Am J Physiol Endocrinol Metab 292: E394 –E399, 2007.
`First published September 19, 2006; doi:10.1152/ajpendo.00215.2006.
`
`Are blood flow and lipolysis in subcutaneous adipose tissue influenced by
`contractions in adjacent muscles in humans?
`
`Bente Stallknecht, Flemming Dela, and Jørn Wulff Helge
`Department of Medical Physiology, The Copenhagen Muscle Research Centre,
`The Panum Institute, University of Copenhagen, Copenhagen, Denmark
`
`Submitted 5 May 2006; accepted in final form 11 September 2006
`
`Stallknecht B, Dela F, Helge JW. Are blood flow and lipolysis in
`subcutaneous adipose tissue influenced by contractions in adjacent mus-
`cles in humans? Am J Physiol Endocrinol Metab 292: E394–E399, 2007.
`First published September 19, 2006; doi:10.1152/ajpendo.00215.2006.—
`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 min followed by
`exercise at 55% Wmax for 120 min with the other leg and finally exercised
`at 85% Wmax for 30 min with the first leg. Subjects rested for 30 min
`between exercise periods. Femoral SCAT blood flow was estimated from
`washout of 133Xe, and lipolysis was calculated from femoral SCAT
`interstitial and arterial glycerol concentrations and blood flow. In general,
`blood flow and lipolysis were 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䡠100 g⫺1 䡠min⫺1, P ⬍ 0.05; 55%
`Wmax 7.3 ⫾ 0.6 vs. 5.0 ⫾ 0.6 ml䡠100 g⫺1 䡠min⫺1, P ⬍ 0.05; 85% Wmax
`6.6 ⫾ 1.3 vs. 5.9 ⫾ 0.7 ml䡠100 g⫺1 䡠min⫺1, P ⬎ 0.05; lipolysis: 25%
`Wmax 102 ⫾ 19 vs. 55 ⫾ 14 nmol䡠100 g⫺1 䡠min⫺1, P ⫽ 0.06; 55% Wmax
`86 ⫾ 11 vs. 50 ⫾ 20 nmol䡠100 g⫺1 䡠min⫺1, P ⬎ 0.05; 85% Wmax 88 ⫾
`31 vs. ⫺9 ⫾ 25 nmol䡠100 g⫺1 䡠min⫺1, 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.
`
`exercise; spot lipolysis; microdialysis
`
`OBESITY CAN BE DEFINED AS a condition where the amount of
`adipose tissue is increased to such a degree that it has conse-
`quences for the health of the person. In addition to the amount,
`also the distribution of fat is important. Obesity can be dimin-
`ished by increased physical activity and/or reduced caloric
`intake (11, 21) and, at least in the short term, the size of the
`negative caloric balance is the primary factor determining the
`weight loss (22, 28). There is evidence that exercise-induced
`relative loss of fat is higher in visceral and abdominal subcu-
`taneous adipose tissue (SCAT) than in femoral SCAT (23).
`This indicates that regional adipose tissue depots are regulated
`independently, and for many years it has been discussed
`whether specific exercises can reduce local adipose tissue
`depots, i.e., induce a “spot reduction” of adipose tissue, and
`thus modify fat distribution (19, 20).
`A number of studies have examined the spot reduction
`theory, and conclusions have been contradictory (12, 16, 19,
`20). A valid study design to test
`the hypothesis of spot
`reduction is one in which the muscles in one part of the body
`are trained and the muscles in the contralateral side are not, and
`
`the size of the adipose tissue depots adjacent to the trained
`respective sedentary muscles are measured before and after the
`study period. One study using this design (19) found a decrease
`in skinfold thickness of the trained arm, but in another study
`(20) the skinfold thickness decreased significantly in both the
`trained and the sedentary arm during the study period. The
`latter finding is essentially supported by a study in which the
`skinfold thickness of both arms was measured in tennis players
`and control subjects (12). The skinfold thickness did not differ
`between arms in tennis players or control subjects, but skinfold
`thickness of both arms was lower in tennis players compared
`with controls. Krotkiewski et al. (16) had 10 healthy middle-
`aged females exercise one leg for 5 wk while the other leg was
`resting, and ultrasound measurements revealed that the thick-
`ness of the femoral SCAT of the trained leg was significantly
`decreased, whereas the thickness of the SCAT of the sedentary
`leg was unchanged. However, a reduced thickness of the
`subcutaneous tissue layer could be because of a training-
`induced enlargement of the underlying muscle, which could
`result in a compression of a possibly unchanged amount of
`SCAT. To clarify this, Krotkiewski et al. took two biopsies of
`the SCAT from each thigh and found that fat cell weight
`decreased nonsignificantly in both biopsies from the trained leg
`{⫺7% [0.60 ⫾ (SE) 0.07 to 0.56 ⫾ 0.05 ␮g] and ⫺26%
`(0.42 ⫾ 0.07 to 0.31 ⫾ 0.08 ␮g)} and increased nonsignifi-
`cantly in both biopsies from the sedentary leg [⫹11% (0.54 ⫾
`0.03 to 0.60 ⫾ 0.03 ␮g) and ⫹7% (0.46 ⫾ 0.08 to 0.49 ⫾ 0.08
`␮g)]. Based on the biopsy data, Krotkiewski et al. turned down
`the spot reduction hypothesis, but it may be speculated that
`their nonsignificant changes in fat cell weight could be because
`of a type 2 statistical error.
`In the present study, we evaluated one component in the spot
`reduction hypothesis, namely if spot lipolysis occurs in SCAT
`overlying contracting skeletal muscle. Our subjects performed
`acute one-legged knee extension exercise, and, by use of 133Xe
`washout and microdialysis techniques, we estimated blood
`flow and lipolysis in femoral SCAT adjacent to contracting and
`resting skeletal muscle.
`
`MATERIALS AND METHODS
`
`Subjects. Ten healthy, moderately active, overnight-fasted males
`[age: 26 ⫾ 2 (SE) yr, weight: 82 ⫾ 3 kg, height: 183 ⫾ 2 cm, BMI:
`24.5 ⫾ 0.8 kg/m2, V˙ O2 max: 49⫾ 2 ml 䡠 kg⫺1 䡠 min⫺1] gave their
`written consent according to the declaration of Helsinki II to partic-
`ipate in the study, which was approved by the Ethics Committee for
`Medical Research in Copenhagen (KF 11– 055/03).
`
`Address for reprint requests and other correspondence: B. Stallknecht, Dept.
`of Medical Physiology, The Panum Institute, Blegdamsvej 3, DK-2200 Copen-
`hagen N, Denmark (e-mail: B.Stallknecht@mfi.ku.dk).
`
`The costs of publication of this article were defrayed in part by the payment
`of page charges. The article must therefore be hereby marked “advertisement”
`in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
`
`E394
`
`0193-1849/07 $8.00 Copyright © 2007 the American Physiological Society
`Downloaded from journals.physiology.org/journal/ajpendo (038.099.035.066) on November 24, 2021.
`
`http://www.ajpendo.org
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`SPOT LIPOLYSIS
`
`E395
`
`Protocol. Before the experiment, subjects were accustomed to
`exercise on the knee extension ergometer, and maximal work capacity
`(Wmax) was determined for each leg as described by Andersen et al.
`(1). At least 5 days before the experimental day, subjects performed a
`V˙ O2 peak test on a bicycle ergometer using a standard progressive
`exercise test. Subjects were asked to refrain from vigorous physical
`activity for 2 days before the experiment. After a 12-h fast and
`abstinence from coffee, tea, alcohol, and tobacco, the subjects arrived
`at the laboratory at 8:00 A.M. During the experiments, subjects wore
`shorts and t-shirt, and the room temperature was 23 ⫾ 1°C. A catheter
`(Arterial Cannula with FloSwitch; Becton-Dickinson) was inserted in
`the brachial or radial artery for blood sampling. Microdialysis cathe-
`ters were inserted, and 133Xe was injected in SCAT of both thighs (see
`below). After a 90-min equilibration period, the experiment was
`initiated.
`The experiment consisted of a 15-min resting period and three
`consecutive periods of one-legged knee extension exercise (Fig. 1).
`First subjects exercised with one leg for 30 min at 25% of Wmax (13 ⫾
`1 watts, heart rate 81 ⫾ 3 beats/min). After a 30-min rest, subjects
`exercised with the other leg for 120 min at 55% of Wmax (26 ⫾ 1
`watts, heart rate 84 ⫾ 4 beats/min), and after another 30-min rest they
`exercised with the first leg again for 30 min but now at 85% of Wmax
`(44 ⫾ 2 watts, heart rate 107 ⫾ 4 beats/min). Selection of the leg
`eligible for low-high respective moderate intensity was done by
`randomized stratification such that dominant and nondominant legs
`were similarly represented.
`Both during the resting and the exercise periods, subjects were
`sitting in a chair with the torso strapped to the back of the chair.
`Subjects had free access to water throughout the experiment. Pulmo-
`nary oxygen uptake and carbon dioxide excretion were measured
`regularly during exercise using an automated on-line system (Oxycon
`Champion; Erich Jaeger, Hoechberg, Germany).
`Microdialysis. Microdialysis was performed in principle as de-
`scribed previously (27). After anesthesia of the skin (0.2 ml lidocaine,
`5 mg/ml) at the sites of perforation, two microdialysis catheters (CMA
`60; CMA/Microdialysis, Stockholm, Sweden) were placed in the
`SCAT adjacent to the vastus lateralis part of the quadriceps muscle in
`each thigh. Catheters were placed equidistant from the skin and the
`muscle fascia, 13–15 cm above the patella, and with 2–3 cm between
`catheters. Catheters were perfused at a rate of 1.0 ␮l/min using
`high-precision syringe pumps (CMA 100; CMA/Microdialysis). The
`perfusate consisted of Ringer acetate with 2 mM glucose, 5 kBq/ml
`[3H]glycerol (NEN, Zaventem, Belgium), and 5 kBq/ml [14C]ethanol
`(NEN). Seven out of 40 catheters ceased to function at some point
`during exercise.
`The in vivo relative recovery (RR) for glycerol was determined by
`the internal reference calibration technique (24). This technique as-
`sumes that the relative loss of [3H]glycerol from the microdialysis
`catheter to the interstitial fluid equals the RR of glycerol from the
`interstitial fluid to the microdialysis catheter. The RR of glycerol was
`calculated as (dpmp ⫺ dpmd)/dpmp, where dpmp is 3H disintegrations
`per minute in 5 ␮l perfusate and dpmd is 3H disintegrations per minute
`
`in 5 ␮l dialysate. Interstitial concentrations were calculated as (Cd ⫺
`Cp)/RR ⫹ Cp, where Cd is dialysate concentration and Cp is perfusate
`concentration.
`SCAT blood flow. Adipose tissue blood flow (ATBF) was measured
`by the local 133Xe washout technique (27), which has the advantage
`that it is a quantitative method. At least 30 min before start of the
`resting period, 0.5–1 MBq gaseous 133Xe (Amersham Health) in a
`volume of 0.05– 0.1 ml was injected in SCAT adjacent to the rectus
`femoris part of the quadriceps muscle. The 133Xe depot was placed
`equidistant from the skin and the muscle fascia and 13–15 cm above
`the patella. The washout rate of 133Xe was measured continuously by
`a scintillation counter system (Oakfield Instruments, Eynsham, UK)
`strapped to the skin surface above the 133Xe depot. ATBF was
`determined in 15- or 30-min periods and calculated as ⫺k 䡠 ␭ 䡠 100
`(ml 䡠 100 g⫺1 䡠 min⫺1), where k is the rate constant of the washout and
`␭ is the tissue-to-blood partition coefficient for 133Xe at equilibrium.
`␭ was assumed to be 10 ml/g (15).
`Changes in ATBF in areas surrounding microdialysis catheters
`were also estimated by the microdialysis outflow/inflow technique
`(13, 25). The technique was originally described using ethanol as a
`marker of blood flow (13), but we have demonstrated that [14C]etha-
`nol is a valid alternative to ethanol (25). The blood flow marker is
`added to the perfusate (inflow), it diffuses out through the membrane,
`and is washed away by the blood. The higher the blood flow, the more
`marker is washed away, and the less marker remains in the dialysate
`(outflow). Accordingly, the outflow-to-inflow ratio of marker varies
`inversely with blood flow (9, 25). The advantage of the microdialysis
`outflow/inflow technique is that it estimates changes in blood flow in
`the same area as interstitial concentrations of metabolites are mea-
`sured.
`Sampling and analyses. Dialysate for analysis of glycerol was
`collected in 200-␮l capped microvials at 15- or 30-min intervals,
`immediately frozen, and kept at ⫺20°C until analysis. Dialysate
`sampling was delayed by 2 min relative to the rest of the experimental
`protocol to compensate for the transit time in the outlet tubing. Blood
`for determination of hormones and metabolites was sampled in iced
`tubes and immediately centrifuged. Blood was sampled immediately
`before and every 15 min during the first 30 min of the exercise periods
`and additionally at time 60 and 120 min during the 120-min exercise
`period. Blood for determination of glycerol was stabilized with
`EDTA, and plasma was kept at ⫺20°C until analysis. Microdialysate
`and plasma glycerol concentrations were determined by a CMA 600
`microdialysis analyzer (CMA/Microdialysis). Blood for determina-
`tion of insulin was stabilized with trasylol and EDTA and kept at
`⫺20°C until analysis. Arterial plasma insulin concentrations were
`determined by a commercial ELISA (DakoCytomation). Blood for
`determination of epinephrine was stabilized with reduced glutathione
`and EDTA and kept at ⫺80°C until analysis. Arterial plasma epineph-
`rine concentrations were determined by a commercial RIA (High
`sensitive 2 CAT RIA; Labor Diagnostika, Nord, Germany).
`Calculation of adipose tissue lipolysis. Adipose tissue venous
`glycerol concentrations were calculated based on “Ficks law of
`
`Fig. 1. Experimental protocol. Ten males performed knee exten-
`sion exercise with one leg (leg 1) at 25% of maximal workload
`(Wmax) for 30 min while the other leg (leg 2) was resting. After a
`short rest, subjects exercised with the other leg (leg 2) at 55%
`Wmax for 120 min while the first leg (leg 1) was resting. After
`another short rest, subjects exercised with the first leg (leg 1) at
`85% Wmax for 30 min while the other leg (leg 2) was resting.
`Arterial blood samples were obtained as indicated with arrows,
`whereas microdialysis samples and 133Xe washout readings were
`collected across sampling periods indicated by brackets.
`
`AJP-Endocrinol Metab • VOL 292 • FEBRUARY 2007 • www.ajpendo.org
`Downloaded from journals.physiology.org/journal/ajpendo (038.099.035.066) on November 24, 2021.
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`E396
`
`SPOT LIPOLYSIS
`
`RESULTS
`
`ATBF. Knee extension exercise with one leg at 25, 55, and
`85% Wmax increased (P ⬍ 0.05) femoral subcutaneous ATBF
`in both legs (Fig. 2A). In general, blood flow was higher in
`adipose tissue adjacent to working muscle than in adipose
`tissue adjacent to resting muscle. At 25 and 55% Wmax, the
`ATBF difference between legs (rest vs. exercise) was signifi-
`cant, but this was not the case at 85% Wmax. The changes in
`ATBF detected by the microdialysis [14C]ethanol technique
`were similar to changes detected by the 133Xe washout tech-
`nique (Fig. 2, A and B).
`Adipose tissue interstitial and arterial plasma glycerol con-
`centrations. Knee extension exercise with one leg at 55 and
`85% Wmax increased (P ⬍ 0.05) the femoral SCAT interstitial
`glycerol concentration compared with rest (Fig. 3A). At 85%
`Wmax, the interstitial glycerol concentration was higher (P ⬍
`0.05) in adipose tissue adjacent to working muscle than in
`adipose tissue adjacent to resting muscle. At all three intensi-
`ties, knee extension exercise with one leg increased (P ⬍ 0.05)
`the arterial plasma glycerol concentration compared with rest
`(Fig. 3B).
`Adipose tissue lipolysis. During knee extension exercise
`with one leg at 25 and 85% Wmax, the lipolysis was signifi-
`cantly higher in femoral SCAT adjacent to working muscle
`than in adipose tissue adjacent to resting muscle (Fig. 4).
`During the first 60 min of exercise with one leg at 55% Wmax,
`the lipolysis seemed higher in adipose tissue adjacent to work-
`ing muscle than in adipose tissue adjacent to resting muscle,
`but the difference was not significant. The difference in adi-
`pose tissue lipolysis between the two legs (lipolysis in exer-
`cising ⫺ resting leg) during time 0 –30 min showed that
`lipolysis was larger (P ⬍ 0.05) than zero at 25 and 85% Wmax,
`but not at 55% Wmax (Fig. 5). Incremental lipolysis did not
`change with exercise intensity (P ⬎ 0.05).
`Arterial plasma hormone concentrations. Knee extension
`exercise with one leg at 55% and at 85% Wmax decreased (P ⬍
`0.05) the arterial plasma insulin concentration compared with
`rest (Table 1). Exercise with one leg at 85% Wmax increased
`(P ⬍ 0.05) the arterial plasma epinephrine concentration com-
`pared with rest (Table 1).
`
`DISCUSSION
`
`Specific exercises can induce spot lipolysis, since we found
`blood flow (Fig. 2) and lipolysis (Figs. 4 and 5) to be higher in
`SCAT adjacent to contracting than adjacent to resting muscle.
`Based on the present results, it cannot be foreseen if specific
`exercises can induce spot reduction, since triacylglycerol (TG)
`stores could be fully replenished or even supercompensated
`between exercise sessions.
`During exercise, temperature increases in the contracting
`muscles (10), and this would increase temperature also in the
`tissues adjacent to the contracting muscles. An increase in
`adipose tissue temperature induces an increase in ATBF (9),
`and this mechanism could potentially explain the increased
`blood flow in the adipose tissue adjacent to the contracting
`muscle in the present study (Fig. 2). During knee extension
`exercise, the increase in temperature of the contracting quad-
`riceps muscle has been found to be ⬃2°C (10). Fella¨nder et al.
`(9) heated SCAT and increased the temperature in the tissue by
`4°C, which elicited an increase in ATBF of ⬃1.5 ml 䡠100
`
`Fig. 2. Adipose tissue blood flow. Ten healthy, overnight-fasted males per-
`formed one-legged knee extension exercise at 25% of Wmax for 30 min
`followed by exercise at 55% Wmax for 120 min with the other leg and finally
`exercised at 85% Wmax for 30 min with the first leg. Subjects rested for 30 min
`between exercise periods. Femoral, subcutaneous adipose tissue blood flow of
`both legs was measured using the 133Xe washout (A) and the microdialysis
`[14C]ethanol outflow/inflow (B) techniques. Adipose tissue blood flow is
`inversely related to [14C]ethanol outflow/inflow. *P ⬍ 0.05 vs. rest. (*)P ⬍ 0.1
`vs. rest. ⫹P ⬍ 0.05 between legs. (⫹)P ⬍ 0.1 between legs.
`
`diffusion for a thin membrane,” as described previously (27). Subse-
`quently, adipose tissue glycerol output was calculated as venous
`minus arterial glycerol concentration multiplied by ATBF (27). Adi-
`pose tissue glycerol output equals adipose tissue lipolysis, since
`glycerol is not reused to any significant extent in adipose tissue (3).
`Statistics. The computer program SigmaStat for Windows version
`2.03 (SPPS, Chicago, IL) was used for statistical analysis. All data are
`presented as means ⫾ SE. A two-way repeated-measures ANOVA
`(RM ANOVA) with leg and time as factors was used to test for
`differences between legs and changes with time in ATBF and micro-
`dialysis-associated variables. A one-way RM ANOVA was used to
`test for changes with time in plasma concentrations. If a difference
`was present according to the ANOVA, a Student-Newman-Keul’s test
`was used post hoc to locate the difference. A one-sample t-test was
`used to test if incremental lipolysis differed from zero. A significance
`level of 0.05 in two-tailed testing was chosen a priori.
`
`AJP-Endocrinol Metab • VOL 292 • FEBRUARY 2007 • www.ajpendo.org
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`
`E397
`
`Fig. 4. Adipose tissue lipolysis. Ten healthy, overnight-fasted males per-
`formed one-legged knee extension exercise at 25% of Wmax for 30 min
`followed by exercise at 55% Wmax for 120 min with the other leg and finally
`exercised at 85% Wmax for 30 min with the first leg. Subjects rested for 30 min
`between exercise periods. Femoral, subcutaneous adipose tissue lipolysis of
`both legs was calculated from the interstitial and arterial glycerol concentra-
`tions and adipose tissue blood flow. *P ⬍ 0.05 vs. rest. ⫹P ⬍ 0.05 between
`legs. (⫹)P ⬍ 0.1 between legs.
`
`This would increase the interstitial concentration of epineph-
`rine in the adipose tissue, which could be one of the mecha-
`nisms behind the higher lipolysis in SCAT adjacent to con-
`tracting than adjacent to resting muscle.
`Norepinephrine is not only a hormone but also a neurotrans-
`mitter in the sympathetic nervous system, and a selective
`stimulation of adipose tissue adjacent to contracting muscles
`could also be via local sympathetic nerves. In favor of this
`mechanism, studies in humans have demonstrated that regional
`differences are present in sympathetic nervous activity (5) and
`that direct stimulation of a cutaneous sympathetic nerve in-
`
`Fig. 3. Glycerol concentrations. Ten healthy, overnight-fasted males per-
`formed one-legged knee extension exercise at 25% of Wmax for 30 min
`followed by exercise at 55% Wmax for 120 min with the other leg and finally
`exercised at 85% Wmax for 30 min with the first leg. Subjects rested for 30 min
`between exercise periods. The interstitial glycerol concentration in femoral,
`subcutaneous adipose tissue of both legs was measured by microdialysis
`technique (A), and the plasma glycerol concentration was measured in arterial
`blood (B). P ⬍ 0.05 vs. rest (*) and between legs (⫹).
`
`g⫺1 䡠min⫺1. We did not measure the temperature of the adipose
`tissue adjacent to the contracting muscles, but, assuming that
`the adipose tissue temperature increased 1°C, this could ac-
`cording to the data by Fella¨nder et al. (9) at most explain an
`increase in ATBF of 0.4 ml 䡠100 g⫺1 䡠min⫺1.
`Circulating epinephrine and norepinephrine are potent stim-
`ulators of ATBF and lipolysis (17, 26), and, in the present
`study, we found the plasma epinephrine concentration to in-
`crease significantly at the highest exercise intensity (Table 1).
`Circulating hormones influence all adipose tissue depots and
`not selectively adipose tissue adjacent to contracting muscles.
`However, because of the relatively increased blood flow in
`adipose tissue adjacent to contracting muscles, a larger amount
`of the circulating epinephrine will be delivered to this tissue.
`
`Fig. 5. Incremental adipose tissue lipolysis. Ten healthy, overnight-fasted
`males performed one-legged knee extension exercise at 25% of Wmax for 30
`min followed by exercise at 55% Wmax for 120 min with the other leg and
`finally exercised at 85% Wmax for 30 min with the first leg. Subjects rested for
`30 min between exercise periods. The difference in mean femoral, subcutane-
`ous adipose tissue lipolysis between exercising and resting legs was calculated
`for the time period 0 –30 min for each exercise period (25, 55, and 85% Wmax).
`*P ⬍ 0.05 vs. 0.
`
`AJP-Endocrinol Metab • VOL 292 • FEBRUARY 2007 • www.ajpendo.org
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`SPOT LIPOLYSIS
`
`Table 1. Arterial plasma hormone concentrations
`
`Exercise
`
`Time, min
`
`Insulin, pM
`
`Epinephrine, nM
`
`Rest
`25% Wmax
`
`55% Wmax
`
`85% Wmax
`
`Rest
`15
`30
`15
`30
`60
`120
`15
`30
`
`45⫾6
`41⫾8
`37⫾5
`35⫾5*
`31⫾4*
`30⫾4*
`25⫾3*
`29⫾5*
`31⫾4*
`
`1.1⫾0.3
`0.8⫾0.1
`0.9⫾0.2
`0.8⫾0.1
`0.8⫾0.1
`0.7⫾0.1
`0.8⫾0.1
`1.1⫾0.3
`1.3⫾0.1*
`
`Values are means ⫾ SE. Wmax, maximal workload. *P ⬍ 0.05 vs. rest.
`
`creases lipolysis in the adipose tissue innervated by the stim-
`ulated nerve (6). Also, denervation of a rat retroperitoneal fat
`pad induces an increase in fat pad weight and adipocyte
`volume 1 wk after denervation, indicating that lipolysis is
`diminished when no sympathetic innervation is present (4).
`Another mechanism to explain the increase in ATBF (Fig. 2)
`and lipolysis (Figs. 4 and 5) adjacent to contracting muscles
`could be release of paracrine substances from the contracting
`muscles, which could diffuse from the muscle to the adipose
`tissue to stimulate blood flow and lipolysis. Contracting skel-
`etal muscle has been shown to release the myokine interleu-
`kin-6 (8), which among other things has been shown to stim-
`ulate adipose tissue lipolysis (18).
`It is evident that several potential mechanisms can explain
`the increased ATBF (Fig. 2) and lipolysis (Figs. 4 and 5) in
`adipose tissue adjacent to contracting muscles, but it is more
`difficult
`to understand the rationale for the increase. The
`muscle and the SCAT superficial to the muscle have separate
`blood supplies and drainages. Accordingly, fatty acids released
`from adipose tissue during exercise are transported to the heart
`and reach all parts of the body, not specifically the muscle
`beneath the subcutaneous tissue from which the fatty acids
`were released.
`In the present study, we measured changes in ATBF by two
`independent methods, the 133Xe washout technique (27) and
`the microdialysis [14C]ethanol outflow/inflow technique (25),
`and findings were similar (Fig. 2). Both methods showed a
`general increase in ATBF during exercise and that blood flow
`was higher in adipose tissue adjacent to contracting muscle
`than in adipose tissue adjacent to resting muscle. The 133Xe
`washout and the microdialysis ethanol outflow/inflow tech-
`niques have previously shown comparable results in adipose
`tissue during external heating of the skin (9).
`We found lipolysis to be higher in adipose tissue adjacent to
`contracting muscles than in adipose tissue adjacent to resting
`muscle (Figs. 4 and 5), but, in contrast to findings for ATBF
`(Fig. 2), we did not find a general exercise-induced increase in
`femoral adipose tissue lipolysis. Cycle exercise of moderate
`intensity increases lipolysis in abdominal SCAT (2, 14), but, in
`accordance with our findings, Horowitz et al. (14) found that
`exercise at 50% of V˙ O2 max did not increase femoral SCAT
`lipolysis. We examined femoral SCAT because this tissue has
`a contralateral tissue site that can be used as a control, which
`abdominal SCAT clearly do not.
`Reliability of techniques used in the study should be con-
`sidered. We placed the microdialysis probes and the 133Xe
`depot in the femoral SCAT equidistant from skin and muscle
`
`fascia. We did not measure the thickness of the femoral SCAT,
`but,
`in studies of similar subjects, we found the femoral
`skinfold to be ⬃10 –30 mm (unpublished results). We believe
`that measurements of lipolysis and blood flow in adipose tissue
`depots of this thickness are reliable. Theoretical predictions (7)
`suggest that a microdialysis probe estimates the metabolite
`concentration in a radius of a few millimeters from the probe,
`and probes thus should mirror adipose tissue metabolism and
`not metabolism in skin or muscle. In theory, also the 133Xe
`depot could come in contact with skin or muscle, but, if this
`had occurred, the washout curve for 133Xe would have become
`multiexponential, and this was not the case.
`More calories are expended during aerobic, whole body
`exercise than by exercise with local muscle groups, and,
`accordingly, a person seeking to loose fat must be advised to
`perform whole body exercise. However, the present study has
`shown that blood flow (Fig. 2) and lipolysis (Figs. 4 and 5) are
`stimulated more in adipose tissue adjacent to contracting mus-
`cles than in adipose tissue adjacent to resting muscles. The
`incremental femoral SCAT lipolysis (Fig. 5) showed no clear
`connection with exercise intensity and amounted to 22– 80
`nmol 䡠100 g⫺1 䡠min⫺1 during the first 30 min of the exercise
`bout. Assuming a molecular weight of 860 g/mol for TG, this
`corresponds to an extra breakdown of 0.6 –2.1 mg of TG in 30
`min/100 g of adipose tissue adjacent to contracting muscles.
`These figures are comparable to the increase in lipolysis
`induced by cycle exercise at 50% of V˙ O2 max, which was found
`to be ⬃50 nmol 䡠100 g⫺1 䡠min⫺1 in femoral SCAT and 200
`nmol 䡠100 g⫺1 䡠min⫺1 in abdominal SCAT (time 15– 40 min;
`see Ref. 14), corresponding to a breakdown of 1.3 and 5.2 mg
`of TG in 30 min/100 g of femoral and abdominal adipose
`tissue, respectively.
`In conclusion, an acute bout of exercise can induce spot
`lipolysis and increased blood flow in adipose tissue adjacent to
`contracting skeletal muscle.
`
`ACKNOWLEDGMENTS
`
`We highly appreciate the expert technical assistance of Thomas Beck, Jeppe
`Bach, and Regitze Kraunsøe.
`
`GRANTS
`
`The study was supported by The Danish Ministry of Culture Committee on
`Sports Research.
`
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