\nOnline Courses: Contact us at seminars@crossfit.com \nCrossFit Games Support: Reach out to support@crossfitgames.com \nFor T-Shirt Purchase: Check your inbox for instructions from customer@trackorder.site
\n","orderHistoryHeadlineText":"Order History","orderHistoryLabelText":"Order History","viewOrderDetailsText":"View order details"},"resourcesKickerText":"Resources","rulebookLabelText":"Rulebook","rulebookLinkUrl":"https://games.crossfit.com/rules","preferenceCenter":{"checkAllText":"Check All","emailCommunicationBodyText":"Select which lists you would like to receive communication from","emailCommunicationHeadlineText":"Email Communication","newsletters":[{"bodyText":"Every day since 2001, CrossFit has published a Workout of the Day for new CrossFit athletes, seasoned veterans, and anyone in between. Subscribe to Workout of the Day emails, and you'll receive CrossFit programming in a three-days-on, one-day-off, two-days-on, one-day-off cadence.","brazeGroupId":"d68551b9-ac7e-437e-bfd2-d225702413cc","headlineText":"Workout of the Day"},{"bodyText":"Get inspired with the latest and/or trending articles, stories, videos, and podcasts focused on the CrossFit community and methodology.","brazeGroupId":"1bfd806e-efe3-404d-9980-c8f38c39490b","headlineText":"What's Trending"},{"bodyText":"Be the first to know when official updates and announcements are released from CrossFit HQ.","brazeGroupId":"cb28cb07-ca09-4739-b73b-7413f95a4892","headlineText":"Updates and Announcements from CrossFit HQ"},{"bodyText":"This subscription is for those interested in announcements, updates, and stories about the CrossFit Games season and its competitors. ","brazeGroupId":"e56abfcc-c940-482d-879c-eed93958cbbe","headlineText":"CrossFit Games"},{"bodyText":"This monthly newsletter includes important CrossFit Games competition season updates, resources, and tips. It is intended for competitive athletes but is open to anyone interested in learning more about the CrossFit Games season.","brazeGroupId":"fce49890-9b3c-4e1f-9e06-1bd06cd696a3","headlineText":"The Hopper"},{"bodyText":"The Professional Coach provides a wealth of articles, media, and webinar opportunities that cover all aspects of coaching, including best practices, real-world coaching application, scaling, methodology, nutrition, CEU opportunities, and more. With contributions from experts inside and outside the CrossFit space, this twice-monthly newsletter is the ultimate tool for any coach looking to improve their skills and knowledge. This newsletter is exclusively available to those who hold a Level 1 Certificate or higher. ","brazeGroupId":"653207fb-9734-44c9-a988-23eb18142529","headlineText":"The Professional Coach"},{"bodyText":"The Affiliate Update is a newsletter for CrossFit affiliate owners and includes upcoming event details, business and marketing resources, and general updates from CrossFit HQ. The Affiliate Update is only available to licensees of record (LOR).","brazeGroupId":"1d3e4c63-f03f-4b61-8453-1fbb186ae27e","headlineText":"CrossFit Affiliate Update"},{"bodyText":"An email series for learning what it takes to open and run a successful CrossFit gym","brazeGroupId":"6ab8a53a-167c-4c74-b5ea-3a06cb857068","headlineText":"Interested in Affiliation"},{"bodyText":"CAP is a weekly email available exclusively to affiliate owners that provides comprehensive class plans, resources, and educational tips to help coaches deliver an exceptional experience to their members.","brazeGroupId":"ba7e977e-ec76-41e3-8465-158d38167ed6","headlineText":"CrossFit Affiliate Programming (CAP)"},{"bodyText":"CrossFit Health serves as a vital bridge connecting the realms of fitness and healthcare. Committed to delivering valuable insights, CrossFit Health harnesses the expertise of renowned professionals from the health, wellness, and CrossFit communities. Our mission is to educate individuals on the transformative potential of CrossFit as a powerful lifestyle intervention, ultimately optimizing health outcomes.","brazeGroupId":"a9c5a8a4-df0a-4b0c-acb6-e9b4631fc00c","headlineText":"CrossFit Health"},{"bodyText":"Be the first to know when new products are added to the Official CrossFit Store and receive special offers and discounts conveniently delivered directly to your inbox.","brazeGroupId":"905db0be-a3c8-4f5b-8903-536a04cb0a40","headlineText":"The CrossFit Store"},{"bodyText":"This subscription is for companies interested in on-site event activations and vendor booths at the CrossFit Games and other events hosted by CrossFit.","brazeGroupId":"92fa7fe8-262a-4d6a-9b0d-9fcc8cc17e7d","headlineText":"Interested in On-Site Event Activations / Vendor Booths"},{"bodyText":"Get alerted for upcoming courses. CrossFit courses and certifications are open to individuals and trainers seeking to improve their health and fitness through effective training and nutritional strategies.","brazeGroupId":"dd1ee7a4-2ef5-477b-affb-77347ce81684","headlineText":"Interested in Finding a Course Near You"}],"preferenceCenterHeadlineText":"Newsletter Preferences","preferenceCenterLabelText":"Newsletter Preferences","uncheckAllText":"Uncheck All"}}},"pages":{"breadcrumbs":{"links":[{"text":"Essentials","url":"/essentials"},{"text":"Muscle Basics, Part 3: Hypertrophy","url":"#"}]},"contentPublishDate":"20190911","contentType":"article","commentTopics":[{"title":"Muscle Basics, Part 3: Hypertrophy","topicId":"article.20190828154126257"}],"title":"Muscle Basics, Part 3: Hypertrophy","topicId":"article.20190828154126257","socialMetaData":{"title":"Muscle Basics, Part 3: Hypertrophy","image":"https://www.crossfit.com/wp-content/uploads/2019/09/04084039/CF_Hyperthrophy_r2-th.png"},"categoryLinks":[{"text":"Essentials","url":"/essentials"},{"text":"Anatomy & Physiology","url":"/essentials/anatomy-physiology"},{"text":"update","url":"/update"}],"path":"/essentials/muscle-basics-part-3-hypertrophy","components":[{"name":"ArticleHeader","props":{"topicId":"article.20190828154126257","date":"20190911","categoryLinks":[{"text":"Essentials","url":"/essentials"},{"text":"Anatomy & Physiology","url":"/essentials/anatomy-physiology"},{"text":"update","url":"/update"}],"articleDate":"20190911","authorName":"CrossFit","bylineText":"By","headlineText":"Muscle Basics, Part 3: Hypertrophy"}},{"name":"TextBlock","props":{"children":"
The physiological process of increasing the size of an entire muscle is known as hypertrophy. Human muscle has a huge capacity for hypertrophy and is able to increase in size by 200% or more. A person maintains this ability throughout his or her lifespan.
\n
Hypertrophy is considered a fairly straightforward process that adds thickness to muscle. Adding girth to muscle is also known as increasing cross-sectional area. Muscles get bigger in circumference; despite the claims from some exercise systems, muscles do not get bigger by becoming longer (other than in pediatric growth) since the distance between skeletal attachments cannot be extended by exercise.
\n
Figure 1: Muscle hypertrophy
\n
Although conceptually simple, the precise mechanism behind muscle growth largely is not understood. We know a good amount about the individual cellular players. However, the ways in which those players interact to contribute to cell and muscle growth are often debated to no resolution because there is very little quality research that provides definitive answers. In fact, there are numerous and differing methods for measuring hypertrophy and similarly many different laboratory models used to mimic real-world hypertrophy. These various methods and models create discord within the data.
\n
A basic concept with robust support is that in order to increase muscle cross-sectional area, individual cells within the muscle enlarge and cumulatively increase the size of the complete muscle (1). Cellular hypertrophy results in whole-muscle hypertrophy.
\n
A secondary route to muscle hypertrophy is through hyperplasia, where one muscle cells divides into two (basically mitosis) or a new cell is created from a progenitor cell. Hypertrophy through this mechanism occurs via increased cell number. Research on hyperplasia is not strong — if it does occur, it may be only a transient step in satellite cell fusion into an existing cell, or at best, a contributor of only about 3% toward overall muscle hypertrophy.
\n
What Gets Added?
\n
When we look at the chemical composition of whole muscle, we find there are four basic groups of components: (1) water, (2) cellular proteins, (3) carbohydrate and lipids, and (4) connective tissue proteins. Adding to any of these components can positively affect muscle hypertrophy.
\n
Figure 2: The four components of a muscle
\n
We see a similar distribution of components at the level of the individual muscle cell. If we look at which proteins are present inside individual muscle cells, we see a separation into three categories: (1) myofibrillar proteins, such as myosin, actin, titin, and more than a dozen more; (2) sarcoplasmic proteins, such as creatine kinase, lactate dehydrogenase, pyruvate kinase, myoglobin, and about 80 more; and (3) mitochondrial proteins, such as citrate synthase, ATP-synthase, cytochrome-C, and many more.
\n
The composition of the increase in cellular mass is dependent on the type of training performed. Higher-intensity training is most likely to result in myofibrillar hypertrophy, whereas architectural and contractile protein additions provide the lion’s share of increased muscle mass. Lower-intensity and exhaustive exercise will most likely result in sarcoplasmic hypertrophy, where the added mass results from increased intracellular energy stores, increased presence of metabolic chemicals, increased mitochondrial content, and augmentation of other metabolic elements. It is important to note that this is not a black-and-white, either-or circumstance — myofibrillar and sarcoplasmic component additions occur in both types of hypertrophy, though there tends to be a bias toward one or the other end of the continuum. It is also important to understand the concepts of myofibrillar and sarcoplasmic hypertrophy are based upon conjecture. The weakness of the body of evidence related to hypertrophic mechanisms allows no more.
\n\n
Reference
\n\n
Gollnick, P.D., B.F. Timson, R.L. Moore, and M. Riedy. Muscular enlargement and number of fibers in skeletal muscles of rats. Journal of Applied Physiology. 50(1981): 936–943.
\n","hideText":"Hide","status":"active","type":"alert_banner","userCanHide":"no"},"header":{"desktopLinks":[{"below":[{"id":93961,"parent":"93960","target":"_self","text":"What is CrossFit?","url":"/what-is-crossfit"},{"id":93962,"parent":"93960","target":"_self","text":"Find a Gym","url":"/map"}],"id":93960,"parent":"0","target":"_self","text":"Getting Started","url":"/what-is-crossfit"},{"below":[{"id":93964,"parent":"93963","target":"_self","text":"About","url":"/education/about"},{"id":93966,"parent":"93963","target":"_self","text":"Level 1 Certificate Course","url":"/certificate-courses/level-1"},{"id":93965,"parent":"93963","target":"_self","text":"Explore All Courses","url":"/education/explore-courses"},{"id":109033,"parent":"93963","target":"_self","text":"Private Courses","url":"/private-course/"},{"id":109034,"parent":"93963","target":"_self","text":"Military Resources","url":"/army-ignited"},{"id":93967,"parent":"93963","target":"_self","text":"Coaching Resources","url":"/education/resources"}],"id":93963,"parent":"0","target":"_self","text":"Courses","url":"/education/about"},{"below":[{"id":95951,"parent":"93968","target":"_self","text":"Workout of the Day","url":"/wod"},{"id":93969,"parent":"93968","target":"_self","text":"Explore Workouts","url":"https://www.crossfit.com/workout"},{"id":101892,"parent":"93968","target":"_self","text":"Hero Workouts","url":"https://www.crossfit.com/heroes/"},{"id":93970,"parent":"93968","target":"_self","text":"Movements","url":"https://www.crossfit.com/crossfit-movements"}],"id":93968,"parent":"0","target":"_self","text":"Workouts","url":"https://www.crossfit.com/workout"},{"id":93971,"parent":"0","target":"_self","text":"Learn","url":"/media"},{"id":93972,"parent":"0","target":"_blank","text":"Games","url":"https://games.crossfit.com"},{"id":105467,"parent":"0","target":"_blank","text":"Store","url":"https://store.crossfit.com/?utm_source=owned&utm_medium=nav&utm_campaign=main"},{"id":106137,"parent":"0","target":"_self","text":"Open A Gym","url":"/open-crossfit-gym"}],"mobileLinks":[{"text":"Open a CrossFit Gym"},{"text":"Browse","links":[{"below":[{"id":93961,"parent":"93960","target":"_self","text":"What is CrossFit?","url":"/what-is-crossfit"},{"id":93962,"parent":"93960","target":"_self","text":"Find a Gym","url":"/map"}],"id":93960,"parent":"0","target":"_self","text":"Getting Started","url":"/what-is-crossfit"},{"below":[{"id":93964,"parent":"93963","target":"_self","text":"About","url":"/education/about"},{"id":93966,"parent":"93963","target":"_self","text":"Level 1 Certificate Course","url":"/certificate-courses/level-1"},{"id":93965,"parent":"93963","target":"_self","text":"Explore All Courses","url":"/education/explore-courses"},{"id":109033,"parent":"93963","target":"_self","text":"Private Courses","url":"/private-course/"},{"id":109034,"parent":"93963","target":"_self","text":"Military Resources","url":"/army-ignited"},{"id":93967,"parent":"93963","target":"_self","text":"Coaching Resources","url":"/education/resources"}],"id":93963,"parent":"0","target":"_self","text":"Courses","url":"/education/about"},{"below":[{"id":95951,"parent":"93968","target":"_self","text":"Workout of the Day","url":"/wod"},{"id":93969,"parent":"93968","target":"_self","text":"Explore Workouts","url":"https://www.crossfit.com/workout"},{"id":101892,"parent":"93968","target":"_self","text":"Hero Workouts","url":"https://www.crossfit.com/heroes/"},{"id":93970,"parent":"93968","target":"_self","text":"Movements","url":"https://www.crossfit.com/crossfit-movements"}],"id":93968,"parent":"0","target":"_self","text":"Workouts","url":"https://www.crossfit.com/workout"},{"id":93971,"parent":"0","target":"_self","text":"Learn","url":"/media"},{"id":93972,"parent":"0","target":"_blank","text":"Games","url":"https://games.crossfit.com"},{"id":105467,"parent":"0","target":"_blank","text":"Store","url":"https://store.crossfit.com/?utm_source=owned&utm_medium=nav&utm_campaign=main"},{"id":106137,"parent":"0","target":"_self","text":"Open A Gym","url":"/open-crossfit-gym"}]}],"brandLinks":[{"id":93974,"parent":"0","target":"_self","text":"Open a CrossFit Gym","url":"/open-crossfit-gym"}],"loggedInMenu":[{"id":72863,"parent":"0","target":"_self","text":"Manage Account","url":"https://www.crossfit.com/dashboard"},{"id":72864,"parent":"0","target":"_self","text":"Competition Dashboard","url":"https://games.crossfit.com/manage-competition/athlete"}]},"footer":{"mainLinks":[{"below":[{"id":9764,"parent":"511","target":"_self","text":"What Is CrossFit?","url":"/what-is-crossfit"},{"id":9765,"parent":"511","target":"_self","text":"Get Started","url":"/get-started"},{"id":45861,"parent":"511","target":"_self","text":"Workouts","url":"/workout/"},{"id":45862,"parent":"511","target":"_self","text":"Movements","url":"/essentials/movements"},{"id":1741,"parent":"511","target":"_self","text":"FAQ","url":"/faq"},{"id":90183,"parent":"511","target":"_self","text":"Help Center","url":"https://crossfit.my.site.com/Support/s/"},{"id":45103,"parent":"511","target":"_self","text":"Careers","url":"/careers/"}],"id":511,"parent":"0","target":"_self","text":"About CrossFit","url":"#"},{"below":[{"id":45864,"parent":"45863","target":"_self","text":"Courses Near You","url":"/courses-near-you/"},{"id":45865,"parent":"45863","target":"_self","text":"Certificate Courses","url":"/certificate-courses/"},{"id":45866,"parent":"45863","target":"_self","text":"Certifications","url":"/certifications/"},{"id":45868,"parent":"45863","target":"_self","text":"Online Courses","url":"https://www.crossfit.com/online-courses"}],"id":45863,"parent":"0","target":"_self","text":"Education","url":"#"},{"below":[{"id":45870,"parent":"45871","target":"_self","text":"Open a CrossFit Gym","url":"/open-crossfit-gym"},{"id":45884,"parent":"45871","target":"_self","text":"Field Leaders","url":"/field-leaders"},{"id":90935,"parent":"45871","target":"_self","text":"Global Mentor Program","url":"/global-mentor-program/"},{"id":93982,"parent":"45871","target":"_self","text":"Affiliate Portal","url":"https://affiliate.crossfit.com/tools/"}],"id":45871,"parent":"0","target":"_self","text":"Affiliates","url":"#"},{"below":[{"id":16638,"parent":"45875","target":"_self","text":"Find a Trainer","url":"https://trainerdirectory.crossfit.com/"},{"id":45876,"parent":"45875","target":"_self","text":"Scholarship Program","url":"/scholarship-program-inquiry"},{"id":45877,"parent":"45875","target":"_self","text":"Foundation","url":"/foundation"},{"id":104122,"parent":"45875","target":"_self","text":"CrossFit Medical Society","url":"https://www.crossfitmedicalsociety.com/"}],"id":45875,"parent":"0","target":"_self","text":"Community","url":"#"},{"below":[{"id":45881,"parent":"45879","target":"_self","text":"About the Games","url":"https://games.crossfit.com/"},{"id":45880,"parent":"45879","target":"_self","text":"Leaderboard","url":"https://games.crossfit.com/leaderboard/games/2022?division=2"},{"id":45882,"parent":"45879","target":"_self","text":"Schedule","url":"https://games.crossfit.com/games/schedule?_ga=2.142929340.802559833.1690817966-401013740.1685640771"},{"id":91727,"parent":"45879","target":"_self","text":"Workouts","url":"https://games.crossfit.com/workouts/games/2023"}],"id":45879,"parent":"0","target":"_self","text":"The CrossFit Games","url":"#"}],"brandLinks":[],"socialLinks":[{"id":66715,"parent":"0","target":"_self","text":"facebook","url":"https://www.facebook.com/crossfit"},{"id":66716,"parent":"0","target":"_self","text":"twitter","url":"https://twitter.com/CrossFit"},{"id":66717,"parent":"0","target":"_self","text":"instagram","url":"https://www.instagram.com/crossfit/"},{"id":66718,"parent":"0","target":"_self","text":"youtube","url":"https://www.youtube.com/channel/UCtcQ6TPwXAYgZ1Mcl3M1vng"}],"contactLinks":[{"id":531,"target":"_self","text":"Careers","url":"https://www.crossfit.com/jobs"},{"id":532,"target":"_self","text":"Contact Us","url":"https://www.crossfit.com/contact-us"}],"legalLinks":[{"id":533,"parent":"0","target":"_self","text":"Terms & Conditions","url":"https://www.crossfit.com/terms-and-conditions"},{"id":534,"parent":"0","target":"_self","text":"Privacy Policy","url":"https://www.crossfit.com/privacy-policy"},{"id":10717,"parent":"0","target":"_self","text":"Cookie Policy","url":"https://www.crossfit.com/cookie-policy"},{"id":57312,"parent":"0","target":"_self","text":"Disclaimer","url":"https://www.crossfit.com/disclaimer"},{"id":10883,"parent":"0","target":"_self","text":"Contact Us","url":"https://www.crossfit.com/contact-us"},{"id":45883,"parent":"0","target":"_self","text":"Report IP Theft","url":"https://www.crossfit.com/iptheft"}]},"locationPages":{"simpleTiles":{"cards":[{"bodyText":"CrossFit offers a results-based, community-driven approach to functional training that helps you build strength and improve your health—over your lifetime.","headlineText":"Functional Fitness for Everyday Life","icon":{"alt":"Lifting Icon","url":"https://www.crossfit.com/wp-content/uploads/2024/04/26123658/crossfit-icon-workout-barbell-overhead-press.svg"}},{"bodyText":"Stay motivated with our community of coaches and members, who support your goals through approachable group training classes, helping you stay accountable and excited for each session.","headlineText":"Community Support and Motivation","icon":{"alt":"Heart Icon","url":"https://www.crossfit.com/wp-content/uploads/2024/04/26123700/crossfit-icon-heart.svg"}},{"bodyText":"Coaches scale class workouts to your fitness level to help you achieve your strength building goals.","headlineText":"Tailored to Your Fitness Levels","icon":{"alt":"Graph Icon","url":"https://www.crossfit.com/wp-content/uploads/2024/04/26123649/crossfit-icon-levels.svg"}},{"bodyText":"CrossFit coaches are experienced and trained to provide well-rounded and personalized guidance to individuals with varying fitness levels and goals.","headlineText":"Industry Certified Coaches","icon":{"alt":"Certification Icon","url":"https://www.crossfit.com/wp-content/uploads/2024/04/26123656/crossfit-icon-check-badge.svg"}}],"headlineText":"Build Strength for a Fuller Life"},"gymFinderPromo":{"bodyText":"Contact CrossFit to start your fitness journey. We’ll connect you to the closest gym in your area.","headlineText":"Get Started today","image":{"alt":"Man Lifting Barbell","sizes":{"1536x1536":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","1536x1536Height":512,"1536x1536Width":768,"2048x2048":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","2048x2048Height":512,"2048x2048Width":768,"hero":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","heroHeight":512,"heroWidth":768,"heroLarge":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","heroLargeHeight":512,"heroLargeWidth":768,"large":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","largeHeight":512,"largeWidth":768,"medium":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","mediumHeight":512,"mediumWidth":768,"mediumLarge":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1.jpeg","mediumLargeHeight":512,"mediumLargeWidth":768,"small":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1-300x200.jpeg","smallHeight":200,"smallWidth":300,"thumbnail":"https://www.crossfit.com/wp-content/uploads/2018/12/13135656/aa6daff2983e555e3688654515568d25-1-768x512-1-150x150.jpeg","thumbnailHeight":150,"thumbnailWidth":150}},"links":[{"link":{"priority":"primary","text":"Find a Gym","url":"/map"}},{"link":{"priority":"secondary","text":"What Is CrossFit?","url":"/what-is-crossfit"}}]},"locationCourseCards":{"courseLinkText":"Register Now","findCourseLink":{"text":"Find More Courses","url":"https://www.crossfit.com/courses-near-you"},"headerText":"Courses Near You","seminarType":["level-one","level-two"]},"socialSharing":{"facebook":{"description":"Jump into CrossFit in [City Name]! Our certified coach led group training and fitness classes feature strength, conditioning, and functional workouts.","title":"CrossFit Gyms in [State] | Functional Fitness Classes & Group Training"}}}},"user":{},"coachCertifications":{}}
The physiological process of increasing the size of an entire muscle is known as hypertrophy. Human muscle has a huge capacity for hypertrophy and is able to increase in size by 200% or more. A person maintains this ability throughout his or her lifespan.
Hypertrophy is considered a fairly straightforward process that adds thickness to muscle. Adding girth to muscle is also known as increasing cross-sectional area. Muscles get bigger in circumference; despite the claims from some exercise systems, muscles do not get bigger by becoming longer (other than in pediatric growth) since the distance between skeletal attachments cannot be extended by exercise.
Figure 1: Muscle hypertrophy
Although conceptually simple, the precise mechanism behind muscle growth largely is not understood. We know a good amount about the individual cellular players. However, the ways in which those players interact to contribute to cell and muscle growth are often debated to no resolution because there is very little quality research that provides definitive answers. In fact, there are numerous and differing methods for measuring hypertrophy and similarly many different laboratory models used to mimic real-world hypertrophy. These various methods and models create discord within the data.
A basic concept with robust support is that in order to increase muscle cross-sectional area, individual cells within the muscle enlarge and cumulatively increase the size of the complete muscle (1). Cellular hypertrophy results in whole-muscle hypertrophy.
A secondary route to muscle hypertrophy is through hyperplasia, where one muscle cells divides into two (basically mitosis) or a new cell is created from a progenitor cell. Hypertrophy through this mechanism occurs via increased cell number. Research on hyperplasia is not strong — if it does occur, it may be only a transient step in satellite cell fusion into an existing cell, or at best, a contributor of only about 3% toward overall muscle hypertrophy.
What Gets Added?
When we look at the chemical composition of whole muscle, we find there are four basic groups of components: (1) water, (2) cellular proteins, (3) carbohydrate and lipids, and (4) connective tissue proteins. Adding to any of these components can positively affect muscle hypertrophy.
Figure 2: The four components of a muscle
We see a similar distribution of components at the level of the individual muscle cell. If we look at which proteins are present inside individual muscle cells, we see a separation into three categories: (1) myofibrillar proteins, such as myosin, actin, titin, and more than a dozen more; (2) sarcoplasmic proteins, such as creatine kinase, lactate dehydrogenase, pyruvate kinase, myoglobin, and about 80 more; and (3) mitochondrial proteins, such as citrate synthase, ATP-synthase, cytochrome-C, and many more.
The composition of the increase in cellular mass is dependent on the type of training performed. Higher-intensity training is most likely to result in myofibrillar hypertrophy, whereas architectural and contractile protein additions provide the lion’s share of increased muscle mass. Lower-intensity and exhaustive exercise will most likely result in sarcoplasmic hypertrophy, where the added mass results from increased intracellular energy stores, increased presence of metabolic chemicals, increased mitochondrial content, and augmentation of other metabolic elements. It is important to note that this is not a black-and-white, either-or circumstance — myofibrillar and sarcoplasmic component additions occur in both types of hypertrophy, though there tends to be a bias toward one or the other end of the continuum. It is also important to understand the concepts of myofibrillar and sarcoplasmic hypertrophy are based upon conjecture. The weakness of the body of evidence related to hypertrophic mechanisms allows no more.
Reference
Gollnick, P.D., B.F. Timson, R.L. Moore, and M. Riedy. Muscular enlargement and number of fibers in skeletal muscles of rats. Journal of Applied Physiology. 50(1981): 936–943.
Muscle Basics, Part 3: Hypertrophy