RG.. er, I mean 6xlegz ...lol I would lean toward a larger, more sturdy chi if you want to take him running with you.. My keely(Yorkshire terrier) is from an excellent breeder but she is over the standard at 8.5 lbs. But I still consider her tiny. But she is also very very sturdy and can handle runnign with me and even loves to run along side my bike .. Sometimes breeders have dogs that will be a little out of standard so its something to think about. Was it you that posted on the other forum about seeing the man running with his chi? Is that what drew you to the breed? lol.. If I were you I would not go under a 5 lb dog. The smaller they are the more steps they need to take to catch up with you. lol.