Eur J Appl Physiol DOI 10.1007/s00421-009-1162-y
ORIGINAL ARTICLE
Cardiac output and oxygen uptake relationship during physical effort in men and women over 60 years old Paulo T. V. Farinatti Æ Pedro P. S. Soares
Accepted: 4 August 2009 Ó Springer-Verlag 2009
Abstract This study investigated the relationship between oxygen uptake (VO2), cardiac output (Q), stroke volume (SV), and heart rate (HR) in 54 men and 77 women (age = 69 ± 5 years) during incremental effort. Subjects performed a maximal cycle-ergometer test and VO2 was directly measured. HR and SV were assessed by ECG and cardiograph impedance. Regression equations were calculated for Q–VO2, HR–VO2, and Q–HR relationships. The equations obtained for women were (a) Q (l min-1) = 2.61 ? 4.67 VO2 (l min-1)(r2 = 0.84); (b) HR (bpm) = 62.03 ? 46.55 VO2 (l min-1) (r2 = 0.72); (c) 1 SV (ml) ¼ 100:6½1 e2:6 VO2 ð1 min Þ (r2 = 0.41); (d) HR -1 (bpm) = 41.48 ? 9.24 Q (l min ) (r2 = 0.73). Equations for men were (a) Q (l min-1) = 2.52 ? 5.70 VO2 (l min-1) (r2 = 0.89); (b) HR (bpm) = 66.31 ? 32.35 VO2 (l min-1) 1 (r2 = 0.72); (c) SV (ml) ¼ 143:7½1 e1:7 VO2 ð1 min Þ (r2 = 0.47); (d) HR (bpm) = 56.33 ? 5.25 Q (l min-1) (r2 = 0.69). The intercepts for Q–VO2 and HR–VO2 equations were similar for both genders, but the slopes were different (P \ 0.05). The SV increased from baseline to 50–60% of VO2 peak in both groups. No gender effect was
P. T. V. Farinatti (&) Physical Activity and Health Promotion Laboratory - LABSAU, Physical Education and Sports Institute, State University of Rio de Janeiro - UERJ, Rua Sa˜o Francisco Xavier 524, sala 8133, Bloco F, Maracana˜, Rio de Janeiro, RJ 20550-013, Brazil e-mail:
[email protected];
[email protected] P. T. V. Farinatti P. P. S. Soares Sciences of Physical Activity Graduate Program, Salgado de Oliveira University, Nitero´i, RJ, Brazil P. P. S. Soares Department of Physiology and Pharmacology, Fluminense Federal University, Nitero´i, RJ, Brazil
found in SV increasing pattern, but the absolute values were in general higher for men (P [ 0.05). A significant difference between men and women was observed for both slopes and intercepts in the Q–HR relationship (P \ 0.05). In conclusion, (a) Q–VO2 relation was linear during progressive effort; (b) regression intercepts were similar, but the slopes were higher for men compared to women; (c) SV–VO2 relationship was nonlinear and maximum SV was reached at very submaximal workload; (d) older men exhibited higher Q upward potential as well higher SV but lower HR for a given submaximal workload than women of similar age. Keywords Exercise Aging Cardiopulmonary exercise test Cardiograph impedance Linear regression
Introduction Cardiac output (Q) is an important indicator of the heart function, being defined as the product between stroke volume (SV) and heart rate (HR). In respect to exercise, HR is probably the most studied cardiac parameter, and its relation with effort intensity in all ages is largely accepted (Stamford 1988; Panton et al. 1996). On the other hand, most common techniques used to measure SV and Q are invasive, which limit their applicability (Miles and Gotshall 1989). The development of indirect methods of estimation, as CO2 rebreathing or impedance cardiography, enhanced the possibilities of understanding cardiac mechanisms in situations of physical strain. The validity, accuracy, and reproducibility of these methods were documented by several studies (Tochikubo et al. 1990; Pianosi 1997; Rodrigues et al. 2007). There is an increasing body of evidence about the importance of cardiac function assessment as a measure of
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functional fitness in older persons, and many studies have examined cardiovascular dynamics during the aging process. However, most researchers had examined the cardiac function in young and middle-aged subjects (McKelvie et al. 1987; Miyamoto et al. 1992). As a matter of fact, few studies attempted to observe SV and Q evolution during exercise in large samples of elderly subjects, and even less in elderly women. Although most of available data suggest that SV and Q associations are similar to those observed in young subjects, the generalization of such results is frequently limited due to the small samples used, rarely exceeding 20 subjects (Granath and Strandell 1964; Faulkner et al. 1977; McElvaney et al. 1989; Thomas et al. 1993; Bogaard et al. 1997a, b). Therefore, less-than-optimal information is available on the relation between VO2 and cardiac function during exercise in elderly healthy subjects of both sexes. It is well known that in the aging process there is a decline in maximal heart rate (Fleg et al. 2005; Christou and Seals 2008), cardiac output, arteriovenous oxygen content, and maximal oxygen consumption (Weiss et al. 2006). However, data specifically concerning the relationship between oxygen uptake (VO2) and cardiovascular variables in healthy elder subjects were found in few studies (Proctor et al. 1998; Vella and Robergs 2005a, b; Weiss et al. 2006). Regarding gender, endurance-trained young and old women seem to present lower SV for submaximal and near-maximal exercise compared to men, but similar rate of linear increase in Q (Proctor et al. 1998). While Q and HR increase linearly and positively associated to the increase in VO2, SV might present nonlinear increase with a plateau, a plateau with a drop, a plateau with a second increase, or even progressive increasing to maximal intensity (Vella and Robergs 2005a, b). However, consistent data regarding cardiovascular responses in elderly persons of both sexes are lacking. Limitations associated with sample size, physical status, and disease preclude comparisons between older men and women. Therefore, the aim of this study was to investigate sex-related differences in the relationships between VO2, Q, SV, and HR during incremental exercise in a sample of 131 untrained healthy men and women over 60 years old. We hypothesized that in healthy older subjects the VO2–Q relationship would remain linear; however, females would have a lower Q relative to VO2 at any given work rate, and this would be related to a higher HR and lower SV relative to males.
Methods Subjects A healthy group of 54 men (age = 69 ± 4 years, range 60–86 years) and 77 women (age = 69 ± 7 years, range
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61–93 years) participated in this study. An initial sample of 300 subjects was randomly selected from elder associations in Brussels, Belgium, and underwent clinical evaluation, including medical and physical activity history questionnaires, physical examination, and ECG Bruce maximal treadmill exercise test. Subjects were only admitted for study if they did not show any evidence of blood pressure abnormalities, heart disease, pulmonary function limitation, locomotion impairment, or other condition that could preclude maximal exercise performance or affect the results from impedance cardiography. Athletes were also excluded of the sample, in order to reduce the possible influence of outliers. This study has been approved by Institutional Ethical Committee and informed consent has been obtained prior to participation, as recommended by the Helsinki Convention. Instrumental Subjects performed a graded effort test in an Ergo-LineTM 900 cyclo-ergometer (model D7474, UK). A paramagnetic O2 analyzer, an infrared CO2 analyzer, and a pneumotachograph (MorganTM, UK) were used to assess the ventilatory components. Cardiograph impedance was registered with a Minnesota Cardiograph Impedance RecorderTM (model IFM 304b) in a tetra polar configuration, an ECG recorder Fukuda DenshiTM FD-36 (Japan), and a phonocardiograph Fukuda DenshiTM PL-16 (Japan). Arterial blood pressure was assessed by the auscultatory method (TycosTM, USA), and the hematocrit was quantified after centrifugation process. Data assessment The exercise test protocol had three phases: (a) a 3-min warming-up at 5 W; (b) incremental effort, beginning at 25 W for men and 20 W for women, with a similar workload being added every 2 min; (c) a 5-min recovery phase. The duration of the exercise testing has been 8–12 min according to the American Heart Association recommendations (Fletcher et al. 2001). Some previous studies have applied similar protocols in elderly subjects (Brischetto et al. 1984; Bovens et al. 1993). Criteria for test interruption followed the American College of Sports Medicine recommendations (ACSM 2006). The test was considered as maximum if at least three of the following criteria were observed: (a) respiratory quotient C1.06; (b) heart rate C80% of the estimated maximal heart rate (220—age); (c) VO2 leveling off despite further workload increment (VO2 increase B2.0 ml kg-1 min-1 between the two last loads); (d) maximal volitional exhaustion. The reliability of the protocol was previously tested in a subgroup of 12 subjects (8 women and 4 men) at rest and at 50
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and 100% of the Wmax, producing intra-class correlation coefficients of 0.73 at rest, 0.81 at 50% Wmax, and 0.85 at 100% Wmax (P \ 0.05). A bipolar chest lead (V5) was used to continuously monitor the heart rate and ECG tracing. Oxygen uptake was measured by an open-circuit gas analyzer. The ventilation variables (VE, VO2, VCO2) were determined in l min-1 STPD over the same period as the impedance data, and averaged every 30 s. Cardiac output and stroke volume were estimated every 2 min, by the method of impedance cardiography, according to the equation: Q (l min-1) = 0.001 SV (ml syst-1) HR (bpm). Considering that the thoracic impedance variation due to blood ejection is related to the ejection volume (19), stroke volume (SV) can be calculated from the equation: SV (ml syst-1) = (q) (L/Z0)2 (LVET) (dz/dt), where q stands for blood resistance (ohm cm); q = 53.2e0.22Hct, where Hct is the hematocrit (Geddes and Sadler 1973); L is the distance between the internal electrodes (cm); Z0 is the impedance of the thorax (ohm); LVET is the left ventricular ejection time (s); and dz/dt is the first derivate of thoracic impedance changes (ohm s). These equations were previously validated (Miles and Gotshall 1989; Bogaard et al. 1997a, b; Rodrigues et al. 2007), by comparison with direct and indirect Q assessment. The equation components for stroke volume estimates were obtained from ECG, phonocardiograph, and thoracic impedance data, according to the methods described elsewhere (22). Cardiovascular data were collected at rest, and during 50 and 100% of maximal workload capacity (Wmax). Statistical analyses The relationships between Q–VO2, HR–VO2, SV–VO2, and Q–HR were determined by linear and nonlinear regression whenever appropriate after best-fit adjustment evaluation (GraphPad Prism, San Diego, CA, USA). The difference between two regressions lines was tested by t-test as described in details elsewhere (Zar 1984). Differences between sample characteristics were verified by the Student’s t-test. A two-way ANOVA followed by the Tukey post-hoc test was applied to test possible gender effects at rest and the two exercise conditions. In all situations, a P \ 0.05 was considered significant.
Results Table 1 provides information about the general characteristics of the sample. Table 2 presents the results from the ANOVA at rest, and during submaximal and maximal exercise conditions (50 and 100% Wmax). Maximal values of SV were attained prior to maximal Q, the larger
Table 1 Characteristics of the sample Women (n = 77)
Men (n = 54)
Height (cm)
1.6 (0.1)
1.7 (0.1)*
Weight (kg)
63.1 (8.7)
77.1 (10.0)*
BMI (kg/m2)
24.6 (2.9)
26.2 (3.1)
Skinfolds (cm) [Hct]%
7.3 (2.1)
4.9 (1.7)*
39.4 (3.0)
44.5 (3.8)*
All values correspond to means, with standard deviation in parenthesis BMI body mass index, Skinfolds total of skinfolds, Women triceps, supra-iliac, and anterior thigh, Men pectoral, abdominal, and anterior thigh, [Hct]% percentage of hematocrit measured after the effort test * Statistically significant difference between women and men (P \ 0.05)
increasing being observed in men and no differences being identified between 50 and 100% Wmax. The two-way ANOVA revealed significant differences among resting conditions, 50 and 100% Wmax. Gender-related differences have been identified for the peak Q and for SV along all exercise intensities. The HR at 100% Wmax was similar in both sexes, but women had significantly higher values at 50% Wmax. Scatter plots for Q and VO2 (both sexes), the related regression equations—including the adjustment coefficient (r2), the standard error of estimate (SEE), and the significance level (P)—are shown in Fig. 1. The intercepts for the two equations were statistically similar, but the slopes were higher for men (P \ 0.01). The absolute Q values for a given VO2 became higher for the male group for exercise intensities above approximately 50% VO2peak (P \ 0.01). The HR–VO2 relationships for men and women are shown in Fig. 2. The intercepts were equivalent in both sexes. However, women have shown a higher upward drift for HR (P \ 0.05). The HR absolute values were higher than men’s in submaximal exercise [VO2 above 1.0 l min-1] (P \ 0.05), but no differences were found for the peak HR (P = 0.36). Figure 3 shows the SV–VO2 scatter plot. As expected, the nonlinear relationships showed that maximal SV values were attained at very submaximal intensities. Gender effects have been identified for the adjusted lines. Hence, the SV for men was higher than for women along all the exercise intensities while the increasing pattern was similar. For men, SV ¼ 143:7ð1 e1:7 VO2 Þ and for women SV ¼ 100:6ð1 e2:6 VO2 Þ: Figure 4 presents the Q–HR relationship. A significant difference between men and women was observed for both slopes and intercepts (gender effect; P \ 0.05). Despite starting from a lower intersection with the y-axis, during the exercise the women generally showed higher absolute HR for a given Q value (P \ 0.05). On the other hand, no gender-related differences have been found for the peak HR.
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Eur J Appl Physiol Table 2 Descriptive statistic for the variables at rest and during exercise Women (n = 77) Rest W
Men (n = 54) 100% Wmax
50% Wmax
0.0
Rest
81.8 (19.5)*,?
45.0 (11.9)*
4.5 (0.9)
7.9 (0.9)*
10.4 (1.6)*
SV
60.0 (11.6)
96.5 (24.2)*
93.4 (24.1)*
VO2
0.4 (0.2)
HR
0.8 (0.1)*
77.3 (11.5)
1.6 (0.3)*
116.7 (12.4)*
,?
140.8 (15.1)*
,?
100% Wmax
70.4 (14.6)*,¥
0.0
,?
Q
50% Wmax
125.5 (30.5)*,?,¥
4.9 (0.8)
10.8 (1.9)*
14.7 (3.6)*,?,¥
69.9 (12.5)
132.6 (34.6)*,¥
132.8 (34.7)*,?,¥
0.5 (0.1)
1.2 (0.2)*
2.1 (0.5)*,?,¥ ,¥
77.1 (13.7)
139.2 (16.5)*,?
108.0 (14.7)*
All values correspond to means, with standard deviation in parenthesis W work output (Watts), Q cardiac output (l min-1), SV stroke volume (ml), VO2 oxygen uptake (l min-1), HR heart rate (bpm) * Significant difference from rest conditions (P \ 0.05), genders (P \ 0.05)
significant difference from 50% Wmax (P \ 0.05);
¥
significant difference between
200
Males Females
Heart Rate (bpm)
Cardiac Output (L min-1)
30
?
20
10
0 0
1
2
3
4
Oxygen Uptake (L min-1) Fig. 1 Cardiac output (Q) versus oxygen uptake (VO2) at rest and during exercise in men and women aged C60 years. Solid lines are the mean regression lines. Two-way ANOVA—gender effect (P \ 0.05). Open square men (n = 54)—Q (l min-1) = 2.52 ? 5.70 VO2 (l min-1); r2 = 0.89; SEE = 1.53; P \ 0.01. Filled circle women (n = 77)—Q (l min-1) = 2.61 ? 4.67 VO2 (l min-1); r2 = 0.84; SEE = 1.08; P \ 0.01
Discussion This study has investigated the association between the VO2 and cardiac variables in a relatively large elderly population of men and women. The major findings have indicated that the Q–VO2 relationship was linear for both sexes and that the absolute Q associated with a given oxygen uptake was similar among the groups. Men and women have shown a reduced capacity to increase SV, the peak SV being reached at 50–60% VO2peak. Above this threshold, it was not possible to identity an increase pattern for the SV, especially in women. Men exhibited higher Q maximal levels and therefore have attained higher workloads, which seemed to be explained by a higher absolute SV along all exercise intensities. In contrast, women have shown significantly higher HR values during sub maximal exercise, but not in maximal workload.
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150
100
Males 50
Females
0 0
1
2
3
4
-1
Oxygen Uptake (L min ) Fig. 2 Heart rate (HR) versus oxygen uptake (VO2) at rest and during exercise in men and women aged C60 years. Solid lines are the mean regression lines. Two-way ANOVA—gender effect (P \ 0.05). Open square men (n = 54)—HR (bpm) = 66.31 ? 32.35 VO2 (l min-1); r2 = 0.72; SEE = 15.65; P \ 0.05. Filled circle women (n = 77)— HR (bpm) = 62.03 ? 46.55 VO2 (l min-1); r2 = 0.72; SEE = 15.53; P \ 0.01
Absolute values for Q, HR, and SV were within the range reported by previous studies and were compatible with the level of effort intensity. Thomas et al. (1993), for instance, observed at maximal incremental exercise test a Q of 15 l min-1 and SV of 95 ml in 96 elderly men. McElvaney et al. (1989) found Q values of 12.2 and 8.4 l min-1, and SV of 96 and 63 ml, for 41 men and 68 women aged C60 years, respectively. Seals et al. (1994) observed in a sample of 9 active and 9 sedentary elderly men SV from 111 to 132 ml at maximal effort. Finally, Proctor et al. (1998) reported for Q values that averaged from 8.3 to 9.2 and 13.8 to 14.8 l/min at VO2 of 1.0 and 2.0 l/min, respectively. This indicates that the use of impedance cardiography to assess SV and Q during exercise is effective in comparison with other techniques as the Fick method or acetylene rebreathing. Data for HR and VO2 have also corresponded to the ranges established in
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Stroke Volume (mL)
250 200 150 100 Males
50
Females
0 0
1
2
3
4
Oxygen Uptake (L min-1) Fig. 3 Stroke volume (SV) versus oxygen uptake (VO2) at rest and during exercise in men and women aged C60 years. Solid lines are the nonlinear regression lines. Two-way ANOVA—gender effect (P \ 0.05). 1 Open square men ðn ¼ 54Þ—SV (ml) ¼ 143:7½1 e1:7 VO2 ð1 min Þ ; 2 r = 0.47; Ymax SEE = 5.16. Filled circle women ðn ¼ 77Þ—SV (ml) ¼ 1 100:6½1 e2:6 VO2 ð1 min Þ ; r2 = 0.41; Ymax SEE = 2.58, P \ 0.001 between gender
Heart Rate (bpm)
200
150
100 Males 50
Females
0 0
10
20
30 -1
Cardiac Output (L min ) Fig. 4 Heart rate (HR) versus cardiac output (Q) at rest and during exercise in men and women aged C60 years. Solid lines are the mean regression lines. Two-way ANOVA—gender effect (P \ 0.05). Open square men (n = 54)—HR (bpm) = 56.33 ? 5.25 Q (l min-1); r2 = 0.69; SEE = 16.48; P \ 0.05. Filled square women (n = 77)— HR (bpm) = 41.48 ? 9.24 Q (l min-1); r2 = 0.73; SEE = 15.14; P \ 0.01
previous research (McElvaney et al. 1989; Thomas et al. 1993; Astrand et al. 1997; Bogaard et al. 1997a, b; Proctor et al. 1998). A few previous studies investigated the Q–VO2 relationship in elderly and young subjects. In general, the available regression equations are similar across the age groups, despite of slight differences in the slope and intercept values (slopes = 4.0–7.0 l min-1 and intercepts = 3.0–5.0 l min-1 in men and women) (5, 8, 10–13, 15, 17). Such range is consistent with our findings
(slopes of 5.70 l min-1 for men and of 4.67 l min-1 for women). We though were able to detect a significant difference between male and female responses to workload (P \ 0.05). This is in contrast to the findings by McElvaney et al. (1989) and Proctor et al. (1998), which did not identify differences for the Q–VO2 relationship within genders. However, the coefficients reported by the first were quite close to ours (5.0 l min-1/l min-1 oxygen for men and 4.6 l min-1/l min-1 oxygen for women), while the latter examined trained subjects only during submaximal exercise intensities (in which the correspondence between Q and VO2 is practically the same regardless age or gender). The intercepts for the Q–VO2 were lower than those reported in the literature for younger subjects (Granath et al. 1964; Faulkner et al. 1977; McElvaney et al. 1989). It is therefore feasible to speculate that while regression slopes between Q and VO2 do not depend on age (Bovens et al. 1993; Proctor et al. 1998), the intersection point with the y-axis is probably lower in elder populations. In this case, for a given workload the absolute Q is probably lower in elder subjects than in younger subjects. This phenomenon is well accepted since the evidences indicate that the decline of maximal Q is the most important determinant of a lower aerobic power in the elderly (Stamford 1988; Docherty 1990; Lakatta 1990). In comparison with younger populations, elderly subjects generally present relatively higher end-systolic volumes, mainly due to a decrease in the strength and speed of myocardial contraction (Pearson et al. 1991). Thus, it is probable that SV is more dependent on the Frank-Starling mechanism in elder than in young subjects (Lakatta 1990; Shibata et al., 2008). In all levels of exercise, the older heart, on average, pumps blood from a larger filling volume (Gates et al. 2003; Gates and Seals 2006; Weiss et al. 2006). However, because the end-systolic volume tends to be larger than in younger persons, agerelated changes in the stroke volume are unlikely to occur. It has been demonstrated that the ejection fraction does not increase as much in response to an increase in end-diastolic volume, which means that the Frank-Starling mechanism is blunted with age (Lakatta 1990; Shibata et al. 2008). Cardiac dilatation capacity during high intensity efforts is relatively more important in elder groups, partially compensating for HR limitations. Unfortunately, this compensatory mechanism seems not to be sufficient to raise Q to the levels usually observed in young adults (Gates et al. 2003; Nottin et al. 2004; Gates and Seals 2006; Popovic´ et al. 2006; Weiss et al. 2006). The gender effect on Q–VO2 relationship has not been extensively investigated. Our study provides information in this issue, having detected a significant difference between the regression curves for men and women. Some previous
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studies have demonstrated that although women are able to increase SV and Q similarly to men [similar slopes], they have lower values for Q for any given relative exercise intensity. Women seem to have a lower ability of elder women to maintain SV in comparison to men, especially at high exercise intensities (Proctor et al. 1998). Such limitation contributes to a lower absolute and relative VO2max in women (Wiebe et al. 1998). Our data ratify this premise—despite of similar starting points (intercepts), as the effort intensity increases, Q values become progressively higher in men than in women. These results concur with those reported by previous studies in elderly women and younger populations (Becklake et al. 1965; Zwiren et al. 1983; McElvaney et al. 1989; Astrand et al. 1997). Stroke volume normally increases up to exercise intensities of 40–60% of VO2max in sedentary subjects and then plateaus or falls slightly (Granath et al. 1964; Stamford 1988; Miles and Gotshall 1989; Gledhill et al. 1994; Lakatta 1998; Proctor et al. 1998; Vella and Robergs 2005a, b). Usually the highest SV is attained in exercise intensities below the anaerobic threshold, and it is unlikely to rise much further with increasing exercise in normal subjects (Stringer et al. 1997). In the observed subjects, the maximal SV have been reached at 50–60% VO2peak. The pattern of increase in SV was the same for men and women, but the formers have exhibited in general high absolute values in all effort intensities. These results partially agree with those of Proctor et al. (1998), who have found lower absolute SV values for women than for men in spite of the age. However, at near-maximal intensities of cycling (90% of VO2peak), only the older women have shown an impaired ability to maintain their SV. Such impaired response has not been observed in the men group. Some explanations for the differing results between studies may include differences between exercise protocols and subjects training level (our sample was clearly less trained). Hence, the possibility of a training conditioning effect on the capacity of elder men and women to increase and maintain SV at maximum workload deserves further attention. It is well known that the HR increases linearly as a function of exercise intensity and is closely related to the percentage of maximal VO2. As presumed in this study, the HR–VO2 relationship has been linear all along the workloads. However, women have shown higher HR values in submaximal intensities while men have reached superior absolute values in maximal effort. The same pattern has been observed for the HR–Q relationship, women exhibiting higher HR values for a given cardiac output. These differences between the genders probably reflect the need of women to compensate for a lower SV (see Fig. 3). As before mentioned, such increase in the HR seemed not to be enough to counterbalance the inability to increase the SV and therefore the Q.
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In summary, the Q–VO2 relationship was, as expected, linear during incremental exertion in elderly men and women. The intercepts were equivalent for men and women, but the male slope was higher, which suggests that men have a higher capacity to increase Q in close-tomaximum exercise intensities. Maximal SV was attained at submaximal exercise levels and the increasing pattern was similar in both sexes. SV values for men exceeded SV in women at all workloads. Probably to overcome this limitation, women showed higher HR at submaximal workload, but not at maximal exercise. Maximal Q was also higher in men, contributing to the higher peak VO2 observed in men relative to women. In this study, we investigated the cardiovascular adaptations during exercise in a large sample of healthy, older male and female subjects who were not taking any medications and were not athletes. Future studies using large samples in the later decades of life may clarify the relations between exercise training and the aging process in males and females. Acknowledgments This study was partially supported by a grant from the Brazilian Council for Research Development (CNPq, process 305729/2006-3) and Carlos Chagas Foundation for the Research Support in Rio de Janeiro (FAPERJ, process E26/102.916/2008). The authors thank Prof. Jacques Henri-Paul Vanfraechem from the Universite´ Libre de Bruxelles for the valuable support during data assessment.
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