Table 3 Factors contributing to perceptions about intervention arm assignment among participants and outcome assessors

Study participants (n = 24)

 Uncertainty

5 (20.8%)

Participants expressed uncertainty regarding the intervention assignment, and the intervention comparison

‘I am not sure what the intervention was.’

(Female, 28 years old, control intervention)

 Immediate effect

4 (16.7%)

Participants based their response on the perceived immediate effects after intervention

‘I felt tension release in the back musculature after the manipulation.’

(Female, 26 years old, active manual soft tissue mobilisation)

 Manual pressure

4 (16.7%)

Participants based their response on manual pressure exerted by the intervention provider

‘The hand pressure felt too soft.’

(Female, 28 years old, control intervention)

 Breathing

3 (12.5%)

Participants pointed to the associated breathing exercise of the intervention as the main element informing their response

‘Because a researcher forced breathing.’

(Female, 32 years old, control intervention)

 Misconception

3 (12.5%)

Participants exhibited misconceptions surrounding the manual therapy intervention

‘I did not received [sic] an active massage, therefore I believe that I received the control intervention’

(Male, 29 years old, active manual soft tissue mobilisation)

 Atmosphere

1 (4.2%)

Participant expressed expectations for certain contextual elements

‘There was no additional thing such as music.’

(Male, 36 years old, control intervention)

 Misunderstanding

1 (4.2%)

Participants lacked understanding regarding the applied manual therapy intervention

‘I did not understand the intervention.’

(Male, 32 years old, active manual soft tissue mobilisation)

 Non-response

3 (12.5%)

-

-

Assessors 1 and 2—measuring outcome assessors (possible responses = 48)

Selected verbatim (identifier, intervention assigned to participant)

 Uncertainty

23 (47.9%)

Outcome assessors were uncertain or lacked confidence in their response

‘I don’t know.’

(Assessor 1, active manual soft tissue mobilisation)

 Movement quality

5 (10.4%)

Outcome assessors pointed to certain movement quality elements, such as speed or stability

‘Shaking when leaning backwards (extension).’

(Assessor 2, active manual soft tissue mobilisation)

 Range of motion

4 (8.3%)

Outcome assessors were under the impression that a change in range of motion had occurred

‘Impression: more degrees (flexion).’

(Assessor 2, active manual soft tissue mobilisation)

 Verbal cues

2 (4.2%)

Outcome assessors took note of certain verbal cues by the participants when performing the assessments

‘I think participant thinks she got the treatment, said ‘it works’.’

(Assessor 1, control intervention)

 Non-response

14 (29.2%)

-

-

Assessor 3—documenting outcome assessor (possible responses = 24)

Selected verbatim (identifier, intervention assigned to participant)

 Movement quantity

16 (66.7%)

The outcome assessor compared pre- and post- measurements to justify response

‘Much improved flexibility in both directions.’

(Assessor 3, control intervention)

 Uncertainty

8 (33.3%)

The outcome assessor expressed uncertainty about the pre- and post- measurements or had difficulty recalling the exact values

‘I don’t think there was a big change in measurement but not sure.’

(Assessor 3, control intervention)

 Non-response

0 (0.0%)

-

-