Whether your goal is hypertrophy, strength, or achieving/maintaining fitness, your progress will slow down eventually. Or maybe you haven’t hit that plateau yet, but you have a muscle group that’s not responding to training as well as others. One solution for this is with 100 reps. Yes, 100 reps. There are a few ways to use this technique, but the goal in all of them is to complete 100 reps with as little rest as necessary. Sounds crazy, but it’s very do-able. Choose an exercise and use a weight that 15-20 reps would be challenging. Do 20 or so reps, almost to failure. Rest for 30-40 seconds, do more reps almost to failure. Repeat this until you get to 100 reps.
There are many benefits to the 100’s technique. You will increase your muscle and mental stamina. You will increase your rate of fat burning. And most importantly, you will get through your plateau/get the stubborn muscle group to grow. The effectiveness of 100’s is mostly in the way the muscle fibers are activated. At the relatively low weight you’ll be using your type I(slow twitch) fibers will be used. As you progress through the 100 reps those fibers will begin to fatigue and type II fibers will be activated.
For more info, variations, and more detailed explanations: