## 4 Discussion  
Current advances in 3D printing technologies have enhanced the production of custom orthopedic devices fitting patients' anatomy and with personalized mechanical properties. While 3D-printed custom orthoses are still more expensive than similar off-the-shell solutions, the costs are increasingly offset by the higher performance and the better comfort. In addition, significant anatomical alterations can only be addressed by such custom devices. PD-AFOs are recommended for individuals with mild foot drop instability, which may also need support in the push-off phase of walking due to weakness or insufficiency of the ankle plantarflexor muscles. While several commercial and custom AFOs are reported in the literature for different lower limb pathologies, only a few studies have investigated the energetics of PD-AFOs with respect to their design and mechanical properties [9; 11]. In this study, we aimed at calculating the energetics of a novel custom PD-AFO in a population of individuals with mild foot drop condition. Quantifying the energetic effects of a novel custom AFO in patients with foot drop is crucial for several reasons. First, this study provides objective, data-driven evidence of the  
Figure 4: Mean temporal profiles of body-weight normalized ankle power (W/kg) in the custom AFO, Codivilla Spring, and in shed conditions over normalized stance phase (%). Figure 3: Each curve represents the work normalized to body weight (J/kg) performed by each of the 8 AFOs over the normalized stance phase (%). From heel-strike to t1, the calf-shell absorbs energy by flexing posteriorly. The calf-shell releases energy from t1 up to the neutral position at mdistance and absorbs energy again by flexing anteriorly up to t2. From t2 to toe-off, the calf-shell releases energy by rotating posteriorly back to the neutral position. This work released by the AFO supports ankle plantarflexion in the push-off phase. AFO's energetic contribution to gait dynamics. In vivo biomechanical measurements offer a quantitative assessment of how the device influences patients' physiological exertion during ambulation, adding instrumental evidence to the subjective evaluations on comfort and ease of use. This is essential for validating the AFO's potential to enhance functional mobility. Second, by quantifying the AFO's impact on energy expenditure, clinicians can make informed decisions regarding prescription and customization of the device. Understanding the energetic benefits allows for personalized treatment plans, optimizing design and stiffness properties to maximize patient outcomes. This is particularly vital for patients with chronic conditions, where even small reductions in the metabolic cost per gait cycle can substantially improve quality of life. Furthermore, this study contributes to the broader scientific understanding of AFO interventions. These investigations allow researchers to better correlate AFO design parameters with AFO mechanics in gait and to identify key biomechanical parameters influencing AFO effectiveness. This knowledge can drive the development of more efficient and patient-centered orthotic solutions for foot drop and other gait impairments. The present PD-AFOs were characterized by relatively low bending stiffness with respect to the average data reported for individuals with similar conditions. While no specific data are available in the literature to establish the correct stiffness of PD-AFOs for different degrees of ankle dorsi/plantarflexion deficits, in this study, a reference stiffness was used and adjusted according to the weight of each participant. Low bending stiffness allows for better foot and ankle dynamics in gait as it minimizes the restraint of the ankle in dorsiflexion, while providing sufficient support to resist passive ankle plantarflexion. A gait analysis study by [PERSON] et al.