Abstract
ackground: Amateur runners may benefit from combining respiratory muscle training (RMT) with resistance or aerobic modalities, but direct comparisons are scarce. This study compared different RMT-based combinations on pulmonary function, respiratory muscle strength, and whole-body exercise capacity. Methods: In this randomized four-arm trial, 48 amateur runners were allocated equally to stand-alone RMT, RMT plus upper-limb resistance (RMT + ULRT), RMT plus lower-limb resistance (RMT + LLRT), or RMT plus aerobic exercise (RMT + AET). All groups completed supervised sessions three times per week for six weeks. Pulmonary function (forced vital capacity [FVC], forced expiratory vol- ume in one second [FEV1], FEV1/FVC), respiratory muscle strength (maximal inspiratory and expiratory pressures, MIP and MEP), and cardiopulmonary exercise test indices (peak oxygen uptake [VO2peak], VE/VCO2slope) were assessed before and after training using standardized spirometry, mouth-pressure measurements, and treadmill cardiopulmonary exercise testing (CPET). Pre–post changes within groups and the overall between-group dif- ferences were evaluated using standard parametric methods. Results: All four interventions were associated with improvements in at least one respiratory or cardiopulmonary domain. FVC and FEV1tended to improve more in the resistance-combination groups, whereas the FEV1/FVC ratio increased with RMT alone and when combined with resistance. MIP increased in the RMT, RMT + ULRT, and RMT + LLRT groups, and MEP increased across all groups. VO2peak rose in every group, while the VE/VCO2slope improved only when RMT was combined with upper- or lower-limb resistance or aerobic exercise. Between-group differences in change scores were not statistically significant and did not clearly favor any single regimen. Conclusions: In amateur runners, six weeks of
RMT + ULRT, and RMT + LLRT groups, and MEP increased across all groups. VO2peak rose in every group, while the VE/VCO2slope improved only when RMT was combined with upper- or lower-limb resistance or aerobic exercise. Between-group differences in change scores were not statistically significant and did not clearly favor any single regimen. Conclusions: In amateur runners, six weeks of RMT-based programs are feasible and associated with domain-specific improvements in lung function, respiratory muscle strength, and exercise capacity. Because between-group differences in change scores were not statistically significant and the sample size was modest, these findings should be considered exploratory and may inform hypothesis generation regarding the use of different RMT combinations in future, larger trials. Keywords:pulmonary ventilation; exercise tolerance; resistance training; cardiopulmonary exercise testing; running; respiratory muscles 1. Introduction Running performance and injury risk in amateur runners are influenced by training load, intensity, and how training volume progresses over time. Compared with world-class Bioengineering2026,13, 11
Bioengineering2026,13, 11 2 of 20 distance runners, recreational runners often follow less structured periodization; their outcomes are closely related to total weekly volume, longest-run duration, and week-to- week load changes [1–3]. In practice, training commonly emphasizes lower-limb strength and aerobic capacity, whereas respiratory muscle function and ventilatory efficiency receive less attention, despite the importance of monitoring training dose in this population [4]. Respiratory muscle fatigue can act as an independent limiter of high-intensity and sustained exercise. A substantial body of evidence shows that respiratory muscle training (RMT), including inspiratory muscle training (IMT), improves inspiratory and expira- tory strength (MIP/MEP), pulmonary function, and functional capacity across clinical populations [5–8]. Beyond clinical settings, RMT has been linked to upward shifts in lactate threshold and improved high-intensity performance in healthy participants and athletes [9–13], and a recent randomized trial in amateur runners reported IMT-related attenuation of lactate accumulation alongside performance gains [14]. When RMT is com- bined with other modalities, additional pathways may be targeted: aerobic exercise and combined rehabilitation frequently improve ventilatory efficiency (lower VE/VCO2slope) and exercise tolerance [15–18], whereas upper- or lower-limb resistance training can en- hance thoracic expansibility, trunk/pelvic stabilization, and accessory-muscle recruitment, thereby supporting more economical breathing mechanics [19–24]. At the same time, proto- col heterogeneity and short intervention windows often yield small or inconsistent changes in spirometric indices, and practical constraints—such as transient post-session decrements in respiratory strength after high-volume resistance work or device-related psychophysio- logical responses—counsel careful periodization and monitoring [25,26]. Related clinical literature (e.g., pulmonary hypertension, obstructive sleep apnea) strengthens the plausibil- ity of efficiency-focused mechanisms but also illustrates variability across populations and protocols [27,28]. Head-to-head comparisons of respiratory muscle training (RMT) alone versus RMT combined with upper-limb resistance training (ULRT), lower-limb resistance training (LLRT), or aerobic exercise training (AET) under a unified protocol are scarce in healthy amateur runners. Addressing this gap, the present randomized four-arm trial compares these strategies to describe their effects on pulmonary function (forced vital capacity [FVC], forced expiratory volume in one second [FEV1], FEV1/FVC ratio), respiratory muscle strength (maximal inspiratory and expiratory pressures, MIP and MEP), whole-body aerobic capacity (peak
aerobic exercise training (AET) under a unified protocol are scarce in healthy amateur runners. Addressing this gap, the present randomized four-arm trial compares these strategies to describe their effects on pulmonary function (forced vital capacity [FVC], forced expiratory volume in one second [FEV1], FEV1/FVC ratio), respiratory muscle strength (maximal inspiratory and expiratory pressures, MIP and MEP), whole-body aerobic capacity (peak oxygen uptake [VO2peak]), and ventilatory efficiency (VE/VCO2 slope) in amateur runners. Rather than establishing superiority of any single regimen, this study aims to characterize the within-group response patterns associated with different RMT-based combinations and to generate hypotheses for future, larger trials. 2. Materials and Methods This study used a randomized, four-arm, parallel, pre–post design to compare (i) stand- alone respiratory muscle training (RMT), (ii) RMT plus upper-limb resistance training (RMT + ULRT), (iii) RMT plus lower-limb resistance training (RMT + LLRT), and (iv) RMT plus aerobic exercise training (RMT + AET). All outcomes were assessed during two dedicated laboratory visits: a baseline (pre-intervention) assessment before the start of the 6-week program and a post-intervention assessment after completion of the 6-week program, using identical procedures at both time points. No additional daily or weekly outcome measurements were collected during the intervention; the thrice-weekly sessions were reserved for training. Participants were not prescribed a standardized running program during the 6-week period. Therefore, overall running training load (e.g., weekly volume and intensity) and any concurrent strength training outside the supervised sessions were not formally monitored or controlled. After baseline assessments, participants were https://doi.org/10.3390/bioengineering13010011
Bioengineering2026,13, 11 3 of 20 randomly assigned in a 1:1:1:1 ratio to the RMT, RMT + ULRT, RMT + LLRT, or RMT + AET group using a simple drawing-lots procedure without stratification. Randomization was performed by an investigator who was not involved in outcome assessments, and outcome assessors were kept unaware of group allocation to maintain a single-blind design. In Figure, R denotes randomization. The protocol received approval from the Institutional Review Board of Sun Moon University (SM-202509-017-2), and all participants provided written informed consent prior to enrollment. Figure 1.Study design. Eligible participants were adults aged 20–45 years who met an operational definition of “amateur runner”: they had run at least twice per week for≥6 months and aver- aged15–80 kmper week over the preceding 3 months, with non-elite competitive status. Exclusion criteria comprised very low recent running exposure (<5 km/week over the past 3 months or <10 km total in the past year), medical contraindications to exercise involving cardiovascular, respiratory, neurological, or musculoskeletal systems, and any investigator-determined factors (e.g., medication or alcohol use) that could render partici- pation inappropriate. An a priori power analysis (G*Power 3.1.9.7) for a one-way ANOVA on change scores (∆= post−pre; four groups) assumed an effect size of f = 0.50,α= 0.05 (two- tailed), and power (1−β) = 0.80, yielding a required sample ofn= 12 per group (total N = 48). Given the modest per-group sample size and limited head-to-head evidence, this trial was designed as exploratory (pilot-scale) and hypothesis-generating rather than confirmatory for establishing between-group superiority. The assumed effect size(f = 0.50) was selected to represent a moderate-to-large between-group difference, informed by previous trials reporting clinically relevant improvements in spirometric indices, respiratory muscle strength, and VO2peak following respiratory muscle training or combined aerobic– resistance interventions in adults [5–14,29]. Eligibility was prescreened; after consent, baseline characteristics (sex, date of birth, height, weight), health status (recent illness, injuries, medications), and self-reported running training habits (e.g., sessions per week and weekly running distance) were recorded. Participants were then randomly assigned by drawing lots to one of the four groups (n= 12 each), and assessors remained unaware of allocation
in adults [5–14,29]. Eligibility was prescreened; after consent, baseline characteristics (sex, date of birth, height, weight), health status (recent illness, injuries, medications), and self-reported running training habits (e.g., sessions per week and weekly running distance) were recorded. Participants were then randomly assigned by drawing lots to one of the four groups (n= 12 each), and assessors remained unaware of allocation to the extent possible. The flow diagram of the study procedure is presented in Figure. https://doi.org/10.3390/bioengineering13010011
Bioengineering2026,13, 11 4 of 20 Figure 2.Flow diagram of the study procedure. All participants completed a six-week program consisting of three supervised sessions per week. Respiratory muscle training (RMT) formed the common core across arms and was delivered with a pressure-threshold inspiratory muscle training device (Threshold, Yiwu Shimai Trade Co., Ltd, Yiwu, China) while seated with back support. Each session comprised three sets of 30 breaths with 30 s inter-set rest. The initial inspiratory load was set at approximately 30% of each participant’s baseline maximal inspiratory pressure (MIP). The inspiratory load was then progressed by about 5–10% of MIP between sessions when the participant could comfortably complete all three sets of 30 breaths using a stable diaphragmatic breathing pattern (full expiration→deep inspiration→full expiration) at a target rating of perceived exertion (RPE) of 13–15, without dizziness, headache, chest discomfort, or disproportionate dyspnea. Sessions were paused or terminated if dizziness, headache, chest discomfort, or disproportionate dyspnea occurred. Standardized warm-up and cool-down were applied in all arms, and adherence was monitored with attendance logs and home record sheets. Adherence was operationalized as attendance at the supervised sessions (18 planned sessions over six weeks) and was tracked using session attendance logs. https://doi.org/10.3390/bioengineering13010011
Bioengineering2026,13, 11 5 of 20 Because all training was supervised, completion of the prescribed sets/repetitions/breaths and tolerance to the session were checked in real time by study staff, and any deviations (e.g., pausing/termination due to symptoms) were noted. For the RMT component, protocol fidelity was supported by standardized progression criteria (load increased by ~5–10% of baseline MIP when participants completed all sets with stable diaphragmatic breathing at target RPE 13–15 and without disproportionate symptoms). For the aerobic arm, heart rate was continuously monitored and RPE was recorded to verify internal load at the prescribed intensity. The respiratory muscle training procedure is illustrated in Figure. Figure 3.Respiratory Muscle Training. In the RMT + ULRT arm, the RMT session was followed—after a 3 min seated recovery—by upper-limb resistance exercise emphasizing scapulothoracic control (shoul- der press; LS-701; LEXCO, Daegu, Republic of Korea). Loads were prescribed at 70% of one-repetition maximum (1RM), performed for 3 sets of 8 repetitions with 60 s inter-set rest. One-repetition maximum for the shoulder press was determined at baseline using a supervised incremental loading test and defined as the highest load that could be lifted once with full range of motion and proper technique; the 70% 1RM load was then used to prescribe training intensity across the 6-week intervention. Repetitions were executed through the full range of motion without momentum, with coaching cues to maintain scapulothoracic rhythm and avoid excessive rib-cage elevation. The shoulder press exercise setup is illustrated in Figure. In the RMT + LLRT arm, participants completed the same RMT protocol and then— after a 3 min recovery—performed lower-limb resistance exercise on a legpress (LS-117; LEXCO, Daegu, Republic of Korea) at 70% 1RM, 3×8 with 60 s inter-set rest. For the leg- press exercise, 1RM was likewise assessed at baseline with a progressive loading procedure under supervision and training loads were set at 70% of this baseline 1RM value for the duration of the program. Technique instruction prioritized alignment, lumbopelvic stability, and coordinated breathing to support intra-abdominal pressure and lower-extremity–core coupling (Figure). In the RMT + AET arm, RMT was followed—after a 3 min recovery—by tread- mill(NR20;
assessed at baseline with a progressive loading procedure under supervision and training loads were set at 70% of this baseline 1RM value for the duration of the program. Technique instruction prioritized alignment, lumbopelvic stability, and coordinated breathing to support intra-abdominal pressure and lower-extremity–core coupling (Figure). In the RMT + AET arm, RMT was followed—after a 3 min recovery—by tread- mill(NR20; DRAX Inc., Anyang-si, Gyeonggi-do, Republic of Korea)-based aerobic exercise at 70% of age-predicted maximal heart rate for 20 min per session. Each bout included a 3–5 minwarm-up to the target intensity, steady-state maintenance at the prescribed work- https://doi.org/10.3390/bioengineering13010011
Bioengineering2026,13, 11 6 of 20 load, and a 3–5 min cool-down. Heart rate was continuously monitored, and ratings of perceived exertion (RPE 13–15) were recorded in parallel to verify internal load (Figure). Figure 4.Shoulder press. Figure 5.Leg press. Figure 6.Treadmill training. https://doi.org/10.3390/bioengineering13010011
Bioengineering2026,13, 11 7 of 20 Respiratory function and respiratory muscle strength were assessed using standard spirometry (PONY FX, COSMED, Albano Laziale, Italy) and mouth-pressure maneuvers. Forced vital capacity (FVC, L) was defined as the total volume of air forcibly exhaled after a full inspiration, providing an index of overall ventilatory capacity. Forced expiratory volume in one second (FEV1, L) was defined as the volume exhaled during the first second of the FVC maneuver, reflecting expiratory flow and large-airway function. The FEV1/FVC ratio expressed the proportion of the vital capacity exhaled in the first second and was used to screen for obstructive ventilatory patterns. Maximal inspiratory pressure (MIP, mmH2O) and maximal expiratory pressure (MEP, mmH2O) were measured at the mouth as the peak inspiratory pressure from near residual volume and the peak expiratory pressure from near total lung capacity, respectively, and were used as global indices of inspiratory and expiratory respiratory muscle strength. For spirometry and respiratory pressures, three technically acceptable trials were obtained for each outcome, and the highest value was retained for analysis (Figure). Figure 7.Spirometry. Whole-body aerobic capacity and ventilatory efficiency were measured by cardiopul- monary exercise testing (CPET). From breath-by-breath gas exchange, peak oxygen uptake (VO2peak) and the ventilatory equivalent for carbon dioxide slope (VE/VCO2slope) were derived. Before each test, the metabolic cart and flowmeter were calibrated per manu- facturer guidelines, and a size-appropriate facemask was fitted to ensure an airtight seal. Cardiopulmonary exercise testing was performed on a motorized treadmill using the Mod- ified Bruce Protocol, which begins with two low-intensity 3 min stages at 1.7 mph with 0% and 5% grade, respectively, followed by the standard incremental Bruce stages until voli- tional exhaustion [30]. Ratings of perceived exertion (RPE) were monitored continuously, and all test procedures and termination criteria were explained in advance. Whole-body aerobic capacity was expressed as peak oxygen uptake (VO2peak, mL·kg −1 · min −1 ), defined as the highest 15–30 s time-averaged oxygen uptake value attained during the treadmill cardiopulmonary exercise test and normalized to body mass. VO2peak was selected as the primary index of aerobic performance in amateur runners. VO2peak
procedures and termination criteria were explained in advance. Whole-body aerobic capacity was expressed as peak oxygen uptake (VO2peak, mL·kg −1 · min −1 ), defined as the highest 15–30 s time-averaged oxygen uptake value attained during the treadmill cardiopulmonary exercise test and normalized to body mass. VO2peak was selected as the primary index of aerobic performance in amateur runners. VO2peak and VE/VCO2slope were selected a priori as complementary CPET outcomes to capture whole-body aerobic capacity and ventilatory efficiency, both of which are physiologically relevant to endurance exercise in runners. These indices were expected to be responsive over a six-week period because improvements in respiratory muscle strength with RMT may reduce the relative https://doi.org/10.3390/bioengineering13010011
Description
This study compares different RMT-based combinations on pulmonary function, respiratory muscle strength, and exercise capacity.