Since aerobic exercise (e.g., walking) and resistance exercise (e.g., lifting objects and mopping) are both parts of the activities of daily living, an exaggerated elevation in systolic blood pressure (SBP) during aerobic and resistance exercise is an early marker of cardiovascular disease. This study investigated the effects of habitual exercise on SBP during low-intensity resistance exercise using both cross-sectional and interventional approaches. First, in 57 normotensive women (61.9 ± 1.0 yr of age), daily physical activity level, as assessed by triaxial accelerometry, was correlated with SBP during resistance exercise at 20 and 40% of the 1 repetition maximum (r = −0.408 and r = −0.348, respectively). Maximal oxygen uptake was correlated with SBP during exercise at 20% (r = −0.385) and 40% (r = −0.457). Physical activity level or maximal oxygen uptake was identified as a predictor of SBP during the exercise in stepwise regression analysis, independent of SBP at rest and other factors (R2 = 0.729–0.781). Second, 66 men and women (64.6 ± 0.9 yr of age) participated in a 6-wk intervention as a part of the training (walking, 4.3 ± 0.3 days/wk, 55.6 ± 4.1 min/day, 70.7 ± 1.2% of maximal heart rate) or control group. SBP during resistance exercise in the training group decreased after the intervention (before vs. after: 20%, 143 ± 4 vs. 128 ± 4 mmHg; and 40%, 148 ± 5 vs. 134 ± 4 mmHg). In the control group, there were no significant differences in SBP before and after the intervention. SBP during resistance exercise after the intervention was lower in the training group relative to the control group. These results suggest that habitual exercise decreases SBP during low-intensity resistance exercise.
- aerobic exercise training
- daily physical activity
- low-intensity resistance exercise
- maximal oxygen uptake
- systolic blood pressure
NEW & NOTEWORTHY
Systolic blood pressure (SBP) during aerobic and resistance exercise is an independent risk factor for cardiovascular disease. This is the first study to demonstrate that SBP during resistance exercise is correlated with daily physical activity level and decreased by aerobic exercise training in middle-aged and older individuals.
blood pressure transiently increases during exercise as a response to the increased demand for blood flow to the muscles. The transient elevations in blood pressure increase 24-h ambulatory blood pressure, an independent risk factor for cardiovascular disease (15, 38). Since aerobic exercise (e.g., walking and cycling) and resistance exercise (e.g., lifting objects, mopping, and climbing stairs) are both parts of the activities of daily living, an exaggerated blood pressure response to aerobic (31) and resistance (3) exercise is a risk factor for future cardiovascular disease. Lifestyle modification to decrease blood pressure during aerobic and resistance exercise may be of significance because ischemic heart disease and stroke are major public health problems that have resulted in 14.1 million deaths in 2012, according to the World Health Organization. Habitual exercise attenuates blood pressure elevation during aerobic exercise (treadmill exercise or cycling) in middle-aged and older individuals (11, 12, 27). However, effects of habitual exercise on blood pressure during resistance exercise are equivocal. In previous studies, 12 or 19 wk of resistance training did not decrease blood pressure during resistance exercise at 50–100% of 1 repetition maximum (1 RM) when the exercise tests before and after the training period were performed at a similar intensity (i.e., % 1 RM) (14, 30). These results may be due to the intensive training load on the skeletal muscles. For example, resistance training on a regular basis increases arterial stiffness, a determinant of blood pressure (5, 17). However, habitual exercise that does not require intense muscle contraction (e.g., increased levels of daily physical activity and aerobic exercise training) may attenuate blood pressure elevation during resistance exercise, because aerobic exercise training improves arterial stiffness (5, 36), vascular conductance (5, 26), and blunting of sympathetic vasoconstriction during exercise (20).
This study investigated whether habitual exercise decreases blood pressure during resistance exercise using both cross-sectional and interventional approaches. First, relationships between daily physical activity level and blood pressure during resistance exercise were investigated. Second, the effects of 6 wk of aerobic exercise training on blood pressure during resistance exercise were examined. We measured blood pressure during flexion and extension of the elbow (one-hand arm curl exercise) at 20% and 40% of 1 RM because various upper-arm activities at low intensity are needed during activities of daily living, and it allows for noninvasive brachial blood pressure measurements during exercise.
We recruited subjects older than 40 yr through the Ryugasaki city's public relations magazine. In the advertisement for subjects, we specified that the inclusion criteria of this study included the absence of any disorders in which exercise is contraindicated (e.g., unstable ischemia, acute low back pain, etc.). In the cross-sectional study, subjects who had treated or untreated hypertension [systolic blood pressure (SBP)/diastolic blood pressure (DBP) ≥ 140/90 mmHg], were on hormone replacement therapy, or smoked tobacco were excluded, because these factors can affect associations between physical activity level and blood pressure. The formulas to calculate daily physical activity level used in this study were different between men and women. There are sex differences in maximal oxygen uptake (32). These sex differences might affect correlations between blood pressure and physical activity level or maximal oxygen uptake. Since the number of male subjects who met the inclusion criteria was only 18, the remaining 57 women between 45 and 74 yr of age were analyzed (Table 1). In the interventional study, 76 men and women chose the control or training group and volunteered to participate in this study. However, only 66 subjects between 46 and 74 yr of age enrolled and completed the study protocol (Table 2). Since the aim of interventional study was to compare blood pressure before and after the intervention period, men and women were included. Subjects refrained from alcohol consumption and intense physical activity starting on the day before testing and caffeine consumption on the day of testing.
A power calculation was performed for Pearson's correlation coefficients between daily physical activity level and SBP during exercise in the cross-sectional study and for repeated measures two-way ANOVA in SBP during exercise of the intervention study using G*Power 3 (9). The sample size of this study was enough to detect the exercise effects at 90% power and with an α of 5% when effect size was assumed as intermediate between the medium and large (4).
This study was approved by the Ethics Committee of Ryutsu Keizai University and conformed to the principles of the Helsinki Declaration. All participants gave their written, informed consent before study participation.
Resistance exercise test protocol.
Subjects performed two sets of 10 repetitions of the one-hand arm curl exercise at 20% of 1 RM using an arm curl bench and dumbbells. Each repetition was performed for 8 s (3 s of concentric contraction, 1 s of maintaining full flexion, 3 s of eccentric contraction, and 1 s of maintaining a slightly flexed position), according to the Exercise Guide 2006 published by the Ministry of Health, Labour and Welfare of Japan. The interset recovery period was 100 s. Subjects were instructed to continue breathing normally during the exercise. After completion of the 20% 1-RM session, 160 s elapsed before the 40% 1-RM session commenced in a similar fashion. In the exercise test after the intervention, postintervention 1 RM was used to determine exercise intensity.
Blood pressure and heart rate measurement.
Resting blood pressure was measured in quintuplicate by oscillometry after at least 30 min of rest (DINAMAP; GE Healthcare, Buckinghamshire, UK). A three-lead electrocardiogram (ECG) was recorded at 1,000 Hz to calculate the heart rate (HR; LRR-03; GMS, Tokyo, Japan). During resistance exercise, blood pressure measurements were taken by oscillometry 20 s after the onset of exercise until the end of exercise. Exercise was performed with the dominant arm, and blood pressure was measured in the nondominant arm. The mean value of each parameter over two sets at 20% and 40% of 1 RM, respectively, was calculated.
Daily physical activity level assessment.
Daily physical activity levels were measured using an accelerometer (Active Style Pro; Omron Healthcare, Kyoto, Japan). This device estimates the intensity of physical activity [metabolic equivalents (METs)] over 10-s intervals based on accelerations in three dimensions (sampling rate, 32 Hz). The estimation of METs for household and locomotive activities using this device has been validated (22). The device automatically calculates physical activity levels (kcal/day) based on all levels of METs, and basal metabolic rate, estimated from age, sex, height, and body weight, but the manufacturer has not disclosed how it does so in detail. All subjects wore an accelerometer on the waist continuously for 14 days, except during sleeping and bathing. However, subjects sometimes forgot to wear the accelerometer and spent a day as unusual (e.g., staying in bed due to poor health). In addition, especially in the first few days, wearing the accelerometer could have psychological influence on behavior of subjects. Therefore, data from a continuous 7-day period that began 3–4 days after the commencement of monitoring were used to assess the level of daily physical activity (34). The accelerometer measures nonwear time, defined as periods with no acceleration for longer than 20 min. All subjects wore the accelerometer over 10 h per day for at least 7 days.
Maximal oxygen uptake estimation.
Three-lead ECG (LRR-03; GMS) and breath-by-breath oxygen uptake (AE300S; Minato Medical Science, Osaka, Japan) were monitored during incremental cycling [4 min at 30 W, with a 20 W (male) or 15 W (female) increase every 2 min to 85% of age-predicted maximum HR: 208 − 0.7 × age (37)]. The linear regression line between HR and oxygen uptake was determined using values from the last 30 s of each workload. Oxygen uptake corresponding to the maximum HR was considered the maximal oxygen uptake.
The one-hand arm curl 1 RM was assessed using an arm curl bench and dumbbells. Subjects performed a single repetition of the exercise using their dominant arm with progressively heavier weights; the heaviest weight that a subject could lift once through a complete range of movement was considered to be his or her individual 1 RM.
Blood chemical analysis.
Blood samples were collected from the antecubital vein by venipuncture after an overnight fast. Serum concentrations of cholesterol, triglycerides, and insulin, as well as plasma level of glucose, were determined according to our laboratory's previous study (23). In the intervention study, serum high-sensitivity C-reactive protein (hsCRP) concentrations and creatine kinase (CK) activity were measured by using a commercial immunonephelometry kit (CardioPhase hsCRP; Siemens Healthcare Diagnostics, Tokyo, Japan) and the Japan Society of Clinical Chemistry transferable method kit (L-type CK; Wako Pure Chemical Industries, Osaka, Japan). In addition, plasma levels of interleukin-6 (IL-6) were determined by using an enzymatic kit (QuantiGlo Human IL-6, R&D systems, Minneapolis, MN).
Arterial stiffness assessment.
In the interventions study, brachial-ankle pulse-wave velocity (baPWV) was measured using air plethysmography, as in our laboratory's previous studies (24, 25). Briefly, in supine position, brachial and posttibial artery pulse waves were obtained in triplicate (BP-203RPE II; Omron Colin, Tokyo, Japan). Pulse wave transit time was automatically determined by the device, as the delay between the proximal and distal waveforms. The distance traveled by the pulse waves was calculated based on each subject's height. BaPWV was calculated as the distance divided by the transit time.
Subjects in the training group underwent supervised walking (35–50 min) once per week for 6 wk. Initially, subjects walked at a relatively low intensity (60–65% maximal HR). As their exercise tolerance improved, the intensity of walking was increased to 75% maximal HR. In addition, subjects walked two to four times a week on their own at the same pace as the supervised walking and recorded the actual duration of their walks. Adherences to the prescribed walking frequency and time were calculated without distinction between supervised and unsupervised walks. Mean HR during walking was calculated based on HR during supervised walking. Subjects in the control group participated in a muscle stretching class (30–45 min) at local community centers every other week.
Results are expressed as means ± SE. Relationships between two variables were investigated using Pearson's correlation coefficients and partial correlation analysis. Stepwise regression was used to identify independent predictors of SBP during exercise. In the cross-sectional study, changes in blood pressure and HR during exercise were evaluated using repeated-measures one-way ANOVA. Effects of intervention on blood pressure during exercise and other variables were tested using repeated-measures two-way ANOVA. If a significant F value was found, a Fisher's post hoc test was performed. The unpaired t-test or χ2 test was used to detect intergroup differences in variables before the intervention, as appropriate. P values < 0.05 were considered statistically significant.
SBP (rest, 114 ± 2 mmHg; 20% 1 RM, 136 ± 3 mmHg; 40% 1 RM, 142 ± 3 mmHg), DBP (66 ± 1, 78 ± 1, and 81 ± 2 mmHg, respectively), HR (65 ± 1, 75 ± 1, and 78 ± 1 beats/min, respectively), and rating of perceived exertion (Borg's 6–20 scale; 20% 1 RM, 10.6 ± 0.2; 40% 1 RM, 13.0 ± 0.2) increased during resistance exercise in an exercise-intensity dependent manner.
Physical activity level (Fig. 1) and maximal oxygen uptake (Fig. 2) were correlated with SBP during resistance exercise at 20% and 40% 1 RM. In partial correlation analysis, physical activity level and maximal oxygen uptake were correlated with SBP at 20% and 40% 1 RM, independent of resting SBP (partial r = −0.318 to −0.464, P = 0.01-0.0002). Physical activity level or maximal oxygen uptake, age, and SBP at rest were identified as independent predictors of SBP during exercise in the stepwise regression analysis that included 1 RM, body mass index (BMI), DBP at rest, and blood levels of cholesterol, triglycerides, glucose, and insulin (Table 3).
Physical activity level was not associated with DBP and HR both at rest and during resistance exercise. Maximal oxygen uptake was correlated with DBP (rest, r = −0.389, P = 0.002; 20% 1 RM, r = −0.480, P = 0.0001; and 40% 1 RM, r = −0.432, P = 0.0007) and HR (r = −0.286, P = 0.03; r = −0.366, P = 0.004; and r = −0.370, P = 0.004; respectively). In partial correlation analysis, only DBP at 20% 1 RM was correlated with maximal oxygen uptake, independent of the resting value (partial r = −0.306, P = 0.02).
There were no intergroup differences in male-to-female ratio, age, BMI, laboratory values, and exercise parameters before the intervention (Table 2). Subjects in the training group exercised for an average of 4.3 ± 0.3 days/wk and 55.6 ± 4.1 min/day at 70.7 ± 1.2% of maximal HR. Subjects in the control group participated in the stretching class for an average of 0.3 ± 0.3 day/wk. The subjects did not change their lifestyle during the experimental period, except for participation in this study. There was an interaction between group and training period in maximal oxygen uptake; maximal oxygen uptake increased in the training group after the intervention (Table 2).
An interaction between group and exercise intensity was identified in SBP (Fig. 3). In the training group, SBP at 20% and 40% 1 RM were lower after the intervention compared with before the intervention, whereas there were no differences in SBP in the control group before and after the intervention. After the intervention, SBP at 20% and 40% 1 RM were lower in the training group than in the control group, but there were no intergroup differences in SBP before the intervention. There were no differences in resting SBP between groups and before and after the intervention. ANOVA demonstrated that trends in DBP changes during exercise were affected by the exercise training, although these multiple comparisons did not reach statistical significance. Results in women were similar to results in all subjects, although the decrease in SBP at 40% 1 RM of the training group from before to after the intervention did not reach statistical significance (P = 0.05).
There was an interaction between group and training period in baPWV; baPWV in the training group decreased after the training period compared with baseline (Fig. 4). Changes in baPWV of the training group from before to after the intervention were correlated with the changes in SBP at 20% (r = 0.488, P = 0.003) and at 40% (r = 0.488, P = 0.003) 1 RM.
The main new findings of our study are as follows. In the cross-sectional study, daily physical activity level and maximal oxygen uptake were independently correlated with SBP during resistance exercise at 20% and 40% 1 RM. In the interventional study, SBP during resistance exercise at 20% and 40% 1 RM decreased after a 6-wk aerobic exercise training program. In addition, SBP during resistance exercise after the intervention was lower in the training group relative to the control group. These results suggest that habitual exercise decreases SBP during low-intensity resistance exercise.
SBP during low-intensity resistance exercise may be a more sensitive marker of the effects of habitual exercise than SBP at rest. Even though resting SBPs in the normotensive subjects with higher and lower levels of physical activity are similar, SBP during exercise may be lower in those who are more physically active. These results do not contradict previous studies that demonstrated that there are individuals with exaggerated blood pressure responses to exercise, even though resting blood pressure is normal (3, 13, 18). In the interventional study, SBP during resistance exercise decreased after the 6-wk aerobic exercise training program, whereas changes in SBP at rest did not reach statistical significance, possibly due to the normotensive level at the time of enrollment. In previous studies, exercise training decreased not only SBP during aerobic exercise, but also SBP at rest (11, 27). However, preintervention resting SBP was higher in previous studies [138 and 131 mmHg, respectively (11, 27)] than in this study (115 mmHg). Improvements in the cardiovascular system due to aerobic exercise training in normotensive individuals without changes in resting blood pressure are frequently observed (34, 36). SBP during low-intensity resistance exercise also seems to be lowered by habitual exercise, independent of SBP at rest.
Blunting of sympathetic vasoconstriction during exercise (functional sympatholysis) may be associated with mechanisms responsible for the effects of habitual exercise on SBP during resistance exercise. Sympathetic vasoconstriction in contracting muscles is attenuated by local factors (e.g., endothelium-derived relaxing factor) during exercise. However, endothelial function decreases with aging (2, 7, 35). Thus functional sympatholysis is impaired in older individuals with a sedentary lifestyle (8, 10). Aerobic exercise training improves endothelial function (1, 28) and functional sympatholysis (20). In addition, Mortensen et al. (21) reported that functional sympatholysis was preserved in physically active older individuals. A decrease in vasoconstriction due to endothelial function lowers blood pressure via reduction of vascular resistance. In this study, an index of arterial stiffness (i.e., baPWV) was measured, because arterial endothelial function is a potent regulator of arterial stiffness (33, 39). baPWV in the training group decreased after the training period compared with baseline. This result is in agreement with the previous studies that aerobic exercise delays or prevents age-related increases in arterial stiffness (5, 26, 36). In addition, the changes in baPWV from before to after the intervention were correlated with the changes in SBP during exercise. Improvement of functional sympatholysis may be implicated in the association between habitual exercise and lower SBP during low-intensity resistance exercise in middle-aged and older individuals.
Previous studies have reported that hsCRP and IL-6 were associated with blood pressure responses to aerobic exercise in normotensive women (16) and to muscle contractions in decerebrate rats (6). Therefore, blood levels of hsCRP, IL-6, and CK activity were measured in the intervention study to investigate whether reductions in vascular inflammation are associated with decreases in SBP during resistance exercise. However, there were no differences in these indexes before and after the intervention. In the present subjects, serum concentrations of hsCRP before the intervention were low; Ridker (29) has reported that the lowest quintile of blood hsCRP concentrations among men and women with no history of cardiovascular disease and cancer were 0.01 to 0.069 mg/dl. In individuals with low inflammation levels, other mechanisms such as nitric oxide bioavailability and antioxidant capacity may be implicated in the effects of aerobic exercise training on SBP during low-intensity resistance exercise.
The present results have implications for older individuals that exercise habitually. Daily physical activity of 200 kcal/day was associated with a 10-mmHg reduction in SBP during resistance exercise in the cross-sectional study (please see the regression equations of Fig. 1). The 6-wk walking program induced 15-mmHg decreases in SBP during exercise, although it might partly include familiarity with the exercise test. Schultz et al. (31) reported that the relative risk of cardiovascular events and mortality increases 4% per 10-mmHg increase in SBP during moderate-intensity aerobic exercise. Physically active individuals may have a lower SBP not only during the arm curl exercise, but also during activities of daily living, such as lifting objects, mopping, and climbing stairs; these smaller responses may be lead to lower cardiovascular risk.
This study has some limitations. First, subjects of the intervention study were not randomized. Second, subjects with known cardiovascular disease were excluded and most of subjects (cross-sectional study, 79%; intervention study, 76%) had a normal BMI for Japanese (18.5–24.9 kg/m2). A previous study reported that there were differences in effects of aerobic exercise training on exercise pressor reflex overactivity between normotensive and hypertensive rats (19). The present results may not be generalized to individuals with cardiovascular disease and to lean or obese individuals.
In conclusion, this study demonstrated that daily physical activity level was correlated with SBP during resistance exercise at 20% and 40% 1 RM, and that SBP during resistance exercise decreased after 6 wk of aerobic exercise training. These results suggest that habitual exercise decreases SBP during low-intensity resistance exercise.
This work was supported by Japan Society for the Promotion of Science KAKENHI Grant no. 23650437, and funding from the Meiji Yasuda Life Foundation of Health and Welfare and the Uehara Memorial Foundation.
No conflicts of interest, financial or otherwise, are declared by the author(s).
T.O., T.K., and A.Z.-M. conception and design of research; T.O., T.K., and A.Z.-M. performed experiments; T.O. analyzed data; T.O. and A.Z.-M. interpreted results of experiments; T.O. prepared figures; T.O. drafted manuscript; T.O. and A.Z.-M. edited and revised manuscript; T.O., T.K., and A.Z.-M. approved final version of manuscript.
We thank Ryugasaki City for supporting our study based on a partnership agreement between Ryugasaki City and Ryutsu Keizai University (Ryu Ryu Renkei).
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