Endurance refers to the body's physical capacity to sustain exercises for a prolonged period of time. Endurance activities keep your heart, lungs, and circulatory system healthy and improve your overall fitness. A high endurance individual can perform physical activities for a prolonged duration with relatively less discomfort and fatigue than a low endurance individual. Genes that influence the fuel usage for energy production, distribution of muscle fibers (slow twitch and fast twitch), and oxygen-carrying capacity of the blood vessels, all directly affect the level of endurance. Individuals with certain genetic types are better at endurance-based activities than others.

Aerobic capacity (AC), also known as the VO2 max, is the body's maximum capacity to transport and utilize oxygen during exercises. Whatever your fitness goals may be, improving your AC can help you reach them faster. Around 4.8 calories are burnt for every liter of oxygen used. By improving the aerobic capacity, you essentially train your body to burn more calories for the same oxygen usage. The maximum oxygen uptake is determined partially by your genetic makeup. People with certain genetic types may require additional aerobic training to achieve the optimal VO2 max than others.

Cardiac output is the amount of blood the heart pumps out in a minute. At rest, the average cardiac output of a healthy individual is 1.3 gallons (5 liters). When you exercise, your body's muscles require more oxygen. So the blood flow, and hence the cardiac output increases. Heart capacity is defined as the ability of the heart to increase the cardiac output during exercise. Heart capacity is not just an important determinant of fitness levels but also clinically relevant for examining heart disease risk. People of certain genetic types have better heart capacity than others.

Total lung capacity, or TLC, refers to the total amount of air present in the lungs after taking the deepest breath possible. During exercise, your body uses up more oxygen and expels out more carbon-dioxide. In order to cope with this extra demand, your breathing has to increase (from about 15 times a minute during rest periods to about 40–60 times a minute). When your lung cannot increase this breathing rate, you'll tend to feel "short of breath" soon after you begin working out. People with certain genetic types may have a lower TLC than others. Such individuals may benefit from deep breathing exercises.

Power is an important component of physical fitness. In power training, you apply the maximum amount of force as fast as possible. Certain muscle fibers contract quickly and powerfully and play an important role in power-based activities, like sprinting and weight lifting. These are known as fast-twitch muscle fibers. People of certain genetic types have a lesser distribution of these fast muscle fibers than others. Endurance-based training may be more suitable for such individuals. A workout regime combining high-strength and high-speed exercises may lead to an increased ability to apply power.

Handgrip strength is a vital force that is required to pull, push, or suspend objects. It is a part of hand strength or physical strength utilized by animals or humans, especially athletes such as rock climbers. Handgrip strength is associated with frailty and risk of fracture. It has also be used to measure the risk of the onset of cardiovascular disease in adults. 65% of a person's grip strength is genetically determined. People of certain genetic types have a lower handgrip strength than others and may benefit from focusing more on opening grip, closing grip, and hand stabilization exercises.

Flexibility describes the extent to which you can move your joints and muscles freely. The full movement potential of the joint is called the range of motion. Improving the range of motion can increase your flexibility, resulting in improved physical performance and fewer injuries. Collagen is a protein that is a key constituent of ligaments, tendons, and muscles. The COL5A1 gene is associated with the synthesis of type V collagen. People with certain types of COL5A1 gene may have stiff tendons and ligaments, leading to a lower range of motion. Such individuals will benefit from focusing more on flexibility-oriented exercises.

Tendons are fibrous tissues that connect bones to muscles. They are found throughout the body, the Achilles tendon (connects the back of the calf to the heel bone) being the largest of them. Tendons have great strength, which is necessary to withstand any stress that is caused by muscle contraction. Tendinitis and Achilles tendon tear are some of the common tendon injuries. A particular class of collagen (produced by the COL5A1 gene) has been associated with tendon injuries. People with certain types of the COL5A1 gene have weaker tendons than others. Such individuals may benefit from focusing more on tendon-strengthening exercises.

Ligaments are tough elastic tissues that surround the joints. A ligament connects one bone to another. You have ligaments around your knees, ankles, elbows, shoulders, and other joints. The knee and ankle ligaments are more vulnerable to tearing because they are weight-bearing ligaments that are often under stress. ACL (Anterior Cruciate Ligament) is the most common ligament injury that occurs in the knee. Several risk factors like weak ligament strength, female sex, specific bone geometry, and poor conditioning contribute to ligament injury. Individuals with certain genetic types may have weaker ligament strength than others and may benefit from focusing on ligament strengthening exercises.

Are you the kind of person who is hardwired to exercise, or do you look for excuses to skip your workouts? Your genes influence the answer to this. In response to exercise, the brain releases neurochemicals. The production of neurochemicals increases as you get habituated to exercises and motivate you to work out more. However, inactivity results in lesser production of these chemicals, making you feel sluggish. This explains why exercise is difficult when starting out and why it becomes less challenging over time. People with certain genetic types may have lower levels of these chemicals and may require some extra motivation to exercise.

A growing body of research suggests that genetic makeup may play an important role in injury risk. These studies focus on how the difference in the structure of collagen protein can contribute to injury risk. For example, the COL1A1 (collagen producing) gene has been linked to soft-tissue injuries, like Achilles-tendon ruptures and shoulder dislocations. Some genes that affect the bone mineral density (amount of bone mineral in bone tissues) also contribute to injury risk. People with certain genetic types are more prone to injury than others. Including more muscle and bone-strengthening foods and adequate physical training can benefit these people.

Under normal activity levels, the muscles mostly rely on oxygen for energy production. However, lactate (a substance produced by the body when it converts food to energy) is the preferred energy source for high-power activities. Lactate build-up can lead to fatigue. So the onset of fatigue is directly related to how soon the lactate is cleared from the body. In addition to this, exercise-induced inflammation and flexibility could also be contributing factors. The MC1 gene partly influences lactate clearance. People with certain types of the MC1 gene may experience fatigue sooner than the other due to the slow clearance of lactate.

HDL or the high-density lipoprotein cholesterol is what is called the 'good cholesterol.' It is rightly called so, as it transports the extra cholesterol from the walls of the arteries to the liver, which is then used for digestion or excreted. If the HDL levels are low, the build-up of cholesterol can lead to diseases like atherosclerosis. Research indicates that regular exercise increases the level of this good cholesterol in the body. Even activities like brisk walking were seen to boost HDL levels. People with certain genetic types respond to exercises better in terms of an increase in HDL cholesterol levels than the others.

Insulin is a hormone made in the pancreas that plays an important role in controlling blood sugar levels. When the blood sugar levels are high, the pancreas secretes more insulin. Insulin sensitivity describes how responsive your cells are to insulin. Improving insulin sensitivity can lower your risk for conditions like type 2 diabetes and obesity. Research indicates that physical activity has a beneficial effect on insulin sensitivity. The LIPC gene regulates the fat stored in the liver, which, in turn, influences insulin resistance. People with certain types of the LIPC gene experience greater improvements in insulin sensitivity than others.

The amount of physical activity or exercise required for weight management varies greatly between individuals. Exercising improves metabolism, which is vital for both weight loss and weight management. How your body responds to exercise is mediated by several genes like FTO, ADRB2, and INSIG2. These genes influence factors like fat metabolism, energy expenditure, hormonal changes, metabolic rate, and even stress levels, all of which can contribute to weight fluctuations. Exercising, gradually spins the effects of these genes in our favor. People with certain genetic types experience a better response to exercises than others.

Exercising muscles cause microscopic tears, hormonal changes, and inflammation. While they all sound negative, these are undoubtedly positive effects on the body. During rest periods, the body heals and recovers from this damage. Muscles do not grow as you work them but grow as you actively rest. Like several fitness traits, the average time of recovery you would need post-intense workout is determined by your genes. Individuals with certain genetic types recover quickly, while others require more extended periods, which influences the frequency of exercise, rehab intensity, and supplementation needs to aid in timely recovery.