Blood Flow Restricted LISS, but not HIIT, Will Boost VO2Max (5%), as Well as Strength (20%) - Perfect for Athletes' Rehab

I have to admit: Unless you're injured and in rehab or belong to any other group of athletes where high mechanical loading is contraindicated or impractical, BFR is not exactly something you "have" to do, because everything else was worse.

If you want to improve both strength and conditioning, there is usually no way to train accordingly, i.e. do "cardio" (aerobic training) at high(er) intensities and lift weight (enough to make gains). But is this actually true? What about HIIT, for example? Could that help increase both, VO2max and strength at the same time? How intense do you have to train and does adding cuffs and blood flow restriction have a value of its own?

In their latest study, a group of Brazilian scientists tried to answer these and related questions. In short: de Oliveira et al. (2016) tested the VO2max and strength response to both, low intensity blood flow restricted training, high intensity interval training (HIT) and regular low intensity "cardio".
To this ends, the researchers recruited thirty-seven recreationally active (but not endurance trained) subjects (23.8 ± 4 years; 171.7 ± 9.5 cm; 70 ± 11 kg) who were then assigned to one of four groups: low-intensity interval training with (BFR, n = 10) or without (LOW, n = 7) blood flow restriction, high-intensity interval training (HIT, n = 10), and combined HIT and BFR (BFR + HIT, n = 10, every session performed 50% as BFR and 50% as HIT).

Figure 1: Graphical illustration of the study de Oliviera et al. used in their recent experiment (de Oliveira. 2016).

Here are the details: For all groups (BFR, HIT, HIT + BFR, and LOW) the training program consisted of three exercise sessions per week on a stationary cycle ergometer for a total duration
of 4 weeks. For all training groups, every training session was preceded by 5-min warm-up at 30% of Pmax. The training power output was 30% of Pmax for LOW and BFR training groups.

Each training session consisted of two sets of five "repetitions" (meaning intervals of exercise) for the first three sessions, after which one repetition per set was added each week. Therefore, in the fourth training week, the session consisted of two sets of eight repetitions. Each repetition lasted 2 min, interspersed by 1-min passive rest. The rest interval between sets was 5 min (3-min active recovery at 30% Pmax followed by 2-min passive rest). The individual protocols are descibed as follows:

• The BFR group wore pressure cuff belts (18 cm wide, Missouri, São Paulo, Brazil) on the proximal portion of both thighs during all training sessions. In the first week, cuff belts were inflated to 140 mmHg during the 2-min repetitions and deflated during the 1-min rest periods. The pressure was progressed by 20 mmHg after three completed sessions, thus, in the last week, the pressure applied was 200 mmHg. 
• In the HIT group, the subjects completed a variable power output training protocol. Each repetition began at 110% Pmax with a progressively 5% decrease in the intensity every 30 s (110%, 105%, 100%, and 95% Pmax, respectively). This training protocol was designed to increase the average power output of the training, as fast-start protocols have shown faster VO2p kinetics and higher exercise tolerance compared with constant work rate exercise (Turnes et al., 2014). 
• For BFR + HIT one set was performed as BFR and the other as HIT. The order of the sets was alternated at every session and the total exercise time was the same for all training protocols.

As previously hinted at, both, the maximal oxygen uptake (VO2max), as well as the maximal power output (Pmax), the onset blood lactate accumulation (OBLA), and the muscle strength were measured for all subjects, before and after 4 weeks training (3 days a week).

Figure 2: Only the low intensity BFR training triggered both fitness and strength gains.

As you can see in Figure 2, all training groups were able to improve the onset blood lactate in W/kg accumulation (OBLA | BFR, 16%; HIT, 25%; HIT + BFR, 22%; LOW, 6%), with no difference between groups. The subjects' fitness as measured by VO2max and Pmax, however, improved only for BFR (6%, 12%), HIT (9%, 15%) and HIT + BFR (6%, 11%) - statistically speaking without inter-group differences.

Table 1: Description of training | Perceived exertion, [La], Peak HR and Peak VO2 represent the mean of avg. exercise values obtained during the 1st & 12th training session. Rating of perceived exertion on 0 to 10 scale (de Oliviera. 2016).

In contrast to the conditioning which improved in all but the light intensity trial, however, muscle strength gains were observed only after BFR training (11%) - not without effort, though, as the data in Table 1 indicates. After all, the perceived exertion at only 66W with your legs cuffed all up is almost identical to the one in the HIT group with its sign. higher avg. intensity of 236 Watts.
References:

• de Oliveira, Mariana Fernandes Mendes de, et al. "Short‐term low‐intensity blood flow restricted interval training improves both aerobic fitness and muscle strength." Scandinavian Journal of Medicine & Science in Sports (2015).
• Loenneke, Jeremy P., et al. "Effects of cuff width on arterial occlusion: implications for blood flow restricted exercise." European journal of applied physiology 112.8 (2012): 2903-2912.
• Sundberg, Carl Johan. "Exercise and training during graded leg ischaemia in healthy man with special reference to effects on skeletal muscle." Acta physiologica Scandinavica. Supplementum 615 (1993): 1-50.