Harrie Irving Hancock - Physical Training for Business Men (1917)
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Need a few exercise tips? Here you go! Don't worry, there's also another one for women (though the photos are much more bland). It's all the usual kind of vague clean living ideas that still exist in new forms a century later.
Not all the advice will be very useful today. For instance at one point he suggests "Should the reader live or at any time be near an American Army post, he should make an effort to secure permission to be present at one or more of the drills." Just imagine how such a request would go over today.
Hancock (1866/68-1922) mainly wrote juvenile adventure books such as the Motor Boat Club and Grammar School Boys series. In 1916 he wrote four such books describing a German invasion of the US in 1920. For such a prolific author surprisingly few titles seem to have been digitized - the most are at Project Gutenberg.