Hypertrophy and heart muscle changes

Long-term aerobic training, which involves sustained activities like running or swimming, leads to significant adaptations in the cardiovascular system. One key change is in the structure of the heart itself.

Hypertrophy

Hypertrophy is the process where the muscle walls of the heart become thicker and stronger due to regular training.

As a result of hypertrophy, the heart increases in size overall. This makes it a more efficient pump, capable of holding a larger volume of blood in its chambers and contracting with greater force.

Increased stroke volume

With a hypertrophied heart, the stronger muscle walls can push out more blood with each contraction. This leads to an important physiological adaptation.

Stroke volume

Stroke volume is the volume of blood pumped out by each ventricle of the heart in one beat.

For a person with average fitness, stroke volume is around 70 ml per beat. In contrast, a trained athlete might achieve around 90 ml per beat.

Bradycardia and resting heart rate

Another adaptation from long-term training is a change in how often the heart beats at rest, reflecting the heart's improved efficiency.

Bradycardia

Bradycardia is a slower than normal heart rate, typically fewer than 60 beats per minute (bpm).

Elite athletes often develop bradycardia as their hypertrophied hearts pump larger volumes of blood per beat. This results in a low resting heart rate, usually between 40 and 60 bpm, compared to around 70 bpm for an average person.

Visible and invisible changes from regular exercise

Regular exercise brings about a range of adaptations that enhance overall physical performance. These can be categorised into changes you can see and those that occur internally.

Visible changes

• Increased muscle size - Muscles grow larger and stronger through repeated training.
• Reduced body fat - Consistent activity helps burn excess fat.

Invisible changes

• Improved speed - Training enhances neuromuscular efficiency.
• Enhanced stamina - The body becomes better at using energy sources.

Lactic acid production and fatigue

During intense exercise, the body sometimes relies on energy production methods that don't require oxygen, leading to the buildup of a byproduct that affects performance.

Anaerobic respiration and lactic acid

Anaerobic respiration is a process where the body generates energy without oxygen, typically during short, high-intensity efforts. This process produces lactic acid as a byproduct, which accumulates in the muscles.

Lactic acid can cause fatigue, muscle soreness, and impaired performance. When an athlete increases their speed or intensity beyond their aerobic capacity, more lactic acid is produced than the muscles can clear. This buildup leads to slowing down or pain.

Building lactic acid tolerance through training

Regular exercise can improve the body's ability to handle lactic acid, reducing its negative effects and allowing athletes to perform at higher intensities for longer.

Interval training

Interval training is a method that alternates periods of high-intensity activity with recovery periods. This approach helps build tolerance by repeatedly exposing the body to lactic acid buildup.

How interval training works:

1. During the high-intensity phase, the athlete works at or above their lactic acid threshold.
2. This causes lactic acid to build up.
3. In the recovery phase, lower-intensity activity allows the body to clear some of the lactic acid.
4. Repeating this cycle over multiple sessions trains the body to tolerate higher levels of lactic acid.

To be most effective, interval training should use movements specific to the athlete's sport.