A rep (repetition) in weightlifting is one complete cycle of an exercise, from the starting position through the full range of motion and back again. Most reps can be broken into three phases:

  • Eccentric: the muscle lengthens under load, usually during the lowering.
  • Isometric: the brief turnaround, which may last only a fraction of a second.
  • Concentric: the muscle shortens to move the weight, usually during the lifting.

To do a rep correctly, lower under control, transition without bouncing, and lift with intent. Use the same range of motion every time.

Why a Rep Is a Unit of Measurement

Most beginner guides treat a rep as something you count to reach a number. A more useful view is that a rep is a measurement. Like any measurement, it is only useful if the unit stays the same.

Here is a concrete example:

  • Week 1: You squat 5 reps at 60 kg, reaching parallel on every rep.
  • Week 2: You squat 5 reps at 60 kg, stopping a few centimetres above parallel.

In your log, both sessions read "60 kg × 5." They are not the same stimulus. The shallower reps cover less range of motion and are easier, so the second session looks equal to the first when it was actually less demanding.

Now picture this drift continuing over time. You add 2.5 kg, and your depth creeps up a little. You add another 2.5 kg, and it creeps up again. On paper, your squat climbs steadily. In reality, part of that "progress" is a shrinking range of motion. Nothing in the log flags it, because the log only records weight and reps, not how deep each rep went.

That is how inconsistent reps silently inflate apparent progression. Your progression is only as reliable as your definition of a rep. A rep is comparable across sessions when three things stay consistent:

  1. Range of motion: the same depth or lockout every time.
  2. Tempo: a similar speed for each phase.
  3. Proximity to failure: how many reps you had left in the tank.

The Three Phases of a Rep: Concentric, Eccentric, Isometric

Eccentric (Lowering)

The muscle lengthens while resisting the load, as when you descend into a squat or lower the bar to your chest on a bench press. This is where beginners most often lose control and let gravity do the work.

Muscles can produce more force eccentrically than concentrically. A controlled lowering therefore keeps tension on the muscle instead of letting the weight drop. A systematic review of eccentric training describes its chronic adaptations in detail (Douglas J, Pearson S, Ross A, McGuigan M. "Chronic Adaptations to Eccentric Training: A Systematic Review." Sports Medicine. 2017;47(5):917-941). The practical takeaway for beginners is simple: control the descent rather than letting it happen to you.

Isometric (Transition)

The isometric phase is the brief turnaround at the bottom or top of the movement, where the weight changes direction. In a squat, this is the moment at depth before you drive back up.

How long it lasts depends on the lift and the style:

  • In a paused squat, it might last a full second or more.
  • In touch-and-go or stretch-shortening movements, such as a touch-and-go bench press or a rebounding jump, it is close to zero.

For most beginner strength work, a controlled transition is the better default. It keeps the load on the muscle instead of on stored elastic energy and momentum.

Concentric (Lifting)

The muscle shortens to move the weight, as when you stand up from a squat or press the bar off your chest. Aim to move the weight with intent, even if the bar moves slowly under heavy loads.

Which Phase Comes First

Not every lift starts with the eccentric:

  • A deadlift begins from the floor with the concentric.
  • A squat and a bench press begin with the eccentric.

Knowing which phase comes first helps you set up correctly.

Tempo Notation: Writing Down How a Rep Is Performed

Tempo notation describes the speed of each phase in seconds. It turns "lift slowly" into something you can repeat and record.

The 3-digit format (eccentric-pause-concentric). A tempo of 3-1-1 means:

  • 3 seconds lowering
  • 1 second pause at the turnaround
  • 1 second lifting

The 4-digit format. A tempo of 3-1-1-0 adds a fourth number for the pause at the top, before the next rep begins:

  • 3 seconds lowering
  • 1 second pause at the bottom
  • 1 second lifting
  • 0 seconds at the top

By convention, the first number is the eccentric, even for lifts like the deadlift that start with the concentric. An "X" in place of a number usually means "as fast as possible," which is common for the concentric under heavy loads.

The checklist below translates to a beginner tempo of roughly 2-1-1 to 3-1-2. Written in 4-digit form, that is about 2-1-1-0 to 3-1-2-0.

How to Do a Rep Correctly: A Beginner Checklist

  1. Define your range of motion before the set. For example, squat until the hip crease is below the top of the knee, or touch the bar to your chest on the bench press.
  2. Lower for about 2-3 seconds. This is the first number in your tempo. Count it at first; it will become automatic.
  3. Pause briefly at the transition. This is the second number. Under a second is fine, as long as there is no bounce.
  4. Lift in about 1-2 seconds with intent. This is the third number. Drive through the same path you lowered on.
  5. Count only reps that meet your standard. A half-depth squat is not a rep, even if the set felt hard.
  6. Note how close to failure you finished, using reps in reserve or RPE (see below).
  7. Keep the standard identical across sessions so your numbers stay comparable.

Proximity to Failure: Making Effort Comparable

Two sets of 8 at the same weight can be very different efforts. One set might leave 4 reps in the tank. The other might be a grind to the last rep. You can track this difference in two common ways:

  • Reps in reserve (RIR): how many more reps you could have done with good form. "2 RIR" means you stopped with about two reps left.
  • Rate of perceived exertion (RPE): a 1-10 effort scale. On this scale, an RPE of 8 roughly corresponds to 2 reps in reserve, and an RPE of 10 means you could not have done another rep.

Recording effort alongside reps and weight gives you more context when you compare sessions. For example, a rep count that holds steady while your RPE drops is a sign of progress that the numbers alone would not show.

How This Fits Into Your Training Log

In Kenso, you can log RPE on each set alongside reps and weight, so effort sits right next to the numbers. Kenso's rule-based double-progression engine then uses the reps you log to recommend your next weight or rep target. It follows fixed rules, not AI or machine learning.

Kenso can't see your reps. It trusts the numbers you enter, so log only reps that meet your standard. If your depth or range of motion drifts, the recommendations will drift with it.

If you have an Apple Watch, the Kenso 3.0 Watch app's crown-stepped logger lets you enter reps and weight between sets without picking up your phone. Logging is still manual: you count the reps, and the Watch records what you enter.

The Takeaway

A rep is the smallest unit of training, and it shapes everything above it: sets, sessions, and programs. To keep each rep consistent:

  • Control the lowering.
  • Respect the transition.
  • Lift with intent through a range of motion you define in advance.
  • Keep your tempo and proximity to failure consistent.

Do that, and "60 kg × 5" means the same thing in week 10 as it did in week 1. That makes your logged numbers a trustworthy record of real progression.

Frequently Asked Questions

What is the difference between a rep and a set?

A rep is one complete cycle of an exercise. A set is a group of consecutive reps performed without rest. Three sets of 8 means 8 reps, a rest, and then two more rounds of 8.

Should I lift fast or slow?

Lower under control, roughly 2-3 seconds for most beginners, and lift with intent. A tempo around 3-1-1 is a sensible starting point. Heavy loads will move slowly even when you try to move them quickly, and that is normal.

Does a partial rep count?

For your main working sets, count only reps that meet your predefined range of motion. Partial reps can be used deliberately in some programs. If you do them, keep them out of your full-range numbers so they don't distort your progression data. You can do this in two ways:

  • Log the partials as a separate set and label them clearly.
  • Write them in a note on the set.

How many reps should a beginner do per set?

Many beginner programs use 5-12 reps per set for compound lifts. This is a practical range that builds both strength and size for beginners.

Heavier loads at lower reps (roughly 1-6) best develop maximal strength. For muscle growth, the load matters less than effort. Hypertrophy is similar across a wide range of loads when sets are taken close to failure (Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW. "Strength and Hypertrophy Adaptations Between Low- vs. High-Load Resistance Training: A Systematic Review and Meta-analysis." Journal of Strength and Conditioning Research. 2017;31(12):3508-3523).

You can ask the Kenso AI Coach how a rep range applies to your current program and training history.

Consistent reps make your progression data accurate. Download Kenso on iOS to log reps, weight and RPE on every set.