Effect of respiratory muscle strengthening with breathing exercises on Ventilatory functions, aerobic tness and their association with performance in elite rowers

Objective Rowing is one of the most physically demanding endurance sports requiring high levels of ventilation. The aim of this study was to investigate the effect of RMT on ventilatory parameters, aerobic tness and rowing ergometer performance among 20 professional rowers (experimental (n = 11) and control (n = 9) aged 20–35 years in Sri Lanka. Results Rowers in the experimental group were prescribed a RMT program comprising of breathing exercises while control group was prescribed a general exercise program for a 12 weeks. There were signicant improvements in PIF, FVC, and VO 2 maxin the experimental group after 12-weeks (p < 0.05) while only VO 2 max improved non-signicantly in the control group (p > 0.05).Compared to the control, PIF improved signicantly in the experimental group (p < 0.05). The rowers in the experimental group with higher PIF and VO 2 max performed better at 2000 m and 5000 m ergometer whereas in the control group, only VO 2 max was associated with better performance in 5000 m ergometer. This suggests that the RMT program had a signicant effect in improving some ventilatory parameters and VO 2 max of the rowers resulting in better performance.


Introduction
Rowing is one of the most physically demanding endurance sports requiring high levels of ventilation [1].
Rowing involves not only the locomotor muscles of the body but also the respiratory muscles as well [2].
Oxygen consumption increases by about 20-fold from the resting state of 250 ml/min to 4000 ml/m during exercise in the well-trained athlete at sub-maximal intensity level [6].The most limiting factor for oxygen uptake during exercise is the pumping ability of the heart compared to the respiratory system [7]. But breathing does limit exercise performance because respiratory muscles enforce their own demands upon the oxygen delivery system [8]. Recent investigations have shown that an increase in respiratory muscle demand during intense exercise reduces the limb blood ow [9,10] by diverting blood ow from limb muscles to the respiratory muscles, the metabore ex. This accelerates muscle fatigue which has detrimental effects on sports performance [11,12]. Therefore, respiratory muscle training (RMT) becomes useful to augment respiratory muscle functions in high intensity sports like rowing [13].Further, it has been shown that improvements in lung functions help to improve exercise performance in trained athletes [12,14]. In addition, it is well documented that yoga, which comprises of breathing exercises, improves respiratory parameters [13,15] and respiratory muscle strengthening [17,18].
RMT can be carried out using many training devises. However, the high cost in purchasing such devises is a drawback for many developing countries like Sri Lanka. This novel RMT program, which included speci c exercises for respiratory muscles, was designed to assess its effects on ventilatory parameters, aerobic tness and performance among professional rowers in Sri Lanka.

Materials And Methods
A case controlled randomized study was conducted in 20 male rowers aged between 20-35 years during the competitive periodat General Sir John Kotelawala Defence University. Age, body weight and height matched rowers were divided into an experimental (n=11) and a control group (n=9). Prior to data collection, written informed consent was obtained from all rowers. This study was conducted in accordance with the declaration of Helsinki and Ethical Clearance was obtained from Ethics Review Committee, Faculty of Medicine, University of Peradeniya (2016/EC/52). The current research study adheres to the CONSORT guidelines and completed CONSORT checklists are attached in the additional le A.

Data Collection
Initially, the assessment of lung volumes, capacities and ow rates namely; peak inspiratory ows (PIF), peak expiratory ows (PEF), forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV 1 ) were done using a portable spirometer (Spiro analyzer ST-75) in the standing position according to joint American Thoracic Society and European Respiratory Society guidelines [19].Astrand-Ryhming submaximal bicycle ergometer test was used for the determination of aerobic tness (VO 2 max) using a Monark cycle ergometer 828E. VO 2 max in litres/minute was predicted using standards tables and a nomogram [20]. The test distance of 2000m and 5000m are commonly used to monitor rowing training and performance. The concept II, (Nottingham, UK) ergometer machine and stopwatch were used for the test and the time spent on the rowing ergometer machine was assessed.
Subsequently, rowers in the experimental group were prescribed aRMT program is included as Additional le 1.The general exercise program followed by the control group includes a full description of general exercise program in Additional le 2.
The RMT program and the general exercise program were conducted for 7 days per week for 12 weeks after which assessment of the lung parameters, VO 2 max and ergometer performance were repeated.
During the training program, all participants in both groups were requested to maintain a detailed physical activity-training schedule and an "Exercise program training diary" in order to monitor training adherence.

Statistical analysis
Data was entered and validated in a SPSS data base. The descriptive statistics were calculated for respiratory parameters, aerobic tness and rowing ergomtere performance tests in both groups. Changes in lung parameters and aerobic tness were considered as outcome variables. Above measurements were taken prior to the test (pre-test data at rst session) and after the test (post test data after 12 weeks of exercise program) in both groups. They were compared before and after the exercise programs in both groups using paired sample t test and between two groups using independent sample t test. The relationship between the two variables was assessed with the Pearson Correlation. Statistical analysis was conducted at a 95% con dence interval, and p < 0.05 was considered statistically signi cant.

Results
The Mean age of study sample was 25.3 ± 3.5 years. Table 1 shows lung parameters namely: PIF, PEF, FVC and FEV 1 in the control (n = 9) and the experimental groups (n = 11) before and after introducing the 12-week non-respiratory muscle and RMT programs respectively. After introducing the RMT program, asigni cant difference was observed in PIF and FVC (p < 0.05) in the experimental group with no signi cant difference in other parameters. In contrast, no signi cant difference was observed in all the respiratory parameters in the control group after introducing the non-RMT program.   Figure S1 re ects the aerobic tness in the control and the experimental groups before and after the 12 weeks respective training programs. The experimental group showed 2% signi cant improvement (p < 0.05) in aerobic tness while the improvement in the control group was 1% which was not signi cant (p > 0.05). However, there was no statistically signi cant difference in the improvement in aerobic tness between the control and the experimental groups after the respective training programs (p > 0.05). Table 3

Discussion
Lung volumes, capacities and ow rates have been observed to be greater in high-intensity endurance sports like rowing, cycling, boxing, football, basketball, rugby and water polo in comparison to power, mixed and skill groups of sports [23]. In addition, studies have shown that elite rowers require extremely high levels of ventilation with them showing higher ventilatory parameters [3,4].
In the present study, when comparing the pre and post-training values of ventilatory parameters, it was observed that PIF and FVC improved signi cantly in the experimental group (p < 0.05) while no improvements were observed in all lung parameters in the control group (p > 0.05) after the respective training programs (Table 1). Furthermore, PIF was signi cantly higher (p = 0.04) in the experimental group compared to the control group after the 12 weeks RMT program ( Table 2). Several past studies have also shown similar ndings with improvement in PIF following RMT using the RMT device [24,25].PIF is known to be the fastest ow rate achieved during a maximum inspiration and provides a measure of the maximal contraction of the inspiratory muscles [26].
The novel RMT training program conducted in this study included profound (deep) inspirations and inspiratory hiccups, exercises that strengthen the inspiratory muscles, while isometric side bridge, curls ups improved expiratory muscles strength. In addition, it also included exibility training to stretch the chest wall. These techniques would have helped to strengthen the respiratory muscles, improve the lung capacity (FVC) and PIF and increase chest expansion in the experimental group compared to the control group. These exercises have similarities with deep breathing techniques used in pranayama yoga practice during which the respiratory muscles are stretched fully towards the chest wall represented by increased chest wall expansion together with increased lung volumes, capacities and ow rates namely FVC, FEV 1 and PEF in healthy subjects [13,27,28]. Long term bene ts of yoga has been shown to increase chest expansion, breath-holding time and PEF [28,29].
Healthy respiratory systems are anatomically well equipped to meet the oxygen requirements at rest and during increased exercise intensities. In the present study, signi cant improvement was seen in VO 2 maxovertime in both groups with only the experimental group showing signi cant improvements. No signi cant difference was observed in VO 2 maxbetween the two groups after the RMT program (p > 0.05).
Many studies have examined the effect of RMT on VO 2 maxin different sports and revealed that VO 2 max was not altered by RMT while a small group of studies have shown a statistically signi cant decrease in sub-maximal O 2 following RMT across different sports [25,30].
When considering the relationship between ventilatory functions and performance it was observed that there was a negative relationship between lung functions and 2000 m and 5000 m ergometer performance in both groups in the present study. However, only PIF signi cantly correlated with 2000 m performance in experimental group. This indicates that higher PIF are associated with lower ergometer time performance. However, contradictory outcomes have been observed concerning the relationship of ventilatory functions with sports performance following RMT. One study in athletes' documented that there was a signi cant negative relationship with FVC and running times [31] while in another study done on cyclists observed improvements in cycle endurance time subsequent with improved ventilatory functions following RMT [32].
When considering aerobic tness, the present study revealed that there was a signi cant negative correlation between VO 2 max, and 2000 m and 5000 m ergometer performance test in the experimental group (r= -0.68; p < 0.05) (  [33,34].However, another study stated that no signi cant correlation exists between aerobic tness and 2000 meter ergometer performance in both male and female rowers [35]. Though past research has consistently demonstrated that success in rowing is associated with higher VO 2 max, some studies stated that VO 2 max alone is not a good predictor of rowing performance in rowers with similar endurance capacity [4,33].
The effect of RMT on lung functions and exercise performance has been inconclusive because of the differences in research design such as inappropriate performance outcome variables, ineffective RMT protocols, small sample sizes and the lack of carefully matched experimental and placebo groups [35]. Some studies have suggested that a well-designed case-controlled study with an appropriate RMT protocol [36] and self-motivation of athletes also contributes to a positive impact on exercise performance [8,24,].
Overall, our ndings suggested that applying this novel RMT program in the training schedules of rowers resulted in improving some respiratory functions (PIF) and aerobic tness and these were associated with greater performance in both 2000 m and 5000 m rowing ergometer tests. This highlights the importance of introducing RMT in training protocols of sportsmen and women in Sri Lanka, in addition to peripheral muscle training program, as a routine practice to improve the sports performance. This novel RMT could also be used in rehabilitation of clinical populations, especially in developing countries, as RMT devices are costly and inaccessible for many.

Limitations
To the authors' knowledge,it is the rst time that the Sri Lankan rowers have been introduced to RMT they had lack of awareness about RMT which would have resulted in insu cient self-motivation to follow the training schedule daily.The present study alsois limited to male rowers. Female rowers have weaker respiratory muscles than male rowers and that RMT may bene t female rowers more than male rowers. Participants provided written informed consent prior to participation following a verbal explanation and reading an information sheet explaining the rationale and all measurements, testing and respective training programs regarding the study.

Consent for publication
Not applicable as the manuscript does not contain any data from any individual person.