UNLABELLED: Resistance training at low loads with blood flow restriction (BFR) (also known as Kaatsu) has been shown to stimulate increases in muscle size and strength. It is unclear how occlusion pressure, exercise intensity, and occlusion duration interact, or which combination of these factors results in the most potent muscle stimulus. PURPOSE: To determine the effect of eight BFR protocols on muscle fatigue (decrement in maximal voluntary contraction (MVC) after the performance of exercise), and to compare the decrement in MVC with the currently recommended resistance exercise intensity (~80% MVC). METHODS: During five test sessions, 21 subjects (14 males and 7 females, 27.7 +/- 4.9 yr) completed nine protocols, each consisting of three sets of knee extensions (KE) to failure. One protocol was high-load (HL) exercise (80% MVC) with no BFR, and the other eight were BFR at varying levels of contraction intensity (20 or 40% MVC), occlusion pressure (partial (~160 mm Hg) or complete (~300 mm Hg)), and occlusion duration (off during the rest between sets or continuously applied). To evaluate each protocol, MVC were performed before and after exercise, and the decrement in force was calculated. RESULTS: Three sets of KE at 20% MVC with continuous partial occlusion (20%(ConPar)) resulted in a greater decrement in MVC compared with HL (31 vs 19%, P = 0.001). None of the other BFR protocols were different from the HL protocol, nor were they different from 20%(ConPar) (P > 0.05). CONCLUSION: All BFR protocols elicited at least as much fatigue as HL, even though lower loads were used. The 20%(ConPar) protocol was the only one that elicited significantly more fatigue than HL. Future research should evaluate protocol training effectiveness and overall safety of BFR exercise.