Abstract
ssociation of respiratory muscle strength with aerobic endurance kinetics among athletes, with a specific focus on maximal oxygen consumption (VO 2max). Previous research has elucidated the complex interactions between respiratory and skeletal muscles during ex- ercise, highlighting the critical role of efficient respiration in maximizing athletic performance. The in- terplay between active skeletal muscles and respiratory muscles, especially the influence of respiratory muscle fatigue on exercise capacity, is well-documented. High-intensity exercise has been shown to ac- tivate the respiratory muscle metaboreflex, which can restrict blood flow to working
between respiratory and skeletal muscles during ex- ercise, highlighting the critical role of efficient respiration in maximizing athletic performance. The in- terplay between active skeletal muscles and respiratory muscles, especially the influence of respiratory muscle fatigue on exercise capacity, is well-documented. High-intensity exercise has been shown to ac- tivate the respiratory muscle metaboreflex, which can restrict blood flow to working muscles, thereby impacting the energy required for respiration. A total of 41 athletes, drawn from the disciplines of biathlon, judo, and cross-country, participated in this study. Respiratory function tests (RFTs) were administered to assess various respiratory parameters, including changes in chest circumference. Ad- ditionally, maximal oxygen consumption (VO 2max) and heart rate were measured during a treadmill test. To explore the associations between VO2max and ventilatory parameters—namely, ventilation (VE), oxygen consumption (VO 2), carbon dioxide production (VCO 2)—as well as respiratory metrics, linear regression analysis was employed. Based on the standardized regression coefficients (β), it was found that maximum expiratory pressure (MEP) (mean±SD:130.95±42.82 ) and inspiratory di- aphragmatic circumference values were significantly associated with VE, VO 2, and VCO 2. Conversely, the other predictor variables did not exhibit a significant effect on VE (mean±SD :134.80±36.69 ), VO 2(mean±SD:3877.52±868.47 mL ), and VCO 2(mean±SD:4301.27±1001.07 mL ). Similarly, measurements of chest circumference (mean±SD:91.40±10.72 cm ), MEP, and diaphragmatic cir- cumference during inspiration (mean±SD:95.20±10.21 cm ) were significantly associated with VO 2max (mean±SD:58.52±10.74 mL/kg/min ), while the remaining predictor variables did not demonstrate a significant effect on VO 2max. Additionally, a multiple linear regression analysis was conducted to examine the combined effects of respiratory muscle strength and ventilatory factors on VO 2max. The model, which included interaction terms, explained 89.9% of the variance in VO 2max (R 2 = 0.899, adjusted R 2 = 0.859). Significant interactions were found between MIP and VE (B =−0.084, p= 0.006), as well as MEP and VE (B = 0.072,p= 0.012). These findings suggest that respiratory muscle strength plays a more substantial role in determining VO 2max in individuals with higher ventilatory efficiency, highlighting the importance of both respiratory strength and breathing efficiency in aerobic performance. Our
= 0.859). Significant interactions were found between MIP and VE (B =−0.084, p= 0.006), as well as MEP and VE (B = 0.072,p= 0.012). These findings suggest that respiratory muscle strength plays a more substantial role in determining VO 2max in individuals with higher ventilatory efficiency, highlighting the importance of both respiratory strength and breathing efficiency in aerobic performance. Our findings underscore the importance of considering respiratory muscle strength in assessing and enhancing athletes’ aerobic performance. Integrating objective measurements such as maximal inspiratory and expiratory pressure assessments into routine performance evaluations Appl. Sci.2024,14, 8976.
Appl. Sci.2024,14, 8976 2 of 17 allows coaches and sports scientists to monitor changes in respiratory function over time and adjust training protocols accordingly. Keywords:maximum inspiratory pressure; cardiopulmonary test; maximum expiratory pressure; athletes 1. Introduction The capacity for proper respiration, which includes supplying enough oxygen to the working muscles and removing carbon dioxide, depends on the efficiency of gas exchange during both external and internal respiration [1,2]. The gold standard for evaluating func- tional response through gas analysis is the cardiopulmonary exercise test (CPET), which helps identify functional and pathophysiological limitations [1]. This test is particularly im- portant for scuba divers, pilots, soldiers, and professional athletes who experience high levels of physical stress. During physical activity, lung ventilation increases to meet the oxygen needs of the skeletal muscles and activates the accessory respiratory muscles alongside the diaphragm [3]. Respiratory muscle function depends on the strength and endurance of these muscles [4]. Some studies have shown that inspiratory muscles can become fatigued after short periods of intense exercise. This phenomenon underscores the significant physiological demands placed on the respiratory system during vigorous physical activity [5,6] and after long periods of moderate-intensity exercise [7]. Also, during these exercises, the respiratory muscles share the amount of oxygen consumed [8,9]. It has been determined that fatigue occurs in the diaphragm muscle with increased respiratory need during high-intensity exer- cises of 85% VO2max and above. Also, during these exercises, the respiratory muscles share the amount of oxygen consumed [10]. The findings from previous studies mentioned above underscore the shared demand for cardiac output and oxygen consumption between active skeletal muscles and respiratory muscles during exercise. Optimizing respiration plays a pivotal role in enhancing the efficiency of working skeletal muscles by facilitating the accelerated delivery of blood to the relevant regions. This interplay highlights the interconnectedness of respiratory and skeletal muscle function in supporting overall exercise performance and underscores the importance of respiratory optimization strategies in maximizing athletic potential [11]. However, if the endurance of the respiratory muscles is not sufficient, it is predicted that exercise performance may decrease due to early fatigue of the diaphragm
blood to the relevant regions. This interplay highlights the interconnectedness of respiratory and skeletal muscle function in supporting overall exercise performance and underscores the importance of respiratory optimization strategies in maximizing athletic potential [11]. However, if the endurance of the respiratory muscles is not sufficient, it is predicted that exercise performance may decrease due to early fatigue of the diaphragm [11]. High-intensity exercise causes periph- eral vasoconstriction [12]. In addition, it triggers the respiratory muscle metaboreflex, a high sympathetic nerve activity that limits blood flow to the working muscles and thus the energy output and consumption required for breathing [12,13]. The demanding work of the muscles used for inhalation has significant effects on the nervous system and the heart. In healthy people, voluntary resistance during inhalation that leads to muscle fatigue has been found to cause increases over time in muscle sympathetic nerve activity, heart rate, and mean arterial pressure. This is accompanied by a gradual decrease in arterial blood flow to inactive limbs [14]. Research also suggests that the reflex triggered by the fatigue of the inspiratory muscles is activated during full-body exercise. Specifically, blood flow to the legs is inversely related to the effort of breathing during high-intensity exercise, and changes in leg blood vessel resistance are directly related to the amount of noradrenaline (norepinephrine) released [15]. During prolonged intense full- body exercise, the response of the reflex associated with fatigue of the inspiratory muscles may limit exercise performance [16]. However, training the inspiratory muscles can delay the activation of the respiratory muscle reflex, potentially improving performance [12]. Our study represents a rare investigation that comprehensively evaluates both respira- tory muscle parameters. The literature suggests that respiratory muscle fatigue typically does not manifest during exercise at intensities below approximately 80% of VO2max [17]. In another study, it was observed that during intense exercise (>85% of VO2max) in highly trained individuals, respiratory muscles require approximately 15–16% of VO2max and
approximately 80% of VO2max [17]. In another study, it was observed that during intense exercise (>85% of VO2max) in highly trained individuals, respiratory muscles require approximately 15–16% of VO2max and
Appl. Sci.2024,14, 8976 3 of 17 cardiac output, whereas, in untrained individuals, this proportion is≤10% [18]. Con- sidering these studies, our study aimed to investigate the impact of athletes’ respiratory muscle strength, as measured by maximal inspiratory and expiratory pressure, on aerobic endurance kinetics, specifically VO2max. Given the widely acknowledged importance of respiratory muscle strength in athletic performance, understanding the association between respiratory muscle strength and aerobic endurance kinetics can inform training strategies aimed at optimizing performance and minimizing fatigue, ultimately enhancing athletes’ competitive edge. It is worth mentioning that MIP/MEP are also quasi-isometric and static measures and it was suggested that dynamic assessments may be more suitable in an athletic environment [19]. Therefore, our study not only advances scientific knowledge but also has practical implications for enhancing athletic performance and improving training regimens in various sports contexts. In light of this information, we hypothesize that respiratory muscle strength will be associated with the kinetics of maximal oxygen consumption in athletes. 2. Materials and Methods 2.1. Study Design and Participant Selection The participants, who were selected by the convenience sample method, included in the research consisted of 14 biathlon, 14 judo, and 13 cross-country skiing athletes (22 men and 19 women), who applied to the Ministry of Youth and Sports, Department of Athlete Health, Performance and Service Quality Standards in Ankara, Türkiye to become volunteer participants (Table). It is noteworthy that all participants in the study were of Caucasian descent. Determination of the requisite sample size for this study was conducted through the utilization of G-power Software 3.1.9.7, developed by the University of Dusseldorf, Germany, aiming for a power of 0.80 and an effect size of 0.30 [20]. This analysis indicated a minimum sample size of 38 participants for a regression analysis involving predictors. Inclusion criteria were being a non-smoker and not having a respiratory tract disease such as asthma, pulmonary tuberculosis, emphysema, or chronic bronchitis. Athletes on medication, especially those on cardiac glycoside orβ-receptor antagonist-derived drugs, were not included in the study. Moreover, none of the participants had reported any history of lung disease in the past three months,
regression analysis involving predictors. Inclusion criteria were being a non-smoker and not having a respiratory tract disease such as asthma, pulmonary tuberculosis, emphysema, or chronic bronchitis. Athletes on medication, especially those on cardiac glycoside orβ-receptor antagonist-derived drugs, were not included in the study. Moreover, none of the participants had reported any history of lung disease in the past three months, nor had they undergone any prior respiratory muscle strength training. All athletes under the Ministry of Youth and Sports undergo regular health examinations to detect any illnesses. For our study, we selected athletes who had previously undergone these examinations. Importantly, all participants were athletes actively competing at the national level, demonstrating a high level of physical fitness and athletic proficiency within the study group. Additionally, no participants had recently recovered from injuries or were under significant medical treatment that could influence the study outcomes. Athletes who met the inclusion criteria were evaluated on the same day. The study was approved by the Gazi University Ethics Committee (No: 2022-941). The study was conducted according to the Declaration of Helsinki. All participants signed an informed consent form. Table 1.Demographic information of the research group. Characteristics Judo Biathlon Cross-Country Skiing Female (N = 7)Male (N = 7)Female (N = 6)Male (N = 8)Female (N = 6)Male (N = 7) Training Experience (years) 13.14±3.24 12.71±4.07 6.83±2.04 7.13 ±1.64 6.17±1.72 8.71 ±2.81 Age (years) 22.63 ±3.06 22.62±4.80 19.24±1.46 18.73±2.21 17.83±1.34 20.21±2.81 Height (cm) 163 ±7.57 175.93±6.99161.33±5.06 170.63±4.72161.42±6.00 174.57±8.40 Body Weight (kg) 68.59 ±26.07 91.64±19.1156.97±5.46 64.81±8.41 51.33±5.82 68.30±9.32 BMI (kg/m 2 ) 25.08±6.94 29.42±4.52 21.89±1.40 22.05±2.20 20.05±1.79 22.35±1.97 VO 2max (mL/min./Kg) 48.21 ±8.48 49.50±6.47 56.92±6.92 67.08±5.08 60.49±6.80 69.47±7.22 BMI: Body Mass Index.
Appl. Sci.2024,14, 8976 4 of 17 2.2. Procedures To ensure accurate results, we implemented various measures to minimize the impact of factors that could affect respiratory function and VO2max. We controlled respiratory diseases and medication use and instructed participants to maintain their normal training routines. Any deviations from their usual training schedules were reported and docu- mented. To account for differences in dietary habits, participants were required to follow a standardized pre-test meal protocol at least 2 h before each testing session. This was aimed at reducing the influence of recent food intake on exercise performance and respiratory function. In addition, all tests in the laboratory environment were conducted while main- taining strict limits: the temperature ranged from 18 to 23 ◦ C, and the relative humidity was kept below 70% to ensure consistency across trials. Furthermore, participants were asked to refrain from consuming caffeine or alcohol for 24 h before testing and to avoid strenuous exercise for 48 h before the testing sessions to minimize fatigue-related effects. These measures were taken to ensure that the respiratory and aerobic performance mea- surements accurately reflected the participants’ baseline capabilities under standardized conditions. Before starting the test period, demographic information of the athletes (age, year of sport, smoking habits, medication) was recorded first, and then Respiratory Func- tion Tests (RFT) were performed to evaluate respiration and respiratory muscle strength. The circumference measurements of the athletes were recorded by measuring the axilla and subcostal circumferences. Then, the athletes’ VO2max values were measured on the treadmill with a CPET K5 device, and the data were recorded. Finally, respiratory function tests for athletes in each sport were conducted from 10:00 to noon, and cardiopulmonary performance tests were conducted from 16:00 to 18:00. These measurements were carried out by expert personnel, including a specialist physician and a training science specialist, and took place over three days. Upon scrutinizing the gender distributions within the various disciplines, it was discerned that male cross-country skiing athletes exhibited divergent training ages com- pared to their female counterparts. Furthermore, statistical analyses of heights and body weights revealed notable differences favoring male
carried out by expert personnel, including a specialist physician and a training science specialist, and took place over three days. Upon scrutinizing the gender distributions within the various disciplines, it was discerned that male cross-country skiing athletes exhibited divergent training ages com- pared to their female counterparts. Furthermore, statistical analyses of heights and body weights revealed notable differences favoring male athletes across all three disciplines (p< 0.05). Conversely, similar values were observed between male and female athletes in other assessed parameters. These findings underscore potential gender-specific dis- parities in training backgrounds and anthropometric characteristics within the studied athlete cohorts, highlighting the importance of considering gender-related factors in athletic performance analyses. 2.3. Data Collection Tools 2.3.1. Measurement of Chest Circumference To assess the chest circumference accurately, two distinct methods were employed: Axillary Circumference Measurement: This technique entailed the assessment of chest circumference at two pivotal junctures—during maximal expiration and maximal inspiration. The circumference was gauged from the level of the chest apex, encircling the axilla (or armpit), employing a rigid tape measure to ensure precision [19]. Subcostal Circumference Measurement: This approach aimed to capture variations in diaphragmatic circumference. Measurements were conducted during specific respiratory phases—mid-inspiration, maximal expiration, and maximal inspiration. The circumference was evaluated just below the ribcage, utilizing the same rigid tape measure for consistency across assessments [21]. 2.3.2. Assessment of Respiratory Muscle Strength Athletes were briefed on the procedures before the tests. Respiratory function and respiratory muscle strength were assessed utilizing a digital spirometer (Pony FX Cosmed, Italy). The evaluations were conducted with athletes seated comfortably in an upright position. Throughout the tests, participants utilized a mouthpiece and wore a nose clip. They were instructed to seal their lips tightly around the mouthpiece to prevent any air
Appl. Sci.2024,14, 8976 5 of 17 leakage from the spirometer. To familiarize athletes with the device’s operation, a few trial tests were conducted before the formal assessments. Each test was repeated thrice with a maximum rest period of three minutes between trials. The highest measurement score obtained was utilized for statistical analysis. During the maximal voluntary ventilation (MVV) test, athletes were directed to breathe deeply, rapidly, and forcefully for 12 s. Following the completion of the test, athletes were asked to briefly hold their breath to prevent respiratory alkalosis, and the MVV value was recorded. MVV: The greatest amount of air that can be inhaled and exhaled within a given period. MIP (Maximal Inspiratory Pressure): The maximum pressure generated during inhalation. MEP (Maximal Expiratory Pressure): The maximum pressure generated during exhalation. To evaluate respiratory muscle strength, MIP and MEP tests were administered. For the MIP test, athletes were instructed to fully exhale before taking a deep, rapid, and forceful inhalation. Conversely, for the MEP test, athletes were prompted to inhale fully before exhaling swiftly and forcefully. Each test was repeated thrice with rest intervals between measurement cycles. The most favorable results obtained from all tests were selected for inclusion in the subsequent analysis [22]. Additionally, the MIP and MEP tests, which provide information about respiratory muscle strength using the intraoral pressure method, are tests accepted by the European Respiratory Society (ERS) and American Thoracic Society (ATS). These tests are recognized as non-invasive methods for measuring respiratory muscle strength. During exercise, respiratory muscle activation can be assessed by intramuscular EMG or surface electrodes. However, invasive procedures should be performed under medical supervision, while action potential measurements taken using surface electrodes can be challenging to control during high-intensity exercise due to factors like electrode displacement or excessive interference. In previous studies that examined the relationship between respiratory muscle strength and exercise, the MIP/MEP method (which measures intraoral pressure) has been used [23,24]. 2.3.3. Assessment of Aerobic Capacity (VO2max) In this study, maximal oxygen uptake (VO2max) was evaluated using a portable cardiopulmonary exercise test system (Cosmed K5, Italy, Serial No: 2019030706), renowned for
like electrode displacement or excessive interference. In previous studies that examined the relationship between respiratory muscle strength and exercise, the MIP/MEP method (which measures intraoral pressure) has been used [23,24]. 2.3.3. Assessment of Aerobic Capacity (VO2max) In this study, maximal oxygen uptake (VO2max) was evaluated using a portable cardiopulmonary exercise test system (Cosmed K5, Italy, Serial No: 2019030706), renowned for its precision in automatically analyzing expiratory gases. The system was calibrated with a known gas mixture (5.0% CO2and 16.0% O2) to ensure accuracy in measurements. The VO2max test protocol started with a 2-min warm-up phase at a constant speed of 5.0 km/h on the treadmill. After this initial phase, the treadmill speed increased incremen- tally by 0.016 km/h every second, providing a gradual rise in intensity. This specific speed increment was selected to ensure a smooth transition between workloads while pushing the participants toward their maximal aerobic capacity. Athletes were monitored through- out the test, with adjustments continuing until they met at least three of the following termination criteria: a rating of perceived exertion (RPE) of 17 or higher on the Borg scale, verbal indication of exhaustion, no further increase in oxygen consumption despite rising workload, a respiratory quotient (RQ) of 1.15 or above, achieving 85% or more of their maximal heart rate, or a plateau in heart rate despite increasing effort. The average values recorded during the final 30 s of the test were used to calculate the participants’ maximal oxygen consumption, normalized to their body weight [25]. The measurements included minute ventilation (VE), oxygen uptake (VO2), and carbon dioxide production (VCO2), all captured in real time by the gas analysis system. To avoid bias, different researchers conducted the test administration and data analysis, ensuring that the study’s blinding technique was effectively implemented. 2.4. Statistical Procedures Statistical analysis was performed using IBM SPSS Version 21 (IBM Corp., released 2012, Armonk, NY, USA). The normal distribution of the data was assessed visually and using the Shapiro-Wilk test. Both linear regression and multiple linear regression with
Description
The study investigates how respiratory muscle strength affects VO2max in athletes.