Mental practice in isolation improves cervical joint position sense in patients with chronic neck pain: a randomized single-blind placebo trial

Action observation group

Patients in this group performed an exclusive AO protocol of 2 commonly used MCEs in the treatment of patients with NSCNP (Jull et al., 2009; Jull et al., 2007; O’Leary et al., 2007). Both exercises were based on the motor gesture of craniocervical flexion (Fig. 2). Patients in the AO group performed the observation by watching a video of the continuous performance of both exercises repeatedly during 2 series of 1 min for each exercise, with a total duration of 4 min.

The first exercise consisted of maintaining the cervical spine in a neutral position in a sitting position and performing a deep muscle contraction to flatten the curve of the neck, nodding with the head. The second exercise involved a deep muscle contraction by performing the craniocervical flex-extension gesture with the resistance of an elastic band.

Motor imagery group

The patients in this group performed an MI protocol of the same cervical exercises as the AO group (Fig. 2). Patients were instructed on the movements they were to imagine by showing both exercises and the precise instructions for each movement. After this, they were instructed to perform a third-person mental task of visual MI of both exercises during 2 series of 1 min for each exercise, with a total duration of 4 min.

Placebo observation group

Patients in the placebo observation (PO) group underwent a placebo AO protocol. The patients watched during the same intervention time as both previous groups. This documentary video was composed of video clips of nature landscapes, without any human agent or motor gesture.

This type of placebo AO protocol has been used in previous studies (Bang et al., 2013; Buccino et al., 2012).

Primary outcomes

Cervical joint position sense.

CJPS is an objective measure of neck repositioning sense and can quantify the alteration in neck proprioception. CJPS was assessed with a visual feedback device, the SenMoCOR LED (Sensory Motor Control-Oriented Rehabilitation, IAOM-US). This device consists of adjustable straps and a fastening support for a laser beam. It is adjustable to the evaluator’s desired position, allowing projection of the light beam.

The experimental procedure for assessing CJPS with a laser beam has been described by Revel, Andre-Deshays & Minguet (1991). First, patients were asked to sit in a comfortable position at 90-cm distance from the bullseye with the SenMoCOR Kit correctly placed. With eyes closed, they were asked to point to the neutral position of the head and memorize it to return to after the completion of the movement. This point was recorded as a reference for each patient. The patient subsequently performed a maximal movement of cervical flexion and then attempted to find the initial reference position with a maximum of accuracy without speed instructions. The point on which the light beam stopped indicated the global error measured in centimeters (cm) in relation to the center of the target recorded previously. The assessor measured the deviations from de target position for each trial on both axes (x∕y). Values of x (abscissa) and y (ordinate) were recorded according to the Cartesian coordinate system. The same protocol was used for the extension, right and left rotation movements. Ten trials were performed with head repositioning after each movement, and the mean measure was recorded. No feedback was given to the participants about their actual performance. This CJPS testing method offers an easy, quick and inexpensive method for measuring cervical joint position sense. The test presents inter-rater reliability ranging from moderate to good/substantial agreement (intraclass correlation coefficient [ICC] ≥ 0.51–0.75); it also presents intra-rater reliability ranging from moderate to almost perfect agreement (ICC ≥ 0.48–0.82) (Juul et al., 2013). The minimal detectable change ranged from 0.52–0.75 cm (Juul et al., 2013).

Secondary outcomes

Ability to generate mental motor imagery.

The movement imagery questionnaire-revised (MIQ-R) is an 8-item self-report inventory that was used to assess visual and kinesthetic motor imagery ability. Four different movements are included in the MIQ-R, which is comprised of four visual and four kinesthetic items. For each item, participants read a description of the movement. They then physically performed the movement and were instructed to reassume the starting position after finishing the movement and before performing the mental task, imagining the movement visually or kinesthetically. Each participant then rated the ease or difficulty of mentally generating that image on a 7-point scale, in which 7 indicates “very easy to see/feel” and 1 “very difficult to see/feel”. The internal consistencies of the MIQ-R have been consistently adequate, with Cronbach’s α coefficients ranging above 0.84 for the total scale, 0.80 for the visual subscale and 0.84 for the kinesthetic subscale (Campos & González, 2010).

Mental chronometry.

Mental chronometry (MC) is a reliable measure that has been widely used to record objective measurements of the ability to create mental motor images (Guillot & Collet, 2005; Malouin et al., 2008; Williams et al., 2015). To assess MC, first, the time dedicated to imagining each task was recorded using a stopwatch. The time between the interval command to start the task (given by the evaluator) and the verbal response at the conclusion of the task (given by the participant) was recorded. After the MI task, the participants were asked to perform the real movement execution of the task, and the time dedicated to performing each task was recorded using a stopwatch. Both time measurements were taken to obtain the temporal congruence between the tasks. In healthy participants, for the temporal congruence test, the ICC ranged from 0.63 to 0.95, whereas the ICC for intrasession reliability ranged from 0.95 to 0.97 (Malouin et al., 2008).

Pain-related fear of movement.

Pain-related fear of movement was assessed using the 11-item Spanish version of the Tampa Scale of kinesiophobia, whose reliability and validity have been demonstrated (Gómez-Pérez, López-Martínez & Ruiz-Párraga, 2011). The Tampa scale for Kinesiophobia consists of 2 subscales, one related to fear of activity and the other related to fear of harm. The final score can range between 11 and 44 points, with higher scores indicating greater perceived kinesiophobia (Gómez-Pérez, López-Martínez & Ruiz-Párraga, 2011). Internal consistency ratings were moderate. In the chronic pain sample, Cronbach’s α = 0.79 was obtained using total TSK items (Gómez-Pérez, López-Martínez & Ruiz-Párraga, 2011).

Neck disability.

Disability was measured using the Spanish-validated Neck Disability Index (NDI), which consists of 10 items related to daily functional activities. Each question is measured on a scale from 0 (no disability) to 5, and an overall score out of 100 is calculated by adding each item score together and multiplying it by 2. A higher NDI score indicates greater perceived disability due to neck pain. It has been shown to have high “test-retest” reliability and to have appropriate psychometric properties (Alfonso Andrade Ortega, Damián Delgado Martínez & Almécija Ruiz, 2008). MacDermid et al. (2009) concluded that differences in 7 points out of 50 in the NDI should be considered as clinically relevant. In addition, intraclass correlation coefficients (ICCs) ranged from 0.50 to 0.98.

Level of physical activity.

The level of physical activity was assessed using the IPAQ questionnaire, which allows the participants to be divided into 3 groups according to their level of activity, which can be high, moderate, and low or inactive (Roman-Viñas et al., 2010). This questionnaire has shown acceptable validity and psychometric properties to measure total physical activity. Therefore, the psychometric properties of the questionnaire were accepted for use in studies that required the measurement of physical activity; reliability was approximately 0.65 (r = 0.76; 95% CI [0.73–0.77]) (Mantilla Toloza & Gómez-Conesa, 2007).

X-plane

Regarding the flexion range of motion (ROM) in the X-plane, the ANOVA revealed significant changes in group*time (F = 4.06, p = .006, ${\eta }_p^2=0.231$) and time (F = 17.45, p < .001, ${\eta }_p^2=0.393$). The post hoc analysis revealed significant within-group differences in both the MI and AO groups, with a moderate-large effect size for the MI group at postintervention (p < .001, d = 0.95) and at post 2 intervention (p = .021, d = 0.72), as well as with a moderate-large effect size for AO at postintervention (p < .001, d = 0.96) and at post 2 intervention (p = .001, d = 0.74). The post hoc analysis revealed no significant within-group differences in the PO group (p > .05) (Table 2). However, no significant differences were found between the groups (p > .05).

Y-plane

Regarding the flexion ROM in the Y-plane, the ANOVA revealed significant changes in group*time (F = 4.14, p = .005, ${\eta }_p^2=0.235$) and time (F = 8.83, p < .001, ${\eta }_p^2=0.246$). The post hoc analysis revealed significant within-group differences only in the AO group, with a moderate-large effect size at postintervention (p < .001, d = 1.01) and at post 2 intervention (p = .005, d = 0.77). The post hoc analysis revealed no significant within-group differences in the PO or MI groups (p > .05) (Table 2). Regarding the between groups comparison, only the AO group showed significant differences with the PO group at post 2 intervention, with a moderate effect size (p = .035, d = 0.72) (Fig. 3).

X-plane

Regarding the extension ROM in the X-plane, there were no significant differences in time (F = 1.87, p = .16, ${\eta }_p^2=0.065$) or in group*time (F = 0.33, p = .33, ${\eta }_p^2=0.024$).

Y-lane

Regarding the extension ROM in the Y-plane, the ANOVA revealed significant changes in group*time (F = 6.87, p < .001, ${\eta }_p^2=0.337$) and time (F = 8.56, p = .001, ${\eta }_p^2=0.241$). The post hoc analysis revealed significant within-group differences in both the MI and AO groups, with a moderate-large effect size for MI at postintervention (p = .017, d = 0.77) and at post 2 intervention (p = .007, d = 1.04), as well as with a large effect size for AO at postintervention (p < .001, d = 1.01) and at post 2 intervention (p = .006, d = 1.05). The post hoc analysis revealed no significant within-group differences in the PO group (p > .05) (Table 3).

Regarding the between groups comparison, the AO group showed significant differences with both the MI and the PO groups at postintervention, with a large effect size (p = .041, d = 1.17, and p = .001, d = 1.81, respectively) and at post 2 intervention with only the PO group, with a large effect size ( p = .004, d = 1.74) (Fig. 3).

X-plane

Regarding the left rotation ROM in the X-plane, the ANOVA revealed significant changes in group*time (F = 3.08, p = .023, ${\eta }_p^2=0.186$) but not in time (F = 1.53, p = .226, ${\eta }_p^2=0.054$). The post hoc analysis revealed no significant within-group differences in any group (p > .05) (Table 4). However, both the MI and AO groups showed significant between group differences with the PO group at postintervention, with a large effect size (p = .035, d = 1.29, and p = .005, d = 1.54, respectively) (Fig. 4).

Y-plane

Regarding the left rotation ROM in the Y-plane, the ANOVA revealed significant changes in group*time (F = 5.44, p = .002, ${\eta }_p^2=0.287$) and time (F = 9.58, p = .001, ${\eta }_p^2=0.262$). The post hoc analysis revealed significant within-group differences in both the MI and AO groups, with a large effect size for MI at postintervention (p = .012, d = 1.18) and at post 2 intervention (p = .009, d = 0.87), as well as with a large effect size for AO at postintervention (p = .004, d = 1.71) and at post 2 intervention (p = .001, d = 1.25). The post hoc analysis revealed no significant within-group differences in the PO group (p > .05) (Table 4). In addition, both the MI and AO groups showed significant between group differences with the PO group at postintervention, with a large effect size (p = .016, d = 1.24, and p = .001, d = 1.70, respectively) (Fig. 5).

X-plane

Regarding the right rotation ROM in the X-plane, the ANOVA revealed significant changes in group*time (F = 2.81, p = .034, ${\eta }_p^2=0.172$) but not in time (F = 1.98, p = .147, ${\eta }_p^2=0.069$). The post hoc analysis revealed significant within-group differences in the AO group, with a moderate effect size, only at postintervention (p = .011, d = 0.72). However, significant within-group differences were also found between post-post2 intervention in the AO group, showing a loss of effect after 10 min (p = .02, d =  − 0.61) (Table 5). Finally, no significant differences were found between the groups (p > .05) (Fig. 4).

Y-plane

Regarding the right rotation ROM in the Y-plane, the ANOVA revealed significant changes over time (F = 7.53, p = .003, ${\eta }_p^2=0.218$) but not in group*time (F = 1.75, p = .151, ${\eta }_p^2=0.115$). The post hoc analysis revealed significant within-group differences only in the AO group, with a large effect size, at postintervention (p = .006, d = 1.24) and at post 2 intervention (p = .043, d = 0.94). The post hoc analysis revealed no significant within-group differences in the PO or MI groups (p > .05) (Table 5). Finally, no significant differences were found between the groups (p > .05) (Fig. 5).