J Appl Physiol-2010-Krogh-Madsen-1034-40 by lanyuehua


									A 2-wk reduction of ambulatory activity attenuates
peripheral insulin sensitivity
Rikke Krogh-Madsen, John P. Thyfault, Christa Broholm, Ole Hartvig Mortensen,
Rasmus H. Olsen, Remi Mounier, Peter Plomgaard, Gerrit van Hall, Frank W. Booth and
Bente K. Pedersen
J Appl Physiol 108:1034-1040, 2010. First published 31 December 2009;
doi: 10.1152/japplphysiol.00977.2009

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J Appl Physiol 108: 1034–1040, 2010.
First published December 31, 2009; doi:10.1152/japplphysiol.00977.2009.

A 2-wk reduction of ambulatory activity attenuates peripheral insulin
              Rikke Krogh-Madsen,1 John P. Thyfault,2 Christa Broholm,1 Ole Hartvig Mortensen,1 Rasmus H. Olsen,1
              Remi Mounier,1 Peter Plomgaard,1 Gerrit van Hall,1 Frank W. Booth,3 and Bente K. Pedersen1
               Centre of Inflammation and Metabolism at Department of Infectious Diseases and Copenhagen Muscle Research Centre,
              Rigshospitalet, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark; 2Harry S. Truman Memorial
              Veterans Hospital, Health Activity Center, Departments of Nutrition and Exercise Physiology and Internal Medicine,
              University of Missouri, Columbia, Missouri; and 3Health Activity Center, Departments of Biomedical Sciences and of Medical
              Pharmacology and Physiology, University of Missouri, Columbia, Missouri
              Submitted 30 August 2009; accepted in final form 29 December 2009

    Krogh-Madsen R, Thyfault JP, Broholm C, Mortensen OH, Olsen                and at the low range may increase risk for developing chronic
RH, Mounier R, Plomgaard P, van Hall G, Booth FW, Pedersen BK.                 metabolic disease(s) (4). We postulated that healthy, nonexer-

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A 2-wk reduction of ambulatory activity attenuates peripheral insulin          cising subjects who transitioned from a high to low level of
sensitivity. J Appl Physiol 108: 1034 –1040, 2010. First published De-         ambulatory activity (from 10,000 to 2,000) would quickly
cember 31, 2009; doi:10.1152/japplphysiol.00977.2009.—US adults                display metabolic alterations. Our initial findings showed that
take between 2,000 and 12,000 steps per day, a wide range of
                                                                               healthy young men who reduced their daily steps from an
ambulatory activity that at the low range could increase risk for
developing chronic metabolic diseases. Dramatic reductions in phys-
                                                                               average of 10,501      808 to 1,344       33 for a 2-wk period
ical activity induce insulin resistance; however, it is uncertain if and       displayed a clustering of metabolic alterations including in-
how low ambulatory activity would influence peripheral insulin sen-             creased insulin response to an oral glucose tolerance test
sitivity. We aimed to explore if healthy, nonexercising subjects who           (OGTT), increased plasma triglyceride response to an oral fat
went from a normal to a low level of ambulatory activity for 2 wk              tolerance test, and a 7% increase in visceral fat (21). These
would display metabolic alterations including reduced peripheral               findings led us to question if the loss of insulin sensitivity
insulin sensitivity. To do this, ten healthy young men decreased their         induced by reduced ambulatory activity was due to peripheral
daily activity level from a mean of 10,501         808 to 1,344       33       or hepatic decreases in insulin sensitivity. Moreover, if there
steps/day for 2 wk. Hyperinsulinemic-euglycemic clamps with stable             was a decline in peripheral insulin sensitivity we questioned if
isotopes and muscle biopsies, maximal oxygen consumption                       it was associated with reduced activation of the insulin signal-
(VO2 max) tests, and blood samples were performed pre- and postint-            ing pathway in skeletal muscle as has been shown in rodent
ervention. A reduced number of daily steps induced a significant                models in which daily physical activity was ceased for acute
reduction of 17% in the glucose infusion rate (GIR) during the clamp.
                                                                               periods of time (16). We additionally wished to determine if
This reduction was due to a decline in peripheral insulin sensitivity
with no effect on hepatic endogenous glucose production. The insulin-
                                                                               reduced ambulatory activity would negatively impact lean
stimulated ratio of pAktthr308/total Akt decreased after step reduction,       body mass or cardiorespiratory fitness [maximal oxygen con-
                                                                               sumption (VO2 max)], two factors strongly linked to metabolic
with a post hoc analysis revealing the most pronounced effect after 4
h of insulin infusion. In addition, the 2-wk period induced a 7%               health and mortality risk. Herein we provide evidence that 2
decline in VO2 max (ml/min; cardiovascular fitness). Lean mass of legs,         wk of reduced daily ambulatory activity in healthy young,
but not arms and trunk, decreased concurrently. Taken together, one            nonexercising subjects decreases peripheral insulin sensitivity
possible biological cause for the public health problem of Type 2              and insulin stimulation of Akt in skeletal muscle without
diabetes has been identified. Reduced ambulatory activity for 2 wk in           change in rate of glucose appearance during a hyperinsuline-
healthy, nonexercising young men significantly reduced peripheral               mic-euglycemic clamp. In addition, we show evidence that
insulin sensitivity, cardiovascular fitness, and lean leg mass.                 reduced ambulatory activity significantly lowers both lean
insulin resistance; clamp; insulin signaling                                   body mass and cardiorespiratory fitness.
EPIDEMIOLOGICAL EVIDENCE indicates that low physical activity
                                                                                  Ethical approval. All subjects gave oral and written consent, and
plays a causal role in the development of Type 2 diabetes (11,                 the study was approved by the Scientific-Ethics Committee of Copen-
12, 17). Our longer-term hypothesis is that reductions in daily                hagen and Frederiksberg Municipalities (file no. KF01268925) in
ambulatory activity levels (reduced steps taken throughout the                 accordance with the Helsinki Declaration.
day) initiate attenuation in skeletal muscle insulin sensitivity                  Subjects. Ten healthy human males (mean age 23.8           1.5; body
that precedes a later development of overt insulin resistance. It              mass index of 22.1 0.7 kg/m2) participated in the study [reported in
is estimated that most free-living, nonexercising US adults take               a preliminary report (21)]. Before the study all 10 subjects underwent
between 2,000 and 12,000 steps per day, a wide range of                        a thorough clinical examination. All subjects were nonsmokers,
                                                                               asymptomatic, with no family history of diabetes, did not take med-
ambulatory activity that at the high range may decrease risk
                                                                               ications, and revealed no physical abnormalities during examination.
                                                                               All subjects had normal resting values of blood pressure, normal
  Address for reprint requests and other correspondence: R. Krogh-Madsen,      plasma levels of glucose, insulin, total cholesterol, low-density li-
Centre of Inflammation and Metabolism, Rigshospitalet-Section 7641, Blegdams-   poprotein (LDL) cholesterol, high-density lipoprotein (HDL) choles-
vej 9, DK-2100 Copenhagen, Denmark (e-mail: krogh-madsen@inflammation-          terol, and triglycerides (TG), normal hematological parameters in-
metabolism.dk).                                                                cluding leukocyte counts, and normal hepatic, thyroid, and renal
1034                                                                                                                                http://www.jap.org
                                             AMBULATORY ACTIVITY AND INSULIN SENSITIVITY                                                          1035
parameters. None of the participants performed planned exercise                HR variability, and ECG magnitude for epoch settings of 15, 30, and
sessions of 2 h/wk or walked 3,500 steps/day.                                  60 s and can be recorded for a set time. Data on interbeat intervals (IBI
   Study design. In a free-living environment, participants were in-           logging) and ECG waveforms can also be recorded. Acceleration is
structed to nightly record their daily steps (cycling not included) for 1      measured by a piezoelectric element within the Actiheart with a
inclusion-week and then reduce steps to 1,500 per day for 14 days              frequency range of 1–7 Hz (3 dB). For every participant, the Actiheart
(cycling not allowed). Step number was measured using a simple                 monitor was tested for adequate HR pickup by recording ECG
pedometer (Yamax Digi-Walker SW-200, London, UK); daily phys-                  waveforms for 30 s before the rest test. If pickup was adequate, the
ical activity was also monitored by an Actiheart monitor (Cambridge,           Actiheart was set up to record HR and movement continuously for 1
UK). Subjects did not exercise more than 2 h/wk on a recreational              wk, after which it was reloaded for the rest of the study period.
level. Subjects who walked less than 3,500 steps per day or performed             Fat and fat-free tissue masses for the whole body, trunk, and
regular exercise were excluded. All subjects agreed to refrain from            extremities were measured using a dual-energy X-ray absorptiometry
vigorous physical activity and only performed physical activity cor-           (DXA) scanner, Lunar Prodigy Advance (GE Healthcare, Madison,
responding to their normal routines, for 2 days preceding the first test        WI) (21).
day. The number of steps was registered every night at bedtime.                   Hyperinsulinemic-euglycemic clamps were performed after an
Dietary records were taken during the inclusion-week. The subjects             overnight fast (Fig. 1). Peripheral catheters were placed in an ante-
carefully noticed what they consumed day by day, and they main-                cubital vein for blood sampling, in the contralateral antecubital vein
tained their usual dietary habits during the whole study. Subjects were        for infusion of glucose, insulin, and stable isotopes, and in a dorsal
not allowed to consume alcohol 2 days preceding the first test and              hand vein for blood sampling; the catheterized hand was wrapped in

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during the study period. Participants agreed to weigh and register             a heating blanket to obtain arterialized venous blood for measurement
consumed food the day before pre- and post-insulin clamp and the               of glucose and potassium during the clamp. The experiment was
VO2 max tests. Figure 1 illustrates testing times.                             commenced by priming the glucose pool by administrating a bolus of
   Determinations. An incremental exercise test was performed on a             17.5 mol/kg of [6,6-2H2]glucose (Cambridge Isotopes Laboratories).
cycle ergometer (Monark 839E, Monark Ltd, Varberg, Sweden) to                  This was followed by a continuous infusion (rate 0.4 mol·kg 1·min 1)
obtain VO2 max for each participant with indirect calorimetry system           for 2 h before the start of the clamp.
(Moxus modular VO2 system, AEI Technologies, Pittsburgh, PA) as                   Insulin (Actrapid, Novo Nordisk Insulin, 100 IE/ml) was infused
previously described (1). Preceding the study, subjects performed a            continuously at a rate of 40.0 mU·min 1·m 2, and the plasma glucose
familiarization test.                                                          concentration was kept at 5.0 mM by a coinfusion of glucose (200
   The Actiheart monitor [used to measure daily energy expenditure             g/1,000 ml, enriched with [6,6-2H2]glucose to 2.5%) at a variable rate.
(7)] is attached to the chest with two standard electrocardiogram              During the 4-h clamps the infusion rate of [6,6-2H2]glucose was
(ECG) electrodes and is able to measure acceleration, heart rate (HR),         reduced to 0.08 mol·kg 1·min 1. Arterialized blood was analyzed

                                                                                                             Fig. 1. Experimental design. Time lines of
                                                                                                             the study (A) and of the hyperinsulinemic-
                                                                                                             euglycemic clamp (B). VO2 max, maximal ox-
                                                                                                             ygen consumption; DXA, dual-energy X-ray

                                                   J Appl Physiol • VOL   108 • MAY 2010 •   www.jap.org
1036                                            AMBULATORY ACTIVITY AND INSULIN SENSITIVITY

for glucose and potassium concentrations at intervals of 5 min during            from a baseline of 10,000 per day, as published previously
the first hour, and every 10 min during the last 3 h of the clamp. Blood          (21), resulting in reduced energy expenditure (kJ/day; esti-
samples were collected in heparin-containing tubes and immediately               mated by Actiheart) from a mean of 5,020 515 to 3,010
centrifuged for 15 min at 3,500 rpm, and the plasma was stored at                294 kJ/day. The decline in number of steps from baseline to 2 wk
  20°C until further analysis.
   The plasma glucose enrichment was measured as previously de-
                                                                                 significantly correlated with the decline in daily energy expenditure
                                                                                 (kJ/day) (r 0.922; P 0.001), and decline in VO2 max (ml/min)
scribed (23). The glucose turnover rate of appearance (Ra) and rate of
                                                                                 (r 0.960; P 0.001) or VO2 max (ml·min 1·kg 1) (r 0.921; P
disappearance (Rd) were calculated assuming steady state:
                                                                                 0.01) (Table. 1).
          baseline: Ra Rd                                                           Cardiovascular fitness and body composition (DXA). A
                                 Eglucose                                        significant 7.2% and 6.6% decline was observed in VO2 max    ˙
                                     Ftotal               Ftotal                 (ml/min and ml·min 1·kg 1, respectively) following reduced
          clamp: Ra endogenous                 GIR, Rd                           stepping (Table 2). Lean mass of legs, but not arms or trunk,
                                    Eglucose             Eglucose
                                                                                 also decreased significantly after reduced ambulatory activity
where Finfusion is the infusion rate of glucose tracer ( mol·kg 1·min 1)         (Table 2). The decline in number of steps from baseline to 2 wk
in terms of lean body mass; Eglucose is the enrichment of glucose in             did not correlate with the decline in lean mass of the legs
plasma; Ftotal is the sum of Finfusion; and the [6,6-2H2]glucose infused by      (Table 1). There was no change in total fat mass (21).
the clamp; GIR is the glucose infusion rate; and kilograms refers to lean
                                                                                    Metabolism. GIR during the 240-min clamp significantly

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body mass.
    Baseline blood samples were obtained before initiation of the stable         declined 17% after 2 wk of reduced stepping (pretesting
isotope infusion (time point 2 h, Fig. 1). Glucose, triglyceride (TG),           6.29      0.62 mg·kg 1·min 1; posttesting             5.22     0.54
and free fatty acids (FFA) were measured with an automatic analyzer              mg·kg 1·min 1) (Fig. 2A). Plasma glucose was kept at 5.0
(Cobas Fara, Roche, Basel, Switzerland); insulin and C-peptide by                mM during the clamps (pretesting          4.96      0.05 mM; post-
ELISA (DAKO, Glostrup, Denmark); tumor necrosis factor- (TNF- ),                 testing 4.92      0.08 mM) (Fig. 2B). Reduced stepping also
interleukin (IL)-6, IL-15, and leptin by ELISA (R&D Systems); and                resulted in reduced insulin-stimulated glucose disappearance
adiponectin by a RIA kit (LINCO Research).                                       rate (Rd) (an index of decreased peripheral insulin sensitivity),
    Vastus lateralis muscle biopsies were taken before and 1 and 4 h             but did not change endogenous hepatic glucose production rate
after the starting of the clamp. Muscle was quickly frozen in liquid
                                                                                 (Ra) (Fig. 2C) or basal glucose turnover (data not shown).
nitrogen and stored at 80°C until later analysis. Muscle tissue was
homogenized in ice-cold buffer containing protease inhibitors and                Calculations for glucose metabolism were performed during
phosphatase inhibitors as previously referenced (13, 29). Insulin                steady-state euglycemia (120 –240 min of clamp).
receptor (IR ), phosphorylation of Akt at threonine 308 (pAktthr308), total         There was no significant difference in baseline values pre-
Akt, phosphorylation of AS160 (pAS160), and AS160 total content                  and postintervention with regard to plasma levels of TG, FFA,
were performed as referenced previously (29). Regarding tyrosine                 glucose, insulin, and C-peptide (Table 2). The decline in
phosphorylation of IR (pTyIR ), muscle homogenate was incubated                  number of steps from baseline to 2 wk did not correlate with
overnight with anti-phosphotyrosine agarose beads (Sigma). Both                  the decline in GIR (Table 1).
immunoprecipitates and muscle homogenates were separated by SDS-                    Insulin signaling. Insulin stimulation increased ratios of
PAGE and transferred to PVDF membranes before probing with                       phosphorylated to total protein for both Akt protein (pAktthr308/
appropriate antibodies. The protein bands were detected using Super-
signal West femto (Pierce, Rockford, IL, USA) or enhanced chemi-
                                                                                 total Akt) and AS160 protein (pAS160/total AS160) in the
luminescence (Amersham Biosciences, UK) and quantified using a                    vastus lateralis muscle at 1 and 4 h of the clamp compared with
CCD image sensor and software (Quantity One, Bio-Rad, CA).                       baseline (time point 0 h) (P       0.05 for all comparisons), but
    Total RNA was extracted and analyzed from skeletal muscle using              not for IR protein (pTyIR /total IR ) (Fig. 3). Reduced
previously referenced methods (15). The primers and probes for                   stepping led to a significant reduction in insulin-stimulated
TNF- and 18S rRNA were predeveloped TaqMan probes and primer                     pAktthr308/total Akt (pre- vs. postintervention) at the 4th hour
sets from Applied Biosystems (Foster City, CA). The relative expres-             of clamp (P 0.03) (Fig. 3) and although pAS160/total AS160
sion of TNF- was normalized to endogenous 18S.                                   and pTyIR /total IR signaling tended to decrease from pre-
    Statistical analyses. Data were tested for normal distribution by the        vs. postintervention, the changes were not significant (Fig. 3).
Kolmogorov-Smirnov analysis. Variables were analyzed using para-
                                                                                    Inflammation. Baseline (time point 2 h) plasma levels of
metric methods (paired t-tests; pre vs. post) on the absolute data, and
reported values are means SE. Correlations were determined with                  TNF, IL-6, IL-15, leptin, and adiponectin (Table 2) and skel-
a Pearson correlation test. All Western blots were normally distributed
when log-transformed before analysis and then analyzed using para-
metric methods and expressed as geometric mean (95% confidence                    Table 1. Correlation coefficients
interval). Within-subject variation over time and variation between
trials were analyzed using repeated-measures (2-way ANOVA, time-                                                                             Daily Steps
by-trial). If a significant interaction (time trial) was found, Bonfer-
                                                                                               Physiological Variables                 r                   P value
roni-corrected P values were obtained as appropriate to identify
significant differences between trials and to identify significant dif-              Daily energy expenditure, kJ/day                  0.922                  0.001
ferences from baseline values. P          0.05 was considered statistically        ˙
                                                                                   VO2max, ml·kg 1·min 1                             0.921                  0.01
                                                                                   VO2max, ml/min                                    0.960                  0.001
significant. Analysis was performed using a statistical software pack-
age (SAS version 9.1.3 SAS Institute).                                             Leg lean mass. kg                                 0.262                  NS
                                                                                   Glucose infusion rate, mg·kg 1·min    1
                                                                                                                                     0.225                  NS
RESULTS                                                                             Pearson correlation coefficients (r) are given between in daily steps and
                                                                                 in physiological variables, where represents a decrease from pre- to postint-
  Pedometer and Actiheart data. For a 2-wk period, partici-                                                                                  ˙
                                                                                 ervention. No other but the mentioned factors correlated. VO2max, maximal
pants reduced the number of daily steps by more than 85%                         oxygen consumption; NS, nonsignificant; n 10.

                                                     J Appl Physiol • VOL   108 • MAY 2010 •   www.jap.org
                                                 AMBULATORY ACTIVITY AND INSULIN SENSITIVITY                                                   1037
Table 2. Pre- and post-2-wk intervention results                                  ity. A remaining question to be answered is whether reduced
                                                                                  ambulatory activity either increases susceptibility to or is a
                               Preintervention     Postintervention
                                                                                  necessary component of insulin resistance. There is strong
       Measurement            Mean         SE      Mean        SE     P Value     support for the latter suggestion as high-fat diet-induced insulin
VO2max test                                                                       resistance or obesity-associated insulin resistance does not
  VO2max, ml/min            3,435       149      3,194       130       0.01       normally occur in skeletal muscle when a sufficient level of
  VO2max, ml·min 1·kg 1        47.7       1.3       45.1       1       0.01       increased physical activity or acute exercise is imposed (19, 22,
  Maximal power, W            259        11        243        11       0.01       26, 29), and epidemiological evidence clearly shows that re-
  Maximal HR, beats/min       194         3        193         4       NS
DXA scan                                                                          duced physical activity is a major risk for Type 2 diabetes
  Total body mass, kg           70.9       1.9      69.7        2      0.001      while high activity levels is protective (11, 12, 17).
  Trunk lean mass, kg           26.3       0.8      25.6        0.6    NS            Previous studies have shown that acute, 7-day exercise
  Arm lean mass, kg              6.7       0.3       6.7        0.3    NS         protocols dramatically improve insulin sensitivity (10, 27).
  Leg lean mass, kg             18.6       0.5      18.1        0.5    0.001
                                                                                  However, the ability of increased physical activity (7 days of
  Glucose, mmol/l               5.39   0.11     5.26   0.11            NS         exercise) to improve insulin sensitivity is blocked if subjects
  Insulin, pmol/l              31.9    3.7     31.8    3.6             NS         are maintained in an energy balance by consuming postwork-
  C-peptide, pmol/l           337.6   27.5    335.4   22.6             NS         out calories that match the amount of calories expended in each
  FFA, mmol/l               1,001    199    1,266    430               NS         daily exercise bout (3). This evidence strongly suggests that the

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  TG, mol/l                   617     56      647     47               NS
  TNF, pg/ml                    1.31   0.13     1.38   0.16            NS         ability of increased activity to improve insulin action is linked
  IL-6, pg/ml                   0.79   0.22     1.02   0.19            NS         to acutely induced energy deficits. Because the subjects in the
  IL-15, pg/ml                  1.29   0.1      1.27   0.2             NS         present study maintained the same caloric intake but dramati-
  Adiponectin, ng/ml        5,056    803    4,841    812               NS         cally lowered their daily activity it is likely that they were in a
  Leptin, pg/ml             2,334    389    2,676    410               NS
                                                                                  state of positive energy balance. This concept is contradicted
   VO2max test results, dual-energy X-ray absorptiometry (DXA) scans, and         by the evidence that subjects had a 1.6% reduction in total
plasma concentrations on lipid and glucose metabolism as well as inflamma-         body mass. That being said, if the subjects were in a positive
tion are shown. Total lean mass decreased significantly post-2 wk intervention
vs. preintervention (see Ref. 21). HR, heart rate, FFA, free fatty acids; TG,
                                                                                  energy balance, it is likely that this excess energy played a role
triglycerides. n 10.                                                              in the loss of peripheral insulin sensitivity after reduced step-
                                                                                  ping. A followup study could examine this link by having one
                                                                                  group of subjects consume a reduced caloric intake that
etal muscle TNF mRNA and protein expression (data not                             matches the reduction in energy expenditure that occurs after
shown) were not affected by 2 wk of reduced daily stepping.                       reducing daily stepping from 12,000 to 2,000 steps. This type
                                                                                  of design would not only help to define the role of energy
                                                                                  balance on insulin resistance induced by reduced stepping but
   Major novel findings of this study were that 2 wk of reduced                    would also help to determine the impact of positive energy
daily ambulatory activity in a free-living condition resulted in                  balance on the loss of total body mass and lean body mass that
decreases in insulin-stimulated muscle Akt phosphorylation,                       was witnessed.
peripheral insulin sensitivity, leg lean mass, and VO2 max in                        Although we provide novel evidence that acutely reducing
young healthy men who had not been previously exercise                            ambulatory activity negatively impacts insulin sensitivity, pre-
trained. As shown by others in previous studies, the later three                  vious examinations have found that exercise cessation in en-
aforementioned decreases are primary decrements that can lead                     durance athletes has a similar impact. Heath et al. (9) showed
to chronic metabolic disorders and premature mortality.                           that 10 days of exercise cessation in endurance athletes dra-
   Importantly, the experimental design, used here, models the                    matically increased insulin responses to an OGTT. A similar
extremes [ 2,000 to 12,000 (4)] in numbers of daily steps in                      result was witnessed in master endurance athletes ( 61 yr old)
the majority of free-living adults in developed countries, most                   who ceased exercise training for 10 days (25). King et al. (14)
of whom do not partake in structured exercise programs (4).                       showed that endurance athletes who cease training for 10 days
Therefore, the present study is distinctly different from previ-                  have a reduction in peripheral insulin sensitivity measured by
ous studies in which nontypical and extreme changes in activ-                     hyperinsulinemic-euglycemic clamp. They further determined
ity levels were deployed including continuous bed rest in                         that this was due to a loss of insulin sensitivity and not a total
which subjects are not allowed to stand or walk (8) and                           loss of insulin responsiveness as a much larger infusion of
detraining studies in which intense structured-exercise pro-                      insulin actually sustained insulin sensitivity after 10 days of
grams ceased (2, 18). Furthermore, subjects served as their                       exercise cessation. In a study from another group, the cessation
own control, eliminating potential gene differences that might                    of exercise in endurance athletes for only 60 h lowered insulin
occur by comparing separate groups of active and less active                      sensitivity to what was measured in sedentary age-matched
subjects.                                                                         controls (6). Similar results have been found in rodents. Kump
   The attenuation of peripheral insulin sensitivity after 2 wk of                and Booth (16) have shown that rats allowed daily access to
the decreased ambulatory activity occurred without any detect-                    voluntary running wheels for 3 wk (average daily run distance
able alteration in endogenous hepatic glucose production, im-                     equaled 5.7 km) display rapid losses of insulin-stimulated
plying that a peripheral decrement in insulin sensitivity is                      glucose uptake and insulin signaling in skeletal muscle after
primary to hepatic insulin resistance on reductions in daily                      their daily running was inhibited by wheel lock for only 2
stepping. These findings further reinforce the dogma that                          days (53 h).
glucose entry is exquisitely matched with substrate usage in                         Although the evidence that exercise cessation or reduced
skeletal muscle, in part by modulating muscle insulin sensitiv-                   ambulatory activity leads to a rapid decline in skeletal muscle

                                                      J Appl Physiol • VOL   108 • MAY 2010 •   www.jap.org
1038                                                AMBULATORY ACTIVITY AND INSULIN SENSITIVITY

Fig. 2. Glucose values during hyperinsuline-
mic-euglycemic clamp. A: glucose infusion rate
(GIR) during the euglycemic clamp. B: blood
glucose concentration just before (time point 0)
and during the euglycemic clamp. C: area un-
der the curve (AUC) for glucose rate of appear-
ance (Ra) and rate of disappearance (Rd) during
the euglycemic clamp (120 –240 min). *Signif-
icant difference between preintervention (Pre)
and postintervention (Post) (paired t-test, P
0.01) Preintervention is before reduced daily
steps; postintervention is final 3 days of 14-day

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period of reduced daily steps. , Preinterven-
tion determination; , postintervention deter-
mination; filled bars, preintervention determina-
tion; open bars, postintervention determination.
Data are presented as mean SEM. n 10.

insulin sensitivity in human and animal models is very strong,                        most common experimental model for studying insulin resis-
it remains underappreciated as an initiator of metabolic disease                      tance is acute and long-term high-fat diets, which, as we have
and an underused model to study initial declines in insulin                           already stated, appear to be effective in sedentary conditions
sensitivity that likely precede overt insulin resistance. The                         only. A recent study by Brons et al. (5) showed that a 5-day

Fig. 3. Insulin signaling in skeletal muscle during
hyperinsulinemic-euglycemic clamp. Akt, AS160, and
insulin receptor (IR)- protein content and phosphor-
ylation (p) were examined in biopsies taken from
vastus lateralis muscle pre- and post-euglycemic
clamp. Muscle biopsies were obtained at time points 0
h (before insulin clamp) and 1 h and 4 h (after initiation
of insulin clamp); labels on x-axis indicate these times.
Labels on y-axis indicate: phosphorylation of IR beta
expressed relative to IR protein (A); phosphorylation
of Akt at threonine308 expressed relative to Akt pro-
tein (B); phosphorylation of AS160 expressed relative
to AS160 protein (C); and representative immunoblots
of signaling proteins. pTYIR , tyrosine phosphory-
lated IR . Data are expressed as geometric means
(95% confidence interval). *Post hoc analysis, P
0.03 (difference between pre- and postintervention). **Post
hoc analysis, P 0.05 (different from 0 h). n 10.

                                                          J Appl Physiol • VOL   108 • MAY 2010 •   www.jap.org
                                                   AMBULATORY ACTIVITY AND INSULIN SENSITIVITY                                                                   1039
high-fat/high-calorie diet in young healthy men (daily activity                       REFERENCES
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believed to be a primary initiator of many chronic diseases                               ing and dietary protein: effects on glucose tolerance and contents of
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ACKNOWLEDGMENTS                                                                           Wikstrom K, Aunola S, Keinanen-Kiukaanniemi S, Laakso M, Valle
   All authors have contributed to the conception and design, or the analysis             TT, Ilanne-Parikka P, Louheranta A, Hamalainen H, Rastas M,
and interpretation of data; the drafting of the article or revising of the article;       Salminen V, Cepaitis Z, Hakumaki M, Kaikkonen H, Harkonen P,
and the final approval of the version of the article to be published.                      Sundvall J, Tuomilehto J, Uusitupa M. Physical activity in the preven-
   Ruth Rousing and Hanne Villumsen are acknowledged for technical assis-                 tion of type 2 diabetes: the Finnish diabetes prevention study. Diabetes 54:
tance.                                                                                    158 –165, 2005.
                                                                                      18. Mikines KJ, Sonne B, Tronier B, Galbo H. Effects of acute exercise and
GRANTS                                                                                    detraining on insulin action in trained men. J Appl Physiol 66: 704–711, 1989.
                                                                                      19. Morris RT, Laye MJ, Lees SJ, Rector RS, Thyfault JP, Booth FW.
   The study was supported by the Commission of the European Communities                  Exercise-induced attenuation of obesity, hyperinsulinemia, and skeletal muscle
(contract no. LSHM-CT-2004-005272 EXGENESIS) and by grants from the                       lipid peroxidation in the OLETF rat. J Appl Physiol 104: 708–715, 2008.
Augustinus Foundation, The Novo Nordisk Foundation, and from Unilever.
                                                                                      20. Newman AB, Kupelian V, Visser M, Simonsick EM, Goodpaster BH,
R. H. Olsen received a scholarship from the Danish Research Council. The
                                                                                          Kritchevsky SB, Tylavsky FA, Rubin SM, Harris TB. Strength, but not
Centre of Inflammation and Metabolism is supported by a grant from the
                                                                                          muscle mass, is associated with mortality in the health, aging and body
Danish National Research Foundation (DG 02-512-555).
                                                                                          composition study cohort. J Gerontol A Biol Sci Med Sci 61: 72–77, 2006.
                                                                                      21. Olsen RH, Krogh-Madsen R, Thomsen C, Booth FW, Pedersen BK.
                                                                                          Metabolic responses to reduced daily steps in healthy nonexercising men.
   No conflicts of interest are declared by the authors.                                   JAMA 299: 1261–1263, 2008.

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                                                        J Appl Physiol • VOL   108 • MAY 2010 •   www.jap.org

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