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