Weider´s training principles: The isolation principle
Several muscles can be trained as a unit or isolated and trained individually. All muscles are involved more or less in every movement – either as stabilizers, agonist, antagonists or synergistic. If a particular muscle is to be built up, it needs to be exercised as separately as possible from the other muscles.
The isolation principle
The main focus for isolation work is to concentrate fully on using the main muscle to move the weight.
Main Muscles Worked: The muscles that are used the most during the exercise.
Secondary Muscles Worked: Muscles that assist the main muscles in the exercise.
Stabilizers: Muscles that are not worked by movement, but rather assist in stabilizing the body in addition to the weight of the exercise.
Let´s analyze the Barbell Curls, for example:
Main Muscles Worked:
- Biceps Brachii
Secondary Muscles Worked:
- Brachialis
- Brachioradialis
Stabilizers:
- Deltoid, Anterior
- Trapezius, Upper
- Trapezius, Middle
- Levator Scapulae
- Wrist Flexors
Some people often make the mistake that isolation work is useless and a full compound routine is all one needs to build muscle. While compounds are the quickest way to work your body, they fail to fully exhaust the muscles. This is where isolation work is needed.
While a compound workout is faster, isolations will better target each individual muscle, resulting in a complete workout. This puts more stress on the muscles, and thus makes them grow better than a full compound workout.
What Are Some Of The Benefits Of An All Isolation Workout?
Results: Put in simpler terms, it will give you maximum muscle growth. When body parts are neglected they won’t be able to grow. Isolation movements give you the ultimate edge. You get to hit the muscle group that couldn’t be hit with compound movements, or it wasn’t hit as good and that’s why it’s lacking.
Completely exhausting a muscle. Compounds work multiple muscles at once, yet it is impossible to work each of those muscles to its max with a single compound exercise. One muscle will tire out before the other. Thus the only way to get a complete workout with compounds would be to do a compound exercise for every muscle in your body. And that is not feasible due to energy and time. This is where isolation work shines, each muscle can be worked to its maximum potential that does not take an extreme amount of time or more energy than one has.
Fewer opportunities for injuries: Injuries can arise in all types of workouts, but they are much less common in isolation exercises. This being because compounds are more intense than isolations. They use several muscles at once, which greatly opens the door for one muscle overpowering another, thus resulting in a pulled muscle. Examples are the “Big 3”: squats, deadlifts, and bench press. Squats and deadlifts put a great deal of pressure on your spinal column while bench press puts pressure on your chest and shoulders at once, often contributing to a pulled muscle if the barbell slips.
Who Would Benefit From Using An All Isolation Workout?
The people who gain the most benefit from an all isolation workout would definitely be people looking for a symmetrical body.
Others who would benefit from an all isolation workout would be older people who may not have the strength or bone support to do squats, deadlifts, bench presses or pull-ups.
Also for beginners, who may not know correct form for the big compound exercises or have enough strength to perform them, would benefit from an all isolation routine.
There are not many people that can do pull-ups on their first day in the gym or can do a set of squats in proper form. An isolation workout would give these people an introduction to weightlifting before they start doing the more advanced exercises. Whatever the reason, an all isolation routine has its place.
Results: Put in simpler terms, it will give you maximum muscle growth. When body parts are neglected they won't be able to grow. Isolation movements give you the ultimate edge. You get to hit the muscle group that couldn't be hit with compound movements, or it wasn't hit as good and that's why it's lacking.
Completely exhausting a muscle. Compounds work multiple muscles at once, yet it is impossible to work each of those muscles to its max with a single compound exercise. One muscle will tire out before the other. Thus the only way to get a complete workout with compounds would be to do a compound exercise for every muscle in your body. And that is not feasible due to energy and time. This is where isolation work shines, each muscle can be worked to its maximum potential that does not take an extreme amount of time or more energy than one has.
Fewer opportunities for injuries: Injuries can arise in all types of workouts, but they are much less common in isolation exercises. This being because compounds are more intense than isolations. They use several muscles at once, which greatly opens the door for one muscle overpowering another, thus resulting in a pulled muscle. Examples are the "Big 3": squats, deadlifts, and bench press. Squats and deadlifts put a great deal of pressure on your spinal column while bench press puts pressure on your chest and shoulders at once, often contributing to a pulled muscle if the barbell slips. 
You break it down in a way that makes sense and is easy for everyone to understand
Thank you! That was the plan but one never knows… ;)
You did well
Really great post, Chape. This is all new information for me, and quite fascinating! You’re making me want to work out 😉
Thank you so much, Josh! Are you doing your exercises for the knees?
I’ve been doing the quad wall stretch, the quad clenches, and the clam exercise daily. The quad clenches in particular seem to be helpful.
I’m very happy to hear that 😀
This is awesome advice. I do a full body workout three times a week, but unfortunately I am visibly more muscular on my dominant side. It’s a subconscious thing that I’m trying to work on, but maybe an isolation work out would solve my problem.
Thank you 😀 In this case, you should work each side of the body separately, with dumbbells. Start on the non-dominant side every set and exercise. The non-dominant side should set the pace. For example, you plan to do 12 reps of biceps curls but your non-dominant side is exhausted at 10. It’s OK. Then you should perform only 10 reps on your dominant side 😉
Hugs,
David
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