Hiking and running are different questions here
Split the question in two, because a Bernese Mountain Dog gives you two different answers. As a hiking companion, a fit adult Berner is a cheerful partner for moderate trails: steady walking pace, regular stops, and the kind of unhurried exploration where a dog can sniff, paddle in a stream, and rest in the shade. As a running partner, the breed is a poor fit, and choosing one for road miles usually ends in disappointment for the owner and strain for the dog.
Understanding why comes down to how the dog is built. A Berner is a heavy, deep-chested giant wrapped in a thick double coat designed for Swiss winters.
Why sustained running does not suit a Berner
Weight and heat are the twin limits. Every stride lands with a giant breed's mass behind it, and repetitive pounding on pavement is unkind to hips, elbows, and shoulders that are already carrying a lot. At the same time, that dense coat traps heat, and a large dog generates plenty of it while running. Berners overheat faster than most owners expect, and a dog who is eager to please may keep going past the point where he should stop.
Short, easy jog intervals on soft ground in cold weather are a different matter, and a fit Berner may enjoy them. But if your training plan involves regular distance running, especially in a warm climate, a lighter sporting breed will match your life far better.
Getting the most from Berner hikes
Build distance gradually, the way you would for any deconditioned walker, and let the dog's recovery tell you the pace: a Berner who is bright and keen the next day coped well; one who is stiff or reluctant did too much. Carry water for the dog as well as yourself, stop in shade before he is panting hard, and favour morning outings and wooded or higher trails in warmer months. Winter is this breed's season — many Berners are visibly happier and more energetic in snow than on a summer path.
Check paws after rough ground, watch for limping that appears after rest, and keep puppies and young dogs to short, gentle walks while their growth plates are still closing. A young giant's enthusiasm is not a safe guide to what his skeleton can handle.
Conditioning and health checks for an active Berner
Keep an active Berner lean, because extra weight multiplies every joint concern and heat problem described above. A pre-season vet check is worthwhile for a dog you plan to hike regularly, particularly as he moves into middle age, and any new reluctance to climb, lagging on familiar routes, or heavy panting that settles slowly deserves a vet conversation rather than more conditioning.
Records that travel with an active dog
Hiking often means crossing into new areas, using new boarding kennels for part of a trip, or occasionally needing a vet who has never met your dog, and KinsLe Pet Passport keeps your Bernese Mountain Dog's records together in one portable packet, ready for vet visits, travel, and boarding handoffs when you are far from your usual practice.