###### Abstract  
Wearable technologies have become increasingly popular in recent years, as athletes and coaches look for ways to gain a competitive edge. These devices can track a variety of metrics, including heart rate, sleep quality, and movement patterns. This information can be used to identify areas for improvement and make small, incremental changes that can lead to significant gains in performance. The purpose of this narrative review is to provide an integrative overview of the literature on the impact of wearable technologies on marginal gains in sports performance. The literature review was conducted using the Scopus, PubMed, and Web of Science databases, and a total of 55 papers were considered eligible. The results of the literature overview suggest that wearable devices can be classified into three main categories. (1) Location-based wearables (LBW) track an athlete's location and movement, which can be used to analyze training patterns and identify potential injury risks. (2) Biometric wearables (BMW) track physiological data such as heart rate, sleep quality, and body temperature; these data can be used to monitor an athlete's fitness levels and identify signs of overtraining. (3) Performance wearables (PMW) track performance metrics such as power output, speed, and distance; this information can be used to optimize training programs and track progress over time. For each category, this paper provides the five most important data points measured by each suggested device. Additionally, sport-specific examples are provided for each category based on the literature data. The limitations of wearable devices, such as accuracy, validity, reliability, interpretability, and cost, are also discussed. However, despite these limitations, the results of the literature review suggest that wearable technologies can be a valuable tool for athletes and coaches who are looking to improve performance. Ultimately, this technological evolution in sports science is likely to dramatically change the state of the art in athletic monitoring and sports analytics. wearable technologies; marginal gains; sports performance; research +
Footnote †: journal: Medical Sciences for Health, Universita degli Studi di Milano, 20133 Milan, Italy; [EMAIL_ADDRESS]  
Footnote †: journal: Medical Sciences for Health, Universita degli Studi di Milano, 20133 Milan, Italy; johnny. all the difference\" [3]. While this perspective has merit, the challenge lies in quantifying these marginal gains to facilitate their management. Although not all marginal gains can be measured by wearable devices (e.g., wheel pressure, cushion density, seat comfort), these technologies can capture a vast array of data pertinent to sports performance and sports medicine [4; 5]. Nevertheless, despite their increasing popularity, a significant number of wearable devices lack rigorous and independent testing to ascertain their accuracy, reliability, and validity [6; 7]. There are several types of wearable trackers that may be able to provide information to performance athletes (wristbands, bracelets, smartwatches, headbands, rings, and more) [8]. These wearable detectors are an integral part of a family of technologies called consumer technologies (CSTs) [9]. Consumer technologies (CST) encompass not only smartphones and various sensor types, but also a range of sophisticated devices with clinical applications. These advanced systems are capable of monitoring diverse parameters, including movement [10] and biological [11], physiological [12], and behavioral [13] factors. The data generated by these devices provide coaches with valuable insights, enabling them to make informed decisions regarding the modification of these parameters to optimize athletic performance [14]. Wearable devices, commonly referred to as fitness trackers, have gained significant popularity due to their accessibility, affordability, and non-prescription nature [15].