I'm a runner. I love it. The only exercise I love more than running is sex. I love the personal solitude and the struggle to beat the clock and the honesty of that objective achievement. For me, running is the purist measurement of my personal performance. But I really shouldn't run and you probably shouldn't either.
Running is terrible for your body.
Every serious runner has an injury. Probably right now. This is because running is ballistic and load bearing. The forces generated by running are many times greater than the force of gravity and repetitive stress is really the whole point. Knees tweak (runner knee), tendons slowly tear (achilles tendonosis), and muscles literally swell out of their fibrous capsules (shin splints). And if you continue to train hurt, you can actually break bones from the strain. I had to take 6 months off because I nearly ran both of my achilles tendons in half. Tim Noakes estimates that every healthy person has 15 years of running improvements in their bodies before the accumulated damage is permanent and you start to get worse no matter how well to you train.
It just doesn't burn that many calories.
Compared to other non-ballistic activities like swimming or biking, even walking, the amount of calories burned is even or slightly less. Rowing burns 50% more calories per hour and will not destroy you.
It makes you hungry.
The ballistic damage to your muscles combined with the acute glycogen depletion creates an instantaneous feeling of hunger that is higher than other non-ballistic forms of cardio.
Running is terrible for fat loss.
Because it makes you hungry and it doesn't burn that many calories comparatively, running is not a great way to lose weight. In fact, if you want to actually go faster, you end up having to eat a lot of carbohydrates to restock your glycogen levels before you run again the next day. Most relatively healthy people who decide to run a marathon to get healthier actually find they gain weight during training.
It is actually expensive.
I have 10 pairs of running shoes. Asics Gel-DS Trainers for pavement, Salomon Speedcross 2s for trails, La Sportiva Fireblades for hybrid trail running, Adidas Adizeros for races over 10k, Nike Lunarracers for races 10k and under, Nike Bowerman Victory track spikes, 3 pairs of Nike Zoom+ Hayward 3 Prefontaines that I bought on eBay because they stopped making them, and a pair of very expensive Kahrus that destroyed my shins before I relegated them to the back of my closet. I have 2 camelbacks (one for pavement, one for trails), an emergency kit for trail running, 6 or so special water bottles and water bottle belts, 5 pair of Nike running shorts, a pair of split leg racing shorts, 5 Nike compression shirts, a racing singlet, 3 pair of cushioned socks, 5 pair of drimax socks that are left and right footed, 3 tubes of bodyglide, zensha compression sleeves, 2 "the sticks," a foam roller, Endurox R4 Recovery Powder, Nuun electrolyte tablets, boxes of GU glucose gels, and a $400 Garmin GPS enabled watch that ranks with my most prized possessions. Do I need all of this to run? No. I just need it all to run fast.
You're never going to win a race.
There's always someone faster than you. I am in the 99th percentile for running performance which means there are 65 million people faster than me.
It will fuck up your brain.
After you run a marathon, you will be in a deep depression for at least a month. The depletion of neurochemicals is the traumatic equivalent of getting struck by lightning. It is also addictive for these same reasons.
Everyone and their grandmother has run a marathon.
No one cares that you did unless you qualified for Boston.
It will destroy your sex drive.
Running destroys muscle which causes a release of cortisol (the body's stress hormone) and other chemicals to remove the torn tissue by converting protein to carbohydrates. Cortisol also messes with your body's ability to receive testosterone which is the chemical that makes you horny. So the more you run, the less muscle mass you have and the less you want to have sex. This is the main reason my wife will not let me run more than 25 miles a week or run any race longer than 10k.
The point of this article is not to scare you off running, just to educate you and help you prioritize your fitness goals. I run because I love it. If you hate running and don't have to, why do it? Find another form of cardio that you do enjoy and do that. That way you won't be in my way at the next 10k.