Improved cardiorespiratory fitness from high-intensity interval training did not protect against the vascular effects of prolonged sitting. Digest
People who exercise regularly can still spend most of their day sedentary. A new study examined whether the cardiovascular benefits of exercise training also extend to maintaining artery function during prolonged sitting.
Eleven young, healthy adults completed 12 weeks of supervised high-intensity interval cycling three times weekly, while 10 adults maintained their usual activity and served as a control group. Before and after the program, ultrasound tests assessed the popliteal artery behind the knee before and after approximately two hours of uninterrupted sitting. One test measured artery widening in response to increased blood flow to assess the function of the artery lining. A second used nitroglycerin to assess how well the artery widened without relying on signals from the lining.
- Before the intervention, sitting reduced resting blood flow by about 30–51%, blood-flow-triggered artery widening by 33–56%, and nitroglycerin-triggered widening by 35–38%.
- After 12 weeks, high-intensity interval cycling improved fitness but did not clearly lessen any of these sitting-related declines compared with usual activity.
Increased blood flow can prompt an artery's lining to release nitric oxide, which relaxes the muscle wall and allows the artery to widen. Sitting reduces local blood flow, while bending the knee disturbs flow in the popliteal artery. Those conditions may increase reactive oxygen molecules that interfere with the muscle's sensitivity to nitric oxide. They could also reduce the amount of nitric oxide available, including that generated from administered nitroglycerin. Either route could leave the artery less able to widen despite improved cardiorespiratory fitness.
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Regular exercise is essential for cardiovascular health, but it may not cancel out the harmful effects of prolonged inactivity. Even physically active people therefore benefit from breaking up long periods of sitting.