"Facemask Use During High-intensity Interval Exercise in Temperate and Hot Environments"
Phase: NA
Conditions: Hypoxemia, Physiological Stress
Sponsor: University of New Mexico

Document date: 2/26/2022 
NCT number: NCT05143801 
 
 
 
 
 
 
Official Title:  
Facemask use during high intensity interval exercise in temperate and hot environments.  
 
 
 
 
 
 
 
 
 
 

Objectives, Methods and Protocol 
Objectiveː The purpose of this study was to investigate the effects of surgical mask use during 
high intensity interval exercise (HIIE) on physiological and perceptual responses in hot and 
temperate environments. 
Methods, Protocol, and Statistical Analysis 
Participants 
Ten recreationally trained participants (5 males; 5 females) were recruited for this study (Table 
1). Participants were free from known cardiovascular, renal, metabolic, or chronic respiratory 
disease (i.e., asthma) as determined from a health history questionnaire. Participants were 
excluded if in the last 6 months they smoked and performed less than 150 minutes of moderate-
intensity exercise per week, had a VO2max below the 50th percentile for age and sex according to 
the ACSM guidelines for aerobic fitness 18, or reported no experience performing HIIE. A 
pregnancy test was completed for female participants to include only non-pregnant participants.  
Prior to any exercise and data collection, the study protocol was explained, all participant 
concerns were addressed, and written consent was obtained. This study was registered at 
Clincialtrials.gov (NCT05143801), approved by the university’s Institutional Review Board, and 
was in compliance with the Declaration of Helsinki 19.  
Prior to each visit the participant was screened through Zoom™ (Zoom Video Communications, 
Inc, Version 5.4.9), email, or by phone for possible exposure to, and symptoms of COVID-19 
using a screening checklist. Additionally, they were instructed to avoid eating a filling meal 1-
hour, consuming caffeine 4 hours, and vigorous exercise 24 hours before the first visit.  
Procedures 
Anthropometrics and maximal Oxygen uptake measurements 
Before the experimental trials, participants visited the Exercise Physiology laboratories for 
anthropometrics and VO2max measurement. Body height was measured using a stadiometer 
(SECA, seca 216, Chino, CA, USA) and weight was measured using a digital scale (Cardinal 
DETECTO 758C, Webb City, MO). Then, participants completed a 5-minute warm-up at a self-
selected exercise intensity prior to the VO2max test on an electrically braked cycle ergometer 

(Lode, Excalibur Sport, Groningen, The Netherlands). During the VO2max test, HR was 
measured using a Polar HR monitor (Polar, Polar H10, USA) with each test designed to last 
between 10 and 12 minutes. The starting resistance and the continuous increase in resistance 
(between 20-40 watts) throughout the test was based on the participants’ self-reported fitness. 
Termination of the VO2max test occurred at volitional fatigue or when the participant could no 
longer maintain a cycling cadence of 60 revolutions per minute or higher. Gas-exchange was 
measured using a metabolic analyzer (Parvo Medics Inc, TrueOne 2400, Salt Lake City, UT) and 
data were analyzed using an 11-breath rolling average20. Primary criteria for a VO2max was 
categorized as an observed plateau that varied by less than 150 mlO2/min21. To determine a 
plateau using primary criteria, the mean of the absolute difference from each neighboring data 
point in the last 30 seconds of the 11-breath rolling average VO2 was compared against 150 
mlO2/min21; if the average value was smaller, the test was categorized as a VO2max. In the 
absence of a plateau, a VO2max was confirmed if two of the three secondary criteria were met: 
1) an RPE ≥17, 2) a respiratory exchange ratio (RER) of 1.1 or greater, and 3) a HR within 10 
beats of estimated heart rate max using the Jones et al.22 equation (202 - 0.72 x age). The highest 
power output recorded from the VO2max test was used to calculate the high intensity and active 
recovery bouts for the HIIE sessions.   
Environmental control 
All trials were performed indoors within the University of New Mexico exercise physiology lab. 
The environmental conditions for all trials were monitored using the same wet bulb globe 
temperature (WBGT) device (Metrosonics, hs-3600 Portable Heat Stress Monitor, QUEST 
TECHNOLOGIES INC., GA, USA). Dry and wet bulb temperatures were recorded at the end of 
each active rest and HIIE bout for each trial. 
A heat chamber with two electric heaters connected to a thermostat set to 36°C was used for both 
HIIE-HOT/CON and HIIE-HOT/MASK trials. This room was ventilated with the use of a ceiling 
fan set to low and by having the door slightly open. To control for any deviations in room 
temperature additional heaters were placed in the room and manually controlled to keep the room 
temperature stable. Humidity buildup in the heat chamber was prevented by having the door 
slightly open to allow humidity to escape the room.  

Both HIIE-TEMP/CON and HIIE-TEMP/MASK trials were performed in a well-ventilated 
room. The room temperature was controlled for using the same methods for the HIIE-HOT/CON 
and HIIE-HOT/MASK trials.  
High Intensity Interval Exercise Trials 
Before all HIIE sessions participant’s hydration status was assessed measuring urine specific 
gravity (USG) using a handheld refractometer (Cole-Parmer, RSA-BR90A, Vernon Hills, IL). A 
USG measurement lower than 1.020 g/cc allowed participants to proceed to the HIIE sessions. If 
USG was greater than 1.020 g/cc, then participants consumed 500 ml of water, and were 
reassessed after 30 minutes. This water provision was only repeated twice if USG remained 
above 1.020 g/cc.  
A randomized non-counterbalanced crossover repeated measures design was used to compare 
cardiovascular, thermoregulatory, metabolic, and perceived responses before and during HIIE 
across four experimental trials performed during two visits. For each visit, which was separated 
by a minimum of 72 hours, the participants completed two HIIE sessions separated by 3 hours of 
rest. Each HIIE bout consisted of 10 bouts lasting 30 seconds performed at 85% Pmax followed 
by 90 seconds of active recovery at 30% Pmax. The HIIE sessions were performed in a temperate 
environment (23°C, 25% relative humidity) with (TEMP/MASK) and without a surgical mask 
(TEMP/CON), and in a hot environment (36°C, 14% relative humidity) with (HOT/MASK) and 
without a surgical mask (HOT/CON). During the exercise protocol participants were allowed to 
drink water. Although most participants chose not drink water during all HIIE sessions, one 
participant chose to ingest water during two of the four HIIE sessions while another participant 
chose to ingest water during one of the four HIIE sessions.   
During HIIE sessions with a mask, all participants were instructed to wear the surgical mask 
snuggly over their nose and mouth. The participants fitted the flexible metal plate within the 
surgical mask over the bridge of the nose and had the bottom of the mask cover underneath the 
chin. During the 3-hour rest period participants were provided a 350-calorie meal (7g of Fat; 64g 
Carbohydrate; 9g Protein) and water ad libitum.  
Cardiovascular Measurements  

Before every HIIE trial and after 5-minutes of seated rest, resting blood pressure was measured 
using a sphygmomanometer, and stethoscope. A cardiac impedance device (PhysioFlow®, 
NeuMeDex, Bristol, PA) calibrated per manufacturer guidelines was used to indirectly measure 
cardiac output (CO), stroke volume (SV), and HR. These measurements were taken continuously 
using 10-second averaging provided by the PhysioFlow® software during each HIIE session.  
Metabolic Measurements 
A near infra-red spectroscopy (NIRS) device (Moxy, Moxy Monitor System, MN, USA) was 
used to measure muscle tissue oxygenation every second during each HIIE session. The highest 
muscle tissue oxygenation value from each active rest period (MTO active rest %) was averaged 
for each HIIE session. Additionally, the lowest muscle tissue oxygenation (MTO during HIIE %) 
value per high intensity bout was recorded and averaged from each HIIE session. The difference 
of the average MTO active rest % and MTO during HIIE % was used to calculate the muscle 
tissue oxygenation difference (MTO difference %). All MTO measurements were taken on the 
dominant leg at a marked location on the vastus lateralis that would allow movement without 
interference from the NIRS device. A pulse oximeter (Caretaker, Caretaker Medical, USA) was 
used to measure SpO2 during HIIE. Blood lactate measurements (Lactate Plus, NOVA 
Biomedical, MA) were taken in duplicate at the ear lobe immediately before, and 5-minutes post 
HIIE. 
Perceptual Measurement before and during HIIE 
Borg’s rating of perceived exertion (6 rest to 20 maximal effort) scale (RPE)23 and thermal 
sensation (0 very cold to 8 very hot)24,25 was measured immediately before and every four 
minutes into HIIE. A breathlessness scale (0 mm no breathlessness to 200 mm maximal 
breathlessness)26 was used immediately before, at 10-minutes, and immediately after exercise to 
record subjective change in difficulty breathing. The highest measurements for both RPE (peak 
RPE) and thermal sensation (peak thermal sensation) were recorded per HIIE session performed. 
Additionally, RPE (RPE avg) and dyspnea scores were averaged over time for every HIIE 
session. 
Thermal strain and hydration measurements 

During each HIIE exercise session continuous core temperature measurements were taken using 
rectal thermistors (Level 1 esophageal/rectal temperature probe, Smiths Medical, Minneapolis, 
MN, USA) connected to a thermometer (Precision 4000, YSI Incorporated, Yellow Springs, OH, 
USA) and monitored to ensure participant safety. Additionally, ∆ core temperature (i.e., the 
difference between peak core temperature and core temperature prior to starting exercise) and 
peak core temperature were recorded for each HIIE session. Sweat rate and dehydration were 
calculated from pre-exercise nude weight, post-exercise nude weight, water ingestion, and post-
exercise urine output measurements27. Participants were asked to measure and report their pre-
exercise and post-exercise nude weight using a digital scale (Cardinal DETECTO 758C, Webb 
City, MO) in a private room. 
Statistical Analysis  
Female and male descriptive data in terms of mean and standard deviation (SD) were compared 
using an independent t-test. If normality was violated, a non-parametric Mann-Whitney U test 
was performed. A 2x2 repeated measures ANOVA was performed to investigate statistical 
differences for all variables across TEMP/CON, TEMP/MASK, HOT/MASK, HOT/CON 
conditions except for a 2x2x3 repeated measures ANOVA being performed for perceived 
dyspnea data where time was an additional independent variable. Both main and interaction 
effects were calculated along with effect size, reported as partial ⴄ2. Effect size benchmarks were 
defined as small (partial ⴄ2 =0.01), medium (ⴄ2 =0.06), and large (ⴄ2 =0.14)28. A Bonferroni post-
hoc test was used to determine specific differences with significant interaction effects. All 
statistical tests were performed using JASP (version 0.14.1.0); statistical significance was set at p 
< 0.05.