UNIVERSITY Hypertrophy Training Mechanisms of hypertrophy and application to training The Lesson •The hypertrophy stimulus •Mechanisms of hypertrophy •How a muscle contracts •Types of muscle growth •How hypertrophy mechanisms relate to training •The variables to manipulate in training Stimulus to Fatigue Overload: Acute disruption to homeostasis ie resistance training stress Adaptation: Process leading to functional improvement in performance Fatigue: reduction in the capacity to produce performance ie strength (fitness) Recovery: return to previous performance levels or better prior to disruption We want the RIGHT amount of stimulus to create a hypertrophy adaptation! Then manage fatigue to create another overloading hypertrophy stimulus again Performance Training Overload Stimulus Fitness (gains) Time Fatigue Recovery Fitness Fatigue Model What is the Hypertrophy Stimulus? Initial Stimulus > Molecular Signaling > muscle protein synthesis Initial Stimulus: 1. Mechanical Tension (Primary): mechanoreceptors within the muscle sensitive to tension magnitude and duration at the fiber level. 2. Metabolic Stress: accumulation of metabolites during training (lactate, H+, inorganic phosphates) generating fatigue 3. Muscle Damage: Disruption to muscle fiber structure All 3 occur simultaneously at varying degrees and metabolic stress and muscle damage may be more related to effects of imposed mechanical tension on fibers Potentials for Metabolic Stress and Muscle Damage Metabolic Stress Increased fiber recruitment Increased myokine production Increased cell swelling Increased GH and testosterone levels Concentric muscle contractions most energetically demanding Higher repetition training, closer to failure, BFR, Super sets, drop sets *additive effective to hypertrophy still uncertain Muscle Damage Increased inflammatory initiation Satellite cell activity Cell swelling Too much damage limits hypertrophy Eccentric muscle contraction most damaging *Side effect of tension forces from contraction Types of Hypertrophy Muscle hyperplasia: increase in muscle cell number, evidence limited and not a primary contributor to growth Myofibrillar hypertrophy: increase in size and amount of contractile elements of skeletal muscle. Sarcoplasmic hypertrophy: increase in all cellular components (ribosomes, anerobic metabolism enzymes, T-tubules, etc) Myofibrillar, fiber # increase, sarcoplasm unchanged Sarcoplasmic, sarcoplasm increases, fiber # unchanged How Does a Muscle Produce Tension/Contract? Muscle contracts (shortens and lengthens) by sliding filaments (actin and myosin) binding together and pulling the sarcomere closer together Motor units are the nerve cells and muscle fibers they innervate. You have small and large motor units that can innervate 2-3 fibers or up to 1000s of fibers. What Determines Level of Tension in a Muscle? More External Resistance DOES NOT mean more internal tension 1. Size Principle: Recruit low and high threshold motor units to have all fibers exposed to tension. The motor units are activated in order from small (low threshold) to large (high threshold) depending on the amount of force needed and rate of force. “Henneman’s Size Principle”. 2. Force-Velocity Relationship: The fibers then must be contracted at highest forces possible which also means slow velocities as slow velocities allow for more binding of actin and myosin filaments 3. Length-tension Relationship: muscles produce more force at certain lengths. More force is produced at longer muscle length. Long muscle lengths also add a passive force from the “stretch tension” add to the active tension of a muscle contracting. 4. Internal moment arm: The leverage of a muscle on a joint determines degree of force needed to create torque at the joint. 5. Fatigue: Causes early recruitment of high threshold motor units, reduces contraction ability of fibers requiring unfatigued fibers to contribute to force production. How Do You Create High Tensions Lifting Weights? Hard sets! A set must be very challenging and close to muscular failure to recruit high threshold motor units (HTMU) and maximal tension via slow velocities. Heavy loads >85% (1-5RM) will recruit HTMU early in the set and all reps will be stimulating via high tension Light (15+ 1RM ) and moderate (6-15RM) loads will recruit HTMU later in the set as fatigue is generated and more fibers must contribute to keep muscle contraction occurring. So, the later reps will be more stimulating and early reps not as much. This gives notion to the idea of “effective” or “stimulating reps” One set provides a level of magnitude of tension that increases as we approach muscular failure and the muscle fibers have a longer time duration of exposure to that tension. Is There a Dosage of Tension For Growth? Hypertrophy RATE OF GROWTH Atrophy No Sets Optimal Sets Too Many Sets Volume Dosage Inverse U shaped Curve Programming Variables for Tension Stimulus Volume: Dosage of stimulus = # of hard sets Intensity: Degree of stimulus magnitude = % 1 rep max and proximity to failure Frequency: Organization of stimulus = training split Exercise Selection: Regional stimulus= movement pattern choice and muscles it involves Exercise execution and tempo: Focus of stimulus = way in which you move during a repetition and intention Exercise order: Stimulus sequence and effectiveness = order of movements Rest periods: Removal of stimulus= time between sets Summary The main driving mechanism for hypertrophy is mechanical tension Mechanical tension can be created with heavy and light load sets taken near or at proximity to muscular failure A certain number of “hard sets” is needed to optimize hypertrophy Metabolic stress and muscle damage may be additive factors to hypertrophy, but may also only be resultant factors of mechanical tension Programming variables for hypertrophy revolve around how we will apply tension (stimulus) in an organized manner. Let’s Program! Reference Encyclopedia Britannica. striated muscle; human biceps muscle. Available at: https://www.britannica.com/science/muscle#/media/1/398553/4693 9 Access Date: July 28th 2020. Schoenfeld B. Science and Development of Muscle Hypertrophy. Champaign, IL: Human Kinetics; 2021. Beardsley, C. Hypertrophy: Muscle fiber growth caused by mechanical tension. Strength and Conditioning Research Limited, 1 edition; 2019.
