This question has been asked in different ways. Let me try another just to create a better understanding…
Over a specific period of time and with daily frequency, I do as many bench press reps as I can with just the bar (no weights). What physiological differences would there be as compared to as many reps as I can, over the same period of time, with a constant amount of weight on the bar?
In both cases, aren’t the muscles being taxed to their capacity?
Somebody else can post a more detailed explanation. The short version: Benching with just the bar will build up your muscular endurance. Benching with enough weight on the bar that you can only manage about 10 reps or less builds muscular strength.
You can work muscles in different fashion by doing either of the above mentioned regimes. Muscle endurance is different from muscle strength. If you can do the bar 45 times but you can’t lift your weight once, is that going to be good enough?
Myself, I lift primarily for strength. 6-8 reps (usually of increasing weight). Once I get my 8 reps (if I get all 8) my muscles are taxed so much so that doing a 9th isn’t possible.
I guess it all comes down to personal preference. Do you potentially want bigger muscles, prettier muscles or muscles that perform a different function all together.
This is the “toning” vs “bulking up” myth: lots of reps equals tone, few but difficult reps equals bulk. It’s commonly purported in the fitness world but it’s not how the body works.
Building muscle happens through small ‘tears’ in the muscle being created through exercise. The body then rebuilds stronger than it was. There are no “endurance” cells or “strength” cells that grow differently on the same anatomical muscle based on what you do.
I am not a medical expert but I have not seen any studies which indicate if there is an ideal number of reps to gain muscle, but you do need to be working to the point of muscular failure. If you are doing a lot of reps of a weight-training exercise that is easy for you to finish, you are basically doing a (shoddy) cardio workout.
I agree about the toning myth; muscle tone is the always-on tension in the muscle. Exercising doesn’t really affect true tone. What is happening instead in an overall fitness program that includes a sensible diet is that when you reduce fat, you see more muscle. Fat has no tone. It’s the fat that you see jiggling and wiggling around, so reducing fat gives an illusion of greater muscle tone.
However, bodybuilders know how to increase muscle size, and they don’t do it by lifting an empty bar 1,000 times.
There are two types of muscle fibers. I’m not sure that completely contradicts your point but it should be considered.
In general, you get better at what you train to do. If you lift a lighter weight a lot of times, you will be able to lift it even more times. If you keep adding more weight then you will be able to lift heavier weights. Bodybuilders aren’t looking for the ability to lift heavy weights per se, they are looking for whatever will increase size for specifically targeted muscles, and this is typically done by repeated sets (anywhere from 6-12 reps per set, depending on who you talk to) of heavy weights.
However, a bodybuilding approach isn’t necessarily the best road to overall fitness.
Well I agree with what fluiddruid said but the OP’s specific question hasn’t really been addressed. There is really no difference between the two options he presents.
The bar is normally 20kg’s so you’ll just get really good at lifting 20kg and depending on starting strength this will either reduce or grow your muscle (also depending on diet and length of time you’re on the routine.
Is exactly the same + arbitrary weight. You’ll simply reach a plateau and get good at lifting that amount of weight. It’ll just be a higher plateau than the bar alone.
To really force physiological change you have to keep increasing the amount of weight you bench, its the change that’s important as that’s what’s breaking down muscle fibres and forcing your body to react.
The OP doesn’t state a goal but if you want to get stronger you have to lift bigger weights and if you want to get bigger muscles you have to lift bigger weights. That’s why lifting is called progressive resistance.