Leg Extensions vs Leg Presses for Building Bigger Quads
A 12-week MRI study pitting the two exercises head-to-head and it's much closer than you think.
The leg press builds a lot more muscle than most lifters realise, but it has one notable issue. A study published in Medicine & Science in Sports & Exercise by Maeo and colleagues put the knee extension machine against the leg press in the most rigorous comparison so far. Let’s dive in.
Aim
The aim was to figure out if single-joint and multi-joint exercises are equally effective for building the quadriceps, and whether it matters which one you choose. Specifically, the researchers wanted to compare knee extension (KE) and leg press (LP) for their ability to grow not just the quads overall, but each muscle within the quadriceps femoris (QF), along with the glutes, hamstrings, and adductors.
Methods
Seventeen untrained adults participated in a within-subject, contralateral design, meaning each person trained one leg with knee extensions and the other leg with leg press simultaneously, eliminating the usual confounds of between-group studies. Both legs were trained at 70% of one-repetition maximum (1RM), 10 reps per set, 5 sets per session, twice per week for 12 weeks. MRI was used before and after the intervention to measure the volumes of 17 individual muscles, including all four quadriceps heads (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius), the gluteus muscles, hamstrings, and adductors. A follow-up experiment using surface electromyography (EMG) was conducted to examine whether muscle activation during each exercise mirrored the hypertrophic outcomes.
Results
The headline finding is this: both exercises grew the quadriceps overall, but they did so differently depending on which muscle you look at.
Rectus Femoris
Knee extension: +13.2% volume increase
Leg press: +1.1% volume increase (non-significant, p = 0.379)
The difference between conditions was statistically significant (p ≤ 0.001)
Vasti Muscles (vastus lateralis, medialis, intermedius)
Knee extension: +5.0–7.2%
Leg press: +4.4–6.2%
No significant difference between conditions (p ≥ 0.319)
Whole Quadriceps Femoris
Knee extension: +7.1%
Leg press: +4.9%
No significant difference between conditions
Glutes and Adductors (leg press only)
Gluteus maximus: +15.4% (leg press only, p ≤ 0.001)
Adductor magnus: +6.2% (leg press only, p ≤ 0.001)
Neither muscle changed significantly with knee extension
The EMG follow-up confirmed that muscle activation patterns closely matched these hypertrophy outcomes — muscles that grew more also showed greater electrical activity during the exercise that produced the growth.
Takeaways
The leg press is highly time-efficient. In a single exercise, it builds comparable vasti and overall quad size to the knee extension, while also substantially growing the glutes (+15.4%) and adductor magnus (+6.2%). For anyone short on time, the leg press delivers more muscle development per session than many lifters give it credit for.
The knee extension is non-negotiable for the rectus femoris. The leg press essentially failed to grow the rectus femoris (+1.1%, non-significant), while the knee extension grew it by 13.2%. This is not a small margin — it is a functionally different outcome.
Clinical relevance is significant. The rectus femoris is the quadriceps head most susceptible to strain injuries in sport, meaning targeted knee extension work may matter for injury prevention and rehabilitation, not just aesthetics.
Neither exercise is superior overall — they are complementary. The leg press covers the hip-dominant lower body; the knee extension fills the gap the leg press leaves at the rectus femoris.
This was conducted in untrained adults, so results may differ in trained lifters who may already have adapted neural patterns and muscle activation strategies.
The practical recommendation: if you are only doing leg press and skipping the knee extension machine, you are likely leaving meaningful rectus femoris development on the table. For a complete quad training program, both belong in the program.
Nothing new to see here.
Reference
Kinoshita M, Maeo S, Kobayashi Y, Eihara Y, Nishizawa N, Kusagawa Y, Sugiyama T, Wakahara T, Kanehisa H, Isaka T. Hypertrophic Effects of Single- versus Multi-Joint Exercise: A Direct Comparison Between Knee Extension and Leg Press. Med Sci Sports Exerc. 2026 Feb 5. doi: 10.1249/MSS.0000000000003957. Epub ahead of print. PMID: 41630124.
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