## 1 Introduction  
The overload sprint is a unique form of resistance training that has attracted a great deal of research attention over the past decade [1, 2], primarily because it has been shown to be a beneficial stimulus for improving acceleration performance, an important component in many sports disciplines [3]. Compared to sprinting without resistance, an athlete generates higher horizontal forces during overload sprints (i.e., resisted sprints) [4]. As different overloads biomechanically replicate different acceleration phases of the sprint [5], resisted sprint training has been utilised in practise with different equipment and overloads [6]. Although it would be beneficial in practise, there is still no consensus on whether lighter or heavier overloads are preferable for resisted sprint training [1; 2; 5]. Similarly to other fast actions, sprint performance is determined by the ability of the neuromuscular system to generate horizontal force and power [7; 8]. Therefore, improving power output during sprinting (i.e., generating higher horizontal forces at a given sprint speed) leads to faster acceleration and also a higher maximal velocity (\(\mathrm{v_{max}}\)) [9]. The generally accepted approach in resistance training, whereby the overload which results in maximal power output during exercise is considered optimal [10; 11], could also be applied to resisted sprinting [12; 13]. However, the power output (determined as the product of velocity and horizontal force) during an overloaded sprint is poorly understood. Thus, it is questionable whether the power output is greater at higher overloads, which increase horizontal force production more but decrease the sprint velocity, or at lower overloads, which increase horizontal force production less and almost maintain a normal sprint velocity. To calculate these parameters when sprinting with overload, the velocity and the applied resistance force (\(\mathrm{F_{r}}\)) must be known. This is a challenge and requires advanced devices that accurately monitor the magnitude of \(\mathrm{F_{r}}\)[14]. Previously, such calculations were performed using motorised sprint resistance devices and sleds that allowed monitoring of the resultant horizontal force (\(\mathrm{F_{h}}\)), power output, and the so-called force-velocity-power profile (FvP) [13; 15; 16; 17]. This profile is based on the progression of changes in \(\mathrm{F_{h}}\) and power over the sprint velocity and reflects the neuromuscular ability of the human body to generate maximal theoretical horizontal force (\(\mathrm{F_{0}}\)), maximal theoretical velocity (\(\mathrm{v_{0}}\)), and maximal theoretical power (\(\mathrm{P_{max}}\)) during sprinting [18]. Profiling is a popular method for monitoring the biomechanics of normal sprinting [19; 20; 21]. In contrast, there are few studies on force output, power output, and FvP profile during overloaded sprints [13; 17]. There is a lack of studies in which non-motorised devices are used to apply the overload and acquire force and power metrics. The main reason for this is the difficulty in predicting Fr with such devices and, furthermore, calculating \(\mathrm{F_{h}}\) and power output [14]. As more affordable non-motorised devices using hydraulic resistance have not yet been evaluated in the context of the biomechanics of sprinting with overload, a hydraulic resistance device (HRD) was tested in this study. The HRD is a technical solution that generates and measures \(\mathrm{F_{r}}\) during overloaded sprints [22]. The device also offers the possibility of measuring sprint velocity. With the HRD, it is possible to obtain measurements during a resisted sprint that allow the calculation of force, power output, and FvP profile, similarly to sprints with sleds [17; 23]. The use of the HRD for such purposes is still unexplored, so it remains questionable whether the device can be successfully used for such monitoring.