Quantity Matters?

Every Thursday is my swimming course. I went for the 4th lesson this week. The routine was to swim 2 laps of the standard 50 metres pool. I was breathless after just ONE lap. *SHOCK* 20+ laps was what I used to swim, every week (about 8 years ago). In disbelief, I continued to swim the 2nd lap and I almost did not pull through! Goodness! My fitness level is bad =(

Surprisingly after just 3 weeks, my fitness has improved. I suspect it is due to my weekly schedule packed with exercising activities. There are 7 days a week, I swim 4 times a week, go for yoga once and badminton once a week. That means I exercise 6 days a week!! I was not breathless after 2 laps at my 3rd lesson =)

Can I conclude that for exercising: quantity matters?