Effect of energy expenditure on postprandial triacylglycerol in adolescent boys

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<ul><li><p>ORIGINAL ARTICLE</p><p>Effect of energy expenditure on postprandial triacylglycerolin adolescent boys</p><p>Keith Tolfrey Conor Bentley Mary Goad </p><p>Joanna Varley Sebastian Willis Laura Barrett</p><p>Received: 21 December 2010 / Accepted: 18 March 2011 / Published online: 6 April 2011</p><p> Springer-Verlag 2011</p><p>Abstract This study examined the effects of 30 and</p><p>60 min of moderate intensity exercise on postprandial</p><p>triacylglycerol concentration [TAG] in 11 healthy, 13-year-</p><p>old boys. The boys completed three counterbalanced</p><p>conditions. On day 1, they either rested (CON), or jogged</p><p>for 30 min (EX30) or 60 min (EX60) at 55% peak _VO2:</p><p>Following a 12-h fast, on day 2 a capillary blood sample</p><p>was taken for fasting [TAG] before a high fat milkshake</p><p>was consumed. Further blood samples were taken every</p><p>hour over a 6-h postprandial rest period for [TAG]. The</p><p>estimated energy expenditure for EX30 (982 kJ) was</p><p>doubled in EX60 (1967 kJ). Differences in fasting [TAG]</p><p>between the conditions were small (ES = 0.23, P = 0.35).</p><p>Differences in postprandial TAG over time between</p><p>conditions were identified (ES = 0.41, P = 0.03). Mean</p><p>[TAG] was lower in EX60 than CON (-33 to -3%,</p><p>P = 0.03) with a similar strong trend for EX30 (-29 to</p><p>1%, P = 0.06); EX60 and EX30 were not different from</p><p>each other (-21 to 14%, P = 0.62). The total area under</p><p>the [TAG] versus time curve was different between con-</p><p>ditions (ES = 0.42, P = 0.03). Again, EX60 was lower</p><p>than CON (-31 to -2%, P = 0.02) with a strong trend for</p><p>EX30 (-31 to 4%, P = 0.06); EX30 and EX60 were not</p><p>different from each other (-17 to 16%, P = 0.58). This</p><p>study shows for the first time that both 30 and 60 min of</p><p>jogging, with energy expenditures equivalent to 982 and</p><p>1,967 kJ, attenuates postprandial [TAG] in adolescent</p><p>boys, but not in a dose-dependent manner.</p><p>Keywords TAG Intermittent exercise 30 min PPL</p><p>Introduction</p><p>The evidence supporting the paediatric origins of athero-</p><p>sclerosis are compelling (Malcom et al. 2009) and</p><p>long-standing (Zeek 1930). This has prompted calls for</p><p>preventive steps to be taken during childhood (Froberg and</p><p>Andersen 2005). Postprandial plasma triacylglycerol con-</p><p>centration ([TAG]) has a strong independent relationship</p><p>with cardiovascular events in adult population studies</p><p>(Bansal et al. 2007; Nordestgaard et al. 2007; Sarwar et al.</p><p>2010). In contrast, similar independent associations with</p><p>fasting [TAG] have not been reported so consistently</p><p>(Sarwar et al. 2007), highlighting the importance of the</p><p>postprandial period. There is a dearth of research on the</p><p>postprandial lipaemic response to exercise in young people.</p><p>Consequently, the identification of effective intervention</p><p>strategies to reduce postprandial [TAG] in young people is</p><p>critical.</p><p>Several reviews of studies with adults have indicated that</p><p>aerobic exercise-induced energy expenditure (EE) reduces</p><p>postprandial [TAG] (Hardman 1998; Petitt and Cureton</p><p>2003; Katsanos 2006). Two recent separate studies with</p><p>lean and obese adults, respectively, found that exercise EE</p><p>of only 1.10 and 0.87 MJ (*262 and 208 kcal) wererequired to reduce [TAG] significantly compared with a</p><p>non-exercise control condition (Miyashita et al. 2008;</p><p>Miyashita 2008). Moreover, the efficacy was achieved</p><p>equally by accumulation or continuous exercise EE models.</p><p>In stark contrast, similarly designed exercise interventions</p><p>Communicated by Klaas R Westerterp.</p><p>K. Tolfrey (&amp;) C. Bentley M. Goad J. Varley S. Willis L. BarrettPaediatric Exercise Science Research Group, School of Sport,</p><p>Exercise and Health Sciences, Loughborough University,</p><p>Loughborough, Leicestershire LE11 3TU, UK</p><p>e-mail: k.tolfrey@lboro.ac.uk</p><p>123</p><p>Eur J Appl Physiol (2012) 112:2331</p><p>DOI 10.1007/s00421-011-1936-x</p></li><li><p>have been restricted to only three studies with adolescents</p><p>boys as far as we are aware (Barrett et al. 2007; Tolfrey</p><p>et al. 2008; MacEneaney et al. 2009). Each of these studies</p><p>reported attenuated postprandial [TAG] following the</p><p>exercise interventions. The minimum estimated exercise EE</p><p>across the conditions used in these studies was *1.5 MJ(*366 kcal; Tolfrey et al. 2008). The overweight, late-adolescent boys in the MacEneaney et al. (2009) study</p><p>experienced a similar reduction (*20%) in postprandial[TAG] as normal weight boys.</p><p>Previously, we compared 60-min bouts of moderate and</p><p>vigorous intensity intermittent exercise, but did not identify</p><p>a dose-dependent effect with both bouts leading to similar</p><p>reductions (*22%) compared with a non-exercise control(Tolfrey et al. 2008). We chose 60 min of exercise because</p><p>international guidelines for recommended daily physical</p><p>activity for adolescents tend to range from 60 to 90 min,</p><p>depending on the participant characteristics and country of</p><p>origin (e.g. Department of Health, Physical Activity,</p><p>Health Improvement and Prevention 2004; Janssen and</p><p>LeBlanc 2010). In light of previous findings, the purpose of</p><p>the current study was to reduce the exercise time to only</p><p>30 min in an attempt to identify the lowest dose of mod-</p><p>erate exercise intensity EE that could still reduce post-</p><p>prandial [TAG] in healthy, though not endurance trained,</p><p>adolescent boys. This reduction in exercise time represents</p><p>a significant and important advance in research with young</p><p>people in this area.</p><p>Methods</p><p>Participants</p><p>Eleven adolescent boys volunteered for this study after</p><p>giving their written assent; written informed consent was</p><p>also provided by a parent for each boy. The university</p><p>ethical advisory committee approved all of the study pro-</p><p>cedures. A general health questionnaire showed that they</p><p>were all in good health, not taking any substances known to</p><p>influence fat or carbohydrate metabolism, and physically</p><p>active through participation in sports, but not engaged in</p><p>specific endurance training. Baseline participant charac-</p><p>teristics are shown in Table 1.</p><p>Anthropometry and physical maturation</p><p>Body mass (Seca, Hamburg, Germany) and stature (Holtain,</p><p>Crosswell, UK) were measured with the boys wearing run-</p><p>ning shorts, socks, and T-shirt. Triceps and subscapular</p><p>skinfold thickness was measured using Harpenden callipers</p><p>(John Bull, St. Albans, UK) on the right hand side of the</p><p>body with the median of three measurements calculated as</p><p>the fold thickness. Triceps and subscapular skinfold thick-</p><p>nesses were used to estimate percent body fat (BF%) using</p><p>maturation, race, and sex-specific equations (Slaughter et al.</p><p>1988). A self-assessment of secondary sexual characteristics</p><p>by the boys was used to estimate physical maturity. The</p><p>boys used drawings of the five stages of genitalia and pubic</p><p>hair development to provide this information (Morris and</p><p>Udry 1980). The parents were asked to assist the boys with</p><p>this assessment by (1) discussing the schematic illustrations</p><p>with them, and (2) comparing their sons genital and pubic</p><p>hair development with the schematics and accompanying</p><p>written descriptions.</p><p>Preliminary exercise measurements</p><p>Before the main trials, the boys were habituated to exercise</p><p>on the treadmill (Technogym Runrace, Gambettola, Italy)</p><p>set at 1% gradient. Next, 4 3 4 min incremental exercise</p><p>stages were used to identify the steady-state relationship</p><p>between treadmill speed, oxygen uptake ( _VO2), and heart</p><p>rate. The starting speed was 6.5 with 0.5 km h-1 incre-</p><p>ments up to 8.0 km h-1. Heart rate (HR) was monitored</p><p>continuously via radio telemetry (Polar PE4000, Kempele,</p><p>Finland) whenever the boys exercised on the treadmill, and</p><p>ratings of perceived exertion (RPE) were measured using</p><p>the 620 scale (Borg 1974) in the final 15 s of each exer-</p><p>cise bout. Expired gas samples were collected into 100-L</p><p>Douglas bags (Cranlea and Company, Birmingham, UK)</p><p>during the final minute of each progressive bout. Oxygen</p><p>and carbon dioxide concentrations in each Douglas bag</p><p>were analysed using a paramagnetic oxygen analyser and</p><p>an infrared carbon dioxide analyser (Servomex 1400,</p><p>Sussex, UK) calibrated against gases of known concen-</p><p>tration before and after each series of four bags. The vol-</p><p>ume of expired gas was determined using a dry gas meter</p><p>(Harvard, Kent, UK). For each sample, oxygen uptake</p><p>( _VO2), expired carbon dioxide ( _VCO2), minute ventilation</p><p>( _VE), and respiratory exchange ratio were calculated. These</p><p>Table 1 Physical and physiological characteristics</p><p>Age (years) 13.3 (0.8)</p><p>Genital developmenta 3 2</p><p>Body mass (kg) 51.3 (14.6)</p><p>Stature (m) 1.64 (0.14)</p><p>Body mass index (kg-1 m2) 18.6 (2.6)</p><p>Percent body fat (%) 14.6 (4.1)</p><p>Lean body mass (kg) 43.6 (12.1)</p><p>Peak _VO2 (mL kg-1min-1) 53.6 (6)</p><p>All values are mean (SD) where n = 11</p><p>_VO2oxygen uptakea Self-assessmentmedian (interquartile range)</p><p>24 Eur J Appl Physiol (2012) 112:2331</p><p>123</p></li><li><p>submaximal _VO2 data were used subsequently to (1)</p><p>choose an appropriate speed for each individual at which</p><p>their peak _VO2 could be determined (below) and (2) to</p><p>establish the speed required to elicit 55% peak _VO2 for the</p><p>two experimental exercise conditions described below.</p><p>Peak oxygen uptake (peak _VO2)</p><p>After a standardised 10-min rest period, peak _VO2 was</p><p>determined with each boy running at a fixed individual</p><p>speed (911 km h-1), while the treadmill belt was raised</p><p>by 1% each minute until volitional exhaustion. Oxygen</p><p>uptake, HR, and RPE were measured using the methods</p><p>described previously. The boys were asked to run until</p><p>volitional exhaustion, which was verified using the fol-</p><p>lowing criteria: (1) a plateau in _VO2 (B3%) with an</p><p>increase in treadmill gradient; (2) a maximum heart rate</p><p>(HRmax) C 95% of age-predicted maximum (220chro-</p><p>nological age); and (3) respiratory exchange ratio C1.10.</p><p>Experimental design</p><p>A within-measures, counterbalanced crossover design was</p><p>used in which the boys completed three separate condi-</p><p>tions, each separated by a standardised 14-day period.</p><p>A 2-day model was used similar to our previous study</p><p>(Tolfrey et al. 2008). A schematic representation of the</p><p>design is shown in Fig. 1.</p><p>Day 1</p><p>On the first day, the boys either (a) rested in the laboratory</p><p>for 110 min (CON); (b) completed 60 min of intermittent</p><p>treadmill exercise (EX60); or (c) completed 30 min of</p><p>intermittent treadmill exercise (EX30). The exercise was</p><p>designed to be of moderate intensity and to elicit *55%peak _VO2. An intermittent exercise model was used because</p><p>initial pilot work with the boys indicated that they preferred</p><p>to complete it in this manner, and some suggested that they</p><p>might not be able to exercise continuously for 60 min. The</p><p>boys arrived at the laboratory at 15:30 h on each occasion,</p><p>and each condition was completed at 17:30 h on day 1. The</p><p>30 and 60 min bouts of exercise were completed in 3 or</p><p>6 3 10 min blocks separated by passive rest periods ofequal duration. During each 10-min interval of exercise,</p><p>samples of expired gas were collected in the fourth and</p><p>tenth minute and analysed using the procedures described</p><p>previously to verify the relative exercise intensity. Subse-</p><p>quently, assuming that the urinary nitrogen excretion rate</p><p>was negligible and that the participants had reached a</p><p>physiological steady state, these samples were used to</p><p>estimate exercise EE and the oxidation of carbohydrate and</p><p>fat (Frayn 1983). The treadmill speed was adjusted peri-</p><p>odically throughout each condition in an effort to match the</p><p>target exercise intensity (Table 2). Heart rate was recorded</p><p>continuously and RPE was recorded during the last 15 s of</p><p>each expired air sampling period as described previously.</p><p>Day 2</p><p>Following a standardised 12-h overnight fast, the boys were</p><p>driven to the laboratory. After providing an initial fasting</p><p>capillary blood sample at *07:55, a high fat test milkshakewas consumed within 10 min and then six further blood</p><p>samples were taken at hourly intervals (Fig. 1). The timing of</p><p>the postprandial period commenced when the boys started</p><p>consuming the milkshake (08:00) and was standardised so</p><p>that it occurred *14.5 h after completion of the treadmillexercise or rest period the previous day. During this post-</p><p>prandial period, the boys were asked to remain seated</p><p>throughout whilst they read, played on a non-active computer</p><p>games console or watched DVD films. One-and-half litres of</p><p>plain water was provided, and the boys were asked to drink</p><p>this in small quantities divided equally over the 6 h.</p><p>Standardisation of diet, physical activity, and milkshake</p><p>With parental assistance, the boys recorded their food</p><p>and drink intake and all physical activities in the 48-h</p><p>Day 2 Day 1</p><p>Evening meal </p><p>Milk shake </p><p>15:40 to 17:30 </p><p>Rest (CON) </p><p>30 min intermittent exercise (EX30) </p><p>60 min intermittent exercise (EX60) </p><p>Exercise completed at 17:30 </p><p> ** </p><p>Evening meal was replicated from 1st condition 07:55 08:00 09:00 10:00 11:00 12:00 13:00 14:00 </p><p> * Key: capillary blood sample for </p><p>[TAG] and [glucose] capillary blood sample for [TAG], </p><p>[glucose], [haemoglobin], and haematocrit </p><p>Fig. 1 Schematic of 2-dayprotocol</p><p>Eur J Appl Physiol (2012) 112:2331 25</p><p>123</p></li><li><p>period leading up to day 2 of the first assigned experi-</p><p>mental condition (including the evening meal shown in</p><p>Fig. 1). This information was used to match their diet</p><p>and activity patterns across the three experimental con-</p><p>ditions. The boys were reminded verbally of this</p><p>requirement to replicate their nutritional intake and</p><p>activity just prior to the second and third conditions. In</p><p>addition, the boys were asked to minimise their</p><p>engagement in physical activity, other than the prescribed</p><p>treadmill exercise, in this 48-h period; however, no</p><p>measurements were taken to verify this. Before leaving</p><p>the laboratory on day 1 of each experimental condition,</p><p>the boys were reminded that they could drink plain water</p><p>but should not consume any food after 20:00 h that</p><p>evening. They were asked to eat a small cereal snack bar</p><p>at 19:45 h to standardise the fasting period across par-</p><p>ticipants and experimental conditions. They were also</p><p>asked to remain as inactive as possible after leaving the</p><p>laboratory in an effort to minimise this as an extraneous</p><p>factor on measurements during day 2.</p><p>The milkshake was a 3:1 mix of vanilla dairy ice</p><p>cream and double cream with 10 g of either powdered</p><p>strawberry or chocolate flavour added. It provided 1.50 g</p><p>of fat (70% of total energy), 1.20 g of carbohydrate</p><p>(25%), and 0.21 g of protein (5%) per kilogram of</p><p>body mass (80 kJ kg-1). The composition of the milk-</p><p>shake consumed differed slightly in the current study to</p><p>account for the small changes to the macronutrient</p><p>content of the ice cream and double cream by the</p><p>manufacturers since our last study (Tolfrey et al. 2008).</p><p>None of the boys reported any gastrointestinal problems</p><p>when consuming the milkshake or during the 6-h post-</p><p>prandial period.</p><p>Analytical methods</p><p>The fasting and postprandial capillary blood samples were</p><p>used to quantify [TAG] and glucose concentration ([glu-</p><p>cose]). Haematocrit and haemoglobin concentration were</p><p>determined from the fasting and final samples to estimate</p><p>change in plasma volume (Dill and Costill 1974). The</p><p>whole hand was pre-warmed for 5 min in water heated to</p><p>40C whilst the participant remained seated. Th...</p></li></ul>

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