How Intense Should Your Exercise Be? It’s Complicated.

I am finally back to finish the second half of a conversation I started recently regarding how important it is to monitor exercise intensity. So, now that we know why it’s important to keep an eye on it, the next question would naturally be: how intense should your workout be?  The answer is a little bit more complicated, which is why it’s taken me so long to get to part two of this topic!

This is not a one size fits all scenario. Your workout intensity will depend on MANY things, a few of the most important include:

• Medical history and body mass
• Age and gender
• Exercise history
• Physical ability and fitness level
• Goals

There are a few methods by which you can determine a recommended intensity for exercise sessions. We will assume we are dealing with an otherwise healthy person who has been cleared to exercise.  It’s important to note that exercising at too high of an intensity too often can cause problems. (I think that will be my part three of this series so watch for that in the coming weeks!)

1.  Target Heart Rate: This method involves using a range of heart rates to achieve fitness goals.  It is determined by calculating a percentage of your maximum heart rate. The intensity of exercise needs to raise the heart rate to be at least 55% of the maximum heart rate in order to get some cardiovascular benefit.  If someone is trying to improve their fitness level, their exercise intensity should elevate the heart rate to at least 75% of his or her maximum heart rate.  But what if someone doesn’t know his or her maximum heart rate? They can either get it measured directly or they can estimate it.

• Direct:  Maximum heart rate can be measured through a complex test that is administered by a trained professional and involves very expensive equipment.  It usually is conducted on a treadmill or bike and requires the client to exercise over a period of several minutes with incremental increases in intensity. The test runs until the client performs to their maximum ability. During the test, heart rate and other measurements are monitored and collected.  The highest heart rate collected during the test is understood to be the maximum heart rate. That value can now be used to calculate where a workout heart rate should be. This procedure might be a good idea for people who are really interested in improving performance. This type of testing is typically found at colleges with a human performance lab, sports training centers, or research facilities.
• Indirect: This involves a simple math calculation. Subtract your current age from 220. This is your estimated maximum heart rate.220-age = Estimated Maximum Heart RateAlthough this is quick and easy, it doesn’t really take current fitness levels into account. It is REALLY general. But, for those who are new to exercise it is a conservative place to start. Work at a minimum of 55% of this estimated maximum heart rate for cardiovascular benefit. Work at 75%-92% of this maximum if improved cardiovascular fitness is the goal.

2. Heart Rate Reserve: This method basically takes the maximum heart rate and resting heart rate into account. The difference between the two is known as heart rate reserve.

• Heart rate reserve = Maximum heart rate – resting heart rateTo get cardiovascular benefit an individual would need to work at 60% or higher of heart rate reserve. To calculate this, use the Karvonen formula equation, which would look like this:
• Exercise Heart Rate = .60(Maximum heart rate – resting heart rate) + resting heart rate.
  
  To work on improving cardiovascular fitness, you would want to be working closer to 80% of heart rate reserve.

3. Anaerobic Threshold (AT):  This method of measurement is done in an effort to determine what type of fuel someone is using at various exercise intensities. With training, clients and athletes can adapt to being more efficient and tolerating exercise at higher intensities for longer periods of time.

• Estimated: You can attempt to estimate AT, however, it is only recommended for those who are very physically fit and able to sustain continuous exercise bouts that are over 30 minutes.  This can be done by performing a sustained exercise at the highest effort an individual can maintain without compromising form or safety.  Heart rate is tracked with the use of a rate monitor. When the test is complete, the average heart rate of the last 20 minutes of the test is used.  This is believed to be the estimated AT. No more than two workouts a week should be performed at or above AT.
• Direct: This method is done in a laboratory where a face mask can be worn and gases can be collected. Like the maximum test, this is not practical for everyone and is typically conducted for athletes or research.

  4.  Lactate Threshold (LT): This method of determining exercise intensity involves the body’s ability to clear lactate, which is a byproduct of exercise. The less lactate you accumulate in your muscles when exercising, the longer you can go without experience negative consequences that would alter performance.

• Direct: This test is typically done while exercising. A trained professional would coach you through a warm-up and sustained exercise session of increasing intensity.  Throughout the test, (very) small samples of blood are taken via finger poke and measured to determine your threshold for clearing lactate, which is a byproduct of exercise.  The professional can determine at what point you are no longer clearing lactate from your system at the rate that you are producing it.   Your corresponding heart rate at that time would be considered your LT heart rate.  You can then develop your workouts around this heart rate by working at or below that heart rate, depending on goals. This can be done in an interval fashion or in a steady state fashion. Working at LT should only be done 1-2 days per week so as not to overexert.

  5.  Rating of Perceived Exertion: Using this RPE reference to estimate intensity, you will want to make sure that the exercise rating is equivalent to the intensity the client is pursuing. For increased fitness, they will want to be at minimum of what is considered “somewhat hard”.   If the goal were merely calorie burn and cardiovascular health benefits, they would have to be at least a “moderate” pace. Findings from studies have indicated that the lactate threshold occurs between 13 and 15 on the RPE scale, which corresponds to feelings of ‘somewhat hard’ and ‘hard’.