This only leads to additional muscle growth distally, not overall. This difference may not even be visible.
Many assume that most single-joint muscles, such as the vasti of the quadriceps along with the lateral and medial heads of the triceps, can’t be stretched.
While not to the same degree as a multi-joint muscle like the rectus femoris or the long head of the triceps, which each can stretch so far that they reach a state called passive insufficiency, this is just not true.
The solution is correct positioning.
To stretch the single-joint muscles of the quads and triceps, you must get your knees or elbows as far in front of your body as possible during the exercise, albeit a bit differently for each muscle group.
This loads the stretched positions, which promotes a unique form of muscle growth, by preventing the thighs or upper arms from impeding the range of motion.
Vince Gironda realized the value of these unusual exercises, though without understanding the modern science supporting them, many trainees would have rightfully been skeptical of such odd movements requiring less weight.
Quads: Hack Squat
For the quads, the best way to stretch then monoarticular muscles is to use a hack squat machine, though other options are possible with some creativity.
This means bending with your knees as far in front of you as possible at the bottom of the movement. Unlike the image above, I suggest the knees traveling in front instead of outward to stretch both the vastus medialis and vastus lateralis. You will need to allow your heels to rise off the platform to do so, while placing your feet as low as possible.
You want to minimize yet still allow some extension of the hips, so that your rear drops down instead of forward, so that your heels may even touch it. Your hips will travel forward a bit away from the platform, while staying upright, which maximizes the bending of the knees. If you throw your hips forward like on a sissy squat, the rectus femoris will bear the stretch, not the vasti.
Triceps: Leaning Arm Extensions
For the triceps, you want to use a cable machine with the pulley about 45°. You will then face away from the stack, using arm extension alone to lift it, allowing the weight to pull each hand back as far as possible. You’ll assume the elbows-out position right away, unlike the hack squat which occurs at the bottom.
For better stability, place one foot forward and the other back, adopting a staggered stance.
Unlike a more conventional triceps press-down, you’ll be able to load the most stretched position with the elbows bent fully. This really can’t be achieved due to the pull of gravity acting up and down. You’ll be able to tell because you can likely touch your shoulder in this position, achieving more range of motion.
Though shown with both limbs here, I suggest using a single rope attachment, working one arm at a time. You can more easily move into the proper position without worrying about ideal positioning, which otherwise can distract you.
Choose somewhere between a neutral and overhand grip, not to emphasize any head of the triceps but to allow maximum range of motion.
You may find that a close-grip bench press or close-grip triceps dip may work even better, at for the single-joint heads and not the long head, since the ascending strength curve overloads the stretch position. Nonetheless, it can be a bit tricky to achieve enough range of motion due to arm impediment. These exercises have their own pros and cons but should be considered.
Why Stretch Muscles at All?
Generally, a muscle contracts optimally at medium lengths according to the length-tension relationship, where leverage tends to be worst for most movements. The actin and myosin filaments overlap best here, neither too stretched nor too shortened. This makes sense as muscles would need to function most strongly at these positions as the weight feels heavier, such as the midpoint of a barbell curl, since the elbow is furthest from the resistance.
Overloading a muscle with exercises that feels heaviest at the midpoint seems optimal. This leads to muscle growth mostly by adding sarcomeres in-parallel, through active tension that occurs when muscles contract. This overload is well-aligned with the working muscles on basic exercises like squats and bench presses.
But muscle doesn’t just grow through active tension. It grows through passive tension as well, which develops when a muscle stretches by reaching long muscle lengths. Active lengthening, which occurs when lowering weights that elongate the muscle while contracting, increases passive tension even further.
Even more interesting, the body will adjust the fascicle lengths of the muscle. This means that the sarcomeres added in-series are meant to help you contract with higher active tension at longer-than-medium lengths. This adaptation, especially if you haven’t practiced similar exercises, leads to explosive muscle growth.
We know that overloading the stretched positions will therefore increase growth from the overstretch. Not only this, but we also know the body adapts in this way to increase active tension at long muscle lengths too, as evidenced by the repeated bout effect that reduces soreness. Furthermore, connective tissue adapts to better handle the stress.
This means that these two exercises achieves a unique form of muscle growth that cannot be attained by only working muscles at medium lengths through simpler exercises.
Stretching the Single-Joint Quads & Triceps for Explosive Muscle Growth
What ought to be done must be learned from one who does it.
You will notice a greater pump, more soreness, and ultimately explosive muscle growth from the hack squat and the leaning arm extension.
Nonetheless, these exercises can stress the joints since they apply shear forces in addition to destabilizing the joint at an extreme endpoint for the range of motion.
If you progress sensibly, while moving smoothly and not too slowly, taking advantage of the stretch-shorten cycle, you should be okay. If not serious about maximizing growth via all possible sources though, you may want to stick with the basic compound exercises like leg and bench presses. These overload the midrange where muscles and joints function strongly.
Some experts raise the point that not all sarcomeres stretch out fully for certain muscles like the triceps and deltoids. This would mean stretch-mediated hypertrophy wouldn’t seem possible. While partially true, the sarcomeres may still lengthen in a similar yet lesser degree (2) or perhaps some sarcomeres lengthen more even if many do not. Maybe the greater muscle damage itself, along with increased blood flow restriction through stretch, could encourage more growth independently with the increased range of motion.
Be wary of only relying on research versus direct experience and the wisdom of bodybuilders to guide your decisions. The science is complex and may not fully explain yet what trainees figure out on their own. Even if bodybuilders lack scientific explanations, they may be right for the wrong reasons.
Give the hack squat and the leaning arm extension a try. Notice the additional muscle growth through a deeper stretch as a general principle, like I have, by applying these unusual exercises. Let your results dictate if they belong in your program.