They may be little, but are mighty. I am a runner (not as fast as in my younger days, of course, but still run). My Cali is $ pounds and 7.5 years old. Has been running and swimming laps with me since day one. She can do a 5Knwith no trouble (if the concrete if not hot, if it is, forget it). My son is military and he runs about 8-9 miles a day - when she goes out touring with him (and usually about a dozen other airmen) they say she can make about 5 - 6 miles (remember she has been doing this since 10 months old, and does agility daily) before she starts to give out, at which time he pops her in his jacket or shirt with her he's hanging out and they finish.
Message here is - they are very capable of the exercise and it is good for them. Keep them hydrated and watch out for hot Tarmac! Truth is most of them could out run us
Got to tell you how darling it is to see her running her little heart out with a dozen tough looking guys on the airbase