Tag: cardiac output

Performance Benefits of Training

Exercise taxes the various physiological systems of the body beyond their normal resting level of performance. Two of the most important purposes of training are to increase the rate of energy release during races and to delay fatigue.

Training the ATP-CP System

The energy for muscular contraction comes from ATP, which is the only chemical stored in muscles that can provide that energy. The primary purpose for all other phases of metabolism is to replace the energy in ATP so that contraction can continue.  The ATP-CP system can provide energy for muscular contraction more rapidly than any other phase of metabolism, but it can do so for only 4 to 6 seconds.

After ensuring that technique is good, an athlete can improve maximum speed most significantly by 1) increasing the size and strength of the fibres in particular muscle groups so that the fibres can generate more power and 2) improving the rate and pattern of fibre recruitment by the central nervous system so they can be brought into play quickly and in the proper sequence for a particular skill without involving unneeded fibres.

Increasing the quantities of ATP and CP stored in muscle fibres represents another possible training effect that might increase athletic speed. Increases could extend the maximum rate of ATP recycling for an additional few seconds, which in turn may allow athletes to maintain their sprint speed slightly longer. Training has been reported to increase the storage of both ATP and CP by 18% and 35%, respectively (MacDougall et al. 1977).

Besides training, athletes have tried to improve the creatine phosphate supply in their muscles by supplementing their diets with creatine. This procedure has been reported to increase the free creatine in muscle fibres by about the same amount as training does, 20% (Hultman et al. 1996). The results have been equivocal about whether creatine loading can improve the performances of sprint athletes.  Some have reported improved performances, but others have not.

Training Anaerobic Metabolism

The anaerobic breakdown of muscle glycogen supplies approximately half the energy for ATP-CP recycling during the first 5 to 6 seconds of a race. Thereafter, the proportion will increase considerably until anaerobic metabolism will be supplying by far the greatest amount of energy for sprinting within 10 to 15 seconds after the race begins.

Because anaerobic glycolysis involves 11 steps, the power available for speed will decline somewhat after the first few seconds of a race. An athlete’s ability to generate muscular power will decrease by approximately 10% after the first 4 to 6 seconds of effort when the muscle’s creatine phosphate supply is partially depleted and anaerobic glycolysis becomes the primary source of energy for ATP recycling. For this reason the rate of anaerobic glycolysis has a greater influence than the ATP-CP system does on how fast athletes can perform in sprint events.

Training appears to increase both the quantity and activity of many of the enzymes of anaerobic glycolysis. Sprints are particularly good for bringing about these increases, whereas endurance training tends to suppress their quantity and rate of activity. In general, training-induced increases of anaerobic enzymes have not been as great as those reported for the enzymes of aerobic metabolism. Most of the increases in anaerobic enzymes have ranged between 2% and 22%.

The major obstacle to increasing the quantities of anaerobic enzymes is the endurance training that athletes must engage in. Endurance training suppresses the activity of most anaerobic enzymes.

The dilemma most athletes face is that they must improve both endurance and speed to improve their performance in many events. But athletes typically do so much endurance training that the best they can do is maintain their innate ability to recycle ATP rapidly through anaerobic metabolism. More often, their rates of muscle contraction and anaerobic metabolism decline during most of the season because of the large volume of endurance training they perform. Lucky athletes manage to regain their speed during the taper. When the loss of speed has been extreme, however, the taper may not be long enough and speed will not return to inherited levels until several weeks after endurance training has been terminated or considerably curtailed.

Training to Delay Acidosis – Training Aerobic Metabolism

The desired training effect is to reduce the rate and severity of acidosis during races. That effect is the result of two factors – reducing the rate of lactic acid production within muscles and increasing the rate of lactate removal from them.

1. Many training adaptations reduce the rate of lactic acid production:

  • Increased diffusion of oxygen from the lungs, which results from improved volume of air exchanged each minute and an increase in the capillaries around the alveoli of the lungs
  • An increase in blood volume that permits blood to circulate through the body faster
  • An increase in red blood cells so that the blood can carry more oxygen
  • An increase in cardiac output so that the blood makes a quicker round-trip from the lungs to the muscles
  • An increase in capillaries around the muscles so that more oxygen can be made available for diffusion
  • Improved blood shunting so that more of the blood supply and its oxygen can reach the working muscles during each minute of exercise
  • An increase in myoglobin so that more oxygen can be transported to the mitochondria of the muscles each minute
  • An increase in the size and number of mitochondria in muscles so that the receptacles for aerobic metabolism will be larger and more numerous
  • An increase in the activity of the aerobic enzymes so that aerobic metabolism can proceed at a faster rate
  • An increase in the rate of the glucose-alanine shuttle so that more pyruvate can be removed before it combines with hydrogen ions to form lactic acid

2. Several training adaptations increase the late of lactate removal from working muscle fibres:

  • Increased activity of the lactate transporter in working muscle fibres and receptor fibres
  • Increased blood volume and improved cardiac output so that more blood can make the trip to and from working muscle fibres in a shorter time, thus transferring more lactate from the working muscle fibres to the blood and then to areas where it is removed during each minute of exercise
  • An increase in capillaries around the working and receptor muscle fibres so that more lactate can be transferred into and out of the blood during each minute of exercise
  • Improved blood shunting so that more lactate can be carried away from the working muscle fibres with each minute of exercise

Training Effects that improve the Ability to Train

  1. An increase in the amount of glycogen stored in working muscle fibres so that athletes can train more intensely more often.
  2. An increase in the rate of fat metabolism so that the muscles use more of this compound for energy and less glycogen, leaving more glycogen for a greater number of intense training sessions.

Circulatory System

This post will be longish seeing as there is nothing difficult in it, pretty much a refresher for most.

Circulatory System

The circulatory system is essentially like the filtering system of a swimming pool. The pool is like the tissues of the body, principally the muscles. The heart is the pump. The arteries and veins are the pipes going to and from the pool. The blood is like the water that is pushed out to the pool after being cleaned and then pulled back from the pool for subsequent cleaning. The left side of the heart pumps blood out to the muscles and other tissues of the body through the arteries and arterioles which are like branching sets of pipes that become smaller in diameter until they reach their destinations in the tissues. Arterioles end in capillaries which are the smallest vessel units and surround individual muscle fibres.

The blood delivers oxygen, glucose, and other substances to the capillaries. At that point, blood is at its greatest proximity to muscles, and some of these substances diffuse out of the capillaries and into the muscle fibres they surround. At the same time the carbon dioxide, lactate, and hydrogen ions produced in the muscles during exercise diffuse and are transported out of them into the capillaries. Blood then leaves the tissues through the same capillaries and travel through another set of progressively larger tubes, the venules and veins, back to the right side of the heart. The heart pumps the blood out to the lungs through pulmonary arteries and arterioles, ending in pulmonary capillaries that surround small sacs in the lungs called alveoli. Here, carbon dioxide diffuses out of the blood and into the alveoli when it reaches the lungs, where it is exhaled. At the same time, oxygen inhaled into the lungs diffuses into the capillaries, and blood transports it back to the left side of the heart through venules and veins. Once it reaches the heart, the process begins again.

The lactic acid picked up from the muscles will be dropped off at several locations as the blood makes its way back to the heart. Some of it will be dropped off at other muscle fibres and the liver, where it will be converted back to glycogen for use later as a source of energy. Some of the remaining amount will be picked up by the heart muscles and used as fuel or converted to glycogen and stored for later use.

Heart Rate

The number of times your heart contracts during each minute is your heart rate (right and left sides contracting simultaneously counting as one beat). Resting heart rates are in the neighbourhood of 60 to 80 beats per minute (bpm) for most untrained persons and 30 to 50 bpm for trained athletes. Cardiac muscles of the heart become larger and stronger from training, and they can push more blood out with each beat so the heart requires fewer beats to supply the usual quantity of blood the athlete needs at rest.

Stroke Volume

The amount of blood pushed out of the ventricles of the heart with each beat is termed stroke volume. A normal range of values at rest is between 60 and 130ml per beat. These amounts can increase to between 150 and 180 ml per beat during exercise. These values refer only to blood pumped out of the left ventricle. Stroke volume increases with endurance training. Many factors contribute to the increase, including increased strength of the cardiac muscle fibres, an increase in ventricle size, and a decrease in the thickness of the blood. The stroke volumes of athletes are usually greater after training than before, which explains why they have a lower resting heart rate.

Cardiac Output

The amount of blood ejected from the heart during each minute is referred to as cardiac output. Again, we consider only the amount ejected from the left ventricle when citing values for the cardiac output (right ventricle will eject an equal amount).

Cardiac output is calculated by multiplying the heart rate by the stroke volume. Normal cardiac output for a person at rest is between 5 and 6 L per minute (L/min). The bodies of females and males contain between 4 and 6 L of blood; therefore, each red blood cell usually makes one round-trip from the lungs to the muscles and back again in approximately 1 min when athlete’s bodies are resting. Resting cardiac output does not increase with training, but the heart becomes more efficient in the way it supplies the blood. Stroke volume increases and heart rate decreases. So when a person is resting the heart does not have to work as hard to push the same 5 L of blood out to the body each minute. Training does not increase an athlete’s cardiac output during similar submaximal efforts because there is no need for it.

Athletes can increase their maximum cardiac output by training. Maximum cardiac output values of 30 and 35 L/min are not unusual for trained endurance athletes.

Blood Pressure

Blood flowing through vessels exerts pressure on the walls of those vessels. This pressure is measured by the number of millimeters that the blood causes a column of mercury (Hg) to rise. Two measurements of pressure are needed to identify the force of blood flow: (1) the pressure when the heart beats, known as systolic pressure, and (2) the pressure when it is resting between beats, diastolic pressure. Typical resting systolic and diastolic blood pressures are 120 and 80 mm Hg, respectively.

Systolic blood pressure increases in proportion to the intensity of work because a larger amount of blood is present in the vessels at any one time.

Endurance training reduces both systolic and diastolic blood pressure by 6 to 10 mm Hg at rest and by an equal amount during submaximal exercise. This reduction in pressure probably occurs because the elasticity of blood vessels increases through constant expansion and constriction that occurs in training.

Ok, so nothing hard there. We’re up to the respiratory system. I’m going to leave that to another post because this goes a bit into what we do with the oxygen we take in and measuring VO2max, oxygen debt and some other stuff so is probably worthy of its own post. Then we get into energy metabolism (that we use up our creatine phosphate in the first few seconds of exercise is a bit of a downer isn’t it but hey, we’ve got glycogen so why did we even get given CP in the first place I don’t know – actually, because it can be utilized really really quickly), how we produce and clear lactate. Then there is a section on metabolic training. Finally we get to the info on the energy zones – EN1, EN2, EN3, SP1, SP2, SP3.