CSCS Study Guide Chapter 2: Biomechanics

Edited by: Danielle Abel

Chapter 2 covers a wide range of topics as it relates to the biomechanics of exercise and human movement, including the muscular system, classes of levers, mechanical advantage, planes of motion, open and closed chain movements, force, work, power, & torque, strength to mass ratio, bracketing for overspeed and underspeed, inertia, friction, fluid resistance, & elasticity along with joint biomechanics & concerns. 

Muscular System

When referring to how the body moves, you'll want to know some anatomy terminology that describes the locations of body parts or movements relative to one another, including proximal vs. distal and superior vs. inferior. 

• Proximal means closer or more near, for example the neck is more proximal to the shoulders, compared to the feet. 
• Distal is used to describe something that is farther away. For example, the feet are distal to the neck. 
• Superior is used to describe a body part or movement that is above another area of the body. A good example here would be that the elbow is superior to the wrist. 
• Inferior is the opposite of superior and is used to describe a body part or movement below another body area. Keeping with the above example, the wrist is inferior to the elbow. 

Types of Levers in the Body

There are 3 different types of levers in the body 1st class, 2nd class, & 3rd class levers. 

• 1st class: Ex: Tricep extension.
  • The fulcrum of the tricep extension is still the elbow, with the muscle force on the back of the arm (behind the elbow)
    • The moment arm of the muscle is on one side of the fulcrum (still a shorter distance like in the bicep curl)
    • The moment arm of the resistance is on the opposite side of the fulcrum (still a longer distance like in the bicep curl)
    • So the moment arm of the muscle (MAm) is shorter < than the moment arm of the resistance (MAr)
• 2nd class: Ex: Calf raise
  • The fulcrum of the calf raise is the toe
    • The moment arm of the muscle is on the back side of the lower leg in this case the achilles tendon
    • The moment arm of the resistance is all the way from the achilles tendon to the toes where you would raise up from in the calf raise 
    • So the moment arm of the muscle (MAm) is longer > than the moment arm of the resistance (MAr)
    • BONUS: It's common to think of the ankle as the fulcrum, but that is not the case, since the movement is being initiated from the toes, the toes are the fulcrum 
• 3rd class: Bicep curl
  • The fulcrum of the bicep curl is the elbow, with the muscle force being the upper arm
    • The moment arm of the resistance (MAm) is shorter < than the moment arm of the resistance (MAr) 

Mechanical Advantage

If you've ever heard of mechanical advantage, it's just a ratio that refers to the moment arm of the muscle (MAm) in relationship to the moment arm of resistance (MAr).

• MAm:MAr
• ex: 1:4
  • Meaning the muscle (the moment arm of the muscle) has to work 4 times as hard as the resistance does to overcome the mechanical advantage
  • A nice analogy is shutting a door; when you push the door on the opposite side from the hinge, it will be much easier than if you are trying to push the door shut closer to the hinge

The Planes of Motion

The planes of motion help define the directions that the body moves within and gives structure and logic to exercise selection and program design. 

There are 3 planes of motion:

• Sagittal plane
• Frontal plane
• Transverse plane

These planes "cut" or "slice" the body in different ways. It's really easy to get confused when you're thinking about complex compound movements and the different joints that are involved. 

• Sagittal Plane - You can do these exercises in a narrow hallway. Imagine your shoulders were touching the walls, and you could only move forward and backward; this is considered the sagittal plane. This plane cuts the body into left and right halves. 
• Frontal Plane - These exercises would cause you to hit the wall in the same narrow hallway. These movements are from side to side or occur to the sides of the body, laterally. This plane cuts the body into front and back, or anterior and posterior, halves. 
• Transverse Plane - These movements would cause you to hit one side of the wall or the other while moving in a rotational fashion from head to toe or superior (towards the head) to inferior (towards the toes). This plane cuts the body into upper and lower halves. 

Open Vs. Closed Chain Exercises

These movements described how the load is being applied to the body. 

For example, open chain exercises arrange the joints in terminal segments that move freely. Whereas closed chain movements are where the distal aspect of the extremity is fixed to an object that is stationary. You can also have movements that are mixed, meaning they include both open and closed chain movements. 

• Open Chain examples: Bench press, seated leg curl, hamstring curl, lat pulldown 
• Closed Chain examples: Chin up, push up, squats, deadlift, power clean
• Mixed Open & Closed Chain examples: Running, lunges

Isotonic and Isokinetic Exercises 

These terms describe tension and speed applied to the body. For example isotonic movements are those that provide constant tension as muscle length changes. Whereas, constant speed that is applied to the body would be referred to as isokinetic. Isokinetic exercises are typically found in rehab and lab settings. 

• Isotonic Exercise example: Bicep curl machine
• Isokinetic Exercise example: Biodex machine

Force, Work, & Power

Force is simply the product of mass x acceleration, expressed in Newtons.

• Example: Lifting 100kg 
• Force = Mass x Accerlation
• Force = 100kg x 9.8 meters per second squared (gravity is 9.8 meters per second)
• Force = 980 Newtons
  • If you wanted to accelerate the barbell at 1 meter per second, you would take the acceleration of gravity plus, 1 meter = 10.8 meters per second squared
  • Which would produce 1080 Newtons (100kg x 10.8 meters per second squared)

To understand the amount of work being done, you must first find force. Once you have force, you can multiply the force x the amount of displacement.

• Work = Force x Displacement
• Work is expressed in Joules, which is Newtons x Meters
• Lifting a 100kg barbell 1 meter
  • Work = Force x Displacement
  • 100kg x 9.8 meters per second squared x 1 meter
  • Work = 980 Joules
    • For multiple reps you would multiple it by the number of reps, for example 10 reps = 9800 Joules in total

To determine how much power an athlete has, you must combine the amount of work divided by the amount of time, to get Watts. 

• Power = Work / Time
  • 980 Joules / 1 second = 980 Watts
  • 980 Joules / 3 seconds = 327 Watts
 

Pennation Angle

Muscle pennation is simply the concept that different muscles have muscle fibers that go in different directions. The muscle fibers have different origins and insertion sites on bones. Origin and insertion sites can be 2 or more different locations. 

In general, if a muscle has more pennation, it can transmit more force, but it is capable of less velocity. 

Interestingly enough, pennation angle can change with training. 

Muscle Contraction Types

There are 3 different types of contractions that you need to know, concentric, eccentric, and isometric. 

• Concentric muscle actions involve shortening of the muscle
• Eccentric muscle actions involve lengthening of the muscle
• Isometric muscle action refers to the time when the muscle is under a constant length

Joint Angular Velocity 

This is simply the rate of muscle flexion and extension of a joint. Joint angular velocity essentially tells us more about the dynamics of muscle activation and force generation. Different joints will have different angles, and so therefore different velocities. 

The highest muscle forces are seen during eccentric muscle contractions. 

Strength vs. Mass Ratio

When you think of two people who have relatively the same skeletal size, the athlete with more muscle has the potential to express more force because they have more muscle cross-sectional area to activate. However, smaller athletes (meaning athletes who have less fat mass) are stronger pound for pound than larger athletes. 

Moment Arm

The moment arm is also referred to as the lever arm, force arm or torque arm. The moment arm describes the perpendicular distance from the place where the force is applied to the fulcrum. If you think about a deadlift set up, a set up where the hips are slightly higher (as compared to a squatting crouched position) is more efficient because the moment arm of the hips is shorter. 

Inertia 

Inertia is simply the concept that an object in motion or at rest tends to remain in said state. On top of gravitational forces, weight stacks, dumbbells, or barbells also exert inertial forces. Keep in mind gravitation force acts downward only, but inertial force can be exerted in any direction. 

When thinking of training, each of these exerts different inertial forces:

• Heavy, 1RM back squat
• Accommodating resistance chains or bands
• Squat jump performed explosively

Bracketing Training Technique

Bracketing involves speeding up or slowing down movements in order to generate higher speed or higher forces. 

• Overspeed: Use bands to decrease the body weight by up to 10% which provides greater acceleration
• Underspeed: Use weights to increase the body weight up to 10% which provides greater forces

You typically don't want to go above or below 10% of body weight. 

Friction, Fluid Resistance, & Elasticity 

The equation for friction is, friction = kinetic energy x normal force. Keep in mind it takes more force to initiate movement than it does to keep it going. Concentric-only muscle forces tend to be efficient for conditioning. You can increase friction by increasing the load or changing the surface of training (rougher surfaces have higher kinetic energy). 

Fluid resistance doesn't generally provide an eccentric phase, for example movements like swimming, rowing, and machines that employ fluid resistance. 

Elasticity training is when bands are applied to equipment (barbell back squat) or the body (Vertimax) in a way that both increases the acceleration (as the band shortens) and increases force production (as the band lengthens). 

Valsalva Maneuver 

Instructing an athlete to use the Valsalva maneuver, sometimes referred to as bracing, simply means instructing them to expire against a closed glottis (airway). As a result of exhaling against a closed airway, the muscles of the abdomen and rib cage contract resulting in a rigid torso. However, the Valsalva maneuver does increase blood pressure, so it may not be appropriate for those with high blood pressure or older adults.

Weight Belts

Weight belts can be helpful as an additional tool when athletes can successfully brace and use the Valsalva maneuver to make the torso even more rigid. Weight belts help increase intra-abdominal pressure and are only needed for exercises that directly load the lower back/spine. Keep in mind it is not recommended to go from using a belt to not using a belt abruptly. Weight belts should also not be used for lighter sets. 

Shoulder & Knee Joints

The shoulder and knee joints are some of the most common areas of injury for athletes. It's important to know that the glenohumeral joint, a shallow ball & socket joint, has the greatest range of motion in the body, as a result it has less stability. 

The knee on the other hand is situated between 2 long levers, the femur, and the tibia & fibula of the lower leg. As a result, the knee has an increased mechanical advantage because the patella (the knee cap) functions to increase the moment arm of the quadriceps. 

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