Italian to English Medical Sports / Fitness / Recreation flexibility exercises

I need to correct the translation of the above phrase (highlighted with *) in the following text, which concerns flexibility exercises.

TARGET
A stretching session in itself creates a general feeling of relaxation, both by relieving tension in the actual muscle and indirectly reducing the basal tone of all the body’s musculature, as well as slowing the heart rate. These last effects are above all evident in the case of comfortable stretching postures which are held for long periods and are accompanied by controlled breathing. In fact, it is difficult to relax the muscles if the positions assumed are difficult to hold, whether due to balance requirements or tension in muscles which are **supporting the weight of other regions**, or simply due to pain caused by pressure at certain contact points.

SOURCE (last sentence only)
Difficilmente, infatti, si ottiene un effetto rilassante se le posizioni assunte sono difficili da mantenere per la richiesta di equilibrio o di tensioni muscolari **a carico di altri distretti**, o addirittura dolorose, per la pressione che si verifica in alcuni punti di contatto.

The meaning of the translated phrase given here seems to be in contrast with the meaning of the source, but am not sure how to amend it. I thought of translating 'a carico di' as 'reliant/dependent on' and am thinking that the concept of weight doesn't come into it.

Any further suggestions appreciated!