- Email: [email protected]
Physical Activity Duration, Intensity, and Arterial Stiffening in Postmenopausal Women
AJH
2006; 19:1032–1036
Physical Activity Duration, Intensity, and Arterial Stiffening in Postmenopausal Women Jun Sugawara, Takeshi Otsuki, Takumi Tanabe, Koichiro Hayashi, Seiji Maeda, and Mitsuo Matsuda Background: Aerobic exercise training is associated with lower central arterial stiffness, but little information exists on the effects of physical activity intensity or duration on central arterial stiffness. Using a cross-sectional and interventional approach, we tested the hypothesis that both moderate and vigorous physical activity reduce central arterial stiffness in postmenopausal women. Methods: Carotid arterial stiffness (via ultrasound and applanation tonometry) and duration of physical activity at low, moderate, and vigorous intensities (via electronic accelerometer) were measured in 103 apparently healthy sedentary or recreationally active women 47 to 82 years of age. Moderate intensity physical activity was defined as 4.0 to 6.0 metabolic equivalents (MET) in subjects aged ⬍65 years and as 3.0 to 5.0 MET in subjects ⱖ65 years. A subgroup of 17 sedentary subjects was randomly assigned to moderate (n ⫽ 8) or vigorous (n ⫽ 9) intensity cycling exercise training (900 kcal/week, three to five sessions per week, for 12 weeks). Carotid arterial stiffness was measured before and after training.
Results: Carotid -stiffness index was significantly correlated with the duration of moderate and vigorous intensity physical activity (r ⫽ ⫺0.25 and r ⫽ ⫺0.22) even after adjustment for age, height, and mean BP. Carotid -stiffness index significantly decreased after moderate and vigorous intensity cycling training. There were no significant group differences in the magnitude of -stiffness index change even after adjustment for expected confounders (eg, baseline -stiffness index, height, body mass index, heart rate, and post-training body mass, body mass index, and mean BP). Conclusions: These results suggest that both moderate and vigorous physical activities have favorable effects on central arterial stiffness in postmenopausal women. Am J Hypertens 2006;19:1032–1036 © 2006 American Journal of Hypertension, Ltd. Key Words: Arterial compliance, aging, -stiffness index, exercise training.
tiffening of the large elastic arteries impairs the buffering function of the arterial system and contributes to cardiovascular disease.1 The incidence of cardiovascular disease in women increases sharply after middle age, and menopause is thought to be a major determinant of this increase.2 Hormone replacement therapy (HRT) may partly lower central arterial stiffness in postmenopausal women,3 but it has been recently identified as a risk factor for breast cancer development.4 Thus it is necessary to explore alternative methods of cardiovascular protection in these women. For the prevention of cardiovascular disease, the Centers for Disease Control and Prevention (CDC) and the
S
American College of Sports Medicine (ACSM) recommend that individuals engage in physical activity at a relative intensity of 40% to 60% of maximal oxygen consumption (or heart rate reserve) or at an absolute intensity of 3 to 6 metabolic equivalents (MET) most days of the week.5,6 Increased central arterial stiffness, a risk factor for cardiovascular disease, is significantly lower in endurance-trained postmenopausal female athletes than their sedentary peers.3,7 Moreau et al3 reported that regular aerobic exercise (defined as ⬃70% of maximal heart rate) at the upper end of the recommended physical activity level,5,6,8 lowered central arterial stiffness even in sedentary postmenopausal women who had previously used
Received December 21, March 10, 2006. Accepted March 11, 2006. From the Institute for Human Science and Biomedical Engineering (JS, KH), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan; Center for Tsukuba Advanced Research Alliance (TO, SM, MM), University of Tsukuba, Tsukuba, Japan; Institute of Health and Sport Sciences (TO, TT, SM, MM), University of Tsukuba, Tsukuba, Japan. This work was supported by Special Coordination Funds of the
Ministry of Education, Culture, Sports, Science, and Technology of Japan, by Tsukuba Advanced Research Alliance at the University of Tsukuba, and by DESCENTE. Address correspondence and reprint requests to Dr. Jun Sugawara, Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology, Higashi, AIST Tsukuba Central 6, Tsukuba, Ibaraki 305-8566, Japan; e-mail: jun. [email protected]
0895-7061/06/$32.00 doi:10.1016/j.amjhyper.2006.03.008
© 2006 by the American Journal of Hypertension, Ltd. Published by Elsevier Inc.
AJH–October 2006 –VOL. 19, NO. 10
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
hormone replacement therapy. However the effects of moderate versus vigorous intensity exercise on arterial stiffening of central arteries are unknown. Accordingly we used a cross-sectional approach to determine the relationship between central arterial stiffness and the duration of low, moderate, and vigorous intensity physical activity. In the intervention study, we compared the effects of aerobic exercise training at moderate and vigorous intensities on carotid arterial stiffness. The intensity of moderate exercise training was lower than in a previous study by Moreau et al3 to mimic common exercise prescriptions and practices. We hypothesized that both moderate and vigorous intensity physical activity would lower central arterial stiffness in postmenopausal women.
Methods Subjects In the cross-sectional study, 103 sedentary or recreationally active, nonsmoking, postmenopausal women 47 to 82 years of age (Table 1) were followed for 14 days. Subjects were not taking hormone replacement therapy or other medications and were free of cardiovascular disease as assessed by a medical history questionnaire and a submaximal exercise test. Electrocardiograms and blood pressure (BP) were monitored for myocardium ischemia or excessive BP elevations during cycling exercise at intensities up to 85% of age-predicted maximal heart rate (220 ⫺ age). In the intervention study, a subgroup of 17 sedentary women was studied before and after 12 weeks of aerobic exercise training. These studies were approved by the Human Research Committee and all subjects signed an informed consent statement before participation.
Table 1. Subject characteristics in the crosssectional study (n ⫽ 103) Variable Age (y) Height (cm) Body mass (kg) Body mass index (kg/m2) Heart rate (beats/min) Brachial SBP (mm Hg) Brachial MAP (mm Hg) Brachial DBP (mm Hg) Brachial PP (mm Hg) Carotid SBP (mm Hg) Carotid PP (mm Hg) Carotid diameter (mm) Carotid -stiffness index (AU) Duration of physical activity Low intensity (min/day) Moderate intensity (min/day) Vigorous intensity (min/day)
Mean ⴞ SD 64 152 53 22.9 63 120 92 74 45 116 42 6.1 10.2
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
7 6 6 2.5 9 12 9 7 8 15 13 0.7 3.7
53 ⫾ 21 17 ⫾ 12 9 ⫾ 10
DBP ⫽ diastolic blood pressure; MAP ⫽ mean arterial blood pressure; PP ⫽ pulse pressure; SBP ⫽ systolic blood pressure.
1033
Measurements Before the measurements, subjects abstained from caffeine, fasted for 4 h, and abstained from exercise for at least 24 h. Height, body mass, and body mass index (BMI) were measured with conventional methods. After resting supine in a temperature-controlled room (24° to 26°C) for 10 to 15 min, heart rate and brachial BP were measured with a semi-automated electrocardiograph and an oscillometric device (form PWV/ABI, Colin MT, Komaki, Japan). A combination of ultrasound imaging on the right carotid artery with a high-resolution (10-MHz) linear transducer (SonoSite180PLUS, SonoSite Inc., Bothell, WA) and simultaneous applanation of tonometrically obtained arterial pressures from the left common carotid artery (form PWV/ABI, Colin MT, Komaki, Japan) permitted noninvasive determinations of arterial stiffness, as previously described.9 B-mode longitudinal images were obtained 1 to 2 cm proximal to the carotid bulb and were analyzed by image analysis software. The BP values at the carotid artery were adjusted for hold-down pressure by equilibrating the carotid mean and diastolic BP to that of the brachial artery. -stiffness index was calculated by the following equation: (ln [P1/P0])/([D1⫺ D0]/D0), where P1 and P0 are carotid systolic and diastolic BP and D1 and D0 are the maximal and minimal diameter, respectively. The duration and intensity of physical activity were evaluated for 14 days by a uniaxial electrical accelerometer (Lifecorder, KENZ, Nagoya, Japan) worn continuously on the iliac spine. Acceleration in the vertical direction is calculated by a sensor that samples at 32 Hz and the maximal pulse per 4 sec is integrated into an algorithm that organizes physical activity intensity into nine levels based on calculated MET. A previous validation study showed a significant correlation between treadmill walking speed, VO2, and the activity level measured by the accelerometer.10 We obtained daily physical activity duration corresponding to ⬍4.0 MET (low), 4.0 to 6.0 MET (moderate), and ⬎6.0 MET (vigorous) in subjects ⬍65 years of age and those corresponding to ⬍3.0 MET (low), 3.0 to 5.0 MET (moderate), and ⬎5.0 MET (vigorous) in subjects ⬎65 years of age8 from the data acquired over a continuous 7-day period beginning 3 to 4 days after the commencement of monitoring. Exercise Training Intervention Subjects were randomly assigned to 12 weeks of cycling training on an electric-braked ergometer (180 to 300 kcal per session, three to five sessions per week) at 40% HR reserve (⬃4 MET; moderate training group; n ⫽ 8) or 70% heart rate reserve (⬃7 MET; vigorous training group; n ⫽ 9). The moderate and vigorous training groups had target heart rates of 103 ⫾ 4 beats/min and 128 ⫾ 4 beats/min, respectively.
1034
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
Statistical Analysis Univariate and partial correlation analyses were used to determine the relationships between variables of interests. Repeated-measures ANOVA was used to evaluate the effects of exercise training and its intensity. In the case of a significant F value, Fischer PLSD testing was performed. One-way ANOVA and ANCOVA were used to determine significant group differences. Data are reported as mean ⫾ SD. Statistical significance was set at a value of P ⬍ .05.
Results In the cross-sectional study, -stiffness index was higher in older individuals (r ⫽ 0.43, P ⬍ .0001) and was inversely related to the duration of physical activity at all intensities (r ⫽ ⫺0.23 to ⫺0.28, P ⬍ .05) (Fig. 1). -stiffness index was significantly correlated with the duration of physical activity at moderate (r ⫽ ⫺0.25, P ⬍ .05) and vigorous (r ⫽ ⫺0.27, P ⬍ .01), but not low intensities, even after adjustment for age, height, body mass index, and mean arterial BP. Older subjects spent
AJH–October 2006 –VOL. 19, NO. 10
less time engaging in low intensity physical activity (r ⫽ ⫺0.35, P ⬍ .0001), whereas time spent at moderate and vigorous intensities were not significantly correlated with age. All subjects in the intervention study completed the training program although several subjects in both groups required 13 to 14 weeks to finish the required amount of training (10,800 kcal of total energy expenditure). Adherence rates to the exercise program were similar between the moderate and vigorous intensity training groups. As shown in Table 2, the groups were identical in measured variables at baseline with the exception of heart rate being significantly lower in the vigorous intensity training group (P ⬍ .05). Body mass and body mass index decreased in the vigorous intensity but not the moderate intensity training group (P ⬍ .05). Heart rate, brachial and carotid BP, and carotid lumen diameter did not change significantly in the moderate or vigorous intensity training. -stiffness index decreased significantly by both moderate and vigorous intensity training (P ⬍ .05). The magnitude of the change in -stiffness index in the moderate intensity training group did not differ from that of the vigorous intensity training group (⫺4.0 ⫾ 4.8 v ⫺4.1 ⫾ 4.9 AU, P ⫽ .97), even when ANCOVA was performed using the following covariates: baseline -stiffness index (⫺3.5 ⫾ 3.8 v ⫺4.5 ⫾ 3.8 AU, P ⫽ .62), height (⫺4.0 ⫾ 5.1 v ⫺4.1 ⫾ 5.1 AU, P ⫽ .97), baseline BMI (⫺3.3 ⫾ 3.9 v ⫺4.7 ⫾ 3.9 AU, P ⫽ .48), baseline heart rate (⫺3.3 ⫾ 6.3 v ⫺4.7 ⫾ 6.1 AU, P ⫽ .70), post-training BMI (⫺3.1 ⫾ 3.9 v ⫺4.9 ⫾ 3.9 AU, P ⫽ .37), or post-training mean arterial BP (⫺3.8 ⫾ 5.2 v ⫺4.3 ⫾ 5.1 AU, P ⫽ .84).
Discussion
FIG. 1. Relationship between -stiffness index and duration of physical activity at low (A), moderate (B), and vigorous intensities (C).
The primary findings of this study are as follows. Carotid -stiffness index was significantly correlated with the duration of moderate and vigorous intensity physical activity even after adjustment for known confounders such as age, height, body mass index, and mean arterial BP.7 The intervention study showed that moderate and vigorous intensity exercise training programs induce parallel reductions in -stiffness index. There were no significant group differences in the magnitude of change in -stiffness index even after adjustment for expected confounders (eg, baseline values of -stiffness index, height, BMI, and heart rate and the training-related changes in body mass, BMI, and mean arterial BP).7 These results indicate that the effects of moderate intensity physical activity on central arterial stiffness did not differ from those of vigorous intensity physical activity. Our findings have important clinical implications because moderate intensity physical activity can be easily incorporated into daily life. Tanaka and colleagues demonstrated that central arterial stiffness is significantly lower in endurance-trained postmenopausal women than in their age-matched sedentary peers.3,7 Moreau et al3 reported that carotid arterial stiffness was decreased by ⬃25% in healthy postmenopausal
AJH–October 2006 –VOL. 19, NO. 10
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
1035
Table 2. Subject characteristics in the intervention study Moderate intensity training group (n ⴝ 8) Variable Age (y) Height (cm) Body mass (kg) Body mass index (kg/m2) Heart rate (beats/min) Brachial SBP (mm Hg) Brachial DBP (mm Hg) Brachial MAP (mm Hg) Brachial PP (mm Hg) Carotid SBP (mm Hg) Carotid PP (mm Hg) Carotid PP (mm Hg) Carotid diameter (mm) Carotid -stiffness index (AU)
Before training 58 155 61 25.5 63 121 93 77 44 112 35 35 6.2 13.5
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
4 3 9 3.6 8 11 10 8 4 10 4 4 0.5 4.4
After training
60 25.1 61 125 98 80 45 115 35 35 6.3 9.5
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
Vigorous-intensity training group (n ⴝ 9) Before training
8 3.1 8 7 8 5 5 7 4 4 0.5 4.2‡
59 155 58 24.2 51 116 89 72 44 107 34 34 6.0 12.3
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
6 3 7 3.0 5† 14 12 9 7 13 6 6 0.2 4.6
After training
56 23.5 52 119 92 75 44 110 35 35 6.1 8.2
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
7* 3.0* 6† 12 11 8 7 12 6 6 0.5 3.6‡
DBP ⫽ diastolic blood pressure; MAP ⫽ mean arterial blood pressure; PP ⫽ pulse pressure; SBP ⫽ systolic blood pressure. Data are mean and SD. * P ⬍ .01 v before training; † P ⬍ .05 v moderate-intensity training group; ‡ P ⬍ .05 v before training.
women taking hormone replacement therapy after 3 months of aerobic exercise training, corresponding to ⬃70% of age-predicted maximal heart rate. However, little information is available on the effects of moderate intensity exercise training on carotid arterial stiffening in postmenopausal women not taking hormone replacement therapy. Therefore, we determined the relationship between the duration of low, moderate, and vigorous intensity physical activity (as stated by the CDC and ACSM5,6,8) and central arterial stiffness. Daily physical activity levels of subjects were evaluated by an electric accelerometer, a relatively objective instrument, because physical activity assessment via self-report may be subject to bias and misclassification. We found that the duration of moderate and vigorous, but not low, intensity physical activity was significantly associated with -stiffness index, even after adjustment for age, height, body mass index, and mean arterial BP. Second, we compared the lowering effects of isoenergetic moderate and vigorous intensity aerobic exercise training on carotid arterial stiffness. Similar reductions in -stiffness index were seen in both training programs (27% to 29%). Although we did not examine a control group, our values of -stiffness index were comparable to those of Moreau et al3 even without the use of hormone replacement therapy. These results suggest, at least in part, that the interaction of intensity (moderate and vigorous) and duration of physical activity are associated with the prevention of central arterial stiffening in postmenopausal women. The mechanisms by which regular moderate and vigorous intensity physical activity lowers central arterial stiffness are not clear. Regular aerobic exercise in older adults results in enhanced endothelium-dependent vasodilation11 and restraint of endothelium-derived vasoconstrictor hormones.12 These changes might be associated with a
decrease in vascular smooth muscle tone, thereby decreasing central arterial stiffness. Interestingly, Goto et al13 reported that in healthy young men, 12 weeks of aerobic exercise training at 50% of maximal oxygen consumption (VO2max), but not at 75%VO2max, improved endothelium-dependent vasodilation and that oxidative stress was elevated only after the vigorous intensity exercise training. These results suggest that augmented oxidative stress in the vasculature may slow the improvement of central arterial stiffness with the exercise training, which might be responsible, at least in part, for the similar changes in central arterial stiffness seen in our moderate and vigorous intensity exercise trained subjects. In our intervention study, body mass index decreased in the vigorous but not the moderate intensity training group. These results should be emphasized because a high body mass index is a known risk factor for cardiovascular disease14 as well as central arterial stiffening. However, the exact mechanisms behind the lowering of central arterial stiffness with physical activity in this study cannot be explained by changes in body mass index. Therefore, additional studies on the mechanisms behind these changes are warranted. In summary, -stiffness index is correlated with moderate and vigorous intensity physical activity and is reduced by 12 weeks of moderate and vigorous aerobic exercise training. Therefore it appears that moderate intensity physical activity induces reductions in central arterial stiffening similar to vigorous intensity physical activity in postmenopausal women.
References 1.
Nichols W, O’Rourke MF: McDonald’s Blood Flow in Arteries. Edward Arnold, London, 1998.
1036
2.
3.
4.
5.
6.
7.
8.
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
van der Schouw YT, van der Graaf Y, Steyerberg EW, Eijkemans JC, Banga JD: Age at menopause as a risk factor for cardiovascular mortality. Lancet 1996;347:714 –718. Moreau KL, Donato AJ, Seals DR, DeSouza CA, Tanaka H: Regular exercise, hormone replacement therapy and the age-related decline in carotid arterial compliance in healthy women. Cardiovasc Res 2003;57:861– 868. Beral V, Banks E, Reeves G: Evidence from randomised trials on the long-term effects of hormone replacement therapy. Lancet 2002; 360:942–944. Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC, et al: Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. J Am Med Assoc 1995;273:402– 407. Thompson PD, Buchner D, Pina IL, Balady GJ, Williams MA, Marcus BH, Berra K, Blair SN, Costa F, Franklin B, Fletcher GF, Gordon NF, Pate RR, Rodriguez BL, Yancey AK, Wenger NK: Exercise and physical activity in the prevention and treatment of atherosclerotic cardiovascular disease: a statement from the Council on Clinical Cardiology (Subcommittee on Exercise, Rehabilitation, and Prevention) and the Council on Nutrition, Physical Activity, and Metabolism (Subcommittee on Physical Activity). Circulation 2003; 107:3109 –3116. Tanaka H, DeSouza CA, Seals DR: Absence of age-related increase in central arterial stiffness in physically active women. Arterioscler Thromb Vasc Biol 1998;18:127–132. Balady GJ, Chaitman B, Driscoll D, Foster C, Froelicher E, Gordon N, Pate R, Rippe J, Bazzarre T: Recommendations for cardiovas-
9.
10.
11.
12.
13.
14.
AJH–October 2006 –VOL. 19, NO. 10
cular screening, staffing, and emergency policies at health/fitness facilities. Circulation 1998;97:2283–2293. Sugawara J, Otsuki T, Maeda S, Tanabe T, Kuno S, Ajisaka R, Matsuda M: Effect of arterial lumen enlargement on carotid arterial compliance in normotensive postmenopausal women. Hypertens Res 2005;28:323–329. Kumahara H, Schutz Y, Ayabe M, Yoshioka M, Yoshitake Y, Shindo M, Ishii K, Tanaka H: The use of uniaxial accelerometry for the assessment of physical-activity-related energy expenditure: a validation study against whole-body indirect calorimetry. Br J Nutr 2004;91:235–243. DeSouza CA, Shapiro LF, Clevenger CM, Dinenno FA, Monahan KD, Tanaka H, Seals DR: Regular aerobic exercise prevents and restores age-related declines in endothelium-dependent vasodilation in healthy men. Circulation 2000;102:1351–1357. Maeda S, Tanabe T, Miyauchi T, Otsuki T, Sugawara J, Iemitsu M, Kuno S, Ajisaka R, Yamaguchi I, Matsuda M: Aerobic exercise training reduces plasma endothelin-1 concentration in older women. J Appl Physiol 2003;95:336 –341. Goto C, Higashi Y, Kimura M, Noma K, Hara K, Nakagawa K, Kawamura M, Chayama K, Yoshizumi M, Nara I: Effect of different intensities of exercise on endothelium-dependent vasodilation in humans: role of endothelium-dependent nitric oxide and oxidative stress. Circulation 2003;108:530 –535. Christou DD, Gentile CL, DeSouza CA, Seals DR, Gates PE: Fatness is a better predictor of cardiovascular disease risk factor profile than aerobic fitness in healthy men. Circulation 2005;111: 1904 –1914.
2006; 19:1032–1036
Physical Activity Duration, Intensity, and Arterial Stiffening in Postmenopausal Women Jun Sugawara, Takeshi Otsuki, Takumi Tanabe, Koichiro Hayashi, Seiji Maeda, and Mitsuo Matsuda Background: Aerobic exercise training is associated with lower central arterial stiffness, but little information exists on the effects of physical activity intensity or duration on central arterial stiffness. Using a cross-sectional and interventional approach, we tested the hypothesis that both moderate and vigorous physical activity reduce central arterial stiffness in postmenopausal women. Methods: Carotid arterial stiffness (via ultrasound and applanation tonometry) and duration of physical activity at low, moderate, and vigorous intensities (via electronic accelerometer) were measured in 103 apparently healthy sedentary or recreationally active women 47 to 82 years of age. Moderate intensity physical activity was defined as 4.0 to 6.0 metabolic equivalents (MET) in subjects aged ⬍65 years and as 3.0 to 5.0 MET in subjects ⱖ65 years. A subgroup of 17 sedentary subjects was randomly assigned to moderate (n ⫽ 8) or vigorous (n ⫽ 9) intensity cycling exercise training (900 kcal/week, three to five sessions per week, for 12 weeks). Carotid arterial stiffness was measured before and after training.
Results: Carotid -stiffness index was significantly correlated with the duration of moderate and vigorous intensity physical activity (r ⫽ ⫺0.25 and r ⫽ ⫺0.22) even after adjustment for age, height, and mean BP. Carotid -stiffness index significantly decreased after moderate and vigorous intensity cycling training. There were no significant group differences in the magnitude of -stiffness index change even after adjustment for expected confounders (eg, baseline -stiffness index, height, body mass index, heart rate, and post-training body mass, body mass index, and mean BP). Conclusions: These results suggest that both moderate and vigorous physical activities have favorable effects on central arterial stiffness in postmenopausal women. Am J Hypertens 2006;19:1032–1036 © 2006 American Journal of Hypertension, Ltd. Key Words: Arterial compliance, aging, -stiffness index, exercise training.
tiffening of the large elastic arteries impairs the buffering function of the arterial system and contributes to cardiovascular disease.1 The incidence of cardiovascular disease in women increases sharply after middle age, and menopause is thought to be a major determinant of this increase.2 Hormone replacement therapy (HRT) may partly lower central arterial stiffness in postmenopausal women,3 but it has been recently identified as a risk factor for breast cancer development.4 Thus it is necessary to explore alternative methods of cardiovascular protection in these women. For the prevention of cardiovascular disease, the Centers for Disease Control and Prevention (CDC) and the
S
American College of Sports Medicine (ACSM) recommend that individuals engage in physical activity at a relative intensity of 40% to 60% of maximal oxygen consumption (or heart rate reserve) or at an absolute intensity of 3 to 6 metabolic equivalents (MET) most days of the week.5,6 Increased central arterial stiffness, a risk factor for cardiovascular disease, is significantly lower in endurance-trained postmenopausal female athletes than their sedentary peers.3,7 Moreau et al3 reported that regular aerobic exercise (defined as ⬃70% of maximal heart rate) at the upper end of the recommended physical activity level,5,6,8 lowered central arterial stiffness even in sedentary postmenopausal women who had previously used
Received December 21, March 10, 2006. Accepted March 11, 2006. From the Institute for Human Science and Biomedical Engineering (JS, KH), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan; Center for Tsukuba Advanced Research Alliance (TO, SM, MM), University of Tsukuba, Tsukuba, Japan; Institute of Health and Sport Sciences (TO, TT, SM, MM), University of Tsukuba, Tsukuba, Japan. This work was supported by Special Coordination Funds of the
Ministry of Education, Culture, Sports, Science, and Technology of Japan, by Tsukuba Advanced Research Alliance at the University of Tsukuba, and by DESCENTE. Address correspondence and reprint requests to Dr. Jun Sugawara, Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology, Higashi, AIST Tsukuba Central 6, Tsukuba, Ibaraki 305-8566, Japan; e-mail: jun. [email protected]
0895-7061/06/$32.00 doi:10.1016/j.amjhyper.2006.03.008
© 2006 by the American Journal of Hypertension, Ltd. Published by Elsevier Inc.
AJH–October 2006 –VOL. 19, NO. 10
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
hormone replacement therapy. However the effects of moderate versus vigorous intensity exercise on arterial stiffening of central arteries are unknown. Accordingly we used a cross-sectional approach to determine the relationship between central arterial stiffness and the duration of low, moderate, and vigorous intensity physical activity. In the intervention study, we compared the effects of aerobic exercise training at moderate and vigorous intensities on carotid arterial stiffness. The intensity of moderate exercise training was lower than in a previous study by Moreau et al3 to mimic common exercise prescriptions and practices. We hypothesized that both moderate and vigorous intensity physical activity would lower central arterial stiffness in postmenopausal women.
Methods Subjects In the cross-sectional study, 103 sedentary or recreationally active, nonsmoking, postmenopausal women 47 to 82 years of age (Table 1) were followed for 14 days. Subjects were not taking hormone replacement therapy or other medications and were free of cardiovascular disease as assessed by a medical history questionnaire and a submaximal exercise test. Electrocardiograms and blood pressure (BP) were monitored for myocardium ischemia or excessive BP elevations during cycling exercise at intensities up to 85% of age-predicted maximal heart rate (220 ⫺ age). In the intervention study, a subgroup of 17 sedentary women was studied before and after 12 weeks of aerobic exercise training. These studies were approved by the Human Research Committee and all subjects signed an informed consent statement before participation.
Table 1. Subject characteristics in the crosssectional study (n ⫽ 103) Variable Age (y) Height (cm) Body mass (kg) Body mass index (kg/m2) Heart rate (beats/min) Brachial SBP (mm Hg) Brachial MAP (mm Hg) Brachial DBP (mm Hg) Brachial PP (mm Hg) Carotid SBP (mm Hg) Carotid PP (mm Hg) Carotid diameter (mm) Carotid -stiffness index (AU) Duration of physical activity Low intensity (min/day) Moderate intensity (min/day) Vigorous intensity (min/day)
Mean ⴞ SD 64 152 53 22.9 63 120 92 74 45 116 42 6.1 10.2
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
7 6 6 2.5 9 12 9 7 8 15 13 0.7 3.7
53 ⫾ 21 17 ⫾ 12 9 ⫾ 10
DBP ⫽ diastolic blood pressure; MAP ⫽ mean arterial blood pressure; PP ⫽ pulse pressure; SBP ⫽ systolic blood pressure.
1033
Measurements Before the measurements, subjects abstained from caffeine, fasted for 4 h, and abstained from exercise for at least 24 h. Height, body mass, and body mass index (BMI) were measured with conventional methods. After resting supine in a temperature-controlled room (24° to 26°C) for 10 to 15 min, heart rate and brachial BP were measured with a semi-automated electrocardiograph and an oscillometric device (form PWV/ABI, Colin MT, Komaki, Japan). A combination of ultrasound imaging on the right carotid artery with a high-resolution (10-MHz) linear transducer (SonoSite180PLUS, SonoSite Inc., Bothell, WA) and simultaneous applanation of tonometrically obtained arterial pressures from the left common carotid artery (form PWV/ABI, Colin MT, Komaki, Japan) permitted noninvasive determinations of arterial stiffness, as previously described.9 B-mode longitudinal images were obtained 1 to 2 cm proximal to the carotid bulb and were analyzed by image analysis software. The BP values at the carotid artery were adjusted for hold-down pressure by equilibrating the carotid mean and diastolic BP to that of the brachial artery. -stiffness index was calculated by the following equation: (ln [P1/P0])/([D1⫺ D0]/D0), where P1 and P0 are carotid systolic and diastolic BP and D1 and D0 are the maximal and minimal diameter, respectively. The duration and intensity of physical activity were evaluated for 14 days by a uniaxial electrical accelerometer (Lifecorder, KENZ, Nagoya, Japan) worn continuously on the iliac spine. Acceleration in the vertical direction is calculated by a sensor that samples at 32 Hz and the maximal pulse per 4 sec is integrated into an algorithm that organizes physical activity intensity into nine levels based on calculated MET. A previous validation study showed a significant correlation between treadmill walking speed, VO2, and the activity level measured by the accelerometer.10 We obtained daily physical activity duration corresponding to ⬍4.0 MET (low), 4.0 to 6.0 MET (moderate), and ⬎6.0 MET (vigorous) in subjects ⬍65 years of age and those corresponding to ⬍3.0 MET (low), 3.0 to 5.0 MET (moderate), and ⬎5.0 MET (vigorous) in subjects ⬎65 years of age8 from the data acquired over a continuous 7-day period beginning 3 to 4 days after the commencement of monitoring. Exercise Training Intervention Subjects were randomly assigned to 12 weeks of cycling training on an electric-braked ergometer (180 to 300 kcal per session, three to five sessions per week) at 40% HR reserve (⬃4 MET; moderate training group; n ⫽ 8) or 70% heart rate reserve (⬃7 MET; vigorous training group; n ⫽ 9). The moderate and vigorous training groups had target heart rates of 103 ⫾ 4 beats/min and 128 ⫾ 4 beats/min, respectively.
1034
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
Statistical Analysis Univariate and partial correlation analyses were used to determine the relationships between variables of interests. Repeated-measures ANOVA was used to evaluate the effects of exercise training and its intensity. In the case of a significant F value, Fischer PLSD testing was performed. One-way ANOVA and ANCOVA were used to determine significant group differences. Data are reported as mean ⫾ SD. Statistical significance was set at a value of P ⬍ .05.
Results In the cross-sectional study, -stiffness index was higher in older individuals (r ⫽ 0.43, P ⬍ .0001) and was inversely related to the duration of physical activity at all intensities (r ⫽ ⫺0.23 to ⫺0.28, P ⬍ .05) (Fig. 1). -stiffness index was significantly correlated with the duration of physical activity at moderate (r ⫽ ⫺0.25, P ⬍ .05) and vigorous (r ⫽ ⫺0.27, P ⬍ .01), but not low intensities, even after adjustment for age, height, body mass index, and mean arterial BP. Older subjects spent
AJH–October 2006 –VOL. 19, NO. 10
less time engaging in low intensity physical activity (r ⫽ ⫺0.35, P ⬍ .0001), whereas time spent at moderate and vigorous intensities were not significantly correlated with age. All subjects in the intervention study completed the training program although several subjects in both groups required 13 to 14 weeks to finish the required amount of training (10,800 kcal of total energy expenditure). Adherence rates to the exercise program were similar between the moderate and vigorous intensity training groups. As shown in Table 2, the groups were identical in measured variables at baseline with the exception of heart rate being significantly lower in the vigorous intensity training group (P ⬍ .05). Body mass and body mass index decreased in the vigorous intensity but not the moderate intensity training group (P ⬍ .05). Heart rate, brachial and carotid BP, and carotid lumen diameter did not change significantly in the moderate or vigorous intensity training. -stiffness index decreased significantly by both moderate and vigorous intensity training (P ⬍ .05). The magnitude of the change in -stiffness index in the moderate intensity training group did not differ from that of the vigorous intensity training group (⫺4.0 ⫾ 4.8 v ⫺4.1 ⫾ 4.9 AU, P ⫽ .97), even when ANCOVA was performed using the following covariates: baseline -stiffness index (⫺3.5 ⫾ 3.8 v ⫺4.5 ⫾ 3.8 AU, P ⫽ .62), height (⫺4.0 ⫾ 5.1 v ⫺4.1 ⫾ 5.1 AU, P ⫽ .97), baseline BMI (⫺3.3 ⫾ 3.9 v ⫺4.7 ⫾ 3.9 AU, P ⫽ .48), baseline heart rate (⫺3.3 ⫾ 6.3 v ⫺4.7 ⫾ 6.1 AU, P ⫽ .70), post-training BMI (⫺3.1 ⫾ 3.9 v ⫺4.9 ⫾ 3.9 AU, P ⫽ .37), or post-training mean arterial BP (⫺3.8 ⫾ 5.2 v ⫺4.3 ⫾ 5.1 AU, P ⫽ .84).
Discussion
FIG. 1. Relationship between -stiffness index and duration of physical activity at low (A), moderate (B), and vigorous intensities (C).
The primary findings of this study are as follows. Carotid -stiffness index was significantly correlated with the duration of moderate and vigorous intensity physical activity even after adjustment for known confounders such as age, height, body mass index, and mean arterial BP.7 The intervention study showed that moderate and vigorous intensity exercise training programs induce parallel reductions in -stiffness index. There were no significant group differences in the magnitude of change in -stiffness index even after adjustment for expected confounders (eg, baseline values of -stiffness index, height, BMI, and heart rate and the training-related changes in body mass, BMI, and mean arterial BP).7 These results indicate that the effects of moderate intensity physical activity on central arterial stiffness did not differ from those of vigorous intensity physical activity. Our findings have important clinical implications because moderate intensity physical activity can be easily incorporated into daily life. Tanaka and colleagues demonstrated that central arterial stiffness is significantly lower in endurance-trained postmenopausal women than in their age-matched sedentary peers.3,7 Moreau et al3 reported that carotid arterial stiffness was decreased by ⬃25% in healthy postmenopausal
AJH–October 2006 –VOL. 19, NO. 10
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
1035
Table 2. Subject characteristics in the intervention study Moderate intensity training group (n ⴝ 8) Variable Age (y) Height (cm) Body mass (kg) Body mass index (kg/m2) Heart rate (beats/min) Brachial SBP (mm Hg) Brachial DBP (mm Hg) Brachial MAP (mm Hg) Brachial PP (mm Hg) Carotid SBP (mm Hg) Carotid PP (mm Hg) Carotid PP (mm Hg) Carotid diameter (mm) Carotid -stiffness index (AU)
Before training 58 155 61 25.5 63 121 93 77 44 112 35 35 6.2 13.5
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
4 3 9 3.6 8 11 10 8 4 10 4 4 0.5 4.4
After training
60 25.1 61 125 98 80 45 115 35 35 6.3 9.5
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
Vigorous-intensity training group (n ⴝ 9) Before training
8 3.1 8 7 8 5 5 7 4 4 0.5 4.2‡
59 155 58 24.2 51 116 89 72 44 107 34 34 6.0 12.3
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
6 3 7 3.0 5† 14 12 9 7 13 6 6 0.2 4.6
After training
56 23.5 52 119 92 75 44 110 35 35 6.1 8.2
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
7* 3.0* 6† 12 11 8 7 12 6 6 0.5 3.6‡
DBP ⫽ diastolic blood pressure; MAP ⫽ mean arterial blood pressure; PP ⫽ pulse pressure; SBP ⫽ systolic blood pressure. Data are mean and SD. * P ⬍ .01 v before training; † P ⬍ .05 v moderate-intensity training group; ‡ P ⬍ .05 v before training.
women taking hormone replacement therapy after 3 months of aerobic exercise training, corresponding to ⬃70% of age-predicted maximal heart rate. However, little information is available on the effects of moderate intensity exercise training on carotid arterial stiffening in postmenopausal women not taking hormone replacement therapy. Therefore, we determined the relationship between the duration of low, moderate, and vigorous intensity physical activity (as stated by the CDC and ACSM5,6,8) and central arterial stiffness. Daily physical activity levels of subjects were evaluated by an electric accelerometer, a relatively objective instrument, because physical activity assessment via self-report may be subject to bias and misclassification. We found that the duration of moderate and vigorous, but not low, intensity physical activity was significantly associated with -stiffness index, even after adjustment for age, height, body mass index, and mean arterial BP. Second, we compared the lowering effects of isoenergetic moderate and vigorous intensity aerobic exercise training on carotid arterial stiffness. Similar reductions in -stiffness index were seen in both training programs (27% to 29%). Although we did not examine a control group, our values of -stiffness index were comparable to those of Moreau et al3 even without the use of hormone replacement therapy. These results suggest, at least in part, that the interaction of intensity (moderate and vigorous) and duration of physical activity are associated with the prevention of central arterial stiffening in postmenopausal women. The mechanisms by which regular moderate and vigorous intensity physical activity lowers central arterial stiffness are not clear. Regular aerobic exercise in older adults results in enhanced endothelium-dependent vasodilation11 and restraint of endothelium-derived vasoconstrictor hormones.12 These changes might be associated with a
decrease in vascular smooth muscle tone, thereby decreasing central arterial stiffness. Interestingly, Goto et al13 reported that in healthy young men, 12 weeks of aerobic exercise training at 50% of maximal oxygen consumption (VO2max), but not at 75%VO2max, improved endothelium-dependent vasodilation and that oxidative stress was elevated only after the vigorous intensity exercise training. These results suggest that augmented oxidative stress in the vasculature may slow the improvement of central arterial stiffness with the exercise training, which might be responsible, at least in part, for the similar changes in central arterial stiffness seen in our moderate and vigorous intensity exercise trained subjects. In our intervention study, body mass index decreased in the vigorous but not the moderate intensity training group. These results should be emphasized because a high body mass index is a known risk factor for cardiovascular disease14 as well as central arterial stiffening. However, the exact mechanisms behind the lowering of central arterial stiffness with physical activity in this study cannot be explained by changes in body mass index. Therefore, additional studies on the mechanisms behind these changes are warranted. In summary, -stiffness index is correlated with moderate and vigorous intensity physical activity and is reduced by 12 weeks of moderate and vigorous aerobic exercise training. Therefore it appears that moderate intensity physical activity induces reductions in central arterial stiffening similar to vigorous intensity physical activity in postmenopausal women.
References 1.
Nichols W, O’Rourke MF: McDonald’s Blood Flow in Arteries. Edward Arnold, London, 1998.
1036
2.
3.
4.
5.
6.
7.
8.
PHYSICAL ACTIVITY AND ARTERIAL STIFFNESS IN WOMEN
van der Schouw YT, van der Graaf Y, Steyerberg EW, Eijkemans JC, Banga JD: Age at menopause as a risk factor for cardiovascular mortality. Lancet 1996;347:714 –718. Moreau KL, Donato AJ, Seals DR, DeSouza CA, Tanaka H: Regular exercise, hormone replacement therapy and the age-related decline in carotid arterial compliance in healthy women. Cardiovasc Res 2003;57:861– 868. Beral V, Banks E, Reeves G: Evidence from randomised trials on the long-term effects of hormone replacement therapy. Lancet 2002; 360:942–944. Pate RR, Pratt M, Blair SN, Haskell WL, Macera CA, Bouchard C, Buchner D, Ettinger W, Heath GW, King AC, et al: Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. J Am Med Assoc 1995;273:402– 407. Thompson PD, Buchner D, Pina IL, Balady GJ, Williams MA, Marcus BH, Berra K, Blair SN, Costa F, Franklin B, Fletcher GF, Gordon NF, Pate RR, Rodriguez BL, Yancey AK, Wenger NK: Exercise and physical activity in the prevention and treatment of atherosclerotic cardiovascular disease: a statement from the Council on Clinical Cardiology (Subcommittee on Exercise, Rehabilitation, and Prevention) and the Council on Nutrition, Physical Activity, and Metabolism (Subcommittee on Physical Activity). Circulation 2003; 107:3109 –3116. Tanaka H, DeSouza CA, Seals DR: Absence of age-related increase in central arterial stiffness in physically active women. Arterioscler Thromb Vasc Biol 1998;18:127–132. Balady GJ, Chaitman B, Driscoll D, Foster C, Froelicher E, Gordon N, Pate R, Rippe J, Bazzarre T: Recommendations for cardiovas-
9.
10.
11.
12.
13.
14.
AJH–October 2006 –VOL. 19, NO. 10
cular screening, staffing, and emergency policies at health/fitness facilities. Circulation 1998;97:2283–2293. Sugawara J, Otsuki T, Maeda S, Tanabe T, Kuno S, Ajisaka R, Matsuda M: Effect of arterial lumen enlargement on carotid arterial compliance in normotensive postmenopausal women. Hypertens Res 2005;28:323–329. Kumahara H, Schutz Y, Ayabe M, Yoshioka M, Yoshitake Y, Shindo M, Ishii K, Tanaka H: The use of uniaxial accelerometry for the assessment of physical-activity-related energy expenditure: a validation study against whole-body indirect calorimetry. Br J Nutr 2004;91:235–243. DeSouza CA, Shapiro LF, Clevenger CM, Dinenno FA, Monahan KD, Tanaka H, Seals DR: Regular aerobic exercise prevents and restores age-related declines in endothelium-dependent vasodilation in healthy men. Circulation 2000;102:1351–1357. Maeda S, Tanabe T, Miyauchi T, Otsuki T, Sugawara J, Iemitsu M, Kuno S, Ajisaka R, Yamaguchi I, Matsuda M: Aerobic exercise training reduces plasma endothelin-1 concentration in older women. J Appl Physiol 2003;95:336 –341. Goto C, Higashi Y, Kimura M, Noma K, Hara K, Nakagawa K, Kawamura M, Chayama K, Yoshizumi M, Nara I: Effect of different intensities of exercise on endothelium-dependent vasodilation in humans: role of endothelium-dependent nitric oxide and oxidative stress. Circulation 2003;108:530 –535. Christou DD, Gentile CL, DeSouza CA, Seals DR, Gates PE: Fatness is a better predictor of cardiovascular disease risk factor profile than aerobic fitness in healthy men. Circulation 2005;111: 1904 –1914.