ANSWER
By straining the weak muscle twice, it is forced to react by growing. To support this growth or to enable it in the first place, you must also provide your body with the necessary nutrients: plenty of protein and carbohydrates as well as a basic requirement of healthy fats. In terms of optimal nutrition, I recommend that you visit my homepage or, of course, read some of my previous columns in which I have already spoken about this.
The third option is to use different intensity techniques (see: INTENSITY TECHNIQUES . The basis should always be the "Kiss principle": short, intense, safe and clean! Negative repetitions, forced repetitions, reduction sets, supersets, pre-fatigue, cheating, partial repetitions and so on are just some of these methods, although negative repetitions are, in my opinion, the most effective intensity technique because they demand everything from the muscles. It has long been scientifically proven that the negative of a repetition provides the greatest stimulus and the associated muscle growth.
The upward movement should last about one to two seconds and the downward movement, i.e. the negative movement of one repetition, about three to four seconds.
This means that the weight is always moved slowly and in a controlled manner. This puts a much more effective strain on the muscle fibers than is the case with conventional repetitions (which you unfortunately see all too often in the gym, according to the motto: "The more repetitions in the shortest time, the better.").
Don't worry so much about reps or weights, but rather pay attention to feeling the muscles working. Many people have problems with muscle growth because they are too busy counting weights and training for their ego.The weights are just a means to an end. Much more important is the feeling of your body, the tension during a set and the visualization - you should mentally visualize what your muscles should look like with each set. The more you can implement this - scientifically proven - visualization, the better!