...vapocoolants work by causing a sudden drop in skin temperature which causes a barrage of sensory impulses to enter the spinal cord. These impulses have an inhibitory effect on local pain and actually cause the muscles under the sprayed area to relax and accept a subsequent stretch.
This stretch may actually break the "contracture knot" that is speculated to exist in most trigger points. This is crucial for trigger point deactivation because under normal circumstances, the muscles which house active trigger points will be painful while under stretch.
The pain activates the sympathetic nervous system (aka the "fight or flight" part of the nervous system,) which creates a reflex contraction of the involved muscle(s), thus limiting the potential range of motion.
To make a long story short, when using the spray and stretch technique, the "stretch" part is the action while the spray is the "distraction." The extreme cold serves as a source of "proprioceptive confusion" of sorts which then allows better muscle excursion and extensibility.
- A Caution:
Since trigger points form for various reasons, one should always ask whether removal of any given trigger point(s) is the wisest choice. Current thoughts by some of the leading experts on trigger points include the theory that trigger points may actually serve as low-energy tension-producers that might be used to splint an unstable joint or assist in the maintenance of a frequently assumed occupational or sporting posture.
In other words, some trigger points could be serving as a functional "crutch" of sorts. Removal or deactivation of the trigger point might remove this crutch.