FINS
Fins are made from different materials such as rubber, silicone, and glass fiber. They enable the artificial enlarge feet area and are widely used for displacements below or on the water surface. The different shapes, lengths, widths, areas, levels of stiffness and density can provide various responses of velocity, economy and swimming efficiency, no matter the comparison between their different types or swimming without them. The principle underlying its use is the same as those used for paddles, i.e., by increasing the area of the feet it is possible to displace a greater mass of water.
In relation to the physical characteristics of the commercial fins available, it was observed that, relative to the area, the larger ones occasion a lower energy cost and a higher thrust (improving the horizontal position of the swimmer's body), while those that have smaller areas produce a higher energy cost and a lower thrust; regarding stiffness, the strictest ones generate a lower maximum velocity and a higher energy cost, compared to less rigid fins.
The use of fins does not affect only the legs, but also swimmer's body as a whole because they improve the propelling efficiency of both lower and upper limbs (in these last ones, less intensely). Zamparo et al. observed that the propelling efficiency may increase, on average, 20% with fins.
Conclusion is that paddles cause major changes in the average stroke length, the average stroke rate, the average swimming velocity, the index of coordination, and duration of the stroke phases, although they do not modify the blood lactate levels in similar velocity (with and without paddles). Similarly, it is observed that fins affect the average swimming velocity, the average stroke rate, the kick dep depth, and frequency, but there is still a lack of information about their effects on the average stroke length, the duration of the stroke phases, the index of coordination and blood lactate levels.
Although not justifiable, it seems natural that most of the publications on the use of external resistance in swimming have focused on upper limbs force development (in this case, the paddle), as they contribute about 85% of the total propulsion in front crawl.
Furthermore, it is important to consider the possibility of different sizes and shapes of paddles and fins that produce different biomechanical and physiological responses. This deserves special attention because it directly influences the organization of training loads throughout the periodization. As reported, acutely, different sizes may affect important parameters of the training load, as the average swimming velocity, for example. Whereas the neuromuscular adaptations are maximized in - or close to - the execution velocity of the training, the effectiveness of situations in which there is a very drastic reduction in the stroke rate could be argued.
Coaches should focus their goals, when using paddles and fins, in order to choose the sizes of them and the intensities that swim will be carried out, considering the changes in the biomechanical and physiological aspects of swimming-related to the use of paddles and fins.