Key words
postural control - youth - intervention - dose-response relationship
Introduction
In childhood, well-developed balance performance is the foundation for successfully
mastering everyday life and sports activities [1] and is associated with a lower risk of sustaining a lower extremity
injury [2]. Particularly, schools offer good
opportunities for promoting balance performance, as children of different physical
activity and fitness levels are required to mandatorily attend physical education
classes regularly several times a week. The effectiveness of balance training to
promote measures of balance performance in children and adolescents has been
demonstrated in several studies [3]
[4]
[5].
Moreover, the existing findings were summarized in a narrative review [6] and a systematic review with meta-analysis
[7]. In addition, the meta-analysis by
Gebel et al. [7] quantified dose-response
relations for several balance training load dimensions (e. g., training
period, frequency, volume). It turns out that when considered individually and not
as complete protocol, balance training programs with a period of 12 weeks, a
frequency of 2 sessions per week, a total number of 24–36 sessions,
durations of 4–15 min of a single session, and total durations of
31–60 min of exercise per week were the most effective single
training modalities for improvements in overall balance.
However, this gain in knowledge is based on an indirect comparison, as the effects
were compared between studies of short (4 weeks) vs. long (12 weeks) training
duration [4]
[8], small (2 times/week) vs. large (7 times/week)
training frequency [9]
[10], and low
(~4 min/session) vs. high
(~9 min/session) training volume [8]
[11].
Further, the reported differences in balance training effectiveness may result from
discrepancies in the applied training approach (i. e., training sessions in
a sports club or physical education lessons at school), the investigated cohorts
(i. e., children or adolescents), the performed balance tests
(i. e., biomechanical or fitness test), and the used outcome measures
(i. e., static or dynamic balance), in addition to differences in load
dimension. Consequently, a direct comparison of differently designed training loads
within a study is necessary to prove reliable statements regarding a lower or higher
effectiveness of balance training on balance performance in youth. To date, there
has been only one study on this topic with adolescent girls [12], but the observed training-related changes
were not significantly different between the low- and high-volume group.
Therefore, the aim of the present study was to investigate differences in the
effectiveness of balance training on measures of dynamic balance performance in
children for the "training volume" modality (i. e., number
of exercises × number of sets × duration per exercise). Since a high
compared to a low training volume means a longer exposure to balance-demanding
stimuli, we hypothesized to find greater effects for the former than for the latter.
From a practitioner's point of view, it is important to investigate the
effects of different balance training volumes in order to determine whether only a
high volume or a low volume already causes significant effects on balance
performance. In the first case, it would suffice to include balance training in the
warm-up part of a PE lesson, whereas in the second case the main part of the PE
lesson should be used for balance training.
Materials And Methods
Participants
Sixty children from three secondary school classes participated in this study
after experimental procedures were explained. Because the classes were rigid in
their composition, randomization was only possible on a class but not on an
individual level. Consequently, each class was randomly defined to be either an
active control group (CON), a balance training group using a low training volume
(BT-LV), or a balance training group using high training volume (BT-HV). For
this purpose, before the pretest the physical education teachers had to assign a
sealed envelope to each class, which contained a slip of paper with the group
designation (i. e., CON, BT-LV or BT-HV). The examiners were blinded to
group allocation and the participants were aware only of their own training
program but did not know how other participants trained. [Fig. 1] provides an overview of the
progress of the study and the group-specific participants’
characteristics are shown in [Table 1].
Maturity offset was calculated in terms of years from peak height velocity (PHV)
for each participant by using the formulas provided by Moore et al. [13]. For girls, the formula for the
calculation is: –7.709133 + (0.0042232 × (age ×
height)), and for boys, the corresponding formula is: –7.999994
+ (0.0036124 × (age × height)). None of the participants
had any history of diagnosed intellectual disabilities and/or
musculoskeletal or neurological disorders that might have affected their ability
to execute the balance training programs, the physical education lessons,
and/or the balance tests. Participants’ assent and
parents’ written informed consent was obtained before the start of the
study. The study protocol was approved by the local ethics committee (reference
number: TM_29.11.2018).
Fig. 1 Flow diagram of the progress of the study according to the
CONSORT statements [25].
Table 1 Group-specific characteristics of the study
participants (N=55)
|
Characteristic
|
CON (n=19)
|
BT-LV (n=16)
|
BT-HV (n=20)
|
p-value
|
|
Age (years)
|
11.7±0.5
|
10.6±0.5
|
10.5±0.4
|
.001
|
|
Sex (f, m)
|
9/10
|
9/7
|
8/12
|
–
|
|
Maturity offset1 (years from PHV)
|
−0.83±0.82
|
−1.62±0.72
|
−1.69±0.80
|
.002
|
|
Body height (cm)
|
154.2±7.5
|
148.8±6.8
|
152.1±6.4
|
.075
|
|
Body mass (kg)
|
47.7±10.9
|
41.9±11.2
|
40.6±5.5
|
.057
|
|
BMI (kg/m²)
|
19.9±3.2
|
18.7±4.2
|
17.6±2.1
|
.078
|
|
Leg length (cm)
|
91.3±5.3
|
92.1±6.0
|
88.7±4.7
|
.166
|
|
Leg dominance (l, r)
|
17/2
|
16/0
|
18/2
|
–
|
Data are group mean values±standard deviations. 1The
maturity offset was calculated by using the formula provided by Moore et
al. [13]. Post-hoc comparisons for age and maturity offset indicate
significant differences between the control group and the two
intervention groups only. BMI=Body-Mass-Index;
BT-HV=high volume balance training; BT-LV=low volume
balance training; CON=active control group (i. e.,
regular physical education); f=female; l=left;
m=male; r=right; PHV=peak height velocity.
Testing procedures
The pre- and post-testing was conducted in a gym hall by the same skilled
assessors (degreed sport scientists) before and after the 8-weeks of training.
All participants received standardized verbal instructions and a visual
demonstration regarding the testing procedure that included assessment of
anthropometric variables and balance performance. All subjects conducted a
standardized 10-minute warm-up prior to each test that consisted of submaximal
running (e. g., skipping, hip in/out) and balance exercises
(e. g., single leg stance on unstable devices, forward/backward
beam walking).
Assessment of anthropometric variables
The anthropometric variables body height, body mass, and length of the
non-dominant leg were assessed. Body height was registered with a Seca 217
(Basel, Switzerland) linear measurement scale without shoes to the nearest 0.1
cm. Body mass was determined without shoes using an electronic Seca 803 (Basel,
Switzerland) scale to the nearest 100 g. Leg length was measured via tape
measure as the distance from the distal end of the anterior superior iliac spine
to the most distal point of the medial malleolus to the nearest 0.5 cm [14]. In addition, the participants were
asked to self-report their non-dominant leg (i. e., “On which
leg do you stand on when kicking a ball?”).
Assessment of dynamic balance performance
Dynamic balance performance was assessed by means of the Lower Quarter Y-Balance
Test Kit (Functional Movement Systems, Chatham, VA, USA). The test kit consists
of a centralized stance platform to which three pipes were attached that
represent the anterior, posteromedial, and posterolateral reach directions. Each
pipe is marked in 1.0-cm increments for measurement purposes and equipped with a
moveable reach indicator. The participants were asked to reach with the dominant
leg as far as possible in the anterior, posteromedial, and posterolateral
directions while standing with their non-dominant leg on the centralized stance
platform. A total of six trials (three practice trials followed by three
data-collection trials) were executed. The maximal absolute reach distance (cm)
per reach direction was used for further analysis. In this regard, the maximal
relative reach distance (% leg length) per reach direction was
calculated by dividing the maximal absolute reach distance (cm) by leg length
(cm) and then multiplying by 100. In addition, the normalized (% leg
length) composite score was computed as the sum of the maximal absolute reach
distance (cm) per reach direction divided by three times leg length (cm) and
then multiplied by 100 and used for analysis as well. The Y-balance test is a
reliable tool to assess balance performance in youth [15].
Dynamic balance performance was further assessed using the Timed-Up-and-Go Test
(TUG) [16]. In this regard, the
participants were asked to rise from a chair, walk three meters, turn around,
walk back to the chair, and sit down. The time (s) needed to perform the TUG was
manually recorded with a stopwatch to the nearest 0.01 s by the same skilled
assessors (degreed sport scientists). Each participant performed two trials (one
practice trial followed by one data-collection trial) with 60 s in between and
the best trial (i. e., shortest time) was used for further analysis. The
Timed-Up-and-Go test is a reliable test of balance performance in children [16].
Balance training programs
Each group trained separately for eight weeks (two times per week) at the school
gym supervised by their respective physical education teacher but the same
graduate student. The first lessons lasted 90 min and the second lessons
amounted to 60 min. Each training session started with a 10- to
15-minute warm-up and finished with a 5- to 10-minute cool down. In between,
participants in the two balance training groups conducted different types of
balance exercises while the pupils in the CON group underwent their regular
physical education lessons including gymnastics and swimming ([Table 2]). The balance training volume
amounted to 4 min/session (i. e., four exercises with
two sets of 30 s per exercise) and 18–24 min/session
(i. e., six exercises with four sets of 45–60 s per exercise)
with 90-s rest periods between exercises for the BT-LV group and the BT-HV
group, respectively. The chosen distinction was based on the results of Gebel et
al. [7]. Although the authors found an
equal effectiveness of both balance training volumes, this finding was based on
an indirect study comparison. It may therefore be confounded by other variables
(e. g., training period, frequency, exercises etc.), which is why a
direct comparison was made in the present study where all other variables were
the same. The lower balance training volume in the BT-LV group compared to the
BT-HV group was filled with gymnastic exercises. After balance training, the
remaining class time in the BT-LV group as well as in the BT-HV group was filled
with the same gymnastic exercises as in the CON group.
Table 2 Group-specific description of the exercise
programs
|
Load dimension
|
CON (n=19)
|
BT-LV (n=16)
|
BT-HV (n=20)
|
|
Training period
|
8 weeks
|
8 weeks
|
8 weeks
|
|
Training frequency
|
2 sessions/week
|
2 sessions/week
|
2 sessions/week
|
|
Balance training volume (incl. rest)
|
–
|
4 min (16 min)
|
18–24 min (54–60 min)
|
|
Exercise number
|
–
|
4
|
6
|
|
Exercise duration
|
–
|
30 s
|
45–60 s
|
|
Exercise sets
|
–
|
2
|
4
|
|
Rest between sets
|
–
|
90 s
|
90 s
|
|
Training exercises
|
P.E. lessons including gymnastics and swimming (each once per
week)
|
static (e. g., standing exercises), dynamic
(e. g., walking exercises), proactive
(e. g., weight shifting while standing), and
reactive (e. g., perturbed standing) balance
tasks
|
|
|
Training progression
|
none
|
-
– reduction in the base of
support
-
– manipulation of the sensory
input
-
– inclusion of unstable devices
(e. g., wobble board)
|
|
BT-HV=high volume balance training; BT-LV=low volume
balance training; CON=active control group (i. e.,
regular physical education); P.E.=physical education
Statistical analyses
Descriptive data are presented as group mean values and standard deviations.
After normal distribution was examined via Shapiro–Wilk Test and showed
p-values>.05, a univariate analysis of variance (ANOVA) was
conducted to test for significant differences in pretest values between the
groups. Significant group differences at the pretest were detected for all
balance parameters and were thus included as covariates in the analyses.
Thereafter, a 2 (Test: pre, post) × 3 (Group: CON, BT-LV, BT-HV) ANCOVA
with repeated measures on Test was used. In the case of a significant
(p<.05) Test × Group interaction, differences between
pretest and posttest values were analyzed for each group separately using paired
t-tests. Further, effect size (Cohen’s d) was
calculated and reported as small (0 ≤ d ≤ .49), medium
(.50 ≤ d ≤ .79), and large (d ≥ .80) [17]. All statistical analyses were
performed using Statistical Package for Social Sciences version 27.0 (IBM Corp.,
Armonk, NY, USA).
Results
All participants received intervention (i. e., balance training lessons) or
control (i. e., regular physical education lessons) conditions as allocated.
None of the participants reported any test- or training-related injury. Overall, the
data of 55 participants were included in the analysis ([Fig. 1]). [Table 3] displays descriptive and inference statistics for all analyzed
variables. For the Y-balance test, the analyses revealed significant main effects
of
Test and Group as well as significant Test × Group interaction effects for
all reach directions and the composite score. Post-hoc analyses yielded significant
enhancements from pre- to post-training in the BT-LV group (posteromedial reach:
p=.003, d=.46; posterolateral reach:
p=.003, d=.70; composite score: p=.012,
d=.46) and in the BT-HV group (anterior reach:
p<.001, d=.94; posteromedial reach:
p=.015, d=.41; posterolateral reach:
p=.007, d=.51; composite score: p<.001,
d=.63) but not in the CON group ([Fig. 2a]). Concerning the Timed-Up-and-Go
test, the analysis showed a significant main effect of Test and Group and a
significant Test × Group interaction. Post-hoc analyses detected significant
improvements from pre- to post-training in the BT-HV group (p=.003,
d=.81) but not in the BT-LV group and the CON group ([Fig. 2b]).
Figure 2 Group-specific performance changes (mean±standard
deviation) during the intervention period in a) anterior reach distance in
the Lower Quarter Y-balance test, and b) Timed-Up-and-Go test. BT-HV,
high-volume balance training; BT-LV, low-volume balance training; CON,
active control group (i. e., regular physical education); LL, leg
length
Table 3 Effects of balance training using a low versus high
training volume on measures of balance performance in healthy
children
|
CON (n=19)
|
BT-LV (n=16)
|
BT-HV (n=20)
|
p-value (Cohen’s d)
|
|
Outcome
|
Pretest
|
Posttest
|
∆%
|
Pretest
|
Posttest
|
∆%
|
Pretest
|
Posttest
|
∆%
|
Test
|
Test x Group
|
Group
|
|
AT [% LL]
|
73.4±10.9
|
65.6±6.9
|
−10.6
|
80.3±15.0
|
80.6±11.3
|
+0.4
|
87.6±13.8
|
100.1±13.0
|
+14.3
|
<.001 (1.67)
|
<.001 (2.50)
|
<.001 (2.50)
|
|
PM [% LL]
|
101.8±9.2
|
102.6±7.8
|
+0.8
|
116.9±19.4
|
125.7±18.0
|
+7.5
|
123.1±14.3
|
128.6±10.9
|
+4.5
|
<.001 (1.34)
|
<.001 (1.34)
|
<.001 (1.34)
|
|
PL [% LL]
|
102.7±9.8
|
103.6±10.7
|
+0.9
|
111.7±15.4
|
122.3±14.5
|
+9.5
|
119.9±16.1
|
127.6±11.5
|
+6.4
|
<.001 (1.40)
|
<.001 (1.37)
|
<.001 (1.37)
|
|
CS [% LL]
|
92.6±8.3
|
90.6±7.1
|
–2.2
|
103.0±15.5
|
109.5±12.1
|
+6.3
|
110.2±13.9
|
118.8±10.9
|
+7.8
|
<.001 (1.74)
|
<.001 (2.21)
|
<.001 (2.21)
|
|
TUG [s]
|
5.1±0.5
|
5.0±0.9
|
+2.0
|
6.0±0.9
|
5.9±0.8
|
+1.7
|
5.6±0.9
|
5.0±0.7
|
+10.7
|
<.001 (1.67)
|
<.001 (2.50)
|
<.001 (2.50)
|
Values are mean values±standard deviations. Figures in brackets are
effect sizes (Cohen’s d) with 0 ≤ d ≤
.49 indicating small, .50 ≤ d ≤ .79 medium, and
d ≥ .80 large effects. AT, anterior; BT-HV, high-volume
balance training; BT-LV, low-volume balance training; CON, active control
group (i. e., regular physical education); CS, composite score; LL,
leg length; PL, posterolateral; PM, posteromedial; TUG, Timed-Up-and-Go
Test
Discussion
We investigated the effects of balance training using a low or a high training volume
on dynamic balance performance in healthy children. The main findings of the study
were that (1) balance performance significantly improved in both balance training
groups compared to the control group; and (2) performance enhancements in some
parameters (i. e., anterior reach distance and Timed-Up-and-Go test
duration) were larger for the high-volume than for the low-volume group.
Effects of balance training on measures of balance performance
In accordance with our hypothesis of balance training-related performance
improvements, we found that both balance training conditions resulted in
enhanced dynamic balance performance when compared with the control condition
(i. e., physical education lessons). This finding corresponds with those
from earlier studies [8]
[18]
[19] investigating the impact of balance training on measures of
balance performance in healthy children. For instance, Kayapnar [19] studied the influence of a 12 weeks (3
times per week) movement education program including basic movements, different
children games, and posture exercises on static balance (i. e., unipedal
stance time within one minute) in preschool children (age range: 5–7
years). When compared with the control group (i. e., received the
regular curriculum), the training group showed a significantly increased stance
time. Further, Altinkök [18]
assigned 6-year-old primary school children to a group that performed an
“Activity Education with Coordination” program or received their
regular activity education without coordination exercises. Following 8 weeks (2
sessions per week) of intervention, the group with the specific program achieved
significant improvements in static (i. e., unipedal stance time within
one minute) and dynamic (i. e., time in balance on a stabilometer within
30 s) balance but not the group with the regular program. Finally, Dobrijevic et
al. [8] examined young rhythmic gymnasts
(age range: 7–8 years) that conducted 12 weeks (biweekly) of balance
training in addition to gymnastic training or gymnastic training only. The
authors detected significantly enhanced static balance performance
(i. e., unipedal stance time within one minute) in favor of the group
with additional balance exercises. In sum, the aforementioned findings and the
observed results of the present study indicate that balance training is an
effective means to improve balance performance in healthy children, although
there is a relatively large heterogeneity in the methodological approaches used.
More importantly, the effectiveness of balance training does not seem to be
limited to certain types of balance as adaptations to training have been shown
for less (i. e., static) as well as more (i. e., dynamic)
demanding postural control tasks.
Effects of balance training volume on measures of balance performance
Partly in line with our hypothesis, we detected greater enhancements in dynamic
balance performance for the high- compared to the low-volume group. More
precisely, only Timed-Up-and-Go Test time and Y-balance test anterior reach
distance but neither the other reach distances nor the composite score showed
superior improvements for the high- compared to the low-volume group. There is
one study available that previously investigated the effect of low versus high
balance training volume on balance performance. More precisely, Bal [12] assigned adolescent girls (mean age:
15.5±1.7 years) to a low-volume group (i. e., 3 exercises with
2–4 sets of 9–13 repetitions or 18–30 s duration) or a
high-volume group (i. e., 3 exercises with 2–4 sets of
8–15 repetitions or 18–35 s duration). Before and after 6 weeks
of balance training (3 sessions per week), both groups were tested on static
(i. e., unipedal stance time on stable ground) and dynamic
(i. e., unipedal stance time on unstable [wobble board] ground within 15
s) balance performance. For both measures, they found a tendency toward
significant improvements for the high-volume but not for the low-volume group.
The fact that significant improvements were found in the present study, however,
may be due to methodological differences. Although the total number of training
sessions was almost the same with 18 sessions in the study of Bal [12] and with 16 sessions in the present
study, there are differences in the sample studied. For instance, Bal [12] investigated female adolescents (mean
age: 15.5±1.7 years) but we studied female and male children (mean age:
11.0±0.7 years). There is evidence that adolescents and especially girls
have significantly better balance skills than children or boys of the same age
[20]
[21], indicating a smaller adaptive reserve in adolescents compared to
children [3]. Therefore, the sample used
in the Bal study might have had a lower reserve to adapt on balance
training-induced stimuli than the individuals in the present study, which would
explain its report of non-significant changes. Further, the difference in
balance training volume between groups was smaller in the Bal study
(i. e., low-volume group: 3 exercises with 2–4 sets of
9–13 repetitions or 18–30 s duration; high-volume group: 3
exercises with 2–4 sets of 8–15 repetitions or 18–35 s
duration) than those in the present study (low-volume group: 4 exercises with 2
sets of 30 s duration; high-volume group: 6 exercises with 4 sets of
45–60 s duration), with the latter leaving more room for volume-specific
adaptations.
The partly larger improvements in the high- compared to the low-volume group can
most likely explained by the fact that a higher training volume results in a
longer exposure to balance-demanding training stimuli that affect postural
control (i. e., vestibular, proprioceptive, and visual system).
Specifically, a total exercise duration of 64 min (i. e., 8
weeks × 2 times/week × 4 min/session)
occurred in the low-volume group and a duration of 288–384 min
(i. e., 8 weeks × 2 times/week ×
18–24 min/session) in the high-volume group. A longer
versus a shorter exposure to the balance training stimuli, in turn, offers the
potential for greater adaptation processes in the postural control system.
Consequently, future studies should investigate whether the expected greater
adaptations are reflected in the underlying neural mechanisms (i. e.,
cortical and spinal plasticity) [22].
The strengths of this study were that a relatively large number of
N=60 healthy children were studied. In addition, the Lower
Quarter Y-Balance Test and the Timed-Up-and-Go Test are valid and reliable tests
to assess children's balance performance. A limitation of the present
study is that it was restricted to children. In fact, previous research suggests
that adaptations to balance training in youth may be age-dependent [3]
[23]. Further, there is evidence that in children the effectiveness of
balance training may differ between males and females [24]. However, in the present study it was
not distinguished between girls and boys. Future studies should therefore
scrutinize the role of age and sex in relation to the effects of different
balance training volumes.
Conclusions
We investigated differences in the effectiveness of balance training using a low
versus a high training volume on balance performance in healthy children. For both
training regimens as compared to the control condition, we found significant
improvements in measures of dynamic balance performance. Further, the performance
enhancements in some parameters (i. e., anterior reach distance and
Timed-Up-and-Go duration) were larger for the group that used a high training
volume. These findings indicate that balance training is an effective means to
improve dynamic balance in healthy children and that a high (i. e.,
288–384 min in 8 weeks, 36–48 min/week)
compared to a low (64 min in 8 weeks, 8 min/week) training
volume is partially more effective.
