## 1 Introduction  
The anterior cruciate ligament (ACL) is the central stabilizer of the knee, stabilizing the tibia against increased anterior translation and internal rotation [1]. It is estimated that approximately 250,000 ACL tears occur annually in the United States [2], resulting in approximately 120,000 ACL reconstructions (ACLR) each year [3]. The incidence increased drastically in the last two decades, both in the general population and in individualswho play sports [4]. Nowadays, the treatment of choice for ACL tears has been surgical intervention in the detriment of non-operative management, which is associated with a poor functional outcome [5], preventing the return to pre-injury activities for most patients and causing an increased incidence in secondary ACL reconstructions [6]. As a result, surgery has become the first-line treatment for ACL-deficient knees in active patients [7]. The two most used autografts for ACLR are the bone-pstellar tendon-bone (PT) and the four-strand hamstring tendon (HT) [8]. ACLR with a PT autograft has shown some advantages, with faster graft incorporation [9], a higher proportion of patients returning to pre-injury activity levels [10] and lower graft failure rates when compared with HT autografts [11]. However, HT autografts have other advantages, with fewer rates of anterior knee pain, extensor strength deficits and osteoarthritis, as well as a lower rate of motion problems requiring surgical intervention, compared to ACLR with a PT autograft [12]. ACLR with a PT autograft appear to result in a loss of extension and preservation of flexion strength. On the other hand, HT reconstructions demonstrate greater flexion strength deficits [11]. After ACLR with a HT autograft, some patients had valgus knee alignment on initial contact during single leg hop landing [13]. Patients who had two HTs harvested (gracilis and semitendinosus) presented flexion and internal rotation strength deficits up to 1 year postoperative [14]. It is important to determine which treatment results in greater benefits or smaller deficits. Because of this, traditional methods have been discontinued since these methods rely on patient self-reports and on visual observations and assessments of different evaluators, which can lead to subjective measurements [15]. Other methods have been used to assess different movements: the use of force platforms has been conducted by authors to collect data from the procedure [16]; in other cases, a kinematic analysis was performed via a two-dimensional (2D) frontal plane projection angle of knee alignment measured during the DVJ [17]. Current motion capture methods, based either on anatomical marker placement or on the new markerless approaches [18; 19; 20], have been used to capture movements and process videos to identify limbs' position and orientation. These methods provide a three-dimensional representation of the body segments, enabling a more precise extraction of the joint centers and angles [21] and the modeling of a six degrees-of-freedom model of the individual's movement, which could not be achieved with other methods. However, there are significant differences between markerless and marker placement approaches. Despite marker-based motion capture still being the gold standard, it is difficult to quantify how reliable the marker position is. First, it is affected by the researcher's ability to identify the anatomical landmarks, which is dependent on experience and the morphology of the individual. Secondly, it is affected by movement/skin artefacts and thirdly, it is affected by the ability of the system to detect the marker, and the position residual [22]. Markerless motion caption, on the other hand, is a more objective method, relying on the system algorithms. The absence of markers also increases the compliance of each participant by not posing a constraint to each participant's movement [23]. However, while validation studies are increasing, they do not cover all movements, such as the drop jump.