Leaning Back on the Seated Leg Extension Exercise Results in More Leg Growth Summary
- The study had 22 untrained men perform seated leg extensions with a 40° hip flexion (leaning further back) or 90° angle (upright) for 10 weeks. Consequently, leaning back further with a 40° hip flexion angle results in greater rectus femoris growth (the muscle that runs down the middle of your leg). At 40°, the muscle grew by 15.8% in the lower part and 12.4% in the upper part. At 90°, it grew by 10.9% in the lower part and 4.6% in the upper part.
- Additionally, the growth of the vastus lateralis muscle (muscle on the side of your leg) was about the same for both hip angles. The 40° angle had 9.9% growth in the lower part and 10.8% in the upper part. The 90° angle had 11.8% growth in the lower part and 9.7% in the upper part.
- To enhance rectus femoris muscle growth, use a 40° hip angle and lean back further on the seated leg extension machine. You can use either angle for the vastus lateralis muscle, whichever feels better.
Introduction
Regional-specific hypertrophy, or the targeted growth of specific muscle regions, is an important consideration for bodybuilders and individuals seeking to optimize muscle growth. Recent studies highlight the benefits of various exercise positions to achieve such targeted muscle growth. For example, performing different curl variations, such as incline and preacher, leads to varying degrees of muscle growth in various regions of the biceps brachii, with preacher curls showing the greatest muscle growth in the lower bicep.
Different selections of resistance exercises can impact regional muscle growth.(Larsen et al., 2024; Maeo et al., 2023) The quadriceps femoris is one muscle group notably influenced by the choice of resistance exercises. Several previous studies using the squat exercise, measuring quadriceps femoris growth (the muscle that runs down the middle of your leg), have reported minimal hypertrophy following weeks of squat training.(Kojic et al., 2022; Kubo et al., 2019; Zabaleta-Korta et al., 2021)
Different Exercise Affect Muscle Growth
Notably, a 2021 study compares the effects of Smith machine squats and leg extensions hypertrophy of the rectus femoris and vastus lateralis during five weeks of resistance training. The researchers observe that all three regions of the rectus femoris had greater muscle growth for the leg extension group. In contrast, muscle growth only occurs at the middle measurement site in the vastus lateralis among the squat group.(Zabaleta-Korta et al., 2021) Furthermore, a new study by Larsen et al. compares the effects of different hip flexion angles on quadriceps hypertrophy during the leg extension exercise.
The researchers hypothesize that performing leg extensions with a greater hip flexion angle (leaning back further) leads to greater hypertrophy of the rectus femoris.(Larsen et al., 2024) This hypothesis is grounded in the understanding that training muscles at longer lengths can enhance hypertrophy, a principle supported by studies on other muscle groups, such as the calves and biceps, where lengthened partials show an increase in muscle growth (Pedrosa et al., 2022); Maeo et al., 2023).
Review of the Literature Leg Extensions and Muscle Growth
Resistance training is well-established as an effective method for increasing skeletal muscle hypertrophy. Regional hypertrophy, where specific muscle regions grow more than others, has been observed with different exercise selections (Maeo et al., 2021). For example, exercises like leg extensions can induce greater growth in the quadriceps compared to multi-joint exercises like squats (Zabaleta-Korta et al., 2021). The rectus femoris, in particular, benefits more from isolated leg extension exercises than compound movements like the squat (Kubo et al., 2019).
Moreover, supporting the principle of training at longer muscle lengths, studies demonstrate that exercises performed with greater ranges of motion or at specific angles that elongate the muscle can enhance hypertrophic responses. For instance, Pedrosa et al. (2022) found that training the calves with lengthened partials led to superior hypertrophy compared to traditional training methods. Similarly, Maeo et al. (2023) find greater triceps hypertrophy when training at longer muscle lengths. While the mechanisms underlying the potential benefit of longer-muscle length training remain unclear, the research suggests that training the quadriceps femoris at longer muscle lengths could be beneficial when training for muscle growth like other muscles.(Ottinger et al., 2022)
Overview of the Study Protocol Seated Leg Extensions
The current study by Larsen et al. involves 22 untrained men training with different positions on the seated leg extension exercise. Each participant performs leg extensions with one leg at a 40° hip flexion angle and the other at a 90° angle. The participants completed a ten-week resistance training program with two sessions per week. Each session consists of three sets of 15-20 repetitions for the first five weeks, increasing to four sets in the final five weeks.
The resistance training program was performed twice weekly for 10 weeks, lasting at least 48 hours between sessions. When a participant reached 20 repetitions in the first set, the load was increased by 0.25-0.5 kg to ensure the repetitions performed per set were within the given repetition range. Training intensity was standardized by having both conditions terminate sets at momentary failure for each set, with around 30 seconds rest between limbs and 2 minutes between sets. Muscle thickness of the distal and proximal regions of the rectus femoris and vastus lateralis was measured using ultrasound imaging before and after the intervention. The training protocol was carefully monitored to ensure consistency, and participants trained to momentary concentric failure to maximize hypertrophy.
Results of the Seated Leg Extensions Study
The main findings of this study indicate that:
1) All quadriceps femoris muscles hypertrophied following ten weeks of resistance training performing the leg extension exercise;
2) Greater hypertrophy occurs in both distal and proximal regions of the rectus femoris following training with 40° of hip flexion compared to 90° of hip flexion and
3) No differences in hypertrophy occur between the training conditions for distal and proximal regions of the vastus lateralis muscle.
What the Study Means for Those Performing Seated Leg Extensions
These findings suggest that leaning back further during the seated leg extension exercise can significantly enhance hypertrophy of the rectus femoris. This outcome supports the hypothesis that training muscles at longer lengths, achieved by increasing the hip flexion angle, can optimize hypertrophic responses. The observed hypertrophy is likely due to the greater mechanical tension experienced by the rectus femoris when trained in a lengthened position while leaning back further on the leg extension machine, aligning with the muscle’s length-tension relationship.
Practical Applications when Performing Seated Leg Extensions
For athletes and individuals aiming to maximize quadriceps hypertrophy, particularly of the rectus femoris, perform seated leg extensions with a greater hip flexion angle (approximately 40°). This training modification can also be beneficial for those looking to enhance specific muscle regions for aesthetic or performance purposes. In conclusion, the practical application of the study by Larsen et al. is that those who aim to maximize quadriceps femoris hypertrophy may do so by performing the leg extension while lying a bit backward (around 40° hip flexion). By leaning back further, individuals can achieve greater growth in the rectus femoris, enhancing overall lower limb strength and functionality.
References
Kojic, F., Ranisavljev, I., Obradovic, M., Mandic, D., Pelemis, V., Paloc, M., & Duric, S. (2022). Does Back Squat Exercise Lead to Regional Hypertrophy among Quadriceps Femoris Muscles? Int J Environ Res Public Health, 19(23). https://doi.org/10.3390/ijerph192316226
Kubo, K., Ikebukuro, T., & Yata, H. (2019). Effects of squat training with different depths on lower limb muscle volumes. Eur J Appl Physiol, 119(9), 1933-1942. https://doi.org/10.1007/s00421-019-04181-y
Larsen, S., Kristiansen, B., Swinton, P., Wolf, M., Falch, H., Tillaar, R., & Østerås Sandberg, N. (2024). The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise. https://doi.org/10.51224/SRXIV.407
Maeo, S., Wu, Y., Huang, M., Sakurai, H., Kusagawa, Y., Sugiyama, T., Kanehisa, H., & Isaka, T. (2023). Triceps brachii hypertrophy is substantially greater after elbow extension training performed in the overhead versus neutral arm position. Eur J Sport Sci, 23(7), 1240-1250. https://doi.org/10.1080/17461391.2022.2100279
Ottinger, C., Sharp, M., Stefan, M., Gheith, R., Espriella, F., & Wilson, J. (2022). Muscle Hypertrophy Response to Range of Motion in Strength Training: A Novel Approach to Understanding the Findings. Strength & Conditioning Journal, Publish Ahead of Print. https://doi.org/10.1519/SSC.0000000000000737
Pedrosa, G. F., Lima, F. V., Schoenfeld, B. J., Lacerda, L. T., Simões, M. G., Pereira, M. R., Diniz, R. C. R., & Chagas, M. H. (2022). Partial range of motion training elicits favorable improvements in muscular adaptations when carried out at long muscle lengths. Eur J Sport Sci, 22(8), 1250-1260. https://doi.org/10.1080/17461391.2021.1927199
Zabaleta-Korta, A., Fernández-Peña, E., Torres-Unda, J., Garbisu-Hualde, A., & Santos-Concejero, J. (2021). The role of exercise selection in regional Muscle Hypertrophy: A randomized controlled trial. J Sports Sci, 39(20), 2298-2304. https://doi.org/10.1080/02640414.2021.1929736
