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

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 3, May/June 2019

140

AFRICA

be concluded that over the 25-year period of follow up, the

development of aerobic fitness between 13 and 36 years of

age was independently and positively related to daily physical

activity in both genders (

0.001). This relationship was

significant in the crude univariate model (corrected for gender

and initial VO

2 peak

value) as well as in the two models adjusted

for lifestyle and biological parameters (Table 3).

However, the functional implications of the statistically highly

significant relationships seem to be small: a 10% difference in

MET-score was positively related to a 0.3% difference in VO

2 peak

By contrast, the results of the auto-regression model, which

was controlled for present VO

2 peak

, revealed no significant

relationship between physical activity and aerobic fitness in both

genders over the period of follow up (13- to 36-year age period).

A difference in physical activity of 10% appeared to be positively

related to a non-significant difference in VO

2 peak

of only 0.04%

(95% CI: –0.06 to 0.13).

The BMD of hip, lumbar spine and wrist was measured three

times by dual X-ray absorptiometry (DEXA) between 27 and

36 years of age. Lumbar and hip BMD was significantly and

positively related to physical activity but not to dietary calcium

intake during the teenage period.

Type of daily physical activity is also important for bone mass.

From animal experiments, it is known that dynamic mechanical

loading of short duration seems more effective than metabolic

In the lumbar spine and femoral neck during youth,

the explained variance was 15 and 11% with mechanical physical

activity (MECHPA) and only 4 and 2% with metabolic physical

activity (METPA). No difference could be observed on the distal

radius.

This last result validates the importance of mechanical

loading, because in general, the daily load on the upper extremities

is far less than on the lower extremities in humans.

Fig. 1 shows the standardised regression coefficients (corrected

for gender, body height and weight, fat mass, biological age

and calcium intake) of the lumbar BMD at age 32 years with

the physical activity pattern during three periods: adolescence

(13–16 years), young adulthood (21–27 years) and the total

period (13–27 years). The highest coefficients (beta) were with

MECHPA over the total period of 15 years (beta

0.33;

0.01). During young adulthood (the seven-year period of age

21–28 years), MECHPA was also significantly related to lumbar

BMD at age 32 years (beta

0.20;

0.01). Only METPA

results during adolescence and during the total period were

significantly (

0.01) related to lumbar BMD at age 32 years,

with beta values of 0.18 and 0.21 respectively.

We investigated the longitudinal relationship between daily

physical activity and daily food intake on one hand, with the

development of overweight and obesity over the 23-year follow-

up period on the other hand. Fig. 2 shows that the percentage

of males and females with a BMI above 25 kg/m

increased

exponentially with age: at 36 years, 43% of the males and 25%

of the females were overweight or obese, while less than 5% were

overweight in adolescence.

The longitudinal relationship of the actual values of daily

physical activity with BMI resulted in significant (

0.02)

negative regression coefficients in males but not in females. As

expected, more daily physical activity resulted in less fat mass

with daily food intake, however, the regression coefficients with

S4S were significant in both males and females, and with BMI

only in females, but these were not in the expected direction

(lower daily food intake resulted in more fat mass) (Table 4).

More daily physical activity resulted in significantly lower fat

mass and less overweight and obesity. Surprisingly, higher S4S

and BMI were related to lower daily food intake. This unexpected

result that a lower energy intake over 23 years was related to

higher fat mass can be explained in two ways: (1) under-reporting

of daily food intake by the more overweight subjects, and (2)

repeated measurements could introduce negative testing effects.

Therefore, the origin of overweight and obesity in this

longitudinal study cannot merely be explained by an increase in

energy intake, but rather by a decrease in energy expenditure.

METPA

MECHPA

beta

0.35

0.30

0.25

0.20

0.15

0.10

0.05

15 years (13–27)

7 years (21–27)

4 years (13–16)

* =

< .01

Fig. 1.

Standardised regression coefficients of lumbar BMD at

age 32 years, and lumbar BMD at age 32 years with

mechanical physical activity (MECHPA) and meta-

bolic physical activity (METPA) over three age periods:

adolescence (13–16 years); young adulthood (21–27

years), and the total period (13–27 years).

13 14 15 16 21 27 32 36

Age (years)

Women

Men

Fig. 2.

The percentage of males and females with a BMI

above 25 kg/m

from age 13 to 36 years.