Exercise Intensity – How Hard Should I Go?

I often get questioned (and sometimes challenged) by athletes about exercise intensity. Competitive athletes generally feel they should always “go hard” as this will make them faster. So that begs the question, “how hard is hard enough” and “when am I going too hard”?

I am afraid there is no simple answer to these questions. The reason for this is that it depends on where you are in your training cycle and, you guessed it, what your goal is and your current fitness level and physiology! So to understand how hard you should go (your exercise intensity) in any training session you need to understand:

  • Your overall goal
  • Your current fitness level
  • You physiology
  • Where you are in your training cycle (Base 1, Base2, Speed)?
  • What is the specific session / workout goal?

A word on your physiology. Do not compare your heart rate figures with other athletes. Having a low resting heart rate is some indication of fitness but does not mean you will perform better in races. The numbers in terms of max HR (MHR) or anaerobic threshold (AT) etc that we use are tools to help you train at the correct intensity. They are not bragging rights in your training group!

If you are training in a group exercise intensity can be a two edged sword. On the one hand group training is a fantastic tool to ensure that you push and reach the workout intensity that is required. On the other hand it often leads to an athletes competitive instinct taking over and cause them to push too hard. An example of this would be where the required workout is a “long slow distance” endurance workout. Often these are performed in a group because the boredom that can sometimes set in with hours of running alone, which can also be a little overwhelming. As the workout progresses the group often start picking up pace until some of the slower members are actually not training at the correct intensity any more! This should be avoided as it prevents the athlete from achieving the correct load for the workout, as well as benefiting from the adaptation that would have followed.

So, how does one prevent this from happening?

How hard is too hard?

Measure Exercise Intensity

Most important is to have a measure of exercise intensity. This measure can either be objective or subjective.

The objective measure is using a heart rate monitor. Once you have calculated your “zones” you can use your heart rate monitor (HRM) to ensure that you stay within the upper and lower limits of the zone required. This is a very good way to ensure that workouts are performed at the correct exercise intensity but it does sometimes take the “fun” out of training.

A subjective measure is using a method known as rate of perceived exertion (RPE). This method relies on how you “feel” to determine how hard you are going. It requires you to rate your exertion on a scale of easy to very, very hard. I have found this is a very difficult measure for most people other than seasoned athletes. Once you have trained with a heart rate monitor for some time and you know what different zones feel like you can use RPE effectively when you do not feel like using your HRM, but not before.

Know Your Zones

There are a lot of resource available on heart rate zone training. Go and do a search online and you will find a lot of information, some good and some not so good. Here is some high level information but I encourage you to do some more research.

Start by knowing what your zones are. Your zones will be a percentage of either your maximum heart rate (MHR), your VO2 Max or your anaerobic threshold. Don’t get too bogged down by the different methods to determine your zones. Look at the following and select a method.

Max Heart Rate (MHR)

As the name suggests, this method uses the number of beats per minute that your heart would beat during an all out effort as your upper limit. There is a simple (but quite inaccurate method to determine your max, MHR = 220 – your age. I say inaccurate because it assumes a very general fitness level and physiology. A better method is to test it. It is however quite hard to get yourself to 100% HR. If you are just starting HR training and need some kind of guidance the simple MHR calculation method could be good enough, but I do suggest that that you do some testing to determine a more accurate method as soon as possible.

Anaerobic Threshold (AT)

This is in my opinion a better method to use. AT is the HR that you will be able to maintain during racing and it is highly trainable (more so than max HR). If you periodically test your AT and train at a percentage of AT I think you will get the most out of your training. The method to determine your AT using a field test is also fairly simple and all you will need is a HR monitor that has a stopwatch. Do a 15-20 min warmup at a very easy pace. Then do a 30 min time trial at the fastest pace that you can maintain for the entire duration. Rather start a bit slower and go faster than to go very fast and then be forced to slow down toward the end. Use the average HR for the last 20 min of the time trial as your AT. A more complicated method to determine your AT (but that has been disputed of late) is the Canconi method.

VO2 Max

This is an indication of your aerobic capacity and measures the volume of oxygen your body can absorb. The higher the VO2 the more oxygen you can absorb and send to your working muscles and the better your capacity to perform in endurance sport. It is however mostly determined by genetics and is not very trainable (it is to some extent possible to improve when just starting out training, but not really for trained athletes). Testing also requires a laboratory and in my opinion is a bit too complex to work with for the average athlete.

Calculate Your Zones

Once you have determined the upper limit of your training using one of the methods above, you can work out your zones. You do this by using the percentage (mentioned below) of your upper limit (determined above). So for instance if I choose to use MHR simple method to determine my upper limit and I am 30 years old, I would use 220-30 = 190 as my max HR and then use the percentages below to define the zone as a percentage of 190.

  1. Zone 1 – Very low intensity (active recovery). Usually <60% of your max HR / <70% of your AT / very, very light to very light on the RPE scale.
  2. Zone 2 – Aerobic conditioning. Usually between 60%-75% of your max HR / 70%-90% of your AT / fairly light to somewhat hard on the RPE scale.
  3. Zone 3 – Anaerobic threshold conditioning (including Tempo training). Usually between 75% – 90% of your max HR / 90%-100% of your AT / hard to very hard on the RPE scale.
  4. Zone 4 – Pure power and speed work. Usually at 90%+ of max HR / 101%+ of AT / Very, very hard on the RPE scale.

So How Hard is Hard Enough?

As I mentioned earlier your plan would largely dictate when you use which zones (exercise intensities). You would for instance use mostly Zone 2, with some Zone 3 in Base1 training. You need to therefore make sure that you have a plan to know when to use which zones. The question about what is the correct exercise intensity is determined by:

  1. Your goal and where you are in your training cycle – Your plan is based on your goal and will determine which zone you should train in. Where you are in the training cycle on your plan will more specifically determine the Zone you are training in.
  2. Your fitness level and physiology – If you do some field testing to determine your MHR or AT you will be working at a percentage of the intensity that was determined by your current fitness level and your physiology.

It is worth spending the time to determine your zones. You will make sure that you reach the intended outcome every time you go and train. You will also make sure you don’t overdo things and get injured or sick because you just went too hard, too soon.

The key is consistency!