Step by Step
Size
Naming by size
Maximus means largest, minimus means smallest, longus means long, and brevis means short — as in gluteus maximus or peroneus longus.
Loc
Naming by location
Muscles are often named for a nearby bone or body region — tibialis (tibia), brachii (arm), femoris (femur).
Act
Naming by action
Action-based names include flexor, extensor, adductor, abductor, rotator, and levator (meaning "raises").
Dir
Naming by fiber direction, and by shape or number of origins
Fiber direction terms include rectus (straight, parallel to the midline), transverse (perpendicular), and oblique (diagonal) — as in rectus abdominis or external oblique. Muscles are also sometimes named by number of origins (biceps: 2 heads, triceps: 3 heads, quadriceps: 4 heads) or by shape (deltoid: triangle, trapezius: trapezoid, serratus: serrated).
The name 'rectus abdominis' directly tells you the fiber direction — 'rectus' meaning the fibers run straight, parallel to the body's midline — which is exactly the kind of naming logic that lets you predict a muscle's fiber orientation just from its name alone, before ever seeing an image of it.
Applied Walkthrough
1
A student encounters the muscle name 'extensor digitorum longus' for the first time and is asked to predict, just from the name, roughly what the muscle does and what it looks like.
2
Ask: what does each part of this name tell you? 'Extensor' indicates the action (it extends something), 'digitorum' refers to the digits (fingers or toes), and 'longus' indicates it's a long muscle — put together, this is a long muscle that extends the toes.
3
Without ever having seen this specific muscle before, the naming convention itself provides enough information to make a genuinely accurate prediction about both its function (extension of the digits) and its relative size (long, rather than short).
4
This is exactly why understanding the naming rules (SLADO) matters beyond simple memorization — it gives you a systematic way to decode unfamiliar muscle names you'll inevitably encounter, rather than needing to memorize every single muscle name as an arbitrary label.
Exam Application
Exams test recognizing and applying all five naming categories (size: maximus/minimus/longus/brevis; location: named for nearby bone/region; action: flexor/extensor/adductor/abductor; fiber direction: rectus/transverse/oblique; origins/shape: biceps/triceps/quadriceps, deltoid/trapezius/serratus), and using these rules to decode the function of an unfamiliar muscle name.
⚠ Common Trap
The most common trap is trying to memorize muscle names and functions as entirely separate, unconnected facts, rather than recognizing that the name itself very often directly encodes the function, location, or structure — making the naming system itself a powerful memory tool rather than an obstacle.
✓ Quick Self-Check
1. What do the terms 'maximus,' 'minimus,' 'longus,' and 'brevis' indicate about a muscle?
Size — maximus (largest), minimus (smallest), longus (long), brevis (short).
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2. What does the term 'rectus' indicate about a muscle's fiber direction?
That the fibers run straight, parallel to the body's midline.
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3. What does the number of heads in 'biceps,' 'triceps,' and 'quadriceps' refer to?
The number of origins — biceps (2), triceps (3), quadriceps (4).
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4. What action-based naming terms indicate a muscle raises or lowers a body part?
Levator (raises) and depressor (lowers).
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5. If a muscle is named 'flexor digitorum brevis,' what can you predict about its action and size?
Based on the name, it flexes the digits (fingers or toes) and is a short (brevis) muscle.
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