Are Blood Flow and Lipolysis in Subcutaneous Adipose Tissue Influenced by Contractions in Adjacent Muscle in Humans – Research Review
Title and Abstract
Stallknecht B et. al. Are blood flow and lipolysis in subcutaneous adipose tissue influenced by contractions in adjacent muscles in humans? Am J Physiol Endocrinol Metab. 2007 Feb;292(2):E394-9.
Aerobic exercise increases whole-body adipose tissue lipolysis, but is lipolysis higher in subcutaneous adipose tissue (SCAT) adjacent to contracting muscles than in SCAT adjacent to resting muscles? Ten healthy, overnight-fasted males performed one-legged knee extension exercise at 25% of maximal workload (Wmax) for 30 minutes followed by exercise at 55% Wmax for 120 minutes with the other leg and finally exercised at 85% Wmax for 30 minutes with the first leg. Subjects rested for 30 minutes between exercise periods. Femoral SCAT blood flow was estimated from washout of (133)Xe and lipolysis was calculated from femoral SCAT interstitial and arterial glycerol concentrations and blood flow. In general, blood flow as well as lipolysis was higher in femoral SCAT adjacent to contracting than adjacent to resting muscle (time 15-30 min: blood flow: 25% Wmax: 6.6 +/- 1.0 vs. 3.9 +/- 0.8 ml 100 g(-1) min(-1), P < 0.05; 55% Wmax: 7.3 +/- 0.6 vs. 5.0 +/- 0.6, P < 0.05; 85% Wmax: 6.6 +/- 1.3 vs. 5.9 +/- 0.7, P > 0.05; lipolysis: 25% Wmax: 102 +/- 19 vs. 55 +/- 14 nmol 100 g(-1) min(-1), P = 0.06; 55% Wmax: 86 +/- 11 vs. 50 +/- 20, P > 0.05; 85% Wmax: 88 +/- 31 vs. -9 +/- 25, P < 0.05). In conclusion, blood flow and lipolysis are generally higher in SCAT adjacent to contracting than adjacent to resting muscle irrespective of exercise intensity. Thus, specific exercises can induce “spot lipolysis” in adipose tissue. Key words: exercise, spot lipolysis, microdialysis.
The idea of spot reduction is one that has floated around the fitness body recomposition world for decades. Men want the ever desirable six-pack and can be seen doing abs until the cows come home, women try to slim hips and thighs with endless reps on the inner/outer thigh machine.
Hour long ‘abs’ or ‘buns/thighs’ classes filled with nearly an hour of high rep movements for the specific area can be found in most commercial gyms. Even in the bodybuilding world, where people really should know better, some still argue that spot reduction can occur and that working a given muscle group will help reduce fat in that specific area. I addressed this topic somewhat in The Stubborn Fat Solution since some of what I discuss in that book could readily be confused with spot reduction (it’s not).
For the most part, the idea of spot reduction has been resoundly denied by folks in the field (with the occasional heretic or book seller suggesting it is still possible). Various lines of research are usually cited including those showing no difference in skinfolds in the arms of tennis players (who typically use one arm more than the other).
An example I’ve often used is that “If spot reduction worked, people who ate a lot should have skinny faces.” A bit silly but I think it gets the point across. If working a specific muscle group reduced fat only in that area, that’s how it should work. But it doesn’t. Or certainly doesn’t seem to. But, for the most part, the idea hasn’t been directly tested to my knowledge.
In that context, I should note for the sake of background that there are three primary steps involved in fat loss that might potentially be influenced although today’s study only focuses on two. Those steps are
- Lipolysis (the actual fat breakdown)
- Blood flow (critical for transport of the broken down fat to other tissues for ‘burning’)
- Oxidation (the actual ‘burning’ of fat in tissues such as the liver or skeletal muscle)
Is it possible that performing local activity can impact on some aspect of the above in a way that might make spot reduction or performing endless reps of local exercises worthwhile in terms of fat loss? That’s what today’s study set out to examine: do contractions in a specific muscle impact on either lipolysis or blood flow (oxidation was not measured) in the adjacent fat cells.
And although it was published several years ago, it still seems to be making the rounds (being cited as ‘evidence’ for spot reduction); as well, the idea of spot reduction is one that refuses to die. So it’s worth seeing what the real or potentially real effects actually are.
Using a couple of different methods (that I’m not going to detail) to measure actual blood flow and lipolysis , the study had subjects perform lower body exercise (they called it one leg leg extension but this probably means one legged cycling) at various intensities while resting the other leg. That way, blood flow/lipolysis could be measured for the exercise versus the unexercised leg.
This allowed them to compare lipolysis and blood flow in response to local exercise to the non-exercised control leg. This is actually critically important as any type of whole body exercise would tend to have systemic effects; that is impacting on fuel metabolism all over the body. By limiting exercise to a single leg, the researchers were able to measure the response only in the fat cells close to the muscles being worked and compare that to the unworked msuscle to see what differences occurred.
Exercise was performed at 25%, 55% and 85% of maximum power output with a 30 minute break and the subjects switched legs from one intensity to the next. This also acted as a control so that the previous bout of exercise wasn’t impacting on the next bout, since the previously exercised leg got the longer break. As mentioned above, blood flow and lipolysis was compared between the exercised leg and the rested leg to see what difference the exercise had.
And, as indicated in the abstract above, both lipolysis and blood flow were increased for the exercised vs. non-exercised leg although this only occurred at the two lower intensities of exercise. At the highest intensity of exercise, no change was seen.
Before getting to specific numbers, a question worth addressing is why this would have happened. The researchers proposed two possible reasons for their observation.
First, local changes in hormones (or a synergy between changes in hormones and blood flow) are most likely responsible but there is a larger question of why this would occur in the first place, a point that the researchers specifically made. By why I mean why the system would work that way in terms of improving physiological functioning.
The reason for asking this question is this: fat mobilized from a specific area of body fat (say the thigh) can’t actually be used for fuel by the muscle underneath it (e.g. the quadriceps). The blood flow of skeletal muscle and fat cells are separate and any fat mobilized from an adjacent area will go into local circulation; again, it can’t be used directly by that muscle.
So there’s no really logical physiological reason that working a given muscle would would cause fatty acids to be mobilized; that muscle can’t use them. Of course, physiology doesn’t have to be logical to work a certain way and worrying about the reasons why instead of the observation of what happened can make you lose the forest for the trees.
Related to this, the researchers point out clearly that there is no indication that these results will actually result in spot reduction as fat stores in the affected areas could simply be replenished after the exercise bout. They didn’t measure fat storage after the exercise bout stopped and process that occurs quite often is fatty acid re-esterification, basically mobilized fat that isn’t burned off elsewhere in the body simply gets stored back in the fat cell. In some exceedingly strange cases, fat mobilized in one area of the body can be restored in fat cells somewhere else.
The researchers also suggest that localized increase in temperature, which can also impact on blood flow may have also been involved in the measured response. I discuss this aspect of fat cell mobilization in The Stubborn Fat Solution as local temperature is known to impact on blood flow in the area. Cold tends to cause vasoconstriction and heat vasodilation so there might actually be some logic to those rubber belts and such that warm the area before exercise.
In any case, for whatever reasons, through whatever mechanism, working a given muscle for 30 minutes at low to moderate intensities did increase fat cell lipolysis in blood flow.
Aha! Spot reduction is possible, right? Hang on.
Although clearly local exercise did impact on fat cell lipolysis and blood flow, you might note something I left out of the above discussion: the acutal quantitative impact of this. That is, how much extra fat was actually mobilized for fuel, potentially to be burned off.
Addressing that very thing, based on the measured changes in blood flow and lipolysis, the researchers estimate that, in 30 minutes of local exercise, an additional .6-2.1 milligrams (one milligram is one thousandth of a gram) per 100 grams of adipose tissue adjacent to contracting muscle was mobilized.
Let me put that in context. First let’s assume that you’re carying a whopping 5 kg (11.1 pounds) of fat in a specific area.
If local exercise can mobilize 0.6-2.1 milligrams of fat per 100 grams of fat mass, that works out to:
0.6-2.1 mg/100 grams * 1000 grams/kg * 5 kg = 30-105 milligrams of fat.
Or 0.03-0.1 gram of extra fat mobilized in 30 minutes of activity.
Now, a single pound of fat (0.454 kg) contains about 400 grams of fat so our hypothetical 11.1 pounds of fat contains 4,440 grams of fat. And 30 minutes of local activity mobilized at most 0.1 gram of fat. Whoo hoo. You’ll be ripped in about 1000 years.
And, so far as I’m concerned, that should be the death knell for the idea of spot reduction. Yes, there appears to be an effect whereby working a given muscle impacts on local fat cell metabolism but the effect is completely and utterly irrelevant in quantatitive terms. The amount of fat mobilized due to increased hormones or blood flow is simply insignificant to anything in the real world.
There is also the fact that, compared to something like full body cardio types of activities, local single muscle group activities burn tiny amounts of calories. Doing cardio for 30 minutes at even a reasonable caloric burn of 5 cal/minute (very easy) burns 150 calories. If you get say 90% fat utilization for fuel, you’ve burned 15 grams of fat. Compared to the 0.1 gram you might mobilize doing crunches or leg lifts.
As well, the whole body activity will impact on fuel utilization and hormones in ways that much more massively impact on lipolysis and blood flow. Simply, spending an hour doing localized exercise pales in comparison to the fat loss effects of even moderate cardio. Wasting time with ab or buns/thighs classes is simply a waste of time in terms of any sort of local fat reduction.