Comparing apples and pears? Evaluating the interchangeability of three different positions for hip abduction and adduction strength testing in academy footballers.

Objectives: To compare strength parameters and pain ratings across three different positions for

isometric hip abduction and adduction strength testing.

Design: Cross-sectional study.

Setting: Two elite European football academies.

Participants: Male football players (n=188, mean age 15.5 ± 1.6) from the U14-U19 teams.

Methods: Isometric hip abduction and adduction were tested in 3 different positions on the ForceFrame: bent-leg with knees on pads, straight-leg with ankles on pads, and straight-leg with knees on pads. The order was randomised. The outcome measures were maximum isometric hip adduction and abduction strength (F_max), limb symmetry index (LSI), hip adduction-to-abduction strength ratio and hip/groin pain numeric rating scale (NRS).

Results: Correlation was moderate to high for F_max in hip adduction (r = 0.64 to 0.73) and abduction (r = 0.78 to 0.84), but low for LSI and strength ratios (r = 0.06 to 0.48). Pain was reported by 19% and 13% of players during adduction and abduction respectively, with the majority (11% and 10%) only reporting pain in one of the three positions.

Conclusions: The findings suggest that maximal strength values from the three test positions can be compared (i.e. using a conversion factor). The interchangeability of test positions is otherwise limited, due to inconsistent pain ratings and low correlation for LSI and strength ratios.