Advances in Tracking Heart Rates Can Improve Clients' Workouts
Stephen A. Black
So, what is new? The science behind cardio training continues to advance, and the technology has taken a quantum leap toward improving the cardiovascular efficiency of the body. Consider the heart and lungs as an engine. In auto racing, the goal is to produce the highest amount of power with the least amount of fuel. The body is the same. The goal is to always increase the efficiency of the engine. Blow the engine, and the body stops.
Heart rate vs. powerTechnology-savvy fitness professionals use two variables to monitor their clients and regulate their workout sessions: heart rate and power. Monitor these and regulate the frequency, intensity and duration of the training sessions to gain the most success for clients.
Lance Armstrong pioneered the use of power to improve his cycling. Mark Allen, one of the most decorated triathletes and a master of all triathlon distances, used a heart rate monitor diligently. Their success gives credence to the use of power and heart rate to prescribe, monitor and progress clients' programs to meet their fitness goals.
What is the difference between power and heart rate? While heart rate (in beats per minute) is a good indicator of whether clients are working hard, or whether they are over-trained, fatigued, etc., it is a poor indicator of the intensity of the workout. Heart rate has a high degree of variability, as it is affected by nutrition, hydration and temperature, along with other extraneous variables.
Power (measured in watts), on the other hand, is a measure of work rate intensity; it is a measure of mechanical work that is executed during activity. Mechanical work is the amount of work that is put into the activity to provide movement (cycling, elliptical training, etc.). Measuring power on the run has not yet caught the eye of the most-visible heart rate monitor manufacturers, but, in time, they will see the value in this measurement for running.
Measuring powerMechanical work is measured in kilojoules (KJ). Work is a direct indication of the amount of energy that has been expended during the workout. This amount of energy can also be measured in calories. The conversion between a kilojoule and a calorie is this:
1 kilojoule = 4.184 calories (food calories, or kilocalories)
1 calorie = 0.25 kilojoules
It is estimated that a cyclist is about 25 percent efficient in performing mechanical work. Now, since 1 calorie = 0.25 kilojoules, and cyclists are 25 percent efficient in performing mechanical work, the total amount of work performed by the cyclist is four times the amount of mechanical work:
Mechanical work = 25 percent of total work
4 x mechanical work = total work
So, if you multiply the amount of mechanical work measured in KJ by 4 to get the total amount of work, then 1 KJ of mechanical work ultimately converts to 1 calorie (Kcal) expended:
1 calorie = 4 x (0.25 KJ of mechanical work)
1 calorie = 1 KJ of mechanical work (work performed while on the cycle)
Since it is known that for every kilojoule of work performed on the cycle (similar to other cardio equipment) is equal to 1 calorie expended, it is now possible to accurately measure the workout by the amount of work (or the amount of energy) in kilojoules and calories. This is an accurate and useful tool for improving fitness, health and caloric expenditure.
Cardio equipment. Armed with this new information, the cardio equipment in fitness facilities can be more useful for fitness, weight loss and performance improvements. Historically, the calorie reading on most cardio equipment is overly optimistic. This is because the formula is often based on the length and pace of the workout, and doesn't consider factors such as body composition and fitness level. Measuring watts (which most machines do) is a more accurate indicator of work performed, and energy and calories expended.
Goal attainment. Instead of looking at sets and reps, consider the total work performed in a workout, which equals the total calories expended. Regardless of the goal (weight gain/loss), measuring work will enhance the ability to accurately prescribe exercise, and ultimately see the results desired. For example, for a weight loss of 1 pound per week, the client needs to expend 3,500 kilojoules in a week (if 1 calorie equals 1 kilojoule). Just think of the results that can be accomplished through the use of measuring mechanical work, and providing the appropriate exercise prescription.
How is heart rate measurement useful?Heart rate has a variety of uses. If nothing else, it is a measure of the response to exercise or stress. Both resting heart rate and recovery heart rate are important variables to measure within a fitness or lifestyle plan.
Stroke volume. Resting heart rate is a measure of the heart's efficiency to pump blood (left ventricle), which is also referred to as stroke volume. The greater the efficiency and volume of blood ejected, the less the heart has to beat to maintain circulation (sustain life). This is important to know when prescribing exercise predicated on heart rate. It is well-known that keeping the heart rate between 55 to 65 percent of actual maximum heart rate is a recovery heart rate, but there is also clinical efficacy to keeping in this zone. Prospective research indicates that maintaining this zone will also increase the mechanical efficiency of the left ventricle, resulting in increased stroke volume.
The ability to meet the intensity of exercise — below 55 to 65 percent — is achieved through a combination of stroke volume and heart rate (primarily stroke volume). Above 65 percent, stroke volume is maxed out, and the demand is met by heart rate. More stroke volume and less heart rate equals greater efficiency, with less stress on the cardiac muscle. This is important when working with an older population (see Cardio Training and Aging).
Recovery time. Heart rate is also a good indicator of recovery time. Most use the measure of heart rate to maintain intensity, but consider using heart rate for recovery. By comparing heart rate vs. power (see Figure 1), it is possible to determine the intensity of the interval and the time that it takes for the individual to recover by measuring the time it takes for the heart rate to decrease and become stable. Therefore, heart rate should be used in parallel to power as a training tool.
Heart rate recovery can also be used as a potential indicator of cardiovascular distress. Studies have shown that the peak heart rate following high-intensity exercise should drop 12 or more beats in the first minute. Most individuals with moderate cardiovascular training will drop 15 to 20 beats within the first minute of recovery. If your client's heart rate is not dropping by at least 12 beats, you may want to recommend evaluation by a physician or cardiologist.
Technology continues to advanceTechnology continues to advance the way clients are tested, monitored and trained. Sports training centers of today, and fitness centers of tomorrow, will facilitate a safe and effective training environment for members. So, stay tuned. Science is just scratching the surface of possibilities. As technology advances and research continues, the information will trickle down to the wellness arena for improved quality of life for all.
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