This study aimed to compare the isometric hip adduction/abduction strength profile of elite and sub-elite female soccer players. In addition, the influence of limb-dominance was analyzed. The main finding of this study was that elite female soccer players showed stronger values than sub-elite female players, both in isometric hip adduction and abduction test. Furthermore, no differences were observed between dominant leg and non-dominant leg, as well as adduction:abduction strength ratios in both elite and sub-elite players.
Many short-speed actions mixed with large number of acceleration/decelerations actions as well as sudden changes of directions, characterize modern soccer 25,26. However, these physically demanding actions requires a well-developed neuromuscular system. In our study, elite female soccer players demonstrated strongest values for adductor and abductor isometric hip strength in comparison to sub-elite players, even when results were adjusted by players´ age, see Fig. 2. Similar results were found by Prendergast et al 18 in a sample of male Australian footballers. In that study, elite male athletes exhibited higher values of adduction and abduction strength test in comparison with sub-elite and amateur athletes. These differences between players level (i.e., elite vs. sub-elite) could be explained by the number of weekly training sessions and match/training intensity.
Regarding players leg limb-dominance, our results revealed that there was no influence of preferred leg on hip adduction or abduction strength test in elite vs. sub-elite female soccer players (see Table 2). For instance, in a sample of male elite soccer players, Thorborg et al 1 revealed differences, although marginally, in hip adduction and abduction strength regarding dominance. However, the authors concluded that the negligeable difference between the dominant and non-dominant side was within the measurement variation of the test procedure. Our results suggested that, in healthy female soccer players, there is symmetry in isometric hip adduction and abduction strength, which may have important clinical implications, for example, when an athlete gets injured. In this sense, the use of a player´s un-injured leg strength, as a reference point for tracking muscle recovery post-injury, could be an option. Specifically in female athletes, although in other sport, Mentiplay et al 17 revealed no clinically relevant effect of leg-limb dominance on isometric strength of hip adduction and abduction. Collectively, these results agree with our findings about the no effect of leg dominance on isometric hip strength profile.
Our findings revealed that independently of players level (i.e., elite vs. sub-elite), no differences were found on adduction:abduction ratios, both in preferred and non-preferred leg (see Fig. 2C). The mean values of hip adduction:abduction ratio for elite and sub-elite female players ranged from 1.13–1.21 (see Table 2). These results were slightly higher ratios in comparison to those reported by Thorborg et al 1 in male soccer players (1.04–1.06) or those found by Prendergast et al 18 in Australian footballers (1.03–1.13). In this sense, a deficit in hip abduction strength could be explain the differences between sex on isometric hip strength ratios. However, our results showed that although isometric hip strength differ between players performance, when adduction:abduction ratios were compared, no differences were found according to players performance or preferred limb. Specifically in female athletes, Mentiplay et al 17 found a median of 1.00 in dominant and non-dominant leg in elite Australian footballers. Previous studies performed in a cohort of male soccer players have shown that reduced adduction strength has been associated with groin injuries 11. Similarly, Roe et al 3 showed that there was an association between changes in adductor strength and distance covered at high-sprint after a competitive match. However, it should be note that little is known about the isometric hip adductor and abductor strength profiles and their relationship with groin injuries and/or players performance in a cohort of female soccer players. Further studies, in elite female soccer players, need be addressing these questions.
There are several limitations to this study that should be keep in mind when interpret the findings. Although the same physiotherapist performed all assessments to ensure an intra-rater consistency, we did not measure isometric hip adduction and abduction test using a fixed-frame dynamometry system to assure no intra-tester biases. Previous studies have shown that HHD is a valid tool to assess isometric hip strength 27 even in comparison to fixed-frame dynamometry system 21. However, to add more quality to our data, we performed a test-retest reliability showing an excellent reliability result both adduction and abduction isometric hip strength. Finally, temporal moment of assessment period corresponded to pre-season. Although all the players had a special routine during off-season period, the differences obtained in isometric hip strength could differ during the competition period.
All in all, this study reported that elite female soccer players were stronger than sub-elite female players in hip adduction and abduction strength test whereas adduction:abduction ratio values did not differ between players performance (i.e., elite vs. sub-elite) or legs (i.e., dominant vs. non-dominant).