From Forbes Online:

A small study is raising big questions about whether statins may blunt the beneficial effects of exercise. The study has been published online in the Journal of the American College of Cardiology and was the subject of a New York Times blog today.

37 previously sedentary overweight or obese adults with at least 2
other risk factors underwent 12 weeks of aerobic exercising training. 19
patients were randomized to also receive a statin (simvastatin 40
mg/day). At the end of the study cardiorespiratory fitness, as measured
by maximal oxygen uptake,  had increased significantly by 10% in the
control group but only by 1.5% in the simvastatin group. The control
group also had a significant 13% increase in skeletal muscle citrate
synthase activity, a measure of mitochondrial activity in muscles,
compared with a 4.5% decrease in the simvastatin group. The authors, led
by John Thyfault at the University of Missouri, said their results
“suggest that simvastatin may mitigate improvements in fitness in
response to exercise training by impairing increases in skeletal muscle
mitochondrial content and function.”

The authors concluded: “Given the strong independent
cardio-protective effects of increasing cardiorespiratory fitness or
lowering LDL, the benefits and risks of each should be carefully
considered when choosing treatment modalities.”

The study raises troubling questions about the interactions of
statins and exercise, but its small size , along with other limitations,
may limit its immediate impact.