High reps do not build high strength. They will help to build muscular endurance (a type of strength), but the Impact on strength output will be minimized.

Let’s take this to a logical extreme. Let’s say you start working out and your maximum reps for pushups at one time is 5. Then, a year down the road it becomes 50. Has your strength increased ten times? No, but between muscle development and the building of your endurance you’ve improved. There will be an increase in strength here, but it won’t be anything grand.

Higher intensity shorter reps grant the most strength gains. Also, try to either work to failure or close to it in order to ensure that you’re actually challenging yourself properly. 12 reps is the standard for a reason, do more or less with an understanding of why. More for endurance, less for strength. Twelve even for a good balance.

Imagine a sort of sliding scale where muscular endurance is on the high rep side and strength output is on the low rep side. The middle area will be approximately 8-12 reps and deviations from there start to focus more on one aspect than the other. Both aspects exist regardless, but the one aspect will start to overshadow the other the further you go from the middle.

Pushups are an interesting example of this, if someone can only do 5 reps to begin with they will primarily be building strength at first. But pushups are easy to progress with and after a year that same individual should be able to do 20+ reps. At that point any strength gains are almost negligible.

If strength is a priority, focus on doing sets in the 5-8 rep zone. If muscular endurance is a priority, focus on doing sets in the 12-20+ rep zone. If you have no preference, working on various rep zones will help you to challenge yourself in different ways. When training, you should always perform your sets to or close to failure in order to ensure that you provide your body a good stimulus for improvement. What is failure? There are two types, but here I am referring to technical failure where you can no longer perform another rep in good form. In decreasing order of importance, progress in the gym is hinged on the following: consistency, quality (of technique), Intensity, and strategy (having a plan). Rep ranges mean almost nothing if you fail to provide sufficient intensity by never coming close to failure. You can certainly build strength at a higher rep range, but it is in a lesser capacity by comparison.