Muscles Part II

MUSCLE CONTRACTIONS

Static Dynamic

Isometric IsotonicIsokinetic

Constant External Resistance Variable

Resistance

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 MuscleTrainable 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