## 4 Discussion
### Timeline of Response Sequences to Mediolateral Perturbations  
An important part of this study was an attempt to create a timeline on which individual postural responses to mediolateral perturbations were presented as a function of time. Due to the small number of available publications on the subject, divisions by weight, height, gender, or the site of the perturbation were abandoned, as the goal was to capture general regularities characterizing the response to this type of perturbation. Based on the [PERSON] et al. [15] paper, it can be concluded that the first reactions to ML perturbations at the pelvic level occur at the hip joints (55 ms). There is a change in angular alignment followed by torques. It is noteworthy that the MMG activity of the hip joint abductors occurs at the very beginning, but the EMG activity is noted with a longer delay. This phenomenon is repeated for other muscle groups in the later stages of the postural response [20]. The cause is most likely the secondary movement of the muscle bellies, due to angular changes in the nearby joint. That is in line with the findings of [PERSON] et al. [15]. They suggest that the initial response to perturbations is due to the flexibility of extra-articular structures rather than muscle activation.  
The response of the ankle joints is observed after the initial displacement of the hip joints. As the onset of CoP displacement is observed (86.7 ms) and immediately afterward (93.1 ms), the CoM motion, the first muscles become activated, as evidenced by the EMG signal from the hip extensors, dorsiflexors, and plantar flexors. Subsequently, there is a noticeable movement in the knee joint, which, at approximately 200 ms, manifests itself in the presence of torques, as well as MMG activity, but no EMG signals [20]. Moreover, in this temporal region, [PERSON] et al. [24] observed an up-down movement of the pelvis, which might correlate with the motion at the knee joints. Perhaps this indicates an attempt to lower the center of gravity to recover faster. However, this hypothesis requires confirmation in future studies. As mentioned above, a series of postural reactions leads to a peak displacement of CoP, followed by CoM. [PERSON] et al. [20] showed that with small perturbations, this relationship occurs earlier than with larger ones. CoP and CoM reach extreme positions within 625-1000 ms, but this does not end positional responses, which last up to 1750 ms, according to the same authors.  
Although there were no studies analyzing the preventing of stepping among the young, some data were acquired from comparative studies between the young and the elderly. Based on studies [5; 23] in which subjects took a step to regain balance, it can be concluded that the loaded side-step (LSS) strategy, which is preferably utilized by the young, allows faster initiation of step response than an unloaded crossover step (UCS). This appears to be especially relevant in the context of deciding if the step is needed or not. The decision to take a step is made by the CNS up to a maximum of 150 ms, allowing approximately 300-450 ms to initiate the step [4]. It is also worth noting, that this decision must be made by CNS before any EMG activity, i.e., before any active trial to restore equilibrium. In that case, the question arises on what basis CNS decides to take a step or not. In future studies, it might be worth investigating if there are differences in primal reactions to perturbations provoking stepping responses, and those that do not provoke one.