Lung Function and Respiratory Muscle Adaptations of Endurance- and Strength-Trained Males

Diverse exercise-induced adaptations following aerobic endurance compared to strength-training programs is well documented, however, there is paucity of research speci cally focused on adaptations in the respiratory system. The aim of the study was to examine whether di erences in lung function and respiratory muscle strength exist between trainers predominately engaged in endurance compared to strength-related exercise. A secondary aim was to investigate if lung function and respiratory muscle strength were associated with one-repetition maximum (1RM) in the strength trainers, and with VO2max and fat-free mass in each respective group. Forty-six males participated in this study, consisting of 24 strength-trained (26.2 6.4 years) and 22 endurance-trained (29.9 7.6 years) participants. Testing involved measures of lung function, respiratory muscle strength, VO2max, 1RM, and body composition. The endurance-trained compared to strength-trained participants had greater maximal voluntary ventilation (MVV) (11.3%,p=0.02). The strength-trained compared to endurance-trained participants generated greater maximal inspiratory pressure (MIP) (14.3%,p=0.02) and maximal expiratory pressure (MEP) (12.4%,p=0.02). Moderate–strong relationships were found between strength-trained respiratory muscle strength (MIP and MEP) and squat and deadlift 1RM (r=0.48–0.55,p 0.017). For the strength-trained participants, a strong relationship was found between MVV and VO2max (mL kg 1 min 1 ) (r=0.63,p=0.003) and a moderate relationship between MIP and fat-free mass (r=0.42,p=0.04). It appears that endurance compared to strength trainers have greater muscle endurance, while the latter group exhibits greater respiratory muscle strength. Di erences in respiratory muscle strength in resistance trainers may be in uenced by lower body strength. Keywords: respiratory mouth pressures; respiratory muscles; resistance training; muscle strength; exercise performance 1. Introduction Aerobic training is well known to induce structural and functional adaptations of the cardiovascular and musculoskeletal systems [1]. During exercise, increased stress is placed upon the respiratory system to meet the metabolic demands of the activity. The

trainers may be in uenced by lower body strength. Keywords: respiratory mouth pressures; respiratory muscles; resistance training; muscle strength; exercise performance 1. Introduction Aerobic training is well known to induce structural and functional adaptations of the cardiovascular and musculoskeletal systems [1]. During exercise, increased stress is placed upon the respiratory system to meet the metabolic demands of the activity. The respiratory system consists of airways, lungs, blood vessels, and muscles. This network of organs and tissues is responsible for gas exchange between inspired air and the circulatory system where oxygen is delivered to the blood, as well as the elimination of carbon dioxide from the blood to the lungs [1]. Improvements in lung function have been shown in healthy inactive women following aerobic exercise combined with resistance training [2]. Improvements in respiratory muscle strength have also been observed following a 4-week high-intensity interval training program [3] and a 16-week resistance training program involving sit-ups and bicep curls [4]. The positive e ects of exercise on the respiratory system are not limited to healthy populations, with positive e ects found in adults with asthma [5], chronic stroke patients [6], Sports2020,8, 160; doi:10.3390 /sports8120160 /journal/sports

Sports2020,8, 160 2 of 13 and obese adolescents [7]. Therefore, it is not surprising that higher levels of aerobic tness are associated with enhanced lung function [8] and a slower decline in lung function during aging with a more physically active lifestyle [9]. In athletic populations, the intense exercise training regimens they typically undergo appears to contribute to enhanced lung function compared to healthy sedentary adults [10] or age-matched reference values [11]. However, lung function between athletes has been shown to vary depending on the sport, with superior performance in endurance-trained athletes compared to athletes involved in strength/power training [10]. Athletes that are considered to be endurance trained predominantly engage in aerobic exercise which is de ned as an activity that uses large muscle groups, can be maintained continuously for extended periods, and is rhythmic in nature (e.g., cycling, running, and swimming) [12]. This type of exercise heavily relies on aerobic metabolism, with maximal oxygen uptake (VO2max) being a criterion measure of aerobic tness [13]. Aerobic exercise is associated with greater ventilatory responses compared to resistance exercise, which is the predominant training type performed by strength/power athletes [14]. The great demands placed on the respiratory system during intense aerobic exercise have been documented in runners, with lung function being acutely impaired following marathon and ultra-marathon events [15]. In comparison, there does not seem to be any detrimental acute change in lung function following resistance training [16] and this lack of training stimulus on the lungs likely explains the similar lung function observed between strength/power athletes and sedentary adults [10]. However, unique respiratory system adaptations appear to take place within strength-trained athletes, as reported by Brown et al. [17], with greater diaphragm mass and respiratory muscle strength in world-class male powerlifters compared to untrained healthy adults. Supposedly, compound exercises such as squats and deadlifts may provide a stimulatory e ect on the respiratory muscles due to their activation to assist with spine stability [18]. To date, there is a paucity of research that has investigated both the lung function and respiratory muscle strength in a given cohort comprising endurance-trained and strength-trained

compared to untrained healthy adults. Supposedly, compound exercises such as squats and deadlifts may provide a stimulatory e ect on the respiratory muscles due to their activation to assist with spine stability [18]. To date, there is a paucity of research that has investigated both the lung function and respiratory muscle strength in a given cohort comprising endurance-trained and strength-trained participants. As such, the lung function and respiratory muscle strength characteristics of these two di erent athletic populations have not been con rmed. Additionally, most studies have included a broad variety of athletes characterised as endurance trained (distance runners, footballers) or strength trained (short-distance runners, wrestlers, weightlifters, martial art ghters) [10,11], which is likely to in uence the results due to the engagement in di erent types of training. This is especially the case for the strength-trained groups since the resistance-training stimulus (e.g., loads, type of exercise, training volume) appears to be important towards inducing respiratory muscle adaptations [4,17]. Therefore, the purpose of this study was to examine whether di erences in lung function and respiratory muscle strength exist between trainers that predominately engage in endurance or strength-related exercise. A secondary aim was to investigate if lung function and respiratory muscle strength were associated with one-repetition maximum (1RM) in the strength-trained group and with VO2max and fat-free mass in each group. It was hypothesised that superior performance in the endurance-trained compared to strength-trained group would be observed for indices of lung function, which is supported by evidence of enhanced lung function in athletes with endurance training experience [10,11]. Greater respiratory muscle strength was expected in the strength-trained compared to endurance-trained group based on the ndings from Brown et al. [17]. Further, it was expected that lung function would be associated with VO2max and that respiratory muscle strength would be associated with 1RM [19] and fat-free mass [20]. 2. Materials and Methods A cross-sectional, descriptive, and correlational study design was employed to examine the lung function and respiratory muscle strength of strength-trained and endurance-trained males. Forty-six males participated in this study, consisting of 24 strength-trained (26.2 6.4 years;1.8 0.1 m) and

with VO2max and that respiratory muscle strength would be associated with 1RM [19] and fat-free mass [20]. 2. Materials and Methods A cross-sectional, descriptive, and correlational study design was employed to examine the lung function and respiratory muscle strength of strength-trained and endurance-trained males. Forty-six males participated in this study, consisting of 24 strength-trained (26.2 6.4 years;1.8 0.1 m) and 22 endurance-trained (29.9 7.6 years; 1.8 0.1 m) participants. Participants in the strength-trained group reported 7.4 5.3 years of resistance training experience and would complete this type of training

Sports2020,8, 160 3 of 13 on 4.0 1.1 days per week. There were 18 participants that were considered recreational resistance trainers, ve participants that had a background in powerlifting/Olympic weightlifting, and one participant with a history of competing in bodybuilding contests. In comparison, endurance-trained participants reported 8.3 6.2 years of aerobic training experience and completing this training on5.8 3.4 days per week (>500 min per week). The predominant training of the endurance group consisted of cycling (n=8), triathlon (n=7), running (n=6), and cycling/running (n=1). Participants provided verbal and written consent prior to study commencement. This study was approved by the University of Sydney Human Research Ethics Committee, project number 2014/996. The general eligibility criteria for this study included being male, aged 18–45 years, and apparently healthy, which was de ned as the absence of asthma, current illness, medications that in uence lung function, and any chronic disease or condition. While pulmonary function and aerobic capacity declines between the ages of 25–80 years, an age of 45 years was considered the upper limit where the e ects of age would have minimal in uence on the respiratory and exercise performance of an active cohort [21]. The speci c eligibility criteria for the strength-trained group included: 1 year resistance training experience with 2 sessions per week currently being performed, and having the ability to perform the bench press, squat, and deadlift. A speci c strength level was also required to be met by participants in the strength group, which included a relative muscle strength(1RM kg/kg body mass (BM)) of 1.2 for the bench press, 1.5 for the squat, and 1.7 for the deadlift. The speci c eligibility requirements for the endurance-trained group included consistent participation in aerobic exercise training sessions (averaging 3 sessions per week) featuring activities such as cycling, running, and swimming. To ensure that the endurance group was adequately trained, a VO2max of>50.0 mL kg 1 min 1 was required since physically active but not highly trained males can be shown to achieve VO2max values of 50.1 3.1 mL kg 1 min 1 [22]. Participants were tested at the Exercise

sessions per week) featuring activities such as cycling, running, and swimming. To ensure that the endurance group was adequately trained, a VO2max of>50.0 mL kg 1 min 1 was required since physically active but not highly trained males can be shown to achieve VO2max values of 50.1 3.1 mL kg 1 min 1 [22]. Participants were tested at the Exercise Physiology Laboratories of The University of Sydney. For the strength-trained group, this involved two to three visits with a cycling VO2max test performed during the initial session, the lung function and respiratory muscle tests in the second session, and the one-repetition maximum (1RM) as the last test to be performed. Body composition was either assessed in a separate visit or at the beginning of other visits. The endurance-trained group completed all testing in one visit in the order of body composition, lung function and respiratory muscle strength testing, and nally the cycling VO2max test. It was decided that the endurance-trained group would not be involved in 1RM testing due to the general lack of resistance training experience. There were 12/22 participants who did not engage in any resistance training, 1/22 participants that performed bodyweight resistance exercise once per week, and 9/22 participants who performed 1–2 days of resistance training. Additionally, it was likely that having novice resistance trainers perform the squat and deadlift 1RM may expose the endurance-trained participants to unnecessary risks and could confound the results due to the highly technical nature of these lifts. Participants were instructed to avoid any strenuous physical activity 24–48 h before the testing session. If a participant reported fatigue or soreness from previous exercise, the testing session was rescheduled. If performing exercise testing in the same visit as the body composition assessment, it was advised to eat a light meal following a dual-energy X-ray absorptiometry (DEXA) scan so that exercise performance would not be negatively a ected. Participants in the strength-trained group completed all testing in 9.0 5.8 days. 2.1. Cycling VO2Max Test The VO2max test was performed by participants exercising on an electronically braked cycle ergometer (Excalibur Sport V 2.0 bicycle, Lode

was advised to eat a light meal following a dual-energy X-ray absorptiometry (DEXA) scan so that exercise performance would not be negatively a ected. Participants in the strength-trained group completed all testing in 9.0 5.8 days. 2.1. Cycling VO2Max Test The VO2max test was performed by participants exercising on an electronically braked cycle ergometer (Excalibur Sport V 2.0 bicycle, Lode BV, the Netherlands) with breath-by-breath recordings of VO2throughout the test (Ultima Series CardiO2 and PFX, Medgraphics, Minneapolis, MN, USA). The protocol commenced at 100 W or 150 W, maintaining a cadence above 70 revolutions per minute with increases of 30 W every minute until exhaustion [23]. Heart rate measurements (Polar T31, Polar Electro Oy, Kemple, Finland) were recorded throughout the test. A 5–10 min warm-up was completed prior to commencing the VO2max test. The VO2values were averaged using a 10 s

Sports2020,8, 160 4 of 13 interpolation and the highest VO2value prior to exhaustion was considered the VO2max. The VO2 max was con rmed by the attainment of two or more of the following criteria: (1) an increase in work rate without an increase in VO2, (2) respiratory exchange ratio exceeding 1.1, and (3) heart rate within 10% of age-predicted maximum. The VO2max was expressed in absolute (L min 1 ) and relative (mL kg 1 min 1 ) terms. 2.2. Body Composition Participants had their body composition assessed by a whole-body DEXA scanner (Lunar Prodigy, GE Medical Systems, Madison, WI, USA). Conditions were standardised to ensure accurate results. This included being in a fasted state (10–12 h prior to scan), minimising uid intake (no more than 200 mL of water prior to scan), bladder/bowel being voided, jewellery removed, and clothes removed down to the underwear with a hospital gown worn. Prior to every DEXA scan, the machine was calibrated (within 24 h). Body composition results were obtained by in-built analysis software (version 13.60.033; enCORE 2011, GE Healthcare, Madison, WI, USA). 2.3. Lung Function The Medgraphics pulmonary function testing system (Breezesuite Ultima PFX, Milano, Italy) was used to assess lung function. Prior to all testing, participants were given information about the protocols for each test and were able to have practice attempts. The lung function measures were performed in a standing position. During the tests, participants wore a nose clip and were instructed to keep their lips securely around the mouth piece to prevent any air escaping. The rst test performed was the forced vital capacity (FVC) test and required participants to empty their lungs of air and then fully inspire, followed by full expiration. The forced expiratory volume in 1 s (FEV1), 3 s (FEV3), and 6 s (FEV6), and ratio of FEV1to FVC (FEV1/FVC) were obtained from the FVC. The slow vital capacity (SVC) test was performed after the FVC test and commenced with a minimum of four stable tidal breaths followed by a maximal inspiration and then a maximal expiration, performed in a slow manner. Both inspiratory capacity

s (FEV1), 3 s (FEV3), and 6 s (FEV6), and ratio of FEV1to FVC (FEV1/FVC) were obtained from the FVC. The slow vital capacity (SVC) test was performed after the FVC test and commenced with a minimum of four stable tidal breaths followed by a maximal inspiration and then a maximal expiration, performed in a slow manner. Both inspiratory capacity (IC) and expiratory reserve volume (ERV) were obtained from the SVC. A minimum of three trials were performed for the FVC and SVC tests, with the best two values needing to be within 5% [24]. The reliability between trials was assessed via the intraclass correlation coe cient (ICC) and coe cient of variation (CV). The reliability was considered good for the FVC (ICC=0.99, 95% CI: 0.90–1.0; CV=1.4%) and SVC (ICC=0.99, 95% CI: 0.99–1.0; CV=1.3%) tests. The nal lung function test was the maximal voluntary ventilation (MVV) test, with the participant required to breathe deeply and rapidly on the command over a period of 12 s. There was approximately a 30 s recovery between lung function testing trials, although generally there was a longer rest between attempts for MVV. At least three trials were performed of MVV, with the best two values needing to be within 10%. The best trial for all measures was used for data analysis. The reliability between trials was considered good for MVV (ICC=0.99, 95% CI: 0.97–0.99; CV=2.4%). Following adequate rest (i.e.,>10 min), residual volume (RV) was assessed using the previously validated O2rebreathing technique [25]. Participants performed two trials and these were averaged to determine RV. If the di erence between trials 1 and 2 was greater than 300 mL, a third RV trial was required (with the two closest two trials averaged for the RV). The total lung capacity (TLC) was calculated through adding SVC (or FVC if greater) and RV. 2.4. Respiratory Muscle Strength Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were assessed using a handheld non-invasive mouth-pressure manometer that digitally displayed pressures on a small MicroRPM screen (Micro Medical/CareFusion, Kent, UK). Prior to each trial, participants wore a nose clip to prevent

total lung capacity (TLC) was calculated through adding SVC (or FVC if greater) and RV. 2.4. Respiratory Muscle Strength Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were assessed using a handheld non-invasive mouth-pressure manometer that digitally displayed pressures on a small MicroRPM screen (Micro Medical/CareFusion, Kent, UK). Prior to each trial, participants wore a nose clip to prevent nasal air leak and were told to hold the device. The MIP was assessed rst and involved emptying the lungs of air and then inhaling maximally for approximately 2–3 s against the resistance of the gauge. As for MEP, the participants fully lled their lungs with air and then exhaled maximally for

Sports2020,8, 160 5 of 13 approximately 2–3 s against the resistance of the gauge. There needed to be at least three trials within 10% of each other for MIP and MEP, with the best performances used for data analysis. Recovery between trials was approximately 30 s, although generally it was adjusted based on participants' perceptions and variation in performances. The reliability between trials was considered good for MIP (ICC=0.99, 95% CI: 0.98–0.99; CV=3.8%) and MEP (ICC=0.99, 95% CI: 0.98–0.99; CV=3.6%). 2.5. Weightlifting Strength The 1RM was assessed for the bench press, squat, and deadlift in participants from the strength-trained group. The order of exercise testing was either the bench press or squat rst (participant could choose), with the deadlift assessed last. A thorough warm-up was completed prior to all 1RM tests. The warm-up involved performing sets using light loads and then progressing to heavier loads, although e orts were made to keep below approximately 80% of the maximum to reduce any possible fatigue e ects. The 1RM test involved performing trials of a single repetition of increasing load with correct technique with a 3–5 min rest between attempts. The heaviest load successfully lifted was recorded as the 1RM. The technique used for the bench press involved lying at on a bench, lowering the barbell close to chest (approximately 2.5 cm from chest) and then pressing upwards until arms were fully extended. For the squat, a successful attempt required the knees and hips to be in a horizontal plane (i.e., thighs parallel to oor) prior to commencing the ascent to an upright position. Finally, the deadlift technique involved the participant lifting the loaded barbell from the oor to a fully upright position with knees extended. Participants could not use weight belts for squat and deadlift but wrist straps and chalk were permitted to assist with holding the bar for the deadlift. The 1RM was expressed in absolute (kg) and relative terms (kg/kg BM). 2.6. Statistical Analyses Data analyses were performed using SPSS version 24.0 for Windows (IBM Corp., Armonk, NY, USA). Normality of data was assessed through using the Kolmogorov–Smirnov test.

The study investigates respiratory adaptations in endurance vs. strength-trained males.