Yeah, you made it just sound like they got good physical condition from just 10 days of training.
A coach can steer a player in the right direction but at the end of the day its all on the player.
At what level?.
You say 10 months of a regular season + cup; which usually is a high level source of competition in Europe but then you state; at a subzero level?.
A subzero level soccer player has only one direction to go when he starts training, physically & technically.
For me personally…
Even on vacation, I make sure of having a gym in the vicinity & do workouts (not to the standard during the season). After the vacation when I return home, I usually note a reduction in every part of physical performance than what I went away prior to my holiday. I have to reduce weight numbers, VO2 is down… Its not long before I start getting it back to where it was, 2 weeks, If I take care, eat, sleep & exercise ‘well’ offseason away from the sport). Again its on the player.
Them ‘10 day’ players you state have probably been at it for 3 months or all year.