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A Benefit for Every Intensity

05/19/2023 By Tucson Medical Center

A benefit for every intensity If you’re starting an exercise plan, you might be thinking it’s as easy as hopping on a treadmill and lifting some weights, but there’s more to it if you want to do it effectively. When you start out, it’s a good idea to learn what your target heart rate should be and what the different zones of intensity are.

How do I know what my target heart rate should be? You should figure out what your target heart rate is so you know how hard you should be working out. Remember that the formula is an estimate. Heart rates are affected by genetics, fitness level, medications, stress hormones, respiratory health, illness and mental state. You may need to adjust your target range. To measure your resting HR, take it first thing in the morning seated and breathing normally. Average this over several days. Resting HR will be higher if you are ill, sleep deprived or stressed. Here’s the formula for finding your low and high target heart rate: [(220 - Age) - (resting HR)] x 0.5 + resting HR = lower end of target HR [(220 - Age) - (resting HR)] x 0.85 + resting HR = upper end of target HR This equation is for a target heart rate of 50-85%, which is a good medium zone that – for most people – will land them in aerobic/threshold training zones. If you’re new to working out, aim for the lower half, if you’re a seasoned exerciser, train in the upper half of the range. At TMC Cardiac Rehabilitation, we use a target range of 40-80%, which is challenging enough to get positive structural adaptions to exercise without creating unnecessary risk. “We want to challenge the heart, but not make the exercise so hard that it deprives the heart muscle itself of oxygen,” said Sabine Harrington, exercise physiologist at TMC Cardiac Rehabilitation.

What are the different zones? Each person has unique physiology, including their own heart rate zones 1-5. Fitness devices can give you an estimate of what your heart rate is and which zone you fall into, but you can also gauge with your breathing. “Breathing doesn’t lie because it is a direct result of carbon dioxide building up in your blood stream as metabolic rate increases,” Harrington said. “Heavy breathing usually indicates heavy workload. Even if your heart rate isn’t in your target, if you are breathing faster and deeper but don’t feel out of breath, it means you are doing metabolic work. Aside from congestive heart failure exacerbation, asthma and other pulmonary conditions, breathing frequency should parallel exercise intensity." Here's an idea of what each zone feels like:

  • Zone 1: Warmup/recovery. This zone delivers more oxygen to the tissues than it consumes, and facilitates the removal of metabolic waste products and immune cell distribution.

  • Zone 2: This is the beginning of exercise. You can carry on this type of light exercise for a long time and can often hold a conversation at the same time. Mitochondrial density and vasculogenesis (formation of new blood vessels) occur at this zone. This is laying the structural foundation for a more efficient metabolism and improving the ability of your cells to burn fat as fuel, and increasing insulin sensitivity, both at rest and during exercise. This is a biomarker of longevity.

  • Zone 3: This is a medium intensity that increases the strength of cardiac muscle, respiratory muscles, and other large muscle groups that you recruit while doing your activity (running, biking, swimming, etc.). This roughly lines up with the 40-80% HRR used in cardiac/pulmonary rehabilitation. Zone 3, like zone 2, can be considered "aerobic" exercise.

  • Zone 4: This is the beginning of more difficulty. It will be hard to carry on a conversation. This zone causes increases in enzymatic buffering capacity of lactic acid (i.e. lactate threshold). This is also most likely where your body shifts to using carbohydrates, rather than fat, as more than 50% of its energy substrate. The more carbohydrate burned, the more carbon dioxide produced, and the faster your body has to breathe to get rid of it. This is sometimes called "anaerobic training" (meaning without oxygen), even though oxygen is still being utilized, but at a rate that the body is outpacing. This intensity may be contraindicated for higher risk cardiac/pulmonary conditions.

  • Zone 5: This is maximal intensity, which most of us will not reach unless forced to! This intensity should be reserved for individuals who have already been regularly exercising and have already "built their base" of zone 2 and 3 work. This intensity may be contraindicated for higher risk cardiac/pulmonary conditions. This is the intensity where "VO2 max", or the maximal rate of oxygen consumption, is achieved. Mitochondrial density and blood vessel building also happen at this zone. It is also the zone of peak carbohydrate usage, so remember to refuel with healthy fat, protein, and carbohydrate.


A few things to keep in mind when starting an exercise plan

  • Many people who are trying to improve their fitness do their cardio workouts most likely in their zone 4 (more carbohydrate usage, more anaerobic pathways, more overall strain), when they would do better do start training in zone 2 or 3 (where they can specifically build mitochondrial density, new capillaries, and greater heart muscle strength without excessive strain).

  • Newer exercisers and those with health conditions should always start their training in the lower HR zones for several weeks until they have developed an "aerobic base" which they can later build upon. Higher zones are great for more seasoned exercisers/athletes who know their body's limitations and already have a foundation.

  • Medications like beta-blockers (i.e. metoprolol, carvedilol, etc.) will suppress both resting and max HR, so this will affect a person's true range.

  • As always, people who don't know how to train should consult with their physician as well as a trained exercise physiologist and/or personal trainer to help guide their exercise program.


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