Cardiovascular Journal of Africa: Vol 30 No 3 (May/June 2019)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 3, May/June 2019 AFRICA 139
circumferences, peak height velocity and skeletal age),
cardiovascular measurements (blood pressure, cholesterol levels,
arterial stiffness) and lung function measurements (FEV1), motor
performance fitness tests (muscle strength, speed, co-ordination,
endurance) and psychosocial tests (personality traits, sociometric
status) have been described previously in detail.3-5
Aerobic fitness was measured with a maximal running test
on a treadmill with continuous measurement of oxygen uptake
(VO2 peak). 6 There after a six-minute sub-maximal running test at
a speed of 8 km/h and increasing slope of 0, 2.5 and 5% was
recorded. After a short rest, running was continued at the same
constant speed of 8 km/h while the slope was increased every two
minutes by 2.5 or 5%, depending on the heart rate. This maximal
test was continued until complete exhaustion had been reached.7
The bone mineral content was measured in the hip, lumbar
spine and wrist with dual X-ray absorptiometry. The BMD was
measured on each side.8,9
Obesity was estimated with body mass index (BMI) from
body mass and body height squared. Fatness was calculated
from the sum of four skinfolds (S4S) from the biceps, triceps,
sub-scapular and iliocristal skinfolds.10
All the participants (and their parents) in the study received
and signed the informed consent prior to and during this
longitudinal research.
Statistical analysis
The statistical methods used in this study are described in detail
elsewhere.3-5 Briefly, four variables (VO2 peak , BMD, obesity from
BMI, and body fatness from S4S), measured 10 times over a
period of 25 years, were included in the analysis. The general
estimated equation and random coefficient analysis were suitable
to answer all the research questions and were much more flexible
than MANOVA for repeated measurements. All analyses were
carried out with the Statistical Package of Social Science, 10.1
for Windows (SPSS, Inc, Chicago, III, USA). The level of
significant was set at p < 0.05.
Results and Discussion
Data on both aerobic fitness and daily physical activity were
gathered nine times. A multilevel auto-regression analysis
revealed paradoxical results (Table 3). From the results, it can
Table 1. Presentation of measurements taken in the
AGAHLS subjects over time from 1977 to 2006
Years
1977–
1980 1985 1991 1993
1996/
97 2000 2006
Age in years 13–16 21 27 29 32 36 42
Body fatness
Dexa scan × ×
Skinfold measurements × × × × × × ×
Body mass index × × × × × × ×
Waist-to-hip ratio × × × × × × ×
Birth weight (retrospective) × ×
Physical activity and fitness
Maximal oxygen uptake (direct test) × × × ×* × × ×*
Motor fitness (MOPER) × × × × × × ×
Muscle strength (quadriceps/
hamstrings)
× × × × ×
Lung function × × × × × × ×
Physical activity (accelerometer) × ×
Physical activity (interview) × × × × × × ×
Sedentary behaviour (questionnaire) × × × × ×
Postural sway ×
Cardiovascular health
Traditional blood markers
(lipoproteins, triglycerides)
× × × × × × ×
Markers of inflammation and
endothelial function
× ×
Systolic/diastolic blood pressure × × × × × × ×
Macrovascular function (carotid
ultrasound)
× ×
Microvascular function (nailfold
capillaroscopy)
×
Lifestyle
Demographic information
(questionnaire)
× × × × × × ×
Geographic mobility (interview) ×
Dietary intake (questionnaire) × × × × × ×
Smoking (questionnaire; dipstick
in 2000)
× × × × × ×
Alcohol consumption
(questionnaire or interview)
× × × × × × ×
Coffee consumption (questionnaire) × × × × ×
TV and computer usage
(questionnaire)
× × ×
Life rhythm (questionnaire) × × ×
Sports motivation × ×
Bone mineral density and osteoporosis
DEXA scan × × ×
Heel bone (ultrasound) × ×
Lumbar spine (X-ray) × × ×
Distal radius and femoral head
(X-ray)
×
Musculoskeletal health complaints
(questionnaire)
× × × × × × ×
Skeletal age (X-ray) ×
*For VO2 max in 1993 and 2006, this was sub-maximal performance
Table 2. A flow chart of the number of participants from the
two schools per year of measurement; school 1 is the
longitudinal school and school 2 the cross-sectional school
Year School 1 Total School 2
1976 340 410 70
1977 259 322 63
1978 251 321 70
1979 238 312 74
1985 200 200
1991 182 182
1993 166 166
1996 236 438 202
2000 213 378 165
2006 192 344 152
Table 3. Standardised regression coefficients (beta) and
p-values obtained by generalised estimating equations (GEE)
regarding the longitudinal relationship between daily
physical activity on one hand and VO2max on the other hand
VO2max
Analysis β p-value
Crude 0.09 < 0.01
Adjusted 1 0.08 < 0.01
Adjusted 2 0.07 < 0.01
Crude: univariate analysis (corrected for gender time and initial value of
VO2max).
Adjusted 1: multiple analysis also corrected for lifestyle parameters.
Adjusted 2: multiple analysis also corrected for biological parameters.