If you ask any athlete what he/she wants to train besides his/her muscles the majority would say that they want to train one of the most important organs, defining and shaping our lives ...
The heart is a large muscular organ, to be precise, it is actually one big muscle and this muscle hangs on in the mediastinum between other organs. That is, the heart has one point of attachment.
The heart muscle differs in many aspects from regular muscles but we are interested in its major function: blood pumping. While regular muscles are permeated with blood vessels and capillars, the heart cannot be supplied in such manner. For instance, there are no blood vessels in the heart since it may impede its contractions, hence myocytes (the heart muscle cells) that lie close to the internal walls are fed from the blood than goes through the heart.
The whole heart muscle contains less blood vessels than a typical skeletal muscle since the heart has to be as effective as possible and works non-stop the whole life. Luckily this is not an issue since the heart muscle is encased with the network of blood vessels and capillars and is thus well-fed.
Two types of workload
1. Volume workload. Blood that flows though the heart stretches inside cavities of the heart called ventricles and atriums. Blood flow under regular conditions is mild but with increase in intensity of exercise the demand for oxygen grows significantly and it causes the blood flow to go up accordingly. Also, skeletal muscles contract and work as peripheral pumps that pump blood back to the heart. If the flow is greatly exceeds normal level and the workload continues for tens of minutes or for hours then the heart is subjected to the increase in size with very moderate increase in the thickness of the heart muscle, that is the heart is stretching. Its ventricles and atriums are getting bigger, especially the left ventricle and it the same time stronger, that enables them to push out more blood in one contraction. This phenomenon is called dilatation.
If this type of workload is being applied regularly for a prolonged period of time, for months and years, then the heart is getting bigger, stronger and more effective. Resting heart rate drops down since the heart pumps more blood wtih one contraction. This is the major cause of low resting heart rates among endurance athletes.
One of the best ways to train the heart in that way is to spend hours in the zone between 110-150 BPM (beats per minutes) or, which is more correct between 55 and 80% of MHR (maximum heart rate), since MHR in general population varies a lot and depends on gender and age and there is no formula that may establish your MHR.
2. Resistance workload. This type of workload happens when the heart has to pump blood into the system overcoming resistance. It happens because of the following reasons:
1) Pumping through resistance of skeletal muscles. If muscles are tense because of effort or static workload, then blood vessels are constricted in diameter. The heart has to overcome this constriction and thus the blood pressure increases.
2) Working on a very high heart rate (180 BPM of higher, 90% of MHR or higher). In this case the heart cannot relax completely and cannot fill ventricles to the maximum volume.
3) Excessive bodyweight. The heart has to deliver blood throughout the whole overweight body thus overstraining itself since this type of workload cannot be stopped or avoided.
It does not matter what creates a hinderance. The heart does not know if it a constricted blood vessel or fat. The only thing that differs between them is that in the case of muscles the heart is also loaded with volume workload and its benefits.
Likewise skeletal muscles the heart under load may go into anaerobic regime with the subsequent acidocis which stimulates its hypertrophy, increase in crosssection of muscle fibres. The volume of its atriums and ventricles remains the same and the minute blood volume does not change. The volume even can go down since growth of the heart walls takes space not only outside but also inside.
Roughly speaking for each beat of the enlarged heart, the hypertrophied heart has to do 2 beats. And it means that it has to do more work during the whole life. That can kind of shorten your life span.
The second issue with the hypertrophied heart is that the blood permeates the thicker walls with difficulty and the heart may experience lack of oxygen and nutrients. The early stages of oxygen deficit provoke more hypertrophy. If nothing changes, the terminal result is dystrophy of the heart muscle due to oxygen deficit, ischemia, which lead to the death of cardiomyocytes and hence to heart attack.
At the same time, mild hypertrophy combined with dilatation can be worth-while, the heart has to have some strength after all. This strength can be trained at heart rates close to 180 BPM (or 90% of MHR). However it is important to understand that the heart cannot work for a long time at this rate. Local ischemia can cause micro heart attacks, which you cannot feel, and deaf fibre muscles are replaced with connective tissue. This type of tissue does not stretch well, thus preventing surrounding area of the hear muscle from effective work.
The heart and physical training
Wrong use of interval training, with spending too much time at very high heart rates can be more harmful than beneficial. Thanks to the general lack of fitness, most people do not have enough endurance to work at such rates for a long time. Nonetheless, it is worth to remember that this type of training should be approached with care.
Strength training is a special case of high intensity interval training combined with resistance created by tense muscles. That is why cardiologists advise their patients against strength training since it can “be harmful for the heart”. With proper approach, strength training is not harmful for the heart (we do not discuss professional athletes, they live in another world by different rules).
Despite the fact that moderate intensity is the best for the heart, it is not enough to train the heart in this mode only.
During strength training avoid overstraining and do not hold heavy weights for long, fighting for another rep. Give some air both to muscles and the heart.
Alternate heavy exercises with light ones or use exercises for antagonists to offload blood from stiff tired muscles.
Avoid prolonged strength training sessions, two hours of work on a high heart rate are not beneficial for your heart, let alone the hormone system is overstrained too. Spend 40-60 minutes, do sessions intensive and versatile.
Another good thing for the heart: shed your excessive weight at the expense of fat. If your probably exessive weight is muscles, take care of feeding them well.
How to find out if your cardiovascular system is adequately developed? First of all, you have to be able to complete a prolonged endurance exercise, such as a run for 3-5 km, or fast paced ride on a bike for 30-40 min. All physical requirements are defined for different age and gender groups, not for your size. You have to be developed harmoniously, although it is very hard to be a bodybuilder and a marathoner at the same time.
The second test is your resting heart rate, which is usually measured in the morning right after waking up. If it is 60-70 BPM or lower that is normal. If it is higher than that then you had rather start worrying.
It is worth to visit a cardiologist once a year. It will not take much time but, at least, there will be no hidden issues.