Nonverbal communication (NVC) is usually understood as the process of sending and receiving wordless messages.
As a trainer you should be aware of the following:
body language or posture;
facial expression and eye gaze;
object communication such as clothing, hairstyles or even architecture;
symbols and info graphics;
features of speech such as intonation and stress and other paralinguistic and as voice quality, emotion and speaking style.
The best known theory is that of the American psychologist Mehrabian.
He states that when it comes to expressing feelings:
55% of the communication consists of body language,
38% is expressed through tone of voice and only
7% is communicated through words