(Vikings, or indeed any historic peoples known for being physically strong in battle.)
If I do any kind of moderate physical exercise, I will be very stiff and unable to run the next day, unless I have properly stretched before and after.
It seems like it would be a big tactical advantage in battle to have warriors who were fully warmed up and stretched beforehand, in order to be able to fight again sooner.
Is there any evidence that cultures like the Vikings did so?
The question of did Vikings/Romans/Greeks/etc. warm up before battle has come up numerous times on the sub, and almost never generated any answers. The best answer for medieval warm ups before battle would be Did knights or other medieval armies stretch, or otherwise "warm up" before a battle? written by u/mrleopards which talks about "10th and 11th century Byzantine Roman armies, as well as their late antique predecessors." They draw a conclusion near the end that might be relevant.
Adding to that, the last paragraph of How much military training did the average European medieval soldier get? written by u/Rittermeister is likely relevant here.