trols). The high LPL levels probably arise from
enhanced capillarization in the muscle of athletes
because the enzyme is bound to the luminal
surface of capillary endothelium.
There are also short-term effects of recent exer-
cise on postprandial TAG clearance. During
recovery TAG clearance rates are increased,
reducing the postprandial rise in plasma TAG
concentration. The effect is greater after moder-
ate intensity exercise (60% V
.
o2max.) than after low
intensity exercise (30% V
.
o2max.) of the same dura-
tion probably because of its greater energy
expenditure; if energy expenditure is held con-
stant the effects on lipaemia of low and moderate
intensity exercise are strikingly similar (Tsetsonis
& Hardman 1996). These short-term benefits
may therefore be potentially greater for trained
people because their higher V
.
o2max. values
and greater endurance capability allow them to
expend more energy than untrained individuals
before becoming fatigued.
People spend the majority of their lives in
the postprandial state and exercise-induced de-
creases in postprandial lipaemia may be clini-
cally important in the long term. When TAG
clearance is good, the postprandial rise in TAG is
reduced and TAG-rich particles will remain in
the circulation for shorter periods, decreasing the
atherogenic stimulus. Clinical evidence is consis-
tent with this view because case-control studies
have shown that postprandial TAG levels accu-
rately predict the presence or absence of coro-
nary artery disease.
Energy balance
In the UK, overweight (body mass index 25–30
kg · m–2) and obesity (body mass index >30 kg ·
m–2) are a serious problem. More than 50% of
men and more than one third of women in the
age group 45–54 are overweight, whilst nearly
20% of both sexes are obese. Figures are even
worse in the US, where mean body weight
increased by 3.6 kg between 1976/80 and
1988/91. The health hazards of carrying excess
weight are well documented so its prevalence
rightly gives rise to concern. Recent findings
have particularly emphasized the importance of
the regional distribution on body fat in relation to
the risk of atherosclerotic metabolic disease. As
with so many aspects of human health, there is
substantial genetic control but environmental
factors—diet, physical activity—modify these
influences profoundly.
The energy stores of the body are, of course,
determined by the balance between energy
intake and energy expenditure and any exercise
contributes to energy expenditure. Although for
most people the expenditure in habitual exercise
rarely accounts for more than 20% of the total,
physical activity is the only way in which energy
expenditure can be increased voluntarily. Its
importance in helping to control body weight
and body fat content—for individuals or for pop-
ulations—is still a matter of debate, despite the
fact that there is a fairly consistent negative rela-
tionship between level of activity and body mass
index or skinfold thicknesses.
The energy stored in 1 kg of adipose tissue
is approximately 32.4 MJ (7740 kcal). Energy
expenditure during weight-bearing activities
depends on body mass; for example, walking
or running 1.6 km expends (net) about 220 kJ
(52 kcal) for a 50-kg person, but about 350 kJ
(84 kcal) for an 80-kg person, i.e. about 4.2 kJ · kg–1
body weight · km–1 (1 kcal · kg–1 body weight ·
km–1). Theoretically, therefore (and disregarding
the small postexercise elevation of metabolic rate
which, in non-athletes, probably never exceeds
10% of exercise expenditure), walking an extra
mile every day for a year would expend (net) an
estimated total of 80–128 MJ (19 100–30 580 kJ),
i.e. the energy equivalent of 2.5–4 kg of adipose
tissue. Resting metabolic rate decreases, how-
ever, as body mass falls and energy intake will
be stimulated, offsetting this deficit. As planned
exercise increases, there may also be a sponta-
neous decrease in the physical activities of every-
day living. The situation is far from simple.
What tends to happen in practice? The consen-
sus in the literature is that relatively small
increases in physical activity (for example,
walking 3.2 km · day–1, three times per week,
adding up to 2.1–2.5 MJ or 500–600 kcal gross) are