The Most IMPORTANT Muscle Building Stimulus (87 Studies)

Summary

Highlights

• Mechanical tension is identified as the primary driver of muscle hypertrophy. 💪
• Traditionally held beliefs about soreness and metabolic stress are questioned. 🤔
• Exercises using both tension and muscle length change are recommended for growth. 🏋️‍♀️
• The role of mechanosensors in muscle fiber growth is explored. 🔍
• Future research may uncover additional stimuli for muscle growth. 🔮

Key Takeaways

• Mechanical tension is a key driver of muscle hypertrophy. 💪
• Metabolic stress and muscle damage are less significant than previously thought. 🤔
• Exercises that utilize both active and passive tension are effective. 🏋️‍♀️
• High mechanical tension can be achieved with a wide range of loads, as long as they approach failure. 🔥
• The importance of scientific research in understanding muscle growth is emphasized throughout. 📚

Overview

Chapters

• 00:00 - 01:00: Scientific Literature & Hypertrophy Stimulus This chapter delves into scientific literature to determine the most crucial stimuli for muscle hypertrophy. It intertwines research on various fascinating topics related to muscle building. Key areas of exploration include the effects of the pump, soreness, Blood Flow Restriction Training, eccentric training, acute spikes in anabolic hormones, antioxidants like vitamin C and E, high rep vs low rep training, failure training, and range of motion.
• 01:00 - 02:00: Distance Training Throughout History This chapter explores the historical progression of distance training, tracing its origins and development across various ancient civilizations.
• 02:00 - 03:00: Understanding Muscle Hypertrophy This chapter explores the scientific understanding of muscle hypertrophy, particularly focusing on the stimuli behind this process. The chapter traces the historical context, noting that significant insights have only been gained in the last 50 to 70 years due to advancements in scientific research. By the end of this section, readers are expected to have a comprehensive understanding of the current scientific perspectives on muscle hypertrophy stimuli.
• 03:00 - 06:00: Mechanical Tension & Muscle Hypertrophy This chapter introduces the starting of a new series on YouTube, focusing on developing each major muscle group through comprehensive and in-depth 'Ultimate Guide' videos. The primary aim is to thoroughly understand what stimulates muscle hypertrophy, as this understanding will significantly influence the recommendations for exercise selection. The chapter also mentions that there will be detailed timestamps available in the description and pinned comment to help navigate through the video parts and subparts.
• 07:00 - 12:00: Metabolite Accumulation & Muscle Growth The chapter titled 'Metabolite Accumulation & Muscle Growth' explores the concept of mechanical tension in muscle fibers and its impact on muscle growth. It posits that the tension generated by a muscle's fibers is crucial for stimulating an increase in both fiber size and overall muscle size. The chapter suggests that intuitively, reducing the tension—as seen during activities like immobilization or when in space—leads to a decrease in whole muscle size.
• 17:00 - 26:00: Role of Muscle Damage in Hypertrophy Researchers since the 1970s have hypothesized the role of both active and passive tension in muscle hypertrophy. Active tension refers to the contractile force produced by muscle fibers, while passive tension refers to the force when fibers and muscles are stretched. Numerous studies in the 1970s to 1990s have linked these tensions to hypertrophy through animal-based research, though ethical concerns regarding the use of animals in such studies are acknowledged.
• 35:00 - 39:35: Conclusion & Insights on Muscle Growth The chapter covers significant studies in the field of muscle growth, particularly focusing on muscle hypertrophy. It emphasizes research where the tendon of the gastrocnemius muscle was cut, preventing this muscle from functioning properly, which resulted in the soleus muscle becoming overloaded and experiencing increased active tension. This change leads to muscle hypertrophy in the soleus, thereby suggesting a strong connection between increased active tension and muscle growth.

The Most IMPORTANT Muscle Building Stimulus (87 Studies) Transcription

• 00:00 - 00:30 we're going deep into the scientific literature on what the most important stimulus for building muscle is along the way the scientific research on many other fascinating topics will be intertwined in our search for what stimulates hypertrophy searches to burn pump soreness Blood Flow Restriction Training eccentrics acute spikes in anabolic hormones the effects of antioxidants like vitamin c and e High ribs low ribs failure training and range of motion
• 00:30 - 01:00 [Music] distance training throughout history from ancient India we have accounts of a piece of exercise equipment noted in writings thought to be compiled between the 3rd Century BC and 3rd Century CE ancient Chinese artwork from a time period I don't know shows weightlifting activities from ancient Egypt we have these tomb paintings from around 2000 to 3500 BC depicting individuals lifting weights moreover ancient Egyptians knew in 1700
• 01:00 - 01:30 BC from poliomyelitis that not moving at all produced a decrease in muscle size but it is only in the last 50 to 70 years that deeper insights into the stimuli behinds muscle hypertrophy have been discovered thanks to the rise of scientific research by the end of the video I'm confident you'll have a thorough understanding of what the current scientific research says on the stimuli behind muscle hypertrophy before diving in I want to mention that in the upcoming year I'll
• 01:30 - 02:00 be releasing free Ultimate Guide videos on developing each major muscle group right here on YouTube my aim for them is to be comprehensive and in depth like no other before these videos its first extremely helpful for us to know what precisely stimulates hypertrophy as this will strongly relate to exercise selection recommendations in the description and pinned comment there will be in-depth timestamps to the parts and subparts of this video Let's Dive In
• 02:00 - 02:30 we'll go into serious depth on what mechanical tension precisely is later but for now think of it as the tension generated by a muscle's fibers does this fiber tension stimulate an increase in fiber size and subsequently whole muscle size intuitively it would as if we substantially reduce the tension produced by muscle fibers like done during immobilization or when in Space the whole muscle decreases in size as
• 02:30 - 03:00 early as the 1970s researchers hypothesize both active and passive tension are stimulators of hypertrophy active tension is the actual contractile Force produced by the muscle fibers while passive tension is the force produced when the fibers and whole muscle are stretched there were four types of studies linking active and passive tension to hypertrophy throughout the 1970s to 1990s all of these studies were conducted on animals and I want to preface this by saying I'm personally opposed to unnecessary animal
• 03:00 - 03:30 studies but as much as it's unfortunate to see the following Studies have all been pivotal in understanding muscle hypertrophy the first type was studies that cut the tendon of usually the gastrocnemius meaning this muscle could no longer carry out plantar flexion this resulted in the supporting soleus muscle being overloaded and exposed to Greater active tension during normal movement in response to this the studies consistently find the Soleus experience substantial hypertrophy therefore linking increased active tension to
• 03:30 - 04:00 hypertrophy the second type of study had a limb immobilized while the muscle was placed in a stretched or shortened position these experiments find muscle size decreases a lot less when the muscle is immobilized at a stretched versus shortened position therefore indirectly linking passive tension to being anabolic the third type of study involved attaching weights to a wing of chickens to produce continuous stretching of their muscles doing so results in hypertrophy of the stretched muscles finally the fourth type of study
• 04:00 - 04:30 was virtually the same as the third except it used a spring-loaded aluminum bar to stretch the muscles of chickens doing so again results in hypertrophy of the muscle but if we carefully think about these four types of studies and this was discussed in future research none of them truly proved tension per se is stimulating hypertrophy could it not be the events before active tension like the electrical signals metabolite accumulation or even damage that is truly stimulating the hypertrophy in
• 04:30 - 05:00 these studies we'll thoroughly explore metabolite accumulation and damage soon but the research in the last 20 years provides us with solid grounds to believe it is truly tension per se stimulating hypertrophy a 2019 Danish study found that when inhibiting the active Force generation from muscle fibers but still allowing electrical signal input to them activation of a key protein complex that signals muscle growth failed to occur it was only when active Force generation from muscle fibers was enabled did
• 05:00 - 05:30 activation of the key protein complex happen this suggests it is the active force from fibers that stimulates hypertrophy Norther electrical signals the same researchers also established that when equating Peak tension between eccentric contractions which involved active and passive tension and pure passive stretching which would not involve active tension only passive tension activation of the key protein complex was the same so this is evidence that its total tension regardless of
• 05:30 - 06:00 whether it's active or passive that stimulates hypertrophy another 2008 study out of the USA found that when keeping electrical input to a muscle constant positioning the muscle at a length that allowed it to generate higher active forces resulted in greater activation of a key protein involved in signaling hypertrophy so this study again demonstrates how it may indeed be tensioned per se that stimulates hypertrophy a 2001 Canadian study found a linear relationship between Peak
• 06:00 - 06:30 tension and activation of a key protein involved in signaling hypertrophy finally in the last 20 years or so researchers gradually accumulating on how precisely these forces can activate key proteins involved in hypertrophy it turns out that within and around muscle fibers are mechanosensors that can detect active and or passive tension and then convert the tension into a signaling pathway that stimulates muscle hypertrophy all of the key proteins explored in the previously mentioned studies are involved in the signaling
• 06:30 - 07:00 Pathways we'll explore what these potential mechanosensors could be soon but this overall evidence for further strengthens the idea that tension per se is what stimulates hypertrophy in humans papers suggest that protocols that presumably involve higher mechanical tension results in Greater muscle growth signaling and long-term muscle hypertrophy moreover in human studies that presumably equate mechanical tension between different protocols muscle growth signaling and long-term muscle hypertrophy tend to be the same so its clear solid research
• 07:00 - 07:30 suggests mechanical tension is a powerful stimulator of muscle hypertrophy but are there any other stimuli I've previously had a shorter video on metabolic stress and hypertrophy although we'll mention things noted in that video we will go into greater depth here with extra topics metabolic stress refers to the buildup of molecules produced by reactions related to energy production within muscle fibers these molecules are called metabolites and
• 07:30 - 08:00 famous examples include lactate and reactive oxygen species the accumulation of multiple metabolites is associated with pain and burning Sensations during training so it's certainly logical to feel these pain and burning Sensations must surely be related to hypertrophy moreover the accumulation of metabolites is closely tied to the pump which is a temporary increase in muscle size so it's certainly logical to think this plays a role in promoting long-term true hypertrophy the oldest research I could
• 08:00 - 08:30 find exploring the role of metabolites in hypertrophy comes from 1995. one of the papers found that concentric only training produce similar quadriceps hypertrophy to Eccentric only training concentric only training is known to produce much higher metabolic stress than eccentric only training so the authors hypothesized metabolic stress was heavily involved in producing the muscle growth seen by concentric only training while perhaps mechanical tension or even damage caused the growth with eccentric only training the second study by the same research team found
• 08:30 - 09:00 holding continuous isometric contractions produced greater quadriceps hypertrophy than holding intermittent isometric contractions The Continuous isometric contractions produce measurably more metabolic stress leading the researchers to hypothesize it was the metabolic stress causing the greater hypertrophy with continuous isometric contractions however both of these classic studies didn't truly isolate metabolic stress and prove it was stimulating hypertrophy concentric only training still involves
• 09:00 - 09:30 High mechanical tension and the continuous isometric contractions due to the training variables used in the study would have likely generated more mechanical tension than the intermittent contractions the authors did allude to this limitation in the paper moving forward to the early 2000s emerging research demonstrated that Blood Flow Restriction Training with very light loads can be highly effective for producing muscle hypertrophy nowadays despite some believing Blood Flow Restriction Training is useless or others believing it is superior to normal training the research
• 09:30 - 10:00 consistently finds Blood Flow Restriction Training with light lows is as effective as heavy load training for building muscle in case you're unaware Blood Flow Restriction Training is where a cough applies pressure to the upper part of a limb completely restricting blood flow from the muscle to the heart and partially restricting blood flow from the heart to the muscle as a fun fact Blood Flow Restriction Training originated in 1960s Japan by yoshiakisato yoshiaki SATA was at a Buddhist Memorial where during mass his leg became numb due to sitting straight
• 10:00 - 10:30 back while kneeling on the floor he noticed his calves had pumped up and he said it was a similar sensation to what he felt during intense calf raise exercises this experience paved the way for Salto to experiment over the ensuing years and develop katsu training which is what he called The Blood Flow Restriction Training back to our discussion performing High rep's net failure with Blood Flow Restriction will result in significant metabolic stress and some speculate it this metabolic stress causing the hypertrophy produced by Blood Flow
• 10:30 - 11:00 Restriction Training they believe mechanical tension must be low since Blood Flow Restriction Training involves using very light loads however as detailed in this great 2017 USA review study this is based on an incorrect view of mechanical tension getting their failure with light loads including Blood Flow Restriction Training will absolutely create high overall mechanical tension the metabolic stress with Blood Flow Restriction Training might just be a byproduct of the effort required to get Nair failure to create
• 11:00 - 11:30 this tension not the cause of hypertrophy again we'll go into depth on what mechanical tension is a little later for the time being just know it seems incredibly likely Blood Flow Restriction Training would produce muscle growth through mechanical tension having said this there have been three studies finding Blood Flow Restriction Training produced preferential growth of slow twitch muscle fibers over fast switch muscle fibers fast twitch muscle fibers have greater growth potential and numerous studies indicate normal training results in more fast versus
• 11:30 - 12:00 slow touch fiber growth and so some speculate the preferential slow twitch fiber growth by Blood Flow Restriction Training cannot be related to Mechanical tension and might be due to some metabolic stress mechanism but I'm very skeptical this is true two of the three studies involve blood flow shoots and training with a very high training frequency one involved Blood Flow Restriction Training for seven consecutive days while the other involved training for 5 days in a week the problem is Central fatigue can be present days after training especially
• 12:00 - 12:30 when muscle damage is high despite previous speculations that Blood Flow Restriction Training produces minimal muscle damage we now know there's research indicating performing reps 2 or net failure with Blood Flow Restriction when you're unaccustomed to it which applies to both studies produce a substantial muscle damage the issue of training while Central fatigue is present is you have a lowered ability to recruit those fast twitch muscle fibers thus the preferential growth of the slow twitch fibers in those two studies may not be because slow twitch fiber growth
• 12:30 - 13:00 was enhanced via some metabolic stress related mechanism rather it might be because fast twitch fiber growth was compromised due to training sessions being performed with Central fatigue what about that third study finding preferential slow twitch fiber growth with Blood Flow Restriction Training it had untrained subjects train Blood Flow Restriction with reps to failure three times per week for six weeks given the subjects were untrained Central fatigue may still have been present in a lot of their training sessions so again perhaps
• 13:00 - 13:30 their findings reflect compromised fast twitch fiber growth furthermore another 2021 Australian paper found that in well-trained individuals training a range of lower body exercises with Blood Flow Restriction three times per week for nine weeks preferential slow twitch muscle fiber growth did not occur so does all of this really mean metabolic stress plays no role in hypertrophy in 2013 Brad schoenfels from New York published a comprehensive review of the potential paths by which metabolic stress could promote muscle
• 13:30 - 14:00 growth five paths were noted the first is metabolic stress and fatigue directly necessitates more muscle fibers getting recruited and therefore exposed attention the second is training that produces High metabolic stress is associated with temporary elevations in anabolic hormones like growth hormone igf-1 and testosterone and this might promote hypertrophy the third is that high metabolic stress could increase myokines that promote hypertrophy like interleukin-6 and decrease myokines that
• 14:00 - 14:30 limit muscle growth like myostatin the fourth is that reactive oxygen species in metabolite could play a role in promoting muscle growth the fifth and final one is that metabolic stress is closely associated with a pump as we already know the pump is swelling of muscle fibers and this swelling might actually activate certain osmoreceptors that go on to promote growth yet all of these five paths have notable problems with the first one about metabolic stress resulting in more muscle fibers
• 14:30 - 15:00 getting exposed attention it still indicates its tension per se not metabolic stress directly that stimulates hypertrophy with the second one we nowadays have several studies consistently finding temporary elevations in anabolic hormones from training are not associated with long-term muscle hypertrophy the increase in these anabolic hormones may be simply a result of energy usage and be unrelated to signaling hypertrophy with myokines the evidence is simply inconsistent on whether metabolic stress truly increases growth promoting
• 15:00 - 15:30 myokines like interleukin-6 and decreases myokines that limit muscle growth like myostatin with the fourth and fifth ones there exists alternative evidence suggesting reactive oxygen species and fiber swelling may not promote hypertrophy further areas of scientific research question the power of metabolic stress to produce hypertrophy 400 meter running and sprint cycling can produce comparable lactate in metabolite increases to weight training yet these
• 15:30 - 16:00 things do not promote hypertrophy anywhere near as effectively as weight training long term a 2021 Brazil study had subject showing leg extensions with these variables one condition rested passively between sets while another condition restricted their leg with a cough during the rest intervals which led to Greater overall lactate elevations versus the first condition if lactate has additive effects on hypertrophy this second condition should seem more hypertrophy yet quadriceps growth ended up being similar between both conditions after eight weeks of training two other papers had two
• 16:00 - 16:30 conditions one condition involves subjects training normally with sets of reps to failure the second condition also involves subjects training with sets of reps to failure but once completing this they had the train to limb blood flow restricted with a cuff for three to five minutes this Blood Flow Restriction wrap the metabolites in the muscle and if metabolites were additive for hypertrophy this condition should see more hypertrophy yet after eight weeks both studies found muscle growth was not enhanced when applying the Blood Flow Restriction after
• 16:30 - 17:00 training one of the papers actually found it reduced muscle growth in the women's subjects so crystallizing this section there's no strong evidence metabolic stress is a potent driver of muscle growth and it doesn't appear to have additive effects on hypertrophy [Music] I've also previously had a shorter video on muscle damage and hypertrophy although we'll mention things noted in that video we will again go into greater depth here with extra topics substantial
• 17:00 - 17:30 muscle damage occurs in the following days after performing intense exercise you're unaccustomed to delayed onset muscle soreness is considered to be a symptom of muscle damage in a scientific literature and it's common for individuals to believe soreness is a strong indicator you've stimulated a muscle well interestingly it isn't entirely clear if muscle damage is truly what independently causes delayed onset muscle soreness there are many candidates on what causes soreness and a lot more research is required before we can be certain of the relationship between damage and soreness besides
• 17:30 - 18:00 soreness it's frequently believed in muscle growth directly occurs because exercising creates micro tears in the muscle your body responds by healing the micro tears and making the muscle bigger these two videos with a combined in their 40 million views both put forth this idea but what does the literature say on the role of damage in muscle hypertrophy it appears the hypothesis that damage could stimulate hypertrophy comes from research in the 1990s it was noted that eccentric only training produces significant muscle damage but
• 18:00 - 18:30 also notable muscle hypertrophy so it was speculated damage could cause hypertrophy it was also widely believed during these years and in the subsequent years their eccentric only training is superior to concentric only training for overall muscle hypertrophy concentric only training produces much less damage nowadays the evidence is very much mixed there are actually more studies than not finding similar overall hypertrophy between eccentric and concentric only training furthermore it's essential to recognize eccentric training absolutely
• 18:30 - 19:00 involves High mechanical tension as eccentric only training involves contraction and stretch at the same time both active and passive tension will occur to high amounts some research directly links to overall tension produced during eccentric contractions to muscle hypertrophy signaling thus its entirely plausible eccentric only training is stimulating hypertrophy via tension itself and damage is just a byproduct but does this really mean muscle damage plays no role in hypertrophy in 2012
• 19:00 - 19:30 Brad schoenfeld from New York the same researcher who performed a comprehensive review on metabolic stress a year later published a comprehensive review on muscle damage and hypertrophy four parts were noted between damage and gains the first is that damage results in an inflammation response and various inflammatory cells have been linked to muscle hypertrophy the second relates to satellite cells this one requires a little bit of explaining but it's highly interesting muscle fibers have nuclei
• 19:30 - 20:00 called myonuclei and the myonuclei are crucial for directing the formation of the proteins that ultimately make muscle fibers bigger each myonuclei is believed to oversee a certain amount of space within muscle fibers term the myonuclei domain but there is a limit to the amount it can oversee call The myonuclei Domain ceiling as a muscle fiber increases in size the myonuclei domain increases until it hits its ceiling limiting further muscle fiber growth from here additional myonuclei would be
• 20:00 - 20:30 needed to enable further fiber growth this is where satellite cells come in they are found surrounding muscle fibers and Confused to muscle fibers and donate nuclei resulting in an increase in my nuclei which increases the muscle fiber growth capacity this is where damage comes into play muscle damage appears to cause a significant increase in Satellite Cell Activation so perhaps damage can ultimately increase the number of myonuclei muscle fibers have thereby meaning greater muscle fiber growth potential
• 20:30 - 21:00 the third path is that damage May potentiate igf-1 production and igf-1 is involved in signaling hypertrophy the fourth and final one is that damage causes muscle fiber swelling note this swelling isn't the pump that occurs during training rather it's swelling in the fiber days after training due to damage but the mechanisms by which the swelling could create hypertrophy are hypothesized to be the same that is the swelling activates osmo receptors that go on to promote hypertrophy yet all four of these paths have notable
• 21:00 - 21:30 problems there is conflicting evidence on the role of inflammatory cells in hypertrophy the events by which inflammatory cells are thought to contribute to hypertrophy May indeed occur in the absence of damage with satellite cells training that does not produce muscle damage can still cause significant satellite Cell Activation in fact aerobic training can activate satellite cells in data indicating muscle damage May potentiate satellite Cell Activation this may potentially be
• 21:30 - 22:00 related to repairing the muscle fiber and connective tissue damage nor increasing the number of myonuclei in fibers as for igf-1 production not all Studies have actually found damage is associated with greater igf-1 production and as discussed in the metabolic stress section several studies indicate temporary increases in anabolic hormones with training do not correlate with long-term hypertrophy finally with muscle fiber swelling also as discussed in the metabolic stress section alternative data exists implying
• 22:00 - 22:30 swelling may not be causative of hypertrophy other lines of scientific research further question the importance of muscle damage for stimulating hypertrophy a 2011 USA study assigned 14 untrained men into a pre-trained or naive group The naive group performed eccentric exercise on a leg cycle ergometer for 20 straight minutes at a somewhat hard exertion level measured using a subjective scale three times per week for 8 weeks the pre-trained group did the same thing but they had a three-week ramp up phase before their eight weeks where they gradually
• 22:30 - 23:00 acclimatize themselves to the training program should due to this acclimatization phase they ended up experiencing little amounts of damage and saunas across the training weeks whereas the naive group experienced much higher damage and soreness levels across the training weeks yet hypertrophy of the quadriceps ended up being comparable between both groups another 2016 study from Brazil found after untrained individuals performed a single training session myofibular protein synthesis expectedly increased fascinatingly
• 23:00 - 23:30 however this increase in myofibular protein synthesis did not correlate with muscle hypertrophy rather it seems it was directed towards repairing the damage induced by that single training session as the same subjects continue training for some weeks which resulted in them experiencing less and less damage as your body produces adaptations that make you resilient to muscle damage it was only then the myofibular protein synthesis increase after training sessions correlated with muscle hypertrophy rephrasing all this this
• 23:30 - 24:00 data suggests after an initial workout that produces High muscle damage the myofibular protein synthesis increase afterward is largely directed towards repairing the damage not increasing muscle size but after a few weeks of consistent training which allows the body to produce adaptations that reduce the damage experienced then the myofibular protein synthesis response is strongly directed towards increasing muscle size various lines of evidence suggest excessive muscle damage may also be
• 24:00 - 24:30 counterproductive for hypertrophy for example a 1999 USA study had men trained eccentric bicep curls with these variables and found signs of damage and swelling persisted for seven days after the session but once it subsided muscle volume actually decreased to 10 percent of what it was before training and it remained at the smaller size for numerous further weeks this might be because excessive muscle damage causes partial or total Destruction of subpopulations of muscle fibers Marathon
• 24:30 - 25:00 running has also been documented to cause significant muscle damage yet some data finds Marathon running decreases muscle fiber sizes furthermore if muscle damage had additive effects on hypertrophy we would expect using trading variables that enhance damage to produce more growth but this isn't the case higher repetitions likely cause more muscle damage but we know they are similarly effective to lower Reps for hypertrophy short rest between sets like likely cause more muscle damage but
• 25:00 - 25:30 short rest between sets of exercises recruiting large amounts of muscle masses actually sub-optimal for hypertrophy finally some individuals have speculated damage and soreness may be involved in hypertrophy based on research and antioxidant supplementation that includes things like vitamin c and e some studies but not all find that antioxidant supplementation reduces damage and soreness after training and there are some studies but not all again finding antioxidant supplementation reduces muscle growth in the long term
• 25:30 - 26:00 thus some presume this is fair evidence showing damage and soreness plays a role in hypertrophy yet this data simply isn't sufficient to prove it is directly lower damage and soreness causing the lower hypertrophy some other Factor could be involved in fact it's very possible antioxidant supplementation reduces the increase in capillaries that comes with lifting weights and this matters as these capillary increases with training seem to be important for sustaining muscle growth long term
• 26:00 - 26:30 therefore the potential reduced muscle growth with antioxidant supplementation might not be due to reduction in damage or soreness but instead may be a reduction in capillary adaptations that usually come along with training but also remember that I noted not all Studies have actually found antioxidant supplementation reduces damage soreness or long-term muscle growth so crystallizing this section there's no strong evidence muscle damage is a potent driver of muscle growth and it doesn't appear to have additive effects
• 26:30 - 27:00 on hypertrophy foreign [Music] outlined so far it appears mechanical tension is probably the primary hypertrophy stimulus there simply isn't compelling evidence that metabolic stress and muscle damage are powerful drivers of hypertrophy let us now dive deeper into what mechanical tension precisely is as this can likely help us understand why certain training produces the results it does I've come up with five depth levels to explain mechanical
• 27:00 - 27:30 tension from the simplest to the most in-depth descriptions at the first level the most simplest description is that muscle tension stimulates hypertrophy going deeper into the second level we know muscles contain muscle fibers it's the tension generated by muscle fibers that can be detected by mechanosensors which are present in and around muscle fibers once these mechanosensors detect this tension they convert it into a signaling Cascade that results in the formation of the proteins that make muscle fibers larger going deeper into
• 27:30 - 28:00 the third level how precisely do muscle fibers generate great force and what are the mechano sensors that detect this Force fibers can produce Force actively or passively through their Force generating units called sarcomas active forces occur when the myosin heads extend out from the myosin filament and attach and pull on actin filaments towards the M line passive forces occur when Titan which is actually the largest protein discovered in the human body stretches though it's
• 28:00 - 28:30 worth noting that extracellular Matrix which surrounds the muscle fiber can also produce passive forces when stretched mechanosensing candidates that can detect these forces include Costa mere related complexes that actually link the sarcomere to The extracellular Matrix filament which is a protein located at the Z discs of sarcomas Titan itself as it potentially has parts that can sense tension the myonuclei of the fibers and stretch activated ion channels interestingly the
• 28:30 - 29:00 mechanosensors that detect either active or passive forces could be different the cost of Mir related complexes and filament might only detect active forces while Titan the myonuclear of muscle fibers and stretch activated ion channels may only detect passive forces now these are just some of the candidates and more research is needed overall before we can make more definitive conclusions on mechanosensors in any case once these mechanosensors detect tension they go on to activate one of the many possible signaling
• 29:00 - 29:30 Pathways involved in forming the proteins that make muscle fibers grow ing deeper to the fourth level is clear to see during an exercise we'd want to recruit as many muscle fibers as possible and have those individual fibers Produce High respective forces yet and this is the key point to the fourth level we also want that tension to be produced for a decent duration merely having high levels of muscle fiber Recruitment and force output from the fibers for a very brief duration isn't great for stimulating hypertrophy
• 29:30 - 30:00 this is demonstrated by the fact that one rep max training that's lifting the heaviest loads you can for a single rep simply doesn't produce much if any hypertrophy despite it involving high muscle fiber Recruitment and fiber forces this is likely because the duration of tension is too short to meaningfully trigger the mechanosensors going to the deepest fifth level we so far know during an exercise we want to recruit as many fibers as possible and have those fibers Produce High forces for a sufficient duration yet and this is the key point to the fifth level this
• 30:00 - 30:30 all needs to be done within a given time window let me explain this with another example compare performing one set of a 30 second maximal isometric bench press contraction to performing 30 one second maximal isometric bench press contractions evenly spread throughout the full day both are maximal isometric bench press contractions so involve high fiber Recruitment and forces from the Vipers and both involve a total of 30 seconds of very high tension at the end of the day but which do you think is more effective for stimulating
• 30:30 - 31:00 hypertrophy probably the first one the one set of a 30 second maximal isometric bench press contraction as it involves all the tension within a given time window which is probably more favorable for triggering the meccano sensors having the duration of high Recruitment and fiber forces spread throughout the day and not in a given time window is presumably not as effective for triggering the mechano sensors optimally so we arrive at our final overview of mechanical tension during an exercise we'd want to recruit as many muscle fibers as possible and have the
• 31:00 - 31:30 individual fibers Produce High respective forces for a decent duration and this needs to be done within a given time window the forces from the fiber can be active and or passive which get detected by mechanic sensors that convert the tension and activate one of the many possible signaling Pathways involved in forming the proteins that make muscle fibers grow so during an exercise how do we ensure High mechanical tension overall many assume training with heavier loads is
• 31:30 - 32:00 the only way to achieve this indeed this is why some speculated that Blood Flow Restriction which involves using light loads isn't causing muscle growth through mechanical tension but as we alluded to this isn't a correct view of mechanical tension let's explore why the characteristics of muscle fibers generally lie across a spectrum on one end are fast twitch muscle fibers that are large High Force producing but very fatigable these fibers have the greatest growth potential as alluded to when discussing Blood Flow Restriction
• 32:00 - 32:30 Training a while back on the other end are slow twitch fibers that are small low Force producing but highly fatigue resistant these fibers don't have the greatest growth potential muscle fibers are recruited sequentially when the muscle needs to generate low forces only slow twitch fibers need to be recruited but as a muscle needs to generate progressively larger forces or as it fatigues while trying to sustain a given Force output those faster twitch muscle fibers eventually get recruited this sequential recruitment of muscle fibers
• 32:30 - 33:00 is known as henerman's size Principle as its eelwood Henneman who first discovered all this during his pioneering research in the 1960s from this its clear heavier loads as it instantly requires higher muscle forces to move the load Produce High muscle fiber Recruitment and it would only increase as you near failure also many of the individual fibers sustain relatively High forces throughout all of this lighter loads including Blood Flow Restriction Training as it initially only needs low muscle forces to move the
• 33:00 - 33:30 load would only require slow twitch fiber recruitment but the key point is that as you continue performing reps and air failure with this light load you eventually recruit those faster twitch muscle fibers many of the individual fibers sustain relatively High forces throughout all this too therefore the last few reps just before failure a weather duration of exposure to overall High mechanical tension would be similar between light and heavier loading this is more than likely why both light and heavy loads have been shown to be able
• 33:30 - 34:00 to produce similar muscle hypertrophy when reps are performed nail or two failure this is also more than likely why training nail or two failure with whatever load you're using is more favorable for hypertrophy than training further from failure now I should note very light loads even if you get nail or two failure probably won't be optimal for stimulating hypertrophy this is because two high rep numbers likely generate excessive within session Central fatigue that inhibits your ability to effectively recruit and expose those faster twitch muscle fibers to tension very heavy loads aren't the
• 34:00 - 34:30 most optimal for stimulating hypertrophy per set either as the duration of overall High mechanical tension would be too brief we alluded to this point earlier when noting how one rep max training doesn't build much muscle at all mechanical tension being the primary hypertrophy stimulus might have another training implication there's an ever increasing number of studies finding that training muscles at stretched positions is powerful for building muscle we have a whole video detailing the research behind this exercises that
• 34:30 - 35:00 train muscles in a stretched position likely involves significant contribution from both active and passive forces and this might potentially explain the greater hypertrophy myosin and actin interact to generate active forces while Titan and the surrounding extracellular Matrix 2 generate passive forces remember different mechanosensors might detect either active or passive forces so ensuring both of these are high in an exercise may have additive effects on signaling muscle growth passive forces from Titan while the
• 35:00 - 35:30 muscle is producing active forces might also be greater versus passive forces from Titan while the muscle is not producing active forces emerging evidence alludes to this you see calcium influx into the muscle fiber is what fundamentally permits myosin and actin to interact to generate active forces but these calcium ions with active tension might also interact with Titan to make it stiffer too allowing it to generate greater passive forces these greater passive forces are probably more
• 35:30 - 36:00 effective at triggering the mechanosensors this could explain why passive forces with no active tension as done when static stretching isn't very effective for stimulating hypertrophy in humans but passive forces combined with active forces as done in exercises training muscles at stretched positions are highly effective though extreme static stretching itself can probably build muscle for example this recent German study found that performing this cough stretch for one hour every day in humans did produce significant
• 36:00 - 36:30 gastrocnemius growth I should mention although I believe the evidence suggests these things about active and passive tension being additive could very much be the case otherwise I would not have detailed it it's 100 not a confirmed definitive fact further research is required to validate it but for the time being I'm comfortable speculating that what I've described may be what's going on before closing out this video I think
• 36:30 - 37:00 it's worth presenting some speculative hypertrophy models it's evident mechanical tension is the primary hypertrophy stimulus and I don't think it's completely crazy to speculate mechanical tension could literally be the sole stimulus behind hypertrophy other things like metabolic stress and muscle damage May simply be a byproduct of training opposed to this although we noted there aren't any strong categorized paths by which metabolic stress or damage promotes hypertrophy nor is there strong evidence that more of them is better or additive this
• 37:00 - 37:30 cannot definitively prove they play a zero percent role in hypertrophy perhaps both metabolic stress and muscle damage at very low levels are involved in hypertrophy with no further benefit Beyond these very low levels thus virtually all types of training pass this threshold explaining why more of these things aren't associated with great hypertrophy furthermore we cannot rule out that future research will will find some categorized path by which low levels of metabolic stress and damage relate to hypertrophy finally it is also
• 37:30 - 38:00 possible that exists other stimuli that play a small role in hypertrophy that have yet to be thoroughly examined in the literature for example some studies find training in hypoxic environments that's environments with lower levels of oxygen produces more hypertrophy than training a normoxic environments that's environments with normal oxygen levels now hypoxia and metabolic stress can be related but hypoxia itself could be a direct stimulus for gains dissociated from metabolite buildup yet it's
• 38:00 - 38:30 essential to note a number of opposing studies find no difference in muscle growth between training in hypoxic and normoxic environments making the overall link between hypoxia and hypertrophy unclear mechanical tension seems to be the primary hypertrophy stimulus there simply isn't compelling evidence metabolic stress or damage are powerful drivers of hypertrophy it's possible small amounts of metabolic stress and
• 38:30 - 39:00 damage play a role in hypertrophy and is also possible other stimuli yet to be properly assessed in the research could play a role in hypertrophy future research is needed to validate whether this is true or not recall our final overview of mechanical tension was as follows during an exercise we'd want to recruit as many muscle fibers as possible and have the individual fibers produce higher respective forces for a decent duration and this needs to be done within a given time window the forces from the fiber can be active and or passive which get detected by mechano
• 39:00 - 39:30 sensors that convert the tension and activate one of the many possible signaling Pathways involved in forming the proteins that make muscle fibers grow ultimately getting to or close to failure with a wide range of loads achieves High mechanical tension moreover it's possible that exercises that train muscles at a fairly stretched length of superior for hypertrophy since it involves both High active and passive tension as always the references to the studies mentioned in this video can be found in the description whether you're curious about reading further into anything mentioned in this video or your
• 39:30 - 40:00 skeptical of anything I've said I highly encourage you to check out any of the references I'm always up for a discussion if you disagree or want anything clarified further in the comment section all the best if you've made it here I have a free ebook you might like The Ultimate Guide to bench pressing for strength and hypertrophy with more than 100 scientific references from technique to training variables to comparisons and other fascinating science we cover it all grab it through the link in the description or comments
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