# Relationship Between Front Crawl Trunk Incline and Lower Limbs' Biomechanics in Non-Expert Swimmers
## 4 Discussion
A steeper trunk angle increases drag [21], requiring greater propulsion to maintain speed. However, if the knee action is insufficient, the swimmer may be unable to counteract this increased resistance, further reinforcing a suboptimal body position. This finding aligns with a previous study on elite swimmers, where a more streamlined posture was associated with an effective kicking technique. For [PERSON] et al. [22], the kicking action in front crawl had a positive effect on reducing the pressure drag acting on the trunk, thereby allowing swimmers to achieve a given velocity with less propulsive force from their hands, with this effect being most notable in low-velocity ranges. Our third finding reveals a negative relationship between the mean kicking force and TI, suggesting that non-expert swimmers with a lower kicking force tend to exhibit a steeper trunk angle. This insight provides a possible explanation for the first two findings, reinforcing the idea that ineffective lower limb action contributes to a suboptimal body position and, ultimately, reduced swimming efficiency. A strong and continuous kicking force plays a crucial role in maintaining a more horizontal body position in the water and not accounting for drag increases [23]. In well-trained swimmers, the propulsive force generated by the legs counteracts the natural tendency of the lower body to sink, allowing for a more streamlined posture with minimal trunk inclination [11]. However, in non-expert swimmers, a weaker kicking force may fail to provide adequate lift, leading to a greater trunk inclination and increased hydrodynamic resistance. This aligns with our second finding, where a restricted knee range of motion and exaggerated knee actions were associated with a greater TI. These factors likely contribute to a less effective kick overall, reducing both propulsion and the swimmer's ability to sustain an optimal body position. This relationship supports the idea that non-expert swimmers rely more on their upper body for propulsion while their lower limbs play a limited role in both forward movement and stability. This imbalance may lead to compensatory techniques, such as increased lateral actions or exaggerated arm strokes directed to the bottom, which could further impair their swimming efficiency. In contrast, elite swimmers demonstrate a well-integrated kicking pattern where the lower limbs not only contribute to propulsion but also help maintain body alignment when coupled with the arms' action [10]. As such, any teaching model for this kind of swimmers should include a longer-lasting phase that works on body alignment derived from the lower limbs' actions alone, which may create a more solid foundation when breathing and the upper limbs come into play later in the teaching model. In the end, these findings benefit the swimming professionals working daily on the pool deck. Since non-expert swimmers are the \"core\" of their population, they should keep their focus on trunk incline behaviors while progressing through each component of a structured swimming program. Some teaching strategies should focus on finding the ideal knee ROM based on in-water contrast drills, emphasizing exaggerated or restricted kick mechanics. This dual work on kick frequency and amplitude can help swimmers generate a more proprioceptive stimulus in order to readjust their trunk inclination based on several task constraints. Some limitations can be assumed while conducting this study: (i) the assessed non-expert swimmers were 19 years of age, so these results cannot be extrapolated to younger ages; (ii) kicking kinematics and kinetics were assessed independently through separate tests, which may hide potential links between both domains and TI. Future studies should try to avoid these issues and explore whether additional interventions may benefit this kind of swimmers. Targeted interventions, such as core stability exercises, flotation drills, or proprioceptive feedback, could help non-expert swimmers achieve a more hydrodynamic and favorable posture.