## 4 Discussion  
### Physiological and Biomechanical Studies of Inline Speed Skating  
The aim of this scoping review was to systematically assess evidence on the physiology and biomechanics of inline speed skating to inform recommendations and guidelines on testing and research strategies. Most of the relevant literature on inline speed skating has evaluated VO2 and [La\({}^{-}\)], with a limited number of studies examining inline speed skating biomechanics. One of the main outcomes of this scoping review was the limited number of studies identified against the inclusion and exclusion criteria, clearly demonstrating the paucity of data and the importance of upcoming research in this area. The available literature on inline speed skating provides preliminary and useful insights into physiological and biomechanical parameters. inline speed skating has attracted attention primarily via the measurement of VO2 and [La\({}^{-}\)]. [La\({}^{-}\)] testing has been widely used to assess the anaerobic (lactate) threshold and associated exercise intensities, and its reliability in inline speed skating has been verified [15]. Similarly to ice speed skating, the low posture in inline speed skating results in a blood flow restriction that contributes to lactate accumulation [5,31]. For example, compared to upright gliding, low body posture skating during maximal exercise elicits a 9% increase in [La\({}^{-}\)] [32]. Another study observed that, at a speed of 27.4 km/h, VO2 decreased by 18% in the bent body position compared to the upright posture [11]. This decrease might be associated with variations in knee and trunk angles, highlighting the utility of VO2 and [La\({}^{-}\)] measurements in understanding the physiological demands of inline speed skating. Clearly, there is a need for more sports-specific research, as direct extrapolation from biomechanically similar movements may overlook critical physiological and technical nuances unique to inline speed skating [17]. For example, inline speed skaters exhibit a knee joint angle approximately 7.5% greater than that of ice speed skaters [5]. Another study compared the oxygen saturation of the vastus lateralis muscle in upright and low-posture skating, where the maximum oxygen saturation during cuff ischemia in upright and low posture  
Figure 4: Risk of bias domains for research articles on inline speed skating expressed as percentage of included studies. See caption for Figure 3 for definition of Domains 1–8. was 60.4% and 74.9%, indicating that the vastus lateralis muscle hypoxia was more severe during low-posture skating [32]. In addition, a marked difference was observed in adductor muscle activation during the recovery phase between elite athletes and novice skaters (17 and 26%) [24]. These data are useful for coaches prescribing technique and positional changes, strength and conditioning coaches delivering gym training, and researchers interested in these questions. Surface electromyography, accelerometers and cameras have provided useful insights into the biomechanical and neuromuscular aspects of inline speed skating. Surface electromyography revealed substantial differences in inline speed skating muscle activation patterns, particularly between the left and right lower limbs. One study demonstrated that the left % root mean square/maximum voluntary isometric contraction of vastus lateralis exhibited greater fatigue resistance than the right (79 and 94%), evidence of asymmetric muscle recruitment [23]. This asymmetry was further influenced by skating velocity, with higher speed increasing muscle activation and influencing coordination [12; 29]. The vertical component of ground reaction forces was correlated significantly with performance times in the start (R2 = 0.62), turning (R2 = 0.65) and acceleration phases (R2 = 0.54) [28]. Meanwhile, compared to ice speed skating, inline speed skating exhibits a higher surface friction loss ratio (18 and 45%) [5].