Muscle Strength and Muscle Endurance

• Muscle strength : The maximum amount of force that any one or combination of muscle(s) can produce in a single maximal effort.
• Muscle endurance: To repeat or sustain a sub maximal force over a prolonged period of time.

Muscle fiber response

• Myofibrils: Smallest functional unit of the muscle fiber. Many myofibrils compose a muscle fiber.
• Myofibrils:

  Increase in number = increase in myofibrils

  Increase in myofibrils = increase size of muscle fiber

  Increase in size of muscle fiber size = muscle hypertrophy

   Facts

• Myofibrils are the building blocks of muscle fibers. Thus, the more fibrils present, the larger the muscle fiber. Hypertrophy is the physical change which is an increased cross sectional area of the muscle(s). Atrophy is the opposite response of hypertrophy, or a decrease in the cross-sectional area of the muscle.
  • Example of Muscular Hypertrophy
• Muscle hypertrophy is the physical change of the muscle tissue in response to musculoskeletal resistance training. The opposite response due to detraining is muscle atrophy.

Fiber types

· Slow Twitch (ST) = "aerobic"

· Fast Twitch (FT)= "anaerobic"

 There are two basic types of muscle fibers.

Slow twitch fibers are those used predominately during aerobic types of activities. These fibers have a low fatigue rate compared to fast twitch and have energy systems that require oxygen in abundant supply.

Fast twitch fibers are more suited for rapid and forceful contractions. These fibers do not require abundant oxygen for performance but these fibers will fatigue rapidly.

Fiber response

• Muscle Strength = FT fiber development
• Muscle Endurance = ST fiber development

 The exercise stimulus from muscle strength exercises (lifting heavy weights) will promote FT development

whereas endurance (lifting light weights with high repetitions) will tend to promote ST involvement.

In the skeleton:

• Increased bone density

  Strength training increases bone density. The increase in bone density is due to an increased force or resistance on the bone tissue from weight training. Thus, more force equals greater bone density. This relationship is why strength training is effective in preventing osteoporosis.

 In the muscle:

• Increased strength
• Increased endurance

Strength of a muscle is related to the cross - sectional area of the muscle. Thus, muscle hypertrophy is one of the primary visible indicators of muscle strength. Strength is really about myofibril number.

Endurance exercises will increase the number of endurance (ST fibers) type fibers.

Body Composition:

• Higher lean body mass = higher resting metabolism

The greater the amount of lean tissue the higher the resting metabolic rate (burn more calories). Thus, musculoskeletal resistance training will enhance weight management programs.

Screening

Purpose: To determine if there are muscle imbalances or skeletal abnormalities which would increase risk of injury or further insult preexisting musculoskeletal conditions. As in cardiovascular screening, the purpose of the musculoskeletal screening is to reduce risk associated with muscular fitness exercises. If the individual has a history of any preexisting conditions, these conditions should be considered when developing the assessment test and when developing the exercise prescription. A screening may also provide insight on conditions not previously documented.

 Methods:

PAR-Q

The PAR-Q contains a question related to the orthopaedic considerations for exercise programming and participation: "Has your physician ever told you that you have a bone or joint problem, such as arthritis that has been or could be aggravated by exercise?"

Health History

Health history questionnaires will contain a set of questions over the history of muscle and bone injuries.

Orthopaedic Examination

Persons with congenital bone and muscle disorders / deformities will have extensive amounts of information over exercise contraindications and modifications via findings of orthopaedic examinations. Those individuals who have experienced significant orthopaedic trauma may also have exercise restrictions, dependent upon the injury type and the phase of rehabilitation.

Assessment

Purpose: The evaluation of the endurance and / or strength of a muscle or muscle group. Results of the assessment are used to design the exercise prescription for muscle fitness.

Methods:

Repetition Maximum (RM)

The maximum amount of weight that can be moved through a full range of motion with the correct body posture required for the safety of the weight lift technique. Repetition is considered one full lift sequence. The RM may be a 1 RM assessment or multiple RM's, (i.e.. 10 RM = the maximum amount of weight that can be lifted, according to the criteria above, in a sequence of 10 lifts.)

Static and dynamic endurance field tests

 Static tests determine the length of time a particular position can be held against the resistance of gravity (ex. flexed arm hang)

Dynamic endurance tests determine:

1) the maximal number of repetitions which can be performed correctly in a set amount of time.

2) the maximum number of repetitions which may be performed until exhaustion.

Setting Goals

Purpose and Method is the same for all components of fitness - (see link on writing goals).

Generic Exercise Prescription for Muscular Fitness

F = 2-3 days per week

I = Strength = 60-90% RM

Endurance = < 40% RM

Combined = 40-70% RM

T = Repetitions and Sets

Muscle Strength:

• For Power = 1-3 reps
• For Size = 4-7 reps
• For Strength = 7-12 reps

Endurance:

> 15 reps

Sets = group of repetitions): for both Strength and Endurance > 2-3 sets

T = (type or mode)

Free Weights

Stacked Weights

Weight Machines

Styles of movements with weight training

Isometric : Iso = same; Metric = length . Muscle conditioning activity where the muscle contracts but no movement occurs in the joint line.

Isotonic: tonic = tone. Muscle conditioning exercise where the muscle contracts and move the joint through a full range of motion. This movement has two distinct phases:

Concentric Phase - movement through the range of motion where the muscle belly shortens. Eccentric Eccentric Phase - movement through the range of motion where the muscle belly lengthens.

Isokinetic: kinetic = movement. Muscle conditioning activity where the speed of movement through the range of motion is held at a constant requires specialized weight equipment, also, contains a concentric and eccentric phase.

Precautions:

Muscle / skeletal disorders, disease, or injury:

Those individuals who do not possess the normal joint integrity or have diseases and disorders which alter the normal distribution of force across a joint, may require modifications to the exercise prescription.

Hypertension

Hypertensive persons should not engage in lifting heavy weights. Heavy resistance activities will further elevate blood pressure.

Proper technique and breathing

One should exhale on exertion when lifting to avoid the valsalva maneuver. Also, proper form should be followed to reduce the risk of injury and from becoming muscle bound.

CHARTING THE PRESCRIPTION :

Muscle Fitness

 

Activity	Frequency	Intensity	Time	Type
Sub-component	( Days/wk )	( %RM )	( Reps/sets )
Muscle Strength	2 to 3 +	60 to 90	Power =1-3 / 2-3 Size = 4-7 / 2-3 + Strength = 7-12 / 2-3 +	Iso - metric tonic kinetic
Muscle Endurance	2 to 3 +	< 40	> 15 / 2-3 +	(same as strength)
Mix	2 to 3 +	40-70	7-15 / 2-3 +	(same as strength)