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Monday, 18 February 2013

Vascular Occlusion: Mechanisms & Benefits For Muscle Growth

It is generally accepted that resistance training using more than 65% of one repetition maximum (1RM) is the minimum stimulus required to achieve noticeable muscle and strength gains.


For the young bucks in my reading-audience, these tidings will have little impact on their training style. Unfortunately, high-intensity training using >65% 1 RM can be potentially problematic for certain population groups such as the injured and elderly.

So what do you do if you find yourself unable to employ more traditional means of hypertrophic training? Should you throw in the towel, buy a yoga mat and take up Pilates? Thanks to emerging research in the area of strength and conditioning training such drastic measures may not be necessary.


In fact, significant and rapid increases in muscle hypertrophy could be gained using a training intensity as low as 20% 1RM. You read correctly ... Low-intensity (20 – 50% 1RM) resistance training, combined with restricted venous blood flow from the working muscle has been shown to provide an alternative training method to traditional HIT programs, giving hope to not only the frail or injured but to individuals looking for an additional burst of growth potential.



A number of studies have investigated muscle adaptations to Kaatsu training protocols. For example, according to Weatherholt et al. (2012), 3 sets (15 reps) of unilateral bicep curls and tricep extensions, 3 times per week for eight weeks, while wearing pneumatic cuffs was stimulus enough to produce increases in both strength and size in participants. Furthermore, a pilot study from the University of Tokyo, examining the impact of occluded-bench press training on hypertrophic responses found that performing bench press (30% 1RM) for four sets (75 reps) twice daily, 6 days a week for 2 weeks led to a significant increase in strength (6%) as well as a increase in major muscle thickness increase of 8% in the triceps and 16% in the pectoral muscles.


Takano, et al. (2005) also investigated the hormonal responses to a short-term low-intensity resistance program with reduction of muscle blood flow. In the study, eleven untrained men performed bilateral leg extensions with a Kaatsu band. At 20% 1RM, the subjects performed 4 sets until failure (which equated to 30 repetitions) with 20 second pauses in-between sets. Blood analysis found that, following this training modality, serum concentrations of growth hormone (GH), vascular endothelial growth factor, insulin-like growth factor (IGF-1) were significantly elevated. For the remaining Doubting Thomas’ out there, Kaatsu may be so powerful that even slow-walk training may induce muscle hypertrophy and strength gains. When individuals trained twice a day, 6 days a week for three weeks using 5 set bouts of 2 minutes slow walking (1 minute rest) researchers found that muscle volume increased by 4 – 7%, alongside a strength increase of 8-10%!




Similar effects have been replicated in a number of additional studies (see reference list).



The Mechanisms

So how exactly does restricting blood flow translate into bigger muscles? Scientists believe that there are three main mechanisms at synergistic work –



1. Fiber Type Recruitment

We know that the ‘fast twitch’ muscle fibers are those with the greatest potential for growth. While low-intensity training will usually activate slow-twitch fibers, a moderate restriction of blood flow causes the body to rapidly recruit fast twitch fibers to handle the workload. In fact, EMG data has revealed no difference in the extent to which fast-twitch fibers are activated using low-intensity occlusion and high intensity exercise


2. Accumulation of Metabolites

Occlusion training also increases lactate and growth hormone. Impressively, the GH spike using this modality has been shown to be even higher than that of traditional training.

3. mTOR pathway activation

Finally, use of restricted blood flow activates the mTOR pathway, which is responsible for protein synthesis. This increased activation is the equivalent of priming your body’s pump for growth.


Reference:

American College of Sports Medicine. Position stand. (1998). The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Med Sci Sports Exerc, 30, 975–991.

Moritani, T., Michael-Sherman, W., Shibata, M., Matsumoto, T., & Shinohara, M. (1992). Oxygen availability and motor unit activity in humans. Eur J Appl Physiol , 64, 552-556.

Yasuda, T., Ogasawara, R., Sakamaki, M., Bemben, M.G., & Abe, T. (2011). Relationship between limb and trunk muscle hypertrophy following high-intensity resistance training and blood flow-restricted low-intensity resistance training. Clin Physiol Funct Imaging, 31(5), 347-51.

Yasuda, T., Fujita, S., Ogasawara, R., Sato, Y., & Abe, T. (2010). Effects of low-intensity bench press training with restricted arm muscle blood flow on chest muscle hypertrophy: a pilot study. Clin Physiol Func Imaging, 30(5), 338-43.

Yasuda, T., Fukumura, K., Fukuda, T., Iida, H., Imuta, H., Sato, Y., Yamasoba, T., & Nakajima, T. (2012). Effects of low-intensity, elastic band resistance exercise combined with blood flow restriction on muscle activation. Scan J Med Sci Sports, DOI: 10.111/L.1600-0838.2012.01489.x [Epub ahead of print].

Nishimura, A., Sugita, M., Kato, K., Fukuda, A., Sudo, A., & Uchida, A. (2010). Hypoxia increases muscle hypertrophy induced by resistance training. Int J Sports Physiol Perform, 5(4), 479-508.

Takano, H., et al. (2005). Hemodynamic and hormonal responses to a short-term low-intensity resistance exercise with the reduction of muscle blood flow. Eur J Appl Physiol, 95(1). 65-73.

Abe, T., Kearns, C.F., & Sato, Y. (2005). Muscle size and strength are increased following walk training with restricted venous blood flow from the leg muscle, Kaatsu-walk training. J Appl Physiol, 100(5), 1460-1466.

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