If you're overweight, combining aerobic exercise with strength training has the biggest effect on frailty. This is a small, but exceptionally well-conducted trial that is getting press because 1) it got into the New England Journal of Medicine, easily the most influential medical journal in the world, and 2) it addresses a functional outcome, not just weight. It seems to go under-recognized that obesity leads not only to inferior cosmesis and an increase in heart disease, sleep apnea, arthritis, and what not, but that it actually makes people frail. In my time running a medical/surgical weight loss clinic, we routinely asked incoming patients if they were able to get themselves off the floor in case of a fall. The patients were almost always surprised by the question, but many of them, after some thought, said that no, they would not be able to get themselves up after a fall. They were that frail. 

Speaking of exercise, your watch or other wearable sucks at telling how many calories you've burned. This isn't a surprise, given the disparate results I've seen from my old, broken Nike Fuel Band, my Garmin GPS, and apps like MyFitnessPal. And even though I've never heard of the Journal of Personalized Medicine before ten minutes ago, the methodology of the paper is solid. But the results were best, strangely, with cycling. This gives ammo to the old argument that people who like data (speed, weight, power, HR, etc) are naturally drawn to cycling.