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“To say that the intensity from external load is the absolute deciding factor on muscle adaptation is inappropriate and...simplistic.” J.P. Loenneke et al (Medical Hypotheses, in press, 2011)

“In some ways, these findings on resistance training (and the recent findings from very short interval training)…are the equivalent of saying the earth isn’t actually flat; it’s round. The way we looked at things before has now been turned upside down.” Richard A. Winett, PhD, Heilig Meyers Professor of Psychology, Director of the Center for Research in Health Behavior, Virginia Tech, Blacksburg

One More for Effort Based Training

Blood Flow Restricted Lifting Shows the Way

The American College of Sports Medicine (ACSM) recommends lifting at least 70% on one repetition maximum (1RM) to achieve muscular hypertrophy; it is believed that anything below that load rarely produces substantial muscle growth. Researchers from the University of Oklahoma and the University of Tampa say that is very likely incorrect. “Numerous studies using resistance exercise combined with blood flow restriction have shown muscle hypertrophy to occur with training intensity [load] as low a 20% 1RM,” they write in a coming paper in the journal Medical Hypotheses (2011).

Blood flow restricted exercise (it’s fairly new and doesn’t sound very pleasant) is of interest primarily as a vehicle to draw attention to factors other than load in the muscle building process. For example, blood flow restriction recruits fast-twitch muscle fibers sooner and with less weight. Depriving the muscle of oxygen creates anaerobic (high intensity) stress more quickly than would otherwise be the case. “Blood flow restricted exercise has been demonstrated to result in numerous positive training adaptations, specifically hypertrophy and strength, at intensities much lower than the [70% 1RM] recommendation,” J.P. Loenneke and colleagues write in Medical Hypotheses (in press).

Before moving on, let’s take a moment to learn about blood flow restricted training. Dr. Loenneke wrote a very helpful overview on abcbodybuilding.com. After introducing the subject and explaining how it produces an environment favorable to muscle growth with low-load training, Loenneke explains how “occlusion training” is done. The idea is instructive but the practice is problematic. (I haven’t tried it and do not recommend it.)

Researchers use something called a KAATSU apparatus (sounds expensive), but elastic wraps can be used in the gym. “If you are hitting biceps that day,” Loenneke writes, “elbow wrap the very top of your upper arm, and for forearms you would occlude the upper portion of your lower arm (elbow area).”

Loenneke readily admits that “having blood flow restricted is very uncomfortable.” Moreover, removing the wraps between sets to restore blood flow “doesn’t allow for the intensity to change enough to see a rapid recruitment of additional fibers. So it seems essential to keep the occlusion on throughout the exercise, to allow for the necessary intramuscular environmental changes to occur leading to muscular growth.”

That brings us back to the issue of relevance. Ronald A. Meyer, Department of Physiology and Radiology at Michigan State University, addressed the issue in an invited editorial in the Journal of Applied Physiology (September 2006). “From the applied point of view, it is not clear that low-intensity resistance training with restricted flow has any advantage over conventional training with higher loads,” he opined. “Exercise of ischemic [oxygen deprived] muscle can be uncomfortable, and it certainly would be difficult to apply the method to training trunk or neck muscles!...In any case, from the molecular point of view, the phenomenon deserves further investigation, because it may provide insight into the initial signaling events that trigger muscle growth.” (Emphasis mine) 

Importantly, Meyer adds: “…The recommendation that hypertrophy requires a load [equal to or greater than] 70% of one repetition maximum might just as well be recast as a recommendation that the training must result in substantial anaerobic metabolism.” (Anaerobic means in the absence of oxygen) 

Now, let’s return to the paper in Medical Hypotheses.  Loenneke and colleagues analyze the literature in three areas: Exercise Intensity, Muscle Fiber Recruitment, and Systemic Hormone Production. Many of the studies reviewed involve regular training. 

(This is pretty heavy going. If you'd prefer to go directly to the bottom line, feel free. For those with an interest in muscle physiology, we believe it's worth the effort and concentration required.)

Let’s begin with intensity.

Exercise Intensity

Loenneke and colleagues seek to determine the role intensity (defined as a percentage of 1RM) plays in building muscle and strength “with blood flow restricted exercise.” They begin by looking at two studies involving regular exercise.

“If we accept that acute imbalances between muscle protein synthesis (MPS) and muscle protein breakdown are the main driving force of muscle hypertrophy, then exercise intensity may actually be of less importance,” they explain at the beginning. That’s what they find. The key is what goes on inside the muscle, not external load.

One study found that the rate of MPS was maximized at 60% 1RM, “showing that the rate of myofibril* MPS could be maximized at a lower intensity than the ACSM recommendation of 70% 1RM.” The second study showed that training at 30% 1RM to failure increased MPS to the same level as 90% 1RM to failure. (We wrote about that study.) This is, of course, contrary to the general statement that training to failure is not an effective stimulus without lifting 70% or more of 1RM; the recommended intensity is often 80% 1RM. (*Myofibrils are the rod-like contractile elements in skeletal muscle.)

“It has always been thought that, without blood flow restriction, high rep training cannot produce a stress that is adequate to recruit and fatigue the highest threshold units [fast-twitch fibers],” they write. Based on these two studies, that is clearly not so. 

Loenneke et al then cite five studies showing that blood flow restricted training elicits muscle hypertrophy with well below 70% 1RM, “often using intensities between 20 and 30% 1RM.” Two more studies showed significantly elevated mixed muscle (strength and endurance fibers) synthesis, “further building the case for accretion of muscle mass independent of external load.”

The Loenneke team says that long term training studies (not blood flow restricted) have shown that increases in muscle size “are accompanied with a concomitant increase in strength, indicating that the increases were functional in nature.” They add that only one study (Campos et al) provides evidence that training to failure at higher intensities is more effective than training at lower intensities for muscle hypertrophy. Another study, they explain, used identical methods and “observed significant increases in muscle hypertrophy, muscular strength, and endurance independent of exercise intensity.”

Available evidence indicates, Loenneke and colleagues conclude, that training intensity below the recommended 70% 1RM is capable of building muscle, particularly with blood flow restriction. And they don’t stop there. They go further, writing: “To say that the intensity from external load is the absolute deciding factor on muscle adaptation is inappropriate and...simplistic.”

They back up that stinging assertion with an explanation, and a practically indisputable illustration, taken from a cited study (Goto et al).

Metabolic stress inside the muscle may play a large role, they suggest. To illustrate, they offer two exercise regimens with the same external intensity, but different muscle adaptations. “The only difference between groups is that one group rested for 30 seconds midway through each exercise set.” Loenneke et al relate. “The group that did not rest midway through each set had greater increases in metabolic stress which resulted in greater gains in strength, endurance, and muscle mass compared to the group that rested during each set.”

Makes sense, doesn’t it? Clearly, the group that didn’t rest in the middle of the set worked harder than the group that did. That's true even though both regimens used the same load. 

“We hypothesize that intensity determined by external load is of less importance than changes in the intramuscular environment,” Loenneke et al write. “Through the application of blood flow restriction, the intensity of exercise is able to be increased, without altering the external load.”

It’s not the external load; it’s the metabolic stress inside the muscle that drives adaptation. Effort, not load, is key factor. 

Now, the second inside-the-muscle factor.

Fiber Recruitment

Loenneke et al stress the importance of muscle fiber recruitment in building muscle—with an eye to intensity, as defined by %1RM. Again, blood flow restriction points the way.  (We’ll cut through the complex signaling physiology, keeping it short and simple.)

“Literature demonstrates similar muscle protein synthesis (MPS) responses independent of exercise intensity as determined by concentric %1RM,” they begin. “MPS signaling from resistance training occurs primarily…in fast-twitch (FT) fibers compared to slow-twitch…This supports FT fiber recruitment being an important variable to consider when assessing potential for the accretion of muscle mass.” In other words, recruitment of fast-twitch fibers is a key factor in building muscle mass; this occurs independent of load as a percentage of 1RM.  

“Blood flow restricted resistance exercise research has demonstrated that recruitment of the higher threshold motor units (containing FT fibers) does occur with lower intensity exercise,” the researchers continue. “Both reduced oxygen and metabolic accumulation can increase fiber recruitment.” In plain language, blood flow restricted exercise shows that muscle can be built with low-load, high-rep exercise; the primary drivers appear be oxygen deprivation and lactic acid buildup, i.e. anaerobic stress.

“Thus, muscle hypertrophy occurs independently of exercise intensity [%1RM], as long as FT fibers are activated,” the Loenneke team writes in summary. “However, such a low load exercise protocol without blood flow restriction would require significantly more repetitions to be completed in order to stimulate an increase in myofibril MPS…Thus, we hypothesize, based on current literature, that blood flow restriction induces muscle failure earlier (i.e. at a lower volume of work) compared to non-restricted exercise at the same intensity.”

In other words, blood flow restricted training clearly shows that muscle can be built with low load, high repetition training. It is not necessary to use at least 70% 1RM in order to induce enlargement in fast-twitch fibers. Lighter loads lifted to failure will do the job.

Now for the last area of inquiry: What’s the role of exercise induced hormone enhancement (Growth hormone (GH), Testosterone, and others), with and without blood flow restriction? You’re in for a surprise.

Endogenous Hormones

First, endogenous means originating from inside the body; we are not talking about hormones that are ingested or injected.

The surprise is that internally produced hormones and muscle hypertrophy do not necessarily go hand in hand.

“Elevated systemic hormones following acute resistance exercise has long been associated with skeletal muscle hypertrophy, with and without blood flow restriction,” the Loenneke team writes. But there’s a problem. “Recent research is calling this association into question, with myofibril muscle protein synthesis (MPS) and muscle hypertrophy occurring independently of exercise induced endogenous systemic hormones.” What we’ve long believed appears to be untrue.

“Systemic elevations of endogenous hormones, specifically GH, do not appear to play a role in myofibril MPS or muscle hypertrophy,” Loenneke et al write. They cite numerous studies confirming this revelation.

One study found that 14 days of administering growth hormone “stimulated collagen synthesis but had no effect on myofibril MPS.” A pair of studies investigated short and long term resistance exercise. “These studies investigated elbow flexion with and without the presence of significant elevations of endogenous hormones (GH, IGE-1, Testosterone). [Short term], resistance exercise resulted in significant elevations in myofibril MPS without additional effect from elevated systemic endogenous hormones. To observe long term exposure to exercise induced hormones, [they] performed a 15-week resistance training study using the same design, and confirmed that muscle hypertrophy increased with resistance training, without an additional effect from the presence of elevated systemic endogenous hormones.”

While some say it’s premature to dismiss earlier research supporting the association between systemic hormones and muscle hypertrophy, Loenneke and his associates conclude as follows: “We hypothesize that an increase of systemic endogenous hormones above basal levels are unlikely to produce an increase in muscle hypertrophy.” Furthermore, they “question the commonly cited role of increased systemic endogenous hormones in training adaptations observed with blood flow restriction. It is likely that these systemic elevations are more to do with fuel mobilization and less with muscle growth.” 

With all that under our belt, what does it mean? (Finally!) 

The Bottom Line

The researchers say essentially the same thing several ways.

“Current literature indicates muscle hypertrophy is largely dependent on elevated myofibril MPS, which is independent of external load as long as the volume and/or metabolic stress is sufficient to recruit fast-twitch fibers,” J.P. Loenneke et al write in the Discussion portion of their paper. In short, percentage of 1RM is not the controlling factor in muscle building; the dominant factor is recruitment of fast-twitch muscle fibers. Any load or volume that triggers FT fibers will build muscle. More volume is, of course, required with less weight or resistance.

But that’s not the whole story.  Building muscle is a complex process. Other factors are likely to be involved.

Loenneke and his team believe that a variety of factors are involved in muscle hypertrophy. “Although we do not believe that FT fiber recruitment is the single factor involved in the hypertrophic response to an exercise stimulus, many of these other mechanisms…likely occur in concert with recruitment of higher threshold motor units observed with blood flow restriction training.” 

Here’s their bottom line:  “We hypothesize that the alterations in the intramuscular environment which results in the rapid recruitment of fast-twitch fibers is the large driving force behind skeletal muscle hypertrophy seen with blood flow restriction, whereas the external load and systemic endogenous hormone elevations may not be as important as once thought.”

*  *  *

Makes the head spin that blood flow restriction, a little known exotic training method (that I do not recommend), shines light on anaerobic metabolism as the overarching factor that triggers muscle growth. Confusing as it may seem, it boils down to one simple proposition. Train to failure and you can’t go wrong.

I described the job of the muscle builder in my second book, Ripped 2: Make as many muscle fibers as possible contract and push the maximum number of those fibers to the point of failure. To make muscles grow and get stronger, the bodybuilder must trigger more and more muscle fibers into action, and force those fibers to work harder than ever before.

Keep that picture in mind when you lift. Make progression your goal. Always try to improve. How you do it is up to you. Poundage and reps make little difference (within reason), as long as you exert maximum effort at the end of the set. As Loenneke and his colleagues concluded, “external load [poundage]… may not be as important as once thought.”

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