How to Fix a Lagging Muscle Group
Most lagging body parts aren't genetic. They're undertrained. Here's how to find the gap, how much volume to add, and how to bring a stubborn muscle up without wrecking your recovery.
By Rayyan Siddique, founder of RepEight
Everyone has one: the calves that won't grow, the chest that lags behind the arms, the rear delts that don't exist. Before blaming genetics, check the maths. Most lagging muscles are simply getting less work than the rest.
Step 1: Find out what you're actually doing
Count your hard sets per muscle over a normal week. Do it honestly:
- Count only working sets near failure
- Count compound lifts for their main muscle, and half a set for helpers
- Notice where each muscle falls in the session. Last usually means tired.
Doing this by hand is tedious. RepEight's muscle heatmap does it automatically: log your workouts and every muscle is shaded by how much you've trained it, so the undertrained ones stand out. Tap a muscle to see exactly which sessions built its colour.
Step 2: Compare against a target
Most people grow on about 10–20 hard sets per muscle per week (the evidence is here). If your lagging muscle is on 4 and everything else is on 14, you've found the problem.
Step 3: Fix it in this order
1. Train it first
Move the lagging muscle to the start of a session, when you're fresh. The same sets done first are usually better quality.
2. Train it more often
Spread its volume over two or three sessions a week instead of one.
3. Add sets gradually
Add 2–4 sets per week to the lagging muscle, not ten. Watch recovery before adding more.
4. Pick exercises that challenge it
Choose movements where the target muscle is clearly the limit, not your grip or lower back. Browse options by muscle: chest, back, shoulders, glutes, calves.
5. Take volume from somewhere else
If your recovery is maxed out, drop a couple of sets from a muscle that's ahead so the total stays manageable.
Common lagging muscles and quick fixes
| Muscle | Usual cause | Quick fix |
|---|---|---|
| Side and rear delts | Only pressing | Add lateral raises and rear-delt flyes 2–3× a week |
| Hamstrings | Only deadlifts | Add a leg curl variation |
| Calves | Rushed reps, trained last | Pause at the bottom stretch, train them first twice a week |
| Upper chest | Only flat pressing | Add an incline press |
| Biceps/triceps | Relying on compounds | Add 6–10 direct sets a week |
Step 4: Check back in 4 weeks
Look at your heatmap and your numbers on the target exercises. If they're moving, keep going. If not, add another couple of sets or change the exercise.
FAQ
Why is one of my muscles not growing?
Usually because it's getting less direct volume than you think, it's trained with exercises that don't challenge it well, or it's always trained last when you're tired.
How long does it take to bring up a lagging muscle?
Expect visible change over 8–12 weeks of focused work, provided the rest of your training and diet support growth.
Should I train a lagging muscle more often?
Often yes. Moving it from once to twice or three times a week, while keeping total volume manageable, is one of the most reliable fixes.
Put it into practice
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