Having a dog with a potential injury is something that can really suck and I feel for you. Dogs are such super athletes and don’t want to slow down for anything and it’s so hard to temper their movements.
I strongly suggest that you invest some of your petting time getting to know your dog’s muscles through massage. You probably already pet him in ways that are massaging, and if you pay attention (and with a little youtube university on massage techniques) to the feel of his muscles (particularly the ones around his trouble spots) you might be able to notice changes. Things like tightness, sensitivity, less relaxed or elastic, even just a different feel that you can’t quite put your finger on, can be useful information. Post activity you can gauge whether an exercise was too much by investigating for soreness. If your dog is sore, you know to back off on the degree (after a little rest). Massage also helps loosen and repair soft tissues. Win-win, right?
There are details about warm up that I can share if/when you are ready. Bodies are bodies and the rules are pretty much the same for physical activity between our species and dogs. Make sure that you don’t overload the system with the occasional long workout. Rather, find outlets to regularly work your dog that DON’T involve fetch. I love fetch just as much as my dog, but I love a sound dog more and there’s just no way that dogs can chase after an erratic bounce, dive down at speed, stress all those already minimally reinforced tendons and ligaments in the shoulders, and not cause themselves harm. Just because you don’t see signs of injury does not mean they are absent. Animals need to hide their injuries as a survival mechanism. That, plus some dogs have so much adrenaline that it makes them unaware of their pain.
Lastly, you need cardio (which is trotting (or swimming), not sprinting) for continued durations (starting with as little as 5 minutes may be necessary). Cardio is often neglected because we humans move so slow that it’s hard to match their trot pace. When biking, soft surfaces are critical (never on roads). Also, keeping them slow as they warm up can be hard, but is necessary.
Don’t know where to start? In Joy would love to help! But, first, you need to find a qualified vet and get the root of the problem. I spent years getting nothing but, “Rest and NSAIDs” advice from vets (and it wasn’t free advice, either). I’m a huge fan of VOSM and they have locations around the world. They are on the leading edge of regenerative therapy and if you’re lucky, you’ll be around the Seattle area and can get Alicia Lamb’s hands on your dog. Once your dog is cleared to return to activity, let’s talk about getting and keeping your best friend fit and healthy.