is tensing
Presente progresivo para el sujetohe/shedel verbotense.

tense

You know, your voice is tensing up.
Tú sabes, tu voz se está tensionando.
I said earlier to someone that if he regulates his speed it shows that he is tensing his muscles.
Le dije a alguien anteriormente que si regulara su velocidad se demostraría que está tensando sus músculos.
Palabra del día
la huella