Background Single leg squat (SLS) is a widely used screening tool to assess lower limb dynamic control especially for knee valgus collapse. Dynamic function is determined from SLS through observation on knee alignment quality, and is proved related to lower limb, hip and core muscle strength,^1–3 flexibilities and neuromuscular control patterns.⁴ On the other hand, the abovementioned items regarding muscle conditions are also well-known elements that contribute to physical fitness performance.^5–9 Whereas there are limited studies on the relationship between SLS performance and lower limb fitness performance. Female youth soccer players were the selected population for this experiment, which was found to be most vulnerable to lower limb injuries due to gender anatomy and structure, for example ACL and ankle injuries.^10–13

Objectives The present study investigated the correlation between subjective assessment on SLS with performance of three fitness elements in youth female soccer players.

Material and method A total of 36 youth female soccer players (age = 13.6 ± 1.1; height = 156.1 & plusmn;7.7 cm; weight = 48.7 ± 10.2 kg) was recruited to perform the SLS and three soccer-specific fitness tests regarding explosiveness, speed, agility after anthropometric measurements and warm-up. The SLS task was recorded in video in frontal plane view then rated by exercise specialist as “good” or “poor” by considering movement quality (Table 1) and joint alignments (Figure 1).^14–16 The fitness performance was compared between the SLS rating “good” and “poor” group using t-test. Spearman correlation coefficients were generated between the fitness performance and SLS ratings.

Result Demographics of participants between 2 SLS groups (good/bad) were no significant difference in age (13.9 ± 1.0/13.5 ± 1.0, P = 0.462), height (156.3 ± 7.0/155.5 ± 9.2, P = 0.785) and weight (48.1 ± 10.0/49.9 ± 10.9, P = 0.640). There was no significant difference between SLS group rated “good” and “bad” performed by dominant leg regarding fitness performance (Table 1). And no significant correlation between SLS performance and any of the three fitness elements.

Conclusion SLS assessment by subjective rating is not capable of reflecting soccer-specific lower limb fitness level. Possible reason could be that current SLS rating method created ceiling effect and mask fitness level difference among players (ie not sensitive enough). Modification in SLS task eg multi-stage weight bearing, as well as increase objectivity of rating criteria may increase sensitivity. Also, comparison between SLS with other fitness parameters such as isometric strength, flexibility etc. could be explored in future studies.

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