Well, at 13, I'd personally tell you that's too young to be doing what you're doing. You should be out playing and discovering the world and developing your brain and your interests. Sports will work more areas of your body and be more fun than doing what you do when you're older and can't get folks together to play so easily. You need cardio, not just resistance training, especially at that age. But let's say this is you and what you're going to do -- there are as many theories about working out as there are people who work out, but most would say to alternate days -- you work arms one day, legs the next, abs the next, for example. If you want to train all parts of your body, you play sports or you do cross training. If you do the same things over and over you work the same few muscles over and over but don't work anything else, and will end up with an unbalanced looking body. I'd also say, nobody does sit ups anymore because it's not great for the lower back -- most would recommend a range of ab exercises, including the planks. Also, planks must be done with the core in perfect posture or you'll again end up hurting yourself, so I hope someone showed you how to do it correctly. Form is very important, and usually if you use good form you can do fewer reps because it hurts more -- if you can do a ton of reps it may mean your posture is off and in the end you will hurt yourself. My own opinion, again, is that if you're truly only 13, your body isn't anywhere near developed yet, your hormones are just getting started, your brain isn't anywhere near developed yet, and what you're doing is very isolating. Maybe it's just me, but I'd urge you to get out and play and diversify your routine. But if this is what you truly love, then it is recommended you alternate days for different body parts.
What about changing it up. Add in some cardio work outs like a run or bike ride and on those days, limit the core and strength work. And take two days off a week. My sons are around your age and both in competitive sports. My 13 year old plays club soccer and besides practice, he's expected to run 8 miles and spring 2 miles a week, and do 500 sit ups, 500 push ups, 200 mountain climbers a week plus an hour a week of soccer ball jugging. That's his conditioning work. He also runs track that makes it easier to accomplish outside of his 3 times a week soccer practice he also does.
Both my boys have done push ups and sit ups daily (well, school days, so 5 days a week) for a couple of years (after getting into the habit having to do it for the physical fitness merit badge in scouts) but not 500. They can both whip out 100 fairly easily. So agree that maybe cutting down on the reps.
I think the school of thought is cross training. No one activity like that every day. Do you do any sports? Play basketball, swim, run, bike ride, kick box? Make sure you do that a couple of times a week and again, maybe on those days, do limited sit ups, push ups, etc. Take your two days off a week. Maybe get a light set of dumb bells and add in some weight work. Change it up.
Paxiled, everyone still does sit ups. It's still part of the fitness test, it's still part of training, it's even still part of my old lady work out classes conducted by certified fitness trainers. Other things like planks are still added in though, that is true.
I also want to say to the poster, that everything you do should be discussed with your parents so that you know it is safe. Being safe is most important. Our gym has a training they do for kids who are 10 and over to know how to use equipment and my husband and I also would make sure our kids are doing their fitness work correctly. :>) good luck to you!
You will find traditional sit ups still done regularly by various sports professionals/trainers and is a part of most physical fitness tests you'll encounter. Add along with it planks (side planks are killer but effective) and other abdominal exercises. If you are thirteen, have you ever worked with a trainer? Again, my kids starting in 8th grade will go to the weight and conditioning room three times a week with the teams they play sports with. And the school offers conditioning as a gym class. So, even if your family does not have access to a gym, you can use your schools and get help there. I admire your determination and being in good shape is for life.
The short answer to your question is, "yes, you should give yourself breaks when you workout to give your muscles a chance to heal."
The longer answer is that it really depends on what your goal is for working out: trying to bulk up, trying to get stronger, trying to lose weight. That will affect the type of exercises you do, and how often you do them.
Paxiled is right, though, you shouldn't be working out so much before you've gone through puberty. Believe it or not, it can actually have a negative effect on your overall growth if you start working out too much too soon. Pushups, situps, planks, kettleballs - these should be OK, but don't overdo it and don't start lifting weights until you're 16 or so. Best thing you can do right now is stay active, get outside and play a sport or two, learn good form and keep stretching.
i'd take breaks every 5-10 minutes just in case. i'm only 15 1/2 thats what i do just to give you the amount of time you should be taking a break