The researchers on the new study theorized that working out might help balance out the effects of unhealthy sleep by combating inflammation or possibly helping to regulate metabolism and sympathetic nervous system activity, Dr. Zhang said. It’s also possible that poor sleep contributes to heart disease risk by elevating blood pressure and inhibiting insulin resistance, said Dr. Virend Somers, a cardiologist who studies the effect of sleep loss at the Mayo Clinic. Exercise might counter this by regulating blood pressure and increasing insulin sensitivity.