Do Heavy and Light Weights Produce Different Regional Muscle Growth?

Do heavy & light loads result in different growth on parts of a muscle?
A 1996 study by Hisaeda et al explored this.
11 untrained women were assigned to a hypertrophy or strength group.
They trained the leg extensions.
The hypertrophy group trained with 15-20 reps, while the strength group trained with 4-5 reps.
Cross-sectional area (CSA) of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
The hypertrophy group experienced greater growth of the vastus lateralis, while the strength group experienced greater growth of the vastus intermedius and rectus femoris.
In this study, they added up the CSA increases for each quadriceps head at 30, 50, and 70% of the quadriceps length and used that value for analysis.
Interestingly, they state the hypertrophy group experienced significant CSA increases at 30% of the thigh-length while the strength group experienced significant increases at 70%. But I don't know if this applies to one of the heads or all of them. They did not go into further detail.
This study isn't without limitations. Both groups also used a different number of sets, rest intervals, and rep tempos. These could have influenced the results.
But, is there any reason why heavy & light loads may cause different regional growth?
One reason relates to fiber types.
Muscles consist of slow & fast-twitch fibers.
With heavy loads, could the body selectively recruit muscle regions more fast-twitch.
With light loads, could the body selectively recruit muscle regions more slow-twitch.
Based on a few studies, the vastus intermedius & rectus femoris appear to be slightly more fast-twitch. Could this explain why the strength group experienced greater growth of these heads?
The vastus lateralis is less fast-twitch than these muscles. It appears to be a near 50/50 split of fast & slow fibers. Could this explain why the hypertrophy group experienced greater growth of this head?
Remember, the researchers broadly stated the hypertrophy group experienced greater upper region growth, while the strength group experienced greater lower region growth.
In most studies that aim to identify fiber type composition of a muscle, they take a tissue sample from one region of the muscle. There is research indicating that when taking samples from many regions of a muscle, the fiber type composition varies between them.
This might explain why the hypertrophy and strength group experienced different upper/lower region growth.
This hypothesis could apply to repetition tempo. Slower rep tempos may selectively recruit muscle regions more slow-twitch, while faster rep tempos may recruit regions more fast-twitch.
But this hypothesis does have problems with it.
The strength group experienced slightly greater growth of the vastus intermedius than the rectus femoris. But, the rectus femoris appears to be slightly more fast-twitch than the vastus intermedius.
If this hypothesis was true, we would expect the rectus femoris to have grown more than the vastus intermedius.
Also, the hypertrophy group experienced the greatest growth of the vastus lateralis. But, evidence indicates the vastus medialis is more slow-twitch than the vastus lateralis.
If this hypothesis was true, we would expect the vastus medialis to have grown more than the vastus lateralis.
Moving on, there is a study exploring how heavy and light isometric training impacts regional muscle growth.
12 untrained men were assigned to a 100 or 60% group.
Both groups performed an isometric contraction for the triceps. The 100% group contracted their triceps to 100% of their force-producing abilities. The 60% group contracted their triceps at 60% of their force-producing abilities
Triceps cross-sectional area was measured at 20 regions across its length.
Increases at all regions were similar between both groups.
But there are some important considerations
Isometric contractions were used. If both groups performed exercises that involve concentric & eccentric phases, we don't know if the results would be impacted
Also, we don't know if long, medial, and lateral head growth differed between the groups, the researchers did explore this.
Ultimately, more research is needed in this area.
As detailed in our alternating rep range video, in the short term, using a variety of loads appears to produce similar muscle growth to using only one load.
In the long term though, using a variety of loads could be superior.
& as demonstrated here, heavy and light loads may produce different regional growth, meaning using a variety of loads would be effective for ensuring more balanced growth across a muscle.
Note, there are still other ways to ensure more balanced muscle growth across a muscle.
Using different repetition tempos could be one way. Another way is to perform a variety of exercises for a muscle group.
Music: Ruck P - A Tribe Called Tenz
Copyright Chillhop Music - chll.to/6945fbe1
/ ruckp

[@Claframb]

Everyone who watches this video will become severely SWOLE.

[@bills6583]

Would be interested in a video analysing the mechanisms behind why a power lift can bench more than a bodybuilder buy might not be able to match their reps on a pec fly for example

[@HouseofHypertrophy]

No problem! I'll probably cover this in a video comparing strength and size. For the time being, there is a really great article by Greg Nuckols that somewhat covers this if you're interested: www.strongerbyscience.com/size-vs-strength/

[@chayoto]

@houseofhypertrophy Much appreciated!

[@honaker1127]

Would love to see a video on bands vs free weights and another video on Olympic lifts vs med ball work for explosiveness. I'm curious on the risk vs reward for the transfer to American football

[@HouseofHypertrophy]

I should have a video on bands at some point. As for olympic lifts and med balls, I'm not sure about this as I primarily cover hypertrophy and strength related things, not neccessarily athletics, sorry :(

[@Witcherworks]

I think this makes logical sense. It makes sense for low twitch muscles to grow more during low intensity vs higher intensive exercises that use faster twitch muscles. I think by the time you try to get fast twitch muscles to do slow twitch work, the mind would shut down the connection for force unless you force it. At that point you just getting the weight up and no longer focused on the isolated area.

[@Witcherworks]

Also for the justification for why didn’t certain muscles not grow even though they had more fibers. Well that’s exercise selection, muscle insertions, and the way the exercise is preformed. A lot of variables that aren’t included in most studies.

[@HouseofHypertrophy]

I think you make some great points! With regards to why certain muscles did not grow even though they were slower or fast-twitch, I 100% agree that exercise selection and even finer intrinsic properties of the muscle could be playing a role. This would mean the limitations I outlined for the fiber type hypothesis may not actually be limitations. Thank you for your interesting ideas :)

[@cv0669]

great stuff hope you keep making videos man

[@HouseofHypertrophy]

Thank you, I will do my best to continue making videos :)

[@jjjjjjjj72]

TH-cam->BibleProject
Thank you for your work sir. God bless you all ❤

[@mikey-wo3fq]

appreciate that man!

[@HouseofHypertrophy]

Thank you, great to hear :)

[@123arjunx]

Great channel!
However, 'eccentric' is pronounced /ɪkˈsɛntrɪk,ɛkˈsɛntrɪk/..."eck-sen-trick"

[@HouseofHypertrophy]

Thank you, and my apologies with the pronunciation. I'll try to not make that mistake again :)