According to a study by Ohio University, body posture affects our self-esteem, and the way other people see and feel about us. In summary:

1. People with good posture, and who stand up straight, are perceived as being more attractive and more confident.

2. People who stretch out their arms and use their hands when they speak seem more alive, at ease and self confident. It also increases testosterone levels – which enhances self confidence and self esteem.

3. Clenching your fist or your hand and arm muscles helps to strengthen resolve, increases self control and enhances our feeling of self-efficacy.

4. Leaning forward in interest when someone is talking shows we’re fully engaged in the conversation. In addition to this, it conveys self assurance and self respect.

5. When we give someone a hug it releases oxytocin. This hormone is associated with trust, loyalty, caring, sympathy and offering encouragement and support.  And when we give to others we feel good about ourselves!  

For more information see: http://www.sciencedaily.com/releases/2009/10/091005111627.htm