# Recommendations for Advancing the Resistance Exercise Overtraining Research
## 1 Introduction  
Overtraining syndrome (OTS) is an accumulation of training and/or non-training stress resulting in a decrement in performance capacity, with or without related physiological and psychological signs and symptoms of maladaptation in which restoration of performance capacity may take several weeks or months [1, 2]. Other than long-term performance decrement, there is no single validated identifier of OTS. Diagnosis requires the exclusion of organic disease, infections, dietary caloric restriction, and insufficient carbohydrate or protein intake [2]. As such, a diagnosis of OTS can only be made once confounding factors have been ruled out [2]. Due to its complex and multifactorial nature, a multidisciplinary approach to understanding and diagnosing OTS is essential [3]. The term \"overtraining\" (OT) describes the imbalance between training demand and recovery that could result in either diminished performance or an improvement above baseline [2, 4]. OT is the _process_ of undertaking training with an increase in training volume or intensity of effort, whilst OTS would be a possible _outcome_ of OT. Our recent scoping review [5], as well as the explorative systematic review published by [PERSON] et al. [6], reported minimal evidence of OTS in either competitive strength sports or those undertaking periods of resistance exercise, even after purposeful attempts to impair performance. Our research has also reported that high-performance strength coaches are not concerned with the risk of OTS, and rarely consider such the disorder a consequence of resistance exercise [4]. In cases where OT results in performance decrement lasting fewer than several weeks, with no observable performance improvement even after sufficient recovery, the term non-functional overreaching (NFOR) is used [1, 2]. There is an implication within expert consensus that while OTS shares similarities to NFOR, these conditions cannot be distinguished by the magnitude or type of symptoms, only by retrospective time course torecovery from impaired athletic performance [2]. Functional overreaching (FOR) is considered to be a desirable training outcome where periods of OT lead to an initial short-term reduction in performance, followed by an improvement or \"rebound\" above the initial baseline [7, 8]. This improvement in performance is only observed after an initial reduction in performance lasting several days [9]. Interestingly, whilst symptoms of increased fatigue, hormonal disruption, and psychological disturbance (e.g., impaired mood, reduced vigor) are associated with NFOR/OTS, these symptoms may also be present in athletes classified as FOR [7]. Consequently, FOR can only be differentiated from NFOR/OTS by resulting change in performance and not the symptoms presented. Research from the endurance sport domain has indicated that the magnitude of performance improvement following FOR is no greater than the improvements observed following the same training without experiencing an initial performance decline [7, 10]. Therefore, intentional attempts to induce a state of FOR through intentional OT might not be required to optimize performance. Nevertheless, high-performance strength coaches regularly use periods of deliberate OT (typically in the weeks preceding competition, referred to as \"planned overreaching\") to invoke the physiological adaptations necessary to achieve FOR, and consequently, a meaningful standard of performance improvement [11]. However, some coaches choose to avoid intentional resistance exercise OT because of a lack of confidence in their ability to _detect_ NFOR, knowledge relating to how OT should be structured to _achieve_ FOR, and uncertainty that OT yields greater performance improvement compared to traditional continuous training. Whilst research into resistance exercise OT has gathered attention from sports scientists in recent years, the field has traditionally focused on the endurance athlete [1, 2, 12].