## 4 Discussion  
This study examined the associations between many gait parameters, derived from wearable sensors, and frailty levels and identified which parameters can differentiate between different levels of frailty. Gait speed was the most sensitive parameter for the identification of frailty. It should be noted that the Fried frailty criteria includes slow gait speed [2], which explains the high discriminative power of this variable. In the present study, the discriminative ability of gait speed can be used as a reference for comparison with other parameters analyzed. We found that the stride time was significantly longer in frail and prefrail compared to robust. This finding is in accordance with the results reported by [PERSON] et al. [16], which revealed the stride time is longest in frail (mean \(\pm\) SD, 1.2 \(\pm\) 0.1 sec. ), followed by prefrail (1.1 \(\pm\) 0.1) and non-frail (1.0 \(\pm\) 0.1). We suggest that stride time is sensitive for discriminating prefrail or frail from robust and determined a value of stride time for identifying individuals with prefrailty or frailty of 1.19 s, with sufficient sensitivity and specificity. We also found that stride time had a good sensitivity to separate frail from prefrail or robust; however, the specificity and area under the ROC curve were quite modest, thus potentially limiting its clinical usefulness. Other gait parameters that significantly differed between frailty levels were stance phase and swing phase. In comparisons of the average duration of the stance and swing phase time, the mean percentage of the gait cycle spent in the stance and swing phases was difficult to interpret due to the lack of sufficient data reported in the literature. We found a sufficiently sensitive and specific stance time estimate to separate prefrail or frail from robust, i.e., 0.68 s. The values for the sensitivity, specificity, and AUC of swing phase and stance phase percentage were quite modest. We found that prefrail and frail subjects had increased double support time. [PERSON] et al. [20] identified double support time as one of the most sensitive discriminators between these three frailty levels. However, in our study, double support time had modest validity to discriminate prefrail or frail from robust (AUC = 0.858), poor sensitivity (62.1%), and high specificity (96.7%). This study revealed that cadence was reduced in frail and prefrail compared to robust; this result is consistent with the results of [PERSON] et al. [16], showing variations in mean \(\pm\) SD cadence (steps/min) in frail (101 \(\pm\) 21), prefrail (106 \(\pm\) 9), and non-frail (118 \(\pm\) 6). Our study showed that cadence is a sensitive and specific gait parameter that discriminates prefrail or frail from robust. The estimated cut-off was 101 steps per minute. Our study has limitations. Even with a sufficient sample for the current study, we consider that it is too small to conduct more comprehensive studies: comparison of frail vs. prefrail having the robust group as reference in unbalanced groups; study specific effects and interactions between factors. The proposed gait parameters derived from our analysis must be validated in a larger sample to evaluate their true predictive potential. Other limitation is related to the gait assessment technique. During the 4-m walk test, additional sections for the acceleration and deceleration phases were not marked. During these phases, the walking speed was usually slower, which affected the measurement of the 4-m walking speed and led to errors. The gait speed was not measured by a dedicated device but calculated as the distance divided by time calculated as number of samples between the first gait event marker and last gait event marker divided by sampling rate. Adding a dedicated gait speed measuring device or increasing the walking distance would allow more consistent gait speed estimation; however, it might be limited by available space constraints during the testing in a clinical setting.