277
3 Physical Exercise, Can One Overdose?
With all the evidence above, the agreement that physical exercise can be applied to
treat atherosclerosis can be reached. Like regular medicine, physical exercise also
has dosage effect. Different dosage of physical exercise refers to the time and
strength spent on exercise. Regular intense exercise brings cardiac adaptations
which comprises the clinical constellation of findings known as the athlete’s heart
[ 162 – 165 ]. However, increasing studied found that these adaptations may also have
deleterious effects. For example, some reports have claimed that atherosclerotic
plaques are present in the carotid or peripheral arteries of 90% of marathon runners
at the age of 50–75 [ 166 , 167 ].
Regular and moderate-intensity exercise, on the other hand, reduces cardiovas-cular morbidity and mortality. It could be served as primary and secondary preven-
tion of CVD [ 165 , 168 – 171 ]. Vigorous exercise training will cause sport-specific
hemodynamic alterations, leading to profitable structural and functional adaptations
in athletes [ 172 – 174 ]. Chronic exposure to high levels of exercise training, which is
equivalent to “exercise overdose”, may bring some adverse effects. Long term stress
on the heart will cause cardiac remodeling. The clinical presentation could be atrial
fibrillation and cardiomyopathy [ 175 , 176 ]. “Overdosed” exercise does more harm
than good. To testify this, 40 elite endurance athletes were included in one study. A
decreased right ventricular systolic function and increased cardiac injury biomark-
ers were detected right after completion of an ultra-endurance exercise. Although in
this study short-term recovery appears complete, chronic structural changes and
reduced RV function have been observed in some athletes [ 176 , 177 ].
4 Summary
In summary, regular physical exercise is highly beneficial in reducing the risk of
atherosclerosis development, and the underlying mechanism could be concluded as
followings: (1) reducing of pro-inflammatory cytokines; (2) counteracting oxidative
stress via decreasing ROS production, Hcy level, NADPH oxidase activity and
increasing NO availability; (3) improving endothelial function; (4) decreasing
endothelial adhesiveness by modulating the expression of ICAM-1, VCAM-1,
E-selectin, P-selectin and ET-1; (5) regulating macrophage function and suppress-
ing the foam cell formation; (6) lowering LDL and triglyceride levels. (7) preserv-
ing atherosclerotic plaque stability. Similar to medicine, the beneficial effect of PE
has dosage effect. Overdosing would also bring “toxicity”. Vigorous exercise train-
ing could adversely affect cardiac function and ameliorate all these beneficial
effects. More clinical trials regarding to the proper exercise training are needed to
establish a more mature physical exercising treatment system.
15 Physical Exercise Is a Potential “Medicine” for Atherosclerosis