One of the things that constantly amazes me about our ancestors is how much more exercise they got in the course of a day, and especially how much exercise writers and scientists would get. Consider, for example, this account of early 19th-century social reformer Francis Place, from Graham Wallas’ biography The Life of Francis Place:
A very good description of Place and his daily life about this time, was given in the Northern Liberator. “Francis Place… is in the sixty-fifth year of his age. He is about five feet seven inches high, with a head which would delight the phrenological taste… and is of a stout, stalwart frame. A walk of twenty or thirty miles a day is one of / his favorite amusements; but his time, from six in the morning to eleven at night, is generally spent in his library, where he is surrounded with books, pamphlets, journals, and memoranda of every kind.” [177-178]
Place also spent some time at Ford Abbey, Jeremy Bentham’s home between 1814 and 1818.
He left this account:
“I rise at six and go to work; at nine breakfast in the parlor…. From breakfast time to one o’clock I am occupied in learning Latin; this is also done aloud in the walks…. At one we all three walk in the lanes and fields for an hour. At two we all go to work again till dinner at six…. After dinner, Mill and I take a sharp walk for two hours, say, till a quarter past eight, then one of us alternately walks with Mr. Bentham for an hour; then comes tea, at which we read the periodical publications; and level o’clock comes but too soon, and we all go to bed.” 
These multi-hour walks were not at all unusual, even for people who spent a lot of time walking to, you know, just get from Point A to Point B. Just one more example, from the biography of one of Place’s intellectual descendants, the late 19th-century Utilitarian philosopher Henry Sidgwick, describing his habits as a student at Cambridge in the 1850s:
For active exercise he was restricted to the daily walk between two and four, which was then the common practice of the reading man who did not boat and could not afford to ride. It must be remembered that in the fifties at Cambridge boating was the only organised sport within the reach of everybody. There was no regular football ; cricket was confined to the May Term, and few colleges had their own grounds; racquets and fives were only just beginning; croquet (if that can be called exercise), lawn-tennis, the bicycle, and polo were none of them yet invented. Sidgwick had no aptitude or liking for boating ; and even if he had tried it, the exertion would have been too great to be permitted after he fell ill. In one way the attack was a blessing in disguise, since it forced him to realise the importance of regularity in open-air exercise, which otherwise, with his insatiable intellectual curiosity and his ever-growing range and variety of interests, he might have been tempted somewhat to neglect.