Table of Contents
Study design and ethical aspects
This study has a randomized controlled cross-over design and was approved by the ethics committee of the Department of Psychology and Sports Sciences of the Goethe University (2022-55, approved 30/08/2022). The trial was registered a priori (German Register for Clinical Trials, DRKS-ID: DRKS00030181, date of registration 05/09/2022) and conducted in accordance with the ethical standards set down by the declaration of Helsinki with its recent modification of 2013 (Fortaleza)15. To address the knowledge gaps and shortcomings of earlier studies, we conducted a randomized controlled study on the effects of wearing a FFP2 during physical activities of different intensities. To enable blood sampling during- rather than after exercise cessation we applied ergometer cycling. To minimize the confounding influence of air leakage during forced exhalation when a FFP2 is worn under a spiroergometric rubber mask16, we analyzed spiroergometric/capnometric measures, such as peak end tidal partial pressures, breathing frequency and the duration of inspiration or exhalation, which are independent of the exhaled air volume as main outcomes for breathing performance and gas exchange.
Participants
Participants were recruited and the study was rolled out between June and October 2022 in a university in Frankfurt Germany. Eligibility criteria included being from 18 and 50 years of age with no (medical or psychosocial) contraindication against vigorous physical activity. Exclusion criteria were cardiovascular-, pulmonary-, or advanced degenerative musculoskeletal diseases, pregnancy and not completely healed musculoskeletal injury (that affect subjective quality of life or physical performance during exercise).
Sample size calculations were performed based on an earlier study comparing CO2 kinetics during steady state exercise with a FFP2 and a surgical mask against a no mask control8. A calculation based on an effect size of Cohen’s d = 0.39 (Partial η2 0.136) a significance level of 5% and an 90% power resulted in a sample size of at least 10 participants adopting a crossover design with 6 measurements in repeated measures analysis of variance (rmANOVA). Calculating with a drop-out rate of 20%, a minimum of 12 participants needed to be included in this study.
Before study participation, participants were informed on voluntary participation and signed a written informed consent. Eligibility, exclusion and randomization scheme of the protocol is shown in the flow diagram in Fig. 1. Order was randomized (simple balanced randomization).
CONSORT flow diagram. Thirteen participants were assigned to either starting with the FFP2 (n = 7) or the unmasked condition (n = 7) by randomisation, followed by crossover to the other condition. CONSORT 2010, Consolidated Standards of Reporting.
Interventions
Participants had to avoid vigorous physical activities in the 48 h preceding each test and to maintain their habitual diet during the timeframe of the baseline assessment and both interventions. Furthermore, participants were requested not to take any food or drinks (except for water) during a period of 2 h prior to each examination.
All participants performed a baseline appointment. Two interventions, one with and one without a fold-flat type FFP2 (FFP2 NR, BB203, IMSTec GmbH, Klein-Winternheim, Germany) with three exercise bouts at different intensities each, followed. The duration of each bout was 10 min and the intensities were 40%, 50% and 70% of the individual maximal oxygen uptake (VO2max in milliliters per kilogram bodyweight per minute, ml/kg/min). The baseline assessment and both interventions were separated by a minimum of 48 h. The manipulation order (FFP2 or no mask) was randomized (simple balanced randomization).
Before each intervention, participants rested for five minutes in a seated position without wearing a FFP2. During this time baseline data for spiroergometric outcomes, blood gas analysis and subjective response were assessed. Thereafter the exercise bouts were rolled out in a randomized order. Participants were instructed to pedal in a seated position with at least 60 revolutions per minute and to maintain a comparable pedalling speed for all trials. Between bouts participants rested without wearing a mask for 5 min. Order allocation was done blinded. The participants were blinded to the respective manipulation until the beginning of each intervention. Each trial was performed at a comparable time of the day and at days with comparable routines (i.e. working days).
Baseline assessment
Assessments at baseline included standard anthropometrical values, educational status (school and study years), habitual physical activity (in Metabolic Equivalent of task hours per week, METh/wk) and sedentary behaviour (International Physical Activity Questionnaire IPAQ)17,18 as well as reference values for all assessments described in the outcomes section of this manuscript. Furthermore, cardiopulmonary exercise testing (CPET) until volitional exhaustion was performed at this appointment to assess VO2max and resistance in watts at the point of 40%, 50% and 70% of VO2max. For CPET a ramp shaped protocol (Increment 30 watts per minute for females and 50 watts per minute for males) was rolled out on a cycling ergometer (Optibike, Software OS 1.2, Ergoline GmbH, Deutschland).
Outcomes
Outcomes included spiroergometric measures, blood gas analysis and subjective data. Spiroergometric measures were taken breath by breath using a wireless system (K5 Wearable Metabolic System, Version 2.0, COSMED GmbH, Werneck, Deutschland) combined with rubber masks with an inspiratory valve covering mouth and nose (V2Mask, Hans Rudolph, Inc. USA). Thirty second floating means were used for analysis. The measuring instrument was calibrated before each test using reference gases (outside air and 5% CO2, 16% O2) and a standardized ventilatory volume (2 L calibration syringe). The device was tested for sufficient reliability and validity19. During cycling interventions rubber masks were either worn with or without a FFP2 underneath. For each subject a tight fit was ensured, and the possibility of escaping air was checked by covering the opening during forced exhalation. Spiroergometric data during interventions were checked for plausibility and analyzed on the basis of a 5 min continuous time block that excluded the first 3 min of each cycling bout to ensure a steady state of metabolism. End tidal carbon dioxide partial pressure (millimeters of mercury), breathing frequency (per minute) and inspiration time (in seconds) were analysed as main outcomes for decreased breathing performance. Additional measures for breathing performance included ventilation (in liters per minute), tidal volume (in liters) and exhalation time (in seconds). Measures for gas exchange were completed by analysing end tidal oxygen partial pressure (in millimeters of mercury) and respiratory exchange ratio (carbon dioxide exhalation divided by oxygen uptake). Heart rate (in beats per minute) was included as outcome for cardiac strain.
For blood gas analysis, capillary blood (100 µl) was drawn from an earlobe of the participant and analysed using a validated on-site device (epoc® Blood Analysis System, Epocal Inc., Ottawa, Ontario, Canada)20. Our main outcome for blood gas analyses was carbon dioxide partial pressure (pCO2 in millimetres mercury, mmHg). Further outcomes included pH, oxygen partial pressure (pO2 in mm/Hg), lactate (in mmol per litre, mmol/l) and base excess (BE in millimoles per litre, mmol/l).
Subjective response included perceived exertion, based on a 15-point Borg Scale ranging from “very very light” (lowest rating 6) to “very very hard” (highest rating 20)21, and affective state, based on a 11-point feeling scale ranging from “very bad” (lowest rating − 5) to “very good” (highest rating + 5)22. Breathing effort was our main outcomes for subjective response and was analysed using a modified 10-point Borg Category Ratio Scale (Borg-CR) to rate breathing effort ranging from “nothing at all” (lowest rating 0) over “extremely strong” (rating 10) to “maximum” (highest rating “maximum”). As an additional measure for dyspnoea a numeric rating scale for pain ranging from “no pain” (lowest rating 0) to “worst possible pain” (highest rating 10) was applied23.
Data analysis and statistics
We applied Microsoft Excel (Version 16.68) for data processing, SPSS Statistics (Version 29) for imputation of missing data and Prism (Version 9) for data analysis and presentation. Data were analysed as intention-to-treat. Imputation, assuming that missing data was missed completely at random, was made using chained equations and a fully conditional specification model with 40 iterations to produce asymptotically unbiased data estimations. Descriptive data were reported as means with standard deviations (baseline values and post intervention values) or 95% confidence intervals. Differences between baseline values of both trial days and the effect of the manipulation (FFP2 versus no mask) on all outcomes were tested using repeated measures analysis of covariance. Analysis of covariance was applied to evaluate the influence of body mass index, habitual physical activity, smoking status, VO2max and habitual sedentary behaviour on the between manipulations effects.
Lastly, pearson correlations were applied to detect associations between subjective measures, spiroergometric and blood gas analysis data which were affected by FFP2 application. We considered p ≤ 0.05 as statistically significant for all statistical analyses.
Ethical approval
The study design was approved by the ethics committee of the Department of Psychology and Sports Sciences of the Goethe University (2022-55, Approved 2022/08/30).
