11
exercise interventions with overweight and obese adults, Kelley and colleagues [ 57 ]
noted a significant decrease in fasting triglyceride levels (11%) but no significant
changes in other lipoprotein parameters associated with cardiovascular risk.
Genetics may also play an important role. For example, in 35 pairs of monozygotic
twins who were discordant for vigorous activity, there were significant correlations
between the twin pairs for HDL-C and HDL subclasses, thus suggesting a substan-
tial influence of genetics over and above exercise [ 58 ]. Data from the Heritage
Family Study also suggest that genetic variation largely explains the substantial
variability in HDL cholesterol responses to endurance training [ 59 , 60 ].
In many studies the favourable alterations in blood lipids have been demon-strated exclusively in a fasted state. Given that humans spend the majority of their
lives in a post-absorptive state and impaired metabolism of postprandial lipopro-
teins are implicated in the development of CVD, the role of physical activity in
altering postprandial concentrations of blood lipids may be more clinically impor-
tant [ 61 ]. Cross-sectional studies show improved clearance of postprandial triglyc-
erides among regular exercisers compared to the inactive, although these alterations
may be due in greater part to the acute effects of a recent exercise bout rather than
any chronic adaptation to regular activity [ 62 ]. These findings underscore the impor-
tance of regular activity and support the recommendation that physical activity
bouts should be daily.
4.2.3 Cardiorespiratory Fitness
Steven Blair’s seminal work has demonstrated that low cardiorespiratory fitness is
among the most powerful predictors of cardiovascular and all-cause mortality in
Caucasian men [ 63 ]. More recent work has found that low cardiorespiratory fitness
predicts mortality in other populations, including women [ 64 ] and black men [ 65 ].
The addition of cardiorespiratory fitness to traditional risk factors significantly
improves the classification of risk and it has been argued that efforts to improve
cardiorespiratory fitness should become a standard part of clinical encounters [ 48 ].
Fitness is developed by moderate to vigorous intensity activity and cardiorespi-ratory fitness is therefore an objective measure this type of activity [ 66 ]. Indeed,
Blair and colleagues have found that cardiovascular mortality is halved in men who
become active and fit compared to those who remain inactive and unfit. Progressive
manipulation of the training variables or ‘dose’ (exercise frequency, exercise inten-
sity and exercise duration) is likely to improve cardiorespiratory fitness [ 67 ]. Indeed,
in a large RCT including 464 overweight post-menopausal women various doses of
walking were shown to produce significant gains in fitness [ 68 ]. Modest gains in
fitness were even observed at the lowest exercise dose of approximately 72 min per
week of moderate-intensity activity. The effect of exercise on fitness was similar
across age, weight, baseline fitness, and hormone therapy usage, suggesting that the
benefits are comparable across a variety of individuals.
1 Physical Inactivity and the Economic and Health Burdens Due to Cardiovascular...