EXSC216 Resistance Training: Science & Application – Introduction 2020 PDF

EXSC216 Resistance Training: Science & Application – Introduction Semester 2, 2020  Content Introduction Part 4 Part 1 – Resistance Training – Motor Units Adaptations...

EXSC216 Resistance Training: Science & Application – Introduction Semester 2, 2020  Content Introduction Part 4 Part 1 – Resistance Training – Motor Units Adaptations Neural – Microscopic structure of muscle Part 5 – Muscular contraction – Resistance Training Adaptations Part 2 Fibre type – Fibre Types Endocrine – Contraction Types Other changes Part 3 Part 6 – Resistance Training – Terminology & Practical Adaptations Concepts Morphological Part 1: Anatomical Concepts ·MOTOR UNITS ·MICROSCOPIC STRUCTURE OF MUSCLE ·MUSCULAR CONTRACTION  Skeletal Muscle Motor Unit A motor unit consists of a motor neuron and the muscle fibres it innervates – Normally several hundred fibres per motor unit Figure 1.4  Skeletal Muscle Motor Unit The following video (0:00 - ~5:30) describes the anatomy of a motor unit https://www.youtube.com/watch?v=vXb0ZvkFkS8  How Do Nervous Impulses Cause Muscle to Contract? The following video demonstrates how a nervous impulse initiates a muscle contraction https://www.youtube.com/watch?v=lRJd56BCidg Microscopic Structure of Muscle Sliding Filament Theory  Actin & Myosin in Muscular Contraction https://www.youtube.com/watch?v=zopoN2i7 ALQ https://www.youtube.com/watch?v=aUc3h6L vdJ4  3D multifilament model of a sarcomere Location of single cross bridge across LT curve Overlap across LT curve LT curve for skeletal muscle Short Long Williams et. al.; 2013  Contracting muscle maintains a constant volume (i.e. when it shortens it expands radially) This means distance (lattice spacing) between actin & myosin filaments must increase Change in lattice spacing play important role in L-T curve of contracting muscle Increase in lattice spacing means myosin head is further from binding site and must diffuse over greater distance to bind & produce a different force vector – Pull at sharper angle over greater distance – Responsible for 20-50% of change in F seen between sarcomere lengths of 1.4 and 3.5μm  Muscle Contraction Molecular Mechanism Part 2: Fibre Types and Contraction Types · CLASSIFICATION METHODS · FIBRE TYPES · CONTRACTION TYPES  Muscle Fibre Typing Initial classification based on whole muscle speed of shortening (i.e. fast or slow). Corresponded with morphological difference of “fast” muscles appearing white and “slow” muscles appearing red (high myoglobin & capillary content) Histological analysis showed correlation between myosin ATPase activity and speed of shortening This led to initial classification of Type I (slow) and Type II (fast) Muscle fibres typed using 3 methods – Histochemical staining for myosin ATPase – Myosin heavy chain isoform identification – Biochemical identification of metabolic enzymes  Myosin ATPase Staining Myosin ATPase rates 2-3 times greater in fast fibres Fibres are separated based on staining intensities due to pH sensitivity Originally, fibres classified as type IA, IIA, IIB Advances in staining techniques have added additional types Myosin Heavy Chain Identification Identification of myosin heavy chain isoforms also used for classification Myosin heavy chains are the motor protein of the thick muscle filaments Identified through histochemical analysis Vizzaccaro, Elisa & Terracciano, Chiara & Rastelli, Emanuele & Massa, Roberto. (2017). Aquaporin 4 expression in human skeletal muscle fiber types. Muscle & Nerve. 57. 10.1002/mus.26024.  Different myosin ATPase based fibres correspond to different myosin heavy chain isoforms – Naming is MHCI, MHCII etc. Each fibre can contain more than one heavy chain isoform which explains existence of myosin ATPase fibre types other than pure Type I, IIA, and IIB – E.g. mixed fibres contain “neighbours” MHCIIA and MCHIIB What was called MHCIIb in humans is actually MHCIIx as humans don’t express the fastest MHC isoform of MHCIIb – Histochemical myosin ATPase fibre type terminology was developed using human muscle, type IIB fibres (which correspond to MHCIIx) unlikely to be renamed Humans have MHCI, MHCIIa and MHCIIx  Biochemical Classification Combines information on fibre myosin ATPase histochemistry and biochemistry of specific enzymes – These enzymes reflect energy metabolism of the fibre Aerobic/oxidative or anaerobic/glycolytic Results in 3 fibre types – Fast twitch glycolytic – Fast twitch oxidative – Slow twitch oxidative  Figure 2 Comparison of 3 different skeletal muscle fiber type classifications: histochemical staining for myosin... Phys Ther, Volume 81, Issue 11, 1 November 2001, Pages 1810–1816, https://doi.org/10.1093/ptj/81.11.1810 The content of this slide may be subject to copyright: please see the slide notes for details.  Fibre Types Type I – slow twitch – fatigue resistant – high capacity for aerobic energy supply – limited potential for high force production due to low myosin ATPase Type IIa & IIx fast twitch fatigable with low aerobic power high force production capacity IIa fibres have higher aerobic capacity than IIx fibres Essentials of Str & Cond 2nd Ed Types of Contraction Isoinertial: constant external mass – Concentric: muscle shortens – Eccentric: muscle lengthens Isometric: no change in muscle length/joint angle Isokinetic: constant angular velocity  Isoinertial Contractions Concentric from bottom position Eccentric from top position  Isometric Isokinetic http://www.youtube.com/w atch?v=kY2EzwrUhCw Part 3: Resistance Training Adaptations ·MORPHOLOGICAL ADAPTATIONS  Resistance Training Adaptations Increased – Hypertrophy – Strength – Power – Strength endurance  Mechanisms Morphological Neural Endocrine Cardiovascular  Morphological Adaptations Hypertrophy – Increase in muscle cross- sectional area (CSA) – ↑ synthesis/↓ degradation of contractile protein – ↑ number of myofibrils within each fibre – Fibre splitting (Hyperplasia)? Fibre Type – Type II fibres more prone to hypertrophy – Transition from I – II or II-I ? Molecular Biology & Cell Signalling Spiering et. al.; 2008 Synthesis of protein from Synthesis of RNA from DNA mRNA Spiering et. al.; 2008  Adenosine monophosphate- activated protein kinase Enzyme to activate glucose & fatty acid MTOR is a protein kinase uptake and oxidation A protein kinase is an enzyme that modifies other molecules (mostly proteins), by adding phosphate groups to them (phosphorylation). Endurance & Resistance Training Signalling Pathways Hawley JA. Appl Physiol Nutr Metab 34:355-61, 2009. Extra Reading Camera. et. al.; 2016  Muscle Memory Classic Model New Model Gundersen et. al.; 2016  Cell Swelling Strength and Conditioning Journal 2015 Part: 4 Resistance Training Adaptations ·NEURAL CHANGES Siddique et. al.; Sports Med 2020  Background Subtle nervous system changes important because increases in strength occur in the absence of hypertrophy – Although hypertrophy can be detected with 3 weeks Traditionally measured as increase in muscle activation from surface electromyography (SEMG) – Increased SEMG amplitude thought to represent increased efferent motor output from cortical motor areas – May underestimates motor unit activity Recent studies assessing H-reflex, V-wave and Transcranial Magnetic Stimulation (TMS)  Definitions Hoffman’s (H-reflex) can be used to evaluate spinal alpha-motorneurone excitability V-wave is measure representing overall efferent motor output of alpha-motorneurone pool  Transcranial Magnetic Stimulation TMS involves placing a magnetic coil over the primary motor cortex to stimulate underlying neurones Results in muscle response known as motor-evoked potential (MEP) Size of MEP represents a measure of corticospinal excitability When MEP is recorded during voluntary contraction there is a pause in the SEMG signal know as “silent period” – Measure of corticospinal inhibition RT reduces inhibition in descending motor pathways  Twitch Interpolation Magnitude of efferent drive to muscle is called “voluntary activation” Determined via magnetic or electrical stimulus to the motor nerve during isometric MVC. Increase in force due to stimulation suggests central drive limitation Representative output from the twitch interpolation method. The participants perform a maximal voluntary contraction, from which peak torque is obtained (a). Once a plateau in torque is observed, a superimposed twitch (depicted by the green line) is administered using a magnetic stimulator (b: maximal voluntary contraction + superimposed twitch; c: superimposed twitch). Approximately 4 seconds post-maximal voluntary contraction, a potentiated twitch is administered (d). These variables are input into a number of equations to calculate levels of voluntary activation. Changes Due To Resistance Training Corticospinal excitability (MEP) – No effect of RT at rest – Increased during MVC Silent period duration – Reduced due to RT H-reflex – No effect at rest or during MVC Voluntary Activation – ? but probably increased  Summary of Neural Change Sites Chronic RT modifies both cortical and sub- cortical motor circuits that improve motoneurone pool excitability – Increased motoneurone activation via: Decreases corticospinal inhibition & short-interval intracortical inhibition (SICI) Increases V-wave amplitude – These factors underpin increase in force  ↑ neural drive – ↑ agonist muscle recruitment – ↓ antagonist inhibition – ↑ MU synchronisation ↑ firing rate more efficient timing & pattern of discharge Impact of – ↑ stretch reflex Motor unit recruitment governed Neural by Size Principle – low threshold MU’s are Changes recruited first – RT results in earlier recruitment of high threshold MU’s Part 5: Resistance Training Adaptations ·FIBRE TYPE CHANGES ·ENDOCRINE CHANGES ·OTHER CHANGES Fibre Type Changes Wilson et. al.; JSCR 2014  Fibre Type Changes Type I fibres Type II fibres Roberts et. al. ; Frontiers 2018  Endocrine Responses Hormones are signaling molecules that co-ordinate & regulate physiological & metabolic functions by acting on receptors located in target cells Involved in wide variety of homeostatic mechanisms Endocrine glands are stimulated to release hormones into the blood by a chemical signal or neural stimulation  Acute Endocrine Response – Testosterone (T) – Growth Hormone (GH) – Cortisol (C) – IGF-1 – Epinephrine, Nor-epinephrine, dopamine – Some question over whether these acute elevations are relevant in driving adaptation (see later lecture on contemporary issues)  Chronic Endocrine Adaptations Testosterone, GH, IGF-1, Cortisol changes unclear Hormone receptor changes Volume & intensity of training important in determining response Cardiovascular Adaptations Acute responses – ↑ Heart rate – ↑ Stroke Volume – ↑ Cardiac Output – ↑ ventilation rate Chronic adaptations – No change in HR or BP – ↑ ventricular wall thickness – Reduced HR & BP to given absolute workload – Ventilation changes Other Tissue Adaptations Bones – ↑ bone mineral density Minimal essential strain – Intensity – Volume – Speed – Direction of force Tendons, Ligaments, Fascia – Requires high intensity training to cause change  Other Changes ↑ myofibrillar volume ↑ cytoplasmic density ↑ sarcoplasmic reticulum ↑ T-tubule density ↑ sodium-potassium ATPase activity ↑ calcium release ↑ pennation angle ↓ mitochondrial & capillary density ↑ stored ATP & CP ↑ muscle glycogen content Part 6: Terminology & Practical Concepts ·ACTIONS ·MUSCLE ACTION ·ETIQUETTE & SAFETY ·TERMINOLOGY  Movements & Muscles Movement classification Agonist/antagonist Prime mover/synergist/stabiliser  Flexion & Extension Flexion: decreasing the angle at a joint Extension: increasing the angle at a joint  Adduction & Abduction Adduction: moving towards the mid-line Abduction: moving away from the mid-line Bench Press Example Prime Mover & Agonist Synergist Stabiliser Antagonist  Gym Etiquette & Safety Hygiene Clothing & footwear Sharing equipment Exercise technique Spotting Use of collars Weight selection Equipment maintenance Floor layout & other hazards  Spotting Insurance against injury Proprioceptive technique feedback Forced (partner assisted reps) Requires concentration Particularly important – Overhead movements – Load on back – Load over face/head Use multiple people if required Exercise Technique  Grip – Hand position Pronated - overhand (palms down) Supinated – underhand (palms up) Neutral - handshake Mixed/Alternating Hook - thumb under index & middle finger – Width Range of Motion Range influences load that can be lifted changes forces on specific structures Desired range depends on: Program goals Individual participant limitations Breathing Generally aim to exhale through sticking point (transition from ecc to conc) Valsalva manoeuvre – Increase abdominal pressure – Increase BP – Beneficial for max effort Weight Belts Provide external support for abdominal muscles May be useful in some circumstances  Terminology Repetition (Rep): 1 cycle of movement from the start to the end of range and return Set: group of repetitions Rest: passive time between sets – 4 x 8/90 s Repetition maximum (RM) – maximum load that can be lifted for a specified number of repetitions  Terminology Intensity – Absolute = load lifted in kg 4 x 3 @ 80 , 90 , 95 , 100 kg – Relative = load lifted as a % of an RM load 4 x 3 @ 70%, 80%, 85%, 90% 1RM Very high intensity = 90-100% 1RM (1-4 reps) High intensity = 80-90% 1RM (4-8 reps) Moderate intensity = 70-80% 1RM (8-12 reps) Low intensity = 60-70% 1RM (12-20 reps)  Terminology Volume – Often calculated as : sets x reps x load lifted e.g. 3 x 10 @ 80 kg = 2400 units Equating volumes using % RM – Allows researchers to compare different training methods & control for volume e.g.3 x 10 x 70% = 2100 units 6 x 4 x 87.5% = 2100 units  Terminology Tempo (s) – Eccentric/Pause/Concentric e.g. 3/1/2 2/0/1 1/0/X