On a cellular level, massage encourages cell proliferation, increases fibroblast activation and collagen production and realignment, essential in scar tissue and wound healing. It also promotes DNA synthesis and replication, increases macrophages and skeletal tissue, and phagocytosis essential for creating an anti-inflammatory response.
The massage techniques also help with inflammation by increasing the circulation both blood and lymphatic to dispose of the toxins, and increasing the oxygen and nutrients brought to the area. This increase of circulation is also essential in releasing muscle tension and improving the muscle quality, this can be in both strong and weak muscles.
In horses I see a lot of asymmetries, however its important to understand that we all have asymmetries and us as riders also are to blame for our horses asymmetries, most of the time I see a horse with a weaker side, and by building this side up with muscle strength it helps to realign the horse again. But, we can improve them by releasing the muscle and allowing the muscle to strengthen, as with any building muscle they get tense and then are used efficiently, the increase in circulation also increases muscle energy, so keeping on top of this is hugely important in any circumstance whether maintenance or rehabilitation.