Effectiveness of different weekly frequencies of nordic hamstring exercise on performance and injury-associated factors in intermittent sports athletes: protocol of a randomised clinical trial

Objectives: This study aims to verify the effectiveness of different weekly frequencies of Nordic hamstring exercise (NHE) on performance and factors associated with injuries in athletes. Methods: Randomised clinical trial in adult male athletes practicing intermittent sports (e.g. soccer and/or rugby). Participants will be allocated into two groups, according to the weekly frequency of NHE practice: G1, submitted to one weekly NHE session; and G2, submitted to two weekly NHE sessions. The intensity and volume will be increased progressively (repetitions and series). Intervention period ranges 10 weeks during which the participants continue with sports training in their respective modalities. One week before (baseline) and one week after the intervention (endline), the athletes will perform the single-leg bridge test, sit and reach test, 10 m sprint test, vertical countermovement jump, and 180° change-of-direction test. Muscle soreness in the hamstrings and training load will be verified on each intervention day. Discussion: The findings of this study may indicate the use of reduced training volumes, especially regarding the weekly frequency of NHE application in athletes, likely increasing their adherence. Trial registration: Brazilian Registry of Clinical Trials (ReBEC): RBR-8mdbmcp (03/17/2021).