## Materials and Methods  
The research was carried out at the Jerzy Kukuczka Academy of Physical Education in Katowice (AWF) at the certified Laboratory of Research on Healthy Physical Activity (PN-EN ISO 9001:2015 [27], certificate validity: 7 December 2021-16 December 2024). The empirical study was conducted in a group of 26 students from AWF, including 13 women (age: 23.4 \(\pm\) 1.0 years, body height: 166.5 \(\pm\) 5.3 cm, body mass: 60.0 \(\pm\) 6.2 kg) and 13 men (age: 23.3 \(\pm\) 2.0 years, body height: 182.0 \(\pm\) 6.0 cm, body mass: 77.5 \(\pm\) 12.5 kg). According to the accepted inclusion criteria, the study participants were healthy and physically fit volunteers. However, the study excluded those sensitive to flashing lights or image sequences found in programs and video games, suffering from epilepsy, having symptoms of motion sickness or balance disorders, with physical limitations (e.g., injuries) that could hinder exercises in a virtual environment, taking any medications that affect heart rate, and those who had previously used the application. The subjects' previous experience with immersive VR technology varied. Nine people (34.6%) had previously used it, while the remaining 17 people (65.4%) had never experienced it. None of the participants had previously walked on the multidirectional treadmill connected with VR used in the study. The study was approved and reviewed by the Research Ethics Committee of the AWF (protocol number 9/2018). The study used the HTC Vive Pro VR headset, Omni omnidirectional treadmill (Virtuix; www.virtuix.com (accessed on 17 October 2023), and an AVRG game TRAVR Training Ops. The game consisted of overcoming obstacles in a virtual tunnel and shooting at designated moving and stationary targets with a laser weapon held in both hands. However, you should only shoot at the yellow targets marked with the \"O\" symbol and ignore those marked \"X\" symbol. The aim of the game is to score as many points as possible. The game result consists of several elements such as the speed of completing the stage, accuracy (the number of targets shot down and missed), and the number of shots fired. At the end of each stage, the participant runs to the board, where they write down their nickname and the number of points they have obtained, and the results of other players are shown, which may provide additional motivation for the user. The necessity to cover a designated route forces the player to perform locomotor movements (running, walking), engaging primarily leg muscles. The research involved two fifteen-minute sessions of AVRGs. There was a 30 min break between sessions, during which the participants rested in a sitting position. Two 2 kg AWs (one for each leg) fastened to the ankles of the left and right lower limbs were used to load the legs. Figure 1 shows the participant playing TRAVR Training Ops and the test stand, whereas Figure 2 shows a screenshot depicting the game environment. Heart rates (HRs) were measured while playing active video games using an HR monitor (Polar Vantage V, Kempele, Finland). PA intensity was estimated based on the average % HR\({}_{\text{max}}\). Before the measurement, HR\({}_{\text{max}}\) was calculated according to the formula proposed by [PERSON] et al. : 208-0.7 \(\times\) age [28]. Exercise load was estimated based on the American College of Sports Medicine classification (average HR \(<\) 64% HR\({}_{\text{max}}\)--low intensity, 64% HR\({}_{\text{max}}\)\(\leq\) average HR \(<\) 77% HR\({}_{\text{max}}\) is moderate intensity, and HR\({}_{\text{avg}}\)\(\geq\) 77% HR\({}_{\text{max}}\) means high intensity) [29]. PA intensity was categorized into HR zones using the Polar Flow software (v.6). The absolute time of HR spent in each of the following zones was  
Figure 1: Study participants playing TRAVR Training Ops game in immersive VR using an Omni treadmill: (**a**) with AWs; (**b**) without AWs. In addition to objective measurements, a subjective survey based on a questionnaire was also conducted.