New Research Says This Leg Extension Hack Could Lead to Stretch Mediated Quad Gains
Stretch-mediated hypertrophy is an area of research that's caused quite a stir, especially if you are interested in simple tricks to get the most out of your sets. The concept includes focusing on training the muscles in the stretched portion of the lift. This could look like 'long-length partials', where you perform 50% of the rep in the elongated position. Or, 'lengthened supersets', where you perform partial reps at the end of your sets after you get close to failure from using full range of motion.
Semantics aside, the method is an area interest for researchers and bodybuilders alike. So much so, that a group of researchers have analysed the effects of using the leg extension machine at different torso angles to see the effects on muscle growth.
The Study
The study preprint by Larsen et al. investigates the effects of different hip flexion angles (leaning back and sitting upright) during the leg extension exercise on muscle hypertrophy in the quadriceps femoris (quad muscles). The study focuses on the rectus femoris (front of the quad) and the vastus lateralis (outer quad muscle).
The Methods
The study involved:
22 untrained men
A 10-week resistance training programme
Leg extensions performed with two different hip flexion angles: 40° (recumbent) and 90° (upright)
Each leg was randomly assigned to one of these angles
The Results
The study found significant evidence that the rectus femoris muscle experienced greater hypertrophy when the leg extension exercise was performed with a 40° hip flexion angle (recumbent) compared to a 90° angle (upright).
For the rectus femoris muscle, the study observed a 15.8% increase in distal muscle thickness with the leg extension performed in the recumbent position, compared to a 10.9% increase in the upright position. Similarly, proximal muscle thickness increased by 12.4% in the recumbent position, compared to just 4.6% in the upright position. No significant difference in hypertrophy was found for the vastus lateralis muscle between the two hip flexion angles.
The Conclusion
The researchers concluded that if the goal is to maximise hypertrophy of the rectus femoris muscle, performing leg extensions with a reduced hip flexion angle (around 40°) and the torso leaning back is more effective
Alternatively, for those focusing on vastus lateralis without additional rectus femoris growth, the choice of hip angle can be based on comfort or personal preference, since no difference was observed between both angles for this muscle.
What Does This Mean for Us?
Realistically, if you are just looking for all round hypertrophy of the quad muscles, there's no harm in completing leg extensions with an upright torso. However, if you have aesthetic goals of increasing hypertrophy of the rectus femoris muscle, then completing leg extensions with the back support reclined would be more beneficial.
Along with additional recent evidence, this further emphasises that training muscles in the stretched position can enhance muscular gains when compared to training in the shortened position. You can take a look at further research on the topic here:
A preprint study by Larsen et al reported that incorporating 'lengthened supersets' at the end of sets, where the muscle is in a stretched position, resulted in significantly greater calf muscle growth.
A preprint review aimed to analyse the current evidence to evaluate if resistance training at longer muscle lengths results in greater hypertrophy compared to shorter muscle lengths. It found that both muscle size and length showed greater increases following longer muscle length training compared to shorter muscle length training.
A recent study published in the European Journal of Applied Physiology investigated a stretching protocol versus strength training. The findings indicated that participants in the stretching group achieved similar increases in muscle thickness as those who followed the lifting routine.
A study featured in the European Journal of Sport Science demonstrated that participants performing knee extensions with partial range of motion (ROM) experienced greater quad muscle growth compared to those who used a full ROM.
Research in the Journal of Strength and Conditioning Research found that participants performing skull crushers with partial ROM experienced nearly twice the muscle growth compared to those using a full ROM.
A separate study from the Journal of Strength and Conditioning Research revealed that participants who performed calf raises at the initial range of motion had twice the increase in calf size compared to those who did the exercises through a full ROM.
In a study published in the Scandinavian Journal of Medicine and Science in Sports, participants performing long-length partial reps on the leg press showed comparable increases in quad size to those who completed full ROM reps.
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