Workload Assessment in Soccer: An Open-Minded, Critical Thinking Approach is Needed

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Authors' Response:
We acknowledge the journal for giving us the opportunity to highlight the key findings and clarify any misunderstandings to the authors (1). Our practical advice that “coaches need to take into consideration that training loads are affected by match-related parameters” is based on actual data which showed that (a) higher weekly loads were reported after a defeat or draw compared to a win, and (b) when preparing to play against a medium level team, average sRPE during the week was higher than that before playing against a top or bottom team (2). With reference to the first point, we commented in the paper that “it was not possible to conclude whether this was a consistent coaching strategy or whether it denoted the difficulty the coaches have to create training sessions as demanding as official matches.”
Our findings are in line with the literature showing that the complex interaction of many factors that contribute to the personal perception of physical exertion, including hormonal and neurotransmitters concentration, substrate levels, external factors (environment, spectators), psychological states, previous experience and memory may limit the use of RPE in accurately quantifying training intensity and workload (3,4). This might explain the high variability we found in sRPE (5–72%). Objective methods, like heart rate monitoring, are suggested as a more accurate way of internal workload calculation. The limitations of RPE use in soccer have also been presented elsewhere, with the correlation coefficients between sRPE and heart rate-based training load ranging from 0.50 to 0.61 (5).
Regarding the second point of this letter stating that the training content of our study was not controlled, we believe this point has been made clear in our manuscript. In fact, this is one of the limitations of sRPE; the fact that no account is taken for the external load. As mentioned on the letter, the authors “are aware that such a study design is almost impossible to set at elite soccer level” (1). Therefore, there is no disagreement between the letter's authors and us.
In summary, our study showed that a RPE-based workload calculation is not without limitations and this should be taken into account from scientists and practitioners. Indeed, this point has been raised by others as well (3,4). Studies showing low-to-moderate correlation coefficients between RPE and GPS-derived workload data are on the same line (6). As mentioned by the letter's author previously, “despite various contributing factors, session rating of perceived exertion has the potential to affect a large proportion of the global sporting and clinical communities” (7). We believe our study has indeed highlighted some of these “contributing factors.” As we acknowledge in our manuscript, “the sRPE is a practical low-cost tool to assess training load in soccer.” However, this does not justify that it can be an accurate and sensitive method in all cases, and all its limitations should be considered. Either subjective or objective data should be combined, or one should move towards assessing the training physiological outcome and eliminate the use of subjective tools, especially with elite players (8,9). There is a risk of spreading inappropriate information by presenting RPE-based method as the gold standard for workload quantification. We strongly suggest a more open-minded and critical thinking approach to the related data presented in the literature. This approach might help advance the knowledge in the field which at the moment is superficial and of limited extent.
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