At any rate, I doubt that a 45 minute stroll around the neighborhood would cause a problem.
Percisely there is a big difference from a liesurely stroll vs jogging etc. The concept of free play is the dog will not engage in activity that cause it pain. But anyone that has watch puppy play is sure to witness activity that is far more stressfull and traumatic on the joints, tendon, muscle and ligiments, than walking is.
she recommends switching the puppies to adult formula at 4-5 months old
Which was sound avice 10-15 years ago. It is not so clear there is benefit to doing so with the advant of Large breed puppy food, that is lower in caloric content and calcium and phosphorous than traditional puppy food and on the calcium and phosphorous font lower than adult food as well. A strong argument can be made for keep a puppy on large breed puppy food until the growth plates close. However there is vast difference between brand of commercial dog food so making a sweeping generalization is not appropriate.
you seem often to reply to messages on here with quotes from books.... and I don't know if you are a vet or something like that..... or maybe you are a Google fan like myself at times!
Not a vet but when it comes to putting forth an argument it is important to substantiate it. So any link Is provided to Either substaintiate and argument or and more likely to provide more detail and elaboration than can be done in this type of forum. Since I know many or most are unlikely to ready said link I include a quote for the purpose of substaination.