 Index | ||||||||||
|
| TETSUO OHKUWA, Corresponding author. e-mail: ohkuwa.tetsuo@nitech.ac.jp phone: +81-52-735-5199; fax: +81-52-735-5199 Published online 29 June 2005 in J-STAGE (www.jstage.jst.go.jp) DOI: 10.1537/ase.040129 |
|
Postural sway is widely used as an indicator of the maintenance of balance (Lichtenstein et al., 1988; Berg et al., 1992). In studies on the elderly, postural sway has been strongly associated with mobility (Berg et al., 1992), falling (Lichtenstein et al., 1988), various disease states (Mauritz et al., 1979; Mathias et al., 1986), and aging (Newell et al., 1997). Postural sway in elderly people can be reduced by raising the level of physical fitness with such exercise or techniques as aerobics, resistance, flexibility, and balance training (Judge et al., 1993; Seidler and Martin, 1997; Messier et al., 2000). In adults, the ability to maintain balance depends on muscular strength as well as the capacity of aerobic and anaerobic function (Era and Heikkine, 1985; Nguyen et al., 1993; Lamb et al., 1995).
Postural sway and the development of static balance ability have been investigated in children from ages 2 to 14 years (Riach and Hayes, 1987) and 3.5 to 17 years (Odenrick and Sandstedt, 1984); these studies have demonstrated that postural sway decreases linearly with age. These previous studies, however, included only two to three children aged 3–5 years. Usui et al. (1995) reported that total area of sway decreased markedly at 3–5 years of age and then slowly after age 6. Several investigators have also reported an age-dependent decrease in postural sway in children (Shambes, 1976; Zernicke et al., 1982; Foudriat et al., 1993). Lebiedowska and Syczewska (2000) found no significant correlation between postural sway and developmental factors such as body height and weight in children from 6 to 18 years of age.
As summarized above, improved physical conditions assist in the balance of elderly people (Era and Heikkinen, 1985; Nguyen et al., 1993; Lamb et al., 1995). This suggests that a marked decrease in the postural sway of children might also be related to an increase in physical fitness. However, the relationship between the magnitude of postural sway and the level of physical fitness in children is not clear. It is not known whether decrease of postural sway in children depends on increase in body size, change in body form such as measured by Caup’s index (weight/height2), or improvement in physical performance levels. Furthermore, previous data have been limited to cross-sectional studies; no longitudinal study on postural sway in children has been reported. Therefore, we performed a longitudinal investigation on the influence of body size, Caup’s index, and physical fitness level on postural sway in children.
Anthropometric measurements were taken, and physical fitness and postural sway tests were conducted, in 16 boys and 18 girls, annually every November for three consecutive years. The children belonged to the Komichi kindergarten, which is affiliated with the Osaka Seikei College. The anthropometric parameters investigated were height, weight, and Caup’s index [weight (kg)/height (m)2]. We measured the height and weight of the children who were only wearing T-shirts and shorts. The 4-year-old group consists of data taken when the children were 3.7–4.6 years of age, the 5-year-old group consists of data taken when the children were 4.7–5.6 years of age, and the 6-year-old group consists of data taken when the children were 5.7–6.6 years of age.
The projected location of the center of gravity was measured by a portable grabicorder (GS-10A, ANIMA, Tokyo), which measures kinetic changes at the center of pressure required to maintain upright posture. We followed the method of Kitamura et al. (1991). A strain gauge was set on a corner of a large 1608 mm × 918 mm hardened piece of glass. The measurement changes detected by the gauges were amplified and analyzed every 50 ms. The children were asked to stand upright on the grabicorder and look at a target about 2 m away. They were asked to stand still as much as possible with their legs straight, knees locked, arms to the side, and eyes open. They were instructed to place their feet, heels together, at an angle of 30° to each other. Body sway was measured as each child stood without shoes for 30 s. The total sway path length of the center of gravity (LNG cm) was derived. The LNG is useful in evaluating postural instability in children (Riack and Hayes, 1987) and as an inverse index of balance (Berg et al., 1992).
Physical fitness levels were assessed by the following tests. In the sprint test, subjects ran as fast as they could for 25 m. In the hopping test, subjects hopped on one leg as long as they could without a time limit. In the ‘standing on one leg’ test, subjects stood on one leg as long as possible with their eyes open. In the standing broad jump, subjects performed broad jumps from a standing position. In the side jump test, the subjects put their feet together and jumped from left to right over a line. The number of jumps over a 10 s period was recorded. These particular tests were chosen as representative examples of agility, power, and balance.
Differences between the mean values were evaluated using a one-way analysis of variance for repeated measurements. A post hoc test (Fisher’s PLSD) was used to decompose significant differences. Relationships between LNG, the results of physical fitness tests, and the anthropometric parameters were evaluated by Pearson’s correlation coefficients. Partial correlation was used to examine the relationship between body size, age, and LNG, and also the relationship between physical fitness level, age, and LNG. In all tests, P < 0.05 was considered statistically significant. Data are presented as mean ± standard deviation (SD).
Table 1 shows the results of the anthropometric measurements (height, weight, Caup’s index) of the boys and girls at the three different ages. In both boys and girls, mean height and weight at 6 years of age were significantly greater than at 5 years of age, and that at 5 years of age significantly greater than at 4 years of age. In the Caup’s index, there were no significant differences between the three ages, in either boys or girls.
Table 2 shows the results of the physical fitness tests. In boys, performance in all tests (25 m sprint speed, hopping, standing broad jump, side jump and standing on one leg) was significantly better at 6 years of age than at 5 years of age, and significantly better at 5 years of age than at 4 years of age. In girls, performance in all tests, except for the standing broad jump, was significantly better at 6 years of age than at 5 years, and in all tests was significantly better at 5 years of age than at 4 years of age.
Figure 1 and Table 3 shows the results of the LNG at the three ages. The LNG at 4 years of age was significantly greater than at the other two ages (P < 0.05). However, there was no significant difference in the LNG measured at 5 and 6 years of age (Figure 1). Table 3 shows LNG/height, LNG/weight, and LNG/(Caup’s index) of boys and girls at ages 4, 5, and 6 years. In both boys and girls, LNG/height, LNG/weight, and LNG/(Caup’s index) at 4 years of age were significantly greater than the corresponding measures at the other two ages (P < 0.01). In the boys, there was a significant difference in LNG/height and LNG/weight taken at 5 and 6 years of age, but this was not the case in the girls.
 View Details | Figure 1. Differences in LNG in boys and girls at 4, 5, and 6 years of age. Values are mean ± SD. * Indicates differences between groups at P < 0.05. |
Figure 2 shows the relationship between age and LNG, height, LNG/height, and weight, respectively. There was a high negative correlation between age and LNG in each subject. Figure 3 shows the relationship between age and physical fitness level. In all the tests (25 m sprint speed, hopping, standing broad-jump, side-jump frequencies, and standing on one leg), physical fitness levels improved with age.
 View Details | Figure 2. The relationship between age and LNG, height, LNG/height, and weight. Circle, 4-year-old group; triangle, 5-year-old group; square, 6-year-old group. |
 View Details | Figure 3. The relationship between physical fitness levels and age. Circle, 4-year-old group; triangle, 5-year-old group; square, 6-year-old group. |
Table 4 shows the correlation coefficients between LNG and the anthropometric parameters. Boys from the 6-year-old group showed a significant relationship between LNG and body height, weight, and Caup’s index. Girls from the 6-year-old group showed a significant relationship between LNG and body weight and Caup’s index. There was no relationship between LNG and body weight or height, in either boys or girls, in both the 4- and 5-year-old groups.
Table 5 shows the correlation coefficients between LNG and physical fitness levels. Children in the 4- and 5-year-old groups showed no significant correlation between LNG and physical fitness levels. However, in both boys and girls, the LNG in the 6-year-old group was negatively correlated with side-jump frequencies (P < 0.05).
Table 6 shows partial correlation coefficients between body size and shape, and age or LNG. In both boys and girls, there was a significant correlation between age and body size and shape (height, weight, Caup’s index) with LNG held constant. There was no significant correlation between LNG and height and weight with age held constant. But there was a significant negative correlation between Caup’s index and LNG with age held constant.
Table 7 shows the partial correlation coefficients between physical fitness levels and age or LNG. In both boys and girls, there was a significant correlation between physical fitness levels and age with LNG held constant, but no significant correlation between LNG and physical fitness levels with age held constant.
The present study provides evidence that postural sway decreases significantly from ages 4 to 5 years, in both boys and girls. However, there was no significant difference in the LNG of children between the ages of 5 and 6 years. Our results are consistent with those of previous studies which showed that the area of total sway decreased markedly at 3–5 years of age and then slowly after 6 years of age (Usui et al., 1995). Postural stability does not appear to take a linear progression in children from 4 to 6 years of age, while in the same age interval, body size (height and weight) increases more linearly.
Lebiedowska and Syczewska (2000) did not find statistically significant correlations between postural sway parameters and developmental factors (body height, body mass, age) in children aged 7–18 years. The results of the present study were consistent with the above study in the lack of significant correlation between physical stability and the measures of body size and shape (height, weight and Caup’s index) at 4 and 5 years of age. However, a significant correlation was found in the 6-year-old age group. It was therefore not clear whether the reduction of LNG with age was related to developmental body size parameters. Partial correlation analysis was conducted to estimate the effect of body size development (height and weight) to LNG while controlling the effect of age (Table 6). LNG was not correlated with either height or weight with age held constant. However, LNG was negatively correlated with Caup’s index, which concerns the balance between body height and weight. This result suggests that physical stability depends on Caup’s index when the effect of age is controlled.
Previous studies in adults reported that the ability to balance depends on physical fitness factors such as muscle strength and anaerobic capacity (Era and Heikkinen, 1985; Nguyen et al., 1993; Lamb et al., 1995). It is considered that stability can be improved by physical training such as by resistance, aerobics, anaerobics, and flexibility training (Judge et al., 1993; Messier et al., 2000). In the present study, physical fitness levels increased linearly with age in both boys and girls. However, no significant correlation was found between LNG and physical fitness levels, except for side-jump frequencies in the 6-year-old group. Moreover, the results of the partial correlation analysis demonstrated that reduction of LNG with age was not correlated with increased physical fitness levels when the effect of age was controlled. These results suggest that physical stability is independent of physical fitness in children at the age of 4–6 years. Thus, control mechanism of postural sway in children of this age might differ from that of adults. In conclusion, results of the present study show that a decreasing LNG depends on age and on Caup’s index, but not on height, weight, or physical fitness levels.
The authors are grateful to the staff of the Komichi kindergarten.