The VMO (vastus medialis oblique) is the teardrop-shaped muscle visible on the inner side of the knee, just above and to the inside of the kneecap. In athletic and rehabilitation settings, it is one of the most frequently discussed muscles in the lower extremity: weak VMO is cited as a contributor to patellofemoral pain, knee valgus, patellar maltracking, and general knee instability.
But VMO strengthening is also one of the more nuanced topics in exercise science, because the question of whether the VMO can be specifically isolated from the rest of the quadriceps is genuinely debated in the research literature. Understanding this debate does not make VMO training less useful: it makes the exercise selection more targeted and the expectations more realistic.
What the VMO Is
The VMO is not a separate muscle from the quadriceps: it is the most distal (lowest) portion of the vastus medialis, one of the four quadriceps muscles. The vastus medialis runs along the inner side of the femur and inserts via the quadriceps tendon into the patella. Its most distal fibres, the VMO, insert at a notably oblique angle (at approximately 50 to 55 degrees from the long axis of the femur, compared to the more vertical fibres of the proximal vastus medialis).
This oblique angle of insertion is what makes the VMO anatomically distinct: while the rest of the vastus medialis primarily contributes to knee extension, the VMO’s oblique fibre angle gives it a specific medial pull on the patella.
Where to find the VMO:
Place the hand on the inner side of the knee, just above the inner edge of the kneecap. The VMO is the muscle belly that becomes visible as a teardrop shape during quad contractions, particularly in the last 20 to 30 degrees of knee extension. It is absent or very small in people with significant VMO weakness, and prominent in people with well-developed VMO strength.
The VMO’s Specific Function
Knee extension: The VMO contributes to knee extension alongside the other quadriceps muscles. Its contribution is greatest in the final 20 to 30 degrees of knee extension (terminal extension), which is why exercises that develop this specific range are particularly effective for VMO training.
Medial patellar stabilisation: The VMO’s oblique pull on the medial aspect of the patella is the primary active counterbalance to the lateral pull of the vastus lateralis and the lateral retinaculum. When the VMO is strong and activates early, it maintains the patella in the correct position within the trochlear groove throughout knee flexion and extension.
Patellofemoral joint protection: By pulling the patella medially, the VMO reduces the lateral contact area between the patella and the femur. When the VMO is weak, the patella tracks laterally, increasing the compressive forces on the lateral facet of the patella and contributing to patellofemoral pain as covered in the patellofemoral pain syndrome physical exercise article on this site.
The VMO Isolation Controversy
Research on VMO isolation has produced genuinely mixed results, and understanding this is important for setting realistic expectations.
The case that VMO can be somewhat preferentially activated:
Several studies have found that specific positions and movements produce relatively greater VMO activation compared to vastus lateralis activation. These include:
- Terminal knee extension (the last 30 degrees of straightening the knee)
- Knee extension with the hip in external rotation
- Closed chain exercises with the foot pointing slightly inward or with hip adduction added
- Squats with the feet turned outward
The case against true VMO isolation:
Other research has found that the VMO and vastus lateralis are so closely coupled neurologically that they cannot be truly isolated from each other through exercise. The motor neurons supplying the VMO and the rest of the vastus medialis largely fire together rather than independently.
The practical conclusion:
True complete VMO isolation from the other quadriceps is probably not possible through exercise alone. However, several exercises do produce relatively greater medial quad activation compared to lateral, and the terminal extension range specifically challenges the VMO’s functional role as a patellar stabiliser. This means VMO-focused training has genuine clinical value even if perfect isolation is not achieved.
The goal of VMO training in practice is not perfect VMO isolation but rather developing adequate medial quadriceps strength and activation in the positions and ranges most relevant to patellar tracking and knee stability.
How to Know if Your VMO Is Weak
Visual assessment:
Compare the VMO muscle bulk between sides. Significant asymmetry (one side visibly smaller than the other) indicates relative VMO weakness on the smaller side. This is commonly seen following knee surgery, immobilisation, or prolonged knee pain.
Functional assessment:
During a wall sit or a slow single-leg squat, observe or palpate (feel with the fingers) the VMO. In the last 20 to 30 degrees of knee extension (returning to standing), the VMO should visibly bulge and feel firm under the fingers. If it remains flat or activates noticeably later than the vastus lateralis, VMO activation is insufficient.
Patellar tracking observation:
During a slow single-leg squat, observe the patella. A patella that visibly moves outward during the descent suggests insufficient VMO pull relative to the lateral structures. This observation requires some experience but becomes reliable with practice.
Clinical indicators:
- Inner knee discomfort during or after activities involving repeated knee flexion
- Patellofemoral pain that is concentrated on the outer patellar region
- Knee that feels unstable during single-leg activities
- Visible difference in quad muscle development between sides following injury or surgery
The Best VMO Strengthening Exercises
Category 1: Terminal Knee Extension (VMO-Specific)
Terminal knee extension (TKE) is the most specifically VMO-targeted exercise because it loads the terminal extension range where VMO activation is greatest and the medial patellar pull is most functionally relevant.
Terminal Knee Extension With Band:
As covered in the terminal knee extensions article on this site, the TKE uses a resistance band to provide resistance against knee extension in the last 20 to 30 degrees.
VMO-specific technique:
- Loop a resistance band around a fixed anchor at knee height behind you
- Face away from the anchor with the band behind the knee
- Stand with a slight knee bend (approximately 30 degrees)
- Straighten the knee fully against the band resistance
- At full extension, actively tighten the VMO: focus the contraction on the inner quad rather than the general thigh
- Hold for 2 to 3 seconds at full extension, palpating the VMO to confirm activation
- Return to the slight knee bend and repeat
- Complete 3 sets of 15 per side
The palpation technique: Place the fingers of one hand on the VMO (inner side of the knee, above the inner edge of the kneecap) during the TKE. The VMO should be distinctly firm and prominent at full extension. If it feels soft while the outer quad (vastus lateralis) feels firm, VMO activation is insufficient and the exercise emphasis should be further inward.
Quad Set (Isometric VMO Activation):
As covered in the what are quad sets article on this site, the quad set is the most basic VMO activation exercise, appropriate for the earliest stages of rehabilitation or for establishing the VMO activation pattern before progressing to more demanding exercises.
VMO-specific technique:
- Sit or lie with the leg extended on a flat surface
- Press the back of the knee downward by tightening the quadriceps
- Focus the contraction specifically on the inner quad: think of tightening the muscle on the inner knee rather than the top of the thigh
- Hold for 5 to 10 seconds
- Palpate the VMO during the hold to confirm activation
- Complete 3 sets of 10 per side
Category 2: Closed Chain Exercises With VMO Emphasis
Closed chain exercises (where the foot is in contact with a surface) produce high VMO activation through the combined demands of knee extension and pelvic stability.
Short-Arc Squat (0 to 30 Degrees):
The most VMO-specific squat range, loading the terminal extension phase where VMO activation is greatest.
How to do it:
- Stand with feet shoulder-width apart, toes pointing forward or slightly outward
- Lower to approximately 30 degrees of knee flexion only
- Return to full extension
- Focus the contraction specifically on the inner quad during the return
- Complete 3 sets of 15
Why limited to 30 degrees: Below 30 degrees of knee flexion, the VMO’s moment arm for knee extension reduces and the patellar stabilisation demand becomes less specific. The short arc from 0 to 30 degrees is the range most relevant to VMO function as a patellar stabiliser.
Wall Slide (Mini Squat):
A controlled partial squat performed against a wall, providing feedback about trunk position and limiting the range to the VMO-relevant zone.
How to do it:
- Stand with the back against a wall, feet 30 centimetres from the wall
- Slide down to approximately 30 to 45 degrees of knee flexion
- Hold for 5 to 10 seconds at the lowest position
- Slide back up, focusing the return contraction on the inner quad
- Complete 3 sets of 10
VMO-specific modification: Placing a ball or rolled towel between the knees during the wall slide and gently squeezing it adds a hip adduction component that some research suggests preferentially increases VMO activation relative to vastus lateralis.
Step-Up With VMO Focus:
As covered in the lateral step down exercise article on this site, step exercises develop the VMO through the terminal extension of each step-up.
VMO-specific technique for the step-up:
- Focus specifically on the final straightening of the knee at the top of each step-up
- At the top, actively tighten the inner quad and hold for 1 second before stepping down
- This deliberate terminal extension and hold develops the VMO contraction most specific to patellar stabilisation
- Complete 3 sets of 10 per side
Lateral Step Down:
As covered in the lateral step down exercise article on this site, the step down develops the VMO eccentrically in the same terminal extension range.
VMO-specific technique for the step down:
- During the lowering phase, focus on the feeling of the inner quad maintaining control rather than simply letting the knee bend
- At the lowest point, begin the return with a deliberate inner quad contraction before the rest of the quad is recruited
- Complete 3 sets of 10 per side
Category 3: Open Chain Exercises
Open chain exercises (where the foot is free, not in contact with a surface) allow specific loading of the knee extension movement without the balance and hip demands of closed chain work.
Straight Leg Raise:
As covered in the seated straight leg raise article on this site, the SLR develops the VMO in the locked-out position where it holds the patella in the correct position throughout the raised leg position.
VMO-specific technique:
- Before lifting the leg, deliberately tighten the VMO: tense the inner quad above the inner kneecap
- Lift the leg with the VMO actively holding the knee in extension throughout
- The VMO should remain visibly prominent throughout the held position
- Complete 3 sets of 12 per side
Short Arc Quad (SAQ):
One of the most specific VMO exercises because it loads the terminal extension range in an isolated, open chain manner.
How to do it:
- Lie on the back with a rolled towel or foam roller under the knee, creating approximately 30 degrees of knee flexion
- Extend the knee from this position to full extension
- At full extension, hold for 2 seconds and actively tighten the VMO
- Lower slowly back to the 30-degree starting position
- Complete 3 sets of 15 per side
Why the short arc quad is particularly effective for VMO: The starting position at 30 degrees means the entire movement is in the terminal extension range where VMO activation is greatest. The isolation from hip movement allows the focus to be entirely on the knee extension and the medial quad contraction.
Seated Knee Extension (Limited Range):
On a seated knee extension machine, performing extension only through the last 30 degrees (not full range) specifically loads the VMO-relevant terminal extension range.
How to do it:
- Set the machine to start at approximately 30 degrees of knee flexion
- Extend to full extension
- Hold for 2 seconds with VMO contraction
- Return slowly
- Complete 3 sets of 12
Note on the full-range knee extension machine: Full-range knee extension machines (0 to 90 degrees) have been associated with increased patellofemoral stress in the deeper flexion ranges in some people with patellofemoral pain. Limited range (30 to 0 degrees) is more appropriate for people with PFPS until sufficient strength is developed.
Category 4: Functional Integration
Once the basic VMO activation is established through the exercises above, functional integration develops the automatic VMO recruitment during dynamic athletic movements.
Single-Leg Squat With VMO Emphasis:
- Stand on one leg
- Lower to 30 to 45 degrees of knee flexion (the VMO-relevant range)
- Focus on the inner quad throughout the descent and return
- Maintain the knee over the second and third toe throughout
- Complete 3 sets of 10 per side
Terminal Knee Extension Sprint Drill:
For athletes returning to sport, performing high-knee marching or bounding with a deliberate knee lock-out at the top of each stride develops the VMO in the dynamic terminal extension pattern most relevant to running mechanics.
Position Modifications That Increase VMO Activation
Based on the available research, the following modifications may increase relative VMO activation compared to standard exercise positions:
Hip external rotation: Performing squats, step exercises, and quad sets with the foot slightly externally rotated (toes out approximately 10 to 15 degrees more than normal) has been associated with increased VMO activation in some studies.
Hip adduction (squeeze): Squeezing a ball or block between the knees during wall slides and squats adds a hip adduction force that appears to increase VMO relative to vastus lateralis activation.
Functional electrical stimulation (FES): In clinical rehabilitation settings, FES applied to the VMO can accelerate its reactivation following surgery or injury, particularly in early-stage rehabilitation where voluntary activation is insufficient.
Programming VMO Strengthening
For rehabilitation (post-surgery, PFPS, patella instability):
Phase 1 (Weeks 1 to 3, daily):
- Quad set: 3 x 10 per side, 10-second hold
- Short arc quad: 3 x 15 per side
- Terminal knee extension: 3 x 15 per side
Phase 2 (Weeks 4 to 6, 3 to 4 times per week):
- Short-arc squat: 3 x 15
- Wall slide: 3 x 10
- Step-up with VMO hold: 3 x 10 per side
- Straight leg raise: 3 x 12 per side
Phase 3 (Weeks 7 to 10, 3 times per week):
- Lateral step down: 3 x 10 per side
- Single-leg squat (VMO focus): 3 x 10 per side
- Terminal knee extension (heavier band): 3 x 15 per side
- Step-up with VMO hold: 3 x 12 per side
For athletes (performance and prevention):
Include VMO-specific work as accessory training alongside the primary lower body programme:
- Terminal knee extension: 3 x 15 per side before or after lower body sessions
- Lateral step down: 3 x 10 per side (primary functional VMO exercise)
- Short arc quad: 2 x 15 per side (if additional VMO volume is needed)
Frequency: VMO exercises at low to moderate intensity (quad sets, short arc quads, TKE) can be performed daily. More demanding exercises (lateral step down, single-leg squat, step-up) benefit from 48 hours of recovery between sessions.
Frequently Asked Questions
Can the VMO truly be isolated from the other quadriceps?
Not completely, based on current research. The VMO and the rest of the vastus medialis share neurological connections that make complete isolation very difficult through exercise alone. However, the terminal extension range, hip external rotation positions, and hip adduction additions do appear to preferentially increase VMO activation relative to the vastus lateralis in several studies. The practical approach is to use these modifications to create the best available VMO stimulus rather than expecting true isolation.
How long does it take to strengthen the VMO?
Early neuromuscular improvements (improved VMO activation and visible muscle response during quad sets and TKE) typically occur within 2 to 4 weeks of consistent daily training. Meaningful strength increases are typically measurable within 6 to 8 weeks. Visible muscle development (the teardrop shape becoming more prominent) typically takes 8 to 16 weeks of consistent progressive training.
Can VMO strengthening cure patellofemoral pain?
VMO strengthening is an important component of PFPS rehabilitation but is not sufficient alone. As covered in the patellofemoral pain syndrome physical exercise article on this site, the most effective PFPS rehabilitation combines VMO strengthening with hip abductor and external rotator strengthening (addressing the femoral internal rotation that increases lateral patellar contact forces) and IT band and TFL flexibility work. VMO strengthening alone addresses only the medial patellar stability component.
Why is my VMO much smaller on one side than the other?
Unilateral VMO atrophy is very common following knee injury, knee surgery, or periods of significant knee pain. Pain inhibition significantly reduces VMO activation, and the muscle atrophies relatively rapidly during periods of reduced use. The daily quad set and short arc quad exercises are specifically designed to reactivate the VMO in the early stages of rehabilitation. Persistent significant asymmetry beyond 12 weeks of rehabilitation warrants assessment by a physiotherapist.
Is the VMO the same as the teardrop muscle?
Yes. The VMO is colloquially called the teardrop muscle because of its characteristic teardrop shape when well-developed, visible on the inner side of the knee just above the inner edge of the kneecap. Both terms refer to the same structure: the oblique fibres of the distal vastus medialis.