J Appl Physiol 114: 1375–1382, 2013.
First published March 7, 2013; doi:10.1152/japplphysiol.01077.2012.
Racial differences in the response of cardiorespiratory fitness to aerobic
exercise training in Caucasian and African American postmenopausal women
Damon L. Swift,1 Neil M. Johannsen,1 Carl J. Lavie,1,4 Conrad P. Earnest,6 William D. Johnson,2
Steven N. Blair,5 Timothy S. Church,1 and Robert L. Newton, Jr.3
1
Department of Preventive Medicine, Pennington Biomedical Research Center, Baton Rouge, Louisiana; 2Department of
Population Science, Pennington Biomedical Research Center, Baton Rouge, Louisiana; 3Department of Physical Activity and
Ethnic Minority Health, Pennington Biomedical Research Center, Baton Rouge, Louisiana; 4Department of Cardiovascular
Diseases, John Ochsner Heart and Vascular Institute, Ochsner Clinical School, The University of Queensland School of
Medicine, New Orleans, Louisiana; 5Departments of Exercise Science and Epidemiology and Biostatistics, University of South
Carolina, Columbia, South Carolina; and 6Department for Health , University of Bath, Bath, United Kingdom
Submitted 4 September 2012; accepted in final form 28 February 2013
race; exercise training; African American; cardiorespiratory fitness
are an important public health problem (23). African American (AA) women have a higher risk of
cardiovascular disease (CVD), stroke, and mortality compared
with Caucasian American (CA) women (21, 23). Higher levels
of cardiorespiratory fitness (CRF) are associated with reduced
risk of CVD and mortality (4, 14, 20), and recent data suggest
that AA women have lower CRF levels compared with their
CA counterparts (11, 17, 18, 28, 31). Specifically, the Coronary
Artery Risk Development in Young Adults (CARDIA) study
(30) found that CRF from a maximal exercise test was higher
RACIAL HEALTH DISPARITIES
Address for reprint requests and other correspondence: D. L. Swift, Dept. of
Preventive Medicine, Pennington Biomedical Research Center, 6400 Perkins
Rd., Baton Rouge, LA 70808 (e-mail: [email protected]).
http://www.jappl.org
in CA women compared with AA women. Similar findings
have been reported in another epidemiological study (28),
larger clinical studies (18, 31), and smaller studies in a variety
of subject populations [adults (31), women (11, 17), type 2
diabetes (9)]. Thus lower CRF may contribute to CVD disparities between CA and AA women; however, racial differences
in CRF have not been evaluated specifically in postmenopausal
women.
CRF is inversely associated with all-cause mortality in CA
and AA adults (16), and increasing CRF levels are associated
with reduced risk of CVD (3). Aerobic exercise training has a
well-documented effect for improving CRF, which occurs in
both CA and AA individuals (8, 31). Thus increasing levels of
CRF should reduce CVD risk, regardless of race. However,
little data exist evaluating racial differences in the improvement of CRF as a result of aerobic exercise training between
CA and AA adults.
Data from the Health, Risk Factors, Exercise Training and
Genetics Family (HERITAGE) study suggest that although
mean CRF [expressed in changes in maximal oxygen consumption (VO2)] increased following 20 wk of cycle ergometer
training to a greater extent in CA (5.5 ml O2·kg⫺1·min⫺1)
compared with AA (4.9 ml O2·kg⫺1·min⫺1) adults, no differences were observed in mean percent change in both groups
(CA: 17.5%; AA: 18.7%). Since no racial differences were
additionally observed in absolute CRF or in CRF corrected
for lean mass, the authors concluded that race had no major
effect on the change in CRF following aerobic training (31).
It is important to note that in HERITAGE study’s sample
included both men and women and had a wide age range
(17-65 yr) (5). Thus, to our knowledge, no studies have
evaluated racial differences in the response to CRF following aerobic training, specifically in postmenopausal women.
This has clinical importance, as postmenopausal women
have a higher risk of CVD compared with premenopausal
women (13).
The purpose of the present study is to determine if there are
differences between CA and AA postmenopausal women in
1) baseline CRF and 2) changes in CRF following 6 mo of
aerobic exercise training in the Dose-Response to Exercise in
Women (DREW) trial. We hypothesized, based on the data
presented above, that AA postmenopausal women would have
lower CRF at baseline, but a similar increase in CRF following
training compared with CA women.
8750-7587/13 Copyright © 2013 the American Physiological Society
1375
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Swift DL, Johannsen NM, Lavie CJ, Earnest CP, Johnson
WD, Blair SN, Church TS, Newton RL Jr. Racial differences
in the response of cardiorespiratory fitness to aerobic exercise
training in Caucasian and African American postmenopausal
women. J Appl Physiol 114: 1375–1382, 2013. First published March
7, 2013; doi:10.1152/japplphysiol.01077.2012.—African American (AA) women have an elevated risk of cardiovascular disease
and have been reported to have lower cardiorespiratory fitness
(CRF) compared with Caucasian American (CA) women. However, little data exist that evaluate racial differences in the change
in CRF following aerobic exercise training. CA (n ⫽ 264) and AA
(n ⫽ 122) postmenopausal women from the Dose-Response to
Exercise in Women study were randomized to 4, 8, and 12 kcal·kg
body wt⫺1·wk⫺13 (KKW) of aerobic training or the control group
for 6 mo. CRF was evaluated using a cycle ergometer. A greater
increase in relative CRF was observed in CA compared with AA
women in the 4 (CA: 1.00 vs. AA: 0.35 ml O2·kg⫺1·min ⫺1, P ⫽
0.034), 8 (CA: 1.59 vs. AA: 0.82 ml O2·kg⫺1·min ⫺1, P ⫽ 0.041),
and 12 (CA: 1.98 vs. AA: 0.50 ml O2·kg⫺1·min ⫺1, P ⫽ 0.001)
KKW groups. Similar effects were found in absolute CRF, with the
exception of the 4-KKW (CA: 0.04 vs. AA: 0.02 l O2/min, P ⫽
0.147) group. However, in categorical analyses, the percentages of
women who improved in both relative (⬎0 ml O2·kg⫺1·min ⫺1)
and absolute (⬎0 l O2/min) CRF were not significantly different
for CA and AA women in all exercise groups (all P ⬎ 0.05). AA
postmenopausal women, in general, had an attenuated increase in
CRF (both relative and absolute) following exercise training, but
had similar response rates compared with CA women. Future
studies should investigate the physiologic mechanisms responsible
for this attenuated response.
1376
Racial Differences in the Response to Fitness with Exercise
METHODS
Design and Participants
Maximal Exercise Testing
Testing was performed using an Excalibur Sport electronically
braked cycle ergometer (Lode, Groningen, the Netherlands). Participants cycled at 30 W for 2 min and then 50 W for 4 min, followed by
increases of 20 W every 2 min until they could no longer maintain a pedal
cadence of 50 revolutions/min. Respiratory gases were measured using a
TrueMax 2400 metabolic measurement cart (ParvoMedics, Sandy, UT).
CRF measures were calculated in relative (ml O2·kg⫺1·min⫺1) and
absolute VO2 peak (l O2/min). Two fitness tests were performed on
different days at baseline, and two tests were performed at follow-up.
The average value for the two tests at each time point was used in the
analyses, unless only one of the two tests was completed at baseline
Swift DL et al.
or follow-up, in which case, we used the single value. At baseline,
96% of participants completed both exercise tests. At follow-up, 95%
of participants completed both exercise tests. The coefficient of
variation for repeated measures of CRF (l/min) at baseline and
follow-up were 5.2% and 4.7%, respectively.
Baseline Physical Activity
Baseline physical activity level was measured using an Eagle
AE1620 (Accusplit, Livermore, CA) pedometer over the course of 1
wk prior to randomization.
Resting BP
Resting BP was evaluated with an automated BP unit (Colin
Medical Instruments, San Antonio, TX) with the participant in the
supine position.
Anthropometric Measures
Weight was measured using an electronic scale (Siemens Medical
Solutions, Malvern, PA). Waist circumference was obtained following
the guidelines of the Airlie Conference (22). Body mass index was
calculated by dividing weight (kg) by height (m) squared.
Participant Randomization
Following baseline testing, participants were randomized to the 4-,
8-, or 12-kcal·kg body wt⫺1·wk⫺1 (KKW) or the nonexercise control
group (25). The final analysis included 84 participants from the
control group, 130 from the 4-KKW group, 81 from the 8-KKW
group, and 91 from the 12-KKW group. The larger sample size in
the 4-KKW group reflects a design feature of DREW that provided
sufficient statistical power for detecting smaller anticipated
changes compared with the 8- and 12-KKW groups following
exercise training (25).
Fig. 1. Consort diagram. DREW, Dose-Response to Exercise in Women trial; KKW, kcal·kg body wt⫺1·wk⫺1; AA, African American; CA, Caucasian American;
VO2, maximal oxygen consumption.
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The full design (25) and primary outcomes (7) for the DREW trial
have been published. DREW was a randomized, controlled trial
evaluating the dose response of CRF with increasingly higher doses of
energy expenditure in sedentary, postmenopausal women with elevated blood pressure (BP). The protocol was reviewed and approved
annually by The Cooper Institute Institutional Review Board and
subsequently approved by Pennington Biomedical Research Center
for continued analysis. Written, informed consent was obtained from
all participants prior to screening. Women recruited for this study
were overweight or obese and had elevated systolic BP. Notable
exclusion criteria included the presence of significant CVD, conditions contraindicated for exercise training, elevated LDL, and significant weight loss in the previous year (25).
A consort diagram for the present study is shown in Fig. 1. We
excluded women who were not CA or AA (n ⫽ 27), had low (ⱕ75%)
exercise-training adherence (n ⫽ 10), did not complete the trial (n ⫽
40), or had missing exercise testing data (n ⫽ 1). Thus 264 CA and
122 AA postmenopausal women were in the analytical sample.
•
Racial Differences in the Response to Fitness with Exercise
Exercise Training
We determined that the exercise-training energy expenditure for
women in the DREW age range, associated with meeting the consensus public health guidelines, was ⬃8 KKW (25). Based on this, we
also determined the energy expenditure at 50% below (4 KKW) and
50% above (12 KKW) consensus public health guidelines. All groups
expended 4 KKW during the 1st wk. Participants assigned to the
4-KKW treatment arm continued to expend 4 KKW for 6 mo. All of
the other groups increased their energy expenditure by 1 KKW/wk
until they reached the exercise dose required for their group (i.e., 8
KKW, 12 KKW). Aerobic training was performed on semirecumbent
cycle ergometers and treadmills, and all sessions were supervised
directly by study staff. Women in the exercise groups participated in
three or four sessions/wk for 6 mo at a heart rate associated with 50%
of peak VO2. Exercise training adherence was excellent in CA
(99.2%) and AA (99.0%) participants. Participants in the nonexercise
control group were asked to not alter their habitual physical activity
level during the study.
Food frequency questionnaires were collected at baseline and
follow-up in DREW to monitor dietary changes. No significant dietary
changes were found following exercise training, which is reported in
the DREW main outcomes paper (25).
Blinding
Separate intervention and assessment teams were maintained, and
assessment staff members were blinded to the randomization of study
participants.
Statistical Procedure
Statistical analyses were performed using SAS version 9.3 (SAS
Institute, Cary, NC). Descriptive data were tabulated as means (SD) or
frequencies (percent) as appropriate.
Baseline characteristics. An ANOVA was performed to evaluate
the significance of the racial difference in each baseline characteristic.
Baseline differences between CA and AA women were found for age
and maximum mean respiratory exchange ratio (RER) value from
baseline exercise testing. Therefore, differences in baseline CRF
between CA and AA were adjusted further for those variables.
Racial differences in the change in weight, RER, and maximum
heart rate following training. An analysis of covariance (ANCOVA)
was used to evaluate the change in weight, RER, and maximum heart
rate following exercise training with adjustment for baseline value.
Adjusted means were reported as least squares means and 95%
confidence intervals.
Evaluation for racial differences in the change in CRF. Changes in
CRF (assessed by VO2 peak) following exercise training between
CA and AA postmenopausal women were compared in relative (ml
O2·kg⫺1·min ⫺1) and absolute terms (l/min): 1) across dose of
exercise; 2) in exercisers only adjusted for exercise dose (total caloric
energy expenditure during training sessions); and 3) in exercisers only
adjusted for exercise dose in those that achieved a RER value ⬎1.05
at baseline and follow-up. All linear statistical models were analyzed
to compare baseline fitness and 6-mo changes in fitness with adjustment for covariates (age, baseline value, and maximum mean RER
from baseline exercise test). Adjusted means were reported as least
squares means and 95% confidence intervals. Statistical significance
was defined as P ⱕ 0.05.
Categorical analysis for change in CRF. Women with change in
relative CRF ⬎ 0 ml O2·kg⫺1·min ⫺1 following exercise training were
classified as relative CRF responders, and those with change in
relative CRF ⱕ 0 ml O2·kg⫺1·min⫺1 were classified as relative CRF
nonresponders. Similarly, those with change in absolute CRF ⬎ 0 l
O2/min following exercise training were classified as absolute CRF
Swift DL et al.
1377
responders, and those with change in absolute CRF ⱕ 0 l O2/min
following exercise training were classified as absolute CRF nonresponders. A general linear model was used to compare CA with AA
women with respect to the percent of responders in each study group
in the entire study sample (n ⫽ 386).
Dose response to fitness. Multiple linear regression analysis was
used to test the significance of the trend of increasing CRF with higher
doses of exercise (4 KKW, 8 KKW, and 12 KKW) for AA and CA
participants. These analyses were performed only in the exercise
groups.
Variance for change in CRF. In exercisers only, linear regression
models were used to estimate the percent of total variance for change
in peak VO2 (relative and absolute) that may be attributed to race.
Variables entered into the model included: exercise-training dose, age,
baseline fitness, and race. Furthermore, within each training dose (4,
8, or 12 KKW) age, baseline fitness, and race were entered into
regression models and analyzed analogously.
RESULTS
Baseline characteristics are summarized by race and exercisetraining dose in Table 1. AA women were generally younger, had
higher body weight, fasting glucose, and diastolic BP but lower
waist circumference and hemoglobin values compared with
CA women. The mean difference between races was not
significant for systolic BP or baseline steps/day (all P ⬎ 0.05).
No significant differences were observed in baseline characteristics across exercise groups or within either race group.
Approximately 23% of women (both CA and AA) were taking
antihypertensive medication, and 50% of CA and 32% of AA
were taking hormone-replacement therapy.
Baseline Fitness
Baseline maximal exercise tests revealed that compared with
AA women, CA women, on average, had significantly higher
relative CRF and maximum RER, but the racial differences in
absolute CRF and maximum heart rate were not statistically
significant. After adjustment for both age and maximum RER,
AA women had significantly lower relative and absolute CRF
compared with CA women (Table 2).
Weight, RER, and Maximum Heart Rate Outcomes
No significant race differences were observed in the change
of weight, maximum RER, or maximum heart rate following
exercise training (Table 3).
Cardiorespiratory Fitness
Mean changes in relative and absolute CRF following exercise training are shown by race in Fig. 2. CA women, on
average, experienced significantly greater changes than AA
women for relative VO2 peak in the 4-KKW (CA: 1.00 vs. AA:
0.35 ml O2·kg⫺1·min⫺1, P ⫽ 0.034), 8-KKW (CA: 1.59 vs.
AA: 0.82 ml O2·kg⫺1·min⫺1, P ⫽ 0.041), and 12-KKW (CA:
1.98 vs. AA: 0.50 ml O2·kg⫺1·min⫺1, P ⫽ 0.001) groups. The
race difference in mean change for relative VO2 peak approached statistical significance (P ⫽ 0.065) in the control
group, with a larger decline occurring in AA women. The race
differences did not vary significantly (P ⫽ 0.390) across
exercise-training doses, indicating an absence of significant
race by exercise-training dose interaction, whereas CA women
demonstrated a more favorable main-effect change in relative
VO2 peak after exercise training (P ⬍ 0.001).
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Dietary Changes
•
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Racial Differences in the Response to Fitness with Exercise
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Swift DL et al.
Table 1. Baseline characteristics stratified by race
Caucasian
Age (yr)
Weight (kg)
Body mass index (kg/m2)
Waist circumference (cm)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Glucose (mg/dl)
Hemoglobin (g/dl)
Baseline physical activity (steps/day)
Exercise testing data
RER (VCO2/VO2)
Maximum heart rate (beats/min)
Percentage of age-predicted
maximum heart rate (%)†
Exercise test max RER value
⬎1.05 (%, n)
African American
Control (n ⫽ 61)
4 KKW (n ⫽ 83)
8 KKW (n ⫽ 53)
12 KKW (n ⫽ 67)
58.3 (6.3)*
83.4 (11.6)*
31.4 (3.9)
101.8 (11.7)*
140.0 (12.9)
80.0 (8.6)*
95.1 (9.4)*
13.2 (0.9)*
4,930.4 (1759.5)
57.8 (6.1)
85.7 (12.9)
32.2 (4.3)
104.5 (12.5)
141.9 (11.8)
80.2 (8.1)
94.6 (13.1)
13.2 (0.8)
5,101 (1685.9)
59.5 (6.3)
82.5 (10.)
31.1 (3.4)
100.1 (10.3)
139.7 (11.9)
79.5 (9.6)
95.0 (7.9)
13.2 (0.8)
4,824.3 (1,886.0)
58.1 (6.3)
85.1 (12.9)
32.0 (4.2)
103.6 (10.3)
140.2 (14.8)
80.3 (8.1)
95.1 (7.5)
13.3 (1.0)
4,706.7 (1,634.5)
57.5 (6.5)
81.2 (10.5)
30.7 (3.7)
100.2 (13.1)
138.5 (13.5)
80.1 (8.2)
95.7 (8.3)
13.1 (0.8)
5,082.1 (1,769.4)
1.15 (0.07)*
151.8 (16.4)
1.13 (0.06)
151.7 (15.2)
1.15 (0.07)
150.2 (17.8)
1.14 (0.07)
152.4 (16.3)
1.16 (0.07)
152.9 (16.2)
90.7 (9.2)
90.6 (9.0)
90.3 (9.8)
91.0 (9.0)
91.1 (8.9)
92.1% (243)*
93.4 (57)
90.4 (75)
92.5 (49)
92.6 (62)
All (n ⫽ 122)
Control (n ⫽ 23)
4 KKW (n ⫽ 28)
8 KKW (n ⫽ 28)
12 KKW (n ⫽ 24)
54.8 (5.9)
85.9 (11.9)
32.2 (3.6)
98.5 (11.2)
138.8 (12.7)
83.2 (8.2)
92.8 (10.8)
12.6 (0.9)
5,087.4 (1,921.6)
55.6 (5.2)
87.1 (10.7)
32.4 (3.0)
98.3 (10.6)
140.0 (11.3)
82.1 (8.1)
95.8 (13.9)
12.8 (0.6)
5,205.6 (1,412.0)
55.4 (6.1)
84.2 (13.0)
31.7 (4.0)
98.7 (12.2)
139.0 (14.8)
83.4 (7.8)
91.5 (9.3)
12.6 (1.0)
4,873.8 (1,822.5)
54.3 (6.8)
85.8 (11.1)
32.8 (3.7)
99.6 (12.6)
137.6 (11.1)
82.9 (7.9)
92.3 (11.8)
12.5 (0.08)
5,281.6 (2,177.6)
53.4 (5.0)
88.6 (11.5)
32.3 (3.0)
97.0 (8.3)
138.9 (11.8)
84.1 (9.7)
93.3 (9.3)
12.6 (1.0)
5,139.2 (2,260.9)
1.11 (0.07)
152.7 (15.8)
1.10 (0.06)
152.0 (16.8)
1.10 (0.08)
152.3 (15.5)
1.12 (0.07)
152.4 (14.4)
1.12 (0.07)
152.9 (17.5)
89.9 (9.1)
89.8 (8.8)
90.1 (9.1)
89.7 (9.0)
89.7 (10.4)
82.8 (101)
78.3 (75)
80.9 (38)
85.7 (24)
87.5 (21)
Values are presented as mean (SD). One-way ANOVA was performed to test for significant differences among groups. KKW: kcal·kg body wt⫺1·wk⫺1; VCO2,
elimination rate of carbon dioxide; VO2, maximal oxygen consumption; RER, respiratory exchange ratio. *Significantly different from African Americans;
†percent of maximum heart rate calculated based on the equation from Tanaka et al. (33).
CA women, on average, had a greater absolute VO2 peak in
the 8-KKW (CA: 0.10 vs. AA: 0.04 l O2/min, P ⫽ 0.031) and
the 12-KKW (CA: 0.13 vs. AA: 0.04 l O2/min, P ⫽ 0.003)
groups but not in the 4-KKW (CA: 0.04 AA: 0.02, l O2/min,
P ⫽ 0.147) group. The race difference for the change in
absolute VO2 peak in the control group was not significant
(P ⫽ 0.155). A significant main effect was observed for race
(P ⫽ 0.001), with no significant race by exercise-training dose
interaction (P ⫽ 0.486).
CRF (Adjusted for Exercise Dose)
As shown in Fig. 3, CA women experienced greater improvements compared with AA women in relative and absolute
CRF following exercise training (P ⬍ 0.05). Similar results
were found when the analyses were restricted to women who
had obtained a maximum RER value ⬎1.05 at baseline and
follow-up from exercise testing (n ⫽ 276).
Categorical Analysis for CRF
No significant race differences were observed in the percentage of participants who increased relative CRF within the
control (45.9 vs. 43.5%, P ⫽ 0.822), 4-KKW (69.9 vs. 57.4%,
P ⫽ 0.121), 8-KKW (86.8 vs. 82.1%, P ⫽ 0.651), and
12-KKW (85.1 vs. 75.0%, P ⫽ 0.336) groups. Similarly, race
differences in the percentage of women who increased absolute
CRF did not differ significantly within the control (37.7% vs.
Table 2. Evaluation for differences in baseline CRF between Caucasian and African American participants
Relative CRF (ml·kg⫺1·min⫺1)
Unadjusted model
Model adjusted for age
Model adjusted for age and maximum RER value
Absolute cardiorespiratory fitness (l/min)
Unadjusted model
Model adjusted for age
Model adjusted for age and maximum RER value
Caucasian
African American
P value
15.7 (CI: 15.5–16.1)
15.9 (CI: 15.9–16.2)
15.8 (CI:15.5–16.1)
15.1 (CI: 14.4–15.4)
14.7 (CI: 14.3–15.2)
15.0 (CI:14.6–15.5)
0.015
⬍0.001
0.011
1.31 (CI: 1.28–1.34)
1.33 (CI: 1.30–1.36)
1.33 (CI: 1.30–1.35)
1.28 (CI: 1.23–1.34)
1.24 (CI: 1.20–1.28)
1.25 (CI:1.21–1.29)
0.24
⬍0.001
0.003
CRF, cardiorespiratory fitness; CI, confidence interval.
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Age (yr)
Weight (kg)
Body mass index (kg/m2)
Waist circumference (cm)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Glucose (mg/dl)
Hemoglobin (g/dl)
Baseline physical activity (steps/day)
Exercise testing data
RER (VCO2/VO2)
Maximum heart rate (beats/min)
Percentage of age-predicted
maximum heart rate (%)†
Exercise test max RER value
⬎1.05 (%, n)
All (n ⫽ 264)
Racial Differences in the Response to Fitness with Exercise
•
Swift DL et al.
1379
Table 3. Change in weight, RER, and maximum heart rate following exercise training in Caucasian and African American
women
Caucasian
⌬ Weight (kg)
⌬ RER (VCO2/VO2)
⌬ Maximum heart rate (beats/min)
African American
⌬ Weight (kg)
⌬ RER (VCO2/VO2)
⌬ Maximum heart rate (beats/min)
Control (n ⫽ 61)
4 KKW (n ⫽ 83)
⫺1.5 (CI: ⫺2.4, ⫺0.6)
⫺1.8 (CI: ⫺2.6, ⫺1.1)
⫺0.005 (CI: ⫺0.013, 0.003) ⫺0.006 (CI: ⫺0.013, 0.001)
⫺3.3 (CI:⫺5.5, ⫺1.1)
⫺1.3 (CI: ⫺3.2, 0.7)
Control (n ⫽ 23)
4 KKW (n ⫽ 28)
8 KKW (n ⫽ 53)
12 KKW (n ⫽ 67)
⫺1.8 (CI: ⫺2.7, ⫺0.8)
⫺0.004 (CI: ⫺0.013, 0.004)
⫺0.6 (CI: ⫺3.0, 1.9)
⫺1.6 (CI: ⫺2.5, ⫺0.8)
⫺0.003 (CI: ⫺0.011, 0.004)
⫺0.3 (CI: ⫺2.4, 1.8)
8 KKW (n ⫽ 28)
12 KKW (n ⫽ 24)
⫺0.5 (CI: ⫺2.0, 0.9)
⫺0.7 (CI: ⫺1.7, 0.3)
⫺2.0 (CI: ⫺3.3, ⫺0.7)
⫺1.3 (CI: ⫺2.7, 0.1)
⫺0.011 (CI: ⫺0.024, 0.003) ⫺0.000 (CI: ⫺0.010, 0.009) ⫺0.016 (CI: ⫺0.028, ⫺0.004) ⫺0.013 (CI: ⫺0.026, 0.000)
⫺3.5 (CI: ⫺7.2, 0.1)
⫺0.2 (CI: ⫺2.8, 2.4)
0.1 (CI: ⫺3.3, 3.4)
⫺2.2 (CI: ⫺6.0, 1.5)
⌬, change. Results are reported as adjusted least squares means with 95% CIs.
30.4%, P ⫽ 0.519), 4-KKW (60.2 vs. 51.1%, P ⫽ 0.276),
8-KKW (75.4 vs. 78.6%, P ⫽ 0.773), and 12-KKW (82.1 vs.
70.8%, P ⫽ 0.305) groups.
Significant trends were observed for increasing CRF with
higher exercise dose in relative fitness (P-trend ⬍ 0.001) and
absolute (P-trend ⬍ 0.001) for CA women. In AA participants,
Percent Variance in the Change in CRF Explained by Race
The results of linear regression models (step-wise elimination)
to determine the percent variance of CRF, explained by participant race, found that the coefficient of partial determination
(partial r2) for race for the change in relative and absolute CRF in
all exercisers was 3.8% and 3.6%, respectively. For change in
relative CRF, the partial r2 for race was 1.6%, 7.2%, and 8.5%
in the 4-KKW, 8-KKW, and 12-KKW groups, respectively. For
change in absolute CRF, the partial r2 for race was 4.3% and 5.1%
in the 8-KKW and 12-KKW groups, respectively, but was not
significant in the 4-KKW group.
DISCUSSION
Fig. 2. Changes in cardiorespiratory fitness (CRF) in CA and AA postmenopausal women. Shown are the change in relative CRF (A) and absolute
(B) CRF across doses of exercise training. Results are shown as adjusted least
squares means with 95% confidence intervals. Analyses of covariance
(ANCOVAs) are adjusted for baseline CRF, age, and baseline mean respiratory exchange ratio (RER) from baseline exercise testing. *Significant difference between CA and AA participants. ⌬VO2, change in VO2.
The primary findings of the present paper were: 1) at baseline,
AA postmenopausal women had lower levels of CRF compared
with CA women; 2) despite improvements in CRF in both CA and
AA women, the overall magnitude of the response was generally
greater in CA women; this relationship was evident after adjustment for potential confounders, such as age, baseline CRF level,
and maximal RER from exercise testing; and 3) the percentage of
responders to aerobic exercise training was similar in CA and AA
participants, suggesting that exercise training is beneficial regardless of race. Our findings have clinical implications, as higher
CRF reduces CVD and diabetes risk (2, 29), both of which are
more prevalent in AA women (10, 21).
Our finding of lower baseline levels of CRF in AA compared
with CA postmenopausal women is supported by large epidemiology studies (28, 30). The CARDIA study (n ⫽ 4,968) found that
CRF [expressed as maximal estimated metabolic equivalents
(METS) from exercise testing] was lower in young (18 –30 yr)
AA (9.4 METS) compared with CA (11.1 METS) women (30).
Similarly, the Action for Health in Diabetes (Look AHEAD)
study (n ⫽ 5,145) found that CRF was lower in AA (6.7 METS)
compared with CA (7.3 METS) overweight and obese adults with
type 2 diabetes (28). In our study, postmenopausal AA women
had lower CRF, despite the fact that they were, on average, nearly
4 yr younger and had similar pedometer-determined physical
activity levels at baseline compared with CA participants. Therefore, it is plausible that lower CRF in AA postmenopausal women
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Dose Response to CRF
no significant trend was observed for higher exercise dose and
increasing CRF in either relative (P-trend ⫽ 0.62) or absolute
(P-trend ⫽ 0.46) fitness. We excluded controls in this analysis,
because the decrease in fitness in the AA control participants
could lead to a spurious interpretation.
1380
Racial Differences in the Response to Fitness with Exercise
•
Swift DL et al.
may contribute to the racial disparities in risk of developing CVD
and type 2 diabetes.
Following the 6 mo of aerobic training, postmenopausal AA
women generally demonstrated an attenuated improvement in
CRF compared with CA women, despite similar adherence to
training regimens and adjustment for potential confounding
factors. When CRF was expressed in relative terms, this racial
difference was found in all exercise groups following the
intervention. Similarly, when CRF was expressed in absolute
terms, AA women demonstrated a lower change in CRF in the
8-KKW and 12-KKW groups compared with CA participants.
When all exercise groups were combined, and statistical models were adjusted for the dose of exercise training, AA women
demonstrated an attenuated improvement in CRF (both relative
and absolute) compared with CA women following exercise
training. According to Mora et al. (24), who evaluated the
effect of CRF on mortality and CVD outcomes, a 1-MET
increase in CRF was associated with a 17% reduction in 20-yr
cardiovascular mortality risk in women. When CRF values are
converted to METS, the racial difference in the change in
fitness observed following exercise training at the various
doses in the present study corresponds to a range of an
approximate 3–7.2% reduction in cardiovascular mortality.
Although the racial differences in the change in CRF observed
in the present study are not large in magnitude, they may have
some clinical impact, especially at higher exercise doses. In
addition, the dose response of greater change in CRF with
higher exercise dose was observed in CA women but not in AA
women.
The HERITAGE Family Study found an attenuated improvement in relative CRF in AA (n ⫽ 198) compared with CA
(n ⫽ 435), but racial differences in absolute CRF following 20
wk of aerobic training were not statistically significant. Nevertheless, the investigators concluded that race explained a
small fraction of the variability in response of absolute CRF
(⬃1%) (6). In the present study, along with finding significant
differences in absolute CRF between CA and AA participants,
race explained ⬃3.6% of the total variability in absolute CRF
response among exercisers, with a greater influence within the
higher exercise-training doses (8 KKW: 4.3%; 12 KKW: 5.1%).
Differences in findings in absolute CRF between HERITAGE and
DREW could be due to differences in study design (i.e., aerobic
training intensity, study length, and exercise session duration).
The age range and gender composition of both studies may also
play a role, as HERITAGE included both men and women
over a wide age range (17– 65 yr), whereas DREW included
postmenopausal women only. Additionally, 20% (n ⫽ 118)
of The HERITAGE Family Study was composed of older
adults (age ⱖ50 yr), of which only 13% (n ⫽ 15) were AA
(31). Our data expand the findings of The HERITAGE
Family Study by evaluating racial differences in CRF,
specifically in postmenopausal women, which may be clinically significant, given the markedly increased CVD risk
following menopause (13).
A potential mechanism that may explain the racial differences in CRF could be the higher proportion of type 1 muscle
fibers observed in CA compared with AA individuals (1a, 32).
Since type 1 muscle fibers are more oxidative than type 2 (32),
this may contribute to the observed racial differences in baseline CRF and changes in CRF following exercise training. It
could be speculated that another potential mechanism could be
the lower hemoglobin levels in AAs compared with CA indi-
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Fig. 3. Change in relative and absolute CRF
in CA and AA postmenopausal exercisers
(n ⫽ 302; A and B) and exercisers who
obtained a RER value ⬎1.05 at both baseline
and follow-up (n ⫽ 276; C and D), adjusted
for total energy expenditure during exercise
training. Results are shown as adjusted least
squares means with 95% confidence intervals. ANCOVAs are adjusted for baseline
CRF, age, baseline mean RER from exercise
testing, and total energy expenditure during
6 mo of exercise training.
Racial Differences in the Response to Fitness with Exercise
ACKNOWLEDGMENTS
This work was performed at The Cooper Institute, and the staff is especially
commended for their efforts. We thank The Cooper Institute Scientific Advisory Board and the DREW participants.
Present address of C. P. Earnest: Dept. for Health, University of Bath, Bath,
BA2 7AY, UK.
GRANTS
Support for this work was provided by the National Heart, Lung, and Blood
Institute (Grant HL-66262) and unrestricted research support from The CocaCola Company. The salary and training of D. L. Swift are supported through
a National Institute of Diabetes and Digestive and Kidney Diseases (T32
Postdoctoral Fellowship; Obesity: from genes to man; DK-64584-10).
DISCLOSURES
The authors have no conflict of interest to declare on the subject matter of
the present paper.
AUTHOR CONTRIBUTIONS
Author contributions: D.L.S., N.M.J., C.J.L., C.P.E., T.S.C., and R.L.N.
conception and design of research; C.P.E., S.N.B., and T.S.C. performed
experiments; D.L.S., W.D.J., and R.L.N. analyzed data; D.L.S., N.M.J., C.J.L.,
C.P.E., W.D.J., S.N.B., T.S.C., and R.L.N. interpreted results of experiments;
Swift DL et al.
1381
D.L.S. prepared figures; D.L.S., N.M.J., S.N.B., T.S.C., and R.L.N. drafted
manuscript; D.L.S., N.M.J., C.J.L., C.P.E., W.D.J., S.N.B., T.S.C., and R.L.N.
edited and revised manuscript; D.L.S., N.M.J., C.J.L., C.P.E., W.D.J., S.N.B.,
T.S.C., and R.L.N. approved final version of manuscript.
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ethnic differences and investigate the physiologic mechanisms
responsible for the attenuated response in AA individuals.
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