Kennemerduinen, today. Interval training [go hard, go easy; united in a balanced training]

"A good walker must connect grace with quickness and perseverance, whatever be the nature of the ground, whether hilly, sandy, or slippery. To walk well, is a great art, and deserves to be attented to by parents from the earliest years of their children; their habit here, as in most cases, is all powerful. It is an exercise which may be practised in any place, though no so well in a common excerise-ground as elsewhere. [...] I. Grace [...] A straight natural carriage of the whole body, particularly of the head, without anything artificial, or affected; a light, yet firm step with the whole sole of the foot at once; the knees straightened, whenever the foot touched the ground. The feet should be turned a little outwards. […], so that the body may not lose its balance. II. Duration, cannot be acquired except by much practice. Walks [regularly] taken, and gradually increased, and then longer excursions and journeys on foot, are requisite. Perseverance in walking and strength to carry some weight, is an important accomplishment. […] IV. Indifference as to locality. Walking over unlevelled ground is much more difficult, but at the same time a greater exercise. The same is the case in walking trough deep sand. If a hill is so steeped, that every step requires considerable exertion, then the motion is called ascending, which may be practiced with and without a load. [...]  Running, if practiced with precautions, is an exercise extremely salutary to the chest and lungs. […] Posture and body: Breast out, shoulders back, upper part of the body forwards; upper arms close to the body, elbows bent, and kept backwards. The steps light, and with the ball of the foot, not with the whole sole. The mouth shut; breathing long, uniform, and more trough the nose, than trough the mouth. […] Cool and calm days are best for this exercise. In the beginning run with, not against, the wind. When very much heated, or out of breath, stop. [...] After running, cool yourself by walking about, not by standing still, nor lying down."

From: 'Treatise on Gymnasticks, taken chiefly from the German of F.L. Jahn'  [ translated ] by Charles Beck in 1828 ("It is a well known fact that a subject, whether it be entirely new, or only more attended to, will exercise an influence upon language, in proportions to its importance; it will either coin new words, or transplant them from other languages, or impart a new shade or greater distinctness of meaning to some already existing [...] If the present work facilitates the introduction and management of gymnastic exercises, my wish is fulfilled, and I shall consider myself richly awarded for the trouble which the execution of it occasioned.") 

See also: Friedrich Ludwig Jahn  a.k.a. 'Turnvater Jahn' (1778 - 1852)  at Wikipedia (English)