Bones do more than just hold you up
The adult skeleton has 206 bones. As a trainer, you don't need to memorize every one — but you need to know how they function as a lever system, what kinds of loads they handle, and which joints have which ranges of motion. Get that wrong and you'll prescribe exercises a client's anatomy literally cannot perform.
The 5 bone types
Long bones — femur, humerus, tibia, radius. The primary levers of the body. They produce the largest movements. Resistance training is what makes them denser and stronger. Short bones — wrist (carpals) and ankle (tarsals). Cube-shaped. Built for stability and shock absorption, not range of motion. Flat bones — sternum, scapula, ribs, skull. Protect organs. The scapula matters enormously for trainers because it's the foundation of shoulder mechanics. Irregular bones — vertebrae, pelvis. Complex shapes with multiple attachment points. The pelvis alone has dozens of muscle attachments. Sesamoid bones — patella (kneecap) and a few in the hands/feet. Embedded in tendons. They change the angle of muscle pull to increase leverage.The 3 joint classifications
Synarthrosis (immovable) — sutures of the skull. No movement, maximum stability. Doesn't matter for training. Amphiarthrosis (slightly movable) — vertebral joints, pubic symphysis. Small range, lots of shock absorption. These contribute to spinal flexion/extension when summed across all 24 vertebrae. Diarthrosis (freely movable) — every joint you train: shoulder, elbow, hip, knee, ankle, wrist. These are synovial joints with cartilage, fluid, and ligaments.The 6 synovial joint subtypes
- Ball-and-socket (shoulder, hip) — most ROM. Three planes of motion. Most injury-prone.
- Hinge (elbow, knee) — one plane (sagittal). Flexion and extension only.
- Pivot (atlas-axis at neck, radioulnar) — rotation around an axis.
- Condyloid (wrist) — two planes. Flexion/extension + adduction/abduction.
- Saddle (thumb base) — two planes plus limited rotation.
- Gliding (between carpals/tarsals) — small sliding movements.
Why this matters for programming
If you're prescribing a deep overhead press to a client with limited shoulder ball-and-socket external rotation, they'll compensate with lumbar extension and risk injury. If you're loading a hinge joint (knee) in a rotational pattern, you're attacking the meniscus.
Match the load to the joint's actual design.