A model for local force dissipation by individual k-fibers to maintain robust mammalian spindle structure. Using micromanipulation to apply sustained forces (yellow circle, arrow) on individual mammalian k-fibers reveals that they locally dissipate force (red circles) using different physical mechanisms over different timescales (blue ramp, dashed lines indicate microtubule turnover) to robustly preserve global spindle structure (gray box). Key to this model is how k-fibers both remodel under and resist sustained force. The k-fibers remodel and locally dissipate force: they bend (second panel), lengthen through suppressing depolymerization at their plus and minus ends (third panel, small black “off” arrows with red X), and gradually break (fourth panel, new black plus and minus ends). In turn, k-fibers also resist force to preserve spindle structure: they do not increase their polymerization rate (third panel, small black “on” arrow), slide their microtubules, or detach from kinetochores or poles under force. Note that for simplicity, we do not diagram whole spindle movements and only show individual microtubules for the manipulated k-fiber. Thus, local dissipation and isolation mechanisms together preserve mammalian spindle structure under sustained forces: the former limit how far and for how long forces can be transmitted across the spindle, while the latter limit the spindle’s deformation rate and preserve k-fiber and spindle structure and their connections. Together, this model suggests local force dissipation at multiple sites as an engineering principle for the dynamic spindle and other cellular machines to robustly maintain their structure and function under force.