In my personal experience it is extremely rare that some form of trauma was responsible for an implant rupture. Both saline and gel implants are very resilient and bend, so to speak, but don't break when absorbing a blow. If I understand the rigors of tubing correctly I would say there is little risk for your implants breaking while doing so. Of course, you want to wait until your surgeon feels you have healed sufficiently to partake in such physical exercise and your incision is properly healed to withstand submersion underwater should you tip over.
There should not be any problems with most any activity, including tubing, after your have recovered form the acute phase of your surgery (after 6 weeks or so). I have seen very few, if any, implant ruptures which were related to trauma (they are usually caused by weakness which forms in the seam or a fold of the implant).