You will be sitting for relatively long periods periods of time which is likely to cause aches and pains.

Hips, knees, backs and shoulders tend to suffer the worst.

Any exercises you can do before the retreat are likely to help to reduce the likelyhood of aches and pains, especially stretching, yoga and 'warming up' exercises.

Exercises that loosen the groin and hips are beneficial as tension in these areas increases strain on the knees. 

Ajaan Po's shoulder swinging exercise can be used in the days leading up to the retreat to loosen shoulders, neck and the upper back.

Thai massages can help you to loosen up generally and relieve back and shoulder pains before attending the retreat.