The purpose of the study was to determine the relationship between internal and external load in physically active subjects (11 men and 5 women) during a high-intensity functional training session, using different load markers: heart rate, perceived effort and the Edwards index.The maximum heart rate was assessed during a maximal incremental endurance test (Course Navette).Thereafter each participant performed a high-intensity functional training session (Workout of the Day -Pukie), while wearing a heart rate monitor, and the perceived effort was assessed with the 0-10 point scale at 0-min, 10-min, 20-min, and 30-min.Thereafter the Edwards index was calculated.The perceived effort was positively correlated with the heart rate and the Edwards index during the different time-points analyzed (Spearman r = 0,76-0,88; p<0,01).In conclusion, perceived effort can be used as a low-cost and logistically convenient method to assess the internal load experienced by physically active participants during a high-intensity functional training session.