Research has confirmed that resistance training while wearing a restrictive breathing mask negatively impacts performance. It was discovered that test subjects wearing a mask were getting to failure after performing fewer repetitions than when they were not wearing a mask. For hypertrophy to effectively occur, muscles must be under tension for ample time, therefore, when fewer repetitions are performed, this may mean that the amount of muscle size growth is reduced because fibers are not being activated to their full potential. Additionally, recovery time between sets is extended with these masks because of the limited oxygen intake.