Heavy Weights and the Heart
Based on the available evidence, lifting heavy weights is not inherently bad for the heart. In fact, it has a positive impact on the pumping function. It leads to beneficial adaptations in the cardiovascular system, such as increased heart size and improved function. However, caution is advised for individuals with pre-existing cardiovascular conditions. As we will see, the relationship between heavy lifting and heart health is complex.
The heart and its function
The heart is a vital organ in the human body. It serves as a muscular pump that keeps the blood circulating throughout the body. It is composed of two main parts which sustain two circulations. The right heart pumps blood through the lungs, the small lung circulation. Here the blood exchanges. It gives away carbon dioxide and accepts oxygen. From the lungs the blood flows to the bigger left heart. The role of the left heart is to pump the blood through the peripheral organs. Each of these "hearts" constitutes two chambers composed of an atrium and a ventricle [1]. All the chambers of both hearts cooperate in a synchronized manner allowing a smooth delivery of nutrients and oxygen to the organs and muscles of the body [2]. During the life the heart contracts approximately a hundred thousand times every day [3].
A note on heart rate
The heart rate is measured in beats per minute (BPM). Adults, not engaged in sport and without stress, should have a heart rate between 60 to 100 BPM. Above 100 BPM it is referred to as tachycardia, fast heart rate. It is physiologically normal only in case of exercise or stress. Below 60 BPM the heart is in bradycardia, slow heart rate. This is normal only in the case of a well-trained heart which is extremely efficient.
The heart as a muscular organ
The heart is a muscular organ and is mostly made of a tissue called the cardiac muscle or myocardium. It is this muscle contraction that allows blood to pump through the body. Together with the muscle, the walls of the heart are made of two other layers. The inner layer, the endocardium, with the middle layer, the myocardium, and the other layer epicardium. Inside the heart are, the already mentioned, four chambers[4]. Two atria, the right and left one. They are the heart’s upper and smaller chambers. The myocardium layer is not thick here. Below them are two big chambers named the right and left ventricles. Especially the left has a strong muscle. The muscular tissue is made of cells which are very oxygen depended, but have incredible stamina. This is the reason why the heart is able to beat for the whole life. On each side of the heart, the chambers end with a plug called a valve. It opens and closes with the beating of the heart, depending on the pressure between the chambers and their outputs.
Types of physical exercise
One of the most common types of physical exercise is strength training, also known as weight training, resistance training, and muscular training. It involves using your body weight or equipment like weights and resistance bands to build muscle mass, strength, and endurance [5].
Strength training can be further divided into several subtypes. Muscular hypertrophy uses moderate-to-heavy weights to stimulate muscle growth. Muscular endurance training, on the other hand, involves high repetition using light weights. It increases the muscles' ability to sustain exercise for a period of time. Circuit training is a form of full-body conditioning. Here a person cycles through various exercises with little to no rest between them. Maximum muscular strength training involves low repetition (usually 2–6) and heavy weights. With it the overall strength improves. Lastly, explosive power training combines power and speed. By doing this type of training the power output increases. This type is often done by trained athletes [5].
A different type of exercise is endurance exercises. With this training the breathing and heart rate are high and it improves overall fitness. Endurance exercises include jogging, swimming, and dancing. [6].
Heavy Lifting
Heavy lifting is a subset of strength training. It is a potent stimulus to the neuromuscular system. The principle involves lifting heavy weights to enhance strength, power, or local muscular endurance [7]. This type of exercise increases the power and strength of the muscles. The key to see the effects is a regular practice of heavy lifting. With this practice daily physical tasks become easier and increase the amount of weight one can lift [8].
Lifting weights can also help fight and reverse the loss of muscle mass. Additionally, it works on other systems too. For example, it strengthens bones and helps prevent osteoporosis, especially in postmenopausal women [8]. However, it has one important drawback. In cases of wrong technic injuries can occur, like muscle tear or even joint dislocation or chronic joint wear off. It is crucial to use proper lifting techniques to avoid them [9].
Heavy lifting impact on the heart
One of the primary impacts of heavy lifting is on heart rate and blood pressure. During intense weight lifting, heart rate and arterial pressure can increase significantly. For instance, during a highly intensive exercise, heart rate increases to 94.4 ± 15.6 beats/min and systolic blood pressure rises to 147.1 ± 15.9 mmHg. However, it's important to note that these changes are temporary and return to baseline levels within 15 minutes post-exercise [10].
Regular weight training can lead to an attenuation of these responses, reducing heart rate and arterial pressure during exercise when lifting the same absolute load [11]. This is a sign of adaptation and increase in muscle strength.
More specifically, heavy lifting also influences the left ventricular function. During a maximal isometric deadlift exercise, the left ventricular ejection fraction initially declined from 57 +/- 2% to 49 +/- 3% at 15 seconds into the lift but recovered to 56 +/- 1% due to significant increases in end-diastolic volume by the end of the lift [12]. Thus regular heavy lifting also trains the heart. It increases the pumping efficiency, so the heart is able to cope the normal contractions during the day with significant easy.
Furthermore, prolonged weight lifting leads to changes in cardiac structure. Resistance trainers with greater fat-free mass and lower body strength appear to have larger cardiac structures. As the heart is a muscle, regular strength training leads to an increase in the size of the muscle [13]. This phenomenon is good, but only to a certain extent. Extensive cardiac muscle increase, so-called hypertrophy, can lead to ischemic events. However, these changes in the structure and size are typically within safe limits for healthy individuals and can even contribute to overall cardiovascular fitness [14, 15].
So is it bad or not?
Weightlifting, like any form of exercise, has effects on the cardiovascular system. However, whether these effects are harmful or beneficial can depend on various factors. Among some important considerations are the intensity of the exercise, the individual's overall health, and their experience with weightlifting.
Based on the available evidence, lifting heavy weights is not inherently bad for the heart. In fact, it has a positive impact on the pumping function. It leads to beneficial adaptations in the cardiovascular system, such as increased heart size and improved function. However, caution is advised for individuals with pre-existing cardiovascular conditions. For instance, people with heart valve disease should avoid heavy lifting due to the sharp pressure changes during the strain[16].