'How Heavy Should My Weights Be?'

"Choose a challenging weight" is a good starting point. It's just not a very complete one. It doesn't tell you what challenging actually feels like on a good day, let alone on the days when you barely slept and you're just trying to show up.

Here's the rest of that answer: a simple test you can run mid-set, a clear rule for when to go heavier, and what to do when you can't. (Spoiler: you don't need a full rack to keep making progress, and the research backs that up.)

How to Pick Your Starting Weight: The Reps-in-Reserve Test

The goal is to pick a weight you can lift for the target reps with about 1–3 reps left in the tank — meaning you could do a few more, but you stop while your form is still solid.

Here's how the test works:

• If you could have done 5+ more reps: Go heavier.
• If you couldn’t finish every rep with the same control as the first (swinging, arching, or cutting the range short): Go lighter.
• If you finished with form intact and 1–3 reps left: That's your weight.

This is called reps in reserve, and it's the most practical way to find your working weight — especially when you're training at home without a spotter or a coach watching.

As Moves Founder Madeline Custer puts it: "Take comfort that if you're struggling for those last few reps, your body is reaping the benefits of muscle growth." That tension isn't a sign something is wrong. It's the signal that something is working.

The reason those last few reps matter so much comes down to how adaptation actually works. According to Dr. Brandon Moss, DPT, CSCS: "Those last few reps, when a muscle is fatigued and really struggling to complete the movement, are where the body recruits its highest-threshold motor units and generates the mechanical tension that signals 'this needs to get stronger.' That's the stimulus for hypertrophy and strength gains,” he explains. “A weight is only heavy or light relative to how many hard reps it forces you to grind out, so two people using completely different dumbbells can generate the same stimulus if they're both training close to failure."

On the flip side, when you consistently stop too far short, "the body has no reason to adapt because it never got pushed past what it can already comfortably do," says Brandon. "Instead of building new muscle or strength, it just gets more efficient at performing the same reps with the same effort — you become a specialist at doing exactly what you were already doing, without ever giving your body a reason to build more capacity."

Also keep in mind that lower body and upper body typically need different weights. Most women need a heavier pair for leg work — squats, hinges, lunges — and a lighter pair for arms and shoulders. If you're working with a single set of dumbbells, you'll adjust your approach based on the movement, not one fixed number.

When to Go Heavier: The 2-for-2 Rule

Once you've found your starting weight, here's how to know when it's time to move up.

If you can complete two or more reps beyond your target on the last set, in two training sessions in a row, it's time to go heavier.

When you do go up, aim to increase by about 2–10%, per ACSM guidance. In practice, that usually means jumping to the next available dumbbell. If you're pressing 20 lbs and the next option is 25, make the jump — but expect to drop a few reps while you adjust, then build back up over the following sessions. This is called double progression: increase reps first, then load, then reps again.

Here’s how Madeline thinks about it: “I love for people to take a step back from the lbs on the dumbbell for a second and keep their eye on the prize — creating mechanical tension in the muscle by getting within 1–3 reps of failure, and that can happen multiple good ways. It could be slightly more reps than prescribed with lighter weights to get there, or it could be a few fewer reps with heavier loads to get there, and both are effective.”

Just don't let the urgency to go heavier compromise your form. "What I would want us to be sure of is that form doesn't get tossed by the wayside in an effort to bump up weights and compromise the intention or muscle we're working."

Can't Go Heavier? Here's What to Do Instead

Not having heavier weights is not a dead end. Research has consistently shown that you can keep building strength and muscle without adding load — as long as you're still making the workout harder in other ways.

One study, Plotkin et al. (2022), found that adding reps produced strength and muscle gains comparable to adding load. That's encouraging news if you're working with a fixed set of dumbbells at home. 

And the range of what counts as "enough" might surprise you. "In well-loaded movement patterns,” Madeline explains, “you could accomplish effective muscle growth with rep ranges from 4–30 reps as long as you're reaching proximity to failure. That said, most of us value our time and the 6–12 range (and variety) tends to thread the needle perfectly for most women."

Here are six ways to keep progressing without buying all new equipment:

1. Add reps. This is the most direct swap for heavier weight. If you've been doing 10 reps, work toward 12 or 15 before you reach for a heavier dumbbell. Research confirms it: adding reps can drive the same muscle and strength gains as adding load (Plotkin et al., 2022).

2. Add sets. Total weekly volume (roughly 10 or more challenging sets per muscle group per week) is one of the biggest drivers of muscle growth. Adding a set is a meaningful step up. For a deeper dive on this, read our full guide on progressive overload.

3. Slow down the movement. Spend 3–4 seconds lowering the weight, or add a pause at the bottom of the rep. Slowing down is a real form of progression, not a workaround.

4. Make sure your rest duration aligns with your goals. Newer data, including a 2024 meta-analysis by Singer et al., suggests that longer rest periods (around 90 seconds or more) can produce slightly better muscle growth than shorter ones. So keep your rest if strength and size are the goal. Shorten it only if you want a cardio challenge or need to fit a workout into a tighter window.

5. Increase your range of motion. Going deeper in a squat, lengthening an RDL, working toward your chest at the bottom of a push-up: training through a fuller range is a real form of progression. It increases the mechanical demand on the muscle and is often harder than it looks.

6. Add a band on top of the dumbbell. Loop a resistance band under your foot and around the dumbbell to add extra resistance at the top of the movement, where the dumbbell is easiest and the band is hardest. It's a simple way to increase the challenge without buying expensive new equipment.

Where Bands Fit In: Resistance Decoded and Why They Work

If you use resistance bands, keep in mind that band colors are not standardized across brands. A "medium" band from one company isn't the same as a "medium" from another. And because band resistance increases as you stretch it, you get different resistance at different points in the movement.

A few ways to get a clearer read:

• Check the brand's chart for its lb rating at a specific stretch length.
• DIY test: Hook the band to a luggage scale and pull it to your usual exercise stretch. That reading is your real tension at that point in the move.
• Or skip the numbers entirely and use the reps-in-reserve test from the first section. If you finish with 1–3 reps left in the tank, the band is doing its job.

But are they as effective as dumbbells? Brandon makes clear: "Resistance is resistance — your muscles don't know or care whether the tension resisting them is coming from a dumbbell, a machine cable, a barbell, or a band. What matters is whether that resistance can create an effortful contraction, ideally one that pushes you close to failure. If it can, it's a legitimate tool for building muscle and strength. Bands aren't a lesser or 'backup' option — they're a fully valid way to train, and in some cases they're actually the better tool for the job."

Brandon points to the lat pulldown as the clearest example. "Dumbbells simply can't replicate that line of pull or degree of lat activation — something like a dumbbell pullover gets you part way there, but nothing free-weight-based hits the lats as directly or as hard as a pulldown pattern, which is exactly what a band can reproduce."

The bottom line on progressive overload with bands: "Bands become genuinely effective the moment you can manipulate the difficulty over time — moving to a heavier band, adjusting your position to increase tension, slowing the tempo, or simply increasing reps or closeness to failure with the same band,” Brandon says. “As long as you have a way to make the exercise harder over time and you're training with real effort, bands check every box progressive overload requires."

For more on keeping your training moving forward without always going heavier, read our full guide on progressive overload.

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