Blood Lipid Responses After Continuous and Accumulated Aerobic Exercise

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1 International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16, Human Kinetics, Inc. Blood Lipid Responses After Continuous and Accumulated Aerobic Exercise Michael L. Mestek, John C. Garner, Eric P. Plaisance, James Kyle Taylor, Sofiya Alhassan, and Peter W. Grandjean The purpose of this study was to compare blood lipid responses to continuous versus accumulated exercise. Nine participants completed the following conditions on separate occasions by treadmill walking/jogging at 70% of VO 2max : 1) one 500-kcal session and 2) three 167 kcal sessions. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) concentrations were measured from serum samples obtained 24 h prior to and 24 and 48 h after exercise. All blood lipid responses were analyzed in 2 (condition) 3 (time) repeated measures ANOVAs. HDL-C increased by 7 mg/dl over baseline at 48 h post-exercise with three accumulated sessions versus 2 mg/dl with continuous exercise (P < 0.05). Triglyceride concentrations were unchanged in both conditions. These findings suggest that three smaller bouts accumulated on the same day may have a modestly greater effect for achieving transient increases in HDL-C compared to a continuous bout of similar caloric expenditure. Key Words: intermittent bouts, lipoproteins, cholesterol Consistent, moderate-intensity physical activity using large muscle groups with significant caloric expenditure has been shown to improve markers of physical health and reduce cardiovascular disease (CVD) risk (26, 34). Several international and national health organizations recommend regular moderate-intensity physical activity as a vital component of a healthy lifestyle (36, 37). Even though the health benefits and recommendations for quantity and quality of regular physical activity are widely published, most of the population still does not meet the activity levels recommended for good cardiovascular health (at least 200 kcal expenditure per day) (37). In addition, the prevailing evidence suggests that physically inactive and/or sedentary individuals remain unlikely to participate in a regular exercise program (16). Lack of time is the most popular reason individuals do not participate or drop out of exercise programs (15). Several studies have suggested that accumulated exercise bouts might improve rates of exercise adherence in most individuals (11, 17). It has also been sug- Mestek, Garner, Plaisance, and Grandjean are with the Dept of Health & Human Performance, Auburn University, Auburn, AL Taylor is with the Dept of Medical Technology, Auburn University- Montgomery, Montgomery, AL Alhassan is with the School of Medicine, Stanford University, Stanford, CA

2 246 Mestek et al. gested that encouraging shorter multiple bouts of exercise rather than one long bout would improve physical activity rates by accommodating busy schedules (4). The Centers for Disease Control and Prevention (CDC), American College of Sports Medicine (ACSM), and the US Surgeon General recommended that every US adult should accumulate 30 min (or the equivalent of 200 kcals) or more of moderate-intensity physical activity on most, preferably all, days of the week to improve health (35). Physical activity and/or exercise may reduce CVD risk, at least partially, through a favorable effect on blood lipids and lipoproteins (21, 23). The favorable changes induced by physical activity and/or exercise can include an increased concentration of high-density lipoprotein cholesterol (HDL-C), cholesterol in the HDL 2&3 subfractions (29), reduced triglyceride (TG) concentration (39), and, in some instances, lower total cholesterol (TC) (13) and low-density lipoprotein cholesterol (LDL-C) (22). HDL-C and TG changes appear to be more consistent responses to exercise than are changes in LDL-C and TC (19). In general, HDL- C and TG are thought to respond in a dose-response fashion to increased energy expenditure through exercise (18). Little work has been done to study the difference between exercise accumulated throughout the day and a single long bout of exercise on many health parameters, including blood lipids and lipoproteins (24, 41). Preliminary findings are extremely limited and inconsistent, especially when including basic lipid parameters, and do not address short-term changes that may be conferred after a daily dose of exercise. To date, the lowest exercise threshold for individual blood lipid changes is not known and may be related to fitness and health status (8). In those who are not physically active or of low cardiovascular fitness, exercise resulting in 350 to 500 kcals of energy expenditure can significantly increase HDL-C and decrease TG concentrations (25). A substantially greater exercise energy expenditure is thought to be required for similar blood lipid changes in aerobically fit individuals (25). Yet, it is still unclear if the additive effects of short bouts of exercise throughout the day can induce comparable lipid and lipoprotein changes seen in a single continuous bout of identical caloric expenditure. At present, very few studies have attempted to quantify the acute effects of exercise accumulated throughout the day on blood lipid concentrations. Given the dearth of well controlled published research related to accumulated bouts of aerobic exercise and blood lipid responses, the purpose of this study was to compare blood lipid responses to accumulated bouts of aerobic exercise in 1 d versus one continuous bout of aerobic exercise of similar total caloric expenditure. Participants Methods Male volunteers between the ages of 20 to 40 y were considered for the study if they were moderately fit (VO 2max between the 50th and 80th percentile based on age), a non-smoker, and free of known or suspected cardiovascular, metabolic, pulmonary, immune, or other disease processes that may affect the safety of the participant (1). All participants were fully informed regarding the study purpose and requirements and signed an institutionally approved informed consent document prior to their participation.

3 Blood Lipid Responses After Aerobic Exercise 247 Eleven of eighteen volunteers qualified to participate; however, two dropped out due to scheduling conflicts. Nine participants completed all experimental procedures. Physiological Testing Anthropometric measurements, including height, weight, waist and hip circumferences, and relative body fat were taken. Relative body fat was measured by skinfold testing (1, 33, 38). Body-mass index (BMI) and waist-to-hip ratio were also calculated for each participant. Participants performed a maximal graded exercise test (GXT) on a motor driven treadmill using the Bruce protocol (5). Gas analysis data were obtained using an automated breath-by-breath system (Medical Graphics Cardio 2 Integrated Metabolic System, MedGraphics Corp., Minneapolis, MN). Heart rates were measured using a Polar heart rate monitor (Polar Electro Inc., Woodbury, NY) following a 5-min supine rest, a 1-min standing rest, at the end of each minute during the exercise test, at maximum exercise intensity, and at 1, 3, and 5 min during an active cool down. Rating of perceived exertion (RPE) was obtained during the last 30 s of each protocol stage. The GXT was considered to be a maximal test if two of the following were achieved: a respiratory exchange ratio (RER) of greater than 1.1, a maximum heart rate within ± 10 beats per minute of age predicted maximum, an RPE of 18, or if the participant experienced volitional fatigue (1). GXT data was used to determine the individual required intensity and duration of experimental exercise sessions for each participant. Diet and Physical Activity Records Participants completed an initial 3-d dietary record which was analyzed to determine baseline total caloric intake and nutrient composition. This information was used to describe dietary habits, nutrient intake and composition to each participant and they were then instructed to maintain these dietary variables as consistently as possible for each of the experimental conditions. To quantify dietary compliance, participants completed dietary records during each week of the study. The records were analyzed using a commercially available software package (Food Processor version 7.4, ESHA Research, Salem, OR). Participants were also asked to refrain from any prolonged or strenuous physical exertion outside of that required by the experiment. Compliance was verified both verbally and by questionnaire prior to the start of each bout of exercise. Exercise Protocol Participants completed both of the following exercise conditions in a randomized order: 1) a single, continuous exercise session expending 500 kcals (CON) and 2) three accumulated bouts, expending 167 kcals per session (ACC). For the accumulated condition, exercise sessions were separated by at least a 4-h interlude to simulate circumstances that may occur in a typical daily routine (morning, mid-day, and evening exercise or physical activity) (11). Exercise conditions were separated by at least 1 wk. Participants self-selected to walk or jog at 70% (29) of their observed VO 2max until the required caloric expenditure was achieved. Respiratory gas analysis was

4 248 Mestek et al. used at 5-min intervals to quantify caloric expenditure during the exercise sessions. The observed VO 2 was multiplied by the caloric equivalent, estimated as observed RER + 4 (7), to obtain a per-minute estimate of kcals expended during each interval, which was then added to the session total. The total caloric expenditure from each interval was subtracted from the remaining kcals until the kcal expenditure goal for the session was met. Other mean physiologic values from the exercise sessions (HR, % HR max, % HRR, % VO 2 R, and % VO 2max ) were averaged for each exercise session. Blood Sampling. Blood samples from each participant were obtained following a minimum of a 6-h fast and at approximately the same time of day under both experimental conditions. Blood samples were collected at three time points for each exercise condition: 24 h prior, and 24 and 48 h after the final exercise bout. Samples were obtained in a seated position after 5 min of seated rest from an antecubital vein using a Vacutainer system to draw blood into 2 ml tubes containing no additives, then immediately placed on ice. Serum was obtained by centrifugation at 1500g for 15 min and serum samples were subsequently stored at 70 C for future analysis. Hematocrit and hemoglobin concentrations were measured at all time points to estimate shifts in plasma volumes (14). Lipid Concentrations. HDL-C was isolated prior to frozen storage of serum by the methods of Warnick (40) and Gidez (28). HDL-C and total serum cholesterol were then analyzed using the colorimetric enzymatic determination methods of Allain (2) and Grande (30). Cholesterol values were estimated using a Raichem cholesterol reagent diagnostic kit (Raichem, Div. of Hemagen Diagnostics, Inc., San Diego, CA). TG concentrations were estimated using the enzymatic methods of Bucolo and David (6). A Raichem triglyceride GPO reagent diagnostic kit was used to estimate triglyceride concentrations. All samples were analyzed in triplicate and each participant s samples were analyzed within the same run for each measure. Our lab intra-assay and inter-assay coefficients of variation were 1.9% and 0.42% for HDL, 1.8% and 0.36% for TC, and 3.2% and 1.6% for TG. LDL-C was calculated from concentrations of TC, HDL-C, and TG (27). Statistical Analysis. Dependent variables (TC, TG, HDL-C, and LDL-C) and plasma volume were analyzed by 2 (condition) 3 (time) repeated measures ANOVAs. Significant interactions were further explored by simple main effects analysis. Because dietary and nutrient variables [total calories, grams of fat, protein, and carbohydrate, and polyunsaturated-to-saturated fat ratio (P/S ratio)] were obtained 3 d before and throughout blood sampling, these variables were analyzed using 2 (condition) 6 (time) repeated measures ANOVAs. The comparisonwise error rate was set at the P < 0.05 level for all statistical tests. Results Participant characteristics at baseline are presented in Table 1. There were no significant differences in total exercise time, exercise intensity, or caloric expenditure between the exercise conditions. Exercise session data is presented in Table 2.

5 Blood Lipid Responses After Aerobic Exercise 249 Plasma volume was not significantly altered during each condition relative to the baseline measure (P = 0.92); therefore, blood concentrations were not adjusted for changes in plasma volume. Total cholesterol was significantly lower in the CON condition compared to the ACC condition; yet, remained unchanged with exercise in either condition. LDL-C and TG concentrations were unaltered by exercise (P > 0.05). HDL-C increased by 7 mg/dl over baseline at 48 h post-exercise with three accumulated sessions versus 2 mg/dl with continuous exercise (P < 0.05); see Figure 1. Blood lipid responses to exercise are summarized in Table 3 and graphically depicted in Figure 1. There were no statistically significant differences in any of the dietary variables between the conditions. The dietary variables were collapsed across days for each exercise condition. These values are listed in Table 4. Table 1 Participants Baseline Descriptive Data (N = 9) Variable Value (M ± SD ) Range Age (y) Height (in) Weight (kg) BMI (kg/m 2 ) % Fat VO 2max (ml kg -1 min -1 ) VO 2max (L/min) All values are means ± standard deviation. % Fat = body fat expressed as a percentage of body weight Table 2 Exercise Condition Characteristics Variable CON ACC Total caloric exp. (kcals) ± ± 3.0 HR (bpm) ± ± 9.1 % HR max 84.3 ± ± 4.9 % HRR 74.0 ± ± 8.6 % VO 2max 72.4 ± ± 1.6 % VO 2 R 69.9 ± ± 1.7 Total exercise time (min) 39.3 ± ± 2.6 Values are means ± standard deviation. Total caloric exp.= total caloric expenditure for the condition; HR = heart rate; % HR max = percentage of maximal heart rate; %HRR = percentage of heart rate reserve; % VO 2max = percentage of maximal oxygen uptake; % VO 2 R = percentage of VO 2 reserve; Total time = total time needed to reach necessary caloric expenditure.

6 250 Mestek et al. Figure 1 HDL-C responses to accumulated (ACC) and continuous (CON) aerobic exercise. Means with the same superscript are similar within each condition. Error bars represent standard deviation. * = significant difference between conditions Table 3 Blood Lipid Changes Variable Baseline 24 h post 48 h post TC CON 185 ± 23 a 185 ± 24 a 189 ± 24 a ACC 200 ± 22 a 197 ± 23 a 197 ± 15 a LDL-C CON 104 ± 33 a 103 ± 23 a 105 ± 27 a ACC 117 ± 35 a 118 ± 24 a 114 ± 23 a TG CON 155 ± 84 a 154 ± 84 a 153 ± 66 a ACC 159 ± 78 a 128 ± 49 a 134 ± 64 a HDL-C CON 50 ± 7 a 50 ± 4 a 52 ± 7 a ACC 49 ± 8 a 54 ± 8 ab 56 ± 7 b* All blood lipid concentrations are reported as mg/dl (means ± standard deviation). Means with the same lower case superscript are similar within each condition (P > 0.05); = TC concentration was lower in the CON condition compared to ACC (P < 0.05); * indicates significant difference between conditions.

7 Blood Lipid Responses After Aerobic Exercise 251 Table 4 Dietary Variables Variable CON ACC Total calories ± ± Fat (g) 62.1 ± ± 27.8 Carbohydrates (g) ± ± Protein (g) 72.7 ± ± 38.0 P/S ratio 0.46 ± ± 0.80 All values are reported as means ± standard deviation. Discussion Because strong scientific consensus advocates equivalent health benefits with continuous or accumulated exercise, our intent was to characterize the acute blood lipid responses to aerobic exercise performed either in one continuous bout or accumulated in three smaller bouts of similar caloric expenditure. Our most significant finding was that exercise accumulated in smaller bouts throughout the day was more effective in terms of raising HDL-C than a single continuous bout of exercise of similar caloric expenditure. The HDL-C responses we observed after exercise are consistent with those reported previously for young males after exercise of moderate intensity and duration (22). Indeed, the changes after accumulated and continuous exercise compare with the transient 2 to 8 mg/dl increases commonly reported after aerobic exercise (20). It should also be recognized that the average HDL-C change (14.3%) observed after accumulated exercise remains relatively modest and within what may be observed for daily variation (12) and is comparable to the 5 to 25% increase that would be expected with targeted pharmaceutical intervention (34). Our findings indicate that when extraneous variables such as diet and outside physical activity are accounted for, accumulating exercise throughout the day in three bouts enhances the HDL-C response observed with daily exercise of modest caloric expenditure. In hypercholesterolemic men of low cardiorespiratory fitness, Crouse and colleagues (8) reported that a caloric expenditure of 350 kcals was sufficient to induce significant increases in HDL-C. Likewise, Grandjean et al. (31) showed that a single continuous exercise session with a caloric expenditure of 500 kcal led to a 6 mg/dl increase in HDL-C at 48 h post-exercise in men differing in their baseline blood lipid status. Single sessions of exercise with similar caloric expenditure have also been shown to raise HDL-C in young, moderately-trained males similar to those in our cohort (4, 9, 32); however, this is not always the case. For example, Davis et al. (10) found that a caloric expenditure of 950 kcals was insufficient to induce lipid changes in habitually active males. Indeed, Ferguson et al. (25) showed that a caloric expenditure threshold of 1100 kcals may be required for HDL-C changes to occur in healthy moderately and well-trained males. Our data suggest that in young, moderately-trained males a total exercise energy expenditure of 500 kcals may result in a larger increase in HDL-C when accumulated in smaller bouts throughout the day compared to a single, continuous bout. At present we do not have an explanation for this finding.

8 252 Mestek et al. It has recently been reported by Altena et al. (3) that accumulation of intermittent exercise lowers post-prandial lipemia (PPL) more effectively than a continuous bout of exercise with similar caloric expenditure in a cohort similar to ours. It was postulated by this group that the mechanism responsible for the reduction of PPL is an increase in lipoprotein lipase (LPL) activity that is known to occur after exercise. Although the current study did not measure LPL expression or activity, a similar mechanism may be responsible for the increase in HDL-C with accumulated exercise (31). Speculatively, the difference between the PPL response with accumulated versus continuous exercise was thought to be due to an increased metabolic rate during and after exercise that may be sustained throughout the day with accumulation of aerobic exercise in middle-age apparently healthy males (3). The exact signaling mechanism to support this contention is currently unknown. Other factors influencing lipid and lipoprotein metabolism, such as the activity of lecithin:cholesterol acyltransferase, hepatic lipase, and cholesterol ester transfer protein may come into play in the hours and days after exercise (22). The extent to which these biochemical factors are influences of continuous and accumulated exercise remains to be tested. Exercise training studies comparing blood lipid responses to accumulated and intermittent exercise have yielded mixed results. Ebisu (24) showed that previously untrained males who accumulated a consistent, selected running mileage throughout the study in three accumulated bouts increased HDL-C by 5 mg/dl 24 h after the final training session. Participants completing the same mileage in two accumulated bouts or a single continuous bout did not show any increase. Our results are consistent with those of Ebisu and indicate that the accumulation of three or more exercise bouts per day is more effective in increasing HDL-C values than a single continuous bout. In contrast to our findings, Woolf-May and colleagues (41) reported no changes in HDL-C for any group and a decrease in LDL-C in groups assigned to a continuous and two accumulated sessions per day group. To be sure, we are not directly comparing our results to training studies. Although much of the training effect may be attributed to a response observed after a single bout of exercise, training effects would also include chronic adaptations. However, given that Ebisu s blood sampling times were similar to ours and occurred within 48 h of the last bout of exercise, the reported increase in HDL-C may be the result of an acute response. In conclusion, the findings of this study show that an accumulation of moderate intensity aerobic exercise performed on multiple occasions throughout the day may have a greater effect on increasing HDL-C than a single, continuous bout of aerobic exercise in moderately fit, apparently healthy males. These findings are of value to health care practitioners because they corroborate current physical activity recommendations that suggest accumulating exercise throughout the day will impart a health benefit and possibly reduces the risk of cardiovascular disease while promoting adherence to exercise. References 1. ACSM s Guidelines for Exercise Testing and Prescription. 6th ed. Baltimore: Lippincott, Williams, and Wilkins, Allain, C. A., L.S. Poon, G.S.G. Chan, et al. Enzymatic determination of total serum cholesterol. Clin. Chem. 20:470, 1974.

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