show. There was no significant association between age and BMD or OSI.

　

　

　

　

Non adjusted logistic models examined the association of osteoporosis with the 10-m rapid walking time (sec) (Fig. 2). In the third and highest quartile of 10-m walking time, the odds ratio of reporting was 1.6 (95% CI: 0.8-3.4) compared with the lowest quartile.