I will use the term alignment to refer to the expanding the chest. We want to keep our ribcage lifted and expanded throughout the dance. A raised, open ribcage is necessary in order to maintain a good connection with our partner at the heart. A good practice to develop a sensation of good alignment is the bow:
- Begin by interlacing the fingers of your hands, or better still, grip one hand with the other
- Raise your interlaced hands them above your head so that your upper arms are in line with your ears; elbows do not have to be straight
- Take a few breaths in this position and you will feel your chest naturally expanding
Maintaining alignment during the dance
We want to maintain the sensation of an open chest throughout the dance. This may be difficult to do if we just have to focus on it. There is a workaround and it has to do with the tango estilo milonguero embrace. Throughout the dance we should keep the arms high at around shoulder level. In other words, in your dance hold the elbows at around the level of the shoulders (see also Floating Elbows practice and Visualisation and partnering technique).
If you have weak shoulders due to a sedentary lifestyle and struggle to keep your arms high for extended periods of time you can practice this by yourself regularly until your shoulders strengthen.
Dancing usually requires some strength but is not in itself efficient as a strength building activity because that is not its purpose.
Weak shoulders can be helped by bodyweight training such as Yoga (downward dog, head stands and hand stands) but in my own experience the most effective method to develop strength in the shoulders is the standing barbell press. This will lead to increased strength, given appropriate rest and nutrition, at any age.
* I will reserve the term posture to refer to the head-neck position as it was specified by F. M. Alexander, that is, floating the head over the spine and lengthening the neck.