QUADRICEPS DEVELOPMENT STRATEGY

Development and Function of the Quadriceps Muscle Group

The quadriceps muscle group is located in the front of the leg and consists of four muscles that cross the knee joint: rectus femoris , vastus lateralis , vastus medialis , and vastus intermedius . These muscles contribute significantly to knee movement and leg stability.

The rectus femoris , unlike the other quadriceps muscles, crosses both the knee and hip joints. Therefore, in addition to providing extension (opening) to the knee joint, it also provides flexion (bending) to the hip joint. The vastus lateralis , vastus medialis and vastus intermedius muscles form the quadriceps tendon, also known as the patellar tendon . This tendon covers the knee joint and attaches to the tibia (shin bone).

Having a strong quadriceps muscle group is especially important for knee health. Weakness of the quadriceps muscles can lead to a common problem called patellofemoral pain syndrome . This causes pain around the knee joint and results in atrophy (muscle loss) in the quadriceps muscles, negatively affecting the person's quality of life. Therefore, strengthening the quadriceps muscles is important for general mobility and a pain-free life.

Regional Anatomy of the Quadriceps Muscles

The quadriceps muscles are innervated by the femoral nerve . However, since each muscle has different innervations, they perform different functions. Some studies provide evidence that there are different innervated regions within the quadriceps muscle. These regions can be divided into proximal and distal (e.g. vastus lateralis and rectus femoris ) or proximal , medial and distal (e.g. vastus medialis ) according to innervation (1).

Studies examining this regional differentiation have found that the rectus femoris muscle shows greater activation in the proximal region during hip flexion, while greater activation occurs in the distal region during knee extension (2). These findings provide important evidence that the rectus femoris has separate innervation points.

As a result, the rectus femoris should be trained not only for knee extension but also for hip flexion (1).

Quadriceps Moment Arm

The quadriceps muscle group exhibits the greatest moment arm length in the midline of knee extension. The rectus femoris muscle is known to have a significant internal moment arm length during hip flexion. However, the moment arm length of the rectus femoris may vary among individuals (1-3).

The rectus femoris acts as an antagonist to the hip extensors in deep squat variations because it has a significant internal moment arm length. Therefore, using weight instead of elastic resistance in straight leg deadlifts and bent leg hip flexion exercises, placing the peak contraction point at full hip extension can maximize the contribution of the rectus femoris to hip flexion movements (1).

This strategy is an especially effective approach for athletes and trainers who want to isolate and strengthen the rectus femoris muscle.

Quadriceps Muscle Fiber Distribution

Many studies have examined the muscle fiber distribution of the quadriceps muscle group. In a study conducted by Gouzi et al. (4), it was reported that the vastus lateralis muscle contains 50% Type 1 muscle fibers. Quadriceps sections that tend to have Type 1 muscle fibers are less likely to experience muscle damage than other muscles because they have slower-twitch fibers. Jennekens et al. (5) stated that the Type 1 muscle fiber ratio of the rectus femoris muscle is less than 50%. However, contrary to this finding, Johnas et al. reported the Type 1 muscle fiber ratio as 30-40%.

Rectus femoris has the lowest values in terms of Type 1 muscle fiber ratio, while the Type 1 muscle fiber ratio of vastus lateralis , vastus medialis and vastus intermedius muscles varies between 44-64%. These results show that training the quadriceps muscle with both heavy and light loads is beneficial.

In summary, the quadriceps femoris muscle is one of the muscle groups with the fastest recovery capacity in the body (6-7). Although there are some differences between studies due to inter-individual differences and insufficient sample sizes, in general, studies show that the quadriceps muscles have equal proportions of fast- and slow-twitch muscle fibers (8-9).

Rectus Femoris

Rectus Femoris is a part of the quadriceps muscle group. However, there is a feature that makes this muscle different. It crosses both the hip and knee joints. It can perform both knee extension and hip flexion thanks to its double joint cross. The other muscle groups only perform knee extension because they cross a single joint.

THE ROLE OF COMPOUND EXERCISES IN QUADRICEPS DEVELOPMENT

They are called exercises that involve two or more joint movements. In lower extremity exercises, squats, leg presses and lunges are examples of compound movements. So how is the quadriceps muscle activated in compound exercises?

Lunge

Leg Press

Back Squat

Rectus Femoris and Muscle Activation During Squat Exercise

Research has shown that during the back squat exercise, the majority of the quadriceps muscle group is highly active, but the rectus femoris muscle shows lower activation. Assessing muscle activation with electromyography (EMG) can be difficult due to cross-talk between muscles. However, examining temporal changes in muscle cross-sectional area using magnetic resonance imaging (MRI) allows for more precise detection of this difference (10).

Biomechanically, when the rectus femoris muscle is activated, it produces rotational forces for hip flexion and knee extension . Therefore, during exercises that involve both hip and knee extension, such as the squat and leg press, the rectus femoris muscle acts as an antagonist (working in the opposite direction) at the hip and an agonist (working in the same direction) at the knee. This dual function may result in decreased rectus femoris activation during these exercises.

In parallel with these findings, longitudinal hypertrophy studies have shown that squat exercises do not cause significant hypertrophy in the rectus femoris muscle (11). This confirms that compound exercises such as squats target other quadriceps muscles and that the rectus femoris is less active due to its hip flexion and antagonist role.

As a result, it may be beneficial to work with exercises that isolate hip flexion (e.g., straight leg raise , hip flexion ) to increase activation and hypertrophy of the rectus femoris. Compound exercises such as squats focus more on activation and hypertrophy of the vastus lateralis , vastus medialis , and vastus intermedius muscles.

Similarly, leg presses, lunges, and deadlifts do not cause hypertrophy in the rectus femoris muscle. Research shows that these types of exercises do not cause hypertrophy in the rectus femoris muscle.

The Role of Isolated Exercises

Leg Extension

Activation of the Rectus Femoris Muscle and Quadriceps Development

The rectus femoris muscle is activated more during knee extension exercises than the other quadriceps muscles. This results in the muscle being subjected to greater loads during isolated exercises and therefore experiencing more pronounced hypertrophy during such exercises (12).

These findings suggest that both isolation exercises (such as leg extensions or straight leg raises ) and compound exercises (such as squats and leg presses ) should be included in training programs for effective quadriceps development. Isolation exercises help target less active muscles, such as the rectus femoris, while compound exercises increase overall strength and endurance of the quadriceps muscle group.

This strategic combination ensures balanced development of the quadriceps muscles and improves sports performance by increasing knee stability.

Resources

1.) How should we train the quadriceps? Beardsley. Medium.com/@SandCResearch.2019f

2.) Task-dependent spatial distribution of neural activation pattern in human rectus femoris muscle (2012) Author links open overlay panelKohei Watanabe ab, Motoki Kouzaki c, Toshio Moritani, Journal of Electromyography and Kinesiology

3.) Variability of femoral muscle attachments Author links open overlay panelGeorg N. Duda ∗, Doris Brand †, Sabine Freitag ∗, Werner Lierse ‡, Erich Schneider ∗ Journal of Biomechanics 1996

4.) Reference values for vastus lateralis fiber size and type in healthy subjects over 40 years old: a systematic review and metaanalysis

Fares Gouzi, Jonathan Maury, Nicolas Molinari, Pascal Pomiès, Jacques Mercier, … See all authors

5.) Data on the distribution of fiber types in five human limb muscles An autopsy study☆

Author links open overlay panelF.GI Jennekens, BE Tomlinson, JN Walton

6.) Damage and the repeated bout effect of arm, leg, and trunk muscles induced by eccentric resistance exercises Trevor C. Chen, Tsung-Jen Yang, Min-Jyue Huang, Ho-Seng Wang, Kuo-Wei Tseng, Hsin-Lian Chen, Kazunori Nosaka

7.) Saka, T., Akova, B., Yazici, Z., Sekir, U., Gür, H., & Ozarda, Y. (2009). Difference in the magnitude of muscle damage between elbow flexors and knee extensors eccentric exercises. Journal of sports science & medicine, 8(1), 107–115.

8.) Holzbaur, KR, Murray, WM, Gold, GE, & Delp, SL (2007). Upper limb muscle volumes in adult subjects. Journal of biomechanics, 40(4), 742–749.

9.) Resistance exercise-induced fluid shifts: change in active muscle size and plasma volume

LL Ploutz-Snyder,VA Convertino, andG. A. Dudley

01 SEP 1995

10.) Effects of squat training with different depths on lower limb muscle volumes Original Article Published: 22 June 2019 Volume 119, pages 1933–1942, (2019) Keitaro Kubo, Toshihiro Ikebukuro & Hideaki Yata

11.) Resistance training does not induce uniform adaptations to quadriceps

Gerald T. Mangine, Michael J. Redd,Adam M. Gonzalez,Jeremy R. Townsend,Adam J. Wells,Adam R. Jajtner,Kyle S. Beyer,Carleigh H. Boone,Michael B. La Monica,Jeffrey R. Stout ,David H. Fukuda,Nicholas A. Ratamess,Jay R. Hoffman

Published: August 30, 2018

12.) Maeo, Sumiaki & Shan, Xiyao & Otsuka, Shun & Kanehisa, Hiroaki & Kawakami, Yasuo. (2018). Single-joint eccentric knee extension training preferentially trains the rectus femoris within the quadriceps muscles. Translational Sports Medicine. 1. 10.1002/tsm2.38.

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