Sometimes during intense exercise sessions, we ask ourselves if we are pushing too hard. Checking your heart rate (HR) can be as easy as taking your radial or carotid pulse yourself, or putting your finger over the camera sensor on your smartphone — but HR provides only a part of the picture of your body’s current state during exercise.
The correlation between HR and exercise is due to the use of blood as a buffer in the energy production of our muscles. Our bodies use carbohydrates to create energy for different cells in the body. Carbs go through three processes to create cellular energy, called ATP: glycolysis, the Krebs cycle, and the electron transport cycle. There’s some great stuff on YouTube about these cycles, but for our purposes it is important to know that making more energy means releasing many electrons that float around in the blood. Our muscles use this energy to contract and release, with more contractions equaling a demand for more energy, resulting in more electrons in the blood. Cells then release lactate or lactic acid (the name comes from its first identification in sour milk 200 years ago, “lac” meaning “milk” in Latin) from these same cycles to clean up the mess left by all of the ATP production.
Lactate levels are an accurate reflection of one’s current intensity level during exercise. An initial spike in lactate levels means that the body is ready for intense activity. Heart rate by itself does not reflect this metabolic change, but tested in tandem with lactate levels will give us an easy way to know if we’re starting to push ourselves too hard. The spikes in lactate levels in the blood are called “lactate threshold.”
Lactate threshold is the most accurate method for finding your safe heart rate zone. A simple blood test with a lactate analyzer provides the level of lactate in the blood, similar to the blood glucose analyzer.
The test begins with a slight warm up, and then continues in regular intervals of increasing intensity. After each interval, the lactate analyzer tests a tiny blood sample for the current level of lactate in the blood. When there is a spike of at least one full unit from one interval to the next, you will have learned your initial lactate threshold. Measuring your heart rate at this point will allow you to safely prepare for a steady endurance event with an HR monitor. The modality of the test should reflect the endurance event for which you are preparing; conduct the test on a treadmill if it’s run-heavy or on a bike if it’s cycling.
By Justin Walls
Justin Walls is an American College of Sports Medicine-certified personal trainer with several specializations. He also has expertise in lifestyle/health management and meal planning, and a background in psychology. Learn more at justinwallsfitness.com.