Effect of Neck Training on Outcomes Related to Sport-Related Concussion

This study aims to evaluate the efficacy and acceptability of a novel evidence-based neck resistance training program for female soccer players. The primary objective is to assess the program's impact on neck strength and head accelerations during impact, with the broader goal of informing strategies to reduce the risk of sport-related concussions in soccer. A pilot quasi-experimental design will be employed to test the intervention and collect preliminary data for future large-scale trials.

Two senior-level female soccer teams will be invited to participate in the study. One team will be allocated to the intervention group, while the other will serve as the control group. The intervention group will undertake an eight-week neck resistance training program designed according to current resistance training prescription guidelines. The program consists of both static and dynamic exercises implemented with a head harness and resistance tubing to allow variable resistance loads. To ensure flexibility and adherence, the program is designed to be conducted either during the team's regular on-field soccer training or off-field gym sessions. Participants will complete the exercises two to three times per week. The control group will continue their usual training practices without incorporating any neck-specific resistance training during the study period.

Before the intervention, participants from both teams will undergo comprehensive baseline testing at Lund University's Movement and Reality Lab (MoRe-Lab). The testing will include three main components: isometric neck strength testing, head acceleration testing, and muscle activation analysis. Neck strength will be assessed in four cervical directions-flexion, extension, lateral flexion, and rotation-using a handheld dynamometer. Athletes will be seated in a high-backed chair and secured with straps to isolate head and neck movement. A snugly fitted head harness will be connected to the dynamometer, and participants will be instructed to exert maximal force during three-second isometric contractions in each direction. Each athlete will perform three repetitions, and the highest force value recorded in newtons will be used for data analysis.

Head acceleration will be assessed using a custom-built device designed to measure safe, controlled head movements. Athletes will be seated in the device and strapped securely to ensure only head and neck movement is permitted. A head harness connected to a drop mechanism will deliver a one-kilogram weight drop from a height proportional to the athlete's stature. This will produce safe, measurable linear and rotational head accelerations, with head movement captured by the Qualisys motion capture system. Data from this system will be used to calculate both linear and rotational accelerations in all four cervical directions.

To evaluate muscle activation patterns during head acceleration testing, surface electromyography (EMG) sensors will be placed on the sternocleidomastoid muscles and the trapezius (pars descendens). These exploratory outcomes will provide additional insights into the neuromuscular responses elicited by the intervention.

Following the baseline assessments, teams will proceed to the intervention phase. After the eight-week intervention, participants will return for follow-up testing, which will replicate the baseline assessments. At the conclusion of the study, all players and coaches will complete a questionnaire designed to evaluate the acceptability of the exercise program. This questionnaire will include both Likert-scale items and open-ended questions, allowing participants to provide detailed feedback and suggest potential improvements to the program.

Data analysis will focus on comparing changes in key outcomes within and between the intervention and control groups. The primary outcomes-changes in isometric neck strength and head accelerations-will be analyzed using repeated measures analysis of variance (ANOVA). Secondary outcomes, including the acceptability data, will be analyzed descriptively for Likert-scale responses, while qualitative feedback from open-ended questions will undergo thematic analysis. Exploratory outcomes, such as muscle activation data, will be evaluated descriptively to assess activation patterns during head accelerations.

To ensure adequate statistical power, an a priori sample size calculation using G*Power (v. 3.1.9.7, Düsseldorf, Germany) determined that a minimum of 34 participants would be required for repeated measures ANOVA (effect size f > 0.25, power 0.80, α = 0.05). Adjusting for cluster randomization using a variance inflation factor with a moderate intracluster correlation coefficient (ρ = 0.05) and accounting for a 25% dropout rate, the target sample size increased to 96 participants. For this pilot study, approximately half of the required sample size-around 50 participants-will be enrolled across the two soccer teams. This approach ensures the safety and feasibility of the intervention, provides preliminary effect sizes, and informs the design of a future full-scale trial.

The research team includes Branimir Ivanic, PT, MSc, Anna Cronström, PT, PhD, Nicholas Ryan, PhD, and Professor Eva Ageberg, PT, PhD, all affiliated with Lund University, Sweden. Professor Ageberg serves as the Principal Investigator for the study.