## 4 Discussion  
This study is part of a larger investigation on the effects of diabetes and DPN on foot and ankle biomechanics. Deeper understanding of multisegment foot kinematics in people with diabetes may help understanding the multiple alterations in foot biomechanics which likely occur at a later stage of the disease, as well as driving early rehabilitation treatments. The present investigation focused on the effect of diabetes type and DPN on multisegment foot kinematics by accounting for some of the main independent variables that may affect outcome. In agreement with previous kinematic investigations [17; 20; 21; 22], foot joints of participants with diabetes showed restricted ROM in gait compared with healthy controls, but some differences were also found between type 1 and type 2 diabetes. This is the one of the few studies reporting multisegment foot kinematics on a rather large population with diabetes which were grouped by diabetes type and by the presence of DPN. In a previous effort by the present authors, several correlations were found between foot morphological parameters, such a decreased metatarsal bone distance from the floor and segments inclination, with respect to plantar-load parameters [37]. To the best of our knowledge, the effects of covariates on foot joints ROM were not accounted for in previous studies thus limiting those investigations to the analysis of populations matched by age or BMI. According to the present dataset, BMI, age and normalized walking speed are significantly correlated to foot joints ROM in gait, albeit most correlation coefficients were small. In particular, age was positively correlated to reduced ROM at several foot joints, which may be associated with the onset of arthritis and the reduced joint distance in the older population [38]. On the contrary, normalized walking speed was correlated to increased ROM at several foot joints. This can be explained by the observed increased stride length (Table 2), which may result in larger joint excursions, at least in the sagittal plane. Participants with diabetes, regardless of its type and the presence of DPN, exhibited reduced sagittal plane ROM at several foot joints with respect to control. The significant reduced ROM was observed by accounting for the reduction in normalized walking speed in the groups with diabetes. Albeit not statistically significant at the ankle joint complex (ShCa), similar to what was reported previously [18; 21], DPN was associated with decreased ROM between shank and foot and at the midtransal joint. Significant reduction in sagittal plane ROM was also observed at the tarsometatarsal joint. This reduced motion may be consequence of altered mechanical properties of tendons [39; 40], of increased stiffness of plantar soft tissues [41] and of bone and joint disorganization [42] due to diabetes and DPN. While, in general, the patterns of joints rotations were similar between groups with diabetes and control throughout the gait cycle, one-dimensional SPM revealed some differences in joints kinematics. This was more significant for the temporal profiles of the midtransal and tarsometatarsal joints which presented significant offsets with respect to the controls. With respect to the control group, the dynamic posture of the midfoot in participants with type 1 and type 2 diabetes resulted more dorsiflexed to the calcaneus, whereas the metatarsus was more plantar flexed and inverted to the midfoot. In addition, participants with type 2 diabetes presented larger adduction of the midfoot to the calcaneus with respect to both control and type 1 for large parts of the gait cycle. These aspects would require additional investigations to be fully unraveled. Both DPN and non-DPN subgroups showed significant kinematic alterations at the distal foot joints. With respect to the control group, the dynamic posture of the DPN and non-DPN midfoot resulted more dorsiflexed to the calcaneus, whereas the metatarsus was more plantar flexed and inverted to the midfoot.