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