Good thermal clothing makes the difference
A good undershirt is very important when training in colder conditions. Both runners and cyclists benefit from an extra layer when conditions are appropriate. Underwear also has a function in the summer, because it wicks away moisture. This way your body can regulate its temperature well in any circumstance.
Undershirts made of merino wool are known to be extremely warm in winter. An ideal first layer. This light fabric feels soft and remains odorless, even after your toughest session.