Does Respiratory Muscle Training Increase Physical Performance?

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 (VO2max) 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. VO2, respiratory exchange ratio, and heart rate were measured breath by breath. Furthermore, maximum running speed (Vmax), 4 mmol·l−1 lactate threshold (V4) and perception of respiratory effort were determined. During pulmonary testing, sustained maximum inspiratory and expiratory pressure (PImax and PEmax) were obtained. RMT was performed daily at approximately 90% PImax 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 VO2max and endurance performance and are unlikely to be of benefit to military or paramilitary training programs for an increase in endurance performance. 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 maximal 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 morphologi* Institute of Training Science and Sport Informatics German Sport University Cologne, Germany Am Sportpark Müngersdorf 50933 Köln, Germany. † University of Nebraska at Omaha, 15201 Locust Street, Omaha, NE 68116. ‡ Head of Institute of Training Science and Sport Informatics German Sport University Cologne, Germany Am Sportpark Müngersdorf 50933 Köln, Germany. This manuscript was received for review in Novermber 2008. The revised manuscript was accepted for publication in June 2009. Reprint & Copyright © by Association of Military Surgeons of U.S., 2009. MILITARY MEDICINE, Vol. 174, September 2009 cally 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 maximum and submaximum 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 maximum and submaximum 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 maximum amount of oxygen taken up by the human body (VO2max) 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 VO2max 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 977 4 6 10 8 x 8 12♂ 20♂ 16♂ 5♂ 2♀ 16♂ McConnell/ Sharpe (2005) Holm et al. (2004) Romer et al. (2002a) Williams et al. (2002) Romer et al. (2002b) Hart et al. (2001) Markov et al. (2001) Sonetti et al. (2001) Stuessi et al. (2001) Voliantits et al. (2001) 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) 15 15 11 8 4 4 4 4 24 8 15 7 10 11 — 6 − 10 5 5 17 16♂ 12♀ 14♀ 20♂ 978 12♀ 10♂ 20♂ 12♀ 7♂ 1♀ 10♂ 10♀ 10♂ 9♂ Device 5 TS/wk at a fixed 15-s MVV value VIH, own construction VIH, own construction VIH, Ambu RT, Threshold Inspiratory Muscle Trainer, Healthscan VIH 2 ×15 min at » 30% PImax (at RV) 5 TS/wk, 30 min/TS 2 TS/day for 10 min at 50% PImax, raising load every wk 3–4 TS/wk with 3 × 8–10 min VIH 5 TS/wk for 30 min RT, Powerbreathe, Gaiam Ltd., U.K. VIH 2 × 30 bc at »50% PImax, RT, Powerbreathe, CG 60 bc at 15% PImax Gaiam Ltd., U.K. 4–5 TS/wk, 5–7 sets, »25 min/TS RT, Threshold Trainer, at 50% PImax + 5%/wk Respironics, Pittsburgh 2 × 30 bc at »50% PImax. RT, Powerbreathe, CG 60 bc at 15% PImax Gaiam Ltd., U.K. 2 × 30 bc from RV to TLC RT, Powerbreathe, Gaiam Ltd., U.K. 40 TS within 15 wk, VIH, own construction 30 min/TS RT, Powerbreathe, Gaiam Ltd., 5 TS/wk, VIH for 30 min, RT for » 3–5 min at 50% PImax U.K. and VIH 30 min/TS, (...truncated)