Exercise with light dumbbells as propagated by the famous bodybuilders at the end of the 19th century (people like Prof. Attila, Sandow, Strongfort) could fit the bill. This training approach goes against many accepted truths today but it's what these people swore by.
If this sounds interesting to you at all I highly recommend David Bolton's book "The Lost Secret to a Great Body". It is very well argued. Here's an excerpt that I found intriguing:
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The first thing you have to realise is that THIS IS NOTHING TO DO WITH WEIGHT TRAINING. THE WEIGHTS THEMSELVES ARE ONLY INCIDENTAL - IT’S WHAT YOU YOURSELF ARE DOING WITH YOUR MUSCLES THAT IS IMPORTANT.
The second thing you have to realise is that the very word “exercising” - as in the previously mentioned Mr Pope’s chapter on “The art of exercising” - was being used then in a different way to mean something totally different from what we think of as “exercising” today. For a start it was supposed to be a physical “art”.
We tend to think of proper “exercise” as something difficult and physically taxing - the man who’s just come back from a ten mile run, panting and bending over to get his breath back, his legs wobbling underneath him, has just finished his “exercise” - the person lying in a sweaty heap of exhaustion after one and a half hours hard cardio on the machines, static bike and cross trainers has just “exercised” etc... by this definition exercise is taxing on one’s system and needs recovering from.
This is not what was understood by the word exercise at the time the light dumbbell protocol was popular - that would have been “hard training” maybe or “a session of thorough physical work”. Exercise was supposed to be invigorating and enervating - to put something into your system rather than take something out of it, to build up rather than tear down.
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Bonus: There is also a chapter how this specific type of training could help in boxing by improving your control over individual muscles and thereby making you less muscle bound.