ABSTRACT

This study aimed to examine the effects of open/ closed eyes and age difference on Center of Foot Pressure (COP) sway during stepping. The subjects were 87 healthy males aged 10 - 80 years. COP was measured 20 times when subjects stepped on two force plates (left and right) at a rate of 60 steps/min. The evaluation parameters selected were: total trace length, velocity, circumference, rectangular area，left-right width, and front-back width. The former four of these parameters were found to be significantly lower with eyes open than eyes closed in 80-year-old subjects, while the last parameter was significantly lower with eyes open in 10-year-old subjects. In 70- and 80-year-old subjects with eyes open, circumference was greater than that in 10- and 40 - 60-year-old subjects; their rectangular area was greater than that in 50- and 60-year-old subjects; and their front-back width was greater than that in 10- and 30 - 60-year-old subjects. With eyes closed, circumference, rectangular area, left-right width, and front-back width in 80-yearold subjects, were greater than those in 10 - 70- year-old subjects. The front-back width during stepping with eyes closed was greater in 70- and 80-year-old subjects than in 30 - 50-year-old subjects. The Romberg quotient for all COP sway parameters revealed no significant age-related differences. From our findings, a difference in body sway was observed in 80-year-old subjects (with eyes open/closed) when compared with the other age groups. In addition, the extent of sway varied little among <60-year-old subjects. However, COP sway was greater with eyes open in 70- and 80-year-old subjects compared with <60- year-old subjects, and greater with eyes closed in 80-year-old subjects compared with <70- year-old subjects. In conclusion, >80 year-oldsubjects have greater body sway during stepping, particularly with eyes closed.

1. INTRODUCTION

Posture control during standing is closely related to basic human movements such as walking and standing up. To date, the Center of Foot Pressure (COP) has been used to evaluate postural control ability of humans [1,2]. COP sway during standing has a close relationship with static balance [3-5], and sway characteristics have been studied in various age groups from infants to the elderly [5,6]. Using COP sway during stepping, Ohnishi et al. [7] evaluated dynamic balance of the movements that change the support base such as walking and ascending and descending stairs. They examined the age-related differences in total trace length of COP sway at 80%, 70%, and 60% of Maximum Step Length (MSL) of the Rapid Step Test (RST) and reported that RST was greater in the elderly than in the young under all MSL conditions. Fujiwara et al. [6] examined age-related differences of COP during forward and backward bending postures in subjects aged 20 - 70 years, and reported that the trace length lengthened with age and that the front-back width of the effective support base (which is an index of balance) differed between 60-year-old and 70-year-old subjects. In recent times, most developed nations comprise a greater proportion of individuals >80 years in their population. Although these individuals are able to live independently, they tend to become unstable even while standing up and walking, which are basic daily movements. This occurs due to a marked reduction in various physical functions including balance and leg strength; hence, falling over is more likely. Therefore, it is important to prevent or discourage the decrease of physical functions that are closely related to daily life movements and to evaluate them accurately. Shin & Demura [8] recently evaluated dynamic balance in the elderly using stepping movements. Because stepping on the spot alters the supporting base in a similar way as in RST, COP during stepping may be different between the young and the elderly.

On the other hand, people normally prevent a collapsing posture by integrating vestibular, visuosensory, and somatosensory information from the central nervous system [1]. Of these three senses, the visual system has a very important role in maintaining stable posture, and it has been postulated that reduced visual function markedly affects postural control [9]. In regard to postural control, the elderly were found to have greater dependence on visual information than the young [10]. Masani et al. [11] reported a difference in COP sway in the elderly between open/closed eyes, but not in the young; in addition, Brenton et al. [12] reported this difference in the elderly. As mentioned above, it is hypothesized that the contribution of visual information to postural control increases with age; in short, an age-related difference in COP exists between the conditions of open/closed eyes. In stepping movements at a set tempo, subjects use only one leg support to control their physical center of gravity while adhering to a set tempo; hence, this may be a more difficult exercise than RST. Consequently, the following is assumed: a difference between open/closed eyes in relation to COP sway during stepping at a set tempo is more marked in the elderly than in the young. In addition, especially the very elderly, find it difficult to maintain stable posture when the weight is supported by one leg due to reduction in strength of the leg musculature; sub sequently, they may show a greater COP change in the left-right direction when compared to the young, particularly with eyes closed.

This study aimed to examine the effect of open/closed eyes and age on COP sway during stepping at a set tempo.

2. METHODS

2.1. Subjects

The subjects were 87 healthy males aged 10 - 90 years. Sample sizes of each 10-year age group ranged from 10 to 13. Table 1 shows means of the age, height, and weight of each group. We explained the purpose, methods, and risks of the study protocol to the subjects and obtained their consent. The study protocol was approved by the Kanazawa University Department of Education.

2.2. Experiment Equipment and Methods

Equipment

A stabilometer (GP-31W; Anima, Tokyo, Japan) was used to measure COP during stepping. This machine calculates COP of vertical loads from the values of three vertical load sensors located at the corners of an isosceles triangle on a leveled surface. The data sampling frequency was 20 Hz.

Study methods

The subjects stood on two platforms (left and right) with arms rested comfortably on their sides. They were instructed to focus on the central fixation target with eyes open and then to gradually close them. After this, they were instructed to step 40 times in synchrony with a beeping sound (60 steps/min). All the trials were conducted once with eyes open and once with eyes closed.

2.3. Parameters

The following evaluation parameters of the center of gravity were selected:

Total trace length (the full length that COP moved during stepping); velocity (mean velocity); circumference

(medial area surrounded by circumference of a trace of COP sway); rectangular area (bounded by front-back circumference and horizontal direction of sway); leftright width (greatest deflection distance); and front-back width (greatest deflection distance). When these have a large variation, postural control ability is evaluated to be inferior.

2.4. Data Analysis

One-way non-repeated analysis of variance (ANOVA) measures were used to clarify age-related differences by Romberg quotient. Two-way ANOVA (one-factor repeated-measures) was used to clarify the mean differences in age and eyes open/closed values for COP sway parameters. When a significant interaction or effect was found, Tukey’s Honestly Significant Difference (HSD) test was used for multiple comparisons. The level of significance was determined as 0.05.

3. RESULTS

Table 2 displays the test results for age-related differences by Romberg quotients for COP sway parameters. No significant age-related differences were found in all the parameters.