Internal versus External Loading

It is common for coaches to calculate external load to guide the training process. It is an easy to use tool that helps one get a better understanding of the total physical work being imposed on the athlete. To calculate external load, a coach may use one of many different metrics (tonnage, raw volume, relative volume, acute to chronic etc…).


At the end of the day, the goal of using external load is to help coaches better understand the internal loading/adaptive process. Ultimately, all we care about as coaches are the internal adaptations that occur. The accumulation and systematic application of the cellular stress-adaptation process is what eventually manifests itself in the form of improved athletic form. In other words, what happens inside of our body determines how we move in the external environment.

“accumulated cellular adaptations lead to systemic change”

If internal load is possibly the most important variable to understand, as coaches, we should then consider all aspects of training that influence internal loading.

Before diving into the process of internal loading, it is wise to first review the adaptive process that takes place in our body. In an unjustifiably short summary, our body:


  • Recognizes a stressor

  • Hormones are released

  • Mobilizes energies to deal with the stressor

  • Structures may be destroyed while dealing with the stressor (myosin heads during a muscular contraction)

  • Magnitude and duration of the stressor determines the amount of destruction and mobilization of energy

  • Once stressor is removed or defeated (like a cold), the body resupplies the energy stores used and rebuilds structures that were broken down

  • Energies that were used and structures broken are rebuilt in a stronger fashion to allow the body to deal with future stressors of the same nature


Above we can see there are a couple important factors regarding any stressor.

  • The body has to mobilize energies to overcome a stressor

  • There is only a finite number of energies

  • The stressor has to be removed for the rebuilding to occur


As coaches, an external load imposed upon the body (training) has two levels of stress to it.

  1. The external load acts a stressor — Body has to find way to overcome the loading
  2. The perception of the workout itself — Body anticipates stress of workout


One the surface, the stress of the external appears to be much easier to control. However, as noted by point number 2, the perception of the workout also influences the magnitude of the external stressor. Thus, the external load and the perceptual response dictate the internal load that the athlete will encounter.


A good example of this can be seen when people have to perform maximal efforts in high arousal situations, such as a max squat in front of the entire team, a 100m sprint at a meet, or a 60 yard touchdown run in front of  60,000 people. Despite the fact the total external load imposed upon the body is relatively small compared to other workouts, the total magnitude of stress is amplified due to the perception of the workout itself. Thus, energies are being mobilized from both the physical stress and from the psychological stress.


Such extreme situations are not the only time psychological and external workload stressors influence the adaptive process. As a fact, they are influencing the body’s adaptive process at all times.


The body’s adaptive processes are driven by the autonomic nervous system (ANS) and guess what? Regardless of the stress, the ANS has to deal with it. Thus, despite the external differences between physical and psychological stressors, the ANS doesn’t really differentiate. It has to activate similar systems and clean up the mess in similar ways. For this reason, to consider a stressor in isolation would be dangerous. Thus, two equal workouts with the same external loading will not elicit the same internal adaptive process. Depending on the internal state of the ANS, the external workload may bring about different internal changes.


What does this mean? Well, the same external load one day can lead to sickness and push the body over the edge, while another day, the same load may not even be enough to promote a stressor large enough for adaptation (this is an extreme example, but during finals week, such extremes do arise).



Understanding a stressor in isolation is not enough. It may seem obvious at first, but to only consider external load in the training process can be quite misleading. For example, non-responders in training studies may not be non-responders at all, but instead overly stressed individuals. At the same time, a positive responder may be only due to the fact that this person was able to handle the given stimulus at that very given moment. In order to get around such stressor related issues, using internal loading metrics, in conjunction with external load quantifications is necessary to pain the best picture. Such internal loading tools consist of HRV, Surveys, RPE, or even just talking to an athlete.


However, it is not always possible to acquire all of this data as a coach (not impossible either). At the end of the day, the internal state of the body will always play a larger role than the external load imposed upon the body. No matter how perfect a training program may appear, if an athlete is not able to deal with such external loads due to a thrashed ANS, there is no way the desired internal adaptations will take place.


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