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Muscle Morphology & the Benefits of Strength Training

    zenith humans strength training

    Strength Training

    Strength training to improve muscular strength can be defined by exercise prescription characteristics. According to Garber et al. (2011) characteristics include high intensity (>80% 1RM), rep range (1-6 reps), number of sets (4-6 sets), tempo (slow-medium lifting speed), and recovery time (3-5 minutes). Notably, it is intensity that determines the constraints for the other characteristics. Lifting a heavier weight means you don’t perform as many reps, reps are performed slower, and you need more time to recover before you can reproduce that intensity for the required number of sets..

    It is generally accepted that if you lift heavy things, you get better at it. Hence you get stronger and is a well-documented benefit of strength training. Becoming stronger makes your daily life easier for one very simple reason. That is, you are stronger relative to your own body mass and the mass of the objects in your environment. So, walking the stairs is easier, riding a bike into strong wind is easier, jogging and running is easier, handling objects and performing manual labour is easier, etc. But what occurs in our muscles to allow this change in strength? Increase in muscle size is usually the answer I get, and this is superficially correct. But what is the mechanism of increased muscle size and the increase in strength?

    Muscle morphology

    Most people will associate increased muscle size with hypertrophy, which is a term used to describe a change in muscle morphology. However, muscle morphology is not a term most people are accustomed to hearing. Muscle morphology encompasses changes to muscle volume and cross-sectional area. This is attributed to changes in muscle architecture characteristics (how a muscle is shaped and structured), muscle fascicle pennation angle, muscle fascicle length (determined by the number of sarcomeres in series), and the number of muscle fascicles attached to the superficial and deep aponeurosis in parallel.

    Muscle shape, fusiform, pennate, circular, convergent etc provide different advantages for force production, and would serve as a separate article for discussion and will not be discussed in depth here. Briefly, an illustration of a bipennate muscle featuring the appearance of a feather, is presented in Figure 1. Pennate muscles allow for more fibres to be attached to tendon, increasing the cross-sectional area of contractile tissue, and providing a greater capacity for force production. This now provides scope for discussion about muscle cross-sectional area (CSA), because CSA is measured a few different ways: anatomical CSA (ACSA), physiological CSA (PCSA), and effective physiological CSA (EPCSA). See Figure 1.

    Figure 1. Characteristics of Muscle Morphology and Cross-sectional Area (cm2).

    zenith humans strength training

    Research

    Researchers recently described how muscle morphology differs between people who have not strength trained for longer than 18 months and people who have strength trained for 3-5 years (Maden-Wilkinson et al., 2020). The outcomes reported were made by measuring muscle morphology using MRI and ultrasound, maximum isometric voluntary torque of knee extension using a dynamometer, moment arm, and specific tension and compared these measurements between untrained and trained participants.

    The study provided key findings that concluded the PCSA was 41% greater in trained participants, indicating that strength trained participants had more fascicles in parallel, and explained much of the 60% greater maximum voluntary torque between groups. Importantly, an 11% greater fascicle length was identified (more sarcomeres in series). Additionally, 13% greater pennation angle contributed to the differences in PCSA between untrained and trained participants.

    These key characteristics of fascicle length (sarcomeres in series) and sarcomeres in parallel (more muscle fibres or thicker muscle fibres), which contribute to a greater total PCSA, describe how strength training changes muscle morphology over time and produces increases in strength (capacity for force production). PCSA describes the amount of contractile muscle tissue that is responsible for mechanical force production. The figure below helps to illustrate the findings reported by Maden-Wilkinson et al. (2020).

    Figure 2. Changes to muscle morphology following long term strength training

    Important

    An important concept to recall is the stimulus required to elicit these adaptions defined by the prescription characteristics at the beginning of this brief article, namely the high intensities associated with strength training. Because of the muscle morphology differences between people and the subsequent ability to produce force, it is important that everyone undertakes strength training, continues to strength train, and importantly trains at a suitable level to achieve optimal individual outcomes.

    One understated benefit of strength training is your ability to produce force readily transfers to other training modes. These other training modes include hypertrophy training (body building), power training (athletic performance), endurance training (sustained work), and sporting performance (application of force and power specific to actions required), and directly improves the outcomes of these other training modes.

    Final words

    To summarise, this post has defined strength training, described how your body changes with strength training, highlighted that increases in strength are earned (both exposure to a stimulus and sustained exposure over time), and identified some of the many benefits of strength training, which are increased muscle volume (PCSA) = increased capacity for mechanical force production = easier daily living.

    At Zenith Humans we strive to provide access to evidence-based exercise prescription to help you achieve your goals. If improving your strength is now one of your goals, get started with one of our Strong & Stronger programs today. Programs are scaled to suit your level of experience (noviceintermediateadvanced).

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