Swimming with fins is sport discipline that is carried out both on the surface and under water at 1-2 metres depth. Fin-swimmers practice apnoea performance with a breathing tube or pressurised bottles that they use for a breathing lung regulator. All these methods of swimming put great demands on breathing, the flexibility of the rib cage (Illi et al., 2012), and the strength of the respiratory muscles (Lindholm et al., 2007).
Fin-swimmers need inspiratory power for sufficient inspiration. Expiratory muscle strength is important for breath out against water resistance. Respiratory muscles are not only essential for breathing but they are also involved in the body movement. The auxiliary respiratory muscles are active only when the main respiratory muscles are tired (Pendergast et al., 2015). However, the auxiliary muscles are involved in locomotion and cannot expend all their activity for respiratory functions.
Another important aspect that also affects the respiratory mechanics of fin-swimmers is the racing swimsuit (Pendergast et al., 2006). This type of swimsuit should encircle the body of a fin-swimmer as much as possible, thus causing considerable muscle compression. However, this feature further increases the work the inspiratory muscles must perform. The inspiratory muscles should overcome not only the hydrostatic resistance, but also the resistance from the swimsuit.
Fin swimming is a specific discipline that has been rapidly evolving. The coaches continuously improve training methods and expand the range of resources to improve the athletic performance of their charges (HajGhanbari et al., 2013; Kilding et al., 2010).
Respiratory muscle training (RMT) is mainly used in the field of pulmonary rehabilitation (Elbouhy et al., 2014; Lacasse et al., 1996) but recently it is used more often also in athletes in various types of sports (HajGhanbari et al., 2013; Kilding et al., 2010; Wylegala et al., 2007). Studies have confirmed that RMT also improves RMS and endurance in healthy people and in athletes (Aspenes and Karlsen, 2012; Illi et al., 2012), but fin-swimmers had not been studied yet. From this point of view, if the use of additional RMT can increase the strength of the breathing muscles, it will be easier for fin-swimmers to overcome hydraulic resistance and thus also delay inspiratory muscle fatigue. Another advantage may be an increased expansion of the rib cage, which affects the overall upward push of water on a fin-swimmer. This is especially relevant for the discipline of swimming on the water surface with bi-fins. Swimmers in this discipline aim among others to swim as fast as possible on the water surface where the resistance of the environment, which acts on the swimmers, is the lowest. If a fin-swimmer manages to stretch more of the ribcage, he or she will be more buoyed to the surface. Higher chest expansion associated with increased inspiration can be also beneficial for underwater swimming. We think that our pilot study can uncover new possibilities for training in young fin-swimmers. It is known that the strength of respiratory muscles as well as the strength of other skeletal muscles increases with increasing age during childhood (Wilson et al., 1984). Therefore, RMT can have potential positive effect on their sports performance.
The hypothesis of this study was that RMT applied to standard fin-swimmer training would have a beneficial effect on fin-swimmers' performance. Therefore, the main aim of our study was to assess the response to RMT in fin-swimmers on their performance in the apnoea (AP) max. The second aim was focused on comparison of maximal inspiratory and expiratory mouth pressures with predicted values for healthy children and on the influence of RMT on RMS in fin-swimmers.
This randomised, evaluator-blinded, controlled crossover experiment was conducted at the Faculty of Physical Culture, Palacky University in Olomouc, Czech Republic.
A group of young Czech fin-swimmers learned in advance basic information about the experimental procedure and the purpose of the present study. We obtained signed approval from the participants and their parents together with completed personal questionnaires and the study was approved by the Faculty Ethical Committee.
The mixed-gender group of 28 youth swimmers was randomly divided into an experimental (EG; n = 14) and a control group (CG; n = 14). Each fin-swimmer had to choose an envelope, which contained either number 1 or number 2. Fin-swimmers who chose an envelope with number 1 were assigned to the experimental group while fin-swimmers who chose an envelope with number 2 were assigned to the control group. Inclusion criterion for both groups was participating in fin-swimming training in a swimming Club twice a week for at least two years. The exclusion criteria for both groups were any kind of chronic or acute diseases to avoid the possible effect of diseases on fin-swimmers' performance and RMS which could negatively affect the results of this study.
After a preliminary examination and the first month of training, they were reduced to 20 participants (EG: n = 12; average age: 12.0 [+ or -] 1.7 years; height: 1.58 [+ or -] 0.11 m; weight: 47.4 [+ or -] 10.5 kg) (CG: n = 8; average age: 11.5 [+ or -] 2.4 years; height: 1.53 [+ or -] 0.18 m; weight: 49.6 [+ or -] 17.0 kg) (Figure 1).
Those in the EG performed regular swimming training with daily RMT for 1 month. Participants in the CG had only regular swimming training. After the EG finished the experimental training, ventilatory parameters and...