J Sports Sci Med. 2013 Dec; 12(4): 630–638.
While some studies have demonstrated that respiratory muscle endurance training (RMET) improves performances during various exercise modalities, controversy continues about the transfer of RMET effects to swimming performance. The objective of this study was to analyze the added effects of respiratory muscle endurance training (RMET; normocapnic hyperpnea) on the respiratory muscle function and swimming performance of young well-trained swimmers. Two homogenous groups were recruited: ten swimmers performed RMET (RMET group) and ten swimmers performed no RMET (control group). During the 8-week RMET period, all swimmers followed the same training sessions 5-6 times/week. Respiratory muscle strength and endurance, performances on 50- and 200-m trials, effort perception, and dyspnea were assessed before and after the intervention program. The results showed that ventilatory function parameters, chest expansion, respiratory muscle strength and endurance, and performances were improved only in the RMET group. Moreover, perceived exertion and dyspnea were lower in the RMET group in both trials (i.e., 50- and 200-m). Consequently, the swim training associated with RMET was more effective than swim training alone in improving swimming performances. RMET can, therefore, be considered as a worthwhile ergogenic aid for young competitive swimmers.
Respiratory muscle endurance training improves performance.
Respiratory muscle endurance training improves the ventilatory function parameters, chest expansion, respiratory muscle strength and endurance.
Respiratory muscle endurance training decreases the perceived exertion and dyspnea.
Respiratory muscle endurance training can be considered as a worthwhile ergogenic aid for young competitive swimmers.
Keywords: Breathing, normocapnic hyperpnea, performance, swimming
While some studies have demonstrated that respiratory muscle endurance training (RMET) improves performances during various exercise modalities, e.g., cycling, rowing, or running (McConnell, 2009) and brings about changes in pulmonary function (i.e., increased vital capacity and decreased residual volume; Esposito et al., 2010), controversy continues about the transfer of RMET effects to swimming performance.
Harms et al., 1997 have found a reciprocal relationship between the work of breathing and legs blood flow during maximal exercise on cycle ergometer. Thereafter, several authors (St Croix et al., 2000; Sheel et al., 2001, 2002) have concluded that the stimulus for limb vasoconstriction was a cardiovascular reflex originating within the inspiratory muscles. As reminded by McConnell, 2009, this reflex seems be activated when metabolites are accumulated within the inspiratory muscles. Indeed, these metabolites stimulate the afferent nerve fibers, which increase their firing frequency. This stimulation precipitates an increase in the strength of sympathetic neural outflow, which induces a generalized vasoconstriction. To resume, the inspiratory muscle fatigue (IMF) reduces active limbs blood flow and exacerbates fatigue in these limbs (Romer et al., 2006). Consequently, it may be supposed that RMET may improve performance. This hypothesis has been confirmed by McConnell and Lomax, 2006 who have suggested that inspiratory muscle training attenuates or delayed the vasomotor changes induced by the inspiratory muscle metaboreflex, which adaptation may produce an improvement of performance.
Recently, IMF after submaximal and/or maximal ‘all-out’ 100-, 200- and 400-m freestyle swim trials was found to be greater than the IMF typically observed for on-land sports (Jakovljevic and McConnell, 2009; Lomax and McConnell, 2003). Although these studies evaluated IMF using the maximal inspiratory pressure (MIP), the real effect on expiratory muscle function has been much less extensively studied and the data are currently contradictory, with significant drops in MIP both with and without declines in maximal expiratory pressure (MEP; McConnell, 2009). In fact, it may be supposed that expiratory muscle fatigue may be specific to the exercise modality (water- or land-based exercise) and/or the race distance. Authors (Brown and Kilding, 2011) have already showed that the swimming distance does not substantially influence the degree of IMF for distances included between 100- and 400-m. Nevertheless, no study to our knowledge has examined IMF and expiratory muscle fatigue from these swimming distances with shorter distances (e.g., 50-m freestyle swim trial).
Therefore, the objective of the present study was to determine the effects of RMET on swimming performances in well-trained swimmers. We hypothesized that the addition of RMET to the usual swim training would increase (i) the strength and endurance of the respiratory muscles and ventilatory parameters and (ii) the swimming performances for short and middle distances (50- and 200-m).
Twenty young (between 13 and 18 years) well-trained (at least 14.0 h of training per week) swimmers of the local swimming pole, non-smoking and with normal lung function (Table 1), volunteered for the study. Then, two homogenous groups were composed: ten swimmers (16.5 ± 2.4 years, 1.76 ± 0.09 m, 70.4 ± 11.7 kg, 4 females and 6 males) in the RMET group performed their usual training sessions (TS) and received RMET (in the form of normocapnic hyperpnea); and ten swimmers (16.1 ± 2.0 years, 1.76 ± 0.07 m, 70.7 ± 4.5 kg, 3 females and 7 males) were assigned to a control group with no RMET (these swimmers performed only their TS). The groups (RMET or control group) were constituted according to gender and age of participants in order to avoid a possible effect of these factors on data. All swimmers were primarily trained for short and middle distances (between the 50- and 200-m) and generally trained 45-48 weeks per year, with pool and dry land training typically reaching 20.0 ± 2.0 hr per week. All swimmers must be able to potentially add a RMET of 30 min, 5 days per week, and follow the study in full. Subjects refrained from strenuous physical exercise for 2 days before the test sessions and performed no physical exercise on the day prior to as well as on the day of the test. Caffeinated beverages were forbidden before the test and subjects ate their last meal at least 2 hr before each test. Subjects did not receive any financial reimbursement for participating, and all gave their written informed consent. The protocol was approved by the local ethics committee and performed according to the Declaration of Helsinki.
|Before RMET||After RMET|
|RMET group||Control group||RMET group||Control group|
|Body mass (kg)||70.4 (11.7)||70.7 (4.5)||69.8 (11.6)||69.8 (3.5)|
|Fat mass (%)||18.5 (9.2)||21.9 (11.7)||18.3 (8.6)||21.4 (10.9)|
|FVC (%)||125 (12)||130 (15)||128 (12) *||129 (17)|
|FEV1 (%)||116 (11)||121 (11)||117 (9)||119 (6)|
|PEF (%)||102 (12)||104 (14)||104 (10)||100 (12)|
|MVV12s (%)||99 (16)||103 (16)||113 (13) *||112 (16)|
|Field swim times on 50-m (s)||27.7 (2.2)||28.1 (1.8)||28.1 (2.1)||28.8 (1.8) *|
|Field swim times on 200-m (s)||136.0 (10.2)||137.5 (11.4)||136.7 (8.4)||138.1 (8.8)|
|Competition swim times on 50-m (s)||27.4 (2.3)||27.8 (2.2)||26.6 (2.1) *||27.6 (2.1)|
|Competition swim times on 200-m (s)||130.7 (12.8)||135.4 (11.4)||125.5 (8.8) *||126.9 (7.7)|
|IPS50m||634 (49)||662 (41)||611 (58)||630 (66) *|
|IPS200m||632 (36)||654 (76)||641 (41)||636 (53)|
|HR50m (bpm)||164 (12)||162 (14)||167 (8)||166 (11)|
|HR200m (bpm)||176 (11)||177 (6)||173 (10)||171 (4)|
|ΔLa50m (mmol·L-1)||5.8 (2.4)||6.3 (1.8)||4.8 (1.8)||5.3 (1.6) *|
|ΔLa200m (mmol·L-1)||8.1 (2.5)||9.1 (1.6)||6.9 (1.8)||7.9 (3.2)|
|Chest expansion (cm)||7.4 (1.4)||7.7 (1.7)||8.2 (1.2) *||7.3 (1.5)|
FVC: forced vital capacity; FEV1: forced expiratory volume in one second; PEF: peak expiratory flow; MVV12s: maximum voluntary ventilation; IPS: international point scores for the 50- and 200-m experimental trials (i.e., simulated competitions); HR: heart rate; ΔLa: delta lactate concentration (i.e., lactate concentration measured 3 min after the end of trials minus lactate concentration at rest).
* denotes p < 0.05 between before and after training.
To test the hypothesis that TS+RMET increase (i) the strength and endurance of the respiratory muscles and ventilatory parameters and (ii) the swimming performances for short and middle distances, the group (i.e., RMET vs control group) and time (i.e., before and after the experimental protocol) effects and the group × time interaction were tested.
In a preliminary session, the subjects were thoroughly familiarized with the RMET device and the laboratory procedures, i.e., lung function measurements, respiratory muscle pressure measurements, and performance of normocapnic hyperpnea as required during the respiratory endurance test (RET). In the first experimental session, the following data were assessed: anthropometric variables, ventilatory function, MIP, MEP, and swim parameters (performances, ratings of perceived exertion: RPE, and ratings of perceived dyspnea: RPD). Following this, the subjects started the 8-week training period (the training group performed their usual TS associated with RMET, while the control group performed only their usual TS). In the second experimental session, at least 2 days after the last TS of the experimental period, anthropometric variables, ventilatory function, maximal mouth pressures (i.e., MIP and MEP), and swim parameters were measured again, and after at least 2 days, the RET was repeated. To avoid a possible circadian effect, all tests were performed at the same hour of day (between 7:00 to 9:00 a.m.).
Measurements of height, body mass and skinfolds were measured at the same time of day (i.e., the morning). The swimmer presented before training in a fasted state and all anthropometric variables were measured by the same investigator. Height was measured with a wall stadiometer (Tanita, Tanita©, Arlington Heights, IL, USA). Body composition (fat mass: FM) was estimated with the skinfold method of Durnin and Womersley, 1974 using a calibrated skinfold caliper (Model HSK-BI, Baty International®, West Sussex, UK). For each skinfold, three measurements were obtained (accuracy ± 2%), then the mean was calculated. Higher chest expansion was measured at the level of the xiphoid process using a tape measure. The subject was instructed to perform a maximal exhalation [to residual volume (RV)] and then an inhalation to total lung capacity (TLC). Chest expansion was calculated as the difference between circumferences at RV and TLC.
Several parameters were measured for the pulmonary function tests: forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), peak expiratory flow (PEF), and maximum voluntary ventilation (MVV12s). For each parameter, the best value was chosen from at least three consecutive maneuvers differing by no more than 5% (Quanjer et al., 1993). All spirometry measurements were performed by the same experimenter according to the guidelines set by the American Thoracic Society and the European Respiratory Society (ATS/ERS, 2002;). Miller et al., 2005). All parameters were measured with a Microquark spirometer (Cosmedä, Rome, Italy) in the same conditions, with the subject in a seated position and breathing through the mouthpiece with a nose- clip (accuracy: ± 2%, Cosmed®). The spirometer volume was calibrated with a 3-L calibrated syringe. The results were corrected to BTPS conditions (i.e., body temperature, ambient pressure and saturated with water vapor) and compared with the predicted values (Quanjer et al., 1993). The MIP and MEP were measured at the end of a normal expiration and inspiration (Esposito et al., 2010), respectively, using a small portable mouth pressure meter (ZAN 100 Flowhandy USB, ZAN Messgeräte GmbH®, Oberthulba, Germany). The occlusion was maintained for 2 to 3 s. Tests were repeated until no further improvement was obtained and at least three satisfactory attempts differed by less than 5%. The swimmers received visual feedback of the pressure generated during each effort by viewing the digital display on a computer screen. The feedback was provided in order to maximize their respiratory effort and ensure that they were at the end of normal expiration and inspiration for MIP and MEP measurements. Sufficient rest periods were provided between the attempts (at least 2 min) and the swimmers were verbally encouraged to reach maximal strength (Larson et al., 1993). The highest value was recorded for comparisons before and after RMET.
Respiratory endurance test (RET)
The RET protocol was incremental, in line with the recommendations from ATS/ERS (2002), and it was performed with the SpiroTiger device (Idiag AG®, Fehraltorf, Switzerland). The size of the rebreathing bag was set at 40-50% of vital capacity, and the target minute ventilation (VE) for the first 3 min was 20% MVV12s. Then, VE was increased by 10% MVV12s every 3 min until the subject could no longer maintain the target respiratory frequency (fR) and tidal volume (VT) despite three consecutive “warnings” by the experimenter. The total test duration and the maximum ventilatory level sustained for at least 3 min were recorded. The RPD was collected before the start of RET and at task failure. A rating of perceived dyspnea scale from 0 to 10 was used, with subjects being asked, “How hard was your breathing during the RET?” The descriptors were 0 = breathing is not hard at all, 2 = breathing is a little hard, 4 = breathing is getting harder, 7 = breathing is hard, 9 = breathing is really hard, and 10 = breathing is very, very hard. Immediately after the rating, a 5-μL capillary blood sample was drawn from a finger and analyzed to determine the lactate concentration (Lactate pro LT-1710, Arkray©, Kyoto, Japan).
Swim tests and swim performances
The field swim performance was evaluated from the swim times on 50- and 200-m during simulated competitions. These exhausting trials were performed in the morning and in randomized order. The swimmers were alone in the lane. Starts were made from the starting blocks with a whistle as the starting signal. Swim times were measured in duplicate by stopwatch, with one stopwatch functioning as backup only. Heart rate (HR) was measured using a heart rate monitor (S810i, Polar Electro©, Kemeple, Finland) continually during each test, then averaged for all trial duration. In addition, at rest and 3 min after the end of each swim trial, the capillary blood lactate concentration was determined (Lactate pro LT-1710, Arkray®, Kyoto, Japan). Then, the delta lactate concentration (i.e., ΔLa: lactate concentration measured 3 min after the end of trials minus lactate concentration at rest) was calculated. The RPE (Borg 6-20 scale) and RPD were also assessed after each swim trial (RPE50m, RPE200m, RPD50m, and RPD200m) (Altose et al., 1985). These assessments were made prior to and at the end of the 8-week RMET program by all swimmers.
Competition performance was assessed by the official international point score (IPS) system used by the International Swimming Federation (Fédération Internationale de Natation Amateur - FINA). The mean time of the eight fastest swims in the history of each event is ascribed the value of 1000 points, with individual performances rated against this reference value. This system allows comparison of a given competitive performance by a male or female athlete in any of the official events (i.e., freestyle, butterfly, backstroke, breast stroke, and individual medley). Competition swim times for each swimmer were also recorded in the most advanced stage reached (i.e., final, semi-final, or heat) in their best competitive event and for the 50- and 200-m trials (IPS50m and IPS200m) 2 weeks before and near the end of RMET.
All athletes were engaged in the same TS program (i.e., all groups together in the same swimming pool) specifically designed to enhance competitive swim performance and followed the training program set by their coaches. The coach kept a detailed training logbook for each swimmer that included the duration, distance, and intensity of each workout in the pool. The study was started at the beginning of the base training period [i.e., after detraining from the previous swimming year (transition phase)] and the RMET protocol was initiated after the preliminary session. None of the swimmers suffered any major injury during the study that prevented them from training.
Respiratory muscle endurance training
In the RMET group (i.e., the group that performed RMET), all subjects used the same training device (SpiroTiger, Idiag®, Fehraltorf, Switzerland), which consisted of a hand-held unit with a pouch and a base station. The properties of the training device allowed personalized respiratory training through voluntary normocapnic hyperpnea and without the limitation of lower limb muscle involvement (Verges et al., 2007; 2009). To avoid hypocapnia despite hyperventilation, the device features a two-way piston valve connected to a rebreathing bag. As the subject breathes out through the mouthpiece, the rebreathing bag stores part of the expired air, which contains increased concentrations of carbon dioxide (CO2). Once the rebreathing bag is filled to capacity, a valve opens and allows the rest of the expired air to be released into the environment. The valve shuts when expiration finishes and inspiration starts. Inspiration empties the rebreathing bag first (containing increased concentrations of CO2), then the valve opens and some fresh outside air is inspired at the end of each inspiration. This apparatus allows the execution of respiratory cycles with high frequency in conditions of normocapnic hyperpnea (Verges et al., 2007; 2009).
The RMET protocol was based on the protocol from Verges et al., 2007 and consisted of 30-min of TS per day, 5 days per week, for 8 weeks. The size of the rebreathing bag was set at 40-50% of vital capacity, and E of the first TS was set at 60% of the MVV12s. During the first week, participants were familiarized with the instrumentation. If, after 25 min of training, they felt that they would not be exhausted after 30 min of training, they were instructed to increase fR by 5 breaths·min-1 for the last 5 min of the session. In this case, the next TS started with fR that was 2 breaths·min-1 higher than an fR at the start of the previous session. Otherwise, if subjects could not increase fR after 25 min of training, the next TS started with fR only increased by 1 breath.min-1. If, after 25 min of training, subjects felt that they would not able to continue for another 5 min at the same target fR, they were allowed to decrease fR by 5 breaths.min-1. In this case, the next TS started with settings identical to those of the previous session. TS were always conducted under expert supervision by an experimenter.
A normal distribution (Ryan Joiner test) and the homogeneity of variance (Bartlett test) were verified and authorized parametric statistics. A two-way analysis of variance (ANOVA) with repeated measures (2 groups × 2 times) was used to assess changes in lung function, respiratory muscle performance, and exercise response in two groups (RMET group vs control group with no RMET) over the protocol period (before vs after). If significance was found, Fisher’s protected least-significant difference post-hoc analysis was applied to locate the difference. Moreover, correlations between some variables were examined with the Bravais-Pearson test and quantified by Pearson correlation coefficients. All statistical evaluations were performed using standard statistical software (Statview 5.0; SAS Institute, Cary, NC, USA). All data are presented as means ± standard deviation and p < 0.05 was considered statistically significant.
During the experimental period, all swimmers followed the same TS 5-6 times per week for a total of 10-15 hr, covering distances of 14,000-34,000 m·wk-1 (attendance during the training sessions: 89%). Their characteristics, lung function data, and swim times for all field and competition trials are shown in Table 1. There were no differences between the two groups in age (F1.15 = 0.10, p =0.75), height (F1.15 = 0.02, p = 0.89), weight (F1.15 = 0.01, p = 0.94) or fat mass (F1.15 = 0.46, p = 0.50), and there were no changes in anthropometric variables (with the exception of chest expansion which was higher after the 8-week training period only in RMET group; F1.15 = 2.48, p = 0.04) over the 8-week training period in either group (p > 0.05).
Pulmonary function and respiratory muscle strength
No change in pulmonary function was observed during the experimental period, except for FVC and MVV12s, which were increased only in the RMET group (F1.15 = 4.16, p = 0.04 and F1.15 = 4.56, p = 0.02, respectively). MEP and MIP were increased only in the RMET group after the program compared with before, and with a difference between groups after the experimental period (F1.15 = 8.11, p = 0.012 and F1.15 = 13.55, p = 0.002, respectively; Figure 1). Any significant group × time interaction was found for pulmonary function and respiratory muscle strength. There was no significant correlation between the individual changes in MIP or MEP and any swimming performance measure (during the field trials or the competitions; p > 0.05).