Understanding Internal and External Load, and how it affects your training

"Load" is often misunderstood and looked at relatively simply. However, there are some complexities to the concept that if you can understand, you can use to your advantage to improve your strength and fitness.

Load can be classified under two categories - Internal and External Load.

External Load is what we typically think of when we use the term 'Load'. It is the weight on the bar, the reps you complete, or the speed and distance you run. Simply, External Load is what is applied to the body during training.

Internal Load however, is the body's response to the External Load. It can be affected by many factors, such as fatigue, training status, psychological status, health, nutrition, environment and genetics. Internal Load can be assessed with measures such as Heart Rate, Heart Rate Variability, Blood Lactate, or RPE (Rating of Perceived Exertion).

Here's why understanding this concept is so important. Internal Load is what drives adaptation for the body to get stronger, fitter or faster. The External Load is just how we apply training.

Looking at it in context can help explain the difference.

Kate has had a good night's sleep before her training session. She feels fresh and stress-free. In her session, she does 3 sets of squats x 5 reps at 80kg. She gives each set an RPE of 7/10, feeling like she has 3 reps left in the tank each set. 3 x 5 x 80kg is the External Load, but the RPE is a measure of her Internal Load.

The next week, she goes to complete the same training session, but she has had a terrible night's sleep, spent the whole week stressed about work, and consequently hasn't eaten well. She completes the exact same sets, reps, and weight of squats, yet her RPE is higher at a 9/10 for each set. Her External Load is the exact same, but the Internal Load is far greater, due to her poor sleep, stress, and nutrition. Kate feels significantly more fatigued and sore after this training session.

The goal of training is to achieve a specific Internal Load, not a specific External Load. This is why RPE is such a powerful tool to prescribe and measure intensity. It is a subjective measure of the Internal Load, that accounts for all of the variables mentioned before that can affect it. If you only record the weight and reps you complete, you are not tracking the Internal Load, which is what is really driving adaptation.

So if you are going into a training session feeling tired or stressed, you may need to adjust some of the variables in the session to account for the increase in Internal Load. Importantly, it doesn't necessarily mean you should have an 'easy' session. It just means you don't need to do the same External Load to achieve the desired Internal Load. The training still needs to be stimulative. The variables you adjust may include reducing reps, sets or range of motion.

I'd highly recommend prescribing and recording your RPE along with your sets and reps. It can take some practice getting used to, but you'll find you're able to make much better decisions regarding training and load selection. This will keep you far more consistent in your training, which is essential for long term improvements.