In this post we discuss why isolation exercises aren’t really isolated and why they’re so important in your resistance training programme.
I often come across posts by trainers who dismiss the value of so-called isolation exercises—movements designed to target a single joint.
They speculate that they don’t transfer to real-life situations (false). Or that they’re a waste of time, as you can get more value from compound lifts like the squat or deadlift.
Before we address those points, let’s take a look at what we’re isolating in something like a leg curl for example.
Below is an image of the back of the knee, dissected to show the muscles, tendons, nerves and blood vessels.
Somewhere in that mass of tissue are the following muscles, which have the primary responsibility for flexing the knee.
Primary movers of knee flexion
- Hamstrings
- Biceps femoris (long & short head)
- Semitendinosus
- Semimembranosus
- Other knee flexors
- Sartorius
- Gracilis
- Gastrocnemius
- Plantaris
- Popliteus (assists, especially in unlocking the knee)
In addition, there will be activity in the muscles that work to stabilise joints both above and below the knee during the movement.
Stabilisers during knee flexion
- Glutes and hip flexors – hold the pelvis / hips stable so the hamstrings can pull efficiently
- Core muscles – prevent unwanted movement at the trunk and pelvis
- Lower leg muscles – stabilise the ankle while gastrocnemius assists at the knee
- Quadriceps – even your anterior thigh muscles are active to balance the forces around the knee
You may also have activity in your upper body as you push yourself into the seat.
The result: even something as “simple” as bending your knee involves a team of muscles across the hip, knee, and ankle.
Isolation exercises versus multi-joint exercises
There’s a time and a place for compound exercises like squats or deadlifts, but the increased skill requirement and overall demand may increase your risk of injury.
From a coaching perspective, it’s almost impossible to decipher what’s actually going on in multi-joint lifts.
It’s difficult enough with single joint exercises as we’ve seen how complex they actually are. Now include more joints to monitor and you can appreciate how challenging this becomes.
A sensible approach is to load joints in as much isolation as possible at the beginning of a programme, then gradually add complexity. This makes it easier to identify weaknesses and target them directly.
Summary
There’s no such thing as pure isolation in resistance training. During single-joint exercises, many muscles and joints contribute — some moving, others holding still.
There is a benefit to adding multi-joint exercises when the time is right, but this must be weighed against the potential risks.
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