# Neuromuscular Excitation Pattern in Expert Indoor Skydivers
## 4 Discussion
### Neuromuscular Activation
Differently, ES and Rabd showed notable excitation, with the former enhancing the lumbar lordosis to achieve the appropriate attitude of the trunk for this specific posture and the latter promoting core stabilization. Regarding the lower limbs, RF actively supported hip flexion with a scarce contribution of the antagonist in the stabilization of the lower limb [26]. During HD, as anticipated, all investigated muscles exhibited a considerable heightened engagement. LD and ES showed the highest enhancement, indicating the critical role of stabilizing the thoracolumbar region, likely to counteract the airstream propensity to turn the participant's body upside down when the skydiver is assuming the reversed position. Moreover, a noteworthy simultaneous activation of RF and BF has been observed, indicating a synergistic action of these muscles in stabilizing the lower limbs against the pressure the aerodynamic force exerted on the lower limbs. Furthermore, it cannot be excluded that the coactivation of RF and BF is aimed at balancing the effort exerted by the arms and trunk against the airstream. The findings of the present study offer insights into the specific muscle contributions required for adopting and maintaining various postures, crucial for indoor skydiving coaches and expert skydivers preparing for choreography in competitions. Moreover, the findings of this study may have important implications for beginners and intermediate fliers. Indeed, mapping the primary muscles used by expert instructors to maintain specific postures could serve as a practical guidance for novices to target the correct muscle activation during training. For example, this study revealed the need for beginners to strengthen the muscles surrounding the shoulder and those stabilizing the lower trunk to effectively manage the first stages of indoor skydiving, where practitioners are asked to master the PRONE position and, subsequently, the SUPINE position. Practical indications can be found for intermediate practitioners, as well. Indeed, once skydivers have become proficient in PRONE and SUPINE and move on to mastering the SIT position, this study, in addition to the shoulder and lower back muscles, recommends including RF in the strengthening program to enhance the lower limb control. Lastly, the outcomes of the current study provide valuable indication to expert skydivers. Indeed, they are advised to focus on strengthening the lower trunk and lower limb muscles to ensure core stability and enhance lower limb control when the HD position has to be maintained. It is plausible that the proper activation of only the relevant muscles will result in a more efficient performance that, in turn, should reduce the onset of fatigue and the risk of muscle-joint overload and injuries. Future studies evaluating the occurrence of muscle-joint injuries in indoor skydiving practitioners with different expertise are advisable to verify the existence of a correlation between a specific neuromuscular activation pattern and injury risk. Nonetheless, future studies on neuromuscular activation in the expert and less skilled groups (beginners, recreational, and intermediate practitioners) could disclose different excitation strategies. Such insights would be valuable to monitor skill progression and retention and adjust pitfalls in a trainee's technique. Another aspect that deserves to be investigated is the application of conventional [27; 28] and novel analysis [29; 30] of sEMG to detect fatigue onset during indoor skydiving. This study presents the following limitations. A surface EMG signal was acquired in a single differential configuration employing bipolar probes. This configuration presents several limitations related to interelectrode distance, conduction volume dimension, muscle length, contraction mode, and electrodes positioning, all of which may impact on the information embedded in the signal [31].