The Effectiveness of Two Different Interventions on Hip Adduction Strength in Junior Floorball Players - A Randomized Controlled Trial

Study type The present study is a two- armed randomized controlled trial. Study setting and participants 50 floorball players in high-school level will be invited to participate. An a priori power calculation indicated that 40 participants are required to detect an effect size of 0,3, with a significance level of 0.05 and a statistical power of 80%.

Recruitment and study procedure The recruitment will be performed in two steps; (1) The project will be presented to responsible floorball coaches at one high-school with the aim to get consent to contact the players in their floorball group. (2) The Research Group will visit the players to ask for individual consent.

Baseline assessment Three assessments will be performed: (a) questionnaire including demographic data, injury history, history of adductor strength training and information dominant leg, history of lower limb and lower back problems and previous experience of groin specific strength training. (b) eccentric hip adductor strength measured with a handheld dynamometer (c) isometric hip adductor and abductor strength measured with the ForceFrame Strength System (VALD).

Randomization, stratification and statistical analysis Randomization will follow an individual-randomization procedure. Randomization will take place after completion of baseline strength measurements. Allocation followed a 1:1 ratio, where the two intervention groups are equal in size. All stratification follows the allocation described under "Randomization" above.

The following variables will be stratified: Sex, and eccentric hip adductor strength (measured with a handheld dynamometer) at baseline. Analyses will follow the intention-to-treat principle using mixed-effects models.

Intervention

The intervention will consist of two parallel groups:

• Progressive training program using the Copenhagen Adductor Exercise (CAE).
• Progressive training program using the Adductor Slide (AS). The interventions followed a progressive protocol. The exercise was incorporated into the participants' regular training and took approximately 10 minutes on the days the intervention was performed. The intervention protocol for both groups followed an 8-week progressive loading structure with gradual increases in training volume over time. During week 1, participants completed 2 sessions per week, performing 2 sets of 6 repetitions per side. In weeks 2 and 3, the number of repetitions was increased to 8 and 10 per side, respectively, while maintaining the same weekly frequency and number of sets. In week 4, the number of sets was increased from 2 to 3, while repetitions remained at 10 per side. During weeks 5 and 6, repetitions were further increased to 12 per side, followed by 15 repetitions per side during weeks 7 and 8. Overall, the protocol progressively increased training load by manipulating repetitions first, then sets, and finally maintaining a higher training volume in the final phase.

For both interventions, each repetition was performed with a 3-second eccentric phase and a 3-second concentric phase.

Implementation and adherence The intervention was supervised by the research group. Attendance was recorded at each intervention session.

Follow-up assessment Three assessments were performed: (a) questionnaire assessing how the players experienced the intervention, if any adverse events occured, their motivation to perform the intervention and if they experienced DOMS (delayed onset muscle soreness) during the intervention (b) eccentric hip adductor strength measured with a handheld dynamometer (c) isometric hip adductor and abductor strength measured with the ForceFrame Strength System (VALD).

Outcome variables and analyses. Between-group effects will be calculated. Main outcome variables will be;

• Eccentric hip adductor strength (measured with handheld dynamometer). The unit used will be Nm/kg.
• Isometric hip adductor and abductor strength (measured with the ForceFrame Strength System, VALD). The unit used will be Nm/kg.
• Ratio between isometric hip adductor and isometric hip abductor strength (measured with the ForceFrame Strength System, VALD). Percentage (i.e a measure of the strength balance between the hip adductors and abductors. Lower values indicate relatively weaker adductors compared with abductors) will be calculated to express this ratio. Potential confounders that will be analyzed as interactions will include;
• Attendance to the intervention
• Motivation to perform the intervention
• Experienced DOMS
• Contamination (i.e if the participant performed hip adductor specific training outside the intervention).