Introduction
Age-related balance impairment is a major risk factor of fall, fracture injury (2,10). There is much evidence that dynamic balance training, which requires postural stability with physical movements such as Tai chi or stepping, is effective in preventing falls and in improving physical function in older persons (4,9,13,18). A previous study demonstrated a tendency for a slow speed or easy task to be selected for balance trainings because of their risk of falling. However, it was thought that even for the frail elderly, a more difficult balance exercise should be recommended under individual supervision to improve postural balance.
Balance training standing on a wobble board is widely used for preventing ankle sprains. An earlier report described that wobble training for 12 weeks is effective for preventing recurrent ankle sprain and instability in young people (25). It has been reported that wobble board training improves the reaction time of the anterior tibialis (19). Numerous reports have described the benefits of wobble board training in young athletes; however, the effectiveness of wobble board training for frail elderly people has remained unclear. Because postural balance using an ankle strategy decreases with age (10), intervention targeted to improve postural balance with ankle strategy such as wobble board training is needed for the elderly.
Because it has been pointed out that the institutionalized elderly have a higher risk of falling and lower physical function than community-dwelling elderly do (5,22), our study focused on the frail elderly living in a nursing home. This study was undertaken to investigate the effects of wobble board training on physical functions in the frail elderly.
Methods
Experimental Approach to the Problem
This study was designed to examine the effects of wobble board balance training using a double-blind and controlled trial. Physical assessments were measured at baseline and 9 weeks in both the intervention and control groups at the same time. We focused on multiple balance-related factors. Balance on a wobble board was measured using standing time and size fluctuation frequency analysis of the board. Balance on an unstable surface was tested using standing time on a balance mat. Static balance was tested using standing postural sway and 1-leg standing. Dynamic balance was tested using maximum center pressure excursion and functional reach test (FRT). Stepping was used to represent agility, which would affect postural control. Ambulatory ability was investigated by 5-m walking and Timed Up and Go test (TUG).
Subjects
Subjects were 23 elderly people aged >70 years residing in a nursing home. The subjects were excluded if they had the following conditions: (a) severe cognitive impairment that prevented them from understanding instructions; (b) serious musculoskeletal, neurological, or visual impairment that might affect measurements; (c) involvement in other exercise programs; (d) residence in the nursing home for <3 months or unstable physical or mental condition; (e) inability to ambulate independently.
All subjects were recruited from the same nursing home; therefore, it was thought that these subjects lived under the same environment, surrounding circumstances, and received the same nutrition. The subjects were informed about the study procedures before participating and provided written informed consent. Subjects who wanted to join the exercise program were allocated to the intervention group. This study was approved by the Medical Ethics Committee (E-461).
Procedures
Intervention
The training program comprised balance training standing on a wobble board (DYJOC board plus SV-200; Sakai Medical Co. Ltd., Tokyo, Japan) with 1 physical therapist supervising. The wobble board was attached to 2 bosses, which restricted tilting back and forth. The tilting direction was restricted because it was difficult for the elderly to remain standing when the tilting direction was not restricted using only 1 boss.
Balance training was performed twice a week for 9 weeks, lasting approximately 10 minutes each time. Stretching was performed before and after training. The training program consisted of the following 2 standing tasks: (a) continued standing on the wobble board (stability task) and (b) following a moving cursor to a specific target (moving task). For all tasks, subjects stood barefoot on the wobble board. During the stability task, subjects were asked to confine their attention to minimize wobble board fluctuation. During the moving task, subjects were required to tilt the board voluntarily to follow a cursor depicting the position of tilting degree on a target projected on a personal computer (PC) screen (Figures 1 and 2).
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Figure 1: Training scene.
Figure 2: Personal computer (PC) screen.
Each task had 3 levels of difficulty (Table 1). In the stability task, 3 levels—arranged as the distribution of attention and postural movement—were used. Subjects performed for about 5 minutes. In the moving task, 3 levels were set for the maximum degree of tilt, target frame size, and holding time. The random target was displayed on the PC screen in a range of the maximum degree of tilt. The tilt degree of this device ranges ±14°, so the target size was shown as a percentage of 14°: 14° was 100%. The next target was displayed if the moving cursor was able to maintain in the target frame for the holding time. Subjects performed 2 trials of 16 targets in a day.
Table 1: Training level.
Criteria of the exercise level to step up were >1 minute in the stability task and <2 minutes to finish 16 targets in the moving task.
Exercises were performed near a walker and with the use of a hip protector for preventing fall-related injuries. There were no limitations in daily living activities imposed on either the intervention or the control group.
Standing Time on the Wobble Board
Subjects were asked to stand on a DYJOC board plus tilting back and forth with eyes open and feet 20 cm apart.
The time during which the participant was able to maintain a standing position with the maximum time of 120 seconds was measured. The subjects stood on the wobble board holding onto a walker before measurement; measurement was then started when the subjects took their hands off the walker. The criteria to fail and finish counting time were that (a) the wobble board be tilted to the maximum range; (b) the subject touched the walker; and (c) the subject touched their foot to the ground. Two trials were performed; the better score was used.
Mean Range of Angular Fluctuation and Frequency Analysis of Wobble Board Tilting
Subjects were instructed to stand for 15 seconds on the DYJOC board plus, tilting back and forth while moving as little as possible. This device recorded the tilt angle, which was measured with a sampling frequency of 40 Hz. The mean range of angular fluctuation (MRF), which was calculated by the integration of tilt angle minus mean tilt angle, was used to represent the fluctuation size.
Test-retest reliability of MRF was assessed by intraclass correlation coefficient (ICC). The ICC of MRF using 2 trials of baseline measurement was 0.77. For assessing training effects, we used frequency analyses of 4 dates: baseline, 3, 6, and 9 weeks. Fast Fourier transforms were applied to the tilt fluctuation. Analysis of spectral power was applied in a manner similar to that in a previous study (1). The total spectral power (0.02-5 Hz) was calculated and distributed in 6 bands: 0.02-0.1, 0.1-0.2, 0.2-0.5, 0.5-1, 1-2, and 2-5 Hz. The power frequency of each band was represented as a percentage of the total spectral power.
Standing Time on a Balance Mat
Subjects were asked to stand on a balance mat (Balance Pad Plus; Airex AG, Sins, Japan) with eyes open and feet together. The subjects stood on the balance mat holding onto a walker before measurement; measurement was then started when the subjects took their hands off the walker. The criteria to fail and finish counting time were (a) the subject touched the walker and (b) the subject touched their foot to the ground. Two trials were performed for up to 120 seconds; the better score was used.
Postural Sway
Postural sway was measured using a center-of-foot-pressure recorder (G-5500; Anima Corp., Tokyo, Japan). The root mean square area (RMS) was used as the body sway parameter. Subjects were instructed to stand for 20 seconds with feet 20 cm apart and to look at a point 1 m ahead.
One-Leg Standing Time
The time during which the subjects were able to stand on 1 leg with eyes open was measured. Two trials were performed with the dominant foot if the maximum time of 120 seconds was not reached on the first trial. The best standing time of the recorded trials was used for analyses.
Maximum Center of Pressure Excursion
Subjects were instructed to move the center of gravity far forward, backward, right, and left with feet 20 cm apart. The distance of anterior-posterior displacement (A-P) and lateral displacement (L-R) were measured as the maximum center of pressure excursion using a center-of-foot-pressure recorder (G-5500; Anima Corp.).
Functional Reach Test
The distance that the subject was able to reach forward was measured using a reach measurement device (CK-101; Sakai Medical Co. Ltd., Tokyo, Japan). Subjects were instructed to stand with a shoulder flexed to 90° with the elbow fully extended, then to reach as far forward as possible without moving their feet.
Stepping
Subjects were instructed to step alternately as fast as possible in a standing position. The total number of steps within 5 seconds was measured using a stepping counter (Takei Scientific Instruments Co. Ltd., Niigata, Japan). The best count of 2 trials was measured.
Timed Up and Go Test
The time necessary for subjects to stand up from a sitting position, walk 3 m, turn around, walk back to the chair, and sit down as fast as possible was recorded.
Five-meter Walking
Subjects were instructed to walk as fast as possible using a 7-m walking course including 1-m acceleration and deceleration zones at each end. The time and steps needed to walk 5 m were measured.
Statistical Analyses
Comparisons of the 2 groups' baselines were done using Student's unpaired t-test. Two-way repeated measures analyses of variance (ANOVAs) were used to analyze the intervention effect. In addition, if significant time × group interaction was determined, then a paired t-test was used to investigate time differences.
Training effects of MRF and power frequency in the training group were examined using a 1-way repeated-measures ANOVA. A clinical p value of ≤0.05 was set.
Results
Twelve subjects (1 men and 11 women) joined the training program (intervention group) and 11 subjects (1 man and 10 women) joined the measurement (control group). One female subject in the intervention group dropped out because of an unrelated medical illness. Therefore, 11 subjects (1 man and 10 women) completed the course in the intervention group. The mean percentage of the exercise attendance rate in the intervention group was 86%. None of the subjects showed any serious medical problems, that is, of cardiac orthopedic origin, fall incident, or any other adverse events such as inflammatory symptoms during exercise.
Table 2 presents the baseline characteristics of subjects. No significant differences were found between the 2 groups in age, height, or weight.
Table 2: Baseline characteristics.
Table 3 shows physical functions at the baseline and at 9 weeks postintervention. No significant differences were found in baseline values between the groups. However, significant interactions were found between time × group for the standing time on the wobble board, standing time on the balance mat, and A-P. After training, standing time on the balance mat and A-P improved significantly, but no significant change was found in standing time on the balance mat in the intervention group (Figures 3-5). No significant change in physical measurements was found in the control group.
Table 3: Outcome of physical functions at baseline and 9 weeks postintervention.*
Figure 3: Standing time on wobble board.
Figure 4: Anterior-posterior displacement (A-P).
Figure 5: Standing time on balance mat.
Figures 6 and 7 show time course changes of MRF and %power frequency in the training group. No significant change in MRF was found. Power spectra of only 0.1-0.2 Hz in 6 bands increased significantly with the exercise period.
Figure 6: Change of mean range of angular fluctuation (MRF).
Figure 7: Change of power frequency.
Discussion
The main findings of this study were that elderly people who took part in the wobble board exercise showed significant improvement in the postural control parameters such as the standing time on the wobble board, standing time on the balance mat, the distance of A-P, and the power spectrum.
The result of this study showed that standing time on the wobble board of intervention group changed markedly in a task-specific manner, as described in a previous report (18).
Reliability of measurements using the wobble board has not yet been demonstrated in previous studies. Therefore, we assessed test-retest reliability of MRF by ICC. The measurement of MRF demonstrated substantial agreement because the ICC score was 0.77 (12). After intervention, no significant change was found in MRF as for indicator of the extent of fluctuation. It is reported that the fluctuation degree of healthy adults standing on an unstable platform does not change according to ankle sprain (20), anterior cruciate ligament reconstruction (16), or ankylosing spondylitis (3). However, postural control is apparently impaired in ankle sprain or anterior cruciate ligament reconstruction (7,11,23). It is doubtful that the fluctuation size is an index of postural stability.
Regarding frequency analysis, the power spectrum of 0.1-0.2 Hz increased significantly with the exercise period. Furthermore, a tendency existed, but not a statistically significant one, by which the power spectra of low frequency decreased and high frequency increased. Training programs can engender improvements in adjusting the tilt frequently to maintain a stable posture because a frequency change from low to high means that fluctuation of the wobble board becomes faster with exercise. Elderly people tend to try to stabilize their ankles with high coactivation of the gastrocnemius and tibialis anterior in a standing posture (17). This high coactivation engenders a disability in reacting rapidly against turbulence (21) because of long onset latency (15) and compensation strategies (10). Our results indicate that wobble board training is an effective way of improving the ability of adjusting the posture frequently and changing the strategy with ankle coactivation and less joint movement.
Our results also indicate the improvement of the standing time on the balance mat. It agrees with those of an earlier study that showed one leg standing time on balance mat increased after wobble board exercise in the healthy young (8). The balance mat has an unstable surface like the wobble board, requiring a similar ability to control posture against fluctuations and to maintain the center of gravity properly.
As for static balance and dynamic balance, only A-P changed significantly in the intervention group. Some reports describe that the ankle strategy is important for excursion of the center of gravity (14,24) and that wobble board training is effective in improve ankle function such as ankle muscle reaction time (19) and to prevent ankle sprain (8,25). Ankle function might improve as a result of wobble training and thereby cause an A-P increase.
No significant changes were found in results of TUG and 5-m walking. It has been pointed out that walking functions are related to dynamic postural control, that is, balance with physical movement (6). Our results show that training for maintaining the center of gravity in a small space on the wobble board does not appear to engender improvement in walking functions.
It was expected that this training task would be a challenge for subjects with poor balance. However, none of the subjects showed any serious medical problems or fall incident, or any adverse event during exercise. Furthermore, the exercise attendance rate was high: 86%. This study demonstrated that wobble board training could be performed safely by frail elderly under supervision by a physical therapist.
One limitation of this study was the restriction of the lateral tilt of the wobble board. We used a board with only tilting anterior and posterior because of the difficulty in maintaining a standing position on wobble board without restriction of tilting in elderly people. Different results might have been obtained if the wobble board with tilting to the lateral side too had been used for this study. The group classification is thought to be another limitation in this study. Participants in this study live in the same nursing home. For that reason, we did not assign subjects randomly to the 2 groups and thereby achieve impartiality. Confounding factors related to subjects' motivation for exercise might affect these results.
Practical Applications
There are many situations that require control of balance or walking on unstable conditions in daily living activities (outdoor ground or even indoor flooring such as a soft carpet), which may cause loss of balance and falls for the frail elderly, often leading to physical inactivity or functional dependency.
Our findings indicate that wobble board training is effective for elderly people to improve their postural balance, which involves maintaining a standing posture and adapting their center of gravity frequently on unstable surface conditions.
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