The purpose of the present study was to investigate the effect of a short-term, high-intensity, low-volume Mixed Martial Arts (MMA) specific strength and conditioning training program on performance in national level MMA athletes. Seventeen experienced fighters were divided into two groups: (A) Specific Training Group (STG; n = 10), which followed a specific strength and conditioning program designed according to the demands of MMA competition and (B) Regular Training Group (RTG; n = 7), in which participants followed a regular strength and conditioning program commonly used by MMA athletes. Before and after the four-week training period (3 days per week), body composition, aerobic fitness, strength, power and speed were evaluated. Significant improvements in estimated VO_2max, average power during the 2000 m rowing, bench press, back squat and deadlift 1RM, SJ power, CMJ height power, medicine ball throw velocity, 10 m sprint and 2 m take down speed and fat-free mass were found only in the STG (3.7 to 22.2%; p < 0.05; Hedge’s g = -0.42 – 4.1). No significant changes were found for the RTG (p = 0.225 to 0.811). Significant differences between the groups were found for almost all post-training assessments (p < 0.05; Hedge’s g = 0.25 – 1.45) as well as for the percentage changes from pre to post training (p < 0.05; Hedge’s g: 0.25 – 1.45). Significant relationships were found between percentage changes in fat-free mass, endurance capacity, muscle strength/power and speed (r: -0.475 to 0.758; p < 0.05). These results suggest that a high-intensity low-volume strength and conditioning training intervention designed according to the demands of MMA competition may result in significant performance improvements for well-trained fighters.

• A 4-week low volume, high-intensity strength and conditioning training program, designed according to the demands of MMA, results in large improvements of MMA related fitness parameters, in well-trained MMA athletes.

• The regular strength and conditioning training program used in the present study did not cause significant improvements in performance in well-trained MMA athletes.

• Physical conditioning training programs of MMAs’ athletes should aim to improve various aspects of fitness, including improvements of anaerobic and aerobic metabolism, specific endurance, strength, power and rate of force development.

• Excessive muscle mass may be a negative contributor to sprinting performance in trained MMA athletes. In addition, participants of the STG increased their muscle strength, without any significant alterations of their FFM, indicating the present of neural adaptations