Dear Editor,
We would like to thank our colleagues who have written to comment1,2 on our recent review about the validity of the training load (TL) concept,3 particularly given their extensive previous scientific and practical contributions on this topic. We are pleased to have the opportunity to extend discussion of the topic further in this reply. We suspect that how TL is conceptualized may lead to important differences in perspective as we find ourselves in broad agreement with several of the points raised in both letters. Therefore, we will respond by briefly outlining our interpretation of the TL concept and the rationale for linking this to an acute performance decrement (APD) and then addressing some specific points that were raised.
Most discussions of the concept of TL begin with the seminal work of Banister et al,4 who proposed that training-induced fatigue could be linked to subsequently observed gains in performance (fitness). Banister’s work was based on fundamental principles of training theory,5,6 and therefore, we conceptualized the TL in the same manner but as a single training dose. The principles of training theory propose that a training session constitutes an overload that causes a training stress and fatigue, which, in turn, provides a signal for adaptation or overcompensation that occurs during the ensuing recovery period (Figure 1). The training session is considered a training dose, and the resultant training adaptations increase fitness and enhance performance. Indeed, the representation of this training process is often described by its effects on performance, that is, an APD occurs in response to the training dose, and then in recovery, performance is restored progressively to an augmented level (Figure 1). Banister et al’s4 thesis was that chronic changes in performance could be modeled as the integrated effects of training fatigue and fitness. As benefits to performance accumulate largely after the session in the recovery period, Banister’s model suggests that the APD observed at the end of a training session is linked to subsequent fitness gains. However, instead of measuring training-induced fatigue or an APD, Bannister et al, instead, modeled the training dose, which they calculated using arbitrary training impulse units (TRIMPs). Thus, the association between TRIMPs (as an indicator of the training dose) and APD was conceptualized by Bannister et al4 but not verified experimentally. Accordingly, we agree that we did not demonstrate the validity of APD as a TL criterion as we were, instead, testing its implicit relationship in the TL model.
—A principles-of-training diagram showing how a training dose leads to an acute performance decrement (black circle). A low training dose is theorized to result in a smaller decrement and performance benefit compared with a larger training dose.
Citation: International Journal of Sports Physiology and Performance 17, 10; 10.1123/ijspp.2022-0247
—A principles-of-training diagram showing how a training dose leads to an acute performance decrement (black circle). A low training dose is theorized to result in a smaller decrement and performance benefit compared with a larger training dose.
Citation: International Journal of Sports Physiology and Performance 17, 10; 10.1123/ijspp.2022-0247
—A principles-of-training diagram showing how a training dose leads to an acute performance decrement (black circle). A low training dose is theorized to result in a smaller decrement and performance benefit compared with a larger training dose.
Citation: International Journal of Sports Physiology and Performance 17, 10; 10.1123/ijspp.2022-0247
Considering an athlete’s TL in the form of a training dose that results in an APD is common practice,4–8 but it may be useful to discuss this in its relation to the broader TL concept. Jeffries et al9 have recently conceptualized TL as the amount of physical training done or experienced by athletes, that is, not solely as a training dose. This very broad definition of TL implies that the training dose is a subcomponent of TL. We can embrace this broad definition of TL but suggest that there is, then, a need to distinguish between different constructs of TL to relate it to training stress and effects and performance outcomes. An example wherein such a distinction has already been made is between internal and external TL.9 If a distinction is made between 2 further TL constructs of training volume and the training dose, controversy regarding the validity of currently used TL metrics may be ameliorated. Traditionally, TL metrics have broadly tended to reflect the volume of training (by multiplying exercise intensity and duration),10 and this includes the criterion measure of total
Slattery et al2 wrote in defense of their earlier study,11 which sought to establish the validity of specific TL metrics. In their letter, Slattery et al sensibly justified their use of total
The fact that
The strong association between total
Why do we continue to find cause for concern with TL where our colleagues do not? Since Banister’s study, TRIMPs have been adopted by practitioners and scientists as a metric of TL, and thus, a key point in our review was to highlight that they have never been validated for this purpose. Indeed, as we pointed out, a consistent theme for the TL metrics in common use today is that they have not been validated adequately. When we examined experimentally the underpinning of the model, which relates a training dose to its fatigue or APD element, our findings suggested that commonly used TL metrics do not quantify the training dose effectively.3,16,20 Although we agree with our colleagues that these findings may not directly challenge the validity of the TL concept, they do question the validity of the TL metrics evaluated—when TL is conceptualized as a training dose. The validity of TL metrics as a representation of the training dose remains untested.
In conclusion, we are grateful for this opportunity to explore some of the issues related to the validity and concept of TL. Specifically, we hope that our response has helped clarify why our recent findings reinforced our concern with the validity of commonly used TL metrics. Finally, we hope that this reply and related discussions contribute to the scientific debate on the TL concept and its subcomponent structure and help shape future experimental work.
References
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