I do them too, but like Danimal and Jumperuk said, not so many.
I like to do them like "Ross" and Verkoshansky" said.
"The quality is more important then the quantity". I use them between weightraining and do only 6 – 7 times after each set.The box is no more then 25 cm. good for older athletes.
After that i go for a warmup-run, some drills, some stadiumsteps and a couple windsprints 60- 80 – 90 %.
The difference with last saison, i feel no pain, no strain and i have no more achillistroubles. I cannot speak for younger athletes, but in our time we tought that quantity was very important and a day rest a great sin.:))
Participant