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Bite Size - Session Intensity Versus Output, Whats The Difference?

Following on from a conversation with one of my athletes I thought I would clarify the differences between the two.

We all love numbers, me more than most as any of my athletes will tell you, but that only tells half the story. Monitoring your training intensity and workload is an art form and we have lots of toys which can help us to achieve it successfully. A lot of athletes have GPS devices, HR monitors, power meters bike or run etc. So, what's the best toy to use and how should it be used to gain the most benefit?

Intensity and Output

Let's just clarify how exercise intensity differs to exercise output. Intensity is simply how hard your body is working. You can measure intensity by checking your heart rate, your breathing rate and perhaps the most reliable gauge, Rate of perceived effort (RPE). RPE is a fancy way to say 'how hard does it feel'?

Output is the speed or power generated as a result of your exercise intensity. For example, you might feel as though you're working really hard and your heart rate may be close to maximum (your intensity is high). A quick glance at your fancy watch tells you your running speed is 6 minutes per mile (that's your output). Alternatively, you might head out for a cycle ride and your heart rate might be mid 'zone 2' and you're feeling comfortable (your intensity moderate) and your cycle power meter shows 190 watts (that's you output).

They are the same, aren’t they?

No. People use heart rate, speed and power to gauge their training, but they are not the same. By choosing one or the other, you're choosing either 'intensity' or 'output' to guide your training.

Example 1:

You go to the running track to run 6 X 800m, but due to a hard week of training, you don't feel great. Nevertheless, you crack on and push your HR up to the planned level for that session. You feel as though you're working hard, and your heart rate is where it should be, but your split times are slower than normal.

So, If your HR is at the correct level, but your pace per 800m is slower than normal, are your running at the right intensity?

Example 2:

You travel abroad for a training camp and find yourself training at altitude. Whilst completing a training ride your HR reaches the correct level and it certainly feels like you're working as hard as you normally do. However, due to the altitude, your power output (watts) is lower than normal. There are also technical reasons why the meter will show a lower reading but the principle still applies.

So, If your heart rate is at the correct level and it feels like you're working at the correct level, but your power output is lower, are you cycling at the correct intensity?

To be fair, scenario 1 is more likely, as not many of us jet set to altitude on a weekly basis, but I'm sure you see what I’m saying. Sometimes, your intensity can be high (heart rate, breathing and perceived effort), but power and speed are lower. Irrelevant of whether power and speed are lower, the truth is, if it feels hard, then it probably is hard.... you're training at the correct intensity.

What's the point?

If you use 'output' to gauge your training, then that means your intensity in some circumstances may be wrong. If you run on the track and use lap splits, or you use a gps and watch your minutes per mile, you're choosing output and not intensity to gauge training. If you're a cyclist and you use either speed or power to dictate training, you too are choosing output and not intensity to gauge your training.


For starters, you need to understand the difference between them, because most endurance athletes don't consider it. Secondly, the key question which needs to be answered... which should you be using to gauge your training sessions? Intensity or output?

Training is about intensity

Training is designed to place a stress or load on your body. As a result, you get an adaptation response and your fitness improves. To measure the training 'stress or load' you need to know how hard your body is working, or the 'intensity' of the workout. Therefore, HR or perceived effort should be used frequently to measure your intensity. If it feels like you're training hard... then you're training hard, irrelevant of what your speed or power output display shows.

Performance is about outcome

Here's the catch. If you want to improve your performance, the simple truth is that you need to run at a faster pace or produce a greater power output. Heart rate is irrelevant, nobody wins a race by saying "yes, I did finish 20 minutes behind the first finisher, but my heart rate was higher than his, so I win". Using outcome measurements such as speed or power give you clear benchmarks for improvement in key sessions. Ultimately, if you want to cycle or run a certain time, you have to produce the right amount of power or travel at a specific speed.

So finally, that means what?

Output should be used for key sessions, but you should be 'fresh' and able to give 100%. There's no point going to the running track and aiming to complete 800m repetitions in a key time, if you're tired from a hard week of training. Your output (speed) will be slow and you'll be disappointed when you don't hit those key times.

Using output such as power or split times for key sessions will allow you to monitor progress and improvement.

Intensity is best used for general training. A long ride or run is best done using intensity. It doesn't matter if you're tired or fresh, go out and run or ride easy/steady as required. Use your heart rate and 'how you feel' as a gauge. Completing the longer sessions at the correct 'intensity' is important, the speed of your run/ride or the power you produce, is NOT important. You don't need to test or measure yourself in general aerobic workouts.

In summary, use both methods to gauge your training, but apply the correct method to the correct session and you will see big gains.

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