Table 3 Reasons for downgrading the certainty of evidence

A

Risk of bias, 9/10 studies were judged as having unclear risk of bias (unclear risk concerning the blinding of the participants, blinding of the data extraction / cleaning process and blinding of the statistician).

Some inconsistency, as 2/6 studies found the effect not to be bilateral and 2/5 not to be present during the post intervention period.

1 level

B

Inconsistency, as 3/8 studies reported a statistically significant effect, the others not.

1 level

C

Indirectness, as there is evidence indicating that skin temperature is not a good marker of skin sympathetic nerve activity (as explained in the Discussion).

2 levels

D

Inconsistency, as studies found both effect and non-effect.

1 level

E

Indirectness, as there is evidence indicating that skin blood flow is not a good marker of skin sympathetic nerve activity (as explained in the Discussion).

2 levels

F

Inconsistency, as 3 studies which could not be pooled in the meta-analysis reported a statistically significant effect.

1 level

G

Indirectness, heart rate variability is a better outcome to assess cardiac autonomic activity (as explained in the Method).

1 level

H

Inconsistency, as 2 studies which could not be pooled in the meta-analysis reported a statistically significant effect.

1 level

I

Indirectness, blood pressure variability is a better outcome to assess cardiovascular autonomic activity (as explained in the Method).

1 level

J

Risk of bias, 3/3 studies were judged as having unclear risk of bias (unclear risk concerning the blinding of the participants, blinding of the data extraction and blinding of the statistician).

1 level

K

Indirectness, respiratory rate seems not to be a well-accepted outcome to assess autonomic activity.

1 level

L

Risk of bias, the study was judged as having high risk of bias (lack of blinding of the participants).

2 levels

M

Inconsistency, as one study which could not be pooled in the meta-analysis reported a statistically significant effect.

1 level

N

Risk of bias, the study was judged as having unclear risk of bias (unclear risk concerning the blinding of the participants, blinding of the data extraction and blinding of the statistician).

1 level

O

Possible indirectness, oxy-hemoglobin concentration is an indirect measure of muscle blood flow.

1 level

P

Imprecision, one study (downgraded by two levels); two to four studies (downgraded by one level).

1 or 2 level(s)

Q

Technical issues, as 1/3 study for respiratory rate, 2/3 or 2/4 studies for Heart rate variability, and 1/3 study for Heart rate had a low technical score.

1 level