Effects of detraining on the training-induced balance ability in humans.
As emphasized in our previous study (7), the ability to keep balance on an unstable support surface is extremely important in many sports events such as surfboarding, skiing, figure skating, gymnastics and our daily life as when standing in moving trains. Especially in the older adult populations, balance ability has also been regarded as an important indicator for musculoskeletal health. As a result, numerous researchers have designed and tested their training programs and investigated the training effects on balance performance (1,9,10,11). They have also discussed the improvements in static and dynamic balance ability in regards to athletics and health.
Very few studies to our knowledge have examined the detraining effects on the subjects' balance performance. To some degree, Toulotte et al. (9) demonstrated that the training effects returned to the initial state after a 3-month detraining period. It is very interesting whether the balance ability decreases or not during more prolonged detraining.
Hence, the purpose of this study was to study the effects of detraining of ~5 months on the training-induced balance ability while recording the changes in the seesaw-like platform movements and head acceleration to better understand the subjects' underlying postural control. The findings should be helpful for both interpreting postural control and developing balance ability.
All the subjects who participated in the present study were healthy male undergraduate students at the School of Health and Sport Sciences of Chukyo University in Japan. They were free from any balancing disorders. Their age ranged from 20 to 22 yrs. Height, body weight, and BMI were 162.4 to 184.7 cm, 55.0 to 80.5 kg, and 19.6 to 26.2 kg x [m.sup.-2], respectively. To investigate the effects of detraining on the subjects' training-induced balance ability, we used a Control Group (n = 9) and 3 Training Groups, which were divided into subgroups: W1 (n = 9), W2 (n = 10), and W3 (n = 7) that consisted of the number of training day(s) per week. Initially, the number of subjects in each group was 10 but, during the course of the study, 5 subjects were unable to carry out the balancing task because of their injuries in physical education classes (2 subjects) or scheduling problems (3 subjects). Their data were eliminated from the statistical analysis. Thirty-five subjects completed the study. There were no significant differences among the 4 groups except in the age of the subjects. The experimental protocol was approved by the Ethics Committee at Chukyo University Graduate School of Health and Sport Sciences in Japan, and also the experiments were conducted in accordance with the Declaration of Helsinki. After the subjects were informed of the experimental advantages and possible risks, they signed their written consent forms prior to participation in this study.
Measurement of Balance Performance
For measuring balance performance, a custom-built seesaw-like platform was used as reported in the previous study (7) on which the subject was instructed to stand barefoot and to do his best to maintain the standing posture as long as possible. This platform is capable of rotating around the pitch-axis in both directions of toes-up and toe-down, and its maximum inclination was set at an angle of 25 [degrees] to the horizontal plane, which was confirmed to be sufficient to cause imbalance in all subjects. An electrogoniometer was installed on the tip of the horizontal pivot to record the changes in platform movement during balancing. Each subject was instructed to look at a fixed eye-level cross mark at a distance of approximately 3 m. Testing consisted of one session of 10 successive trials of balancing per day of which the mean time of each subject's balance keeping time (BKT) was calculated and adopted as his balance ability.
Balance Detraining Programs
In order to investigate the effects of detraining on the training-induced balance ability, training and detraining programs were set. Before training, each subject's BKT was measured as baseline level. Then, the subjects were randomly divided into 3 training groups that participated in the prescribed training programs of either 1 d x [wk.sup.-1] of training (W1), 2 d x [wk.sup.-1] of training (W2), or 3 d x [wk.sup.-1] of training. A 1-day training session consisted of 10 successive trials of balancing. Each subject took an appropriate rest among trials for preventing fatigue. The training period was 8 wks in all groups, and the BKT was recorded on all trials. The training program was immediately followed by detraining during which the BKT was again measured at week 9 and 21. The total duration of the study was 31 wks (~7 months).
Signal Recording and Analyzing system
All the signals, such as angular changes in the platform position, the angular velocity of the platform obtained by the derivative that provides offline calculation of first order derivatives of platform movement, the output from the accelerometer (BAH-10G, Shinko, Japan) attached to the forehead of the subject, the start and stop signals from the button operated by the subject and from the platform contact switch, were collected simultaneously into the Universal Data Recorder (Model A-69, Sony Magnescale, Japan) as a backup device through amplifiers (Model NS901, San-ei, Japan) without working any filters. The signals were then led to the data acquisition system (PowerLab 8/30, A7Instruments Japan Inc.) for signal recording and for further processing and analysis (PowerLab Chart ver.5 software package) in combination with a personal computer (IBM, Taiwan). Root mean squares (RMS) were calculated for both the angular velocity of the platform and acceleration of the head movement, and adopted as indices of platform and head movements, respectively. All the signals were recorded at a sampling frequency of 100 Hz.
All the values were expressed as means [+ or -] standard deviations (SD) unless stated otherwise. Statistical analyses consisted of using both the statistical software packages SPSS version 11.0 for Windows XP (SPSS Inc., Japan) and the statistical analysis add-in software (Statcel 2, SSRI Inc., Japan) for Excel 2002. After confirming normality of distribution (via the Shapiro-Wilk's test) and equality of variance (using the Levene's test), the data were analyzed using a one-way analysis of variance (ANOVA). Significant differences among groups in each phase or among the 3 phases within each group were then determined using Tukey's post-hoc test including Tukey-Kramer one. The level of statistical significance was set at P<0.05, while P-values [less than or equal to] 0.1 were reported to indicate trends.
Detraining Effects on Balance Performance
The absolute changes in BKT ([DELTA]BKT) of each group after training and detraining are shown in Figure 1. At the 9th-wk after the termination of training (7T9-W), the [DELTA]BKT of the W2 Group was significantly larger than those of W1 and the Control (P<0.05, P<0.01, respectively). Also, the [DELTA]BKT of the W3 Group was significantly larger than that of the Control Group (P<0.05), but it was not significantly larger than that of W1 Group (P = 0.117). However, there were no significant differences between the W1 Group and the Control Group, as well as between W2 and W3 Groups. At week 21 after the termination of training (DT21-W), the [DELTA]BKT of the W2 Group was significantly larger than the W1 Group and the Control Group (P<0.05 for both). Also, the [DELTA]BKT of the W3 Group was significantly larger than that of the W1 Group and the Control Group (P<0.05 for both). However, there were no significant differences between the W1 Group and the Control Group, as well as between W2 and W3 Groups.
In order to show the detraining effects more clearly, the [DELTA]BKT was re-arranged across the 3 testing phases within each group (Figure 2). As shown, there were no significant changes in [DELTA]BKT across the 3 testing phases within each Group. Therefore, the positive effects of training in the W2 and the W3 Groups obtained during the training phase were not decreased even at week 9 and 21 (DT9-W and DT21-W, respectively) after the termination of balance training.
Changes in Platform Movement and Head Acceleration during Detraining
Figures 3A and 3B show the changes in [DELTA]RMS angular velocity of the platform movement (Panel A) and [DELTA]RMS head acceleration (Panel B) during balance training and detraining. Although no significant difference was found in Figure 3A, [DELTA]RMS angular velocity in the W2 Group had a tendency to decrease compared to the W1 Group after training (P = 0.100) and the Control Group at week 21 after the termination of training (DT21-W) (P = 0.082).
On the other hand, as shown in Figure 3B, [DELTA]RMS head acceleration in the W1, W2, and W3 Groups was significantly larger than that of the Control Group after training (P<0.01, P<0.001, P<0.01, respectively). However, no significant differences in [DELTA]RMS head acceleration were found among the four Groups during detraining (DT9-W and DT21-W).
Figures 4A and 4B show the changes in [DELTA]RMS angular velocity (Panel A) and [DELTA]RMS acceleration of the head movements (Panel B) across 3 different testing phases within each Group. As shown in Figure 4A, no significant changes in [DELTA]RMS angular velocity of the platform were found within the Groups. On the other hand, as shown in Figure 4B, the training-induced increments of the [DELTA]RMS head acceleration in all training Groups diminished during detraining (DT9-W and DT21-W).
Detraining Effects on Balance Performance
The most interesting finding is that the balance training effects did not decrease at week 21 after the cessation of training (at DT21-W), which adds to the relatively few studies on the detraining effects on balance performance. Fatouros et al. (3) examined the relationship between training intensity and training effects on mobility (time up and go, walking, climbing stairs) in older men and found that training effects on mobility in response to high intensity training lasted for a long time. It is true in general that muscle strength training effects are decreased considerably after the termination of training in young adults (5).
The extent to which the detraining-induced decrease in muscular performance in middle-aged and elderly subjects is related to the duration of detraining is discussed by Hakkinen et al. (4) who reported that short-term detraining of 3 wks caused minor changes in muscular performances, while prolonged detraining of 24 wks decreased maximal strength and cross-sectional area of the rectus femoris muscle. Although a certain limitation on direct comparison between the study by Hakkinen et al. (4) and the present study should be recognized, balance training effects were still maintained after the prolonged detraining of 21 wks while the 24-wk detraining period resulted in a significant decrease in muscle strength. The fact that the training effects on balance performance are maintained for a long period in the present study is an important finding from the muscle strength training effects.
The prolonged maintenance of balance training effects after the termination of balance training suggests the establishment of a new adaptive control system. It also supports the concept proposed by Ito (10) concerning the new formation of neural networks in the cerebellar cortex accompanying the acquisition of motor skills by repeating voluntary movements. Furthermore, the data may suggest the existence of a morphological selective increase in the trained part of the brain that has a favorable effect on maintenance after detraining that is similar to the work of Boyke et al. (2).
Changes in the Platform Movement and Head Movement Acceleration due to Detraining
The present study demonstrated that the increment of head acceleration in training groups at posttraining diminished at 9-wks and 21-wks of detraining, while the decrement of ankle joint movement in the W2 group was maintained during the prolonged detraining period (P = 0.082). These results are partly consistent with the findings of Horak and Nashner (8) who demonstrated, first, the occurrence of progressive changes in the relative amplitude and timing of two joints strategy components and, second, the influence of the subjects' recent experiences on the combination of the strategies.
One possible speculation about the postural control observed in the present study is that at the 21st-wk of detraining in the W2 group, the balancing posture was maintained with less ankle joint angular rotation and without more head moving, which partly relates to the hypothesis concerning training-dependent changes in postural control. This suggests the progressive changes in the combination of postural control strategies and the development of balance ability. Then, too, since there were fewer movements in both the platform and the subjects' head after prolonged detraining, some passage of time may be necessary for working of further developed postural control system that adapts to maintain balance. However, it must be noted that this tendency was limited in the W2 training group.
This study found that the training-induced increases in balance performance as training effects were maintained after the detraining period of 21 wks. There was no significant change in the magnitude of angular velocity of platform movements during detraining. However, we found the returning to the baseline level in head acceleration in all training groups. These data may suggest the progressive changes in the combination of postural control strategies underlying the development of balance ability.
The authors are grateful to both the undergraduate students and Research Institute of Health and Sport Sciences affiliated with Chukyo University in Japan for their participation and support.
Address for correspondence: HN Huang, MA, Center of Physical Education, Ming Chuan University, De Ming Rd. Sec. 5, Guishan District, Taoyuan 333, Taiwan, Phone: +886 3 3507001 # 5340, Fax: +886 3 3593862; Email: email@example.com
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The opinions expressed in JEP online are those of the authors and are not attributable to JEPonline, the editorial staff or the ASEP organization.
Han-Nien Huang , Takashi Yamamoto 
 Center of Physical Education, Ming Chuan University, Taoyuan, Taiwan,  Graduate School of Health and Sport Sciences, Chukyo University, Toyota, Japan
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|Author:||Huang, Han-Nien; Yamamoto, Takashi|
|Publication:||Journal of Exercise Physiology Online|
|Article Type:||Clinical report|
|Date:||Feb 1, 2014|
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