## 3 Results
### Description of the Sequence of Responses to Mediolateral Perturbations  
The postural responses to mediolateral perturbations were obtained and successfully organized as a function of time. EMG activity appears earlier with serve perturbations. All studies show that the activity of the analyzed muscles appears earlier with severe perturbations than with weak ones.  
Appendix A (Table A1) details the postural responses at the ankle-joint to medial variations in equilibrium. Their origin is associated with a change in the angular position of the calf in the transverse plane. It usually occurs 80 ms after the onset of the perturbation force. At this point, the dorsiflexors are activated, and after a slight delay, at 160.5 ms, the plantar flexors are involved. Depending on the severity of the perturbation, the activation of the previously mentioned muscles lasts up to about 250 ms. At lower perturbation intensities, activation of the relevant muscles may be delayed and begin around 400 ms. When strong perturbations occur, peak muscle activities are between 680 ms and 1300 ms. For moderate perturbations, this is between 530 ms and 1203 ms, and for small ones from 458 ms to 1274 ms. Thus, in most cases, the muscles reach maximum EMG activity between 530 ms and 1275 ms [20].  
Respons occurring at the knee joint have only been considered in the study by [PERSON] et al. [20]. First, there are extension torques which occur between 100 ms and 200 ms, depending on the magnitude of the perturbation. Next, flexion torques are observed. The onset of the mechanomyography (MMG) signal of the knee joint flexors and extensors is recorded between 190 ms and 290 ms. Although with a small magnitude of the perturbation, MMG from the knee joint flexors appears around 380 ms. In the first case, the onset of activity in the knee extensors is observed at 250 ms. In the second, the activation of the knee flexors or extensors is observed at 600 ms. The peak of this muscle activity is up to 1250 ms. Muscle activity affects joint positioning and torques, which achieve their maximum values up to 1750 ms. A detailed description of the response of the knee joint to mediolateral perturbations appears in Appendix A (Table A2).  
The behavior of the pelvis is closely linked with the hip joint. From 55 ms, hip torques and almost simultaneous (from 65 ms) angular position of the thigh changes are observed [15]. MMG activity of the hip extensors is visible from the very beginning, from approximately 50 ms, but the first EMG recordings appear at around 100 ms [20]. The first in-sequence EMG recordings come from the muscles responsible for hip abduction [20]. Maximum MMG activity is up to 1050 ms, and peak EMG activity is up to 1200 ms. It is worth noting that motion in the hip joint is not uniplanar. It consists of adduction and abduction, but also flexion and extension motions. Depending on the magnitude of the perturbation, the change in the hip flexion angle occurs in as little as 100 ms. In 450 ms, the hip extension angle changes [20]. Appendix A (Table A3) provides a detailed description of the responses of the pelvis and hips to lateral balance perturbations.  
The joint and body segment responses described above are all reflected in CoP and CoM displacements. The first CoM motions, like those of the ankle joint, occur approximately 80 ms after perturbation initiation [20]. On the other hand, most reactions occur from 95 ms onward. The CoP displacement follows CoM motion. When the perturbation is small, CoP and CoM displacements occur later than during large ones [20]. It is also worth noting that when a perturbing force is applied to the shoulder girdle, CoP motion begins after 157 ms (medial-lateral displacement) and 191 ms (anterior-posterior displacement), respectively [24]. CoP and CoM motions as a function of time are shown in Appendix A (Table A4).