Does Respiratory Muscle Training Increase Physical Performance?

Transcription

1 MILITARY MEDICINE, 174, 9:977, 2009 Does Respiratory Muscle Training Increase Physical Performance? Billy Sperlich, PhD * ; Hannes Fricke * ; Markus de Marées * ; John W. Linville, MPH, CPH ; Joachim Mester, PhD ABSTRACT Special force units and military personnel undergo demanding physical exercise and might benefit from high-intensity respiratory muscle training (RMT) by increasing their endurance performance. This study examined the effects of a 6-week high-intensity RMT on running performance and oxygen uptake (VO 2 ) in a group of German Special Force Squad members. Methods: 17 participants were randomly assigned to a training or control group. Baseline and post-testing included a ramp test, as well as an incremental test on a treadmill, performed to physical exhaustion. VO 2, respiratory exchange ratio, and heart rate were measured breath by breath. Furthermore, imum running speed (V ), 4 mmol l 1 lactate threshold (V 4 ) and perception of respiratory effort were determined. During pulmonary testing, sustained imum inspiratory and expiratory pressure (PI and PE ) were obtained. RMT was performed daily at approximately 90% PI for 6 weeks with 2 30 breath cycles using an Ultrabreathe lung trainer. Results: No statistical differences were detected between the groups for any parameter after RMT. Conclusion: High-intensity RMT did not show any benefits on VO 2 and endurance performance and are unlikely to be of benefit to military or paramilitary training programs for an increase in endurance performance. * Institute of Training Science and Sport Informatics German Sport University Cologne, Germany Am Sportpark Müngersdorf Köln, Germany. University of Nebraska at Omaha, Locust Street, Omaha, NE Head of Institute of Training Science and Sport Informatics German Sport University Cologne, Germany Am Sportpark Müngersdorf Köln, Germany. This manuscript was received for review in Novermber The revised manuscript was accepted for publication in June Reprint & Copyright by Association of Military Surgeons of U.S., INTRODUCTION The proper level of physical fitness and overall stamina of military and law enforcement personnel is paramount to the successful completion of critical military and law enforcement operations. Regular high physical demands are placed on soldiers and special force members to not only be capable of completing a certain distance or task as rapidly as possible, but also with minimal signs of fatigue. Modern technical improvements of special forces equipment, such as heavy body armor, heavy backpacks, self-contained breathing apparatus, and gas masks have resulted in increasingly demanding stress especially on the users respiratory system and on respiratory muscles (RMs). Several studies have demonstrated that the RMs, including the diaphragm, are fatigable during prolonged bouts of loaded breathing and exercising and therefore also contribute to the imal amount of oxygen consumed. 1 3 Methods need to be researched to counteract these negative consequences on military and law enforcement personnel, to allow for both the protection and the high level of stamina needed in today s military and law enforcement arenas. Respiratory muscle training (RMT) has been used in former studies as a beneficial therapeutic tool in patients with chronic airflow restriction, which represents a major limiting factor for physical performance. 4 6 As RMs are morphologically and functionally skeletal muscles, they respond to any applied stimulus in the same manner as any other skeletal muscle. 7 In this context a reduction in blood flow to the RM during imum and subimum exercise may result in decreased muscle cell oxygenation. This, in turn, induces increased metabolic energy demands, which is demonstrated by an elevated level of arterial lactate concentration. The result is an increased perception of dyspnoea and the decreased ability of the RM to generate force. 8,9 RMT may, therefore, improve RM endurance because of an increase in cellular oxidative adaptations, which leads to a delayed onset of metabolic acidosis. The resulting lower levels of blood lactate during exercise, as well as the reduced perception of respiratory effort after RMT may ultimately lead to an increase in imum and subimum physical performance. However, there currently exists a controversy surrounding RMT in the literature regarding its benefits on exercise performance and/or its effects on respiratory parameters. Table I presents an overview of existing data from numerous studies examining the effects of RMT on several physiological variables and physical performance. The imum amount of oxygen taken up by the human body (VO 2 ) represents the most prominent parameter for changes in physical performance. Altogether, Table I illustrates that in 15 of the 17 literature sources reviewed, there were no changes of VO 2 after RMT. There were, however, a number of contradictory values in the studies, especially surrounding achieved performance and perception of respiratory effort. These variations are likely the result of different training methods that were applied to the respiratory muscles (moderate or high intensity, low or high volume), use of different training devices, the failure to control the workload adequately (intensity, duration, and frequency of training), and/or the heterogeneity of overall test procedures. Also low numbers of participants, missing control groups, or moderate MILITARY MEDICINE, Vol. 174, September

2 TABLE I. Overview on International Peer-Reviewed Publication of RMT in Chronological Order Author (year) n CG ( n ) Duration Perception of (weeks) Training Design Device PI 1 PE 2 VO Lac Respiratory Effort Performance 2 McConnell/ RT, Powerbreathe, (1) TG *, CG TG * at Ie at 50% PI, CG 60 Ie at 15% PI Sharpe (2005) Gaiam Ltd., U.K. MLSS Holm et al. (2004) VIH TG: * CG: * TG * * Romer et al. (2002a) Williams et al. (2002) Romer et al. (2002b) Hart et al. Markov et al. Sonetti et al. Stuessi et al. Voliantits et al. Inbar et al. (2000) Chatham et al. (1999) Spengler et al. (1999) Suzuki et al. (1993) Boutelleier et al. (1992) Hanel/Secher (1991) Fairbarn et al. (1991) Morgan et al. (1987) bc at»50% PI, RT, Powerbreathe, CG 60 bc at 15% PI Gaiam Ltd., U.K. 5 RT, Threshold Trainer, CG 60 bc at 15% PI x TS/wk, 5 7 sets,»25 min/ts at 50% PI + 5%/wk 2 Respironics, Pittsburgh 30 bc at»50% PI. RT, Powerbreathe, Gaiam Ltd., U.K bc from RV to TLC RT, Powerbreathe, Gaiam Ltd., U.K TS within 15 wk, 30 min/ts TS/wk, VIH for 30 min, RT min/ts, CG did not 12 perform any training bc at» 50% PI RT, Powerbreathe, Gaiam Ltd., for» 3 5 min at 50% PI U.K. and VIH TG * (1) TG **, CG W. (1) TG *, CG VIH, own construction at 60% W * (1) TG *, CG * VIH, own construction * RT, Powerbreathe, Gaiam Ltd., U.K TS/wk, 30 min RT at 30% RT, Threshold Inspiratory PI, increasing up to 80% TG **, CG TG CG *. * TG *, CG Muscle Trainer, Healthscan wk 80% of effort VIH with PC-Feedback TG *, CG * TS/wk for 30 min VIH * at >200W. at end ** min at» 30% RT, Threshold Inspiratory PI (at RV) Muscle Trainer, Healthscan 7 1 (1) TG ** (2) TG * 4 5 TS/wk, 30 min/ts VIH (1) TG * CG * 10 VIH, Ambu (1) TG ** CG ** TS/day for 10 min at 50% 10 PI, raising load every wk TS/wk with min VIH, own construction TS/wk at a fixed 15-s MVV value VIH, own construction * ** n, number of subjects; CG, control group; TG, training group; PI /PE, in-/expiratory pressure; VO, imum oxygen uptake; lac, lactate; HR, heart rate; RT, resistant training; VIH, voluntary 2 inspiratory hyperventilation;, no changes;, increase;, decrease; *, significant p < 0.05; **, significant p < 0.01; MLSS,. lac steady state; W,. performance; DT, prolonged test; ST, increment test; PL, shuttle run; Ø, mean; C, cycle ergometer; T, treadmill; R, rowing ergometer; RV, residual volume; TLC, total lung volume; TS, training session; bc, breath cycle; Ie, inspiratory efforts; wk, week; 15-s MVV, imum voluntary ventilation in 15 seconds. 978 MILITARY MEDICINE, Vol. 174, September 2009

3 effect size could have led to varying results. Finally, the controversial findings may be the result of a generally insufficient training stimulus applied to the RM. Nonethe less, evidence suggests that high-intensity RMT may increase imum performance in well-trained healthy persons as well as reduce the perception of respiratory effort Members of special force units and military personnel undergo demanding daily physical exercise while loaded down with heavy, pulmonary resistive equipment. As such, this group of persons could benefit from high-intensity RMT if there is a corresponding increase in endurance performance. To our knowledge, there is no published data on the effects of high-intensity RMT on endurance performance in military or federal special force staffs. The purpose of this study was to investigate whether 6 weeks of high-intensity RMT, with an easy-to-use training device, increases running performance, VO 2, and pulmonary values in participating members of a Special Forces Police Squad. METHODS Participants Seventeen (12 male/5 female) healthy nonsmoking members of a German Special Forces Police Squad (mean ± SD rel. VO 2 : 54.6 ± 8.6 ml min 1 kg 1 ; age: 24.9 ± 2.5 yrs; height: ± 9.6 cm; body mass index: 22.6 ± 2.2 kg m 2 ) volunteered and gave written informed consent to participate in this study, which was approved by the university s ethics research board. All participants were fully familiarized with the laboratory exercise procedures before the pretesting phase. They were asked to report to the laboratory on test days in a well-hydrated state, at least 2 hours following a light meal, and without having performed strenuous exercise at least 24 hours before testing. None of the participants demonstrated any pathological pulmonary or cardiac findings during medical examination. They were asked to maintain their current diet and current training programs during the study period. Table II gives an overview of all anthropometric values, running speed at 4 mmol l 1 -lactate threshold, and imum oxygen uptake at baseline. Testing Procedures Initially, the participants reported to the laboratory on 3 separate occasions (T 1 T 3 ). Each session was at least 48 hours apart. T 1 included the assessment of VO 2 and imum running speed (V ) in a ramp test protocol performed on a motorized treadmill (Woodway PPS 90med, Germany). After 10 minutes of warm-up at 7 km/h, velocity was increased by 1 km/h per minute (inclination: 1.5%) until imum volitional fatigue was reached. During T 2, the participants performed a imum incremental treadmill protocol beginning at 2.4 m/s and increasing by 0.4 m/s every 5 minutes on the same treadmill used in T 1 (inclination 1%) to measure the 1 anaerobic threshold at 4 mmol l lactate.20 All respiratory data were collected with an open breathby-breath spirograph (ZAN 600USB, Germany) using standard algorithms with dynamic account for the time delay between the gas consumption and the volume signal. The system was calibrated before each test with a calibration gas (15.8% O 2, 5% CO 2 in N; Praxair, Germany) designed to represent the range of anticipated fractional gas concentrations. The calibration gas was administered with a precision 1-L syringe (ZAN, Germany). The participants heart rate (HR) was recorded online every 5 seconds during testing, using short-range telemetry (POLAR S 710, Finland). All respiratory and HR data were averaged every 30 seconds. A 20-μL blood sample from the right ear lobe was collected immediately after each incremental speed increase and at the completion of the test using a capillary tube (Eppendorf, Germany). The blood was analyzed for blood lactate concentration (Lac) using Ebio Plus, Germany. Additionally, the participants were asked to rate their perception of respiratory effort on a 6-point scale (1, very very easy; 6, very very strenuous). During T 3, the participants were subjected to pulmonary function testing. Data for PI and PE were obtained according to American Thoracic Society Guidelines using a digital manometer (GDH Greisener Electronics, Germany), as specified by the manufacturer. An automated pneumotachograph (Viasys Healthcare Ltd., Germany, former Jaeger, Germany) was used for the determination of vital capacity (VC), forced vital capacity (FVC), peak expiratory flow (PEF), and forced expiratory flow in 1 second (FEV 1 ). The system was calibrated prior to each test using a precision 1-L syringe (ZAN, Oberthulba, Germany) and adjusting for temperature, air pressure, and humidity. Five tests were performed at 1-minute intervals. The lowest and the highest values were discarded. The remaining values were averaged and used for data analysis. The entire test procedure was repeated in random participant order after a 6-week training intervention. Training Period The participants were matched into pairs on the basis of their individual VO 2 and aerobic anaerobic threshold and then TABLE II. Individual Anthropometric Values of All Subjects as well as Running Speed at 4 mmol l 1 - Lactate Threshold and Maximum Oxygen Uptake (VO 2 ) for Training (TG) and Control Group (CG) Group P-ID Heigth (cm) Weight (kg) BMI (kg [m 2 ] 1 ) V 4mmol (m s 1 ) VO 2 (ml min 1 kg 1 ) TG X ± SD ± ± ± ± ± 8.1 CG X ± SD ± ± ± ± ± 8.5 MILITARY MEDICINE, Vol. 174, September

4 randomly assigned to either a training group (TG; n = 9) or a control group (CG; n = 8). On the basis of previous studies, the TG performed daily 2 30 breath cycles (~90% of inspiratory mouth pressure) to near imum fatigue using a lung training device (Ultrabreathe Tangent Healthcare Ltd., U.K.).16,22 25 One minute of rest was set between interval series. The training resistance was adjusted weekly to maintain ~90% of inspiratory mouth pressure. The CG followed the same training protocol without breathing resistance. All participants documented character, length, and duration of their daily individual physical and pulmonary training, including ratings of perception of breathing effort. Statistics Traditional statistical methods were used to calculate mean values and standard deviation (MW ± SD) of the data. The effects of independent and dependent variables were detected by analysis of variance (ANOVA-LSD). Statistical significance was expressed as follows: * p 0.05; ** p The STATISTICA (version 7.1; StatSoft Inc.) software package for Windows was used for all statistical analysis. RESULTS There was a 96.4% adherence to the lung training protocol by all participants. There were no differences in age, mass, stature, body composition, or physical fitness between the groups at baseline. No statistical differences were found in the dependent variables at baseline. There were no differences in imum and subimum measured values between the experimental and the control group or between pre- and posttesting (see Table III ). Furthermore, the results of the post-test showed no differences in any of the variables measured during the pulmonary function test in either the experimental or the control group (see Table III ). DISCUSSION As the results clearly demonstrate, the study showed no effect of 6-week high-intensity RMT on imum or subimum physical performance, cardiorespiratory data, pulmonary parameters, or perception of respiratory effort. The findings for V 4 and V are partially consistent with other published studies, which also could not prove any performance-enhancing effects of RMT. 24,26 28 The minute increase in V in our study from pre- to post-testing may be the result of acclimation of the participants to the treadmill and test procedures or to motivational factors. However, the subimum running performance and HR at 4 mmol l 1 (V 4 ) remained unchanged from pre- to post-test. Similar results for V during incremental testing are published in several studies, 23,24,27 29 whereas test procedures with constant workload show perfor- TABLE III. Mean Pre- and Postvalues and Standard Deviation (mean ± SD) for All Parameters and Groups in Incremental and Ramp Test Step Test as well as Pulomonary Function Testing Maximum (Ramptest) Subimum Values at 4 mmol/l Lac (Incremetal Test) Lung function data Parameter G Pre Post P Rel VO 2 (ml min 1 kg 1 ) HR (1 min 1 ) V (m/s) Rel VO 2 (ml min 1 kg 1 ) HR (1 min 1 ) V 4 (m s 1 ) SRE VC (L ) FVC (L) FEV 1 (L) PI (mbar) PE (mbar) TG 53.5 ± ± 9.1 NS CG 55.7 ± ± 9.1 NS TG ± ± 8.4 NS CG ± ± 7.6 NS TG 4.9 ± ± 0.6 NS CG 4.8 ± ± 0.6 NS TG 44.0 ± ± 7.5 NS CG 45.0 ± ± 12.5 NS TG 182 ± ± 8 NS CG 178 ± ± 10 NS TG 3.8 ± ± 0.7 NS CG 3.9 ± ± 0.7 NS TG 5.6 ± ± 0.9 NS CG 5.5 ± ± 0.7 NS TG 5.40 ± ± 1.32 NS CG 4.97 ± ± 0.81 NS TG 5.02 ± ± 1.27 NS CG 4.90 ± ± 1.04 NS TG 4.4 ± ± 1.0 NS CG 4.0 ± ± 0.8 NS TG ± ± NS CG ± ± NS TG ± ± NS CG ± ± NS Statistical differences between trials are marked as * p < 0.05 and ** p < 0.01 or NS, not significant; G, group; TG, training group; CG, control group; VO 2, oxygen consumption; RER, respiratory exchange ratio; HR, heart rate; V /VO2, ventilatory equivalent for oxygen; V, minute ventilation; V E, running speed at E 4 4 mmol l 1 - lactate threshold; rel, relative; SRE, perception of respiratory effort; lac, lactate; VC, vital capacity; FVC, forced vital capacity; PEF, peak expiratory flow; FEV 1, forced expiratory volume in 1 second (VC); PI, imum inspiratory pressure; PE, imum expiratory pressure. 980 MILITARY MEDICINE, Vol. 174, September 2009

5 mance-enhancing effects of RMT. Volianitis et al. 16 showed a significant decrease in 5,000-m rowing time compared to a control group by 36 ± 9 seconds and an increase in achieved distance in a 6-minute test of 3.5 ± 1.2%. Boutellier et al. 15 demonstrated a clear increase in cycling duration of 38% at the anaerobic threshold of 77 ± 6% of VO 2 after 4 weeks voluntary inspiratory hyperventilation. Spengler et al. 27 also demonstrated an increase of time to exhaustion of 27% during constant workload at 85% of W after 4 weeks RMT. Despite the heterogeneity of materials and methods demonstrated in Table I, none of the earlier studies showed any effect on imum and subimum VO ,18,22,24 29 To our knowledge, only Holm et al. 10 could show an increase in VO 2 and performance; however, no significant differences were found between the experimental and control groups. All lactate values in the present study remained unchanged after RMT. Sonetti et al. 13 and Williams et al. 25 also could not demonstrate any metabolic changes in incremental or prolonged tests. In contrast to these findings, Spengler et al. 27 found significantly reduced blood lactate values during defined workloads after 4 weeks of voluntary inspiratory hyperventilation (VIH), although an increase in performance failed to emerge. No measured pulmonary parameters showed any significant difference after RMT. In particular, PI is a good index for in- and expiratory strength according to Criée 30 and Black and Hyatt. 31 However, the assessment of PI and PE turns out to be problematic. Decreased or elevated values may be the result of motivational factors and/or varying breathing technique.21,32 Therefore, especially values for PI and PE show generally high interindividual variation. 31,33,34 Similar to data from Leech et al. 35 and Enright et al., 36 our results for PI have a large statistical range, from 45.0 mbar to mbar, represented by a high standard deviation (pre ± vs. post ± 34.84). VC, FVC, FEV 1, and PEF also do not show any pre- to post-test effect. Perception of respiratory effort also remained unaltered after training. These findings are similar to data generated by Williams, Sonetti et al., and Holm et al. 10,13,25 However, some studies 11,16,19 found a significant reduction in perception of respiratory effort for the experimental group. This might be the result of an increase in PI reducing the amount of imum tension per breath cycle in respiratory muscles, which would lead to a reduction in perception of respiratory effort.37 CONCLUSION As the results clearly demonstrate, the study showed no effect after a 6-week high-intensity RMT on imum and subimum physical performance, cardiorespiratory data, pulmonary parameters, or perception of respiratory effort. The RMT in this study had no effect on any of the tested variables. The findings are partially confirmed by previous studies. Incongruency with other existing literature is most likely the result of methodological diversity of the pre- post-test design, lack of control groups, and heterogeneous training protocols. In conclusion, on the basis of this study, healthy military and law enforcement personnel, with regular demanding physical exercise, will most likely not achieve an increase in physical performance because of additional high-intensity RMT. REFERENCES 1. 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