EFFETTO DELL’ALLENAMENTO DELLA MUSCOLATURA RESPIRATORIA SUI PARAMETRI VENTILATORI E SULLA CAPACITÀ DI ESERCIZIO NEGLI SPORT DI RESISTENZA

For about 15 years many studies have demonstrated that respiratory muscles fatigue may be a limiting factor during exercise, in particular for exercise intensity >85% of VO2max(4), and negatively affects the ability to perform physical activity(5). Can this muscle limitation be overcome? It has been proposed that an increase in maximal strength of respiratory muscle and/or an improvement in fatigue resistance may indeed reduce the perception of respiratory effort and contribute to the improvement in exercise performance(6). The mechanism underlying the enhancement in exercise performance is controversial. A hypothesis is that if the respiratory muscle training attenuates exercise ventilation the reduction of respiratory muscle blood flow, in turn benefiting the exercising limb muscle with increased blood availability(7- 10). Understanding the effects of respiratory muscle training on exercise performance became an important issue in human performance physiology because offers the promise of improved exercise tolerance and athletic performance in endurance athletes(1,2) . However, numerous studies have been performed to test the effect of respiratory muscle but the results remains controversial. A reason could be that exists three different technique of training: respiratory endurance muscle training (RMET) with normocapnic hyperpnoea (NH), resistive or threshold training. Each of these techniques improves a specific aspect of respiratory muscle function(3,21,22). Moreover the literature shows that the training protocol, the workload, the number of repetitions and the performance tests that were used have also a crucial role in outcomes. The most controlled and rigorously designed study, with the appropriate outcomes, showed an increased in exercise performance and respiratory muscle function(3,23). A specific respiratory endurance training enhanced exercise tolerance and athletic performance in many endurance sports (i.e. cycling(11), swimming(12)), in untrained(13,14) and trained subject (15,16). We need to point out that trained endurance athletes are sensitive to respiratory muscles fatigue(17,18) even if they have a less fatigable ventilatory system than untrained subjects(19,20). The aim of this study was to evaluate the effects of RMET with normocapnic hyperpnea (NH), by means of Spirotiger®, on respiratory parameters, cycling and running performance in a group of age group triathletes. We applied RMET because this technique permits athletes to maintain high level of ventilation like during an endurance competition. Methods and Materials. Study population. 20 male age group triathletes were recruited for this study. They were randomly allocated to two groups: RMET (T) and control (C). The participant’s characteristics are summarized. All athletes were non-asthmatics and with no evidence of respiratory restriction or obstruction. They were required to keep their individual training constant throughout the course of the study. The Ethics Committee of the University of Ferrara approved the study; informed consent was outlined to each subject. Study design. At baseline (T0) all subjects underwent: physical evaluation, pulmonary function tests (PFTs) and exercise tests. After 5 weeks of training (T1) all subject performed the same tests. Pulmonary function test (PFT). PFT were performed by spiromter (Quark b2, Cosmed, Rome, Italy) according to international guidelines(22,): forced expired volume in the first sec (FEV1), forced vital capacity (FVC), 12 sec maximal voluntary ventilation (MVV). The maximal inspiratory pressure (MIP), at residual volume, was measured with a manometer connect to a mouthpiece (Micro RPM, Care Fusion, San Diego, California, USA) in according to international guidelines (23 vb ATS). Subjects repeated the maneuver three times and highest value was considered for comparison before and after RMET. Exercise performance. The subjects were instructed to avoid intensive exercise two days before the test and they don’t eat at least two hours before. None of the subjects consumed any drugs that could influence heart rate (HR), including caffeine. Incremental and endurance tests were performed both during cycling and running. The C group performed the incremental and endurance test only on treadmill. Subjects familiarized with all tests. During each exercise test ventilatory variables (VE, VT and RR) and gas exchange (VO2 and VCO2) where measured breath-by-breathe by a metabolimeter (Quark b2, Cosmed, Rome, Italy). The system was calibrated prior each test. Tests were performed under the similar environmental conditions (room temperature 21-22°C, humidity 45-55%). Subjects’ heart rate was continuously recorded (Polar Electro, Kemple, Finland). Data were mediated every 15 seconds. 1. Maximal incremental test on treadmill (24,25). Subjects warmed up on the treadmill (Excite Med, Technogym, Gambettola, FC, Italia) for 15 minutes according to the protocol. Test started at 8 km/h and the speed was increased by 0.3 km/h every 30 seconds. Regular increases in speed were made until the perceived exertion by the subjects was close to maximum (burning sensation in their muscle and heavy breathing corresponding to a Borg score of 8-9/10) and then they began the final acceleration: 0,5 km/h every 20 seconds until exhaustion. 2. Maximal incremental test on cycle ergometer(24,25). Athletes warmed up at 30 minutes according to the protocol. The test was performed using the triathletes’ bikes fixed on an Elite RealAxion, (Elite RealAxiom, Fontaniva, PD, Italy) which is a roller with an electronically controlled resistance unit. The test started at a pedalling rate of 60 rpm and increased by 1 rpm every 30 seconds. When subjects reached a dyspnea Borg score of 8- 9/10 they made the final sprint. The computer automatically converted the pedalling rates into watts. 3. Endurance test on treadmill and on cycle ergometer. The constant-load tests were both performed in the same day with a rest of 15 minutes. The test lasted 10 minute and exercise intensity corresponded to the ventilatory threshold (RC) heart rate reached during the incremental test (roughly corresponding to 87% VO2 max). The perception of dyspnea was measured by Borg score at the end of the test (modified 0-10 Borg scale). Endurance Respiratory Muscle Training. The training protocol lasted 5 weeks and was performed by means of a specific device (Spirotiger®), which consisted of a hand-held unit with a pouch and a base station. A two-way piston valve connected to a rebreathing bag permits to maintain a constant isocapnic end-tidal CO2 fraction. This apparatus allows executing respiratory cycles with high frequency in condition of NH. To the 10 athletes it was explained how train and it was also illustrated the assembly of the various components of the instrument, how to use the software and hygiene standards. The subjects then underwent several supervised training sessions to learn the technique and to define the appropriate size of the bag and the respiratory rate. Training intensity: the volume of the bag was initially set at value representing approximately 60% of the subject’s VC. The RR start at 24 b/min and progressively increased to a breathing rate until the same ventilation level measured at RC during incremental test (roughly corresponding to 50% of MVV). Training protocol: triathletes trained 20 minutes daily, 7 days a week, for 5 weeks. While performing the breathing exercises, patients wore a nose clip too ensure breathing exclusively through the training device. The compliance to home-based training was evaluated by a diary. Statistical analysis. Data are reported as mean ± SD. Paired t-test was used for comparison between pre- and posttraining. The non parametric Wilcoxon test was used to analyze Borg score. The two ways ANOVA test was used to evaluate the effect of RMET on the ventilatory pattern and VO2 trend; the P values were adjusted according to the Bonferroni correction. Statistical significance was accepted at p≤0,05. All the analyses were performed using GraphPad Prism 40. Results. All subjects completed the training protocol without any problems with RMET. No change occurred in control group so we analyzed only the data of the trained group. Anthropometric parameters. We found a significant lower weight (-1 Kg; p=0,009) and BMI (-0,3 Kg/m2; p=0,002) after the training. Pulmonary function test . No differences were found in FEV1 and FVC. MIP and the MVV significantly increased after RMET: +4,4 cmH2O (p=0,03) and + 16,5 l/min (p=0,01) respectively. Maximal incremental tests. During both cycling and running test, the subjects showed a higher exercise capacity: maximal watt (+ 39,5 watt; p=0,03) and speed (+1,1 Km/h; p=0,002) significantly increased. The data of the maximal incremental test before and after RMET are shown for cycling and for walking. The VO2 trend was analysed by means of ANOVA. We analysed the data at the same time: at rest, after the warming up, at RC reached in the first test (RC T0) and at the maximal work load (max T0) both for cycling and running incremental test. The analysis of variance showed that change in VO2 was significantly affected by RMET, p<0,005 in both tests . V O2 was significantly lower at rest, after the warming up and at RCT0 after RMET in both tests. We also analyzed ventilatory pattern at rest, after the warming up, RC T0 and max T0 both for cycling and running. We found a reduction in minute ventilation and RR significantly decreased, ANOVA test showed that change in VE and RR was significantly affected by RMET, p<0,005. Endurance test on treadmill and on cycle ergometer. We found a lower VO2 (T0: 3558 ± 601ml/min, T1: 3394 ± 513 ml/min; p=0,04) during endurance cycle ergometer test. Fatigue Borg score was significantly lower in both tests: - 0,7/10 on treadmill and -0,6/10 on cycle ergometer. Data are reported in tables 7 and 8 for running and cycling respectively. Discussion. The aim of our study was to determine whether the improvement of the respiratory muscles performance had a positive effect on exercise capacity. The effectiveness of the training program was demonstrated by the significant increased in MVV (+ 16,5 l/min) and MIP (MIP +4,4 cmH2O) by allowing athletes to mobilize greater volume of air. RMET had no influence in FEV1 and FVC as in other study(26). The present study showed that by simulating exercise hyperpnoea, by means Spirotiger®, we found a significant decrease in minute ventilation and respiratory rate during both incremental tests in according to other study . In according to Boutellier’s study(1,27) we found in triathletes, a less impressive reduce in minute ventilation than in the sedentary subject or COPD patients; this probably would suggest that less the respiratory muscle are trained higher is minute ventilation during exercise and bigger can be the decrease after the training. RMET seems also to improve performance during both incremental tests. Data showed a significantly increase of speed (+ 1,1Km/h) and watts (+39,5 watt) at the peak of exercise. The figures 1 and 2 showed the lower trend of VO2 during both incremental tests, which reflect a similar training-induced improvement of RMET. Some degree of controversy exist regarding the effect of this training on VO2, our result is in according with Boutellier(27) but other studies didn’t found any significant improvement(9,28). This is a new result, which reflect the fact of the reduction of ventilatory system fatigue or rather the reduction in the O2 requirement of respiratory muscles during exercise, may increase O2 availability to the limb muscles during exercise(3,6) so athletes can support a higher workload. Moreover during endurance test perception of fatigue was lower in T1 than T0 (- 0,7/10 Borg score on treadmill and -0,6/10 on cycle ergometer), this turn out to be a good indicator of feedback on the improvement achieved. In conclusion, RMET significantly improves the maximal inspiratory pressure and maximal voluntary ventilation in triathletes. Thus, improved fitness of the respiratory muscle enhances exercise performance, improves aerobic capacity and reduces perception of fatigue during exercise test. 1. 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