A study on muscle activity and ratio of the knee extensor depending on the types of squat exercise.
Jeong-Il Kang, Joon-Su Park, Hyun Choi and 3 others
PMID 28210036WHAT IT FOUND
Unstable-surface squats at 15° gave a higher VMO/VL ratio than stable ones in healthy men, while stable-surface squats at 60° gave a higher ratio than unstable ones.
At 45°, no clear advantage. This is a muscle activity result, not pain or function.
Key findings
01At 15° knee flexion, VMO activation averaged 59.66% of maximal voluntary isometric contraction on the unstable surface and 51.03% on the stable surface, and the VMO/VL ratio averaged 0.91 on the unstable surface and 0.81 on the stable surface, with significant differences.
02At 60° knee flexion, VMO activation averaged 176.63% of maximal voluntary isometric contraction on the stable surface and 150.01% on the unstable surface, and the VMO/VL ratio averaged 1.06 on the stable surface and 0.93 on the unstable surface, with significant differences.
03At 45° knee flexion, neither VMO activation nor the VMO/VL ratio differed significantly between surfaces, and VL activation showed no significant difference at any angle.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 24 healthy men, so it does not show what happens in patients with patellofemoral pain, women, older adults, or people with knee surgery. The outcomes were immediate muscle electrical activity during single squat holds, not pain, function, strength gains, or injury risk. Only measurement order was randomised, not participant allocation, and the paper does not report blinding. The study measured the dominant leg only. The paper states it did not target a large population and used healthy persons.
The easy way to misread this
Do not use these muscle activity results to prescribe squats for patients with patellofemoral pain. The study tested healthy men during single holds, and higher muscle activity is not evidence of pain relief or function. The better surface depended on knee angle.