Key Takeaways
- Synovial joints are classified by shape: hinge (elbow), ball-and-socket (hip, shoulder), pivot (atlantoaxial), saddle (CMC of thumb), condyloid (MCP), and plane (intercarpal)
- The three types of muscle contractions are concentric (shortening), eccentric (lengthening under load), and isometric (no length change)
- Closed kinetic chain (CKC) exercises involve the distal segment fixed (squats, push-ups), while open kinetic chain (OKC) exercises have the distal segment free (leg extensions)
- Normal gait cycle consists of stance phase (~60%) and swing phase (~40%), with initial contact, loading response, midstance, terminal stance, pre-swing, initial swing, mid swing, and terminal swing
- Type I (slow-twitch) muscle fibers are fatigue-resistant and suited for endurance; Type II (fast-twitch) fibers generate more force but fatigue quickly
- Wolff law states that bone remodels in response to mechanical stress placed upon it
- The force-velocity relationship shows that as contraction velocity increases, the maximum force a muscle can produce decreases (for concentric contractions)
- Osteokinematic motions (bone movement) include flexion, extension, abduction, adduction, and rotation; arthrokinematic motions (joint surface movement) include roll, glide, and spin
Musculoskeletal Anatomy & Kinesiology
The musculoskeletal system provides the structural framework for movement and is the foundation of physical therapy practice. Understanding joint anatomy, muscle physiology, and biomechanical principles is essential for the NPTE-PT.
Joint Classifications
Synovial Joint Types
Synovial joints are the most common type of joint in the body and are classified by the shape of their articular surfaces:
| Joint Type | Shape | Example | Degrees of Freedom |
|---|---|---|---|
| Hinge | Convex fits into concave | Elbow (humeroulnar), knee (tibiofemoral), ankle (talocrural) | 1 (flexion/extension) |
| Ball-and-Socket | Spherical head fits into cup | Hip (acetabulofemoral), shoulder (glenohumeral) | 3 (flexion/extension, abduction/adduction, rotation) |
| Pivot | Ring rotates around axis | Atlantoaxial (C1-C2), proximal radioulnar | 1 (rotation) |
| Saddle | Reciprocally concave-convex | 1st carpometacarpal (thumb) | 2 (flexion/extension, abduction/adduction) |
| Condyloid | Oval convex fits into oval concave | Metacarpophalangeal (MCP), wrist (radiocarpal) | 2 (flexion/extension, abduction/adduction) |
| Plane (Gliding) | Flat surfaces | Intercarpal, intertarsal, acromioclavicular | Translation/gliding |
Arthrokinematics vs. Osteokinematics
Physical therapists must distinguish between two types of joint motion:
- Osteokinematics: Movement of bones in space (what is visible) — flexion, extension, abduction, adduction, rotation
- Arthrokinematics: Movement of joint surfaces relative to each other — roll, glide (slide), and spin
The Concave-Convex Rule (critical for joint mobilization):
- When a convex surface moves on a concave surface, the glide is opposite the direction of the bone movement
- When a concave surface moves on a convex surface, the glide is in the same direction as the bone movement
Example: During shoulder flexion, the humeral head (convex) glides inferiorly (opposite to the superior bone movement) on the glenoid fossa (concave).
Muscle Physiology
Muscle Contraction Types
| Contraction Type | Description | Example |
|---|---|---|
| Concentric | Muscle shortens while generating force | Biceps curl upward phase |
| Eccentric | Muscle lengthens while generating force | Lowering a biceps curl slowly |
| Isometric | Muscle generates force without length change | Holding a weight at 90 degrees |
Key Clinical Point: Eccentric contractions generate the most force and are commonly used in rehabilitation for tendinopathies (e.g., eccentric heel drops for Achilles tendinopathy).
Muscle Fiber Types
| Fiber Type | Alternative Names | Characteristics | Function |
|---|---|---|---|
| Type I | Slow-twitch, SO (slow oxidative) | High mitochondria, fatigue-resistant, aerobic | Endurance, postural control |
| Type IIa | Fast-twitch oxidative (FOG) | Moderate fatigue resistance, aerobic + anaerobic | Power endurance |
| Type IIx | Fast-twitch glycolytic (FG) | Low fatigue resistance, anaerobic | Maximum force, speed |
Gait Analysis
Normal Gait Cycle Phases
The gait cycle is divided into stance phase (~60%) and swing phase (~40%):
| Phase | % of Gait Cycle | Description |
|---|---|---|
| Initial Contact | 0% | Heel strikes the ground |
| Loading Response | 0-10% | Weight acceptance, shock absorption |
| Midstance | 10-30% | Single limb support, body advances over foot |
| Terminal Stance | 30-50% | Heel rises, body advances past foot |
| Pre-Swing | 50-60% | Toe-off preparation, double limb support |
| Initial Swing | 60-73% | Foot clearance, hip and knee flexion |
| Mid Swing | 73-87% | Limb advancement |
| Terminal Swing | 87-100% | Deceleration, preparation for initial contact |
Gait Parameters
- Cadence: Steps per minute (normal adult: ~110-120 steps/min)
- Step length: Distance from heel strike of one foot to heel strike of opposite foot
- Stride length: Distance from heel strike to next heel strike of the same foot (= 2 step lengths)
- Walking velocity: Distance covered per unit time (normal: ~1.2-1.4 m/s)
During shoulder flexion, which direction does the humeral head glide on the glenoid fossa?
Which type of muscle contraction generates the most force?
Which of the following are characteristics of Type I (slow-twitch) muscle fibers? (Select all that apply)
Select all that apply
What percentage of the gait cycle does the stance phase normally occupy?
The concave-convex rule states that when a convex surface moves on a concave surface, the glide is in the _____ direction of the bone movement.
Type your answer below
The first carpometacarpal (CMC) joint of the thumb is classified as which type of synovial joint?
During which phase of gait does the body have the highest demand for single-limb stability?
Wolff law states that bone:
A closed kinetic chain (CKC) exercise is characterized by: