To make or to break in isometric neck strength testing?

Objectives. - Concussion is the most prevalent injury in Rugby Union. Isometric neck strength tests have been used in Rugby Union to screen for modifiable injury risk factors. Several methods and variations in protocol exist for neck strength tests, including performing these tests in the 'make' or 'break' fashion. We aimed to compare these two methods, determine their association, and their intra-session reliability. Equipment and methods. - A cross-sectional study with 11 semi-professional Rugby Union players and 35 university students. Peak-force from three maximal isometric 'make' or 'break' contractions in neck flexion, extension, and right/left lateral-flexion were recorded with participants seated using a load cell device. Passing-Bablock procedures were used to assess systematic and proportional differences between methods, whereas Bland-Altman plots were constructed to assess bias and variability. Reliability was assessed using typical errors, coefficient of variations (CV), and intraclass correlation coefficients (ICC). Results. - There were no systematic or proportional differences based on the Passing-Bablock procedure. The Bland-Altman plots displayed mean biases ranging from 0.85-1.9 kg across directions, with small (flexion and left lateral-flexion) effect-size differences. Mean break test values (range: 21-26.7 kg) were generally greater than make test ones (range: 19.1-25.8 kg). Both methods demonstrated excellent reliability (ICC = 0.95-0.97, CV = 5.7-12%). Conclusion. - Assessment of maximal isometric neck forces has shown excellent reliability, with no systematic or proportional differences and good correlation between the two methods. The two assessment methods performed in the sitting position can be used relatively interchangeably, although a small difference in flexion and lateral bending exists. (c) 2023 Published by Elsevier Masson SAS.