*Limitations*

A limitation of the current study is that data collection was limited to two days and the maximum covered distance was estimated by multiplying the number of steps, with the step length measured with the 10 MWT. Although a larger number of measurement days than 2 would have resulted in a more accurate estimates of the maximal number of consecutive steps, the walking bouts of at least 300 steps in the elderly control group indicated that 1–2 days was sufficient to indicate their mobility. The estimated covered distance was most likely an overestimate since daily life walking was less regular than walking during a 10 MWT. Inertial measurement units attached to the shoe or ankle would be a better alternative as it estimates gait velocity and step length in a valid and reliable way [36,37]. We chose the most convenient and easy way, by focusing on the number of steps, which could also be simply assessed by using, for example, a smart watch or a smart phone [38–41]. The relatively small sample size did not allow us to perform a sub-analysis within the persons with a lower limb amputation. We expect that the level of amputation and reason for amputation group would affect the maximal covered distance. Persons with a transfemoral amputation would most likely have a reduced walking distance compared to the persons with a transtibial amputation.

### **5. Conclusions**

The current study indicates that mobility is highly affected in most persons with a lower limb amputation and that the SIGAM mobility grade does not reflect what persons with a lower limb amputation actually do in daily life. Therefore, objective assessment of the maximal number of consecutive steps of the maximal covered distance, is recommended for clinical treatment.

**Author Contributions:** Conceptualization, C.J.H. and N.L.W.K.; methodology, C.J.H. and N.L.W.K.; software, N.L.W.K.; validation, C.J.H. and N.L.W.K.; formal analysis, K.T.J.B., M.D. and N.L.W.K.; investigation, C.J.H., K.T.J.B. and M.D.; resources, C.J.H. and N.L.W.K.; data curation, C.J.H. and N.L.W.K.; writing—original draft preparation, C.J.H., K.T.J.B. and M.D.; writing—review and editing, C.J.H., R.F.v.E. and N.L.W.K.; visualization, C.J.H. and N.L.W.K.; supervision, N.L.W.K.; project administration, C.J.H.; funding acquisition, N.L.W.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We thank all our participants for their time and effort. We would also like to thank Ivo Koekkoek, OIM Orthopedie Nijmegen, for inclusion and recruitment of the lower limb amputees.

**Conflicts of Interest:** The authors declare no conflict of interest.
