International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16, 245-254
© 2006 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 VO2max :
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 sugMestek, Garner, Plaisance, and Grandjean are with the Dept of Health & Human Performance, Auburn
University, Auburn, AL 36849. Taylor is with the Dept of Medical Technology, Auburn UniversityMontgomery, Montgomery, AL 36124. Alhassan is with the School of Medicine, Stanford University,
Stanford, CA 94305.
245
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 HDL2&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, HDLC 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.
Methods
Participants
Male volunteers between the ages of 20 to 40 y were considered for the study if
they were moderately fit (VO2max 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.
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 Cardio2 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 VO2max
until the required caloric expenditure was achieved. Respiratory gas analysis was
248 Mestek et al.
used at 5-min intervals to quantify caloric expenditure during the exercise sessions.
The observed VO2 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, % HRmax, % HRR, % VO2R, and % VO2max) 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.
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/m2)
% Fat
VO2max (mL · kg-1 · min-1)
VO2max (L/min)
25 + 4
70.3 + 1.5
86.3 + 7.1
27.1 + 2.5
18 + 7
42.5 + 1.9
3.69 + 0.29
20 – 30
67.8 – 73.0
78.2 – 97.5
24.0 – 31.3
9 – 27
40.0 – 45.3
3.33 – 4.32
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)
HR (bpm)
% HRmax
% HRR
% VO2max
% VO2R
Total exercise time (min)
503.1 ± 6.0
156.2 ± 9.1
84.3 ± 5.0
74.0 ± 8.5
72.4 ± 2.7
69.9 ± 2.6
39.3 ± 3.9
502 .5 ± 3.0
152.6 ± 9.1
82.4 ± 4.9
70.7 ± 8.6
71.5 ± 1.6
69.0 ± 1.7
38.7 ± 2.6
Values are means ± standard deviation.
Total caloric exp.= total caloric expenditure for the condition; HR = heart rate; % HRmax = percentage
of maximal heart rate; %HRR = percentage of heart rate reserve; % VO2max = percentage of maximal
oxygen uptake; % VO2R = percentage of VO2 reserve; Total time = total time needed to reach necessary caloric expenditure.
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
ACC
185 ± 23a
200 ± 22a
185 ± 24a
197 ± 23a
189 ± 24a
197 ± 15a
LDL-C
CON
ACC
104 ± 33a
117 ± 35a
103 ± 23a
118 ± 24a
105 ± 27a
114 ± 23a
TG
CON
ACC
155 ± 84a
159 ± 78a
154 ± 84a
128 ± 49a
153 ± 66a
134 ± 64a
HDL-C
CON
ACC
50 ± 7a
49 ± 8a
50 ± 4a
54 ± 8ab
52 ± 7a
56 ± 7b*
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.
Blood Lipid Responses After Aerobic Exercise 251
Table 4 Dietary Variables
Variable
CON
ACC
Total calories
Fat (g)
Carbohydrates (g)
Protein (g)
P/S ratio
1746.8 ± 600.0
62.1 ± 29.9
221.8 ± 91.9
72.7 ± 35.6
0.46 ± 0.37
1717.9 ± 622.2
60.1 ± 27.8
210.4 ± 109.3
74.1 ± 38.0
0.69 ± 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.
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.
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