When performing Low-Intensity Steady-State (LISS) cardiovascular training, what objective measure of intensity ensures the exercise remains within a fat-burning zone without excessive fatigue?

When performing Low-Intensity Steady-State (LISS) cardiovascular training, the objective measure of intensity that ensures the exercise remains within a fat-burning zone without excessive fatigue is the Target Heart Rate Zone. This zone represents a specific range of heartbeats per minute that an individual aims to maintain during their exercise session. To establish this, one first needs to determine their Maximum Heart Rate (MHR), which is the highest number of times a heart can beat in one minute. A widely accepted and straightforward method to estimate MHR is to subtract one's age from 220. For LISS training specifically designed to optimize fat utilization, the recommended Target Heart Rate Zone is typically between 50% and 70% of the estimated MHR. Maintaining exercise intensity within this precise heart rate range ensures it stays within the "fat-burning zone" because at these lower, sustainable intensities, the body is able to supply ample oxygen to the working muscles. This allows the aerobic energy system to operate efficiently, primarily using fat as its main fuel source for muscle contraction. In contrast, higher intensity exercise, which outstrips the immediate oxygen supply, forces the body to rely more on carbohydrates. Furthermore, keeping the heart rate within this controlled zone directly prevents excessive fatigue because the exercise intensity is sustainable over extended periods. This avoids the rapid accumulation of metabolic byproducts, such as lactic acid, which contribute to muscle fatigue and limit endurance, thereby facilitating the prolonged duration characteristic of LISS training.