Modern fitness culture starts in January and treats winter as the problem. The classical calendar says almost the opposite: this is the six weeks in which the body can actually build, and January is the tail of it, not the beginning.
The reasoning is consistent. Bala — strength, immunity, capacity — peaks in Hemanta and Shishira. Agni is at its strongest, so food is genuinely converted into tissue rather than sitting as residue. And the classical instruction on exercise scales with the season: the texts recommend exertion to half of one's capacity as a general rule, and identify the cold seasons as the only ones where full-strength exercise is appropriate at all. In Grishma and Varsha the same effort is explicitly discouraged.
How you know you are at half capacity, in the tradition's own markers: sweat on the forehead, nose, armpits and joints; breath moving into the mouth. That is the point to stop. Push past it, and you are spending reserves rather than building them — the distinction the texts care about far more than duration or load.
So the fortnight: train properly, and eat to match. This is the one time of year where a genuine surplus is the correct instruction rather than an indulgence. Protein in whatever form you take it, ghee, whole grains, root vegetables, nuts, dates, milk. The strengthening herbs belong here — ashwagandha and bala are named for exactly this — and they work far better in a season with agni behind them than in the monsoon, when most people think to start them.
Also in the window: abhyanga before exercise, not after, which is the classical order and makes more difference than it sounds like it should. Udvartana — dry powder massage — for anyone who needs the warmth without the oil. Warm baths. Real sleep, which the long nights are finally offering.
And one thing to protect: the head, ears and neck against cold wind. It is the cheapest preventive measure of the season and the most consistently ignored.