It's a perfectly good question, and there's no simple answer. It may surprise you to learn that the answer changes depending on your goal. In fact, a number of variables are in play here, so let's go through them one at a time. Doing so will allow you to customize your training program to ensure you're using the right weight every time.
If you're looking to get as strong as possible, you'll be using a heavier weight than someone who is trying to get as big as possible. And to improve muscular endurance, you'll use an even lighter weight.
Training For Strength
What do Strongmen, Powerlifters, and Olympic Lifters have in common? They pick up A LOT of heavy shit. Their objective is to get stronger so they can lift heavier objects in competition. Therefore, they lift very, very heavy shit when training.
- Movements Suggested: Multi-joint movements like bench presses, squats, and deadlifts.
- Rep Range = 1-6 Reps
- Why? Using multi-joint exercises that incorporate the entire body recruits more total muscle mass, allowing you to lift heavier weights. Those muscle that are growing bigger and stronger as a result, those are fast-twitch. They are strong, but they burn out quick which is why we keep the rep count low but weight high.
- Rest Periods = 3-5 minutes between sets. Why? Not recovering properly between sets can inhibit your ability to lift heavy in your next set. Taking sets to failure bodes well when trying to build muscle, but not so much for strength gain. Take your rest, and lift heavy.
Training For Muscle Growth
You ever come across the term hypertrophy? This means increasing muscle size. Although those training for strength can definitely see an increase is muscle size, this way of training may not be optimal for hypertrophy. Training solely for muscle growth requires a different approach to training and selection of how much weight to use.
- Rep range of 8-12 reps
- Train very near muscle failure during those 8-12 reps. WITH GOOD FORM! No rocking, jerking, or bullshit also known as "cheating". If you can do a 13th rep, the weight was too light. If you can only do 1-6 reps, the weight is too heavy. The key is to be able to do 8-12 reps on your own with good form.
- Hypertrophy calls for higher volume of repetitions, usually 3-4 sets per body-part, with body-parts being split up across training sessions to maximize energy resources and train close to failure.
- Also training fast-twitch fibers
- 45-60 second rest periods for smaller muscle groups e.g. biceps/triceps, and 60-90 seconds for larger muscle groups e.g. glutes
Usually, people will use a percentage of their one-rep maximum (1RM) to determine a good "working weight". If you could curl 100 pounds, then 80 pounds would be 80 percent of your one-rep max.
That's one way to structure your weights. Another, more flexible approach is what's known as "rep-max (RM) loading". RM loading is predicting a load based on a specific rep range. So, for example, I might ask you how much you think you could bench press for 10 reps. If you said 225 pounds, that would be your 10RM load. Research shows that using RM loading is actually better than percentage of 1RM for making gains in hypertrophy.
The nice thing about RM loading is that you can customize it to how strong you are, and how strong you feel. For instance, if you're supposed to do 4 sets of 10 reps, start out using what you imagine to be your 10RM. If, after one set, you feel stronger than that, you can adjust upward for the next set. If you feel weaker than that, adjust downward. If you're right on, you'll stay right on that point.
This is known as autoregulatory training, and seems to be superior for skeletal muscle size and strength over strict percentage-based systems. However, it requires you to have enough experience in the weight room to gauge your abilities for a range of lifts.
If you don't have that yet, then you should consider training with me for a while so we can get you comfortable working on your own.
Training For Muscle Endurance
Having "Muscle Endurance" means the muscle can do lots of reps for long periods of time without fatiguing. Take a look at the physique of Ashton Eaton, or if you know any Navy SEALs you know what I'm talking about. This body type is muscular, but aerobically efficient. And you get there by training at a relative lower level of intensity, that is, with a lower weight than your 1RM.
- Rep Range of 15-20 reps (or more)
- Primarily working slow-twitch fibers
A strategic warm up can improve your ability to gain strength, size, and endurance. It's not a waste of time! Perform a Dynamic Warm Up before your workouts to get blood and oxygen flowing. You also mobilize joints used during mutli-joint movements, increasing muscle elasticity in the process; getting deeper in squats, and greater pectoral stretch during benching.
When my goal is hypertrophy, an example bench warm up (if my working weight is 225) would be to perform a warm up set with 135, 185, and 205 X 3 reps each before I start my working sets.
GO HEAVY EARLY
You probably know that when lifting, there is a law of diminishing returns. That is the point at which your benefits gained are less than the energy invested. So, choose the most difficult exercises early on, when you are fresh.
How do you know when to go up in weight?
Try this method: When you can do 2 more reps with a given weight than you started out with, for two consecutive workouts, increase your weight. So if you started on the bench press with 8 reps of 225 pounds, but can now do 10 reps, and you've been able to achieve 10 reps for two workouts in a row, increase the weight.
- For upper-body exercises like the bench press, increase the weight by approximately 5 percent. So instead of using 225 pounds, use 235.
- For lower-body exercises like the squat, increase the weight by approximately 10 percent. So instead of using 225 pounds, use 245.
That's it. Now get your ass out there and do the damn thing!