8.13 Cardiovascular training
In fitness programs, participants must have an efficient respiratory system that can provide adequate oxygen to the blood and a well-functioning cardiovascular system that can transport blood and nutrients throughout the body’s tissues (American College of Sports Medicine, 2018). Personal trainers must possess a thorough understanding of these fundamental physiological concepts and be able to apply the various components of a cardiorespiratory exercise program, including leading warm-ups and cool-downs, monitoring exercise mode, frequency, and duration, and providing necessary information and guidance to ensure client safety (Howley & Franks, 2017). Additionally, trainers can select from a range of training methods and cardiorespiratory activities to cater to the diverse needs of their clients.
This chapter presents fundamental information on the mechanisms of cardiorespiratory exercises, the benefits of participation, and various teaching methodologies.
Cardiovascular Response to Exercise
The human body requires a consistent energy supply to perform its numerous functions. This energy is derived from two primary metabolic processes: anaerobic and aerobic metabolism (McArdle, Katch, & Katch, 2015). Anaerobic metabolism is employed for short, high-intensity exercises, as lactic acid accumulation quickly fatigues the muscles. In contrast, aerobic metabolism meets the energy demand for most low- or medium-intensity cardiorespiratory exercises, allowing individuals to exercise for extended periods due to the slower production of lactic acid, which can be more readily metabolized by the body (Benvenuti & Zanuso, 2021). A well-structured exercise program enhances these metabolic processes’ capabilities and improves overall body functionality.
As the acronym SAID – Specific Adaptation to Imposed Demands implies, the body adapts to the specific type of stress and training we impose on it. For instance, if your client’s primary objective is to develop strength, it is essential to incorporate higher loads in their training program to encourage this type of adaptation.
Conversely, suppose your client’s goal is to run a marathon. In that case, focusing on improving cardiovascular endurance through aerobic training is the most effective approach.
Understanding the distinction between the adaptations resulting from strength training and energy system work is important. Strength training primarily leads to structural changes within the body, such as muscular hypertrophy and increased bone density. In contrast, energy system-dependent training enhances the body’s efficiency in utilizing the existing substrates within our system.
By understanding and applying the SAID principle, trainers can design programs tailored to their client’s specific goals and needs, ensuring that the appropriate adaptations occur to facilitate progress and success in their chosen objectives.
To comprehend cardiorespiratory exercises involving the cardiovascular and respiratory systems, it is necessary to define some terms. In cardiovascular, “cardio” refers to the heart, while “vascular” denotes the circulatory system. The cardiovascular system comprises the heart with four chambers, arteries through which blood moves away from the heart, veins that return blood to the heart, and a capillary system that transports blood between small arteries and veins (Kenney et al., 2015). In exercise physiology, fitness activities involving the heart and lungs are termed cardiorespiratory exercises, with “respiratory” referring to the respiratory system. Cardiorespiratory exercises also enhance the body’s capacity to transport oxygen to working muscles.
Acute response to exercise
Understanding acute and chronic responses to exercise is crucial before exploring the cardiovascular effects of training in detail. Acute responses or adjustments are rapid, temporary modifications from a single exercise. In contrast, chronic responses or adaptations involve changes in a body’s function or structure due to repeated or regular exercise (Bushman, 2017). Practical training often comprises a series of physical and psychological adaptations that contribute to overall wellness.
The benefits of cardiorespiratory activity are linked to adaptations involving the entire oxygen transport system (Powers & Howley, 2017). Acute adaptations to exercise involve several cardiorespiratory and circulatory functions that accommodate the heightened oxygen requirements of active muscles. These adjustments include alterations in heart rate, stroke volume, cardiac output, blood flow, arteriovenous oxygen difference, blood pressure, and pulmonary ventilation.
Heart Rate and Cardiovascular Responses to Exercise
As exercise intensity rises, heart rate (HR) also increases, correlating with the workload and oxygen uptake. The HR response is influenced by various factors, including age, training level, activity type, body position, medications, total blood volume, and environmental factors, such as temperature and humidity (Kenney et al., 2015). Maximal attainable HR declines with age, and various equations (table 3.1) can help trainers estimate this value without conducting maximal exercise tests.
Stroke Volume
Stroke volume (SV) refers to the volume of blood pumped from one ventricle of the heart with each beat, depending on the ventricle’s capacity to fill with blood during the diastolic phase and contract during the systolic phase (Plowman & Smith, 2017). During exercise, SV increases with exercise intensity (expressed as workload) up to 50% of aerobic capacity, where it nearly reaches its maximum, and beyond that point, it only marginally increases.
Cardiac Output
Cardiac output (CO) is the volume of blood pumped by the heart within one minute and is the product of SV and HR (McArdle et al., 2015). In healthy individuals, CO increases linearly with exercise intensity (expressed as workload) from a resting value of approximately 5 liters per minute to a maximum of about 20 liters per minute. Maximum CO response values depend on various factors, including age, training level, activity type (body posture), and medications. At exercise intensities higher than 50% of VO2max, the CO increase results solely from the continued rise in HR.
Blood Flow
Exercise alters blood flow distribution (Joyner & Casey, 2015). At rest, only 15-20% of the cardiac output goes to the muscles, while the remainder goes to visceral organs, the heart, and the brain. During exercise, there is a significant increase in blood flow to the working muscles (up to 90%) and the heart (myocardial blood flow increases up to five times), the blood supply to the brain is maintained at resting levels, and blood flow to internal organs (e.g., liver and kidneys) decrease considerably.
Arteriovenous Oxygen Difference
The arteriovenous oxygen difference refers to the difference between the oxygen content in arterial and venous blood (Bassett & Howley, 2000). At rest, this difference is about 5 milliliters of oxygen per deciliter of blood, yielding an oxygen utilization coefficient of 25%. However, during maximal exercise, the oxygen content of venous blood decreases significantly, increasing the arteriovenous difference from 5 to 15 milliliters of oxygen per deciliter of blood, resulting in an oxygen utilization coefficient reaching 75%.
Blood Pressure
Blood pressure (BP) increases linearly with exercise intensity (expressed as workload), with maximal values reaching up to 220 torrs (mmHg). Conversely, Diastolic BP typically remains unchanged (or decreases only slightly), resulting in a linear increase in pulse pressure (the difference between systolic and diastolic blood pressure) with exercise intensity.
Pulmonary Ventilation
Pulmonary ventilation (V) is the volume of air exchanged per minute. At rest, V is around 6L/min and can reach 150L/min with maximal exertion. Ventilation increases with moderate exercise due to an increase in tidal volume and with vigorous exercise due to an increase in respiratory rate. V has a linear relation to oxygen consumption and carbon dioxide production. However, at high exercise intensity, V increases disproportionately to VO2, increasing lactate production and VCO2. Ventilation does not usually limit aerobic capacity.
Chronic Responses or Adaptations
The consistent repetition of an exercise stimulus over time becomes a chronic stimulus, leading to beneficial permanent adaptations. A substantial body of research demonstrates that well-designed aerobic programs can significantly improve aerobic capacity (expressed as increases in VO2max), with the greatest benefits achieved by individuals with the lowest fitness levels (Kaminsky & Whaley, 1998). The metabolic demand (oxygen consumption) for a specific workload is comparable across varying fitness levels, allowing individuals with lower fitness to enhance their aerobic capacity by exercising at a reduced percentage of their VO2max. Consequently, people of all ages and health conditions can improve their aerobic capacity. This improvement provides protection against cardiovascular mortality and boosts the ability to perform daily tasks. Augmented aerobic capacity is also associated with changes in cardiovascular and cardiorespiratory systems.
Heart Rate
Heart rate plays a crucial role in delivering oxygen to working muscles. After repeated exposure to aerobic training stimuli, resting HR generally decreases, with this reduction being more evident in previously unconditioned subjects (Lewington et al., 2002). Resting HR is regulated by the vagus nerve, and vagal tone appears to increase during rest, leading to a decreased resting heart rate of approximately 10 to 15 beats per minute. After aerobic conditioning, maximal heart rate remains unchanged or slightly decreases (3 to 10 beats per minute).
Stroke Volume
Chronic aerobic training results in increased SV due to improved contractile capacity, which stems from the enhanced mechanical ability of myocardial fibers to produce force and an increase in venous return (Frank-Starling mechanism) (Pluim et al., 2000). The increased SV achieved through chronic aerobic training allows individuals to exercise at similar workloads but with a lower heart rate, thereby decreasing the oxygen demand at the myocardial level.
Cardiac Output
Cardiac output, closely correlated with stroke volume, is significantly higher in individuals exposed to chronic aerobic exercise than in sedentary individuals (Fletcher et al., 1996). However, CO is similar across different fitness levels and before and after training at any given workload.
Arteriovenous Oxygen Difference
Individuals who engage in regular aerobic training improve their capacity to extract oxygen from the blood that circulates throughout their body. As a result, oxygen consumption can be increased, determined by a higher arteriovenous oxygen difference. However, since conditioned individuals have a greater ability to use oxygen at the cellular level, the arteriovenous oxygen difference is similar between trained and untrained subjects at the submaximal level. This parameter is significantly greater in trained subjects only when its value is close to VO2max.
Blood Pressure
Recent evidence indicates that aerobic exercise significantly reduces systolic and diastolic BP in hypertensive, prehypertensive, and normotensive adults (Cornelissen & Smart, 2013). Regarding systolic BP, the outcome of aerobic training is that trained subjects generally exhibit lower systolic BP at any fixed submaximal workload than untrained subjects. Regarding training level, systolic BP is lower in trained subjects than in untrained subjects.
Blood Lactate
Lactic acid, or lactate, is a by-product of anaerobic glycolysis and is associated with the onset of significant anaerobic contribution to exercise metabolism during aerobic exercise. Blood lactate is buffered during aerobic exercise at submaximal intensities to maintain an acceptable acid-base balance. However, when lactate production exceeds the buffering capacity of the metabolic system, fatigue rapidly increases, leading to exercise termination (Beneke et al., 2011). Endurance workouts are designed to enhance the oxygen-processing ability of skeletal muscles, leading to reduced lactate levels in trained individuals during any specific submaximal activity level. This is because they generate less lactic acid and are more efficient at neutralizing it.
Pulmonary Ventilation
As previously stated, ventilation typically does not restrict exercise in healthy individuals and is either unaltered or only slightly impacted by aerobic training. Although exercise training may increase maximal ventilatory capacity, it is unclear whether it provides any advantage other than increasing the buffering capacity for lactate (Wagner, 1996).
Warm-Up and Cool-Down
To ensure safety and an optimal training experience, personal trainers must guide participants in gradually preparing their bodies for the increased physiological demands involved in the training routine before engaging in any cardiorespiratory activity. This section outlines the physiological reasons for warming up and cooling down before and after exercise.
When doing a strength exercise, lifting light weights prepares the body for strenuous exercises by increasing blood flow, warming muscles, and raising the heart rate. Including these exercises in cooldowns helps reduce lactic acid buildup and alleviates muscle soreness from intense activities.
Benefits of a Proper Warm-Up
A proper warm-up increases blood flow to the working muscles and provides several benefits (McGowan et al., 2015):
- Increases muscle temperature: Warmed muscles contract more forcefully and relax more quickly, reducing the probability of overstretching a muscle and causing injury.
- Increases body temperature: This improves muscle elasticity, reducing the risk of strains and pulls.
- Dilates blood vessels: This reduces blood flow resistance and lowers heart stress.
- Improves cooling mechanisms: Activating the body’s heat-dissipation mechanisms (efficient sweating) helps prevent overheating early during the event or exercise.
- Increases blood temperature: As blood travels through the muscles, its temperature rises, weakening the binding of oxygen to hemoglobin, making oxygen more readily available to working muscles, and potentially improving endurance.
- Enhances range of motion: This reduces the risk of muscular-articular injuries.
- Facilitates hormonal changes: The body increases the production of hormones responsible for regulating energy production. During the warm-up, this balance of hormones makes more carbohydrates and fatty acids available for energy production.
- Aids mental preparation: Warm-up serves as an opportunity for mental preparation by clearing the mind of distractions, increasing focus, and promoting positive imagery to help participants relax and concentrate.
Typical Warm-Up Exercises
Low-level aerobic exercise is crucial for maximizing safety and the economy of movement during subsequent aerobic training. The warm-up should progressively increase heart rate, blood pressure, oxygen consumption, and target muscle flexibility.
The ideal warm-up should consist of two components: graduated aerobic movements and flexibility exercises.
Graduated Aerobic Movements
These movements can be performed on machines (e.g., treadmills or stationary bikes) or without machines (e.g., jogging, slow-tempo aerobic movements). The warm-up procedure should provide a graduated activity level similar to the primary conditioning activity but executed substantially lower intensity. The length of the warm-up depends on the duration of the main activity and the participant’s conditioning level (McGowan et al., 2015).
Flexibility Exercises
Flexibility exercises should be related to the participants’ main activity during the session (e.g., rotator cuff stretching before a rowing machine session or calf and hamstring stretching before running) (Behm et al., 2016). To avoid injury, it is best to stretch a muscle after blood flow and temperature have increased; stretching a cold muscle can increase the risk of injury from pulls and tears.
Personal trainers should ensure the warm-up begins gradually and uses the muscles that will be stressed during exercise. Participants should also stretch after exercise when their muscles are warm and pliable due to increased blood flow.
Cool-Down
Each exercise session should conclude with a cool-down, aiming to gradually decrease the load on the cardiorespiratory system that has been elevated during training. Low-level aerobic exercises, such as walking, jogging, or cycling with low resistance, are recommended. Cooldown exercises aid in reestablishing normal blood flow, averting post-workout fainting and lightheadedness, and preventing the abrupt accumulation of blood in the venous system. For individuals at high cardiovascular risk, a gradual decrease in exercise intensity is crucial, as stress hormones are released during exercise (e.g. adrenaline), and sudden cessation of the workout without a proper cool-down may adversely affect cardiac function. Typically, 5 to 10 minutes of cool-down are sufficient. The aerobic component of the cool-down should be followed by stretching the active muscle groups during training.
In order to develop a secure, efficient, and tailored cardiorespiratory exercise regimen, it is crucial to consider pertinent factors associated with exercise response, as well as detailed guidance. We at PTBA endorse the American College of Sports Medicine’s (ACSM) General Exercise Guidelines. Elements contributing to exercise enhancement encompass initial fitness level, exercise intensity, duration, frequency, and modality.
Interval training comprises brief, recurrent bursts of high-intensity physical exertion.
Interval training consists of short, repeated, intense physical efforts (3 to 5 minutes of exercise followed by short rest periods) (Laursen, 2010). The repeated exercise bouts (with resting intervals) can vary from a few seconds to several minutes, depending on the training goal. The variables determining the different effects of this type of training include the intensity and duration of the exercise bouts and the number and duration of the intervals. Modifications of these variables can be made to meet different training purposes: more prolonged exercise bouts improve the aerobic system, while shorter bouts emphasize the anaerobic energy system. The primary advantage of interval training is that it allows participants to perform a high-intensity exercise for a relatively long period by balancing exercise bouts and resting periods (Gibala et al., 2012).
Fartlek Training
Fartlek training combines some or all other methods during a long, moderate-intensity training session (Laursen, 2010). With Fartlek, participants run at alternating fast and slow speeds on a course with both flat and hilly terrain. This training does not include precise manipulation of the intensity and duration of exercise bouts and rests; the overall training intensity is determined by both the course’s physical characteristics and the performer’s subjective sensations. Fartlek training is considered ideal for general conditioning and off-season training.
Dose-Response Relationship based on Evidence
For trainers designing exercise programs, fitting exercise into a client’s busy daily schedule is often challenging. Therefore, making time to move each day is essential. However, the optimal duration varies depending on the objective of the physical activity or exercise program (e.g., general health benefits, physical fitness, or specific performance goals) and factors such as minimum duration and type of activities. However, personal trainers should know these generic, evidence-based guidelines (Garber et al., 2011).
What is the necessary duration of physical activity to attain health benefits? Both the American College of Sports Medicine (ACSM) and the U.S. Centers for Disease Control and Prevention (CDC) have long-established recommendations, stating that health improvements can be achieved through a minimum of 30 minutes of moderate-intensity physical activity on most days of the week. Greater duration and intensity result in increased benefits. The Physical Activity Advisory Committee Report and the World Health Organization support these recommendations, suggesting at least 150-300 minutes of moderate-intensity aerobic activity per week. However, the Institute of Medicine – National Academy of Medicine – recommends 60 minutes of moderate activity daily to maintain weight (IOM 2002). Although the optimal amount of physical activity for maximal health benefits remains unknown, further research is needed.
In addition, adults should engage in resistance exercises targeting major muscle groups and neuromotor exercises involving balance, agility, and coordination two or three days per week. Flexibility exercises for each major muscle-tendon group, totaling 60 seconds per exercise, should be performed at least twice a week to maintain joint range of motion. Exercise programs should be tailored to an individual’s activity level, physical function, health status, exercise responses, and goals. Even if unable or unwilling to meet the outlined targets, adults can still benefit from less exercise than recommended. Health benefits can also be achieved by reducing sedentary time and incorporating frequent, short bouts of standing and physical activity (Garber et al., 2011).
Conclusion
Cardiorespiratory exercises, such as walking, jogging, running, cycling, swimming, and elliptical training, enhance heart and lung function and provide numerous physiological and psychological benefits. In addition, these exercises serve multiple purposes in fitness facilities, such as sport-specific training, body enhancement, weight loss, and socializing. Therefore, personal trainers need to comprehend the fundamentals of aerobic training and various modalities for safe and effective execution.