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Muscles Part II MUSCLE CONTRACTIONS Static Isometric Constant External Resistance Dynamic Isotonic Variable Resistance Isokinetic Plyometrics Muscle Contraction Static contractions The muscle tension or force exerted against an external load is equal to or weaker than the external force No visible movement occurs Dynamic Contractions Internal & external forces are unbalanced External force (gravity, weight of object) is not equal to the internal force (produced by athlete’s muscle) Generates movement Isometric Static Means “Same Length” Work = force x distance Since no movement occurs, no work occurs Instead measured by the rate of tension & duration that tension lasts + Causes hypertrophy - Strength gains are specific to joint angle This is called Specificity Isokinetic Means “same speed” Resistance is changed so speed of movement can be maintained - Requires specialized equipment +/- Trains single joint movements +/- Strength gains are specific to the training velocity Specificity Used primarily in rehabilitative settings + Safe way to train muscles + Muscles can be isolated Isotonic Means “same tension” + Mimics real life movements - Difficult to achieve “same tension” through entire ROM Beginning & end of ROM achieve less tension than middle Two Phases: Concentric: Muscle shortens as it moves through range of motion Moves against gravitational force (overcomes it) Eccentric: Muscle lengthens as it moves through range of motion Moves with gravitational force (resists it) Types of Isotonic Exercise Constant External Resistance Free weights, body weight exercises, medicine ball, etc Enough resistance provided in parts of movement and not enough in other parts Selection of weight is critical - Often training doesn’t occur at ends of ROM Result: appearance of joints that can’t be straightened + May mimic “real world” movements more + Increase activation of stabilizing muscles Types of Isotonic Exercise Variable Resistance Exercise Machines that utilize cams and/or pulleys, elastic bands/tubing, etc Automatically changes the resistive force throughout the ROM + Good for novice, older and/or recreational athletes + Help control motion - Do not promote muscle coordination or balance Types of Isotonic Exercise Plyometric (AKA: Jump Training or Stretch-Shortening Cycling) Trains muscle to reach maximal force in shortest possible time (power) Amortization Phase: amount of time it takes muscle to change direction from “stretch” to “shorten” Ideally this should be as short as possible Places high stress on muscles, connective tissue & joints Requires foundation of physical fitness Intensity, repetitions & sets should be carefully prescribed Training Muscle Trainable Factors Fiber diameter Hypertrophy Atrophy Coordination of muscle fibers Nerve impulse frequency Elasticity of muscle & tendons Energy stores of muscle & liver # of capillaries Non-Trainable Factors Number of fibers Hyperplasia Fiber Type Creating Movement Muscle attaches to bone via tendons Origin of muscle on non-moving bone Insertion of muscle on the moving bone Motor neuron signals contraction Muscle shortens and pulls on bone Movement occurs about a joint Insertion moves towards origin Muscle Teamwork When one muscle contracts, another must relax Agonist (prime mover) creates desired movement Antagonist opposes the desired movement When agonist contracts, antagonist must relax Agonists & antagonists are typically on opposite sides of joints Example: Biceps brachii & Triceps brachii Muscle Teamwork Synergist: A muscle that surrounds the joint being moved Aids the prime mover in creating desired movement On same side of joint as the prime mover Ex: Gluteus maximus & Gluteus medius extend thigh Fixator or Stabilizer: A muscle that contracts with no significant movement to maintain a posture or fixate a joint Ex: Erector spinae during a push-up Muscle Groups Gluteal Group Gluteus Maximus Gluteus Medius Gluteus Minimus Muscle Groups Quadriceps Group Rectus femoris Vastus lateralis Vastus intermedius Vastus medialis Muscle Groups Hamstring Group Biceps femoris Semitendinosus Semimembranosus Muscle Groups Abdominals Rectus abdominis External oblique Internal oblique Transverse abdominis Muscle Groups Erector Spinae Iliocoastalis Longissimus Spinalis
