BACKGROUND: The concept of Maximal Lactate Steady State [MLSS] was traditionally associated with values ~4 mM during continuous exercise. We were able to show in previous research that blood lactate [BLa] values can be maintained above these values for ~20-30 minutes when applying high intensity interval training [HIIT], and [BLa] is sustained throughout passive rest time. PURPOSE: The aim of this research was to assess whether high blood lactate levels [>8 mM] can be maintained in steady state [SS] for almost 60 minutes at HIIT (whole workout). METHODS: Nine trained swimmers (17.8 ± 1.1 y; 73.1 ± 6.9 kg.; 179.6 ± 7.7 cm.) performed HIIT (BLa ~9.5 mM). The workout was 10 x 200-m freestyle with 180 s passive rest (PR). BLa and heart rate (HR) were measured at 10s, 50s, 110 s and 170 s at the same time during PR every 2 reps. We applied Shapiro-Wilk test to analyze for normality. We compared BLa and HR applying RM one-way ANOVA test (p < 0.05) in reps 2, 4, 6, 8 and 10. For time performance, we applied RM one-way ANOVA (p < 0.05) in all reps. Also we determine Spearman (rs) correlation coefficient between BLa and HR. RESULTS: The mean BLa was 9.44 ± 0.16 mM [8.47-10.06 mM]. The time performance was 135.5 ± 0.6 sec. and only rep 2 was faster than rep 5 (p < 0.05). Also, we found no rs between BLa vs. HR (rs = 0.28). CONCLUSION: HIIT workout allows maintaining high BLa levels for ~53 min. (whole bout) with very small variations of these values and performance time. The difference between the highest and lowest average BLa values ​​was only 1.59 mM. Possibly, this value could be lower with a shorter PR. Specifically, with an appropriate selection of the duration of the interval as of the recovery time, HIIT allows to maintain BLa levels above the traditional MLSS values (during continuous efforts) for longer time, during whole bout (work + PR).