Mixed martial arts (MMA) may be classified as a high intensity aerobic endurance event (1). The influence of aerobic capacity (V̇O₂max) on MMA performance is, however, currently unknown. The aim of this study was to compare the laboratory measured aerobic capacities of MMA participants to the external load, internal intensity and external intensity of MMA sparring bouts to examine the influence of aerobic fitness on performance. A cohort of n=10 male MMA participants (age = 24±2.8 years; mass = 74.3±8.2kg; stature = 176.8±7.9cm) completed a treadmill based graded exercise  test (GXT) to measure their absolute (L∙min^-1) and relative (ml∙kg∙min^-1) V̇O₂max. Participants also took part in a 3x5mins MMA sparring bout whilst equipped with a Catapult Optimeye S5 accelerometer which recorded Playerload (PLd_ACC) as external load and Playerload per minute (PLd_ACC∙min-1) as external intensity(2) throughout. Sessional rating of perceive exertion (sRPE) was recorded as internal intensity at the end of each round(3). sRPE of each round was classified as low intensity (≤ 4AU); moderate intensity (5 – 6AU); high intensity (≥ 7AU) as applied previously(4). All data were collected following institutional ethical approval and informed consent. The cohort’s mean V̇O₂max = 53.1±5.9 ml∙kg∙min-1. The cohort’s median V̇O₂max (53.3 ml∙kg∙min-1) was used to split the cohort into top 50% and bottom 50% groups. Top 50% group V̇O₂max = 57.7±3.6 ml∙kg∙min^-1; 4.1±0.5 L∙min^-1. Bottom 50% group V̇O₂max = 48.5±3.6 ml∙kg∙min^-1; 3.8±0.4 L∙min^-1.  Bayesian repeated measures ANOVA (BF₁₀≥3) were used to determine any differences in external/internal intensity between groups, between rounds, and between minutes(5). All analyses were completed using JASP 0.18.3 (JASP Team, NETHERLANDS). Round*group differences in sRPE were found to be decisive with a large effect (BF₁₀ = 143, ω² = 0.15) (Figure 1). The top 50% group were found to maintain moderate sRPE throughout sparring (round 1 = 5.2±1.3AU; round 2 = 5.6±1.3AU; round 3 = 6.4±1.9AU). The bottom 50% group’s sRPE moved from moderate in round 1 (4.6±1.1AU) and round 2 (6.8±1.3AU) to high in round 3 (8.6±1.1AU). Whilst the top 50% group recorded greater PLd_ACC and PLd_ACC∙min-1 than the bottom 50% group in each round, these differences were not statistically relevant between groups or rounds. When analysing PLd_ACC there was a moderate minute*group difference with a medium effect (BF₁₀ = 3, ω2 = .11). Resulting post hoc between groups differences were decisive with a medium effect (BF₁₀ = 380, ω2 = .12) with the top 50% group recording greater PLd_ACC for most of rounds 1 and 2, and displaying an ‘end spurt’ in round 3 (Figure 2). These results indicate having a V̇O₂max <53 ml∙kg∙min-1 is related to increased internal intensity in MMA sparring. Participants with V̇O₂max above this appeared capable of maintaining greater and qualitatively more consistent external intensity throughout the first and second rounds of sparring. These data support the aerobic nature of MMA and may provide minimum aerobic fitness levels to aim for during competition preparation.