The Variables that Affect Repetitions


When training in the gym, we tend to mindlessly complete repetitions of each exercise, without ever contemplating the variables that could affect its quality. One person’s 8 reps are often not equal to another’s 8 reps. One person may be able to get great results doing 4x8, but you may not. You may think to yourself, “My body just doesn’t progress like his”, or “he is more genetically gifted than me”. Maybe before we have these thoughts, we should first analyze the quality of our movement, and see if there are any more results we can squeeze out before thinking that you don’t possess the same muscle building ability.

Many things can affect the quality of your reps. When we compare the work that is done, your 8 reps may equal 5 reps to someone else. A full 8 reps require you to control 100% of the variables, 100% of the duration of the set. You must control the exercise used to target the muscle, the joint angles used during the exercise, full muscle engagement throughout the full range of motion etc.


Each time you fail to control a variable, you lose a little bit of each rep. The fewer variables you control, the less progress you will see.


Variable 1: Exercise Selection

Some exercises target muscles better than others, we all agree on this. That’s why its important that we prioritize the right exercises and keep them as a staple in our program. An example of this is squatting versus leg extensions for leg growth. I see this with beginners often, they will prioritize leg extensions and do them every time they train legs, but they won’t squat each leg day. Squatting provides a huge stimulus to grow your quads, and if you ask any monster with tree trunk legs what they do, they will tell you they squat, a lot. Leg extensions are great for finishing those quads off, but if you really want progress, prioritize the squat movement. On squats we can go much heavier, and really drain the life from the legs. If you compare the quality of progress you get from doing 100 reps of moderately heavy squats per week to the progress of 100 reps of moderately heavy leg extensions per week, squats win.


Variable 2. Tension through the full Range of Motion

Certain exercises target muscles better than others, whether its free weights or machines. Exercise selection somewhat ties into this variable, however, even doing the same exercise using a different apparatus can have huge implications on rep quality. If we compare a dumbbell lateral raise with a machine lateral raise for the shoulders, the movements are nearly identical. However, during a dumbbell lateral raise, the beginning portion of the exercise is relatively easy compared to the top. This is due to the shoulders not being that active in the bottom portion of the range of motion. The shoulders are more active at the top half of the motion because gravity is pulling down from a longer resistance arm (the resistance/weight is farther away from the body). Using a good lateral raise machine can combat this by giving you equal tension throughout the full range of motion. If the machine can create good tension on the muscle 100% of the set while free weights only create good tension 50% of the set, 8 reps on the machine would be more equal to 16 reps on the free weights.


Variable 3. Joint angles

Joint angles play a large roll in how well a muscle is targeted and how much progress you will make. Our example will be the bench press. There are many different forms of benching, and they all revolve around the joint angles used. Elbows tight to your body, you target the triceps, elbows flared, and you’ll target the chest. So, if we want a bigger stronger chest, and one person hits 5 sets of 5 bench presses on chest day with the elbows more flared out, they will have better progress than someone doing the same sets and reps with their elbows tight.


Variable 4: Dropping or Using Momentum

So, you have done everything right to this point, but you aren’t controlling your eccentric movement, or you are using momentum of the concentric. We are still losing parts of our reps. If we are deadlifting, doing 3 sets of 3, but we drop the weight at the top of each rep instead of controlling the weight back down, you are losing the entire eccentric phase. The result leaves you with only completing half the work and half the time under tension each rep. We must do 6 reps to equate work with someone else’s 3 reps. We are robbing ourselves out of potential progress.

If we are doing biceps curls, and the weight is too heavy, we will often resort to swinging the body a little to get some momentum moving the weight. If momentum is used to move the weight the first 25% of the way up, and the bicep takes over for the rest, we lose a little bit of each rep. For every 12 reps we think we complete, we lose 3 concentric reps, while the eccentric may be unchanged. Precious results can be falling away.



Sometimes its useful to change things up, use moment, or change exercises. However, if we simply mindlessly do the workouts, all these things can add up quickly leaving your body unchanged. Understand why each variable matters, and when the right time comes, you’ll know when you can break the rules without hurting your results


Chris Still

BS Exercise Science

CSCS, USAW-L1SP

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