# Multi-Segmental Motion in Foot during Counter-Movement Jump with Toe Manipulation
## 4 Discussion  
In this study, we compared toe abduction manipulation (**TM**) and non-manipulation (**NTM**) conditions to explore the foot inter-segment kinematics and plantar loading pattern during CMJ taking-off and landing phases. It was found that manipulation in toes, during the landing phase, could redistribute forefoot loading from the medial to lateral region. Further, the forefoot inter-segment increased flexibility, and the hallux relative to the forefoot (HXFFA) showed a decreased range of motion while comparing to the non-manipulation.  
As injuries of the ankle and the knee are frequently observed during jump landings, landing tasks are vital not only for performance but also for the prevention of injury risk [26; 27; 28]. For the jump task, larger plantar loading at the forefoot region during take-off and landing phases may increase the risk of metatarsal injuries [4]. Several foot disorders, such as hallux valgus, usually present high plantar pressure in medial forefoot [29; 30]. Modern footwear has been designed with narrow space, especially in the forefoot [6]. Ill-fitted or constrictive toe-box shoes would disrupt the normal alignment of the first metatarsophalangeal joint and even induce hallux valgus [1]. Furthermore, the above issue may affect toe functionality, such as prehensile and ambulatory ability [5; 16].  
In this study, the results showed that hallux abduction manipulation could reduce impulse and pressure-time integral in BT and M1 during the take-off phase. The maximum force increased in BT and M1 and decreased in M2 during landing. This is consistent with our previous work that for hallux valgus patients, the forefoot plantar pressure was redistributed centrally from M1 to M2-M4, after three months of minimal-shoes running intervention [6].  
Footwear with constrictive forefoot space or insufficient footwear width may limit toes' activities during locomotion, thus affecting the lower limb kinematic performance [31]. Foot symptoms, such as hallux valgus, showed a reduced ROM in the lower extremity joints and weaker propulsive function during the push-off phase of gait [32]. A study reported that patients with hallux valgus presented reduced dorsiflexion range of motion in the first metatarsophalangeal joint [33]. [PERSON] et al. [34] found that ankle dorsiflexion decreased in loading response among barefoot runners. [PERSON] et al. [35] found professional dancers exhibited higher forefoot-hindfoot plantar flexion than non-dancers during landing. However, no significant difference exists between non-binding and binding hallux conditions [16].  
In this study, the toes abduction manipulation with subtle foot morphology change exhibited great impact in the HXFFA, which is consistent with our previous hypothesis: an increased dorsiflexion range of motion of HXFFA was presented during take-off and landing phases. However, the ROM  
Figure 4: The sagittal (X-axis) and frontal (Y-axis) HXFFA angles during take-off (**a**) and landing (**b**) phases in Non-Toe-Manipulation (**NTM**) and Toe-Manipulation (**TM**) sessions. Abbreviations: DF: dorsiflexion, PF: plantarflexion, Sup: supination, Pro: pronation.  
of HXFFA showed a decrease, and the pronation angle showed an increase with hallux abduction manipulation. This is consistent with the understanding that toe manipulation may restrict relative foot joint motion. It should be acknowledged that there was only a ten-minute interval between the two CM] sessions, and participants might be accustomed to the toe separator manipulation. Another issue on the potential effect from male and female difference was not considered, which shall be the next study objective.  
However, there is still one main limitation. No muscle activity (EMG) data was involved in this study. Future studies should investigate the acute effect of TM on foot intrinsic and extrinsic muscle activities to further elaborate the potential effect.