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Altitude Training Mask Cardio Breathing Respiratory Strength Trainer 24 Oxygen Deprivation Levels Oxygen Barrier Workout Mask - AliExpress
28 West Gym - I've witnessed guys using oxygen deprivation masks for an hour while doing heavy squats. So, you'll have no problem wearing a simple face mask while doing circuit training.
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Nextgen Altitude Workout Mask Cardio Breathing & Respiratory Strength Trainer 24 Oxygen Deprivation Levels, 8 Replaceable Carbon Filters Sport Elevati | Fruugo NO
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