just lay naked in the sun, you get far infrared, near infrared, and everything inbetween.
Then, for an added kicker, swing an axe or garden hoe or do some other work that makes you sweat.
Explains why most Mexicans are smarter than americans, they've sweated out their toxins, while the americans sit indoors pecking away at their computer keyboards.
I dug a few trenches last week in prep for pouring a concrete slab. Sweated like hell and got a lot of sun. Even had to take a shower because my hair was messed up and I was a little dirty. Such work.