Biomechanics 101: The Foundation Every Trainer and Fitness Enthusiast Needs
If you’re new to fitness or just starting your career as a trainer, there’s one subject that will elevate your knowledge above the average gym-goer: biomechanics. While strength programs, nutrition plans, and motivation all matter, biomechanics is the science of movement that ties everything together. It’s what separates training that’s effective and sustainable from workouts that lead to plateaus and injuries.
Let’s break down the basics in a way you can immediately apply in the gym.
What is Biomechanics?
Biomechanics is the study of human movement using principles of physics, anatomy, and engineering. It answers questions like:
How do muscles, bones, and joints work together to produce movement?
Where do forces act on the body during exercise?
How can we move more efficiently and safely?
At its core, biomechanics looks at the body as a system of levers, joints, and forces. When you understand these mechanics, you can improve performance while reducing injury risk.
The Basics of Biomechanics
1. Levers in the Human Body
Your bones act as levers, your joints are fulcrums, and your muscles provide the force.
Example: In a biceps curl, the elbow is the fulcrum, the forearm is the lever, and the biceps provide the force. A longer forearm increases the challenge because it increases the lever arm.
👉 Takeaway: Not every client experiences the same difficulty in an exercise — limb length changes the mechanics.
2. Planes of Motion
The body moves in three planes:
Sagittal Plane (forward/backward): Squats, lunges, bicep curls.
Frontal Plane (side-to-side): Lateral raises, side lunges, jumping jacks.
Transverse Plane (rotational): Russian twists, cable chops, throwing a ball.
👉 Most people only train the sagittal plane. For balanced performance and injury prevention, you need to work all three.
3. Types of Muscle Contractions
There are three main types:
Concentric: Muscle shortens (lifting the dumbbell in a curl).
Eccentric: Muscle lengthens under tension (lowering the dumbbell).
Isometric: Muscle holds without moving (plank, wall sit).
👉 Eccentric training is especially valuable for building strength and preventing injury, but it’s often overlooked.
4. Force and Torque
Torque is the rotational force around a joint. The farther a weight is from the joint, the more torque it creates.
Example: In a lateral raise, holding the dumbbell with a straight arm creates maximum torque on the shoulder. Bending the elbow reduces torque, making the exercise easier.
5. Kinetic Chain
Movements are never truly isolated; they’re part of a chain reaction.
Closed Chain Movements: Hands or feet are fixed (squats, push-ups). More stable and functional.
Open Chain Movements: Hands or feet move freely (leg extensions, bicep curls). Great for isolation and muscle targeting.
👉 A well-rounded program uses both depending on the goal.
Strength Curves
Another important concept in biomechanics is the strength curve — the relationship between how much force a muscle can produce and how much resistance it faces through the range of motion. Not all exercises challenge the muscle in the same way throughout the movement. Understanding this helps trainers choose the right hinge variation for glute development and posterior chain training.
The Romanian Deadlift (RDL)
Biomechanics: The RDL places the load directly in front of the body, creating significant torque at the hips when the bar moves away from the midline.
Strength Curve: Most difficult at the bottom of the movement (deep stretch) when the glutes and hamstrings are elongated.
Glute Activation: High at end-range hip extension, but limited at the top due to lower mechanical tension. Great for building strength in the stretched position.
45° Back Extension
Biomechanics: Because the torso moves diagonally against gravity, the hips face resistance throughout a greater portion of the range compared to the RDL.
Strength Curve: Moderate challenge at both the mid-range and near lockout.
Glute Activation: Excellent overall glute engagement, especially when cued to drive hips into the pad and squeeze glutes at the top. More constant tension compared to RDL.
Horizontal Back Extension (Glute-Ham or Bench)
Biomechanics: The torso moves parallel to the ground. Resistance peaks when the torso is horizontal and is lowest when the hips are flexed at 90 degrees.
Strength Curve: Hardest in the lockout
Glute Activation: Excellent glute engagement, especially when cued to engage the glutes and hips are fully extended.
Putting It Together
👉 By understanding strength curves, trainers can combine hinge variations strategically. For example:
Use RDLs to build hip hinge strength in the lengthened position.
Use 45° back extensions to target the glutes across the full range.
Use horizontal back extensions as a moderate-load accessory for mid-range strength.
Why Biomechanics is Essential
Better Technique = Better Results
A deadlift with the bar close to the shins reduces lower back strain. A squat with proper knee alignment spares the joints.Personalized Training
Hip socket depth, femur length, or shoulder mobility can drastically change how an exercise looks.Performance Optimization
Athletes use biomechanical analysis to sprint faster, jump higher, and lift heavier.Longevity and Injury Prevention
Respecting biomechanics ensures you train in a way your body can sustain for decades.
Everyday Examples
Squat Depth and Stance: Long femurs may require a wider stance for safe depth.
Deadlift Variations: Sumo or trap bar deadlifts may be more efficient for certain body types.
Bench Press Grip: Wider grip emphasizes chest but stresses shoulders; narrower grip emphasizes triceps.
Running Stride: Midfoot strike reduces braking forces and knee strain.
How to Start Learning Biomechanics
Watch movement from different angles.
Film your training for feedback.
Learn basic anatomy to understand “why” behind movement.
Experiment with grip, stance, and tempo to feel the differences.
Final Thoughts
Biomechanics is not about overcomplicating fitness. It’s about making training smarter, safer, and more effective. For trainers, it’s your professional edge. For enthusiasts, it’s the difference between years of progress versus years of frustration.
Next time you hit the gym, remember: every rep is a lesson in biomechanics. The more you understand it, the better you’ll move — not just in the gym, but in life.