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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 1, January/February 2018
34
AFRICA
Inmales, body fat and IVS thickness correlated negatively with
ejection fraction, while resting heart rate correlated positively.
In females, IVS thickness and LVED correlated positively
with ejection fraction. In males, IVS thickness was positively
associated with body fat, and negatively associated with ejection
fraction, resting heart rate and flexibility. In females, IVS
thickness was negatively associated with lean mass, ejection
fraction, resting heart rate and diastolic BP, while positively
associated with LVED. In males, LVED was positively associated
with BMI. In females, LVED was positively associated with
ejection fraction, resting heart rate and IVS thickness, while
negatively associated with diastolic BP and lean mass.
Table 3 displays the associations for the fitness and cardiac
morphology outcomes of the study population. All models were
adjusted for age and gender. The multivariable regression models
explained 66, 19, 59 and 67% of the variation in VJH, ejection
fraction, IVS thickness and LVED, respectively. VJH was
positively associated with lean mass, and negatively associated
with body fat. Ejection fraction was positively associated with
LVED and resting heart rate. Resting heart rate was inversely
associated with IVS thickness, while body fat and LVED were
positively associated. LVED was positively associated with
ejection fraction, body fat and IVS thickness, while negatively
associated with diastolic BP.
Discussion
Football is the most popular sport globally, with adolescents
making up a large proportion of participants. In most sports that
predominantly utilise the aerobic system, regular participation
provides significant cardiovascular adaptations as an adaptation
to improve performance.
2
Our study findings primarily add to
the limited body of evidence on the cardiac morphology of
adolescent African footballers.
The findings also show the gender differences in physiological
profile and selected performance outcomes, and that selected
cardiac parameters were not associated with dynamic VJH. Males
were taller and weighed more than the female study participants,
which is likely due to the higher lean muscle mass observed in
the male participants.
12
These body composition differences are
expected in adolescents of this age, but little is known about the
differences in cardiac morphology of African populations.
The higher lower-limb dynamic explosive power values
observed in male compared with female footballers supports the
well-known notion of gender functional strength differences. In
this study population, however, the sociopolitical landscape of
South Africa cannot be excluded as an additional source of this
discrepancy.
13
Despite encouraging participation in sport, policy makers
fail to account for the limited resources and lack of accessibility
experienced by female athletes in South Africa. There are still
barriers even when there are opportunities. For example, most
premier league football teams have the capability to allow for
the development of adolescent footballers, but the training
is often performed in the late afternoons to night-time. With
personal safety being a concern, these facilities may not easily
be accessible for adolescent female footballers, even if located
within walking distance. Therefore female subjects may not fully
engage in football training as a consequence.
The daily demands of schoolwork and other life stresses can
further de-emphasise the central focus on football. In addition,
incentives to participate in professional football are currently
more favourable for male subjects compared with females;
however, gender equality in various sports is being addressed.
Although studies have shown that the untrained female can
improve cardiovascular function by participating in recreational
competitive football,
14
males still have a more pronounced
physiological advantage over age-matched females. The diameters
of the male participants’ left ventricles are similar to those of
footballers of African descent living in Europe,
15
suggesting some
degree of genetic heritability.
On the other hand, the female participants seem to be more
aligned with the adaptations experienced by volleyball athletes.
16
This is evident by the finding that females have smaller heart
sizes and lower left ventricular mass compared with males.
17
Therefore, even though the cardiovascular adaptations to aerobic
sport are similar, the absolute difference in cardiac structure
is higher in male subjects. Moreover, the variation in cardiac
morphology can also be explained by the fact that height is
highly associated with heart size and function,
17
and male
subjects in our study were taller compared with females.
The vertical jump test is not only an indicator of explosive
strength, but also of neuromuscular adaptation. Our study
findings show that age, gender and body composition have an
influence on the difference in results for this variable. Therefore,
the lower VJH values in females can be explained by lower
muscle mass, younger age and increased body fat.
It is worth considering the specificity of training to explain
the advantage noted in males. Current knowledge shows that for
optimal neuromuscular adaptation, athletes need to engage in a
progressive strength-training programme, and actively challenge
the neuromuscular system.
18
Tendons assist with functional
movement by acting as shock absorbers and energy capacitors
within the muscle–tendon complex.
19
Further research is needed
to determine whether female footballers have lower jump height
as a result of lower tendon compliance for explosive activities.
The findings of this study highlight the interconnected
characteristic of the various cardiac muscle components. This
points to the complexity involved in trying to comprehend
cardiac development in footballers. For example, our study
findings show that lean muscle mass was associated with LVED
volume in the regression analyses, but football training is
Table 3. Multivariable linear regression models for determining the
influence of body composition, blood pressure, cardiac morphology
and performance on VJH, LVED, IVS thickness and ejection fraction
Exposure
VJH
Ejection
fraction (%)
IVS
thickness
LVED
Body fat
–0.2
*
–0.1
0.2
*
0.2
*
Ejection fraction
0.04
–0.02
0.2
*
Lean mass
0.5
*
0.04
–0.1
–0.1
IVS thickness
0.004
–0.04
0.6
*
LVED
–0.03
0.5
*
0.7
*
RHR
–0.1
0.3
*
–0.2
*
–0.001
Systolic BP
0.1
0.1
0.02
0.1
Diastolic BP
-0.02
-0.04
0.02
–0.2
*
VJH
0.1
0.01
–0.03
R
2
0.66
*
0.19
*
0.59
*
0.67
*
Data presented as adjusted
β
;
*
p
<
0.05. All models were adjusted for age and
gender.
LVED: left ventricular end-diastolic diameter; IVS: interventricular septal thick-
ness; VJH: vertical jump height; RHR: resting heart rate.