Back to the pool

When I was a kid, I remember being a pretty good swimmer. I had completed my grey level - now equivalent to Red Cross AquaQuest 9. Today, I stepped into a pool to train actively again - something I had not done in 15 years. The coach had encouraged us to get into the pool as soon as possible. After today's swim, I understood why he said that. After 6 laps of the pool I was exhausted - I even had to rest in between laps. Each lap is 50 meters. Looks like I have a lot of work ahead of me.