ANZCTR - Registration

Registration number

ACTRN12623000998640p

Ethics application status

Submitted, not yet approved

Date submitted

15/08/2023

Date registered

13/09/2023

Date last updated

13/09/2023

Date data sharing statement initially provided

13/09/2023

Type of registration

Prospectively registered

Titles & IDs

Public title

Testing the Effect of a Plyometric Neck Training Program on Dynamic Head Stabilization in Female Rugby Players.

Scientific title

A Randomized, Controlled Superiority Trial to Compare the Efficacy of Plyometric Neck Training against World Rugby-Recommended Exercises for Optimizing Dynamic Head Stabilization and Eccentric Neck Muscular Strength and Rate of Force Development (RFD) in Female Rugby Players.

Secondary ID [1]

None

Universal Trial Number (UTN)

Trial acronym

Linked study record

Health condition

Health condition(s) or problem(s) studied:

Concussion

Condition category

Condition code

Injuries and Accidents

Other injuries and accidents

Neurological

Other neurological disorders

Intervention/exposure

Study type

Interventional

Description of intervention(s) / exposure

Plyometric Neck Training Program.
Sessions will be delivered (and supervised) in the laboratory, in-person by the primary researcher, so that study groups differ only by the intervention being evaluated. Depending on the stage of training (i.e., what session volume and intensity the participant is at), sessions will last between 30 and 60 minutes).
Given that the training will take place in the lab, under the supervision of the researcher, no protocols will be in place to manage adherence.

Plyometric training protocol
The plyometric training intervention will span 8 weeks, with 2 training sessions completed per week. The program will involve only two different exercises, each with multiple variations/levels of intensity.

Wall rebounds
Variation 1
Participants will begin with the middle part of their feet 40cm from the vertical line of the wall-mounted pad and force plate; they will be leaning back or forward, with either the back of their head or their forehead resting against the padding (depending on whether it is a flexion or extension set). Their hands will be crossed over their chest. They will then use their neck musculature to push their head against the padding and propel themselves away as quickly as possible; they may need to take some steps to regain their balance afterwards.

Variation 2
Participants will begin with the middle part of their feet 30cm from the vertical line of the pad. They will be standing upright, and will slowly lean towards the pad so that their head moves towards it, keeping their body straight (no bend in the knees or hips), and their hands by their sides. The moment their head (either the back of the head or forehead) makes contact with the pad, they will use their neck musculature to propel themselves away as quickly as possible, aiming to minimising pad contact time and maximise force.

Variation 3
The same as variation 2, but beginning 40cm away.

Variation 4
The same as variations 2 & 3, but beginning 50cm away.

Wall rebounds: progression and programming

In session 1, participants will complete 2 sets of 5 repetitions of wall rebounds: Variation 1 in each movement pattern (flexion and extension), with 10 seconds separating each repetition, and a 2 minute rest in-between sets. So, this will total 10 contacts per movement pattern, and 20 contacts on the pad overall in session 1.

If the participant completes session 1 with proper technique, and does not experience any adverse events (such as headaches, severe neck pain) during, or in the 72 hours following session 1, then session 2 will involve 3 sets of 6 repetitions for each movement pattern (therefore, a total of 36 contacts on the pad). From thereon in, progression will be informed by measures of force-time variables from the force plate and LabChart software. When researchers observe that a participant has achieved a 5% decrease in contact time on the pad since beginning that variation, the participant will progress to the next level of intensity in the following session.

If a participant is progressed to Variation 4 of one or both movement patterns, and continues to achieve 5% decreases in contact time in that exercise, then further progression for that exercise will be achieved by increasing the number of repetitions per set by 1.

Sling head-drops
Once positioned on the table with their head resting in the sling, participants will be instructed that the sling will be released at any time in the next 10 seconds. For neck flexor trials, they will be told to begin in a crunch position (i.e., a half sit-up), letting the sling take the weight of their head, and to react to the removal of the head support by returning the head back to its original position as quickly as possible. For neck extensor trials, they will be positioned on their front, engaging the posterior chain but letting the sling take the weight of their head. A random number generator will be used to determine at which second (1-10) the researcher will trigger the release of the electromagnetic catch. This will constitute one repetition. Once the sling has been released and the participant has responded, the positioning of equipment and participant will be restored in preparation for the next repetition.

Sling head-drops: progression and programming.
In session 1, participants will complete 2 sets of 3 repetitions of sling head-drops in each movement pattern (flexion and extension), for a total of 12 repetitions. The rest period between repetitions will be determined by the time taken to restore the set-up. There will be a 2 minute rest in-between sets. The physiotherapy table will be fixed at the highest level of incline.
As with the wall rebound exercise, there is a deliberately low volume of sling head-drops in session 1, to ensure that the participant is able to complete the exercises with proper technique, and without experiencing any adverse events (such as headaches, severe neck pain) during, or in the 72 hours following, the session. If this requirement is met, then in session 2, participants will complete 3 sets of 4 reps for each movement pattern, for a total of 24 reps. From thereon in, the incline of the table may be decreased to increase the intensity of the exercise. The timing of these incline changes will be determined by that participants progression in the wall rebound exercises; the progression in wall rebound intensity level (based on improvements in pad contact time) will be matched by a decrease in the incline of the table. As will be done for the wall rebounds, further progression beyond the last increment of intensity variations will be achieved by increases in volume (1-repetition increases per set).

Intervention code [1]

Prevention

Comparator / control treatment

Active control:
Contact Confident Training Program (WRCC).

Contact confident training protocol
Four exercise patterns have been chosen from the WRCC recommendations to be administered to the second training group. This will run simultaneous to the plyometric intervention; it will span 8 weeks, with 2 training sessions completed per week.
Before performing each new level of an exercise, participants will be shown an instructional video on that exercise from the World Rugby Passport website (https://www.world.rugby). The researcher will also monitor their form and offer verbal cues to prompt proper technique where they deem it necessary. Depending on the stage of training (i.e., what session volume and intensity the participant is at), sessions will last between 30 and 60 minutes).

Deep neck flexor nods
Variation 1: Deep neck flexor nod
Participant will lie flat on their back, with knees bent and feet flat on the ground. They will be instructed to perform a chin tuck to make a double chin by visualizing a stake going through both ears, and rotating their head around the stake, while flattening the curve of their neck against the ground. They may place a finger on their chin to assist the nod. 1 rotation equals 1 repetition.

Variation 2: Deep neck flexor nod and lift
This variation involves the same chin tuck movement as in variation 1, with the addition of a lift; once in the chin tuck position, participants will lift their head 1cm off the ground, and hold it, while maintaining the chin tuck position.

Variation 3: Deep neck flexor nod with a curl
This variation involves the same chin tuck movement as in variation 1, with the addition of a curl; once in the chin tuck position, participants will slowly curl the neck up, vertebrae by vertebrae, until the end range of motion. They will hold the position at the top, before reversing the motion and slowly curling the neck back down, while maintaining the chin tuck.

Deep neck flexor nod: progression and programming
In session 1, participants will complete 2 sets of 5 repetitions of variation 1, with 10 seconds separating each repetition, and a 2-minute rest in-between sets. If this is achieved with no reported or observed adverse events, and researchers observe sufficient technique, then the participant can complete 3 sets of 5 repetitions in session 2.
Participants may progress to variation 2 in week 2, keeping volume at 3 x 5. If that is achieved with no adverse events reported, then in week 3 they will perform variation 3, with volume remaining at 3 x 5. Following that, progression will be achieved via increases in volume. Assuming the participant indicates they are comfortable progressing, and has experienced no adverse events, the volume from week 4 and onward will be as follows:
Week 4: Variation 3, 3 sets, 6 reps each set.
Week 5: Variation 3, 4 sets, 5 reps each set.
Week 6: Variation 3, 4 sets, 6 reps each set.
Week 7: Variation 3, 5 sets, 5 reps each set.
Week 8: Variation 3, 5 sets, 6 reps each set.
*Rest between sets will always be 2 minutes.

Deep neck extensor curl
Participants will be on their hands and knees, with their hands directly underneath their shoulders, a neutral back position, and the head in a fully flexed position (with a chin tuck). They will slowly extend the neck, vertebrae by vertebrae; this action should take 2 seconds, after which their neck should be in a neutral position (eyes looking at the floor). They will hold that position at the top for a pre-specified number of seconds, before reversing the action.

Deep neck extensor curl: progression and programming
The exercise will be progressed by increasing both the time in which the participant holds the neutral position at the top of the movement, and the number of sets and repetitions performed. Assuming no adverse events, and that a participant reports that they are comfortable to progress, the volume of the program will be as follows:

Week 1, Session 1: 2 sets, 5 reps per set, 10 second pause at top.
Week 1, Session 2: 3 sets, 5 reps per set, 10 second pause at top.
Week 2: 3 sets, 5 reps per set, 15 second pause at top.
Week 3: 3 sets, 5 reps per set, 20 second pause at top.
Week 4: 3 sets, 6 reps per set, 20 second pause at top.
Week 5: 4 sets, 5 reps per set, 20 second pause at top.
Week 6: 4 sets, 6 reps per set, 20 second pause at top.
Week 7: 5 sets, 5 reps per set, 20 second pause at top.
Week 8: 5 sets, 6 reps per set, 20 second pause at top.
*Rest between sets will always be 2 minutes.

Backwards roll
Variation 1
Participants will begin seated on the floor, with knees bent and feet out in front of their body. They will roll back onto one shoulder (not onto their head or neck). They will rotate their body backwards so that the legs follow the shoulder all the way over, and they will finish on their knees.

Variation 2
Participants will start on their feet in a crouch or squat position and initiate the backwards roll from there.

Variation 3
Participants will start on their feet in a standing upright position and initiate the backwards roll from there.

Backwards roll: progression and programming
This will be progressed by both increased level of intensity (i.e., variation 1 to variation 2) and increased volume. Assuming no adverse events, and that a participant reports that they are comfortable to progress, the volume of the program will be as follows:
Week 1 Session 1: Variation 1, 2 sets, 5 reps each set.
Week 1 Session 2: Variation 1, 3 sets, 5 reps each set.
Week 2: Variation 2, 3 sets, 5 reps each set.
Week 3: Variation 3, 3 sets, 5 reps each set.
Week 4: Variation 3, 3 sets, 6 reps each set.
Week 5: Variation 3, 4 sets, 5 reps each set.
Week 6: Variation 3, 4 sets, 6 reps each set.
Week 7: Variation 3, 5 sets, 5 reps each set.
Week 8: Variation 3, 5 sets, 6 reps each set.
*Rest between sets will always be 2 minutes.

Front bridge from knees
Variation 1
Participants will begin with their knees and forehead in contact with the floor, and the hips hinged so the buttocks are in the air. They will place their elbows on the ground on either side of their head, dig their toes into the floor, and straighten their legs to lift their knees off the ground. They will be instructed to maintain a chin tuck and engage the neck musculature to hold the position, with the assistance of the arms and shoulders.

Variation 2
This variation will involve the participant placing their hands on the floor on either side of their head for support, rather than their elbows. This will increase the strain on the neck musculature to maintain the position.

Variation 3
The third variation involves the participant maintaining the position while holding their hands behind their back, to maximize the involvement of the neck musculature.

Front bridge from knees: progression and programming
This exercise will be progressed by increasing both variation level and time held in bridge position. Assuming no adverse events, and that a participant reports that they are comfortable to progress, the volume of the program will be as follows:

Week 1 Session 1: Variation 1, 2 sets, 3 reps each set, 10 seconds in bridge position per rep.
Week 1 Session 2: Variation 1, 3 sets, 3 reps each set, 10 seconds in bridge position per rep.
Week 2: Variation 1, 3 sets, 3 reps each set, 15 seconds in bridge position per rep.
Week 3: Variation 2, 3 sets, 3 reps each set, 10 seconds in bridge position per rep.
Week 4: Variation 2, 3 sets, 3 reps each set, 15 seconds in bridge position per rep.
Week 5: Variation 2, 3 sets, 3 reps each set, 20 seconds in bridge position per rep.
Week 6: Variation 3, 3 sets, 3 reps each set, 10 seconds in bridge position per rep.
Week 7: Variation 3, 3 sets, 3 reps each set, 15 seconds in bridge position per rep.
Week 8: Variation 3, 3 sets, 3 reps each set, 20 seconds in bridge position per rep.
*Rest between reps will always be 30 seconds.
*Rest between sets will always be 2 minutes.

Control group

Active

Outcomes

Primary outcome [1]

Difference between the two treatment arms in mean angular acceleration of the head, measured in G-force (g).
This will be measured using video with a high-speed camera (Edgertronic SC1, Sanstreak Corporation, USA), set at a shutter speed of 1/600, a frame rate of 600 fps, pixel resolution of 1264 × 1008 and sensitivity of 6000 ISO. Reflective markers will be placed on the skin of the AC joint, the sternal notch, the C7 vertebrae, and at the front and back of the head, as well as on the perturbation device. This will allow for accurate motion tracking.

Timepoint [1]

A 5-day window before the intervention begins will be available to complete pre-training assessments, and a 5-day window, beginning 2 days after the intervention is complete, will be available to complete post-training (primary time point) assessments.

Secondary outcome [1]

Secondary outcome measures.
Difference between the two treatment arms in mean eccentric neck muscular strength, measured in Nm
This will be measured using a biodex.

Timepoint [1]

A 5-day window before the intervention begins will be available to complete pre-training assessments, and a 5-day window, beginning 2 days after the intervention is complete, will be available to complete post-training assessments.

Secondary outcome [2]

We will also measure magnitude (mV) of upper trapezius muscle activity during perturbation trials.
This will be measured using standard surface EMG procedure.

Timepoint [2]

A 5-day window before the intervention begins will be available to complete pre-training assessments, and a 5-day window, beginning 2 days after the intervention is complete, will be available to complete post-training assessments.

Secondary outcome [3]

Secondary outcome measures.
Difference between the two treatment arms in mean eccentric neck muscular RFD, measured in Nm/s-1
This will be measured using a biodex.

Timepoint [3]

A 5-day window before the intervention begins will be available to complete pre-training assessments, and a 5-day window, beginning 2 days after the intervention is complete, will be available to complete post-training assessments.

Secondary outcome [4]

We will also measure onset latency (ms) of upper trapezius muscle activity during perturbation trials.
This will be measured using standard surface EMG procedure.

Timepoint [4]

A 5-day window before the intervention begins will be available to complete pre-training assessments, and a 5-day window, beginning 2 days after the intervention is complete, will be available to complete post-training assessments.

Eligibility

Key inclusion criteria

participants can be recruited to participate in the study if they are a healthy adult (16+) who was registered as a player with the Otago Rugby Union in 2023, and has taken part in targeted neck warm-up or strength exercises in the last 6 months

Minimum age

16 Years

Maximum age

No limit

Sex

Females

Can healthy volunteers participate?

Yes

Key exclusion criteria

an individual will be excluded from participation if they:
a) in the last 12 months have been diagnosed with a concussion,
b) in the past 3 months have sustained a head or neck injury,
c) have an existing injury that currently prevents regular participation in their chosen sport,
d) have had long-term post-concussion symptoms,
e) scored a six or higher on a 10-point Wong-Baker scale of the self-reported current head or neck pain.

Study design

Statistical methods / analysis

The sample size was calculated based on the primary hypothesis. Peek et al. (2022) reported a 17.2% decrease in peak linear acceleration (g) of the head following a soccer header for female participants in a training group who completed 5 weeks of triweekly neuromuscular neck exercises on top of standard FIFA 11+ training drills. A control group, who completed the standard FIFA 11+ program with no neuromuscular neck exercises, showed a 6.9% decrease. This equated to a group x time interaction effect of partial eta-squared = 0.14, which is equivalent to Cohen's d = 0.8. To allow for participant dropout, we have powered this trial to be able to detect a difference in head acceleration following lab-based perturbation of d = 0.965.
Following apriori for a repeated-measures ANOVA, a total sample size of 24 participants consisting of two groups of 12 (equal world rugby training group and plyometric training group) will have the power of 0.965 to reliably detect effect sizes greater than d = 0.8, assuming a criterion for detection that allows for a maximum Type 1 error rate of alpha = 0.05.

Statistical analysis
Statistical analysis will be performed after post-training. All statistical analysis will be performed using MATLAB and JAMOVI (Version 2.3.26.0) software. Descriptive statistics will be produced, and the primary analysis will consist of a repeated measures ANOVA test conducted for the primary outcome measure of angular head acceleration following perturbation. The within-subjects factor will be time, with 2 levels (pre-training and post-training), and the between-subjects factor will be training group, also with 2 levels (plyometric training group vs WRCC training group). Analysis will determine if there is a significant main effect of time or of training group, and if there is a significant interaction effect. Results of the primary analysis will represent the efficacy of the intervention.
Secondary analyses will involve repeated measures ANOVA’s for each secondary outcome measures, to examine changes in these variables with training. A regression model will also be used to measure the association between the primary outcome measure of angular head acceleration following perturbation, and two secondary outcome measures: both eccentric neck strength and RFD. The strength of these associations will be investigated with a Pearson product-moment correlation coefficient. Correlation coefficients (r) of 0.3, 0.5, and 0.9 will be interpreted as low, moderate and high respectively.

Recruitment

Recruitment status

Not yet recruiting

Date of first participant enrolment

Anticipated

10/11/2023

Actual

Date of last participant enrolment

Anticipated

23/02/2024

Actual

Date of last data collection

Anticipated

24/05/2024

Actual

Sample size

Target

24

Accrual to date

Final

Recruitment outside Australia

Country [1]

New Zealand

State/province [1]

Otago

Funding & Sponsors

Funding source category [1]

University

Name [1]

University of Otago

Country [1]

New Zealand

Primary sponsor type

University

Name

University of Otago

Country

New Zealand

Secondary sponsor category [1]

None

Name [1]

Country [1]

Ethics approval

Ethics application status

Submitted, not yet approved

Ethics committee name [1]

University of Otago Human Ethics Committee (Health)

Ethics committee address [1]

362 Leith Street Dunedin North Dunedin 9016

Ethics committee country [1]

New Zealand

Date submitted for ethics approval [1]

07/09/2023

Approval date [1]

Ethics approval number [1]

Summary

Brief summary

The proposed project will examine whether training the neck with a focus on rapid movement (plyometric neck training) improves the ability of female rugby players to reduce acceleration of the head following an impact, and therefore the forces acting on the brain. The effect of this training program will be compared to a program consisting of head control exercises designed by World Rugby.

It is hypothesized that plyometric neck training will be greater than the World Rugby training program for improving the ability of female rugby players to reduce head acceleration during both expected and unexpected impacts.

It is also hypothesized that the plyometric neck training program will elicit greater increases in the amount of electrical muscle activity, and greater decreases in the time taken to activate the muscle, during an impact, compared to the World Rugby training program.

Similarly, it is hypothesized that the plyometric neck training program will be more effective than the World Rugby training program in increasing the strength and speed characteristics of the neck muscles.

Finally, it is hypothesized that there will be a negative correlation between acceleration of the head following an impact, and both the speed and strength of the neck muscles.

Trial website

Public notes

Contacts

Principal investigator

Name

A/Prof Melanie Bussey

Address

School of Physical Education, Sport and Exercise Sciences, 55/47 Union St West, Dunedin North, Dunedin, 9016

Country

New Zealand

Phone

+64 3 479 8981

Email

[email protected]

Contact person for public queries

Name

Ben Shepherd

Address

School of Physical Education, Sport and Exercise Sciences, 55/47 Union St West, Dunedin North, Dunedin, 9016

Country

New Zealand

Phone

+64 22 129 5652

Email

[email protected]

Contact person for scientific queries

Name

Ben Shepherd

Address

School of Physical Education, Sport and Exercise Sciences, 55/47 Union St West, Dunedin North, Dunedin, 9016

Country

New Zealand

Phone

+64 22 129 5652

Email

[email protected]

Doc. No.	Type	Email
20037	Study protocol	[email protected]
20038	Informed consent form	[email protected]
20039	Ethical approval	[email protected]

Trial Review

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