Importancia de la fuerza muscular sobre el rendimiento físico y deportivo en atletas especialistas de 800 metros de alto nivel

Resumen

SUMMARY IMPORTANCE OF STRENGTH LEVELS ON PHYSICAL AND ATHLETIC PERFORMANCE IN 800 M HIGH-LEVEL ATHLETES This Doctoral Thesis is aimed at discussing the importance of the muscle strength on the physical and athletic performance of high-level male athletes specialized in 800 m. Different variables of the muscle strength related to the 800 m performance have been analyzed together with the hematological, immunological, and hormonal responses, during both general and specific 800 m training, in high-level national male athletes, over a whole training and competition season. To this purpose, the following four studies were carried out. In the Study I we analyzed the effects of resisted sprint training on acceleration with three different loads accounting for 5%, 12.5% and 20% of body mass. Study II aimed to analyze the relationships between sprint, jumping and strength abilities, and 800 m performance in male athletes of national and international levels. In addition, the objective of Study III was to analyze the changes in strength and sprint levels, and changes in blood parameters during a complete athletics season in 800 m high-level athletes. Finally, in the Study IV we investigated the effects of a high-speed strength training on physical performance in 800 meters high-level athletes. In the past decades, sports coaches and scientists showed growing interest in the study of those physiological and mechanical variables allowing an endurance runner to carry out intense effort during long periods of time. Up to now, most research has been focused on the analysis of the determining performance factors in races longer than 1500 m, with less attention been paid to other athletics events such as the 800 m race. As early as the 16th century, the Italian mathematician, physician and astronomer Galileo Galilei reached the following conclusion: "Measured what can be measured, and make measurable what cannot be measured". As Astrand (1992) pointed out, coaches often ask themselves why an athlete is better than another. To answer this question, a series of aspects should be considered: 1) breakdown of the athlete's best performance into several components, 2) selection of the proper test for each component, 3) objective measurement of each component, and 4) use of the results for comparison with benchmarks of athletes in other sports, follow-up of their evolution, prescription of the training, and prediction of the athlete's best performance. Hence, both the assessment and measurement of each and every component having an effect on the athlete's best performance are essential steps of the sports training process, since most decisions to be taken thereupon will be linked to the measurement and assessment processes; in fact, in order to reach appropriate decisions, the sports coaches and/or technicians must be able to gather objective information, in order to analyze it and draw proper conclusions (Morrow et al., 1995). Elite athletes' best performances are the result of the interaction between a series of multiple complex factors: genetic component, training, health status (including the existence or not of lesions, fatigue, diet or drug intake), and good integration of the different physiological, biomechanical, and psychological components inherent in the sport/discipline practiced (MacDougall et al., 1991). According to the aforementioned authors, the main factor related to the athlete's potential is the genetic factor, which encompasses the inherited physical, anthropometric, cardiovascular and muscular characteristics, as well as the so-called "trainability", which is the capacity to improve personal fitness through specific training, and to tolerate and assimilate very intense and frequent training sessions. The second factor linked to the athlete' s best performance has to do with a proper training. Finally, the best performance may also be affected by the general health status or nutrition of the athletes. Currently, the search for greater athletic performance is essentially focused on achieving the highest effectiveness out of training stimuli. From the physiological point of view, it is understood that the training process should involve the repetition of a series of exercises to make the competition gesture automatic, and develop both structural and metabolic functions that would lead to increased athletic performance (Viru, 1995). In this regard, training might be defined as an adaptation process where there is a relationship between the training stimuli and the desired structural and functional effects, by applying specific means and methods, aimed at improving athletic performance (González-Badillo, 2002). In the past few years, there has been a growing interest both from the scientific community and the sports technicians or coaches concerning the assessment of muscle strength and the effect of training in endurance disciplines (Mikkola et al., 2007, 2011; Taipale et al., 2010, 2014). Such interest is due to the benefits observed from strength training on performances achieved in the above disciplines, be it among recreational, high-level, or competition athletes. One of the biggest challenges facing the sports technicians and coaches, nowadays, lies in applying the most adequate means and methods to the specific sports discipline targeted to obtain the best performance. To this purpose, it is essential to know the determining factors for athletic performance in the concerned discipline; this is the prerequisite for deciding which type and amount of training is necessary and how to evaluate it. Furthermore, another important task to be carried out by coaches and sports technicians is to analyze the basic physical qualities and determine the most adequate training methods to optimize athletic performance. In the past decades, many studies dealt with the physiological variables related to performance in endurance events of medium to long duration, such as maximum oxygen uptake (VO2max), lactate, relative contribution from the energy systems, etc. (Hanon & Thomas, 2011; Hill, 1999; Lacour et al., 1990; Craig & Morgan, 1998; Weyand et al., 1994; Spencer & Gastin, 2001; Duffield at al., 2005). However, other determining factors related to performance in endurance events of medium to long duration, such as strength, jump ability and sprint ability, have been less investigated by the scientific community; actually, this issue was not deemed important until the past few years when the concern and need to study such factors started to appear (Aagaard & Andersen, 2010; Mikkola et al., 2007, 2011; Taipale et al., 2010, 2014). Recently, several studies have analyzed the effects of different types of strength training on performance in endurance events of medium to long duration (Aagaard & Andersen, 2010; Mikkola et al., 2007, 2011; Taipale et al., 2010, 2014). Most of these studies tend to underline the importance of carrying out strength training with light-medium or explosive loads, and high or maximum loads achieved with a medium-low number of repetitions, contrary to traditional strength trainings performed by the endurance athletes, known as strength-endurance or circuit training, and consisting in circuit type trainings with very low loads and high number of repetitions (>15) (Mikkola et al., 2011; Taipale et al., 2010, 2014). Furthermore, and in view of the importance of blood and its essential role in the oxygen transport, buffering or thermoregulation, variables which are directly related to performance in endurance capacity (Calbet et al., 2006), part of the scientific community have shown interest in evaluating and monitoring the athletes' hematological profile. Likewise, the endocrine and immune systems play a function as modulators of the stress response caused by intense physical exercise (Crewther et al., 2006; Vleck et al., 2014). Through various mechanisms, both systems could get their functions diminished during intense endurance efforts, which would entail a greater risk of disease or lesion for the athlete (Knez et al., 2006). By monitoring these variables, very precise information could be obtained about the effects of the training stimuli on the body. STUDY I. Effects of resisted sprint training on acceleration with three different loads accounting for 5%, 12.5% and 20% of body mass Purpose: The optimal resisted load for sprint training has not been established yet, although it has been suggested that a resistance reducing the athlete’s velocity by more than 10% from unloaded sprinting would entail substantial changes in the athlete’s sprinting mechanics. Methods: This investigation has evaluated the effects of a 7-week, 14-session sled resisted sprint training on acceleration with three different loads according to a % of body mass (BM): low load (LL: 5% BM, n = 7), medium load (ML: 12.5% BM, n = 6) and high load (HL: 20% BM, n = 6), in young male students. Besides, the effects on untrained exercises: vertical jump (CMJ), loaded vertical jump (JS) and full squat (SQ) were analyzed. The three groups followed the same training program consisting in maximal effort sprint accelerations with the respective loads assigned. Results: Significant differences between groups only occurred between LL and ML in CMJ (p<0.05), favoring ML. Paired t-tests demonstrated statistical improvements in 0-40 m sprint times for the three groups (p < 0.05), and in 0-20 m (p < 0.05) and 0-30 m (p < 0.01) sprint times for HL. Sprint times in 10-40 m (p < 0.01) and 20-40 m (p < 0.05) were improved in LL. Time intervals in 20-30 m and 20-40 m (p < 0.05) were statistically reduced in ML. As regards the untrained exercises, CMJ and SQ for ML and HL (p < 0.05) and JS for HL were improved. Conclusions: The results show that, depending on the magnitude of load used, the related effects will be attained in different phases of the 40 m. It would seem that to improve the initial phase of acceleration up to 30 m, loads around 20% of BM should be used, whereas to improve high-speed acceleration phases, loads around 5 to 12.5% of BM should be preferred. Moreover, sprint resisted training with ML and HL would enhance vertical jump and leg strength in moderately trained subjects.   STUDY II. Relationships between sprint, jumping and strength abilities, and 800 m performance in male athletes of national and international levels Purpose: This study analysed the relationships between sprinting, jumping and strength abilities, with regard to 800 m running performance. Methods: Fourteen athletes of national and international levels in 800 m (personal best: 1:43-1:58 min:ss) completed sprint tests (20 m and 200 m), a countermovement jump, jump squat and full squat test as well as an 800 m race. Results: Significant relationships (p < 0.01) were observed between 800 m performance and sprint tests: 20 m (r = 0.72) and 200 m (r = 0.84). Analysing the 200 m run, the magnitude of the relationship between the first to the last 50 m interval times and the 800 m time tended to increase (1st 50 m: r = 0.71; 2nd 50 m: r = 0.72; 3rd 50 m: r = 0.81; 4th 50 m: r = 0.85). Performance in 800 m also correlated significantly (p < 0.01-0.05) with strength variables: the countermovement jump (r = -0.69), jump squat (r = -0.65), and full squat test (r = -0.58). Conclusions: Performance of 800 m in high-level athletes was related to sprint, strength and jumping abilities, with 200 m and the latest 50 m of the 200 m being the variables that most explained the variance of the 800 m performance.   STUDY III. Enhanced strength and sprint levels, and changes in blood parameters during a complete athletics season in 800 m high-level athletes Purpose: The purpose of this study was to analyze changes in sprint, strength, hematological, and hormonal parameters in high-level 800 m athletes during a complete athletics season. Methods: Thirteen male athletes of national and international level in 800 m (personal best ranging from 1:43 to 1:58 min:ss) participated in this study. A total of 5 tests were conducted during a complete athletics season. Athletes performed sprint tests (20 m and 200 m), countermovement jump (CMJ), jump squat (JS), and full squat (SQ) tests. Blood samples (red and white blood profile) and hormones were collected in test 1 (T1), test 3 (T3) and test 5 (T5). Results: A general increase in the performance of the strength and sprint parameters analyzed (CMJ, JS, SQ, 20 m, and 200 m) during the season was observed, with a significant time effect in CMJ (P < 0.01), SQ (P < 0.01), and 200 m (P < 0.05). This improvement was accompanied by a significant enhancement of the 800 m performance from T3 to T5 (P < 0.01). Significant changes in some hematological variables: hematocrit (Hct) (P < 0.01), mean corpuscular volume (MCV) (P < 0.001), mean corpuscular hemoglobin content (MCHC) (P < 0.001), white blood cells count (WBC) (P < 0.05), neutrophils (P < 0.05), monocytes (P < 0.05), and mean platelet volume (MPV) (P < 0.05) were observed throughout the season. The hormonal response and creatin kinase (CK) did not show significant variations during the season, except for insulin-like growth factor I (IGF-1) (P < 0.05). Conclusions: In conclusion, our results suggest the importance of strength levels in middle-distance athletes. On the other hand, the variations in the hematological parameters analyzed may have an influence on 800 m performance. A depression of the immune system occurred at the end of the season. Therefore, monitoring of the mechanical, hematological and hormonal response in athletes may help coaches and athletes to optimize the regulation of training contents and may be useful to diagnose states of overreaching or overtraining in athletes throughout the season. STUDY IV. Effects of high-speed strength training on physical performance in 800 meters high-level athletes Purpose: Previously, it has been suggested that strength training could enhance endurance performance. The aim of this study was to analyze the effects of a 25-week strength training program in physical performance and hormonal response in 800 m high-level athletes. Methods: Thirteen male 800 m high-level athletes (personal best ranging from 1:43 to 1:58 min:ss) were divided into 2 groups: one group (n=6) followed a 25-week high-speed strength training program (STG), whereas a control group (n=7) followed their habitual strength training (CG). Three tests including sprint and 800 m running, strength exercises and blood hormones samples were carried out during the 25-weeks. Results: Both groups improved significantly performance in 800 m (p ≤ 0.01), however, STG showed an additional improvement in T200 (p < 0.05) and the strength variables: CMJ (P < 0.01; 98/2/0%; 87/12/0%; from T1 to T3 and from T2 to T3, respectively) and V1load (P < 0.05; 91/9/0%; from T1 to T3), whereas CG did not reach significant improvements in any of the strength variables analyzed. Concerning the hormonal variables, only STG showed a significant (P < 0.05) decrease in IGF-1 from T2 to T3. In addition, STG resulted in a likely increase in testosterone from T1 to T3, and CG showed a likely increase in cortisol from T2 to T3. Conclusion: The results of the study suggest that strength training characterized by high-speed intensity and low volume, combined with jumps and resisted sprint training produced improvements in both strength and running performance. These results were accompanied by little or no changes in the hormonal response.