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Title: Effects of inspiratory muscle warm-up on perceptual, physiological, and performance outcomes during high-intensity exercise in normoxia and hypoxia Open Access Deposited

http://creativecommons.org/licenses/by/4.0/
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Methodology
  • To determine our sample size, a power analysis was performed using G*Power (3.1.9.2) based off Marostegan et al. [16] who investigated IMW on exercise performance and revealed a η2 of 0.166. To achieve a power of 0.80 with α = 0.05, ten subjects were required. However, since the literature does not include data on IMW in hypoxia, we elected to recruit additional participants. Thirteen recreationally active individuals (8 men, 5 women) completed the study. Participants were considered recreationally active if they reported at least 150 min·wk-1 of moderate-intensity aerobic exercise [23]. Participants were excluded if they were a trained cyclist, had a current or history of respiratory illness (e.g., asthma), demonstrated pulmonary function measures ≤ 80% of reference, or if they were current or past smokers. Prior to each visit, participants were asked to refrain from intense exercise for 24 h, caffeine and alcohol for 12 h, and food intake for 3 h. Participants were asked to follow a similar diet in the 24 h before each visit, as well as record their regular weekly exercise routine at the first visit and repeat throughout the duration of the study. Participating women were asked to self-identify when their menses occurred. To control for the menstrual cycle, women were only tested in the first five days of menses when estrogen and progesterone are at their lowest levels [24]. All participants provided written informed consent to participate in the study procedures approved by the Indiana University Institutional Review Board. Experimental Design Participants visited the laboratory on five separate occasions, at the same time of day (± 2 h), separated by at least 48 h. Since women were only tested in the first five days of their menstrual cycle, their visits spanned 2-3 months. During the first testing session, participants were asked to complete a medical history questionnaire, a pulmonary function test, familiarization with the POWERbreathe K5 (IMT Technologies Ltd., Birmingham, United Kingdom) IMW device, and an incremental cycle ergometer exercise test to exhaustion to determine V̇O2peak. After a 20 min rest period, participants were asked to complete a fixed-workload test to exhaustion (equivalent to ~80-85% of V̇O2peak) for familiarization with the test and dyspnea measures. Visits two through five were randomized and counterbalanced for four separate experimental conditions: 1. IMW, an inspiratory muscle warm-up protocol, followed by a time to exhaustion (TTE) cycling test breathing normoxia (Bloomington, IN elevation 230 m). 2. SHAM (placebo), a sham inspiratory muscle warm-up protocol, followed by a TTE cycling test breathing normoxia. 3. IMWh, an inspiratory muscle warm-up protocol, followed by a TTE cycling test breathing 16% O2 gas, simulating 2400 m. 4. SHAMh (hypoxia placebo), a sham inspiratory muscle warm-up protocol, followed by a TTE cycling protocol breathing 16% O2 gas, simulating 2400 m. During these visits, participants were blinded to the inspirate as well as the intervention protocol (i.e., IMW or SHAM). The IMW and SHAM protocols have been previously defined by Lomax et al. [25] and are discussed later. Participants were told they were participating in a study looking at the effects of a “resistance-type” and “endurance-type” warm-up protocol at sea-level and at altitude conditions. Participants were also not informed of the hypotheses of the study, and while they could not be totally blinded to their subjective measures, they were not given the results of their trials until they finished the entire study. Measurements Pulmonary Function. After participants were seated and rested for five minutes, pulmonary function tests were performed using a metabolic cart (Vmax-Encore System; CareFusion, Yorba Linda, CA). The test included a forced vital capacity (FVC) maneuver, from which the fraction of expired volume in 1 s (FEV1) to FVC ratio was determined. Spirometry was performed in triplicate according to the American Thoracic Society standards [26] such that 3 FVC maneuvers were within 0.150 L. Perceptual. Ratings of dyspnea during exercise were measured by assessing the sensory (BI) and affective (BU) components on separate visual analogue scales (VAS) [27]. Both scales ranged from 0 to 100 mm (0 = not noticeable/unpleasant, and 100 = maximal imaginable intensity/unpleasantness). The scales differed in color (red = intensity, blue = unpleasantness) and participants were handed a marker and asked to place a perpendicular line on each VAS in accordance with their perceived breathing intensity and unpleasantness. Both VAS were situated on a music stand that was placed within comfortable arm’s reach of the participant. In an effort to avoid participants remembering their subjective ratings, numerical values were not displayed on each VAS, and they were removed from sight immediately after each measure was taken. Participants were asked for their ratings of BI and BU at each minute of the TTE test. A separate ratio was calculated by the VAS value divided by ventilation (i.e., BI/V̇E and BU/V̇E) for each time point of the TTE test as our lab has previously shown this ratio to demonstrate the gain in perception of dyspnea per unit increase in ventilation [28]. Maximal Inspiratory Pressure (MIP). Participants were asked to perform up to five maximal inspiration maneuvers on the POWERbreathe device to determine maximal inspiratory pressure (MIP). To do this, participants were seated upright, facing forward, with the nose occluded. Participants were instructed to breathe out to residual volume, then inhale as forcibly and as quickly as possible against a negligible resistance (3 cmH2O) to total lung capacity and sustain this inspiration for at least 1s. Participants were given visual feedback during inspiratory effort by viewing the BreatheLink software display to maximize their inspiratory effort. The top three measures within 5% of each other were averaged and used as the MIP [9]. The MIP value was then used to calculate the inspiratory loads for the IMW and SHAM interventions, which were 40% and 15% of MIP, respectively. Ventilatory and Metabolic Measures. Ventilatory and metabolic measures were collected using breath-by-breath analysis on a Vmax Encore Metabolic Cart (Vmax-Encore System, CareFusion, Yorba Linda, CA). Participants breathed through an oro-nasal facemask (7450 Series, Hans Rudolph, Kansas, MO) attached to a mass flow sensor that measures inspired and expired flow rates. The O2 and CO2 analyzers were calibrated before each test with room air and calibration gases within the physiological range and the mass flow sensor was calibrated at varying flow rates (30-360 l·min-1) using a 3.0 L syringe. During all trials, the mass flow sensor was attached to a two-way, non-rebreathing valve (2700 Series, Hans Rudolph, Kansas, MO), which was connected on the inspired side to the balloon reservoir. Arterial oxygen saturation (SpO2). SpO2 was measured throughout each testing session using an ear oximeter (Nellcor N-395 Pulse Oximeter, Medtronic, Minneapolis, MN) and recorded at each minute of the TTE test. Skeletal Muscle Oxygenation using Near-Infrared Spectroscopy (NIRS). NIRS (OxyMon MKIII; Artinis Medical Systems, The Netherlands) was used in vivo to non-invasively measure the relative concentrations of heme-O2 carriers in the exercising muscle microcirculation. During the time to exhaustion tests, the device probe was placed on the surface of the right vastus lateralis (15 cm superior and 5 cm lateral to the proximal border of the patella). The optode holder was secured with a Velcro strap and wrapped with an opaque cloth bandage to prevent movement and light leakage. The position of the device probe was marked with an indelible marker and photographed to match placement between trials. In this technique, near-infrared light is transmitted by a fiber optic cable to a photon detector via light source transmitters (with wavelengths of 765- and 855 nm) positioned at 40 mm from the receiver. Measures of local tissue oxygenated ([O2Hb]) and deoxygenated ([HHb]) hemoglobin concentration from rest to exercise were obtained from the multi-distance spectrophotometer. The change (Δ) in [O2Hb] and [HHb] in micromolar units (μM) were obtained by subtracting end exercise values from the end of the baseline (rest) period values. Tissue saturation index (TSI) was calculated by the following equation: TSI= ([HbO2] / ([HbO2] + [HHb]) x 100%) using averages of the last 30 s of baseline (rest) and the last 30 s of exercise. Data were acquired continuously at 10 Hz and the raw data was exported via OxySoft (Artinis Medical Systems, The Netherlands). Experimental Procedures Peak aerobic capacity test. Participants performed an ramp exercise test to volitional exhaustion on a Lode cycle ergometer (Lode Excalibur Sport, Groningen, The Netherlands) to determine peak oxygen uptake (V̇O2peak) and gas exchange threshold (GET). Before beginning this test, seat height and handlebar placement were recorded and remained consistent throughout the rest of the sessions. The highest 30 s average data of the V̇O2peak test was used to describe participants’ baseline fitness levels and used to determine the power to be used in the TTE tests. The graded exercise protocol began at 25 W for women and 50 W for men and increased by 1 W every two seconds (30 W per min) until volitional exhaustion or until cadence fell below 60 rpm. Participants could self-select pedaling cadence but were asked to maintain a cadence above 60 rpm throughout the test. GET was determined using the V-slope [29] and ventilatory equivalents methods [30]. Ventilatory and metabolic measurements were collected using breath-by-breath analysis (Vmax-Encore System, CareFusion) while participants breathed through an oronasal facemask (7450 Series; Hans Rudolph, Shawnee, KS) attached to a mass flow sensor that measures inspired and expired flow rates. Heart rate was continuously monitored using a heart rate monitor (Model FT1; Polar, Stamford, CT). Inspiratory muscle warm-up. Participants were asked to perform two sets of 30 breaths using a POWERbreathe at 40% and 15% of MIP with 60 s of rest between sets for IMW and SHAM protocols, respectively. This IMW protocol and percent of MIP were chosen as it is the most commonly used protocol [31] and has been shown to be the upper limit of inspiratory muscle loading before onset of diaphragm fatigue [32]. Additionally, 15% of MIP has been commonly used as a placebo intensity as it has demonstrated similar outcomes as a control trial [6, 8, 14, 17]. During all trials, participants were instructed to initiate every breath from residual volume and to continue the respiratory effort until further excursion of the thorax was not possible, followed by a slow, 5-7 s exhale to prevent lightheadedness. Both IMW and SHAM protocols were performed while seated in a neutral position with the nose occluded. Time to Exhaustion (TTE) test. A timeline of the inspiratory muscle warm-up and TTE testing session can be found in Figure 1. After a 3 min resting baseline for NIRS data, participants completed a standardized 5 min, 40% V̇O2peak cycle ergometry warm-up. Participants then had 8-10 min of no cycling to complete the prescribed inspiratory muscle warm-up, followed by a 2 min rest breathing the prescribed inspirate while seated on the bike. After the 2 min, participants began performing a cycling test to exhaustion at a workload equivalent to 80-85% V̇O2peak. This workload was determined by the following calculation: GET power output + 60% Δ(peak power output – GET power output), as this concept has shown to reduce interindividual variability in various physiological measures as well as reduce the coefficient of variation in TTE tests [33]. At each minute of this test, participants were asked to indicate their feelings of dyspnea. The test was terminated when cadence dropped below 60 rpm for more than 3 s. Time was recorded to the nearest second. Scripted verbal encouragement was given every 30 s and standardized across all participants and trials. Hypoxic Inspirate Delivery System. During all TTE tests, participants breathed from balloon reservoirs (approx. 850 L) containing either room air or a hypoxic inspirate (FIO2 = 0.16) produced by commercially available, portable nitrogen generators (CAT-12 model, Colorado Altitude Training Systems, Boulder, CO).
Description
  • The purpose of this study was to examine how IMW affects the sensory and affective components of dyspnea, exercise performance, and NIRS-derived metaboreflex effects during a cycling time to exhaustion test. Additionally, to augment the ventilatory response for better elucidation of the cardiorespiratory effects of IMW, we added hypoxia as an intervention. Using both normoxic and hypoxic conditions, our hypotheses were: 1) both sensory and affective components of dyspnea would be attenuated following IMW in each condition, 2) the extent of skeletal muscle deoxygenation (i.e., a NIRS-derived surrogate for the metaboreflex) in the leg would be reduced after IMW in each condition, and 3) participants’ time to exhaustion would be prolonged following IMW in each condition.
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  • migabler@iu.edu
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  • 2022-11-01 to 2023-04-30
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  • 12/06/2023
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To Cite this Work:
Gabler, M. Effects of inspiratory muscle warm-up on perceptual, physiological, and performance outcomes during high-intensity exercise in normoxia and hypoxia [Data set]. Indiana University - DataCORE.

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