Reliability of the isometric mid-thigh pull peak force in Irish schoolboy rugby players

BACKGROUND: Maximal strength is a key variable within youth rugby union and is therefore of merit when testing and monitoring youth rugby athletes. Isometric mid-thigh pull peak force (IMTP PF) has been observed to be a reliable, valid, and safe means of assessing maximal strength in previously researched cohorts. Currently, there exists a distinct lack of literature with regards to the use of IMTP PF with non-elite youth athletes. OBJECTIVES: (1) Investigate the intra-day reliability of the IMTP PF with respect to the three age-grades of Irish schoolboy rugby union, (2) investigate the inter-day reliability of the IMTP PF within Irish schoolboy rugby union. METHODS: The current study utilised self-selected body positions of 84 non-elite schoolboy rugby union athletes (age: 14.7 ±1.7 years; height: 170.6 ±10.3 cm; mass: 63.9 ±14.8 kg). RESULTS: IMTP PF was observed to be a reliable measure of peak force both inter- and intra-day (Intra-day: Coefficient of Variation 3.3%; Interclass Correlation Coefficient 0.99; 95% Confidence Interval 0.99 – 1.00; Inter-day: Coefficient of Variation = 5.1%; Interclass Correlation Coefficient 0.99; 95% Confidence Interval 0.98 – 1.00). A change of 10.9 kg should be deemed worthwhile when working with Irish schoolboy rugby players. CONCLUSION: The IMTP PF is a safe and reliable measure of maximal strength in non-elite youth rugby athletes.