Whenever I do pull-ups, Palms facing in, my body swings forward and backward. I'm trying to avoid this because I was told that swinging will make pull-ups "easier", and take stress off of the target muscles. Is staying straight something that I will have to train myself to do? Am I doing them wrong?
If you cross your ankles while doing pull-ups it will keep your feet from moving upwards, which is the main cause of swinging. Focus on using only your arms to do your pull-ups and try to engage your core (abs and obliques) as much as you can to keep yourself from swinging. If you're still swinging, slow down your pace, not only will this keep you from swinging but it will make the pull-ups harder to do and it will be a better workout for your arms. It may help to pretend that there's a big thick steel bar running from your legs through your pelvis to the tip of your head that is unbendable.
You're absolutely correct that swinging can make pull-ups easier. (It can also make it harder to hold on to the bar. Both of these are not good.) I use two methods to avoid swinging during pull-ups and chin-ups:
Bend my knees at a right angle, without crossing my ankles.
Extend my legs in front of myself, as high as they go. You can do it like the picture, but you don't necessarily need to keep them as high if you're just looking to stop swinging.
(This is somewhat harder. That might be a good thing.)
In addition, coming to a complete stop and pause at the bottom helps me minimize swinging, as does pulling myself up slower (which makes them harder, which might be good or bad depending on circumstance).
Try to slow down the pace until you can do full pull-ups with good form and not swing. If you feel that you do not have the power to do the pull-ups with good form, use alternative ways of doing them until you are strong enough.
Alternative pull-ups can be either with one or two legs on something a bit elevated from the ground so that you can help lifting yourself. You can also do negative repetitions to build strength where you have a chair or such and lift your body up and then slowly sink down without help still with good form.
When you do pull-ups or chin-ups you'll naturally bend at the hips and the knees.
Just straighten your knees at the top of the movement and you'll counter the swinging.
If you are swinging you are most likely trying to go too fast or you are lacking strength so the natural reaction of your body is to generate additional momentum so you can complete your pull-up.
Thus, here's what I suggest to you.
- Find a bar that is tall enough so when you hang off of it your feet won't touch the ground.
- Assure that your whole body is straight as your hanging below the bar.
- Extend your legs, flex them and keep them and your feet together. I don't advise you to cross your feet, that will create a habit of executing the pull-ups in an ugly manner.
- Now try a CONTROLLED pull-up where you don't generate any additional momentum and where you have the whole movement under control. What I mean by "under control" is the ability to stop yourself at any point during the pull-up without swinging additionally.
Keep your whole body straight during the pull-up and this way you will gain the most out of the exercise. In addition I will say that it's normal for your legs to go slightly in front of you as you are pulling yourself up in order for your body to balance itself. So don't worry about that.
Nowadays when I do pull-ups I just keep my legs straight, I straddle them slightly because that helps me to balance it if I am going faster or doing clapping pull-ups, etc etc.
There is nothing wrong with going fast. It sounds like you'd need a lat pull down machine or weights during pull ups if you're going so fast on the pull up bar that the laws of physics and gravity are in your way. Think sprinting vs long distance running.