I feel belastbaarheid has more to do with physical capabilities than mental (i.e. stress) resilience. In my glossary I've noted that it can mean "capacity for work", "work capacity", "workload capacity", "capable of working x hours a week", "capable of performing so many hours work" or that someone has "a work capacity of x hours per week". The problem with a word such as belastbaarheid is that it's not really suited for people, but is used as such. I've also noted the Eurodicautom entry:

beoordeling van fysieke balastbaarheid - physical capacities appraisal
(procedure whereby determination is made of the physical activities which a person is capable of performing and the working conditions under which he can safely be employed).

Submission - Inquiry into Employment and Workplace Relations ...
restrictive work capacity criteria for the pension creates a ”Welfare trap‘ where pensioners have a strong reason not to risk testing their capacity to ...
www.aph.gov.au/Senate/committee/clac_ctte/welfare_to_work/s...

Work and Income | Manuals and procedures
the Medical Appeals Board must decide whether the client meets the Medical criteria or Work capacity criteria for the relevant Benefit and consider whether ...
www.workandincome.govt.nz/.../reviews_and_appeals_child_dis...