A note on necessary conditions for blow-up of energy solutions to the Navier-Stokes equations

In the present note, we address the question about behavior of $L_3$-norm of the velocity field as time $t$ approaches blow-up time $T$. It is known that the upper limit of the above norm must be equal to infinity. We show that, for blow-ups of type I, the lower limit of $L_3$-norm equals to infinity as well.