I wonder this from time to time. I don't recall ever seeing this explicitly mentioned in Scripture. It is implicitly addressed with examples of people standing, kneeling, laying protrate, etc. It has been years since I read this and my memory is NOT infallible but I believe Tertullian, one of my favorite early church writers, said that the proper posture was standing with hands lifted, palms upward and head bowed. I don't recall his justification. I remember this because it was contrary to the hands-lifted, face up posture of the Pentecostal Churches I attended at the time. (My goodness that was over 20 years ago. The years have flown by.) Are there biblically defined postures for prayer especially for New Testament believers or is this subject purely a cultural choice? The prevailing cultural norm as I was was growing up and to a large extent today was and is head bowed, eyes closed and hands clasped, standing or sitting. Ultimately my question is driven by the need to express reverence during prayer. Curious what your thoughts are.