Aim:
To compare the manual diaphragmatic relaxation technique and placebo intervention on selected parameters in the neck in smartphone users with non-specific neck pain.

Material and methods:
A randomized placebo-controlled trial included 38 women. Neck range of motion and pressure pain threshold were assessed in participants who were assigned to the Therapy group or a Placebo group. The intervention consisted of a single manual relaxation of the diaphragm in the supine position. Repeat measurements were taken after the intervention.

Results:
There was a statistically significant effect of therapy on range of motion in both studied groups (p < 0.001; partial .2= 0.58. Statistically significan improvement in the range of motion concerned three planes of movement and all analyzed measurements. There were no statistically significant difference in range of motion between groups. Comparison of pressure pain threshold at the level of the 4th cervical vertebra before and after therapy showed significan differences only in the Therapy group (p=0.04, d=0.45). No statistically significant differences in pressure pain threshold were found between the groups either before or after therapy.

Conclusions:
Global summary of results does not allow for drawing final conclusions regarding the effect of manual diaphragm release on neck parameters in smartphone users with non-specific neck pain, taking into account the results of other researchers, diaphragm therapy is recommended for people with neck pain.