Blood Flow Restriction Does Not Augment Low Force Contractions Taken to or Near Task Failure

Low load [30% of one repetition maximum (1RM)] exercise performed to volitional failure appears to result in similar skeletal muscle adaptations as low load exercise with the addition of blood flow restriction (BFR). However, there may be a point where the training load becomes too low (<20% 1RM) to stimulate an anabolic response without the addition of BFR. PURPOSE: To examine the skeletal muscle adaptations to very low load exercise with and without BFR in the upper body. METHODS: Changes in muscle thickness (MT), one repetition maximum strength (1RM), isometric strength, isokinetic strength and endurance were examined following 8-weeks of training with a traditional high load [70% 1RM,(70/0)], low load (15% 1RM), low load with moderate BFR (15%1RM+40%BFR), or low load with greater BFR (15% 1RM+80%BFR). Results are displayed as mean (95% CI). RESULTS: 40 untrained men and women completed the study. For 1RM strength, there was a condition x time interaction (p = 0.003). 1RM strength changes were greater in the 70/0 condition [2.09 (95% CI=1.35-2.83) kg] compared to all low load conditions. For isometric and isokinetic strength, there were no changes. For endurance, there was a main effect for time [mean pre to post change = 7.9 (4.3, 11.6) repetitions, p <0.001]. At the 50% MT site there was a condition x time interaction (p = 0.004). The mean change in MT in the 70/0 condition [0.16 (0.10-0.22) cm] was greater than all low load conditions. For the 60% MT site there was a condition x time interaction (p = 0.014). The mean change in MT for the 70/0 condition [0.15 (0.08-0.22) cm] was greater than all low load conditions. For the 70% MT site there was a main effect of time (p=0.001). Muscle thickness increased from pre-testing to the midpoint [mean change = 0.06 (0.01- 0.10) cm] and remained elevated above baseline at post-testing [mean change = 0.09 (0.5 - 0.14) cm]. CONCLUSIONS: All groups increased muscle size; however, this response was lower in all very low training conditions compared to high load training. 1RM strength increased in the 70/0 condition only, with no other changes in strength observed. These results suggest that loads as low as 15% 1RM do not provide adaptations comparable to high load resistance training. Further, BFR cannot be used to compensate for an insufficient external load regarding muscle size and strength adaptations.