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Chapter 4

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Biomedical Physio & Kines
BPK 143
Tony Leyland

Chapter 4 BENEFITS OF RESISTANCE TRAINING 1) Increase in: - Muscular strength - Muscular endurance - Strength of bones - Tensile strength of ligaments and tendons - Thickness of cartilage - Muscle mass (hypertrophy) - Stamina ( duration of effort before exhaustion) - Flexibility (assuming full range of movement during training) - Speed and power - Blood volume and haemoglobin (with endurance/circuit training) - Muscle enzyme levels - Skill (free weight programs) - Maximal work capacity - Equalization of muscle development - Capillary density in the muscle (from muscular endurance programs only; programs that focus solely on strength may result in capillary dilution) 2) Decrease in : - Body fat - Stress and tension - Resting heart rate ( with endurance/circuit training) 3) Helps to : - Prevent injuries - Rehabilitate injuries - Improve cardio-respiratory function - Alter metabolism to improve caloric utilization - Facilitate quicker recovery from workout and competitions - Increase self image and confidence - Improve appearance - Increase feeling of well-being - Induce fatigue and relaxation (help sleep patterns) DISADVANTAGES OF STRENGTH TRAINING - When properly performed and supervised weight training is probably one of the safest activities - Less injury risk while weight training than in most sports 1) Increase risk of (sensible goals, correct techniques, and good safety precautions greatly reduce the possibility of the following risks) - Muscle and tendon injuries - Bone and ligament injuries - Low back injuries - Contact with weight plates causing injury - Large transient increase in systolic blood pressure, which may be a problem for some individuals. As most physical training, regular strength training may reduce resting SBP - Excessive fatigue due to over training - Possible inducement to take ergogenic acids such as anabolic steroids and creatine monohydrate DEFINING MUSCULAR STRENGTH, ENDURANCE, AND POWER - Muscular strength: the greatest amount of force that a muscle or muscle group can produce in a single maximal effort - Muscular endurance: the ability of a muscle group to perform repeated contractions against a light load for an extended of time - Muscular power: the ability to produce force quickly. Power can be calculated by multiplying the force of the muscular contraction by the speed of the contraction. Power can also be calculated by measuring the work done (force x distance) per unit time (or work divided by time) TYPES OF MUSULAR CONTRACTION 1) Isometric contraction - Muscular contraction with no change in length of the muscle - Disadvantages of isometric exercises 1. Strength is not increased throughout the joint’s range of motion but is speficic to the joint angle at which the training is performed 2. Isometric training does not optimally improve the ability to exert force rapidly rapidly 3. Motivation is poor with isometric exercises. Unlike isotonic (free weight or machine) exercises, it can be difficult to observe progress 4. Straining-type activities, which involve sustained isometric muscle contractions, greatly increase resistance to blood flow and cause large increases in arterial blood pressure and workload of the heart 2) Isotomic contraction - A muscular contraction where the tension (force) in the muscle is constrant - When movement is performed, the tension is the muscle is not constant throughout the range of motion due to changing leverage considerations and inherent mechanical properties of muscle - Once you have the weight moving, you no longer have to accelerate the load- you only need to keep it moving - An isotomic contract RARELY occurs - In reality, constant means if you are moving a constant mass 3) Isokinetic contraction - A contraction where the muscle shortens or lengthens at a constant velocity - Muscles will generally do this only when working on machines that control the velocity of movement 4) Concentric contraction - When the muscle is contracting and shortening - A unique property of muscle tissue because no other tissue in the human body can shorten when stimulated 5) Eccentric contractions - When the muscle is not only contracting but also lengthening - Muscles only pull, they cant push, but an external force is causing the muscle to be lengthened - Most common cause is gravity - When lowering a weight slowly, the muscles are contracting eccentrically - In the Down phase of a squat, the quadriceps are contracting eccentrically MUSCLE FIBRE TYPES - The differences between muscle types result from different isoforms of the proteins that make up the contractile elements, specifically the protein myosin - A motor unit is a single motor neuron and all of the corresponsiding muscle fibres it innervates (causes to contract) - When a motor unit is activated, all of its fibres contract - Skeletal-muscular motor units are classified based on their speed of contraction – slow of fast - Third set of terms – type I, Type lla, and Type llx- is commonly used by muscle physiologists - * Remember which fibres are slow twitch (ST) and which are fast twitch (FT_ - Also need to know what the abbreviations SO, FOG, and FG mean in relation to skeletal muscle motor fibres - All of the muscle fibres within any given motor unit have identical biochemical and physiological properties; FT motor units contain only FT fibres - The actual force produced by a muscle is strongly correlated with the cross-sectional area of the muscle - FT fibres can produce about 10% more force per unit of cross-sectional area than ST fibres, and contraction and tension development are two to three times faster - FT fibres can generate energy rapidly for quick, forceful contractions and therefore are essential for high-intensity events like sprinting, jumping, throwing - ST fibres are adapted for prolonged work and are used extensively for aerobic activities such as distance running where their fatigue-resistant properties are essential - ST fibres contain large concentration of myoglobin, it is an iron-containing protein that reversibly binds with oxygen molecules and is stored within skeletal muscle - Results in higher aerobic capacity and gives it a red color, in the same way that oxygen-containing hemoglobin makes blood red - Size principle: in most voluntary everyday contractions, slow motor units (TYPE l) are recruited first. With increasing power output, more and more fast units (Type II) are recruited - Smaller Type I motor neurons are excited first - Refers to the central excitation of a motor unit, not the peripheral excitation - However, in extremely fast, high-intensity movements that require a high force output, many motor neurons of both types may be stimulated simultaneously - specific training will force specific adpations in different types of muscle fibres - weight training with low resistance and fast movements will NOT preferentially recuit fast-twitch fibres - there is considerable variation in distribution of fibre types from muscle to muscle and person to person - the muscles used to maintain an upright posture, which is called the anti-gravity musculature, have high levels of slow-twitch fibres - the major muscles of the antigravity musculature are the soleus, quadriceps, glueteus maximus, abdominals ( in particular rectus abbdominus and internal and external obliques), and erector spinae - these muscles prevent the spine from buckling, the hips and knees from flexing, and the ankle from plantarflexing due to the gravitational force - endurance athletes tend to have greater percentage of ST units in the muscles activiated than do non-athletes - non-endurance athletes tend to have greater percentage of FT units - most research studies to date have shown that fibre type distribution in humans is genetically determined - endurance training might promote a transition from Type II to Type I muscle fibre types and occurs at the expense of the Type II fibre population Muscle Mechanics - many factors affect the force generating capacity of human muscle and the torque that ican produce Muscle Size (Cross-sectional area) - the correlation between muscle cross-sectional area and strength is very strong - there is no physiological difference between male and female muscles Time Course of contraction - when you first contract a muscle, it takes a short period for the force to build to maximum, called the electro-mechanical delay - as the force output of the muscle rises ( as more motor units are recruited), the tendon stretches - slightly delaying the rise of force being transmitted to the limb Muscle activation - recruitment, frequency, and synchoronization of active muscle fibres are also important - some individuals can become stronger simply by recurring more of their existing fibres and firing them more frequently rather than actually increasing the zie of their fibres - the amount of force an individual’s muscles exert depends on the number of fibres recuited - All-or-nothing law : it is impossible to fire all of the fibres within a muscle by a small amount, either a muscle fibre is “on”, exerting maximal force, or it is “off” Length-tension relationship - Sliding filament theory: proteins in the muscle msut overlap and attach to each other in order to generate force - The more the proteins are pulled apart, the less overlap and the less force generation is possible - If they get too short, they overlap too much and again cannot generate optimal force - Due to skeletal and soft tissue constraints, you cannot move your muscles to the extreme ranges of called the “physiological range” - Explains why you are stronger when a muscle is at resting length than when it sbeing stretched or shortened - When you stretch a muscle and feel more resistance, it is not just because the muscle is resistant, but also due to the connective tissue around the muscle, and the tendon ligaments and joint capsules involved - Velocity-tension relationship - The faster a muscle shortens, the less force it is capable of generating - This is why you cannot train your more powerful lla and llx fibres by exercising quickly with a low weight - Fast twitch fibres’ “fast” refers to the innervations by the central nervous system and the development of tension, not the speed of shortening - Power = Force x velocity Power Tension Relationship - At zero velocity of shortening (isometric contraction), the power output is zero - An optimal power occurs around one-third of the maximum force and one-third of the maximal speed of shortening - Exp. If you get in the wrong low gear, you can exert a high force on the pedal - Shouldn’t do resistant training at one-third of maximal force output because strength training can shift the curve upwards and sideways to the right so that you can exert more force at a given velocity Eccentric Loading - If a muscle is “pre-loaded” (eccentric contraction) prior to a concentric contraction, it can generate more force - Main advantage of pre-loading is that stretching the tendon stores energy - Tendon is an elastic material that returns 93% of the energy used to stretch it - Exp. A drop-down prior to perform a vertical jump, back swing in track-and-field where muscles must first stop the arm from going backwards and then continue to contract to drive the arm and discus forward Temperature - Muscle temperature is important as deep muscle temperature increases - This is why active warm-up is preferred to just sitting in a sauna Torque output - Torque= force x perpendicular distance - Although torque output is affected by muscle force, the distance that muscle acts from the joint is also a crucial factor - Distance is determined by the insertion point of the muscle on the bone and the joint angle - Muscles tend to have better leverage in the middle of a joint’s range of motion - Any torque produced by the antagonist muscle will reduce the effective torque of the agonist - If contracting both agonists and antagonists, energy will be wasted and effectiveness is reduce Joint angle, torque, and variable resistance machines - Moment arm : the distance from the line of action of the muscle to the joint centre of rotation - Moment arm is less when the arm is flexed - We can generate more toque in the mid-range of a joint angle Torque angle relationship of a human muscle joint system Variable resistance due to non-round pulleys - At the beginning, it is easier to pull in the director of the top arrow, as you have a long lever arm ( more torque for any given force) and weight stack has a short lever arm (less torque, hence less resistance to being lifted) - As the pulley rotates, lever arm decreases as the leverage of the weight increases Nautilus variable resistance and barbell torques in relation to elbow angle - Result suggests that machine can mimic the torque output of the elbow muscle-oint complex better than free weights - *not functional, because we don’t really use this kind of resistance in normal everyday life* - Once we get weights moving, it becomes easier and the torque we produced is reduced - Another type of variable resistance is an isokinetic resistance machine - Muscle speed of shortening during a contraction is determined by instrumentation that sallows a person to exert maximal force throughout the full range of motion - Isokinetic machines develop muscular strength and/or endurance, depending on the speed of contraction - They are excellent for training injured joints, because the resistance adjusts to your effort, reducing the risk of injury compared with other training devices - The MOST effective strength gains come from slower training speeds Machines v.s Free weights 1) Advantages of machines - Safety is easier to achieve with machines - Machines can be designed to provide resistance in certain body movements ( some argue machinee make greater flexibility possible, some argued they are limited) - Patterns of resistance can be designed into machines ( Nautilus machines use a cam-shaped pully to vary resistance throughout the range of joint motion. Isokinetic machines used fluid viscosity to vary resistance) - It is quicker and easier to change weights 2) Advantages of free weights - Usually performed in a standing position, which taxes a greater portion of the body’s musculature than machine exercises - Standing provides an element of weight-bearing exercise, which promotes greater bone mineralization, helping to prevent osteoporosis - Required the use of additional musculature to stabilize the body part(s) being exercised - More skills is required to control the weights - Lifting free weights involves the more natural coordination of several muscle groups, which can stimulate real life activities better than machines - Program design is greater ( bench press, incline, decline presses at various angles) - Most free weight exercises are closed kinetic-chain exercises - Free weights are far cheaper than most machines Adaptations to resistance training - Muscles are strengthened by increasing their size and by increasing their size and by enhaving the recruitment and firing rates of motor units - Hypertrophy : an increase in the size of a tissue such as muscle - it is the major mechanism involved in enlarging muscle in response to overload stress - muscle fibres increase when the size and number of their myofibris, the small parts of the muscles, increase - Hyperplasia: an increase in the number of cells within a tissue - Bone and connective tissues, like muscle tissue, also hypertrophy with use; on the other hand, they atrophy , or get small, with disuse Body composition changes following a resistance-training program 1) Little or no change in total body weight 2) Significant loss of fat 3) Significant gain in lean body mass 4) Maintenance or increase in bone density 5) Increased thickness and strength in ligaments and tendons - Neural adaptation is the most important factor in strength gains in the early stages of training and in the early stages of de-training - Although after a few weeks of resistance work you may be 10% stronger, it is not due to 10% increase in muscle size; but because you are recruiting existing muscle fibres more efficiently (increased firing rate and increased numbers of muscle fibres recruited) - The EMG variable is a measure of increased rate of recruitment and firing of motor units - Age and gender differences in muscular function - Main reasons for strength difference between males and females are that males have higher levels of the hormone testosterone and a faster speed of nervous control of muscle - It is the interaction between testosterone and muscle that is important - Numerous hormones in addition to testosterone exert anabolic (tissue building) effects, and other hormones are converted into testosterone by receptors within the muscle - Age is a big factor, prior to puberty, boys are only slightly stronger than girls - Cultural factors play a role in the differences between gender - The response to training is specific to each individual Developing a successful resistance training program Overload principle - A load that represent 60-80% of a muscle’s maximal force capacity is usually sufficient overload to produce strength gains - There are many different ways to create overload in weight training 1) Increase the amount of resistance once you can complete the required number of repetitions with relative ease 2) Increase the number of repetitions using the same weight. The more repetitions you can do, the more you are training your muscular endurance capability with less effect on your strength 3) Increase the rate of work, so that your average power output increases( perform the exercises or movements more quickly or reduce the length of rest intervals between sets) 4) Increase the volume of work (perform more sets of each exercise or add more exercises to your workout) Principle of progressive resistance - the overload must be progressive throughout the duration of the program - two-for-two rule : increase the load being lifted after being able to complete two repetitions over your target repetitions on the last exercise set on two consecutive days Principle of arrangement of exercise - larger muscle groups should be exercised before small groups - because the smaller muscle groups will be fatigued and limit the amount of work you can do with larger muscle groups Principle of specificity - strength-endurance power development from weight training programs is specific in several ways : 1) it is specific to the muscle groups trained and the movement patterns used 2) strength development is specific to the joint angles at which the muscle groups are exercised 3) it is specific to the type of muscular contraction 4) the body’s response in terms of muscular strength, size, endurance, or power will depend on the type of training undertaken - athletes should use fundamental strength training exercises, such as press, bench-press, squats, deadlifts, cleans, and so on, and then learn to incorporate these strengths gains furing their sport training - helps the body coordinate the changes in the athlete’s body to adapt to the sport PROGRAM DESIGN - The common wisdom is that your program/session should: 1) Fit your skill level (equipment) 2) Fit your program needs (strength, hypertrophy, endurance) 3) Target major muscle groups 4) Target additional muscle groups if needed 5) Fit your desired commitment
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