## 1 Introduction  
Physical fitness investigations in children and adolescents have been led by the identification of alterations in body composition, such as bone development [1; 2; 3] and fat mass accumulation/distribution [4; 5], and to a minor extent the identification of alterations in cardiorespiratory fitness, muscle strength/endurance, and flexibility [6]. As a result, studies that investigated physical fitness in HIV-diagnosed children and adolescents described alterations in fat distribution [4] and increases in body fat [5], low bone development [1; 2; 3], as well as low muscle strength/endurance, flexibility, and cardiorespiratory fitness when compared to healthy populations [7; 8], which can be associated with higher body fat mass [7]. Considering that low physical fitness in childhood and adolescence is related to lower physical fitness and chronical health conditions and mortality in adulthood, there is a need to monitor physical fitness, especially in those who present chronic health conditions in childhood [9; 10; 11], such as HIV-diagnosed children and adolescents. Despite the need for its investigation and the recommendations for developing physical fitness for this population [12], body mass and length/height are the primary measurements recommended for use in monitoring growth development and screening for thinness and overweight in HIV-diagnosed children and adolescents through indexes such as body mass index (BMI), weight-to-age ratio, and height-to-age ratio [13; 14]. Considering the common use of anthropometric measurements and indexes in studies assessing physical fitness in this population [6], and their applicability for monitoring growth development and weight status [13; 14], previous studies have also applied indexes, such as BMI, to investigate their possible association with cardiorespiratory fitness [15; 16; 17], muscle strength/endurance [17; 18], and flexibility [17]. These studies relied on the assumption that BMI can identify increased fat mass in children and adolescents [13; 19], and that these increases in fat mass can negatively impact cardiorespiratory fitness, muscle strength/endurance, and flexibility [20; 21]. However, increases in BMI can also be positively associated with fat-free mass and muscle strength/endurance [17; 22; 23; 24], given that BMI is not capable of distinguishing if an increase in body size is related to increases in fat mass and/or fat-free mass [22; 25], thus limiting its applicability for monitoring muscle strength/endurance. Moreover, when observing the recommendations for monitoring HIV-diagnosed children and adolescents [26; 27; 28; 29] and the results of previous studies that investigated physical fitness [6], there is a lack of standardization regarding which methods and protocols, such as reference values, should be applied for monitoring physical fitness in this population, limiting the comparison between studies and the direction of future research and guidelines [6; 20; 26; 27; 28; 29]. Regarding the applicability of anthropometric parameters, previous studies showed that different anthropometric parameters, such as skinfolds [30; 31] and body circumferences [31], can be used for estimating fat mass, and bone diameters and body circumferences can be used for monitoring the bone parameters [32] of HIV-diagnosed children and adolescents. Moreover, anthropometric parameters have been described as easy-to-use and accessible methods due to their low cost when compared to laboratory tests [33], and they are the main methods applied to investigate physical fitness in HIV-diagnosed children and adolescents [6]. Thus, the addition of anthropometric parameters to a follow-up routine, when it is not possible to carry out a complete assessment of physical fitness, could provide additional information regarding the physical fitness of HIV-diagnosed children and adolescents.