The test and questionnaires were completed by 160–185 participants (74–85%) at the follow-up assessments (Fig. 1). Baseline characteristics were similar between groups, except that more females were included in the NSE group and the participants were generally younger compared with the PPA group (Table 1). There were no differences between drop-outs and those who completed the intervention regarding baseline measurements in NME, AROM, grip strength or pain during testing (p > .27). Adherence to exercise during the 12-week intervention period was in the NSE and NSEB groups 70% and 71%, and in the PPA group 49%, p = .07. At 12 months’ follow-up, 25% in NSE, 34% in NSEB and 42% in the PPA group reported they trained completely or almost completely according to their exercise program and 54% (NSE) respectively 35% (NSEB and PPA) trained to some extent (p = .09). Of the total group (n = 216), individuals below the cut-off reference values in NME, AROM and grip strength had significantly higher NDI at baseline compared with those in line with or above the reference values: below the reference values, NDI median 34 to 38 (IQR, 26–46), in line with or above the reference values, NDI median 26 to 30 (IQR, 18–38), p < .01. There were no differences between WAD grades II and III in the proportion of individuals below against in line with or above the reference values (p > .15) except for grip strength where more individuals with WAD grade III (64%) were below the reference values (p = .05).
Results in neck muscle endurance, active range of motion, grip strength and pain during testing
Unadjusted data from the tests are shown in Table 2. In dorsal NME, there were significant between-group differences: both females and males improved in the NSE and NSEB groups compared to the PPA group (F = 3.6, p < .01). There were significant between-group and sex differences in ventral NME (F = 5.1 to 22.1, p < .01). Males in both the NSE and NSEB groups improved compared to the PPA group (F = 22.2, p < .01). There were no significant between-group differences for females (F = 0.2, p > .91), but females in the NSEB group improved from baseline to 12 months (F = 3.6, p < .03).
Table 2
Ventral and dorsal neck muscle endurance, cervical range of motion and grip strength for neck-specific exercise (NSE), neck-specific exercise with a behavioral approach (NSEB) and prescribed physical activity (PPA) groups.
Variable | Period | NSE | NSEB | PPA |
Ventral NME | | | | |
Women | Baseline | 14 (9–30) [2–222] | 17 (8–33) [2–162] | 24 (13–48) [2–101] |
| | 12 months | 23 (11–40) [2–125] | 25 (9–46) [3–114] | 23 (7–57) [3–79] |
Men | Baseline | 59 (22–91) [5–243] | 40 (21–82) [5–175] | 21 (9–64) [4–373] |
| | 12 months | 67 (42–143) [6–183] | 51 (31–110) [10–258] | 25 (13–65) [1–200] |
Dorsal NME | | | | |
Women | Baseline | 33 (18–79) [0–511] | 37 (17–113) [2–660] | 46 (19–174) [5–540] |
| | 12 months | 89 (34–176) [0–1860] | 74 (37–155) [6–964] | 60 (12–166) [4–450] |
Men | Baseline | 108 (28–202) [10–421] | 66 (32–153) [3–405] | 50 (9–170) [3–347] |
| | 12 months | 127 (47–186) [1–382] | 166 (60–292) [13–1305] | 56 (27–122) [0–634] |
AROM | | | | |
Flexion/extension | | | | |
Women | Baseline | 95 (26.2) [26–138] | 98 (30) [34–152] | 99 (26.1) [22–143] |
| | 3 months | 102 (28.6) [18–147] | 102 (32.9) [20–158] | 98 (25) [42–134] |
| | 6 months | 101 (28.3) [26–156] | 106 (32) [24–172] | 99 (27.6) [26–132] |
| | 12 months | 105 (26.4) [42–156] | 106 (28.6) [28–155] | 94 (29.4) [24–134] |
Men | | | | |
Baseline | 104 (26) [49–150] | 92 (24.4) [25–122] | 89 (19.5) [50–130] |
| | 3 months | 109 (24.2 [60–135] | 94 (21.2) [47–124] | 88 (25.4) [30–125] |
| | 6 months | 113 (26.5) [52–139] | 96 (23.1) [20–135] | 92 (25.6) [33–138] |
| | 12 months | 110 (24.8) [60–143] | 106 (25.7) [60–143] | 94 (27.4) [30–144] |
Lateral flexion | | | | |
Women | Baseline | 66 (18.1) [22–99] | 66 (18.1) [32–108] | 70 (15.9) [20–96] |
| | 3 months | 68 (18.8) [18–110] | 70 (21.7) [24–128] | 67 (18.8) [26–100] |
| | 6 months | 69 (17.7) [28–100] | 71 (20.3) [20–110] | 69 (18.6) [18–104] |
| | 12 months | 70 (19,1) [32–120] | 72 (19.1) [24–115] | 65 (17.5) [30–95] |
Men | Baseline | 68 (15.2) [39–87] | 61 (20.4) [8–92] | 61 (17.4) [30–94] |
| | 3 months | 74 (23.8) [28–110] | 66 (20.6) [15–95] | 59 (16.8) [10–112] |
| | 6 months | 73 (21.6) [32–108] | 66 (20.0) [14–95] | 62 (21.8) [10–112] |
| | 12 months | 73 (21.8) [36–114] | 69 (21.7) [20–104] | 60 (21.6) [18–136] |
Rotation | | | | |
Women | Baseline | 114 (26.4) [30–170] | 112 (27.4) [50–162] | 114 (25.4) [26–166] |
| | 3 months | 118 (21.2) [40–147] | 118 (29.4) [22–172] | 107 (30.4) [36–154] |
| | 6 months | 116 (23.0) [54–155] | 123 (29.1) [22–172] | 110 (24.5) [48–144) |
| | 12 months | 120 (22.7) [28–158] | 121 (27.7) [40–176] | 109 (28.4) [50–154] |
Men | Baseline | 115 (26.0) [58–180] | 107 (31.3) [11–140] | 105 (25.5) [55–155] |
| | 3 months | 118 (27.1) [60–154] | 115 (23.3) [45–146] | 107 (26.7) [34–154] |
| | 6 months | 119 (31.2) [32–164] | 111 (28.4) [34–150] | 106 (27.6) [34–146] |
| | 12 months | 119 (23.1) [74–150] | 117 (24.6) [45–154) | 105 (28.8) [32–150] |
Grip strenght | | | | |
Women | Baseline | 22.6 (6.4) [12–39] | 22.6 (5.8) [9–43] | 23.1 (7.1) [7–40] |
| | 3 months | 22.3 (5.8) [10–36] | 22.7 (6.1) [4–40] | 22.2 (8.1) [1–34] |
| | 6 months | 23.5 (6.5) [12–38] | 24.4 (8.5) [10–59] | 23.6 (7.3) [1–37] |
| | 12 months | 24.9 (6.2) [11–34] | 24.5 (6.1) [4–42] | 22.0 (8.4) [2–35] |
Men | Baseline | 40.7 (10.5) [21–64] | 43.7 (9.5) [30–59] | 40.4 (12.6) [31–49] |
| | 3 months | 42.2 (10.1) [21–57] | 42.5 (10.6) [21–60] | 42.2 (12.4) [11–66] |
| | 6 months | 43.1 (9.9) [19–60] | 46.6 (10,8) [26–66] | 44.8 (10.6) [21–63] |
| | 12 months | 41.7 (10.4) [18–57] | 45.4 (11.1) [26–62] | 44.5 (13.2) [16–66] |
VAS before test | Baseline | 33 (22.1) [0–88] | 33 (25.1) [0–86] | 36 (22.9) [0–91] |
| | 12 months | 20 (21.5) [0–77] | 26 (23.4)[0–80] | 32 (27.4) [0–92] |
VAS after test | Baseline | 40 (23.8) [0–97] | 42 (27.6) [0–95] | 45 (25.2) [0–93] |
| | 12 months | 28 (24.2) [0–88] | 33 (27.8) [0–100] | 40 (28.5) [0–91] |
Values are presented as median and inter-quartile range (IQR) and [range] for neck muscle endurance values (NME) at baseline and 12 months. Active range of motion and grip strength are presented as mean, standard deviation (SD) and [range] at baseline, 3, 6 and 12 months. |
NME, neck muscle endurance; AROM, active range of motion; NSE, neck-specific exercise; NSEB, neck-specific exercise with a behavioral intervention; PPA, prescription of physical activity |
There were significant between-group differences in AROM (F = 5.9 to 14.3, p < .01): the NSE and NSEB groups improved compared with the PPA group in flexion/ extension, and rotation (F = 5.9, p < .01). Lateral flexion was improved in the NSE group compared with the PPA group (F = 10.2, p < .01).
In grip strength, there were no significant between-group differences (F = 2.9, p < .05), but there were significant within-group differences over time (F = 2.9, p = .03). Females in all three exercise groups had improved grip strength (p < .05).
There were significant between-group differences in pain both immediately before (decreased pain in the NSE group compared to the PPA group; F = 4.2, p < .02) and after the tests (decreased pain in both the NSE and NSEB groups compared to the PPA group; F = 16.3, p < .01) at 12 months’ follow up.
Change scores in self-reported disability (NDI) in individuals below or above the reference values for healthy individuals in neck muscle endurance, active range of motion and grip strength
At 12 months, NDI was improved in individuals both below and in line with or above the cut-off reference values for NME, AROM and grip strength (only in line with or above the cut-off for grip strength) in the NSE and/or the NSEB groups compared with the PPA group, (NSE − 3 to -7, NSEB − 2 to -11; PPA − 4 to 8, p < .04) (Table 3). There were no significant differences between the NSE and NSEB groups (p > .07). In the PPA group, NDI increased (worsen disability) for individuals below the cut-off reference values in cervical flexion/extension and lateral flexion (p < .05) from baseline to 12 months’ follow-up.
Table 3
Change score in Neck Disability Index (NDI %) from baseline to 12 months’ follow-up for individuals below and above the normative cut-off reference values for healthy individuals in neck muscle endurance, cervical range of motion and grip strength; differences are between NSE, NSEB and PPA groups.
| | | | | | | P-value, between group differences |
Variable | NSE | NSEB | PPA | NSE - PPA | NSEB - PPA | NSE - NSEB |
| < normal | ≥ normal | < normal | ≥ normal | < normal | ≥ normal | < normal | ≥ normal | < normal | ≥ normal | < normal | ≥ normal |
Ventral NME | − 1 (-11 to 8) | − 6 (-18 to 0) | − 5 (− 14 to 4) | -11 (-18 to -5) | 4 (-4 to 10) | 0 (-8 to 4)* | .12 | .03 | .03 | .003 | .40 | .48 |
Dorsal NME | -3 (-12 to 7) | -9 (-21 to -5) | -8 (-15 to 2) | − 8 (-18 to -4) | 3 (-4 to 10) | -6 (-8 to 0)* | .04 | .16 | .001 | .16 | .19 | .16 |
Range of motion | | | | | | | | | | | | |
Flexion/extension | − 3 (-18 to 5) | − 6 (-14 to 1) | -2 (-16 to 6) | − 8 (-18 to -4) | 8 (0 to 10) | 0 (-8 to 3)* | .02 | .13 | .02 | .004 | .83 | .14 |
Lateral flexion | 0 (-10 to 10) | − 7 (-18 to -1) | -6 (-20 to 6) | -8 (-17 to -3) | 6 (11 to 6) | 0 (-6 to 6)* | .07 | .01 | .07 | .001 | .07 | .61 |
Rotation | − 4 (-16 to 8) | − 6 (-15 to 0) | − 4 (-14 to 6) | − 8 (-18 to -4) | 2 (0 to 10) | − 4 (-8 to 6) | .06 | .07 | .02 | .01 | .76 | .25 |
Grip strength | -2 (-10 to 8) | -6 (-18 to 0) | -6 (-20 to 6) | -8 (-16 to -2) | 2 (-4 to 10) | 0 (-8 to 7) | .08 | .02 | .08 | .003 | .08 | .75 |
NSE, neck-specific exercise; NSEB, neck-specific exercise with behavioral intervention; PPA, prescription of physical activity; NME, neck muscle endurance; Values are presented as median and inter-quartile range (IQR). |
Cut-off normative reference values for healthy individuals; ventral NME ≥ 23 s for females and ≥ 56 s for males, dorsal NME ≥ 173 s for females and ≥ 157 s for males, active cervical range of motion; flexion/extension ≥ 98°, total lateral flexion (right and left) ≥ 43°, total rotation (right and left) ≥ 109°, grip strength ≥ 25 kg for females and ≥ 42 kg for males. |
*= p < .05, significant with-in group differences between individuals < reference values compared to ≥ reference values at 12 months follow-up. |
There were significant differences in the NSE, NSEB and PPA groups at 12 months’ follow-up between individuals below against above the cut-off reference values for NME and AROM. For grip strength, there were differences in the NSE and PPA groups (Table 4, p < .05). In the NSE and NSEB groups, NDI was significantly improved at 12 months’ follow-up for individuals above the reference value (NDI, median (IQR); 22 (7–29) to 6 (0–22) compared with individuals below the reference value (NDI; 36 (23–49) to 23 (7–14) (p < .05). In the PPA group, individuals below the reference values for NME, AROM and grip strength had increased disability (NDI; 48 (32–52) to 42 (28–48) at 12 months’ follow-up compared with those above the reference values (NDI; 30 (18–40) to 20 (14–28) (Table 4, p < .05).
Table 4
Neck Disability Index (NDI) at baseline and 12 months’ follow-up in the NSE, NSEB and PPA groups, number and percentage of individuals below and in line or above cut-offs for normative reference values in neck muscle endurance, cervical range of motion and grip strength.
Variable | Baseline | 12 months |
| | NDI, median (IQR) | | NDI (median (IQR) |
NSE group | n | < normal | ≥ normal | n | < normal | ≥ normal |
Ventral NME | 28 (36%)* | 34 (24–44) | 28 (22–38)* | 27 (52%)* | 30 (19–46) | 18 (12–24)* |
Dorsal NME | 12 (16%) | 30 (24–42) | 26 (22–35) | 14 (27%) | 26 (18–44) | 18 (2–20)* |
Range of motion | | | | | | |
Flexion/extension | 35 (46%)* | 34 (24–33) | 30 (22–40) | 35 (63%)* | 30 (20–48) | 18 (7–29)* |
Lateral flexion | 42 (55%) | 36 (27–47) | 28 (22–32)* | 36 (66%) | 36 (23–49) | 18 (11–26)* |
Rotation | 37 (49%) | 34 (24–42) | 28 (23–39) | 31 (56%) | 30 (18–48) | 18 (7–26)* |
Grip strength | 30 (39%)* | 34 (28–43) | 26 (22–36) | 29 (57%)* | 36 (21–46) | 18 (6–24)* |
NSEB group | n | < normal | ≥ normal | n | < normal | ≥ normal |
Ventral NME | 28 (36%)* | 38 (28–46) | 27 (20–34)* | 30 (53%)* | 27 (17–44) | 22 (7–29) |
Dorsal NME | 14 (20%) | 36 (24–44) | 24 (15–34)* | 15 (27%) | 28 (18–38) | 6 (0–22)* |
Range of motion | | | | | | |
Flexion/extension | 44 (62%) | 42 (26–52) | 30 (22–36)* | 40 (67%) | 30 (15–48) | 20 (10–30)* |
Lateral flexion | 40 (56%) | 38 (26–50) | 30 (22–38)* | 39 (66%) | 32 (12–44) | 20 (11–28)* |
Rotation | 32 (45%)* | 30 (24–44) | 34 (22–39) | 37 (63%)* | 34 (20–46) | 20 (9–28)* |
Grip strength | 29 (41%)* | 35 (22–34) | 30 (23–38) | 35 (61%)* | 23 (7–41) | 22 (12–32) |
PPA group | n | < normal | ≥ normal | n | < normal | ≥ normal |
Ventral NME | 28 (53%) | 36 (28–47) | 28 (18–39)* | 20 (41%) | 44 (31–52) | 24 (12–34)* |
Dorsal NME | 17 (25%) | 37 (28–46) | 24 (16–30)* | 10 (21%) | 42 (28–48) | 20 (14–28)* |
Range of motion | | | | | | |
Flexion/extension | 38 (55%) | 36 (28–48) | 30 (19–40)* | 26 (52%) | 48 (32–52) | 28 (14–40)* |
Lateral flexion | 45 (62%) | 38 (32–50) | 30 (19–41)* | 31 (62%) | 48 (31–56) | 31 (16–42)* |
Rotation | 30 (43%) | 36 (28–48) | 28 (19–38)* | 22 (44%) | 42 (32–52) | 28 (11–41)* |
Grip strength | 35 (51%) | 37 (26–46) | 32 (20–38) | 26 (56%) | 44 (25–52) | 30 (18–40)* |
NDI; Neck Disability Index, median and inter-quartile range (IQR), NME; neck muscle endurance, NSE; neck-specific exercise, NSEB; neck-specific exercise with behavioral intervention, PPA; prescription of physical activity |
n (%); number and percentage of individuals above ( ≥ = on/over) the cut-off (normative reference values for healthy individuals) in neck muscle endurance (NME), active range of motion (AROM) and grip strength at baseline and at 12 months’ follow-up, * = p < 0.05, significant differences between baseline and 12 months’ follow-up for number of individuals above ( ≥ = on/over) the cut-off for normative reference value in NME, AROM and grip strength. |
Cut-off normative reference values in NME, AROM and grip strength; ventral NME ≥ 23 s for females and ≥ 56 s for males, dorsal NME ≥ 173 s for females and ≥ 157 s for males, cervical range of motion; flexion/extension ≥ 98°, total lateral flexion (right and left) ≥ 43°, total rotation (right and left) ≥ 109°, grip strength ≥ 25 kg for females and ≥ 42 kg for males. |
< normal = values below the cut-off for normative reference values, ≥ normal = above (on/over) the cut-off for normative reference values, *= p < .05, significant with-in group differences between individuals < reference values compared with ≥ reference values at baseline and 12 months’ follow-up. |