Normative values, longitudinal trends and usefulness of adductor dynamometry to detect fatigue in professional rugby league players

In rugby league change-of-direction, kicking and running are essential. As such, hip and groin soreness and injuries are common. Dynamometry tests are regularly used to assess adductor strength and monitor groin pain. Test results appear sensitive to changes in acute and chronic training loads (TL), providing further evidence to monitor fatigue. This study aimed to examine the typical error of measurement (TE) and smallest worthwhile change (SWC) of the adductor squeeze test at 60° as well as provide positional differences, normative values and longitudinal trends across a National Rugby League (NRL) season. METHODS: Thirty-three players competing in the NRL (26.3 ± 3.6 yr, 100.6 ± 8.7 kg) were broken into their positional groups (Outside Backs, Adjustables and Forwards) and tested at the beginning of pre-season to limit any TL induced fatigue. Using a hand-held dynamometer, adductor squeeze scores for the 60° test (lying supine with legs bent at 60°) were collected twice, with two minutes separating the test-retest. Intra-individual means were used to calculate positional normative means. Effects sizes (ES) and 95% confidence intervals (CI) were used to describe the magnitude of difference between positional groups, interpreted as; ES 2.1 very large. TE and SWC were calculated with 95% CI to examine reliability and usefulness. To remove variance in individual norms, all data was converted to intra-individual Z-Scores with the squad mean reported across the competitive season. RESULTS: TE (14.4; CI: 11.6 - 19.0) was similar to SWC (14.1; CI: 11.4 - 18.7) of the squad indicating the test is 'satisfactory'. Adjustables had lowest mean squeeze scores (225.8 ± 59.8 N; n=9) behind Forwards (256.5 ± 77.2 N; n=15) and Outside Backs (265.0 ± 67.9 N; n=9). Moderate and small ES were observed (0.6 ± 0.9 and 0.4 ± 0.8; ES ± CI) when comparing Outside Backs and Forwards with Adjustables, respectively. However, all CI overlapped zero and therefore differences were deemed unclear between positional groups. Observation throughout the competition season showed distinct periods of decreased adductor strength output (Figure 1). DISCUSSION: The current findings deem the 60° adductor dynamometry test 'satisfactory' for use in elite rugby league players. Additionally, any change ≥15 N may be practically considered a 'real' change. The longitudinal periods of decreased strength appear related to specific time periods, demonstrating that groin strength is sensitive to changes in TL, however the detailed extent of this relationship requires further examination. PRACTICAL APPLICATION: The current findings provide practitioners a value of 'real' change when using adductor dynamometry tests in rugby league athletes. This may assist performance staff to monitor changes in the ability of the pelvis to produce force that may indicate fatigue or potential for injury