CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 2, March 2012
68
AFRICA
predominance of the sympathetic over the parasympathetic drive,
which was represented by a decrease in HRV.
17
Heart rate variability has the potential to be a useful monitor-
ing tool in the fields of health, fitness and sports performance.
However, currently, there are issues regarding the standardisation
and reproducibility of HRV measurement, as there are many
confounding factors that can influence HRV. These include
factors such as mood, alertness, mental activity, gender and
age.
3,6,18
While the research relating to gender differences is
controversial,
5,7,18
the relationship between age and HRV has been
well documented.
5,6,8,19
Reduced HRV is associated with progress-
ing age and with an increased risk of cardiac events in clinically
disease-free patients.
14
The development of wireless heart rate-monitoring equipment,
which has the ability to record IBIs has provided athletes, coach-
es, scientists and medical practitioners with mobile and easy-to-
use systems that allow for the analysis of HRV. The commercially
available Suunto t6 heart rate system (Suunto; Vantaa, Finland)
is one such instrument that is widely used for monitoring heart
rate during exercise. The validity of the Suunto t6 in measur-
ing IBI for determining HRV has been reported recently.
1
While previous studies have examined the reliability of
other commercially available devices (Polar S810) for measur-
ing HRV,
1,2
there is limited information on the reliability of the
Suunto t6 for HRV measurement.
1,20
Analysis of the IBIs to
determine HRV can be performed using custom software such
as Kubios heart rate variability software version 2.0 (Biosignal
Analysis and Medical Imaging Group, Department of Physics,
University of Kuopio, Kuopio, Finland).
20,21
To date, there are few
publications reporting the use of both the Suunto t6 and Kubios
software together.
20
The primary aim of this study was therefore to investigate the
reliability of Kubios software HRV measures calculated from the
Suunto t-6 IBIs in physically active individuals. Furthermore, we
investigated whether there were any gender differences in HRV
parameters.
Methods
This study was conducted on 50 physically active young adults
(males:
n
=
25; females:
n
=
25), although data analysis was
performed on 21 males and 23 females due to exclusion criteria,
discussed in the statistical analysis of the data (Table 1). There
were significant differences between the genders in terms of
height, mass and percentage body fat, but no differences in age,
body mass index, waist-to-hip ratio or weekly physical activ-
ity levels (Table 1). Participation was voluntary, and written
informed consent was obtained from all participants. The study
was approved by the Institution’s Biomedical Research Ethics
Committee (REF: BE111/010).
Participants were excluded from the study if they had expe-
rienced a cold or feverish illness in the month leading up to the
study, were smokers, had a pre-existing heart condition either
current or in the past, were pregnant, diabetic, had congestive
heart failure, or acute or chronic renal disease, if they have a
pacemaker, or were taking type 1A anti-arrhythmics (quinidine,
procainamide, disopyramide or moricizine).
Assessment of physical activity status
The International Physical Activity questionnaire (IPAQ) is
a validated questionnaire primarily designed for population
surveillance of physical activity among adults (age range 15–69
years).
22
This questionnaire was used to classify the physical
activity status of the participants in the week leading up to the
first (day 1) testing day. The IPAQ requires the summation of
duration (in minutes) and frequency (days) for different catego-
ries of physical activity.
Based on this information, MET-minutes/week are calculated
with the MET minute scores being equivalent to kilocalories
expended per week. The participants were then classified into
low, moderate or high physical activity levels. On average, the
participants in the study were classified as being in the moderate
category, with an average of 5 828 kcals (Table 1) expended per
week (833 kcal expended per day). Moderate is defined by the
IPAQ guidelines as a pattern of activity done on three or more
days, at least 20 minutes per day and described as vigorous-
intensity activity, or five or more days of moderate-intensity
activity and/or walking at least 30 minutes per day.
Protocol
Testing was conducted within the human performance laboratory
(HPL) at our institution. The temperature in the HPL was main-
tained at 22°C with 50% humidity. Participants were provided
pre-test instructions the week before the testing to help control
for factors that could alter heart rate variability readings. They
were asked to avoid caffeine, eating, heavy physical activity,
smoking and alcohol intake for the 10 hours preceding each
laboratory visit. Each participant attended four testing sessions
for four days in a row at the same time of the day. Testing was
performed between 07:00 and 21:00.
On testing day 1, which counted as the familiarisation day,
each participant read the information sheet provided on the
study, signed a written informed consent, completed a pre-test
questionnaire (IPAQ) and medical history questionnaire. The
medical questionnaire examined cardiovascular, metabolic and
respiratory disease history (personal and family) as well as risk
factors and signs and symptoms for these diseases. In addition,
participants provided information on their current medication
and supplement intake.
Height, mass, waist and hip circumferences and three site
skinfolds (females: tricep, supra-iliac and mid-thigh; males:
chest, abdominal and mid-thigh) were then measured. Height and
weight were recorded using a calibrated medical height gauge
and balance scale (Detecto, Webb City, USA). A Harpenden
skinfold calliper was used for skinfold measurements to calcu-
TABLE 1. DESCRIPTIVE DATA, PHYSICAL
CHARACTERISTICSAND PHYSICALACTIVITY
LEVEL OF MALESAND FEMALES (MEAN ± SD)
Males (
n
=
21) Females (
n
=
23)
p
Age (years)
21.17 (1.55)
19.75 (1.76)
0.45
Height (cm)
177.3 (9.09)
160.5 (6.49)
<
0.0001*
Mass (kg)
76.19 (14.69)
60.41 (9.64)
0.0001*
BMI (kg/m
2
)
24.03 (2.64)
23.41 (2.89)
0.467
Waist/hip ratio
0.88 (0.07)
0.85 (0.068)
0.123
Percent body fat
13.73 (4.53)
18.63 (3.77)
0.0004*
IPAQ (Kcals/week)
5828 (3806)
5491 (3751)
0.789
IPAQ
=
International Physical Activity questionnaire.
