Muscle performance and length Unit 3
1. Muscle Performance Testing
Purpose: Vital for diagnosis, identifying causes of activity/participation limitations, and creating personalized rehabilitation programs.
Effects of Deficits:
Direct: Limited muscle performance directly produces a functional deficit (e.g., inability to lift child due to upper extremity weakness).
Indirect: Contributes to poor movement patterns/postures, leading to stress, injury risk, and limiting performance (e.g., hip weakness leading to inefficient gait and knee pain).
Definition: Measures the ability of a muscle to do work, where \text{Work} = \text{Force} \times \text{Distance} . Involves nervous, cardiovascular, and respiratory systems.
Elements of Muscle Performance: Strength, Power, and Endurance. Each has physiological, biomechanical, and neurological components.
Factors Negatively Affecting Performance: Disease, injury, immobility, disuse (leading to atrophy, weakness, loss of endurance/power).
1.1 Muscle Strength
Definition: Ability of a muscle to produce tension and resultant force.
Maximal Strength: Greatest measurable force exerted during a single maximal effort.
Factors Influencing Strength:
Cross-sectional area: Larger muscle = more force/strength.
Length-tension relationship: Greatest contraction in slightly lengthened position; shortened position reduces optimal force.
Motor unit recruitment: Greater number of motor units recruited = greater force output (takes at least five seconds for maximal recruitment).
Type of muscle contraction:
Greatest force: Eccentric contraction against resistance.
Less force: Isometric contraction.
Least force: Concentric contraction.
Muscle fiber types:
Type II (fast-twitch): High tension, built for strength.
Type I (slow-twitch): Sustain low tension for prolonged periods.
Energy stores & oxygenation: Greater means better performance.
Speed of contraction: Lower speeds produce greater torque/force due to more opportunity for fiber recruitment.
Psychological factors: Motivation or stress can negatively affect effort and strength.
1.2 Muscle Power
Definition: Rate of performing work. Product of force and velocity.
Calculation: \text{Power} = \text{Force} \times \text{Velocity} = \frac{\text{Force} \times \text{Distance}}{\text{Time}} .
Description: Function of strength and velocity at rapid speeds.
Example: Performing 10 sit-to-stand movements in 10 seconds demonstrates more power than taking 20 seconds.
Measurement: Equipment in sports/orthopedics, or functional testing.
Clinical Relevance: Declines with age, associated with loss of function (gait speed, fall prevention, independence). Assessment/maintenance is imperative.
1.3 Muscle Endurance
Definition (Aerobic Power): Ability of a muscle or muscle groups to sustain exercise.
Types of Endurance:
Cardiopulmonary Endurance: Taxes cardiovascular system's ability to provide blood and oxygen (e.g., walking, biking, swimming).
Muscular Endurance: Ability to contract a muscle repeatedly against a load/resistance, generate and sustain tension, and resist fatigue over time.
1.4 Methods to Test Muscle Performance
Muscle Strength:
Gross Strength Testing: Manual resistance for cardinal planes of movement (general idea of strength).
Manual Muscle Testing (MMT): Assesses specific muscle or muscle group strength using therapist manual resistance. Quick, no equipment, adjustable.
1 Repetition Maximum (1RM) Test: Gold standard for maximal strength in non-laboratory settings; generally not used in rehab due to exertion.
Dynamometry Testing: Measures strength/force using a dynamometer (medical instrument).
Isokinetic Testing: Evaluates strength, power, endurance, rate of force development using computer-controlled device (measures at constant angular speed with variable resistance).
Isometric Strength Testing for Muscle Integrity (MIT): Resisted manual tests with minimal force (determines pain with contraction, safety for other tests, significant weakness, assists diagnosis).
Muscular Endurance:
Standardized Functional Tests: 6-minute walk test, 2-minute walk test, energy expenditure test.
Clinical Functional Tests: How long a person can run to fatigue, hold a weight, or perform repetitions before fatigue.
2. Manual Muscle Testing (MMT)
Value: Determines cause of functional deficits, aids diagnosis/intervention, identifies neurological pathology/nerve injury.
True Force Output Influencers (not limited to): Muscle size/architecture, musculotendinous stiffness, motor unit recruitment, rate coding, motor unit synchronization, neuromuscular activation.
Definition: Technique for estimating relative strength of a specific muscle, manually assessing strength and contractility.
Manual: Therapist applies resistance vs. machine.
Can test specific muscle (e.g., pectoralis major) or muscle group (e.g., shoulder internal rotators).
Advantages: Applies to almost any clinical setting, no equipment, quick, allows therapist adjustments/assessments during test.
2.1 MMT Terminology
Make Testing: Examiner applies just enough force to prevent joint movement; patient holds test position (isometric test).
Break Testing: Examiner provides enough force to overcome patient's resistance, causing joint movement (commonly used).
Patient Position: Specific, standardized, reproducible position of body part.
Resistance: Force applied by therapist to break test position.
Substitutions: Altered movements or muscle recruitment by patient to create more force (undesired, indicates use of non-target muscles).
Isometric Contraction: Muscle length remains the same while generating force/tension; no joint movement.
Concentric Contraction: Muscle shortens while generating force and overcoming resistance (most common).
Eccentric Contraction: Muscle lengthens under tension, slowing movement caused by external force; also known as negative work (absorbs energy).
Agonist: Muscle producing a movement.
Antagonist: Muscle producing the opposite movement.
Fixation: Stability of the proximal attachment site of a contracting muscle.
Synergists: Muscles assisting a muscle's action (fixate attachment, produce similar action, balance/guide movement).
2.2 Information Gained from MMT
Detect weakness (due to nerve involvement, disuse, atrophy, stretch weakness, pain, fatigue, general status).
Detect muscle imbalances (between synergists or antagonistic muscles).
Determine ability of muscles to function during movement and provide stability.
Determine motor control and movement patterns (optimal vs. substitutions/compensations).
Isolate/identify pain/injury source (contracting muscle/tendon produces pain).
Examine nerve function (central and peripheral nervous systems; identifying neural patterns of weakness).
2.3 MMT Procedures and Concepts
Quantification: Handheld dynamometer provides numerical force output values.
Test Position (optimal for specific muscles):
One-joint muscles: Optimally tested in a shortened range, as this provides a better understanding of true strength and therapist mechanical advantage.
Two or more-joint muscles: To avoid active insufficiency, muscle is placed in the middle of its range of motion.
Active Insufficiency: Muscle is no longer able to generate effective force due to being placed in a shortened position, limiting maximal cross-bridging.
Therapist can manipulate test position to inhibit two- or multi-joint muscles to isolate others (e.g., hamstrings in prone hip extension vs. knee flexion).
Standardized Process (for reproducibility and reliability):
Patient Position: Standard, comfortable position against gravity (gravity-resisted). For significant weakness, use gravity-eliminated/minimized position (horizontal plane, powdered surface if needed).
Passive and Active Range of Motion (PROM & AROM): Perform PROM to assess symptoms/available ROM. Ask patient to perform AROM, noting pain or substitutions. Pain in AROM but not PROM implicates contractile structure. AROM deficit vs. PROM suggests weakness.
Stabilization: Therapist stabilizes proximal attachment site; patient may also self-stabilize (hold table, muscle control, gravity).
Lever Arm: Force applied at the distal end of the bone (long lever arm for mechanical advantage); for very strong muscles (e.g., hip abductors), force may be applied at ankle.
Direction of Pressure: Precise and directly opposite to the muscle's action to isolate the target muscle.
2.4 MMT Grading (0-5 Scale)
0/5 (Zero): No contraction.
1/5 (Trace): Slight contraction felt, no movement.
2/5 (Poor): Full ROM in gravity-eliminated position.
3/5 (Fair): Full ROM against gravity, no added resistance.
4/5 (Good): Full ROM against gravity, moderate resistance.
5/5 (Normal): Full ROM against gravity, maximal resistance.
Most Objective Grades: 2/5 and 3/5.
Applying External Force: Performed for grades 4/5 and 5/5 after patient achieves 3/5. Therapist should use enough force to attempt to break the test position.
3. Manual Muscle Testing: Interpretation of Results
Factors in Grading (4/5 or 5/5): Therapist's clinical skill, knowledge of anatomy/biomechanics (muscle size, type, fiber type, pennation angle, function), and patient demographics (age, gender, athleticism, body type).
Correlating Results to Ramifications:
Direct functional deficit: Inability to lift a child or use a walker.
Negative local biomechanical effects: Overload, tissue stress, injury (e.g., hamstring weakness leading to ACL injury/strain).
Negative kinetic chain/distal biomechanical function: Altered biomechanics, decreased performance, activity limitations, tissue injury (e.g., hip muscle weakness/lower extremity injury, rotator cuff weakness/elbow injury).
Imbalanced muscle use: Increased strain/overload between synergists.
Neurological pattern of weakness: Assess nerve injury (e.g., polio, ALS, Guillain-Barré, SCI, peripheral nerve entrapment).
3.1 Bilateral Testing & Symptoms
Bilateral Testing: Always perform on both sides (if safe) for comparison. Uninjured side can be a goal, but symmetry doesn't always mean normal strength.
Production of Patient Symptoms (Pain):
Stop test, ask for location.
Pain in muscle belly = muscle tissue injury.
Pain in tendon = tendon injury.
Pain in joint = joint movement/compression related.
Impact of Pain: Causes reflexive muscle inhibition; true strength is not assessed. Document pain occurrence and force level.
Clinical Reasoning based on Pain/Strength:
Strong & Pain-Free: Contractile tissues functioning normally.
Strong & Painful: Mild tendon or muscle pathology.
Weak & Painful: Moderate to severe tendon or muscle injury.
Weak & Pain-Free: Complete rupture/tear, neural deficit, disuse, frank strength deficit.
3.2 Limitations of MMT
Ceiling Effect: Therapist may be unable to provide enough resistance for very strong muscles (especially lower extremity). MMT may