Muscle Fiber Typology is Associated with Determinants of Performance in Elite-Level Swimmers

Abstract

The determinants of sporting performance are important when attempting to identify and influence world-class and elite sporting results. This is highly relevant in swimming, as the complexities the aquatic environment creates for swimmers could mean that the determining characteristics could be of greater influence to their overall performance. However, the physiological determinants of world-class and elite swimming performance are underexplored in scientific research because of the complexity the water creates. For example, a protocol to measure gas exchange during swimming has not been developed with the level of accuracy, which can be obtained from a running on a treadmill or cycling on an ergometer. Consequently, research in swimming has primarily focused on the determinants that can be measured or monitored on land, opposed to in the water. In light of the restrictions or undeveloped methodology in swimming, the aim of this thesis was to explore a potential physical characteristic that could be deterministic of swimming performance – muscle fiber typology. In study 1, peer-reviewed literature that described the age, height and body mass of Olympic level swimmers was reviewed to better understand whether these characteristics were deterministic to performance at the highest level of swimming competition, and whether these are still valuable to assess. In addition to this collation of literature, this study also assembled original data on the age, height and body mass of freestyle swimmers at the 1968, 1992 and 2016 Olympic Games. Data from all 4 swimming strokes was also collected form the 2016 Olympic Games in order to describe the current state of these characteristics in world-class swimmers. This assemblage of data highlighted that both female and male FR swimmers were taller at the 1992 (175.0 ± 6.1 cm and 189.0 ± 6.7 cm) Olympic Games compared to FR swimmers at the 1968 (168.2 ± 4.1 cm and 180.9 ± 5.8 cm) Olympic Games and there was no further significant changes in height from 1992 to 2016 (173.2 ± 6.5 cm and 189.0 ± 6.3 cm). Body mass followed the same trend with both females and males increasing from 1968 to 1992 (58.8 ± 0.8 kg to 63.6 ± 0.9 kg; 76.0 ± 0.8 kg to 80.5 ± 0.9 kg respectively) and then also plateauing from 1992 to 2016 (2016: 64.6 ± 0.7 kg and 80.5 ± 0.8 kg). However, the age of female and males differed; female swimmers continually increased in age from 1968 to 1992 to 2016 (16.7 ± 2.1, 19.7 ± 2.4 to 22.7 yr) whereas the male swimmers’ age followed a similar trend and plateau to height and body mass (20.1 ± 2.4, 21.8 ± 2.9 to 22.6 ± 2.8 yr). The plateau in age (males only), height and body mass, suggested that these characteristics may be exhausted in their ability to be deterministic of swimming performance at the world-class and elite level. Indeed, these characteristics could not differentiate between truly world-class swimmers and their elite counterparts. Therefore, it was concluded that new or alternative physical determinants of performance warranted exploration in order to provide new avenues for swimming coaches and applied sports scientists to progress the training and talent identification process of elite swimmers. With new determinants of swimming performance needing to be explored, and a novel non-invasive method of determining muscle fiber typology recently developed, the consequent studies directed their focus on the influence muscle fiber typology has on the key performance determinants. The non-invasive estimation of muscle fiber typology is determined from the measurement of muscle carnosine which is a stable intramuscular metabolite that is two-fold higher in concentration in type II muscle fibers. Study two and three specifically investigated the influence muscle fiber typology has on race specific determinants of performance. Study 2 recruited 46 world-class swimmers, determined their muscle fiber typology using the non-invasive protocol and investigated the influence muscle fiber typology had on the start and turn segments of career best competitive performance. The results suggested that muscle fiber typology was not found to be influential in start time, turn time or turn out time when swimmers competing in all strokes and events were collectively analysed. However, when the start, turn and turn out time were found to be significantly faster in 100-m events compared to events greater than 200-m. It was then discovered that those swimmers who possessed a greater estimated proportion of type II muscle fibers had a quicker start time to 15 m (p = 0.02), whereas turn time and turn out time were not found to be significantly influenced by muscle fiber typology (p = 0.12 and 0.12 respectively). From a practical perspective this was highlighted in the 100-m freestyle, whereby swimmers with a greater estimated proportion of type II muscle fibers were 0.25 s (CI 90%, 0.17 s) faster to 15 m. Study 3 investigated how the pacing strategy of 200-m freestyle swimmers was influenced by muscle fiber typology. After the recruitment of 25 world-class 200-m freestyle swimmers, they too had their muscle fiber typology estimated with the non-invasive methodology, and it was determined that swimmers with divergent muscle fiber typology did pace the 200-m freestyle differently. Swimmers with greater estimated proportions of type II muscle fibers spent a significantly larger percentage of overall race time on the third lap compared to those swimmers with greater estimated proportions of type I fibers (p = 0.02). It was highlight that this difference could be because of the energetic demands of this lap may be preferential for swimmers with greater proportions of type I muscle fibers given that this lap has the greatest contribution from aerobic energy metabolism. Interestingly, the overall performance times did not differ when swimmers with greater estimated proportions of type II fibers were compared to those with greater proportions of type I fibers. In contrast, there were substantial difference in the relative percentage of time spent on each lap. It was concluded that muscle fiber typology is influential in the pacing strategy of swimmers competing in the 200-m freestyle event, and consequently the relationship between pacing strategy of other events should be explored in relation to muscle fiber typology. Study 3 highlighted that the marked differences in pacing strategy could be due to the physiological characteristics of different muscle fibers. Therefore, it seemed warranted to explore how different physiological and performance determinants of overall swimming performance are influenced by training volume and whether the muscle fiber typology is a moderating factor in the responses to training volume. Since physiological tests in swimming are under established, the final study implemented a number of swimming performance tests to determine their relationship with muscle fiber typology. Study 4 recruited 10 elite swimmers for a 7 wk training intervention study that increased the training volume by ~ 30% for 3 wk. The key finding from this study was that 200-m time trial performance was significantly impaired following the period of increased volume training (p < 0.01), and the change in time trial performance from pre- to post high volume training was positively associated with muscle fiber typology (r = 0.697, p =0.025). That is, swimmers with a greater estimated proportion of type II muscle fibers had larger decrements in performance. The findings of this thesis demonstrate that the muscle fiber typology of world-class and elite swimmers is deterministic of swimming performance. It was initially found that previously researched determinants of performance (i.e., age, height and body mass) had started to plateau and may be less relevant for predicting performance, and therefore the exploration of a new determinant of performance is warranted. In light of this, it was found that the novel non-invasive technique to determine muscle fiber typology with the use of magnetic resonance spectroscopy is user friendly in the perception of world-class swimmers and coaches and therefore can be used to study such populations. The muscle fiber typology of swimmers influences determinants of race performance, including the start performance of swimmers in 100-m events and the pacing strategy of swimmers competing in the 200-m freestyle event. The results not only highlight the direct impact muscle fiber typology has on race performance, but also the necessity to individualise racing and training performance in relation to a swimmers muscle fiber typology. Muscle fiber typology has been deemed a moderating factor in how swimmers respond to training overload, with swimmers of greater proportions of type II muscle fiber having greater decrements in performance following high volume training, when compared to those swimmers who possess greater estimated proportions of type I fibers. Collectively, the findings from this group of studies show that muscle fiber typology is influential in the racing and performance determinants of swimming. This research is multi-faceted in that it adds to the knowledge of muscle fiber typology; it’s interaction with swimming performance, and also offers suggestions for how this research can be further explored in the swimming world. Furthermore, this body of work has determined that the non-invasive measurement of muscle fiber typology is embraced by world-class coaches and swimmers.