# Recommendations for Advancing the Resistance Exercise Overtraining Research
## 2 Issues with Identifying Overtraining  
Previous research has indicated that in endurance sports, OTS might affect 20-60% of athletes at some point in their careers [1, 2]. However, [PERSON] and colleagues [13] have cast doubt over those figures, proposing that there are no studies providing objective evidence of performance suppression lasting \(\geq\)4 weeks. The current diagnostic tool presented in expert consensus [2] suggests that for a diagnosis of OTS to be considered, long-term performance suppression and \"persistent fatigue or exhaustion\" lasting \(\geq\)4 weeks are key factors. Whilst performance suppression for <4 weeks might be indicative of NFOR rather than OTS, it might also be reflective of the transient fatigue experienced by athletes in the weeks following OT that might result in FOR given sufficient recovery [11, 14]. Symptoms of OTS can mimic other diseases, therefore only when confounding factors have been ruled out can a diagnosis be made [15]. If a diagnosis of OTS is made without the exclusion of confounding factors, misdiagnosis is more likely, and performance decrement experienced by the athlete could be caused by other factors such as illness, insufficient fueling, or detraining. OTS affects multiple physiological systems and the symptoms presented by athletes vary, suggesting that OTS is a heterogeneous disorder [8, 16]. Existing research has not (and likely will not) yet identified a single reliable physiological or psychological marker to assist in the early detection of OTS [13]. Moreover, because OTS can only be differentiated from NFOR by retrospective time-course to performance restoration, the NFOR to OTS threshold is practically indistinguishable. In our recent review [5] we highlighted two cases where resistance exercise OT resulted in a duration of performance decrement potentially indicative of OTS [17, 18]. However, in both cases, methodological considerations need to be addressed. In the study by [PERSON] and colleagues [17], OTS was diagnosed due to prolonged underperformance (classified as \(\geq\)10% decrease from previous sport-specific performance), persistent fatigue lasting >2 weeks, and a self-reported increase in sense of effort when undertaking resistance exercise. Whilst this goes some way to indicate an attenuation in performance, the duration of performance impairment was not reported, making a diagnosis of the OTS difficult. Further, compared to healthy participants, those classified as OTS-affected reported lower carbohydrate intake (3 times lower than in participants not classified as OTS-affected) and overall lower energy intake. The authors suggested that OTS could be triggered by the combined effects of high training demand and excessive calorie restriction, stating that \"the most remarkable trigger of OTS among high-intensity functional training was the long-term low carbohydrate and calorie intake\". However, expert consensus states that diagnosis of OTS requires excluding factors such as calorie restriction and insufficient carbohydrate intake [2]. Secondly, due to shared pathways, etiology and symptoms, OTS shares several similarities with relative energy deficiency in sport (RED-S); a maladaptive disorder characterized by negative health and performance outcomes triggered by low energy availability [3]. Severe or prolonged low energy availability can perpetuate symptoms of performance decline that are indicative of NFOR and low energy availability might blunt training adaptation [19], therefore decreasing the potential for FOR. It is plausible that participants of this research were suffering from a disruption of physiological processes and compromised performance caused by insufficient fueling, and not OTS [20]. However, because energy availability was not reported, this cannot be confirmed. [PERSON] and colleagues [18], investigated if high-intensity OT would result in OTS. The authors defined OT as an increase in training volume or intensity that results in long-term performance decrement i.e., \(\geq\)2 wks.