Table 2 Summary of findings

Outcome

Results

Summary with the certainty of evidence (GRADE)

 Skin conductance (1) (sudomotor activity)

Mobilizations increased SC compared to sham in 10/10 studies.

Mobilizations produced mean percentage changes of SC ‘integral measurement’ that were 13.75 and 9.34% greater than with the sham respectively for change from baseline to intervention period and change from baseline to post intervention period (3 studies in meta-analysis).

Mobilizations probably produce a bilateral increase in skin sympathetic nerve activity during both the intervention and immediate post intervention periods regardless of the area treated (moderate-certainty evidence).

 Skin temperature (1) (vasomotor activity)

Mobilizations had no effect on skin temperature in 5/8 studies which could not be included in meta-analysis.

We are uncertain whether mobilizations have no acute effect on skin sympathetic nerve activity (very low-certainty evidence).

 Skin blood flow (1) (vasomotor activity)

Mobilizations had no effect on skin blood flow in 1/2 studies, while the other study found effects in opposite directions (both increase and decrease). Studies could not be included in meta-analysis.

Please note that we based our conclusions on skin conductance (higher certainty of evidence). See narrative synthesis for details.

 Heart rate (2)

Mobilizations had, generally, no effect on heart rate. There was no effect during both the intervention (2 studies included in meta-analysis) and post intervention periods (3 studies included in meta-analysis). Another study also reported no effect. However, 2 studies found a significant increase during the intervention period, and another study reported a significant increase during the post intervention period.

Mobilizations may have no acute effect on cardiovascular autonomic activity (very low- to low-certainty evidence).

 Blood pressure (2)

Mobilizations had, generally, no effect on blood pressure. There was no effect during the intervention and post intervention periods (2 studies included in meta-analysis). Another study also reported no effect. However, 2 studies found a significant increase compared to sham.

 Heart rate variability (2)

Mobilizations had no effect on HRV in 1/1 study.

 Respiratory rate (3)

Mobilizations increased respiratory rate compared to sham in 3/3 studies which could not be included in meta-analysis.

We are uncertain whether mobilizations increase respiratory rate via an increase in sympathetic activity (very low-certainty evidence).

 Salivary alpha amylase activity (4)

An atypical mobilization technique decreased the salivary alpha amylase activity compared to sham in 1/1 study.

We are uncertain whether an atypical mobilization technique decreases the salivary glands sympathetic nerve activity (very low-certainty evidence).

Outcome

Results

Summary with the certainty of evidence (GRADE)

 Skin conductance (1) (sudomotor activity)

Spinal SNAGs had no effect on SC in 3/4 studies.

Two studies could be included in meta-analysis, the results showed no statistically significant difference between the technique and the sham for both intervention and post intervention periods.

Spinal SNAGs may have no acute effect on skin sympathetic nerve activity (low-certainty evidence).

A peripheral (elbow) mobilization with movement increased SC compared to sham in 1/1 study.

We are uncertain whether peripheral ‘mobilization with movement’ techniques increase skin sympathetic nerve activity (very low-certainty evidence).

 Skin temperature (1) (vasomotor activity)

Spinal SNAGs had no effect on skin temperature in 2/2 studies which could not be included in meta-analysis.

We are uncertain whether spinal SNAGs have no acute effect on skin sympathetic nerve activity (very low-certainty evidence).

Please note that we based our conclusions on skin conductance (higher certainty of evidence).

 Skin blood flow (1) (vasomotor activity)

A peripheral (elbow) mobilization with movement increased or decreased skin temperature and skin blood flow compared to sham in 1/1 study according to the measurement area.

We are uncertain whether peripheral ‘mobilization with movement’ techniques modulate skin sympathetic nerve activity (very low-certainty evidence).

 Heart rate (2)

A peripheral (elbow) mobilization with movement increased heart rate and blood pressure compared to sham in 1/1 study.

We are uncertain whether peripheral ‘mobilization with movement’ techniques modulate cardiovascular autonomic activity (very low-certainty evidence).

 Blood pressure (2)

Outcome

Results

Summary with the certainty of evidence (GRADE)

 Heart rate variability (1)

Spinal manipulation had no effect on

- various HRV components (results from respectively 3/3 and 4/4 studies included in meta-analysis)

Spinal manipulation may have no acute effect on cardiovascular autonomic activity (very low- to low-certainty evidence).

Please note that we downgraded the certainty of evidence by one level for technical issues.

 Heart rate (1)

- Heart rate (results from 3/3 studies included in meta-analysis)

 Blood pressure (1)

- Blood pressure in 1/1 study

 Pupil diameter (2) (pupillometry)

Spinal manipulation had no effect on pupil diameter in 1/1 study.

Spinal manipulation may have no acute effect on the autonomic control of the pupil (low-certainty evidence).

 Plasma concentrations of epinephrine and norepinephrine (3)

Spinal manipulation had no effect on the plasma concentrations of epinephrine and norepinephrine in 1/1 study.

Spinal manipulation may have no acute effect on the sympathoadrenal system activity (low-certainty evidence).

 Oxy-hemoglobin concentration (4)

Spinal manipulation had no effect on the oxy-hemoglobin concentration measured on the gastrocnemius in 1/1 study.

We are uncertain whether spinal manipulation has no acute effect on muscle sympathetic nerve activity (very low-certainty evidence).