Table 1 Summary of reviewed studies

Beer et al. 2012 [38]

Female (n = 10) Male (n = 10))

Age (y);

Gr.1: 26.8 (±9.6)

Gr.2: 31.7 (±13.3)

1. DCF training in sitting (postural correction exercise) (n = 10)

2. Control Group (no exercise) (n = 10)

Change in muscle activity in the CCFT (EMG)

- SCM

CCFT (EMG)

SCM

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

DCF training in a postural correction exercise decreased SCM activity across all CCFT stages, but differences were significant only at the first and third stages of the test (22 and 26 mmHg levels).

No change observed in the control group who did not exercise.

VAS 0–10;

Gr.1: 3.0 (±1.7)

Gr.2: 2.6 (±1.1)

Intervention period: 2 weeks

NDI 0–100;

Gr.1:18.1 (±9.0)

Gr.2: 20.6 (±10.1)

Duration of pain (y);

Gr.1: 4.7 (±3.3)

Gr.2: 7.9 (±9.0)

Borisut et al. 2013 [32]

Females (n = 100)

Age (y);

Gr.1: 32.7 (±3.1)

Gr.2: 30.4 (±3.4)

Gr.3: 30.2 (±3.0)

Gr.4: 29.3 (±3.1)

1. DCF training (n = 25)

2. Neck flexor, extensor strength and endurance training (n = 25)

3. Combined DCF, strength, endurance training (n = 25)

4. Control group (n = 25)

Cervical muscle activation (RMS EMG amplitude) during a sitting typing task

- Upper trapezius (UTr)

- Cervical erector spinae (ES)

- Sternocleidomastoid (SCM)

- Anterior scalenes (AS)

Muscle activation (EMG):

All exercise intervention groups (Gr’s 1, 2, 3) similarly and significantly reduced muscle activity in all muscles evaluated in the typing task with the exception of the (L) ES.

No exercise group had a superior effect.

(R) (L) UTr -Gr 1 vs 4: ♦ Gr 1 vs 2,3: 0

(R) (L) SCM -Gr 1 vs 4: ♦ Gr 1 vs 2,3: 0

(R) (L) AS - Gr 1 vs 4: ♦ Gr 1 vs 2,3: 0

(R) ES - Gr 1 vs 4: ♦ Gr 1 vs 2,3: 0

(L) ES - Gr 1 vs 2,3,4: 0

VAS 1–100;

Gr.1: 55.0 (±11.0)

Gr.2: 56.0 (±22.7)

Gr.3: 61.5 (±16.7)

Gr.4: 59.0 (±10.5)

Intervention period: 12 weeks

- Gr 1: + All muscles

  Gr 2: + All muscles

  Gr 3: + All muscles

  Gr 4: 0 All muscles except UTr

No changes in EMG activation occurred in the control group except for UTr where, in contrast to the interventions, muscle activity increased.

NDI ;

Gr.1: 28.2 (±5.6)

Gr.2: 30.0 (±4.5)

Gr.3: 29.2 (±5.3)

Gr.4: 31.6 (±5.1)

Duration of pain (months); ≥6.

Falla et al. 2006 [29]

Females (n = 58).

Age (y);

Gr.1: 37.7 (±9.9)

Gr.2: 38.1 (±10.7)

1.DCF training (n = 29)

2. Cervical flexor endurance-strength training (n = 29)

Comparison of effect of each exercise mode on:

Fatigability of cervical flexors, SCM, AS (EMG)

- Mean spectral frequency MSF

- Average rectified value ARV

- Conduction velocity CV

Fatigability (EMG)

MSF:

- Gr 1 vs 2: ★

- Gr 1: 0

  Gr 2: +

DCF training did not improve any measures of superficial cervical flexor fatigability.

Endurance-strength training significantly improved fatigability measures of MSF and ARV, but had no effect on CV.

ARV:

- Gr 1 vs 2: ★

- Gr 1: 0

  Gr 2: +

VAS 0–10;

Gr.1: 3.6 (±2.0)

Gr.2: 4.7 (±2.0)

Intervention period: 6 weeks

CV:

- Gr 1: 0

  Gr 2: 0

Strength (MVC)

Endurance-strength training was superior in improving strength of the cervical flexors compared to DCF training.

NDI 0–50;

Gr.1: 9.8 (±3.3)

Gr.2: 10.4 (±3.4)

Strength (MVC)

- Gr 1 vs Gr 2 ★

- Gr 1: 0

  Gr 2: +

Duration of pain (y); Gr.1: 7.5 (± 5.9)

Gr.2: 8.3 (± 7.0)

Falla et al. 2007 [30]

Females (n = 58)

Age (y);

Gr.1: 37.7 (±9.9)

Gr.2: 38.1 (±10.7)

1. DCF training (n = 29)

2. Cervical flexor endurance-strength training (n = 29)

Change in postural angle during a 10 min computer task

- Cervical angle (line between C7 and tragus to horizontal - forward head position)

- Thoracic angle (line between C7 and T7 to horizontal - upper thoracic flexion posture)

Change in postural angle:

Cervical angle

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

DCF training resulted in a lesser change towards a forward head posture during the 10 min computer task. No change was evident in the endurance-strength training group.

VAS 0–10;

Gr.1: 3.6 (± 2.0)

Gr.2: 4.7 (± 2.0)

Intervention period: 6 weeks

Thoracic angle

- Gr 1 vs Gr 2: 0

- Gr 1: +

  Gr 2: +

Both DCF and strength-endurance training reduced the change in thoracic flexion angle during the 10 min computer task with no difference between groups.

NDI 0–50;

Gr.1: 9.8 (± 3.3)

Gr.2: 10.4 (± 3.4)

Duration of pain (y); Gr.1: 7.5 (± 5.9)

Gr.2: 8.3 (± 7.0)

Falla et al. 2008 [31]

Females (n = 58)

Age (y);

Gr.1: 37.7 (±10.1)

Gr.2: 38.1 (±10.7)

1. DCF training (n = 29)

2. Cervical flexor endurance-strength training (n = 29)

Cervical muscle activation (RMS EMG amplitude) during a pencil tapping task

- SCM (L) and (R)

Muscle activation (EMG):

(R) (L) SCM

- Gr 1 vs Gr 2: 0

- Gr 1: 0

  Gr 2: 0

Neither DCF training nor cervical flexor strength-endurance training translated to a change in SCM muscle activity in a functional pencil tapping task.

VAS 0–10;

Gr.1: 3.5 (±2.0)

Gr.2: 4.7 (±2.0)

Intervention period: 6 weeks

NDI 0–50);

Gr.1: 9.8 (±3.3)

Gr.2: 10.1 (±3.0)

Duration of pain (y); Gr.1: 7.6 (± 6.0)

Gr.2: 8.3 (± 7.0)

Ghaderi et al. 2017 [39]

Females and males (n = 40).

Age (y);

Gr.1: 36.0 (±2.5)

Gr.2: 36.3 (±3.1)

1. DCF training (n = 20)

2. Progressive resistive isometric exercises 30% MVC and neck postural control exercises (n = 20)

Comparison of effect of each exercise mode on:

Change in muscle activity in the CCFT (EMG)

- SCM

- AS

- SC

CCFT (EMG)

- (R) (L) SCM, AS & SC (Gr 1 vs 2): ♦

- Gr 1: +

  Gr 2: -

DCF training decreased SCM, AS and SC EMG during the CCFT compared to isometric exercise group.

Relative latency neck muscle onset (EMG)

- Not clear from paper if difference between groups or not.

- Gr 1: 0

  Gr 2: +

Decreased relative latency of the superficial neck muscle during rapid arm movements were reported for both the DCF training and isometric training groups but differences were reported as significant only for the isometric training group.

VAS 0–100;

Gr.1: 61.4 (±28.0)

Gr.2: 59.7 (±22.7)

Relative latency of superficial neck muscle onset compared to DA during rapid unilateral arm movements (EMG)

Endurance time DCF

- Gr 1 vs Gr 2: 0

- Gr 1: +

  Gr 2: 0

Endurance time increased significantly for the DCF training group but not the isometric training group. There was no significant difference between groups.

NDI 0–100;

Gr.1: 31.3 (±12.1)

Gr.2: 34.3 (±14.3)

Intervention period: 10 weeks

Endurance time of DCF muscles in CCFT

Duration of pain (week); Chronic neck pain >12w

Javanshir et al. 2015 [34]

Females (n = 40)

Males (n = 20).

Age (y);

Gr.1: 36.8 (±3.5)

Gr.2: 35.7 (±5.0)

1.DCF training (n = 30)

2.Cervical flexor strength training (n = 30)

Comparison of effect of each exercise mode on muscle dimensions

(ultrasonography)

-Longus colli

-SCM

Muscle dimensions

Longus colli:

- Gr 1 vs 2: ♦

- Gr 1: +

  Gr 2: 0

DCF training significantly increased the size of longus colli but failed to change the dimensions of the SCM significantly.

SCM:

- Gr 1 vs 2: ★

- Gr 1: 0

  Gr 2: +

In contrast, cervical flexor training significantly increased the size of SCM but did not have significant effects on longus colli dimensions.

Intervention period: 10 weeks

VAS 0–10;

Gr.1: 5.0 (±2.4)

Gr.2: 5.1 (±2.2)

NDI 0–100;

Gr.1: 33.3 (±11.4)

Gr.2: 33.2 (±15.0)

Duration of pain (y); Gr.1: 3.3 (±3.2)

Gr.2: 3.3 (±3.2)

Jull et al. 2007 [35]

Females (n = 58)

Age (y);

Gr.1: 42.7 (±10.8)

Gr.2: 39.0 (±11.6)

1.DCF training (n = 30)

2.Proprioception training (n = 28)

Comparison of effect of each exercise mode on cervical proprioception.

Measure of joint position error (JPE) on return to the natural head posture from:

- Rotation (left and right)

- Extension

Proprioception (JPE)

Right Rotation

- Gr 1 vs Gr 2: ★

- Gr 1: +

  Gr 2: +

Both DCF training and proprioception training resulted in a significant decrease in JPE (improvement) compared to baseline in all the three movement directions.

Intervention period: 6 weeks

NRS 0–10;

Gr.1: 6.3 (±1.7)

Gr.2: 6.7 (±1.5)

Left Rotation

- Gr 1 vs Gr 2: 0

- Gr 1: +

  Gr 2: +

There were no significant differences in gains made by the exercise interventions. The exception was from right rotation where the reduction in JPE was significantly greater with proprioception training.

NDI 0–50;

Gr.1: 17.6 (±4.9)

Gr.2: 21.6 (±9.1)

Extension

- Gr 1 vs Gr 2: 0

- Gr 1: +

  Gr 2: +

Duration of pain (y); Gr.1: 8.7 (±7.1)

Gr.2: 10.6 (±9.3)

Jull et al. 2009 [21]

Females (n = 46)

Age (y);

Gr.1: 39.6 (±12.2)

Gr.2: 37.1 (±10.3)

1.DCF training (n = 23)

2. Cervical flexor strength training (n = 23)

Comparison of effect of each exercise mode on:

CCFT (EMG)

Longus capitis/colli

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

DCF training resulted in a significant increase in EMG amplitude of longus capitis/colli and a significant decrease in SCM and AS activity in the CCFT. No significant changes were observed with cervical flexor strength training.

CCFT (EMG)

- Longus capitis/colli

- SCM

- AS

SCM:

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

NRS 0–10;

Gr.1: 4.5 (±1.6)

Gr.2: 4.2 (±2.1)

Intervention period: 6 weeks

Neither intervention changed the total ROM used in the CCFT, but DCF training resulted in a significant relative increase in the ROM used in each stage of the test.

AS:

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

Range of movement in the CCFT

CCF ROM (full)

CCF ROM at each stage

NDI 0–50;

Gr.1: 11.0 (±2.7)

Gr.2: 9.6 (±3.1)

Duration of pain (y); Gr.1: 10.1 (±10.6)

Gr.2: 9.2 (±6.6)

Relative latency of neck flexor muscle onset in flexion and extension arm movement tasks (EMG)

- Longus capitis/colli

- SCM

- AS

CCF ROM (full):

- Gr 1: 0

  Gr 2: 0

CCF ROM (stages):

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

There was no significant change in the relative latencies of EMG onsets in any cervical muscle during unilateral arm movements with either training regime.

When data were analysed in 10 s epochs, the proportion of participants who showed earlier onsets in the longus capitis longus/colli was significantly greater in the DCF training group compared to the strength training group.

A greater proportion of subjects showed earlier onsets

Relative latency neck flexors (EMG)

Longus capitis/colli, SCM, AS

- Gr 1 vs Gr 2: 0

- Gr 1: 0

  Gr 2: 0

Longus capitis/colli

(proportions achieving earlier onsets)

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

Lee et al. 2013 [33]

Females (n = 30)

Age (y): m = 17

1. DCF training (n = 15)

2. Control group –

Basic stretching exercise (n = 15)

Comparison of effect of each exercise mode on:

CCFT

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

DCF training resulted in significantly improved performance in the CCFT and in the neck-shoulder postural parameters measured.

NDI 0–50;

< 15

CCFT

Clinical assessment of test level achieved

Duration of pain (months); ≥ 3.

Intervention period: 8 weeks

Neck-shoulder posture

HTA; NFA, FSA

- Gr 1 vs Gr 2: ♦

- Gr 1: +

  Gr 2: 0

Basic stretching exercises did not have a significant effect on either CCFT performance or posture.

Neck-shoulder posture

- HTA (head tilt angle)

- NFA (neck flexion angle)

- FSA (forward shoulder angle)

O’Leary et al. 2007 [36]

Females (n = 50)

Age (y):

Gr.1: 36.9 (±9.5)

Gr.2: 37.9 (± 11.3)

1. DCF training (n = 27)

2. Cervical flexion (head lift) exercise (n = 23)

Comparison of effect of each exercise mode on:

Craniocervical flexor strength (MVC)

- Gr 1 vs 2: 0

- Gr 1: +

  Gr 2: +

There were no significant differences between groups in exercise outcomes.

DCF and head lift training both increased craniocervical flexor strength (by 11 and 12.2% respectively).

Strength (MVC)

- craniocervical flexors

Endurance (time to failure 50% MVC)

- craniocervical flexors

Craniocervical flexor endurance (MVC₅₀)

- Gr 1 vs 2: 0

- Gr 1: +

  Gr 2: +

NDI 0–100 (range); 10–28.

Intervention period: 6 weeks

Duration of pain (months); > 3.

Contraction accuracy (force steadiness)

- Percentage of recording remaining within ±3% of torque task

Contraction accuracy

- Gr 1 vs 2: 0

- Gr 1: +

  Gr 2: +

DCF and head lift training both increased craniocervical flexor endurance at MVC₅₀ (time to failure increased by 37 and 16% respectively).

DCF and head lift training both improved contraction accuracy (by 7 and 9% respectively).

^a O’Leary et al. 2012 [37]

Females (n = 35)

Males (n = 25)

Age (y);

Gr.1: 37.8 (±12.6)

Gr.2: 38.2 (±12.8)

Gr.3: 37.7 (±12.7)

VAS 0–100;

Gr.1: 33.2 (±13.0)

Gr.2: 29.9 (±14.5)

Gr.3: 30.6 (±12.1)

NDI 0–50:

Gr.1: 9.8 (±2.1)

Gr.2: 11.0 (±2.2)

Gr.3: 10.5 (±2.5)

Duration of pain (y); Gr.1: 7.1 (±4.6)

Gr.2: 7.2 (±8.2)

Gr.3: 6.2 (±5)

1. DCF training (n = 20)

2. Craniocervical flexor endurance training 20% MVC for 10 weeks progressed by time. For 5 weeks, brief holds at 50% MVC were added. (n = 20)

3. Active cervical mobility training (n = 20)

Intervention period: 10 weeks; 26 week follow up.

Comparison of effect of each exercise mode on:

CCFT: SCM and AS muscle activity (RMS EMG amplitude) in each of the five stages of the test

Craniocervical flexor muscle endurance – Time to failure

Craniocervical flexor muscle strength – Torque

Cervical range of motion (CROM)

- Flexion

- Extension

- Rotation

CCFT Muscle activation (EMG)

Sternocleidomastoid (SCM)

10 weeks

- Gr 1 vs 2: ♦ Gr 1 vs 3: ♦ Gr 2 vs 3: 0

26 weeks- Gr 1 vs 2: 0 Gr 1 vs 3: 0 Gr 2 vs 3: 0

Anterior scalene (AS):

10 weeks

- Gr 1 vs 2: ♦ Gr 1 vs 3: 0 Gr 2 vs 3: 0

26 weeks- Gr 1 vs 2: 0 Gr 1 vs 3: 0 Gr 2 vs 3: 0

CCF Endurance 10 weeks - Gr 1 vs 2: ★ Gr 1 vs 3: 0 Gr 2 vs 3: ★

26 weeks- Gr 1 vs 2: 0 Gr 1 vs 3: 0 Gr 2 vs 3: ★

CCF Strength10 weeks - Gr 1 vs 2: 0  Gr 1 vs 3: 0  Gr 2 vs 3: 0

26 weeks- Gr 1 vs 2: 0 Gr 1 vs 3: 0 Gr 2 vs 3: 0

Cervical range of motion10 weeks - Gr 1 vs 2: 0  Gr 1 vs 3: 0  Gr 2 vs 3: 0

26 weeks- Gr 1 vs 2: 0 Gr 1 vs 3: 0 Gr 2 vs 3: 0

Muscle activation (EMG) DCF training resulted in significant changes (decreases) in SCM activity in the CCFT compared to endurance training and mobility training at 10 weeks at the 24-30 mmHg stages of the CCFT. At 26 weeks, the changes with DCF training regressed and were not significantly different from the endurance and mobility training groups.

DCF training resulted in significant changes (decreases) in AS activity in the CCFT compared to endurance training and mobility training at 10 weeks only at the 28 mmHg stage of the CCFT. At 26 weeks, there were no differences in changes with DCF training compared to the endurance and mobility training groups.

Craniocervical flexor endurance

DCF training resulted in no significant improvements in time to failure. Significant improvements were recorded for the endurance training group compared to the mobility group at both 10 and 26 weeks and compared to the DCF group at 10 weeks.

Craniocervical flexor strength

The endurance training group showed significant improvements in strength pre to post intervention at 10 and 26 week follow up. There were no significant differences in improvements in strength between groups.

Cervical range of motion

Very small gains in ROM were recorded, but there were no significant between group differences.