Exercise Induced CollapseExercise Induced Collapse is caused by a gene in some Labrador Retrievers and is hereditary.
Labs with the gene will suffer a back-end collapse after and during strenuous exercise. The good news is that is doesn't get progressively worse with age, if the dog is calmed down and allowed to rest and relax, it will recover completely within minutes to an hour, and dogs with the gene can live normal, happy, healthy lives as long as their owners restrict their activities so a bout doesn't occur.
While it is disturbing to watch your very eager lab doing what they love to do best (retrieve things) and watch their back ends collapse as they try to drag themselves around (they have no clue that something is wrong), once you recognize that your dog may have the gene, and may suffer from EIC, preventing episodes is completely manageable.
It is important that if your dog does suffer a back-end collapse, or appears to be in distress after strenuous play, that you just don't assume it is EIC. You will want to go to the vet and work with them to determine if it is EIC, or could be the cause of some other problem (such as a slipped disc, neurological issues, or illness). Once you have received a diagnosis of EIC, work with your vet to determine the best course of action, and best level of exercise to give your pup the exercise they do need to maintain fitness and weight, and also keep them from having an EIC episode.
Article about EIC, how it was found, and what you can do to make your dog's life happy and healthy
DVM360 Article on EIC
Videos of dogs experiencing EIC
University of Minnesota Video
One person's experience with their lab and EIC