RiteeshGrandhi/sciclaimeval-shared-task huggingface dataset:
Limitations and future works
First, this study did not consider the differences in the arm swing styles of the volleyball players. The end segment speed is mainly produced by the joint and segmental rotation in most explosive-hitting sports. Different types of arm swings may affect the hand speed during BI. Second, in this study, leveraging angular momentum conservation and the open kinetic chain theory, we investigated the correlation between angular momentum and swinging arm speed. Given the primary rotation of body segments around the sagittal plane during the aerial spike motion of the jump serve, our analysis focused specifically on angular momentum within the sagittal plane (rotated around the X-axis); however, the trunk ( i.e ., pelvic, lumbar, and thoracic regions) during the arm-acceleration phase may exhibit substantial horizontal rotation (rotated around the Z-axis). Future studies could analyse the angular momentum in three dimensions. Third, we observed that the generation of angular momentum from hip flexion and knee extension movements during the arm-acceleration phase enables the balance of the body in the air to be maintained, which is also essential for the motion of the ball spike. Thus, the kinematic and kinetic characterisation of the three joints of the lower limbs, especially the non-attacking leg, during the aerial phase should be analysed. Finally, this study primarily focused on the jump serve movements of male volleyball athletes and did not include female athletes. Previous studies ( Fuchs et al., 2019a , 2019b , 2021 ) have highlighted technical and strength differences between the sexes. Therefore, the findings of this study may not be directly applicable to female athletes. This study represents the first biomechanical investigation aimed at quantifying and analysing the angular momentum of the volleyball jump serve. Furthermore, it employs the theoretical principles of angular momentum conservation and transfer to examine the complex coordinated movement of the jump serve. This approach not only bridges a significant gap in the existing knowledge base of volleyball jump serve but also offers volleyball practitioners and coaches deeper insights into the results, thereby enhancing their understanding and application of the jump serve.
Conclusions
The main findings can be summarised as follows: During the arm-acceleration phase, both the peak counter-clockwise angular momentum of the attack arm and the peak clockwise angular momentum of the non-attack leg exhibit significant correlations with the arm swing speed at ball impact (BI). Regarding the segmental angular momentum of the attack arm, a distinct proximal-to-distal timing sequence is observed in the upper arm, forearm, and hand. The peak counter-clockwise angular momentum of the forearm and hand significantly correlated with the arm swing speed at BI. A stepwise regression model predicted arm swing speed ( R 2 = 0.35) by incorporating the peak angular momentum of the non-attack leg, forearm, and hand. These results suggest that during the arm-acceleration phase, players should generate considerable clockwise angular momentum in the non-attack leg to maintain aerial balance and improve the execution of the arm swing. Additionally, precise control over the magnitude and timing of muscle exertion in the elbow and wrist joints of the attack arm can facilitate the effective transmission of angular momentum, thereby enhancing arm swing speed.
Figure 1: Experimental setup.

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DOI: 10.7717/peerj.18000/fig-1
Figure 2: Locations of reflective markers.

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DOI: 10.7717/peerj.18000/fig-2
Figure 3: Mean (n = 17) time-series data for the angular momentums of the whole body, attack arm, non-attack arm, head–trunk, attack leg, and non-attack legaround the X-axis during the aerial phase.
TO, take-off; MSER, maximum shoulder external rotation; BI, ball impact; LO, landing-on. CC (+), counter-clockwise; C (–), clockwise. The peak angular momentums are marked by black circles (○).

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DOI: 10.7717/peerj.18000/fig-3
Figure 4: Mean (n = 17) time-series data for the segmental angular momentum of the upper arm, forearm, and hand of the attack arm around the X-axis during the aerial phase.
TO, take-off; MSER, maximum shoulder external rotation; BI, ball impact; LO, landing-on. CC (+), counter-clockwise; C (–), clockwise. Peak angular momentums are marked by black circles (○).

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DOI: 10.7717/peerj.18000/fig-4
Peak angular momentum variables and correlations with the arm swing speed at ball impact (BI).