As a PT, I see and hear this all the time - from my client base and from snippets of conversation on the gym floor alike:
"Just do [insert random number] reps."
Why that number? Why fifteen reps and not sixteen? Why have you decided on twelve, eight, ten, seven-point-five?
First and foremost, establish what you're training for and what you're trying to achieve. I always mention this - return to your purpose and your "why".
Based on the premises that you've got your goals in place, there is an important truth about rep-based training: you can't switch off and fall back on just counting.
Whether you're training for strength or for hypertrophy (which are often intertwined), the reps and sets you do simply have to be difficult to evoke a truly potent stimulus.
There are different schools of thought on training to failure (training until you physically cannot carry on) and it's benefits for muscle growth. However, the general consensus is that hovering close to the point of failure is ideal if we're talking classic hypertrophy.
The numbers are there to provide rough guidance and structure to your training as different muscle groups and movements will require a variety of rep ranges (e.g. heavy compound movements that tax your central nervous system and compress your spine like deadlifts are probably best done in a smaller rep range like eight to ten). But as long as it's actually hard, it doesn't matter so much.
But what is failure? Where is failure? Am I truly able to push myself to true failure? Again, debatable. That said, here are some questions to ask yourself while you train to ensure that you're reaching an adequate peak of intensity and not just... well, wasting your time.
1. HOW LONG COULD YOU HAVE CARRIED ON FOR?
As you progressively move through your set, you will naturally get more and more tired - but here's where it's crucial that you are honest with yourself and your workout tracker. How many more did you have in the tank? Two? Three? Endless amount of reps? The only real way to find out is to rest, then do another set with the same weight, but forget about chasing reps and simply go until your body prevents you from carrying on. You will probably surprise yourself.
2. WHAT IS YOUR BODY TELLING YOU?
In a similar vein, a good pastime between sets is doing a quick self-assessment of your physiological response (instead of scrolling Instagram). Are you sweating? Is your heart beating faster than normal? Are your muscles lightly tense, or does your quadriceps feel like it's about to rip off? Are you just sat there, swinging the leg press platform back and forth, or are you truly working at the top of your biophysical capacity? Your mind will give in long before your body does - so once again, just be honest with yourself and your workout tracker.
3. HOW EASY IS IT TO HIT YOUR GOAL REPS?
As a coach, I tend to set rep ranges as opposed to fixed reps (for example, ten to twelve reps as opposed to twelve). This is not everyone's approach nor is it of use to every client or trainee. However, using rep ranges puts the accountability back into your hands - was getting that twelve a breeze, or did you have to fight to get to ten? You should be struggling at the end of your sets, and this is something to simply embrace and welcome as it is a good sign that you're working at the right intensity.
Next time you're in the gym, have a look around you. How are people training? Are there a lot of red, grunting faces? Is there that one person scrolling on their phone while half-heartedly swinging the leg extension pad?
To ensure that your fitness journey yields the most optimal results in the shortest amount of time, you'll do yourself good by making exercise a mindful practice. Meditative, thorough and focused - there doesn't necessarily need to be crazy screaming and grunting to validate your efforts, but your body will follow where your mind goes.