Journal of NeuroEngineering and Rehabilitation

kinetic data were collected, we can just speculate that this TFC pattern is the combined effect of: the Variflex behavior, with strong energy storage in loading response [ 25 , 26 ] ; C-leg knee flexion in loading response [ 40 ] ; the confidence gained by this group of amputees on the capacity of the C-leg to sustain them at heel-strike and loading response, with no need to force extension. The ultimate effect for this pattern is a “ soft landing ” on the prosthetic side, which might increase comfort [ 32 ] . These speculations require future experimental confirmations, but match well with previous evidences that only a fraction of transfemoral amputees can fully rely on C-leg stability despite knee flexion during early stance [ 32 , 40 ] . This might be the effect of a specialized rehabilitation. Question Q2 Question Q2 asked if we can limit the study of temporal symmetry to stance leaving out step symmetry. Results support a positive answer. The regression of SPS vs SNS for each group and for ALL was quadratic, with excellent fits. SNS explained from 70 to 97% of the variance in SPS data in amputees ( R 2 , as reported in Table 2 ) . Even for Controls, who feature a very small peak-to-peak SNS (.97 to 1.01), the explained SPS variance is 50% with a RMSE as small as 0.017. Fig. 6 a Box plot for the first peak symmetry index (P1S) over the groups; b Results of the Kruskal-Wallis test; c Pairwise comparisons: non- overlapping lines indicate a statistically significant difference. TFM: transfemoral mechanical knee users, TFC: transfemoral C-leg users, TT: transtibial amputees Table 3 Numerical values for the indexes of symmetry SNS (stance), IMS (impulse) and P1S (first peak) SNS IMS P1S Median 25th 75th IQR Median 25th 75th IQR Median 25th 75th IQR TFM 1,22 1,20 1,29 0,09 1,32 1,20 1,55 0,36 0,91 0,90 1,06 0,16 TFC 1,11 1,05 1,15 0,09 1,16 1,00 1,24 0,24 0,98 0,80 1,04 0,24 TF 0,94 0,87 1,05 0,18 TT 1,03 1,00 1,06 0,06 1,02 0,96 1,13 0,17 1,07 0,98 1,24 0,26 CONTROLS 1,02 0,98 1,01 0,03 0,95 0,91 0,99 0,09 0,98 0,94 0,99 0,05 For each group, the median is reported together with the 25th, 75th and interquartile range (IQR). TFM transfemoral mechanical knee users, TFC transfemoral C- leg users, TF transfemoral, TT transtibial amputees Cutti et al. Journal of NeuroEngineering and Rehabilitation 2018, 15 (Suppl 1):61 Page 36 of 72