When the body segments act in a closed kinematic chain, are muscles most commonly acting in normal or reverse action?

What will be an ideal response?

ANS: Reverse action. This is when the proximal, rather than the distal, segment tends to be moved. This
will generally only happen when the lighter distal segment has been fixed on or by something.
When one grips a chinning bar, the distal forearms are fixed. A strong contraction of the elbow
flexors will pull the proximal humerus (and the connected body) upwards. Even though reverse
action can occur other than in a closed chain (e.g., chin-up example), fixing the distal segment
frequently results in a closed chain because weight-bearing is a common source of fixation. The
phenomena of closed kinematic chain and reverse action, although frequently associated, may also
be independent of each other.