4.2 Biomechanics
Biomechanics is the study of the mechanical laws relating to the movement or structure of living organisms. In the context of fitness, biomechanics provides an understanding of how the human body moves, how forces are generated, and how they interact with external forces. By applying the principles of biomechanics, individuals can improve their physical performance, reduce the risk of injury, and optimize their overall fitness.
Biomechanics encompasses various aspects, such as analyzing body movements, understanding the forces acting on the body, and identifying the mechanical properties of biological tissues. This field of study integrates knowledge from disciplines like physics, engineering, and anatomy to understand the complex mechanisms of human motion.
Biomechanics in fitness provides an understanding of human body movement, force generation, and interaction with external forces.
Biomechanics is essential for designing effective exercise programs, selecting appropriate exercises, and ensuring proper exercise techniques. By understanding the underlying principles of biomechanics, personal trainers can maximize their client’s training efficiency, enhance athletic performance, and minimize the risk of injuries.
Some key aspects of biomechanics in fitness include:
- Kinematics: The study of motion, including factors such as displacement, velocity, and acceleration, without considering the forces that produce the motion.
- Kinetics: The study of the forces that cause motion, including internal forces generated by muscles and external forces acting upon the body.
- Levers and mechanical advantage: The analysis of how the body’s skeletal and muscular systems function as levers to produce force, speed, and range of motion.
- Joint stability and mobility: Understanding how joints are stabilized and how they move allows for efficient and safe movement patterns.
- Force production and transfer: Examining how forces are generated within the body and how they are transferred to other body segments or the environment.
By applying the principles of biomechanics in fitness, trainers and individuals can make informed decisions about exercise selection, technique, and progression. This knowledge can lead to better performance, improved health, and a reduced risk of injury.
4.2.1. Stability
In personal training, the concept of stability is crucial in ensuring the safe and effective execution of exercises. The basic principles of stability revolve around the size of the base of support and the position of the center of gravity. By incorporating these principles, trainers can help clients achieve a strong foundation for their workouts, preventing injuries and maximizing performance.
Increased stability can be achieved through a larger base of support. Advising clients to adopt a stance with their feet roughly shoulder-width apart or wider can offer a stable foundation, particularly during heavy lifts and overhead exercises (Bryanton et al., 2012). Conversely, a narrow stance, where feet are positioned closely together, may jeopardize stability and elevate the likelihood of injury (Todorov, 2006).
Another way to enhance stability is by bending the knees, which lowers the center of gravity. A lower body position increases stability and helps prevent knee injuries. Foot placement also contributes to maintaining balance during exercises. For example, with parallel feet and shoulder-width apart, a person can better manage the weight close to their body or overhead. A stride position, on the other hand, can improve balance in a forward-backward direction.
When performing exercises on a bench, placing the feet firmly on the floor is essential, as this increases sideward stability. Keeping the feet on the bench creates an unstable position, which can be particularly hazardous when using heavy weights.
A thorough understanding of stability principles is essential for personal trainers to design effective and safe training programs for their clients. By considering factors such as base of support, center of gravity, and foot placement, trainers can help clients optimize their exercise performance and minimize the risk of injury.
4.2.2. Motion and Force
The concept of motion involves the change in an object’s position relative to another object. Therefore, it requires a reference point to determine whether the object is moving or resting.
In the human body, joints, and segments are the primary reference points for motion. A segment is the body part between two joints, such as the upper-arm segment between the shoulder and elbow.
There are four fundamental types of motion:
- Rotary motion occurs when each point of the segment follows the same angle, at a constant distance from the axis of rotation, and at the same time.
- Translatory motion occurs when each point on the segment moves in a parallel path through the same distance at the same time.
- Curvilinear motion is a combination of small gliding motion within the joint and more rotatory motion of the segment, such as throwing a ball.
- General plane motion occurs when motions at various joints are simultaneously linear and rotary, such as when riding a bike.
Muscular force can be manifested through pushing or pulling motions and may stem from external sources, such as gravity, water, air (wind), other objects, or individuals (Hall, 2007). Muscular forces are classified as internal forces when considering the body as a whole. In contrast, when the reference point is the joint axis, these forces are considered external, as they act beyond the joint (Neumann, 2017).
During strength exercises involving lifting weights, four force components must be considered.
The first component is the magnitude, which refers to how much force is applied to the fitness equipment. For instance, if you want to lift a 20 kg dumbbell, you must exert more than 20kg of force to lift it.
The second component is the direction of the force, which can be horizontal, vertical, or a combination of both.
The third component is the point of force application, where the force is applied to the body or equipment being used. For instance, when lifting a barbell, if you hold it in the middle of the bar with your hands close to each other, the force is applied closer to the bar’s center of mass, making the exercise more effective. However, this requires greater balance, especially if the barbell is long. A wider grip is necessary in this case, with force applied at two points to lift one barbell. This may reduce efficiency but enhances safety.
The fourth component is the line of action or line of force, which is depicted by a straight line drawn from the point of force application in the direction of the force. The more directly the force is applied in the same direction, the greater the force in that direction.
4.2.3. Angle of muscle pull
The angle of pull is the angle between the long axis of the bone (for example, the lever arm) and the line of pull of the muscle. The angle of pull and the moment arm of the muscles both change as the joint goes through its range of motion (Houglum 2001).
During strength exercises, the exhibited strength at different points in the range of motion will vary due to the angle of muscle pull.
To better understand the concept of the angle of pull, let’s consider a practical example involving a biceps curl exercise. In this exercise, you hold a dumbbell in your hand and bend your elbow to lift the weight toward your shoulder.
At the beginning of the movement, when your arm is fully extended, the angle of pull of the biceps muscle is almost perpendicular to the forearm. This angle allows the biceps to exert the maximum force in the upward direction, efficiently lifting the weight.
As you continue to lift the dumbbell and your elbow bends, the angle of pull changes gradually. When your forearm is at a 90-degree angle to the upper arm, the angle of pull is the most optimal for generating the greatest force in the upward direction.
As you lift the weight even higher and your elbow approaches full flexion, the angle of pull becomes more acute, resulting in a decrease in the force exerted by the biceps in the upward direction. At this point, the weight might feel heavier, and it becomes more challenging to complete the curl.
The biceps muscle inserts at an approximately 10-degree angle on the radius bone of the forearm when the arm is straight. When the muscle shortens (during the curl), most of its force goes into stabilizing the elbow joint rather than raising the forearm with the weight. When the insertion angle approaches 90°, the muscle’s entire force lifts the weight. The maximal amount of torque is produced when the angle of pull of the muscle is 90° and the moment arm is at its greatest length.
This is called a mechanical advantage, enabling you to do more work at this angle of muscle pull (Houglum 2001). This concept also works for external forces applied to the body. For example, with pulleys, the maximal resistance occurs when the angle of pull of the pulley’s rope is 90° to the extremity being resisted (Houglum 2001).If you lift the heaviest weight you can handle at the beginning of an exercise, it might feel lighter as you bend your elbow to a 90-degree angle. To work your muscles harder in this position, you can either increase the weight or limit the movement (avoid fully straightening your arms at the lowest point). However, keep in mind that consistently doing this might decrease your flexibility over time.
Did you know? Physiological advantage is a muscle’s ability to shorten. A muscle has the most physiological advantage when it is at its full resting length.
The human body is designed to prioritize speed over strength. When muscles contract fast and with power, they produce greater force and speed, giving a physical edge. This advantage allows athletes to respond quicker and excel in their chosen sports or activities.
4.2.4. Levers
The human body works like a system of levers, with bones acting as bars, joints as fixed points, and muscle contractions providing the force to move against resistance or weight. The resistance can range from minimal to maximal.
The location of the axis, force, and resistance determines three classes of levers.
In a first-class lever, the fulcrum is between the force and the resistance, similar to a seesaw. When force is applied to move the resistance or weight, the lever rotates around the fulcrum.
The effort is the applied force, and the lever arm is the distance between the effort and the fulcrum. Thus, a longer lever arm needs less effort to move the load. First-class levers in the human body are rare. An example is the joint between the head and the first vertebra (the atlantooccipital joint), where the weight (resistance) is the head, the axis is the joint, and the muscular action (force) comes from muscles like the trapezius attaching to the skull (Behnke 2012). Therefore, nodding the head would exemplify a first-class lever movement.
In a second-class lever, the fulcrum is at one end of the lever, the load is at the other end, and the force is applied in the middle. This type of lever provides a mechanical advantage, requiring less effort to move the load. In the human body, an example is the lower leg when someone stands on tiptoes. The axis is formed by the metatarsophalangeal joints, the resistance is the body’s weight, and the force is applied to the heel by the gastrocnemius and soleus muscles through the Achilles tendon (Behnke 2012). The push-up would also be an example of the second-class lever.
In a third-class lever, the most common in the human body, the force is applied between the fulcrum and the load, requiring more effort to move the load than the load itself. This is the most common type of lever in the body, found in the elbow and knee joints. For example, in the elbow joint, the joint is the axis (fulcrum), the resistance (weight) is the forearm, wrist, and hand, and the force is the biceps muscle when the elbow is flexed (Behnke 2012).