Interest is rising in various approaches that increase local muscle ischemia during resistance exercise (1). This blood flow restriction (BFR) may be partial or may involve complete occlusion. The more common methods include the application of external devices such as elastic straps or bands, or inflatable cuffs, to reduce muscle blood flow during lower-load resistance exercise; one systematic version of BFR training with a specific cuff apparatus is known as Kaatsu. Other possible methods include the use of slower movements with lower loads than those of typical heavy resistance training and without pause between repetitions nor between phases (concentric or eccentric). This helps maintain an elevated intramuscular pressure, thereby interfering with local blood flow.
BFR is appealing for situations where there is a desire to avoid heavy loads while creating a high degree of metabolic challenge in the muscle. This may stimulate adaptations in strength and particularly in muscle hypertrophy, and the hypoxia resulting from BFR is one of the physiological mechanisms being considered (2). A recent study examined the role of this reduced oxygen availability during low-load resistance exercise in female athletes (3).
Two methods were used to create a hypoxic condition in the leg muscles while resistance training with a low load; one was the breathing of a low-oxygen gas mixture (HT) and the other was thigh blood flow occlusion using Kaatsu cuffs (KT). Female netballers were assigned to one of 3 groups, HT, KT, and control training (CT), all involving a 5-week standardized program of 3 sessions per week. The participants performed training sessions consisting of 3 sets of knee extension followed, after a 2-minute rest period, by 3 of knee flexion, all with a resistance of 20% 1 repetition maximum (RM). Repetitions lasted approximately 1 second per phase, and the rest intervals between sets lasted 30 seconds. All sets were taken to failure by the KT group and the other 2 groups were asked to match that number of repetitions per set to control for training load. The group's respective intervention was maintained throughout each 12–13-minute training session. In the HT, the percentage of oxygen in the inspired air was automatically adjusted to maintain arterial oxygen saturation at 80%. In the KT, cuff pressure was progressed from 160 mm Hg on the first training day to 230 mm Hg on the eighth training day and was kept at 230 mm Hg for the remainder of the training sessions.
Strength and muscular endurance tests for leg extension, which were performed in a separate session under normal conditions without any intervention, showed a much higher benefit of the 2 experimental modes relative to the control condition. Similarly, training with vascular occlusion (KT) and with systemic hypoxia (HT), compared with training with an unimpeded muscle oxygen balance, resulted in changes in voluntary neural activation of the leg extensors and substantial thigh muscle growth.
With regard to the strength and muscular endurance testing, CT resulted in an improvement in the maximal number of repetitions that could be completed with a 20% 1RM load (Reps20) but both KT and HT showed a larger improvement in this variable. KT and HT also showed substantial increases in peak isometric force (maximal voluntary contracting; MVC) and in 30-second isometric muscular endurance, whereas CT showed little change in these variables. Any differences between KT and HT in these 3 performance variables were essentially trivial. Even with the lower training load (20% 1RM) in this study, the KT and HT adaptations were comparable to those expected from BFR training with higher loads (50% 1RM) or from traditional heavy resistance training.
Total quadriceps electromyography intensity was also calculated from the muscle electrical activity as an index of muscle recruitment during these performance tests. During the MVC, it increased in all 3 groups but substantially more as a result of KT. Higher neural activation during maximal efforts indicates that at least some of the strength increase is based on altered neuromuscular functioning, which may include increased motor unit recruitment and synchronization, as well as increased motor unit firing frequency. Furthermore, electromyography intensity during the Reps20 decreased more after KT and HT. This lowered motoneuron activity during the performance of the same task post-training points to a training-induced augmentation in the efficiency of force generation. This makes sense because the same absolute load was used for this test before and after training; the load became, in effect, lighter for the athletes post-training because of their increased 1RM.
The cross-sectional area of the knee flexors and extensors was calculated at the mid-thigh level and was shown to increase substantially in KT and HT compared with CT. This apparent muscular hypertrophy was of a similar magnitude shown by previous studies examining similar protocols. This is the first study, though, showing such an effect in young trained female athletes.
The findings of this study do not amount to a recommendation for these types of protocols in lieu of typical strength training programs in an athletic population. The higher the training status of athletes, the more likely they are to benefit instead from resistance training that adheres more closely to the specificity principle in regard to the sport's demands for strength, this being particularly true for power needs. However, the results of this study do provide additional support for the utilization of these protocols by the strength and conditioning coach who needs to maximize the physiological stimulus and optimize adaptations, especially through the maintenance of muscle mass, during suboptimal circumstances where higher loading is contraindicated due to injury or other factors. This study reinforces this rationale particularly for female athletes.
1. Alberti G, Cavaggioni L, Silvaggi N, Caumo A, Garufi M. Resistance training with blood flow restriction using the modulation of the muscle's contraction velocity. Strength Cond J 35: 42–47, 2013.
2. Loenneke JP, Pujol TJ. The use of occlusion training to produce muscle hypertrophy. Strength Cond J 31: 77–84, 2009.
3. Manimmanakorn A, Manimmanakorn N, Taylor R, Draper N, Billaut F, Shearman JP, Hamlin MJ. Effect of resistance training combined with vascular occlusion or hypoxia on neuromuscular function in athletes. Eur J Appl Physiol 113: 1767–1774, 2013.