  Most QCD models of high energy collisions predict that the inelasticity $K$
is an increasing function of the energy. We argue that, due to percolation of
strings, this behaviour will change and, at $\sqrt{s} \simeq 10^4$ GeV, the
inelasticity will start to decrease with the energy. This has straightforward
consequences in high energy cosmic ray physics: 1) the relative depth of the
shower maximum $\bar{X}$ grows faster with energy above the knee; 2) the energy
measurements of ground array experiments at GZK energies could be
overestimated.
