Table 2 Articles included in this scoping review

Attwood et al. [48]

2015/2016

Seven 6-week phases (294 days) in the UK

Rugby Union

Proprioceptive, strengthening and mobility exercises with

progressive structure targeting the lower limb, shoulder, head, and

neck.

81 community rugby clubs (25.5 ± 5.6 years, 1.86 ± 0.073 m, 94.4 ± 13.9 kg).

To investigate the

efficacy of a rugby-specific movement control

program to reduce injury risk in adult men’s

community rugby union players.

First team match exposure,

exercise program compliance and match injuries were reported on a weekly basis using standardized forms. Injury burden (number of days absence per 1000 player match-hours) and 90% CIs were estimated vis-à-vis for primary and secondary outcome measures. Injury incidence was estimated as the number of injuries per 1000 player

match-hours.

A likely beneficial difference in targeted injury incidence (rate ratio (RR), 90% CI = 0.6, 0.4 to 1.0) with a 40% reduction in lower limb incidence (RR, 90% CI = 0.6, 0.4 to 1.0) and a 60% reduction in concussion incidence (RR, 90% CI = 0.4, 0.2 to 0.7). Clubs with highest compliance

demonstrated very likely beneficial 60% reductions in

targeted injury incidence (RR, 90% CI = 0.4, 0.2 to 0.8) and targeted injury burden (RR, 90% CI = 0.4, 0.2 to 0.7).

No clear effects on overall injury outcomes however, the intervention group had a significant reduction in the incidence of lower limb injury

and concussion. Reductions were greater in clubs who performed the exercises more than those that did not.

Becker et al. [49]

Year of data collection not stated

Six weeks duration including pre- and post-intervention testing phases in Germany

Male soccer

Two training intervention groups and one control group. The training intervention included three resistance neck exercises for 6 weeks (2×/week). Rubber band strength was increased after every 4 sessions.

Thirty-three active male soccer players (20.3 ± 3.6 years, 1.81 ± 0.07 m, 75.5 ± 8.3 kg).

To analyze the effect of a

6-week strength training for the neck flexors and extensors on the acceleration of the head during standing, jumping, and running headers in soccer on a stationary pendulum header

Isometric maximum voluntary contraction (IMVC) measured by a telemetric Noraxon DTS force sensor accelerometer (Noraxon, Scottdale, USA; size: 22 × 16 × 7 mm; weight: 2.8 g; frequency: 1500 Hz, filter: lowpass 500 Hz) fixed in the occipital area of the head. Participants were exposed to two rounds of testing, each round consisting of pre-fatigue test and a post fatigue test. Fatigue was achieved by the Bourban test. The two pre-fatigue tests (standing, jumping, and running header) and the two post-fatigue tests (post-jumping and post-running header) were compared

There was no significant change of the IMVC over time between the groups (F = 2.265, p = .121). Head acceleration was not reduced significantly for standing (IG1 0.4 ± 2.0, IG2 0.1 ± 1.4, CG − 0.4 ± 1.2; F = 0.796, p = 0.460), jumping (IG1 − 0.7 ± 1.4, IG2 − 0.2 ± 0.9, CG 0.1 ± 1.2; F = 1.272, p = 0.295) and running (IG1 − 1.0 ± 1.9, IG2 − 0.2 ± 1.4, CG − 0.1 ± 1.6; F = 1.050, p = 0.362) headers as well as after fatigue of the trunk musculature for post-jumping and post-running headers over time between IG1, IG2, and CG

The presumed preventive benefit of this 6-week strength training of the neck flexors and neck extensors could not be confirmed statistically. The authors recommend a training period of at least 8 weeks.

Caccese et al.

[50]

Year of data collection not stated

A

single round of testing included 1000 simulations of standing headers in experimental test conditions in North America

Boy’s and girls’ soccer

Participants performed a series of 12 standing headers to a target located approx. 2 m in front of them using soccer balls projected (initial velocity = 11.2 m/s at 40° over approximately 12 m) using a machine (JUGS, Tualatin, OR, USA)

One hundred soccer players: 42 males, 58 females, 17.1 ± 3.5 years, 168.5 ± 20.3 cm, 61.5 ± 13.7 kg, and 13.3 ± 3.0 years of soccer participation

To determine the relationships between head and neck size, neck strength and heading technique on head acceleration magnitudes in youth, high school, and collegiate male and female athletes during purposeful soccer heading

Participant height, weight, and head and neck anthropometrics were measured. Isometric strength measurements of the sternocleidomastoid and upper trapezius muscles using a hand-held dynamometer. EMG activity of Sternocleidomastoid and upper trapezius measured using the Trigno™ Wireless System (Delsys Inc., Natick, MA, USA). Heading kinematics were determined using an 8-camera motion capture system (Motion Analysis Corporation, Santa Rosa, CA, USA). Head accelerations were also recorded.

Head mass significantly predicted peak rotational acceleration (β = − 0.404, p = 0.034).

The sternocleidomastoid strength significantly predicted peak linear and rotational acceleration (linear β = − 1.544, p = 0.012; rotational β = − 0.117, p = 0.018).

Technique-related predictors did not significantly predict

peak linear acceleration (R² = 0.066, F (6,87) = 1.029, p = 0.412, ƒ2 = 0.07) or peak rotational acceleration (R² = 0.047, F (6,87) = 0.730, p = 0.627, ƒ2 = 0.05)

Greater head and neck size predicted lower peak linear and

rotational accelerations.

A soccer player with smaller head mass, neck girth, and neck strength may sustain greater head acceleration. The authors recommend that anthropometric and neck strength measures should be considered when determining readiness to begin soccer heading

Collins et al. [27]

2010–2011

One academic year in North America

Boy’s and girls’ soccer, basketball, and lacrosse

Baseline testing of strength and physical measurements taken at preseason and correlated with reported concussion incidence and athletic exposure data

Fifty-one high schools in twenty-five states participated. 6704 high school athletes in boys’ and girls’ soccer, basketball, and lacrosse

To develop and validate a cost-effective tool to measure neck strength. To determine if this tool is applicable by athletic trainers, and to determine if anthropometric measurements can predict concussion risk

A hand-held dynamometer, a hand-held tension scale, Velcro closure head band with D-rings, and a cloth measurement tape to measure head and neck circumference, neck length, and four measurements of neck strength for all athletes participating in school-sports

Neck strength, sex, and sport were significant predictors of concussions. After adjusting for sex and sport, overall neck strength remained a significant predictor of concussion. For every one-pound increase in neck strength, odds of concussion decreased by 5%

Smaller mean neck circumference, smaller mean neck to head circumference ratio, and weaker mean overall neck strength were significantly associated with concussion

Eckersley et al. [51]

Year of data collection not stated

A single round of testing included 192 simulations spanning the experimental test conditions in North America

Non-human simulations of impacts to the head during possible participation in baseball and American Football

Kinematic data of neck models were recorded for impacts to 8 different locations on the head in four different scenarios in six different neck conditions

Impacts using models from Duke University (DUHNM) and the National Crash Analysis Center (NCAC) at George Washington University

To investigate the role of cervical muscle strength in blunt impact head kinematics and the biofidelity of common experimental neck conditions

Four impact scenarios were created. The first scenario simulated a baseball impacting a bare head. The second and third scenarios simulated helmet to helmet collisions with shorter and longer durations respectively. The fourth scenario modeled a lesser helmet to helmet impact force

Kinematic differences from impact location and strength can be ten times greater than cervical muscle activation forces.

Relaxed neck conditions showed lowest peak resultant angular acceleration values for 65% of impacts. Extensor neck conditions showed highest peak resultant angular acceleration values

Results suggest that increased cervical muscle force does not influence short term (< 50 ms) head kinematics.

Impact location and magnitude influence head kinematics more than cervical muscle state

Eckner et al.

[52]

Year of data collection not stated

A single round of testing with three trials in each head position under both muscle activation conditions in North America

Soccer, ice hockey, American Football, martial artists, wrestling and lacrosse

Maximum isometric neck strength was measured using a loading apparatus which applied impulsive test forces to athletes' heads during baseline and anticipatory cervical muscle activation conditions

Forty-six athletes (24 males; 22 females); age range 8–30 years.14 males and 12 females in high school or younger,10 males and females each from college or older. All from a broad range of competitive levels

To determine the influence of neck strength and muscle activation status on resultant head kinematics following impulsive loading

Wrestling headgear was attached to an adjustable cable with an in-line force transducer cable. Head kinematics were measured using an Optotrak motion capture system for peak force values in head flexion, extension, right lateral flexion, or left axial rotation.

Demographic and anthropomorphic measurements were taken. Sonographic cross-sectional area of the right sternocleidomastod muscle was collected

Significant effects for neck strength and cervical muscle activation status across all directions of motion. All neck strength and cervical muscle activation effects remained significant when adjusting for age and sex. Neck circumference and sternocleidomastoid cross-sectional area both had significant effects across all directions of motion, which remained significant when adjusting for age and sex

Greater neck strength attenuates the head's dynamic response to external forces in all planes of head motion and across the age spectrum in athletes of both sexes

Hislop et al.

[53]

2015

One playing season from August to December 2015 in the UK

Rugby Union

Balance training, whole-body resistance training, plyometric training, and controlled rehearsal of landing and cutting maneuvers

Three thousand one hundred eighty-eight rugby players aged 14–18 years.

Twenty schools in each of the intervention and control groups

To determine the efficacy of an exercise program in reducing injuries in youth rugby players and to investigate the effect of program dose on injury measures

Pre-activity exercises for each the intervention and control groups had four phases with increasing difficulty. Coaches recorded training exposure, match exposure, program compliance, and the return-to-play date. School medical staff recorded the injury location and diagnosis

Overall match injury incidence (injuries/1000 player-hours) and burden (days lost/1000 player-hours) rates acted as dependent variables, with further stratification by injury location and event.

Intention-to-treat analyses revealed that the intervention program substantially reduced upper limb injury burden and concussion incidence compared with the control program.

Lisman et al.

[54]

Year of data collection not stated

8 weeks duration in North America

American Football

Isometric cervical resistance-training program of three sets of 10 repetitions of neck extension, flexion, and right and left lateral flexion at 60–80% of 10 repetition maximum (RM), 2–3×/week

Sixteen male participants (age 21.6 ± 2.8 years)

To examine the effects of an 8-week isometric cervical resistance program on the electromyographic (EMG) activity of the sternocleidomastoid (SCM) and upper trapezius (UT) as well as the kinematics of the head and neck in response to a American Football tackle

Isometric cervical strength, neck girth, and both the EMG and kinematic responses of the head and neck during tackling were measured before and after training. Kinematic data were gathered using a ViconNexus® 3D motion capturing system.

Strength measurements in extension and left lateral flexion were statistically significant (73.64–78.81 kg, p = 0.004: 25.49–27.92 kg, p = 0.033). No significant difference was noted for neck girth. No significant effects for peak linear or angular head acceleration, head-cervical segment angular displacement, or time to peak angular acceleration. No influence on the EMG or kinematic responses

This 8-week cervical resistance training program had no effect on the EMG activity of the neck musculature and kinematics of the head and neck in response to a American Football tackle

Mansell et al. [55]

2005

Eight weeks duration in North America

Soccer

Pre-test and post-test study with a control group and intervention group who performed resistance exercises

Thirty-six Division I collegiate soccer players (17 men, 19 women)

To determine the effect of an 8-week resistance training program on head-neck segment dynamic stabilization

8-week cervical resistance training program of 3 sets of 10 repetitions at 55% to 70% of a 10-repetition maximum 2×/week. Participants in the control group performed no cervical resistance exercises

Head-neck segment kinematics and stiffness. Electromyographic activity of the upper trapezius and sternocleidomastoid muscles during force application to the head, and isometric neck strength.

Increases in isometric strength and girth were found in the intervention group. Training did not enhance the head-neck segment dynamic stabilization.

Mihalik et al.

[33]

2011

One playing season duration in North America

Ice hockey

Instrumented helmets collected head impact biomechanics.

Thirty-seven volunteer ice hockey players

To determine the effect of cervical muscle strength on head impact biomechanics

Preseason cervical muscle strength was measured using isometric “break tests” with a hand-held dynamometer

Dependent variables included linear and rotational head accelerations.

Players with greater static neck strength did not experience lower resultant head accelerations

Schmidt et al.

[30]

2014

One off testing procedure in preseason and players followed for a season in North America

American Football

Baseline testing with surveillance of head impact biomechanics

Forty-nine high school and collegiate American Football players (34 high school, 15 collegiate), free of prior head/neck injuries or pain

To determine whether American Football players with stronger, larger, and stiffer cervical muscle characteristics at preseason had reduced odds of sustaining higher magnitude head impacts

Preseason testing: isometric strength using the HUMAC NORM system.

EMG during cervical perturbation was captured. Ultrasonic cross-sectional area was obtained from images using a 7-MHz linear array transducer.

Head impact biomechanics captured using the Head Impact Telemetry System

Players had equal odds for moderate and severe head impacts regardless of cervical muscle strength. Players with larger Sternocleidomastoid, Semispinalis capitis, and composite muscle areas had increased odds, players with stiffer necks during anticipated forced extension and composite stiffness had reduced odds.

The findings did not show that players with stronger and larger neck muscles mitigate head impact severity. Greater cervical stiffness and less angular displacement after perturbation reduced the odds of sustaining higher magnitude head impacts.