Why does sv change with exercise

For the body to function properly, the heart needs to pump blood at a sufficient rate to maintain an adequate and continuous supply of oxygen and other nutrients to the brain and other vital organs. Cardiac output is the term that describes the amount of blood your heart pumps each minute. Doctors think about cardiac output in terms of the following equation:. Your stroke volume is the amount of blood your heart pumps each time it beats, and your heart rate is the number of times your heart beats per minute.

A healthy heart with a normal cardiac output pumps about 5 to 6 liters of blood every minute when a person is resting. During exercise, your body may need three or four times your normal cardiac output, because your muscles need more oxygen when you exert yourself. During exercise, your heart typically beats faster so that more blood gets out to your body.

Your heart can also increase its stroke volume by pumping more forcefully or increasing the amount of blood that fills the left ventricle before it pumps. Generally speaking, your heart beats both faster and stronger to increase cardiac output during exercise. Sufficient cardiac output helps keep blood pressure at the levels needed to supply oxygen-rich blood to your brain and other vital organs.

Author: Healthwise Staff. During an incremental-load exercise, cardiac output should increase to meet the extraordinary blood demands of the working musculature. This additional blood flow provides the major capability for acting exercise.

The manner in which the LV responds to the strain of exercise has intrigued physiologists. In fact, exercise training requires a fast adjustment in heart rate and stroke volume SV [ 1 ].

The heart rate is a mechanism by which cardiac output rises during effort under physiological conditions. It is well known that heart rate increases linearly with exercise load because of an imbalance between sympathetic and parasympathetic autonomic nervous activity.

There are two major mechanisms by which tachycardia occurs during incremental exercise: 1 decreased parasympathetic restraint and 2 increased sympathetic drive. The SV increase is linked to two different situations: 1 low-exercise load, in which the Frank-Starling mechanism has a key role and 2 increased myocardial contractility, shown to occur under maximal-load exercise MLE [ 2 , 3 ]. Currently, the nonlinear SV response to increases in the exercise load is an issue of interest.

Studies using several experimental approaches have shown decreases, plateaus, or increases SV during MLE. In the light of these findings, this systematic review incorporates original articles that assessed changes in SV during incremental-load exercise, to exhaustion, in healthy adult humans. The search was based on the following keywords and MeSH terms: aerobic exercise, cardiac output, dynamic exercise, incremental exercise, health subjects, hemodynamic, maximal effort, stroke volume, and systolic function.

The search sentences were combined to increase the results. The survey was carried out between February and June All studies evaluating the changes in SV during an incremental-load exercise were selected.

Two independent researchers using a double-blind approach performed the analyses. The first step of the search was to analyze the abstracts in the database according to the following criteria: participant profile, trial design, exercise test procedure, and SV evaluate approch. Controlled and uncontrolled trials published in peer-reviewed journals were included. We included only trials published in English, conducted on healthy subjects, and which included full information about the physical test procedure and approach used to measure SV.

Trials containing supplemented diets, diseased subjects, reviews, and case reports were excluded because they did not express the normal baselines. Studies that did not report their experimental design or outcomes were also excluded. Studies without clear detailing of SV approaches, as well as exercise protocol were excluded.

All eligible articles were reviewed and critically evaluated for quality scores, as previously reported in detail [ 4 , 5 ]. In the first screening, we have found articles there were no differences in database search between the two researchers. The abstracts were used to examine duplication in the database. After a search filter application, studies were found. Of these, articles were excluded because they did not meet the eligibility criteria or quality scores. Flow diagram for search procedure and selection of manuscript included in the systematic review.

Several different incremental exercise-load protocols were used in these studies to induce a maximum effort level. In summary, ten studies measured effort level on a cycle ergometer, two with treadmill running, and one with a drop-jumps protocol. Moreover, the studies used several approaches to evaluate SV.

Four studies used cardiac impedance, three used acetylene rebreathing, two used radionuclide ventriculography, and three used catheterization. Only one study applied a predictive equation to evaluate SV. These findings applied mostly to sedentary and moderately active subjects.

This study is the first systematic review to evaluate SV changes during incremental-load exercise. The available evidence shows an increase, as well as a plateau or a decrease, in SV. Gledhill et al. In contrast, there are doubts to SV during MLE in moderately trained subjects, with an SV plateau at submaximal-exercise intensity [ 23 ]. We found only one study that showed an increase in SV in nonathletic subjects [ 24 ].

This evidence indicates that a high level of physical fitness may be required to obtain increased SV during MLE. In respect to a SV plateau Fig. Therefore, SV may be sustained by a decrease in the LV end-systolic volume. Authors whose results support a lower SV during MLE report that the decline coincides with a plateau or decrease in cardiac output, resulting from the regulatory limitations of the heart Fig.

This decrease is linearly related to increases in core temperature, catecholamines, heart rate, and blood pressure. Moreover, one line of evidence supports the hypothesis that SV reduction during MLE could be related to the restrictions on LV filling time and LV end-diastolic volume that accompany tachycardia [ 28 ].

Cardiovascular strain associated with dehydration and hyperthermia may also decrease SV [ 29 , 30 ]. In summary, studies have shown increases, plateaus, and decreases in SV during exercise at submaximal to maximal workloads. These findings are clearly inconsistent and must be resolved by future investigations. Our analysis can help to explain the divergent results.

A detailed article analysis revealed the several exercise protocols were applied to induce high SV levels. Moreover, several approches e. Moreover, it is possible that the lack of study homogeneity may have influenced the interpretation of the results. Thus, limitations relating to the heterogeneity of approaches to SV analysis should also be exposed; some results may be inconclusive when several studies are compared to each other. These issues show to be considered for the current knowledge on the SV performance during exercise at submaximal to maximal loads.

One anatomical explanation for the increase in stroke volume during exercise is the Frank-Starling mechanism, as explained in a June article published by Journal of Molecular and Cellular Cardiology.

Blood is pumped to the body from the left ventricle and when this ventricle fills more completely, it stretches further and produces a more forceful contraction. In other words, more blood entering the heart results in more blood being ejected. This mechanism results in a greater amount of blood being circulated through your body during exercise — which is essential for delivering oxygen to your hard working muscles.

An increase in stroke volume is most commonly seen during aerobic exercises or endurance-type activities like running, swimming or cycling. By Jackie Carmichael Updated February 14, Lisa Maloney, CPT. Lisa holds a personal trainer certification through the University of Alaska Anchorage, with more than 4, hours of hands-on experience working with a variety of client needs, from sports teams to post-rehab populations and weight loss, in one-on-one, small group and large group settings.

Jackie Carmichael. Jackie Carmichael has been a freelance writer for more than 10 years. Her work has appeared in "Woman's World" and "American Baby" magazines.