- Cold medication: can affect a person’s exercising heart rate - Beta blockers are medications that reduce blood pressure by blocking the effects of adrenaline. They act to slow the heart rate and decrease maximum heart rate and are used for cardiovascular and other medical conditions. Monitoring heart rate during a cardiorespiratory fitness test is inappropriate for clients taking a beta blocker. The client should use Rate of Perceived Exertion (RPE) to determine the level at which he or she is exercising as the heart rate will not go up.