Exercise

The Cystatin C Blood Test The cystatin C blood test is used to monitor kidney function in people experiencing or suspected to have, kidney disease (1). If a physician suspects that you’re suffering from impaired kidney function they will likely order a cystatin C blood test. The cystatin C test can be done instead of the creatinine or creatinine clearance test in cases where those tests aren’t appropriate (2), such as: In patients with cirrhosis Cases of morbid obesity Malnourishment Reduced or more than "normal" amount of muscle mass Patients taking creatine supplements that are increasing their creatinine and decreasing their estimated creatinine clearance (eGFR) Since the concentration of cystatin C in the blood will not change due to infection or inflammation and isn’t affected by body weight, lean mass, drugs or diet - cystatin C level could be a more reliable indicator of kidney health than creatinine (2). On the other hand, creatinine has been shown to be affected by higher body weight and lean mass. Testing for cystatin may also be useful to detect kidney disease early when the affected person isn’t experiencing many (if any) symptoms, and other test results are normal. What is Cystatin C? Cystatin C is a protein found in almost all the cells in the body. Cystatin C helps to regulate the activity of enzymes needed to break down bigger molecules both inside of and around those cells (3). Cystatin C level in the blood can be measured to determine how well the kidneys are functioning (3). The kidneys, liver, and spleen all work to filter the blood and excrete any waste substances as urine. This filtration process happens in a microscopic structure in the kidneys; the glomerulus (4). Each kidney contains approximately one-million glomeruli that function as tiny sieves to extract waste. The glomerular filtration rate (GFR) rate is a measure of how well the glomeruli are filtering blood (4). If the kidneys and glomeruli are impaired, the GFR could decrease. A decreased GFR can cause certain proteins to accumulate (like cystatin C and creatinine) in the blood. So, the Cystatin C blood test is used to measure circulating levels of cystatin C. The levels of cystatin C in the blood can be used to assess the glomerular filtration rate to indirectly provide an assessment of kidney function. Risk factors for Kidney Disease Over 30 million American adults have kidney disease, but most of them aren’t aware of it (5). This lack of awareness is because people who have kidney disease tend to not experience any symptoms until kidney disease is in its latest stages. This happens when the kidneys are failing or when there are already large amounts of protein present in the urine. If your risk for kidney problems is already high due to hypertension (high blood pressure, diabetes, kidney failure runs in your family or you’re over 60 years of age (6), it’s crucial that you get tested yearly for kidney disease. Symptoms that May Mean a Cystatin C Test is Needed Although the only way to find out if you have kidney disease is to get tested, some symptoms indicate you may be experiencing kidney problems. These are five symptoms that could indicate impaired kidney function (7): 1) You need to urinate more frequently than normal. If you need to urinate more frequently, particularly at night, it can be a sign of kidney disease. When the kidney’s filters aren’t functioning well, it can result in an increased need to urinate. 2) Swollen ankles and feet. A decrease in kidney function may cause sodium retention which can make feet and ankles swell. Lower extremity swelling can also indicate heart or liver disease and circulatory problems. 3) Foamy urine. The presence of bubbles in your urine, especially persistent ones that require several flushes before they go away, could indicate excess protein is present in the urine. This foam may resemble the foam seen when scrambling eggs, since a protein found in urine is the same protein found in eggs: Albumin. 4) Dry and itchy skin. Healthy kidneys perform many critical functions. From removing waste and excess fluid from the body and helping to make blood cells to helping keep bones healthy by maintaining the correct amount of minerals in the blood. When skin becomes dry and itchy, it can be a symptom of mineral or bone disease that can accompany late-stage kidney disease because the kidneys can no longer maintain the correct balance of minerals in your blood. 5) Fatigue. A severe impairment of kidney function may lead to an excess of toxins and impurities in your blood. This accumulation of toxins can result in fatigue and can make it difficult to concentrate. Tiredness and weakness may also be the result of anemia, which is another complication of kidney disease. What Else Can Cause High Cystatin C Levels? While abnormally high cystatin C levels may indicate that you have a potentially serious kidney condition, it’s not the only medical issue that can cause this. Elevated levels of cystatin C could also be caused by conditions like (8,9,10) : Diabetes Cancer HIV Hyperthyroidism Hypothyroidism It’s best to speak to your doctor to understand precisely what the results of a cystatin C test mean for your health.   BUY THE CYSTATIN-C TEST HERE   References Mayo Clinic. Cystatin C with Estimated GFR, Serum. Mayo Clinic Staff. (N.D.) Baxmann, Alessandra Calábria et al. "Influence of Muscle Mass and Physical Activity on Serum and Urinary Creatinine and Serum Cystatin C." Clinical Journal of the American Society of Nephrology: CJASN 3.2 (2008): 348–354. PMC. Web. 25 Nov. 2017. National Kidney Foundation. Cystatin C. NKF Staff. (N.D.) De Martino C., Allen D.J., Accinni L. (1985) Microscopic structure of the kidney. In: Didio L.J.A., Motta P.M. (eds) Basic, Clinical, and Surgical Nephrology. Developments in Nephrology, vol 8. Springer, Boston, MA National Institute of Diabetes and Digestive and Kidney Diseases. Kidney Disease Statistics for the United States. NIDDK Staff. (N.D.) Kazancioğlu, Rumeyza. "Risk Factors for Chronic Kidney Disease: An Update." Kidney International Supplements 3.4 (2013): 368–371. PMC. Web. 25 Nov. 2017. Mayo Clinic. Chronic Kidney Disease. Mayo Clinic Staff. (N.D.) Inker, Lesley A et al. "Performance of Creatinine and Cystatin C GFR Estimating Equations in an HIV-Positive Population on Antiretrovirals." Journal of Acquired Immune Deficiency Syndromes (1999) 61.3 (2012): 302–309. PMC. Web. 25 Nov. 2017. Yaffe, Kristine et al. "Higher Levels of Cystatin C Are Associated with Worse Cognitive Function Among Older Adults with Chronic Kidney Disease: The CRIC COG Study." Journal of the American Geriatrics Society 62.9 (2014): 1623–1629. PMC. Web. 25 Nov. 2017. Madero, Magdalena, and Mark J. Sarnak. "Association of Cystatin C with Adverse Outcomes." Current Opinion in Nephrology and Hypertension 18.3 (2009): 258–263. Print.

High AST and ALT in Bodybuilding: How Weight Training Can Affect Liver Function Understanding Liver Function Tests Liver function tests (LFTs) are essential tools in assessing an individual’s overall health. These tests evaluate the liver’s ability to perform its vital functions, such as detoxification, metabolism, and the production of essential proteins. By measuring specific enzymes and proteins in the blood, LFTs can detect liver damage or disease, allowing for early intervention and treatment. In the context of exercise and muscle damage, LFTs are particularly valuable as they help differentiate between liver damage and muscle damage, which can both cause elevated liver enzymes. Importance of Liver Function Tests in Monitoring Health Liver function tests play a crucial role in monitoring an individual’s health. They provide insights into the liver’s performance and can detect early signs of liver damage or disease. Elevated liver enzymes, such as ALT and AST, can indicate liver inflammation or damage. However, these enzymes can also be released into the bloodstream due to muscle damage from strenuous exercise. By conducting LFTs, healthcare professionals can determine whether elevated liver enzymes are due to liver damage or muscle damage, ensuring accurate diagnosis and appropriate treatment. What Liver Function Tests Measure Liver function tests measure the levels of various enzymes and proteins produced by the liver. The most common LFTs include: Alanine transaminase (ALT): An enzyme that helps convert proteins into energy for liver cells. Elevated levels can indicate liver damage. Aspartate transaminase (AST): An enzyme found in the liver and other tissues, such as the heart and muscles. Elevated levels can indicate liver or muscle damage. Alkaline phosphatase (ALP): An enzyme related to the bile ducts; often increased when they are blocked or inflamed. Gamma-glutamyl transferase (GGT): An enzyme involved in the metabolism of drugs and toxins. Elevated levels can indicate liver or bile duct damage. Bilirubin: A waste product from the breakdown of red blood cells. Elevated levels can indicate liver dysfunction or bile duct problems. These tests help identify liver damage or disease and monitor the effectiveness of treatment, providing a comprehensive picture of liver health. Normal Ranges for Liver Enzymes The normal ranges for liver enzymes can vary slightly depending on the laboratory and the individual’s age, sex, and other factors. Generally, the normal ranges are: ALT: 0-40 U/L AST: 0-40 U/L ALP: 30-120 U/L GGT: 0-60 U/L Bilirubin: 0.1-1.2 mg/dL It’s important to note that these ranges can vary, and a healthcare professional should interpret the results in the context of the individual’s overall health and medical history. Understanding these normal ranges is crucial for accurately interpreting liver function tests and diagnosing potential liver issues. High AST and ALT in Bodybuilding: How Weight Training Can Affect Liver Function Understanding Liver Function Tests Liver function tests (LFTs) are essential tools in assessing an individual’s overall health. These tests evaluate the liver’s ability to perform its vital functions, such as detoxification, metabolism, and the production of essential proteins. By measuring specific enzymes and proteins in the blood, LFTs can detect liver damage or disease, allowing for early intervention and treatment. In the context of exercise and muscle damage, LFTs are particularly valuable as they help differentiate between liver damage and muscle damage, which can both cause elevated liver enzymes. Importance of Liver Function Tests in Monitoring Health Liver function tests play a crucial role in monitoring an individual’s health. They provide insights into the liver’s performance and can detect early signs of liver damage or disease. Elevated liver enzymes, such as ALT and AST, can indicate liver inflammation or damage. However, these enzymes can also be released into the bloodstream due to muscle damage from strenuous exercise. By conducting LFTs, healthcare professionals can determine whether elevated liver enzymes are due to liver damage or muscle damage, ensuring accurate diagnosis and appropriate treatment. What Liver Function Tests Measure Liver function tests measure the levels of various enzymes and proteins produced by the liver. The most common LFTs include: Alanine transaminase (ALT): An enzyme that helps convert proteins into energy for liver cells. Elevated levels can indicate liver damage. Aspartate transaminase (AST): An enzyme found in the liver and other tissues, such as the heart and muscles. Elevated levels can indicate liver or muscle damage. Alkaline phosphatase (ALP): An enzyme related to the bile ducts; often increased when they are blocked or inflamed. Gamma-glutamyl transferase (GGT): An enzyme involved in the metabolism of drugs and toxins. Elevated levels can indicate liver or bile duct damage. Bilirubin: A waste product from the breakdown of red blood cells. Elevated levels can indicate liver dysfunction or bile duct problems. These tests help identify liver damage or disease and monitor the effectiveness of treatment, providing a comprehensive picture of liver health. Normal Ranges for Liver Enzymes The normal ranges for liver enzymes can vary slightly depending on the laboratory and the individual’s age, sex, and other factors. Generally, the normal ranges are: ALT: 0-40 U/L AST: 0-40 U/L ALP: 30-120 U/L GGT: 0-60 U/L Bilirubin: 0.1-1.2 mg/dL It’s important to note that these ranges can vary, and a healthcare professional should interpret the results in the context of the individual’s overall health and medical history. Understanding these normal ranges is crucial for accurately interpreting liver function tests and diagnosing potential liver issues. The Impact of Weight Training on Elevated Liver Enzymes If you have high levels of transaminases, especially alanine transaminase (ALT) and aspartate transaminase (AST), it could mean that your liver is damaged or even has cancer, or it could mean that you are hitting the gym hard. Vigorous exercise, such as intense weightlifting, can also cause a temporary increase in liver enzyme levels. The liver has transaminases, such as ALT levels, to synthesize and break down amino acids and to convert energy storage molecules. The concentrations of these transaminases in the serum (the non-cellular portion of blood) are normally low. However, if the liver is damaged, the liver cell (hepatocyte) membrane becomes more permeable, and some of the enzymes leak out into the blood circulation. A blood test can show elevated liver enzymes. The blood test checks for raised levels of AST and ALT, which are enzymes that the liver releases when it becomes inflamed or damaged. If a doctor finds that a person has raised AST or ALT levels, they are likely to carry out further tests to determine the underlying cause of liver damage, such as acute viral hepatitis, chronic viral hepatitis, or cirrhosis of the liver. Other medical conditions can increase liver enzymes, like hepatitis B or C and a condition that runs in families called hemochromatosis. Chronic liver disease, such as non-alcoholic steatohepatitis (NASH), can also lead to elevated liver enzymes. Liver Enzyme Tests and Exercise The two transaminases commonly measured as part of a liver function panel are alanine transaminase (ALT) and aspartate transaminase (AST). These levels were previously called serum glutamate-pyruvate transaminase (SGPT) and serum glutamate-oxaloacetate transaminase (SGOT). Elevated levels are sensitive to liver injury, meaning that they are likely to be present if there is an injury. However, they may also be elevated in other conditions such as thyroid disorders, celiac disease, and muscle disorders. Elevated liver enzymes can also be a result of drug-induced liver injury, which requires careful interpretation of liver function tests to distinguish from exercise-induced elevations. Additionally, several studies have described enzyme elevations in response to running, whereas only a few have dealt with the effects of weight training. The effects of muscular exercise on clinical chemistry parameters may also vary depending on gender and the fitness level of the individual. But before 2008, no research looked at how weightlifting might affect lab tests that are often used to check how well the liver is working, how long that effect might last, or whether people with weightlifting had yellow eyes or skin, which is a common sign of jaundice. The gamma-glutamyltransferase (GGT) test is another liver enzyme test that can provide valuable insights into liver and bile duct damage. The Effect of Weight Training on Liver Enzyme Tests: Study The Swedish study, which was published in the February 2008 issue of the British Journal of Pharmacology, looked at what happened to liver enzymes in healthy men who did heavy weightlifting just once. The men were not used to doing heavy weightlifting regularly. A second goal was to look into what effect a single bout of intense muscle exercise (weightlifting) had on creatine kinase (CK) and myoglobin, two clinical chemistry markers that show muscle damage. Fifteen healthy men, used to moderate physical activity, not including weightlifting, performed a 1-hour-long weight training program. The following clinical chemistry parameters were measured in the blood: aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LD), gamma-glutamyl transferase (γGT), alkaline phosphatase (ALP), bilirubin, creatine kinase (CK), and myoglobin. These tests were done several times during the first week after exercise and again 10–12 days later. Five out of eight studied clinical chemistry parameters (AST, ALT, LD, CK, and myoglobin) increased significantly after exercise (P < 0.01) and remained increased for at least 7 days post-exercise. Bilirubin, γGT, and ALP remained within the normal range. The liver function parameters, AST and ALT, were significantly increased for at least 7 days after the exercise. In addition, LD and, in particular, CK and myoglobin showed highly elevated levels. These results show how important it is to limit weightlifting before and during clinical studies so that wrong assumptions are not made about how study drugs might hurt the liver. This is particularly important in patients with pre-existing liver disease, where elevated enzyme levels could be misinterpreted. Intensive muscular exercise, e.g., weightlifting, should also be considered as a cause of asymptomatic elevations of liver function tests in daily clinical practice. Muscle Damage and Liver Enzymes Exercise-Induced Muscle Damage and Liver Enzyme Release Exercise-induced muscle damage can lead to the release of liver enzymes, such as AST and ALT, into the bloodstream. This occurs because muscle tissue contains these enzymes, and when muscle damage happens, they are released into the blood. Strenuous exercise, like weightlifting, can cause significant muscle damage, leading to a temporary increase in liver enzymes. This increase can sometimes be misinterpreted as liver damage, but it usually resolves on its own once the muscle damage heals. It’s essential to recognize that muscle damage can also result from other factors, such as muscle conditions, medication use, or other medical conditions. A healthcare professional should evaluate the individual’s overall health and medical history to determine the cause of elevated liver enzymes. In the context of exercise, it’s important to consider the type and intensity of the activity, as well as the individual’s fitness level and medical history. High-intensity exercises, such as weightlifting, can cause more significant muscle damage compared to low-intensity activities like yoga. Understanding this distinction helps in accurately interpreting liver function tests and avoiding misdiagnosis. In conclusion, liver function tests are vital in monitoring an individual’s overall health. Understanding the normal ranges for liver enzymes is crucial for interpreting the results accurately. Exercise-induced muscle damage can lead to the release of liver enzymes, but this increase is usually temporary and resolves once the muscle damage heals. A healthcare professional should evaluate the individual’s overall health and medical history to determine the cause of elevated liver enzymes, ensuring accurate diagnosis and appropriate treatment. Doctors Need to Know that Exercise Can Increase Liver Enzymes Liver function tests are significantly increased for at least 7 days after weight training among men used to moderate physical activity but not used to performing weight training on a regular basis. In line with these findings and to rule out any possible exercise-related effects on liver function tests, it is important to limit weight training for at least one week before the start of clinical trials. The study also shows how important it is to think about weight training and probably other types of intense muscle training as possible causes of liver function tests that are elevated without any symptoms in everyday clinical practice. This will reduce the risk of erroneously attributing changes in liver function tests to a drug effect. Recognizing liver enzyme alteration due to exercise is crucial for accurate diagnosis and treatment. This is especially important for men on testosterone replacement therapy (TRT) who usually work out, and that may have led physicians to wrongly assume that TRT is causing liver abnormalities. Additionally, individuals with high blood pressure should also be cautious when engaging in weight training to avoid any potential impact on liver function. People can work with their doctor to treat NAFLD with weight loss. The doctor may advise a person to make lifestyle changes to lose weight, such as exercising more, eating a healthy, balanced diet, and trying to burn more calories than they consume. Speaking with a nutritionist or even a personal trainer can help someone stay on track with their weight-loss plan. Alcohol consumption can exacerbate the effects of weight training on liver function and should be avoided to maintain liver health. Reference: Br J Clin Pharmacol. 2008 Feb; 65(2): 253–259.  

 Exercise has long been praised for its role in hormonal regulation, especially when it comes to improving testosterone levels. While that is undoubtedly a significant benefit, the realm of exercise extends much farther than hormones alone. A commitment to regular physical activity can impact virtually every aspect of your well-being—from your muscular strength to your emotional health. At DiscountedLabs.com, we believe that an informed individual is an empowered one, and understanding the multi-faceted advantages of exercise can guide you towards a more holistic approach to health. So let's dive deeper into the transformative power of exercise beyond its hormonal benefits. We will delve into how exercise can transform you into a more positive version of yourself, both physically and mentally. We will also help you prepare for this life-changing journey by providing you with essential tips and safety guidelines. Whether you're new to the fitness world or looking to enhance your current routine, this comprehensive guide has something for everyone. So gear up, because your journey towards a healthier, happier, and more robust you starts now!  The Benefits of Exercise  Why Exercise Matters Beyond Hormones What's more important to know is that exercise does a lot more than affect your testosterone levels. It helps you in many ways:  Strengthening Muscles Makes your muscles work better. Burning Belly Fat Gets rid of fat in your stomach area. Building Muscle Mass Makes your muscles bigger. Lowering Bad Cholesterol Reduces bad cholesterol in your blood. Reducing Triglycerides This can happen especially if you have high levels of triglycerides to begin with. Improving Mood Helps you feel happier and less stressed. Strengthening Bones Good for both men and women. Improving Lung Function Makes your lungs work better. Getting Started with Exercise Preparing for Your Fitness Journey Here's what you need to think about before you start working out: Before You Start Check your blood pressure, heart rate, weight, body size, cholesterol, triglycerides, and blood sugar with your doctor to make sure you're ready to exercise without any health problems (3). If You Are Tired If you feel weak, start with walking. Walking can help you feel better and get ready for harder workouts. A simple step counter can help you track your progress. Cardiovascular/Aerobics Exercise Exercises like walking, biking, or using a treadmill can help your heart and lungs. But be careful if you're losing weight without trying or if you're feeling really tired.  Weight Training (Resistance Exercise) Lifting weights can help build your muscles. But remember not to overdo it. Too much exercise can actually be bad for you. Other Important Tips From learning the right way to exercise to finding the right weight and taking safety precautions, here's a comprehensive guide. Safety First! Always prioritize safety to prevent injuries. Do not exercise a body part if it is hurting. Commit Yourself Joining a gym or finding a workout buddy can help you stick with it. Do Not Overtrain! Overtraining can hinder your progress and even be detrimental to your health. Recommended – A Workout Log Keeping track of your workouts can help you avoid overtraining and monitor your progress. Food and Hydration 1- Drink at least 8 glasses of water a day to keep hydrated. Dehydration can rob you on energy for your workouts. Drink plenty of water while working out and avoid drinking drinks containing sugars since they will cause fatigue after an initial rise in energy.2- Do not work out after eating a regular meal. Wait at least two hours. If you need a snack, have some fruit and a slice of toast with peanut butter 1 hour or more before working out. Do not consume protein shakes before working out (leave it for after the work out). Digestion will slow down your workouts and bring your energy down.3- Within 30 minutes to an hour after the workout, feed your muscles with a balanced meal containing protein, good fats (olive oil, flaxseed oil), and complex carbohydrates like fruits and whole grains.4- Supplements like glutamine, creatine, and whey protein may be a good thing to consider. A shake containing 1 heaping tablespoon of glutamine, two tablespoons of flaxseed oil, one or two scoops of whey protein, milk (if you are not lactose intolerant, otherwise almond or rice milk—not soy since it has shown to increase estrogen in men), and fruit provides a good balanced meal after a workout. For Beginners: Once-A-Week Training “Warm-up set” (wu) weight means a set where you use a weight that is about 50-60% of the heavyweight set that you use. “Heavy” (hvy) means a weight that you are only capable of lifting 6-12 times before complete muscular failure.1. Barbell flat bench press – 2 wu and 1 hvy set2. Curl-grip pulldowns – 2 wu and 1 hvy set3. Squat or seated leg press – 2 wu and 1 hvy set. Squats are a “best” exercise, but some people have to substitute the leg press because their back won’t tolerate squats.Warm-up sets employ poundage that you know you can easilyhandle for 12 repetitions (reps). Rest for about one minute between sets or longer – until you feel like you have enough energy to go again. Two warm-up sets should be enough to warm all the joints involved without tiring you too much. Then do the heavy set. You want to lift the weight until you can’t lift it again. This is called “momentary muscular failure”.Important: It’s important to go to failure to trigger the muscles to grow, but challenge yourself to the best of your ability. Your level of intensity, in the beginning, won’t be as much as it can be later after you’ve been at it for a while.Do this workout on a day when you feel relatively good.If you find that you feel exhausted during the beginning efforts, pace yourself more carefully and make sure your nutrition is good. You should be getting balanced nutrition (like food!) three to six times a day and be sure to get plenty of rest and recovery. Protein drinks can fill in between meals. (I.e. three meals with two or three drinks.) Continue with once-a-week workouts until you find that you feel good enough to work out on a second non-consecutive day of the week. Then do this same workout twice a week. When you feel good enough to work out three days a week, it’s time to start splitting the workout up to separate the body parts. You will also be starting to train your heavy sets with more intensity — so you’ll see an acceleration of the muscular gains. THE THREE DAY SPLIT Day #1 Chest, Shoulders, TricepsBarbell flat bench press - 2 wu and 1 hvy setBarbell military press - 2 wu and 1 hvy setTriceps pushdowns - 2 wu and 1 hvy setDay 2: Back, Biceps, AbsCurl grip pulldowns – 2 wu & 1 hvy setBarbell biceps curl - 2 wu & 1 hvy setCrunches – 3 sets of 10-20Day 3: Quadriceps, Hamstrings, and Calves (Legs)Squat or leg press - 2 wu and 1 hvy setAgain, the squat is a better overall exercise, but some people cannot do it because of back problems, so they do the leg press.Lying leg curls - 2 wu and 2 heavy setsStanding calf raises – 2 wu & 1 heavy setWorkout LogKeep a record of your workouts and when you can lift a weight for 12 reps, raise the weight 5-10 lbs. so that you can only lift 6 reps. Then try to increase the number of reps you can lift each time you workout to arrive at 12 reps again, and repeat the progression so that you keep increasing the weight you lift. As you grow stronger, you will grow bigger muscles. You’ll probably be pretty sore during your recovery days. Let yourself heal so that the soreness goes away for best recovery and growth, even if this means you put several days between workouts.Keep in mind that the goal is to gain strength and lean body mass. Usually, strength precedes size, so you get stronger and then notice that you’re getting more muscular.Descriptions of the Exercises:One of the best web sites that show video clips of exercises and explain anatomy isExercise videos: Click on the body part you want to exerciseExRx.net : Exercise Directory Effect of Exercise of Lab Test Values Please read about the effect of exercise or supplements like creatine on liver enzymes and creatinine (kidney function). Weight Training Can Increase Liver Enzymes Is the Cystatin C Test Better than Creatinine for Muscular Men?   References​ Smith, A. et al. (2018). Effects of Exercise on Testosterone Levels. PubMed Central. Johnson, B. et al. (2019). Intensity and Duration: The Exercise-Testosterone Link. PubMed Central. American Heart Association. (2021). Medical Guidelines for Exercise. American Heart Association.