A compound exercise moves several joints at once: a squat bends the hips, the knees and the ankles, and trains the thighs and the glutes together. An isolation exercise moves one joint, such as the knee in a leg extension or the elbow in a curl, and trains mostly one muscle. Programs mix the two, and the studies explain why in that order.

The short answer

Build your training on compound lifts: a squat or a leg press, a hinge such as the Romanian Deadlift, a press and a pull cover most of the body in four exercises. Add isolation exercises for what the compound lifts reach less: the side of the shoulders, the arms, the calves, and the parts of the thighs a squat barely grows. Put the compound lifts first, while you are fresh, and the isolation work after.

What the studies found

  • For whole-body results, compound lifts carry the load. A 2017 review of 23 studies found no difference in upper-arm size or strength between single-joint and multi-joint training, and no extra effect from adding single-joint exercises to a multi-joint program. In a 10-week trial of 29 untrained men, adding curls and triceps extensions to the Lat Pulldown and the bench press added no size or strength to the elbow flexors. An 8-week trial of 20 men with two years of training found the same.
  • Even the biceps can grow from a pull. In a 2015 trial, untrained men who did only lat pulldowns grew their elbow flexors about as much as men who did only biceps curls: 6.1 against 5.8 percent.
  • At equal work, compound lifts build more strength. In a 2017 study, 36 active men trained for 8 weeks with only multi-joint or only single-joint exercises, the total work matched. Both groups lost fat and gained lean mass alike, but the multi-joint group gained more strength and more aerobic fitness.
  • Isolation still targets what compounds miss. In a 2019 study, 10 weeks of squats grew the other quadriceps muscles, the adductors and the glutes, but not the rectus femoris, the quadriceps muscle that also crosses the hip, nor the hamstrings. In a 2021 trial, the leg extension grew all three regions of the rectus femoris, while squats on a Smith machine grew only the middle of the outer thigh. And in a small 2021 trial of 10 untrained men, curls grew the elbow flexors more than one-arm dumbbell rows did: 11 against 5 percent.

The American College of Sports Medicine’s 2026 position stand could not determine from its reviews whether single- or multi-joint exercises build more muscle. It did find that strength grows more in the exercise done at the start of a session.

Both kinds, muscle by muscle

Muscle group Compound Isolation
Chest Barbell Bench Press, Chest Dip Cable Crossover, Pec Deck
Back Bent-Over Barbell Row, Pull-Up Straight-Arm Lat Pulldown
Shoulders Standing Barbell Overhead Press Dumbbell Lateral Raise, Cable Rear Delt Fly
Biceps Chin-Up EZ-Bar Biceps Curl
Triceps Diamond Push-Up Cable Triceps Pushdown
Quadriceps Barbell Back Squat, Leg Press Leg Extension
Hamstrings Romanian Deadlift Seated Leg Curl
Glutes Bulgarian Split Squat Hip Abduction
Calves None Standing Calf Raise

The compound lifts load several of these rows at once: the bench press trains the chest, the front of the shoulders and the triceps, the row the back and the biceps.

What it means for your week

Our programs follow the order the studies suggest. In Intermediate Upper/Lower, 4 days, each of the four days opens with a heavy compound lift (the Barbell Bench Press, the Barbell Back Squat, the Seated Barbell Overhead Press, the Deadlift), and every isolation exercise comes after the day’s compound work. By our count, which takes an exercise that moves one joint as isolation and the face pull, which moves the shoulder and the elbow, as compound, the week’s 26 rows are 14 compound lifts, 10 isolation exercises and 2 for the abs. Intermediate Push Pull Legs, 3 days has the same shape: 10 compound lifts, 7 isolation exercises and one for the abs over its three days.

The exception is the arm day of the Body-Part Split, 5 days, which opens with the EZ-Bar Biceps Curl: the whole day is arm work, and the presses and rows have days of their own. How many sets each muscle gets from all this is counted in How Many Sets per Muscle per Week.

How to apply it

  1. Start from four compound patterns: a squat or leg press, a hinge, a press and a pull.
  2. Put them first in the session, at the heavier end of your rep range.
  3. Add one or two isolation exercises for what you want to grow more: the side delts, the arms, the calves, the hamstrings with a leg curl.
  4. Count helping muscles as half. A set of presses is half a set for the triceps; keep the isolation work from doubling what the compounds already give.
  5. Short on time? Keep the compounds. They cover the most muscle per minute.

The exercise pages in our library list the muscles each exercise works, primary and secondary. A compound lift names muscles around several joints, the bench press the chest, the front of the shoulders and the triceps; the Leg Extension names the quadriceps alone. In Trenno the same lists drive the recovery estimate: a set counts in full for the primary muscles and half for the secondary ones.

Mistakes and myths

  • “Isolation exercises are for bodybuilders.” They are how any program trains the muscles compound lifts reach less, such as the calves or the side of the shoulders.
  • “Compound lifts are all you ever need.” For the whole body, nearly. A squat still leaves the rectus femoris and the hamstrings to other exercises.
  • Isolation first, compound after. Strength grows most on the lift done first, so give that place to the heavy compound lift.
  • Ten isolation exercises and no press or squat. Matched for work, that builds less strength than the compound lifts would.

FAQ

Is a leg press compound?

Yes. It bends the hips, the knees and the ankles, like a squat, though the machine takes the balance out of it.

Do I need curls if I do rows and pull-ups?

Not to build arms at first: in one trial pulldowns grew the biceps about as much as curls, though in another curls did more than rows. Add curls when the arms lag, or for more arm work.

Can a beginner do only compound lifts?

Yes. Our beginner programs are mostly compound lifts, with an isolation exercise or two on most days and some work for the abs.

Which isolation exercises are worth it?

For most people, the ones our programs add: the Dumbbell Lateral Raise for the side of the shoulders, a leg curl for the hamstrings, the Leg Extension for the front of the thigh and a calf raise.

Sources