Anything taken to the extreme us bad. Like all these long distance runners. Some claim they are in horrible cardiovascular shape, likely to die "early." And of course the legs and feet are toast with osteoporosis. Tons of small fractures. I haven't verified everything here but it's been reported many times that endurance athletes can be quite sickly, gettting heart attacks. Then of course you have the completely decimated testosterone level. They have done a bunch of studies on Clomid for endurance athletes. And antidepressants to combat overtraining symptoms.
How can you be in horrible cardiovascular shape if you can run fast for miles? Strange statement. Running makes bones stronger. Yes, you can get stress fractures from over use can happen. Usually for runners that do stuff like 5-10 plus miles a day every day.
According to very involved stats from the Cooper clinic cardio improves health but extreme mileage decreases health. Doctor Cooper himself that coined the phrase Aerobics as it is applied to cardio said a sweet spot for running is 15 miles a week of running but it's not a hard fast rule. He used a bell graph to show longevity of runners and their mileage.
The first thing they do with many people who had heart attacks or heart surgery in rehab is to get them on a treadmill. Bunch of studies with clomid and runners? Clomid is a banned substance in the Olympics. Yes, extreme running can lower testosterone. It can also increase it. Going out for 10 miles a day is stress on your body. Just like lifting with volume for hours a day.
Very involved many decade research by the Cooper clinic has the stats to show, exercising using cardio just 30 minutes a day, you can increase your longevity up to six years and decrease your risk of all-cause mortality by 58 percent.
The best answer could be running like all cardio is good for your health but like a drug it must be taken in the right dose.
Don't get me wrong. Lifting and eating right is another part of the equation. In the end the most important component is the luck of the gene pool you came from.
What cardio can do.
1. The heart is a muscle and it's strength is measured with how slow the resting heart rate is and the VO2.
2. Cardio decreases triglycerides which is fat in your blood.
3. Cardio lowers blood sugar so it decreases the odds of diabetes.
4. Cardio can decrease fatty liver and having a fatty liver causes metabolic issues.
5. Cardio increases HDL lipids.
6. Weight bearing cardio increases bone density. Of course extremes like marathon training can decrease it.
7. Cardio increases the health of heart capillaries of the heart.
8. Cardio decreases both subcutaneous fat and deadly visceral fat.
9. Cardio decreases depression and improves brain function. Source: Spark by John Ratley MD.
I could go on but the few above come to mind.