How to Pick the Right Weight for Your Workout

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If you're new to the gym and you have no idea how much weight you should be lifting, in this video I'm going to teach you two ways you can measure intensity so that you're training hard enough to see results without getting hurt.

Before any of that works, you need one distinction, and everything else in this article sits on top of it.

There are two different ways a set ends.

The first is when your form breaks down. Your bar path shifts, your spine changes position, a joint starts moving in a direction it wasn't supposed to move, and all of that together is what we call mechanical failure.

The second is when the muscle itself stops producing enough force to move the weight at all, which is muscle failure, and the muscle is done at that point regardless of what your form looks like.

Most people treat these as the same event. They aren't, and on most exercises they happen minutes of effort apart.

On compound lifts, you're going to hit mechanical failure long before you ever reach muscle failure. This is because on compound lifts, there's more than one joint involved in the exercise, which means that there are more points where that form can fall apart.

You pick a weight for a bench press that feels genuinely hard, and the first few reps are controlled and clean. Around rep seven or eight it starts to get difficult. By rep nine your elbows are flaring, your hips are lifting off the bench, and the bar is wandering on the way up, which means your movement pattern has already collapsed under you.

If you kept grinding, your chest would eventually give out completely and the bar would stop moving, and that total shutdown is what muscle failure actually looks like. But you're never going to safely get there on bench press because your form is always going to break down first.

And the reason this distinction matters more than anything else in this article is because of where injuries happen. When your form collapses, that's when joints take stress they weren't designed for.

That's when connective tissue gets loaded in compromised positions.

Think of it like a suspension bridge with multiple cables carrying load. As long as every cable holds its share, the bridge is fine at its rated weight. The moment one cable slackens, the others take a load they weren't sized for, and the failure happens at the weakest remaining point rather than the one you were watching.

Your body works the same way under fatigue. As your glutes tire on a squat, your lower back starts taking a larger share of the job. As your chest tires on a bench press, your shoulders roll forward into a position where the front of the joint carries what the muscle used to.

The muscle you were trying to train hasn't failed. The chain around it has reorganized itself into a worse configuration, and now you're loading tissue that was never assigned that role.

Mechanical failure, in other words, works as your stop sign, the point where you back off no matter how much gas feels left in the muscle itself.

On a leg extension, a cable curl, or a machine chest press, the math shifts completely because the machine is holding the movement pattern for you. You're locked into a fixed path, so as you fatigue, the muscle can actually give out before your form has anywhere to go.

That's where true muscle failure becomes available to you safely.

Which gives you the order of operations for a training session. You start with compounds where you stop at mechanical failure, and then you end with machines where you can push to muscle failure safely.

There are two ways to measure this, and both come down to how many reps you'd guess you had left when you stopped. RIR, which stands for reps in reserve, means how many more reps you could have done at the end of a set. RPE, which stands for rate of perceived exertion, works a bit differently.

And this means on a scale of one to 10, how difficult did that set feel? I personally prefer RIR because it's based on my training history, my knowledge of how strong I am.

Bad sleep, a stressful week, being under-fed, and suddenly the same weight for the same reps feels like a 9 instead of a 7, which is exactly the kind of drift that makes RPE slippery to rely on day to day. RIR asks a different question, which is what your body is capable of, not how the effort registered emotionally on that particular day.

But RIR has a problem nobody warns beginners about. It's a ruler with no markings on it.

To say you left two reps in the tank, you have to know what zero reps in the tank feels like, and the truth is that most people have never actually been there. They've only ever hit mechanical failure on a compound lift, called that "failure," and built their entire sense of intensity around a stopping point that had nothing to do with the muscle.

So they think they're at zero when they've got three or four left. Or they think they've got three left when the real answer is that their form quit and the muscle never got involved.

Without ever experiencing true muscle failure, you cannot calibrate. You're guessing, and the guess is almost always low.

The fix starts with going and finding out what muscle failure actually feels like firsthand. And here's your hint: most of the time, your mind thinks you're done about two or three reps before you actually are.

So for squats, as an example, pick a machine that you're comfortable with, like a hack squat, or you could use something like a chest press where the machine stabilizes you.

Load up a weight that feels moderate rather than maximal. Do reps until you physically cannot complete another one. The muscle burns, you're shaking, your breathing is wrecked, but your form stayed intact the whole time because the machine held the path for you.

And that, my friend, is zero RIR, the exact ceiling RPE 10 is trying to describe.

You don't need to camp out at that ceiling every session. You need to visit it often enough that the top of your scale has a real number attached to it, which usually means the last set of one accessory movement, not every set of every workout.

Now that you have an understanding of this, it gives you a better ability to measure your progress and measure intensity with your training. And if you're working with a good coach, he should be giving you RIR or RPE targets to follow in the program that you're using.

Second, on compounds, mechanical failure is the target rather than the muscle.

Now realize that this is something that's going to improve over time. As you get better, more experienced with lifting, and you've got the muscle memory of what that movement feels like, and more discipline with your form, the gap between mechanical failure and muscle failure is going to get closer and closer together.

A beginner might stop five or six reps short of the muscle's real limit because their pattern falls apart early. Someone with years of practice might stop one rep short. Same rule, narrower gap, more of the muscle's actual capacity available to them.

So for squats, bench, deadlifts, you're going to stop when your form starts to break, and that's your safety limit.

So on squats, if your chest drops forward, your heels start to come off the ground, your knees start to cave in, that's when you stop.

On bench, if your elbows start to flare out and your butt starts to come off the bench, or you start to shake with the bar, that's how you know when you need to stop.

Or with deadlifts, if your back starts to round, your hips start to shoot up first, or the bar drifts away from your body, that's how you know you've reached mechanical failure.

You stop here even though your muscle could technically do more, because if you kept going, that's how you get hurt.

Third, use the number to pick the weight.

On compounds you're aiming for one to two RIR at mechanical failure, meaning when your form starts to slip, it should feel like you could have gotten one or two more clean reps out of it, and they would have been ugly-hard.

If your program says three sets of 10 reps on bench, pick a weight where rep eight or nine feels challenging, but your form is still solid.

If your form breaks at rep six, the weight is too heavy and you go down. If you get to rep 10 and it still feels easy, the weight's too light.