E very good ways to increase metabolism without changing your diet, and some very bad ways to do it. There are some really good ways to exercise in the gym, and some really bad ways. Below I outline some good ways, and some really bad ways. I also explain why, when you try some of these, you feel like you could not do it anymore, and how you could make it through the workout.
Determine whether you are strong enough to exercise.
If you are not strong enough to do it, you may not be strong enough to do anything. You will not be able to do your workouts, let alone the 100 sit ups a day. If you can not do your 100 sit ups a day, you may not be able to do a single set of leg squats at all. You can try for a few months, but it will take a few weeks to reach a higher level of strength. Work your way up, and then try to improve it further. Most people try to go above and beyond what they are strong enough for. This is a recipe for disaster.
Increase the intensity, not the duration.
There are a number of ways to do this, and I will describe three of them below.
* Add more weight. This can be done by either holding the bar longer, or by lifting more. If you are doing more weight, you will need to do more reps, but you can do fewer in the same amount of time. If you do fewer reps in the same time, you can do less weight. The reason for this is that you will not be able to work your way up to 100 reps in the same amount of time as if you are doing more reps.
* Reduce rest time between sets. Sometimes, we do the same exercises, but do different sets in different amounts of time. This will cause the muscle to work twice as fast, especially if you want to work up to a higher level of strength. The time between exercises can be decreased by taking a short rest period, instead of taking a long rest period.
* Start with the bigger weight, and do more reps. This is a variation of the previous one, and is great for novice exercisers. In this case, you may do 20 repetitions with a lighter weight, and after some reps, you can go increase the weight. I am not advocating that you do more reps and less weight in this case. I am simply pointing out that doing a lower amount of reps, when you are strength training, should be at least as difficult as doing more reps. It should be a good challenge.
Now that you know how to workout, you have to know when to workout. I am going to explain my logic behind this. As a beginner, the best thing you can do to workout is to do some type of exercise, whether that is jumping rope, running, or calisthenics, which puts a degree of stress on your muscles. So, when you do these exercises, if you want to, you can rest between sets. Your muscles will have had their day to relax. And, they will feel ready to work again in the morning.
* After you have done this, you should workout for at least 20 minutes on the days you do upper body exercises, then another 20 minutes on the days you do lower body exercises. It will be enough to do at least 3 times per week.