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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 3, May/June 2017
AFRICA
177
In the four studies concerning the effects of RIF on the sports
performance of healthy children, no information was given
on HR and/or oxy-sat.
11-14
In that regard, a recent article
26
has
described and criticised these publications,
11-14
and the authors
recommend studies focusing on the effects of RIF on HR and
oxy-sat.
26
Therefore, the aim of our study was to examine the
effects of RIF on HR and oxy-sat, determined at rest and during
a field exercise test in untrained Tunisian boys.
Methods
Part of this study’s methodology was previously described in
an article reporting on the effects of RIF on first-time fasting
boys’ performance in short-term explosive exercises, as well as in
sub-maximal endurance exercise.
12
The major details concerning
the applied methodology are presented below.
Eighteen healthy non-athletic boys who fasted for the first
time in their lives during Ramadan 2012 were included. The
protocol was approved by the local hospital ethics committee,
and written informed consent was obtained from all children and
their parents. The boys were asked to avoid strenuous activities
24 hours before each testing phase. Participants were informed
that their participation was free of pressure and that they could
withdraw from the study at any time (including that they could
decide to stop fasting).
The experimental design consisted of four testing phases: two
weeks before Ramadan (pre-R), the end of the second week of
Ramadan (R-2), the end of the fourth week of Ramadan (R-4),
and 10 to 12 days after the end of Ramadan (post-R). The
decimal age (accuracy of 0.10 years) was calculated from the
date of measurement and the date of birth. Body mass (
±
1 kg)
was measured during each phase and height was measured to the
nearest 0.1 cm.
12
The boys were familiarised with the six-minute walking
test (6MWT) to minimise the learning effect.
27
6MWTs were
conducted at the same time of day in the interval between 15:00
and 17:00.
28
This period corresponded to the last fasting hours
of the day, with the fast break time ranging from 19:31 at the
beginning to 19:04 at the end of Ramadan 2012 at the location
of the study. During each testing phase, each boy performed one
6MWT.
The following data were collected/calculated: six-minute
walking distance (6MWD, in m, % of predicted value
27
), oxy-sat
(%) and HR [bpm, % of maximal predicted HR (
=
208–0.7
×
age)
29
] determined at rest and in each minute of the 6MWT, and
the 6MWD
×
sixth minute oxy-sat index (m).
17,18
The 6MWTs
were performed according to international guidelines.
30
At the
end of the 6MWT, the 6MWD (m) was noted. HR (Polar RS
800, Polar Electro Oy, Kempele, Finland) and oxy-sat (Nonin
Medical, Inc, Minneapolis, MN) were recorded at rest and in
each minute of the 6MWT. Additional 6MWT methodology
details have been presented in a separate publication.
12
Statistical analysis
Data are presented as mean values
±
standard deviation (SD)
for anthropometric data and mean
±
SD (95% confidence
interval) for HR, oxy-sat and the 6MWD
×
sixth minute oxy-sat
index. The Kolmogorov–Smirnov test for normality revealed
that the data were normally distributed. Analysis of variance
(ANOVA) was then conducted to compare the HR and oxy-sat
data measured at the seven time points of the 6MWT (rest, first,
second, third, fourth, fifth and sixth minutes) during the four
testing phases. ANOVA was also conducted to compare the
6MWD
×
sixth minute oxy-sat index in the four phases. When
appropriate, significant differences between means were tested
using the Tukey
post hoc
test. Statistical analyses were performed
using Statistica software (Statistica Kernel version 6; StatSoft,
Paris, France). Significance was set at
p
<
0.05.
Results
The mean
±
SD of the 18 boys’ age, height and body mass were
11.9
±
0.8 years, 153.00
±
8.93 cm and 55.4
±
18.2 kg, respectively.
The effect of RIF on HR: Fig. 1 shows the HR data (%)
determined during the four testing phases at the seven time
points of the 6MWT. There was no significant difference
between the four testing phases in resting or third-minute HR
values [ANOVA (
n
=
18, df
=
3, F
=
0.82) and ANOVA (
n
=
18,
df
=
3, F
=
1.253), respectively]. However, there were significant
differences between the four testing phases in the:
•
first-minute 6MWT HR values [ANOVA (
n
=
18, df
=
3, F
=
4.32,
p
<
0.008)]. HR was lower during R-4 (69
±
7 bpm)
compared to R-2 (76
±
10 bpm;
p
=
0.04) and post-R (78
±
6;
p
=
0.008).
•
second-minute 6MWT HR values [ANOVA (
n
=
18, df
=
3, F
=
5.447,
p
<
0.0022)]. HR was lower during R-4 (70
±
9 bpm)
compared to pre-R (78
±
9 bpm;
p
=
0.029), R-2 (79
±
10 bpm;
p
=
0.027) and post-R (81
±
7 bpm;
p
=
0.003).
•
fourth-minute 6MWT HR values [ANOVA (
n
=
18, df
=
3, F
=
4.83,
p
<
0.0045)]. HR was lower during R-4 (72
±
9 bpm)
compared to post-R (84
±
6 bpm;
p
=
0.002).
•
fifth-minute 6MWT HR values [ANOVA (
n
=
18, df
=
3, F
=
4.054,
p
<
0.01)]. HR was lower during R-4 (75
±
7 bpm)
compared to post-R (85
±
7 bpm;
p
=
0.009).
•
sixth-minute 6MWT HR values [ANOVA (
n
=
18, df
=
3, F
=
3.43,
p
<
0.023)]. HR was higher during post-R (86
±
9 bpm)
compared to R-2 (77
±
10 bpm;
p
=
0.04) and R-4 (77
±
8
bpm;
p
=
0.04).
The effect of RIF on oxy-sat: Fig. 2 shows the oxy-sat data (%)
obtained during the four phases at the seven time points of the
6MWT. There was no significant difference between the four
testing phases in resting or first, second, fourth and sixth minutes
oxy-sat values [ANOVA: (
n
=
18, df
=
3, F
=
3.52), (
n
=
18, df
=
3, F
=
1.83), (
n
=
18, df
=
3, F
=
2.12), (
n
=
18, df
=
3, F
=
1.41)
and (
n
=
18, df
=
3, F
=
2.13), respectively]. However, there were
significant differences between the four testing phases in the:
•
third-minute oxy-sat values [ANOVA (
n
=
18, df
=
3, F
=
4.07,
p
<
0.01)]. The Tukey test showed a significant difference
between pre-R and R-2 [89
±
7 vs 95
±
2%;
p
=
0.02].
•
fifth-minute oxy-sat values [ANOVA (
n
=
18, df
=
3, F
=
4.55,
p
<
0.006)]. The Tukey test showed a significant difference
between pre-R and post-R (94
±
2 vs 89
±
7%;
p
=
0.04),
between R-2 and post-R (95
±
3
vs.
89
±
7%; p
=
0.008), and
between R-4 and post-R (94
±
6 vs 89
±
7%; p
=
0.04).
Fig. 3 shows the 6MWD
×
oxy-sat indices calculated in the sixth
minute of each 6MWT. A significant difference between the four
testing phases was found [F (3, 53)
=
3.4191;
p
=
0.023]. The
Tukey test showed a significant difference (
p
=
0.019) between
pre-R (67 573
±
7 514 m) and R-4 (56 224
±
12 274 m) values.