Purpose – To assess if wearing a mouth guard effects maximal aerobic capacity in amateur boxers.
Methods – 13 amateur boxers took part in a prospective crossover study to assess maximal aerobic capacity achieved during the 20m Multi Stage Fitness Test (MSFT). Each participant completed the MSFT 7 days apart, under control (no mouth guard – C) and intervention conditions (mouth guard – MG). The order of tests was determined via a coin toss on day 1, and two primary outcomes measures were recorded: (1) the estimated maximum oxygen uptake (VO₂ max  – kg/mL/min) and (2) distance run (meters – m). Data on height, weight, and type of mouth guard were recorded. Complete datasets on Rate of Perceived Exertion (RPE) were available for 10 boxers.
Results – Mouth guard use was shown to reduce estimated VO₂ max and distance run during the 20m MSFT from 56.31 kg/mL/min to 54.12 kg/mL/min and 2572 m to 2380 m respectively, (P>0.05). All 13 participants recorded lower VO₂ max scores when wearing a mouth guard, (Mean= -2.43mL/kg/min, Range = 4.2-0.9 mL/kg/min). 10 participants submitted data on RPE and reported a 32.3% increase in mean RPE scores when completing the MSFT in mouth guards compared to control conditions, (P>0.05). 
 
Conclusions – Mouth guard use was shown to significantly reduce aerobic performance in amateur boxers and increase the perceived rate of exertion during the 20m MSFT.