Understanding your Heart's Role in Exercise
Heart rate (HR) is the number of times your heart beats in a minute as a cycle of asynchronized atrial and ventricular contractions. Your heart plays a crucial role in life, as the pump that pushes blood around the body. Blood is the media in which cells and tissues get oxygen and nutrients they need to sustain their roles and depositing waste to be cycled out. HR is taken manually through pulses throughout the body; most commonly used in the radial artery. In more technical measurements of telemetry and EKG, it is generally measured from the interval of Q-wave to Q-wave. Some important definitions are: - Stroke Volume (SV) – the amount of blood in liters ejected in each heartbeat, the difference between the end diastolic volume minus the end systolic volume (EDV-ESV). - Ejection fraction (EF) – the amount of blood that leaves the heart after a contraction in comparison to the left ventricle’s initial volume (SV/ EDV). - Cardiac Output (Q): the amount of blood that is pumped in one minute, (L/min) or (Q = HR x SV). (1) At the initiation of exercise, the acute increase of the HR is due to parasympathetic withdrawal which accounts for the increases HR to 100 bpm. (2) The increase past this point is increased from sympathetic vagus nerve input and contractility strength through blood plasma catecholamines (norepinephrine & epinephrine). The broad effect of these increases the cardiac output (Q), through an increase in HR, beat contractility strength increase, and decrease ventricular filling time improving SV. (3) Appropriate HR responses to exercise include a rapid increase due to exercise initiation (physical stimulus), a plateau of at the peak of exercise, and a tapering decrease to the body’s higher demand of oxygen post exercise termination, known as exercise post oxygen consumption (EPOC). The duration of EPOC depends on the fitness level of the individual and exercise duration and intensity. HR has a linear increase with intensity and is correlated with maximal VO2 levels, with HR peaking at 100% VO2 (4,5). Improvements in physical function can be seen through changes in HR.