4.1. Kinesiology

The science of kinesiology holds great significance in the realm of personal training, as it delves into the intricacies of human movement and the mechanisms that drive it. Kinesiology examines motion’s physiological, mechanical, and psychological aspects, analyzing how muscles, bones, and joints interact to facilitate movement. This field of study is essential for personal trainers. It equips them with the knowledge and tools necessary to design effective and tailored fitness programs.

One key aspect of kinesiology’s importance in personal training is injury prevention. By understanding the principles of human movement, personal trainers can identify potential risks and implement appropriate measures to minimize the likelihood of injuries. This includes selecting exercises that promote joint stability and muscular balance and teaching clients proper form and technique to ensure safe and effective execution.

Furthermore, kinesiology is vital in enhancing daily functionality for human movement. A strong foundation in kinesiology allows personal trainers to develop training programs that improve their clients’ overall functional capacity. This includes addressing issues related to posture, mobility, and biomechanics, ultimately contributing to a better quality of life. By addressing these components, personal trainers can help clients perform daily tasks with greater ease and efficiency, reduce the risk of chronic pain, and promote long-term health and well-being.

4.1.1. Types of muscle contractions

There are three primary types of muscle contractions: isotonic, isometric, and isokinetic. Each type plays a unique role in the body’s function. Understanding their differences will help you develop a comprehensive and effective training program.

Isotonic muscle contractions involve a change in muscle length while maintaining constant tension. This type of contraction can be further divided into two distinct phases: the positive phase, known as concentric contraction, and the negative phase, referred to as eccentric contraction. Both phases are crucial for functional movement and exercise, as they enable our muscles to effectively control, stop, and generate power in various activities.

A muscle contraction is a process by which a muscle shortens and generates force. During a muscle contraction, the filaments of the actin and myosin proteins slide past one another, producing tension in the muscle and causing it to shorten (see chapter 3.4.9).

Isotonic Contraction

Among the three main types of muscle contractions, isotonic and isometric contractions are the ones we will encounter most frequently in our daily work. Although the definition of isotonic contraction states that “tension remains the same, while the muscle’s length changes,” this is not entirely accurate in resistance training.

For instance, when training with free weights, the muscle’s tension will change due to alterations in the mechanical advantage of the joint where the movement is performed. For example, in the case of a dumbbell bicep curl, the muscle tension will be greatest when the weight is farthest from the joint (approximately a 90-degree angle), whereas the lowest tension will occur when holding the dumbbell in the lowest position.

Despite this discrepancy, we will continue to use the term isotonic (“iso” meaning the same, “tonic” refers to weight) contractions for resistance training where the weight remains constant while performing an exercise.

By modifying the resistance applied to the muscle during the movement, we are manipulating the strength curve of that exercise, which is referred to as Accommodating Resistance Training. Accommodating resistance involves using additional equipment (such as bands or chains) to increase the load’s resistance throughout the range of motion.

Returning to isotonic contraction, it is crucial to better understand its phases to effectively utilize each phase’s specifics in our program development and design.

  • Concentric contraction

Two types of isotonic contractions are concentric and eccentric contraction

Concentric muscle contraction is the positive phase of muscle contraction in which the muscle fibers shorten, producing a force that moves a body part in a specific direction. 

An example is the biceps contracting concentrically to lift a heavy weight toward the shoulder.

Concentric strength is usually measured by the maximum amount of weight that one can overcome in one repetition. In the fitness field, this is commonly referred to as the 1 Repetition Maximum or 1 RM.

  • Eccentric contraction

Eccentric contraction refers to the negative phase of muscle contraction, during which muscle fibers lengthen while still generating force, with resistance greater than the force produced. These contractions can be both voluntary and involuntary, such as a controlled lowering of a weight or an involuntary lowering of a weight that is too heavy to lift.

Eccentric contraction plays a crucial role in controlling and stopping movement and preparing muscles for explosive-type contractions. For example, in a biceps curl exercise, when you return to the initial position, the same muscles are involved, and they remain under contraction as they lengthen while you lower the weight. Since gravity is the force involved in lowering the weight, the eccentric contraction counteracts gravity’s pull to guide the movement.

The intensity of the contraction depends on the resistance being handled. For example, in a ballistic movement, the muscle’s contraction intensity increases as it lengthens and stops the movement once it reaches sufficient strength.

Eccentric contractions can generate up to 50% greater tension than concentric contractions, making the eccentric phase of muscle contraction incredibly powerful. It is responsible for controlling movement, stopping movement, and generating a sufficient amount of muscle tension to enable explosive contractions.

Unaccustomed eccentric exercise can cause more muscle damage than the concentric phase and the well-known delayed pain, commonly known as “Delayed-Onset Muscle Soreness” (DOMS). To date, the most effective preventative strategy to avoid these adverse effects involves repeating sessions of submaximal eccentric contractions, with the intensity progressively increasing throughout the training (Hody et al., 2019).

  • Isometric Contraction

Isometric contraction is a type of muscle contraction in which the muscle maintains a constant length while generating tension. There is no visible movement during isometric contractions, and the joint angle remains unchanged. This form of contraction is essential for maintaining posture, stabilizing joints, and providing the foundation for dynamic movements in everyday life and sports.

 

Isometric exercises are particularly beneficial for building strength, enhancing stability, and improving muscular endurance. They can be easily incorporated into training programs and suit individuals at various fitness levels. Some examples of isometric exercises include the plank, wall sit, isometric push-up, and glute bridge hold.

Isometric contraction is a type of muscle contraction in which the muscle maintains a constant length while generating tension. There is no visible movement during isometric contractions, and the joint angle remains unchanged. This form of contraction is essential for maintaining posture, stabilizing joints, and providing the foundation for dynamic movements in everyday life and sports.

Isometric exercises are particularly beneficial for building strength, enhancing stability, and improving muscular endurance. They can be easily incorporated into training programs and suit individuals at various fitness levels. Some examples of isometric exercises include the plank, wall sit, isometric push-up, and glute bridge hold.

When executing a strength exercise, all three of the muscle contractions are involved. By performing a movement, the main muscles undergo a concentric contraction while the antagonist muscles undergo an eccentric contraction. The adjacent parts of the body that are not in use are stabilized via the isometric contractions. Thus all three operate simultaneously, each with a very important purpose

4.1.2 Breathing during exercise

During exercise, the heart and lungs play crucial roles in providing energy and removing waste products. The lungs bring oxygen into the body and remove carbon dioxide. At the same time, the heart pumps oxygen to the muscles performing the exercise. As your muscles work harder, your body uses more oxygen and produces more carbon dioxide, causing your breathing to increase and circulation to speed up to deliver oxygen to the muscles.

When your lungs are healthy, you maintain a large breathing reserve, allowing you to feel “out of breath” after exercise but not “short of breath.” However, with reduced lung function, you may use up a significant portion of your breathing reserve, resulting in an unpleasant feeling of breathlessness.

It is normal to feel breathless during exercise. However, regular exercise can increase the strength and function of your muscles, making them more efficient and requiring less oxygen to move. This leads to reduced carbon dioxide production and less air needed for breathing during exercise. Exercise also strengthens the heart, improves circulation, and enhances overall physical and psychological well-being. In addition, it can decrease the risk of developing other conditions such as stroke, heart disease, and depression and help prevent the onset of type-II diabetes.

For strength training, exhaling during the concentric phase and inhaling during the eccentric phase of a lift are commonly recommended. This increases core engagement, providing more power and stability during the challenging part of the lift. A tightly contracted core prevents tension leakage from the rest of the body. Moreover, exhaling during the concentric portion of a movement can help stabilize and power you during a lift, acting as a pressure release valve to prevent significant drops in blood pressure and protect against lightheadedness after the lift.

Exhale during the concentric phase and inhale during the eccentric phase

The Valsalva maneuver

The Valsalva maneuver is a technique often used during resistance training, in which an individual forcefully exhales against a closed airway, typically by closing their mouth and pinching their nose shut. This maneuver increases intra-abdominal pressure, providing additional stability to the spine and core, and is thought to improve performance during heavy lifting exercises.

A brief review conducted by Hackett and Chow in 2013 examined the effects of the Valsalva maneuver on intra-abdominal pressure and safety issues during resistance exercise. Their findings suggest that the Valsalva maneuver may benefit lifting performance, including increased trunk stability and improved force transmission through the body.

Some research, such as the study conducted by Alfred A. Bove in “Pulmonary Aspects of Exercise and Sports” (2016), suggests that the Valsalva maneuver (VM) may potentially cause damage to the alveoli, the tiny air sacs in the lungs.

Considering all available data and practical experience, it is generally recommended to monitor clients’ breathing during exercise, ensuring they exhale during the concentric contraction and inhale during the eccentric contraction. This guidance is particularly important for beginners or individuals returning to training after a long period of inactivity.

While the Valsalva maneuver may offer some performance benefits during resistance training, it also carries risks that must be considered, especially for individuals with pre-existing health concerns. For example, the increase in intra-abdominal pressure can lead to a temporary spike in blood pressure, which may pose a danger to individuals with hypertension or heart conditions. Additionally, the increased pressure within the chest cavity may reduce venous return to the heart, potentially causing lightheadedness, fainting, or in rare cases, more severe cardiovascular complications. Therefore, further research is needed to better understand the balance between this technique’s potential advantages and risks.

As in all aspects of training, applying the principle of individuality is crucial. For more advanced clients engaging in heavy lifting, the monitored use of the Valsalva maneuver could offer some benefits. However, assessing each individual’s needs and health status is essential before incorporating the Valsalva maneuver into their training program.

4.1.3 Muscle roles

In Chapter 3.4.11, Interactions of Skeletal Muscles in the Body, we delved into the fundamental roles of muscles. We discovered that most muscles function in pairs, consisting of agonists and antagonists. The muscles responsible for generating movement are the agonists, while those with actions opposing the prime mover are called antagonists. Additionally, we explored the roles of assistant movers, which provide secondary support to the prime mover, and stabilization muscles, which maintain a body part’s position or provide stability.

Furthermore, some muscles, such as the muscles involved in facial expressions, do not exert force against the skeleton for movement. Instead, these muscles serve essential functions in non-skeletal activities and contribute to the overall complexity of the muscular system. By understanding the various roles and interactions of muscles in the body, we can better appreciate the intricacies of human movement and develop targeted training programs to enhance performance and prevent injury.

Prime Mover or Agonist

When a muscle serves as the primary force in a concentric contraction, it is referred to as a prime mover or agonist. For example, during a bicep curl, the biceps brachialis and brachioradialis act as agonists for elbow flexion. It is worth noting that many muscles can function as prime movers in multiple actions, such as the biceps being the prime mover in forearm supination as well.

Assistant Mover

Assistant movers are muscles that play a secondary role to the prime movers involved in an action. These secondary muscles can sometimes assume a primary role in specific ranges of motion or exercises. For instance, the pronator teres is a prime mover in pronation but assists elbow flexion. Assistant or secondary muscles are typically less powerful than the primary agonists or prime movers.

Antagonist

An antagonist muscle opposes the action of the agonist. As the agonist experiences a concentric contraction, the antagonist undergoes an eccentric contraction to guide and stabilize the joint throughout the full range of motion (ROM). The roles of antagonist and agonist can change depending on the action. For example, in a bicep curl, the biceps act as the prime mover, while the triceps serve as the antagonist. However, during elbow extension, the roles are reversed.

uring a muscular contraction, especially with heavy weights, the agonist and antagonist muscles contract simultaneously (co-contraction) to stabilize or hold the joint in place. When the resistance is lighter, the antagonist mainly contracts eccentrically to slow down and prevent injury. With heavier weights, both muscles contract, and the antagonist lengthens eccentrically to enable movement.

Stabilization Muscles

Stabilizer muscles steady or hold a body part in place, providing a solid base for the prime mover to contract against. Stabilization is essential for precise movements of limbs or body parts. Stabilizer muscles generally undergo isometric contractions to hold the bone in place. Some instances involve slight movement but are still considered stabilization. For example, during an overhead press, the quadriceps and erector spinae contract to hold the trunk upright. Breathing also contributes to stabilizing the trunk during strength exercises.

Isometric contractions in stabilization can lead to some muscle development. However, they should not replace other exercises and regimes to strengthen the muscles involved in the action, as concentric and eccentric contractions are more effective for building strength, mass, or definition.

Synergists and synergy

This term has various meanings, but it is commonly used in two ways. The first is helping synergy, where two muscles contract simultaneously to produce a single movement while canceling out their other actions. The second is true synergy, in which a different muscle contracts to counteract the secondary action of another muscle. Synergy can also be synonymous with neutralizer, referring to a muscle that contracts to neutralize an undesirable action of another muscle during its contraction.

4.1.4 Types of movements

Movements take place at joints or articulations and within specific planes. Joints, or articulations, are the connecting points between two or more bones, such as the tibia (shin bone) and femur (thigh bone). Discussing movement within a plane implies that the motion remains confined to that plane. For instance, forearm flexion (drawing the forearm toward the body) by contracting the biceps brachii muscle occurs predominantly within the sagittal plane.

While certain activities may involve movements across two or three planes, it is generally advised in resistance training to initially focus on the primary plane of motion until the individual has developed strength and advanced their training level. For example, a beginner could perform a bicep curl in the sagittal plane, the primary plane of motion for the exercise, until they have achieved adequate strength and proper form. Once they have reached an advanced level, they may then engage in more complex movements, such as a bicep curl in the frontal plane. Executing movements across multiple planes during an exercise significantly increases the risk of injury, particularly when resistance from weights or other means is involved.

In resistance training, it is advised to focus on the primary plane of motion initially until an individual develops sufficient strength and advances their training level.

A muscle can contract with different amounts of force and in different ways to produce different types of movement. This includes:

Sustained Force Movement

Sustained force movement involves muscle contracting and maintaining that contraction for an extended duration. The primary muscle remains under constant contraction throughout the range of motion (ROM). Commonly used in strength training and rehabilitation exercises, this type of movement helps develop strength, endurance, and coordination while increasing flexibility and range of motion.

Ballistic Movement

Ballistic movement involves an inertial motion following a rapid, maximum-force contraction. Ballistic movements involve generating force rapidly and explosively, resulting in high-velocity movements that can improve power, speed, and athletic performance. Typically, the muscle experiences pre-tensing during the eccentric contraction, allowing for a faster and more powerful concentric contraction. These movements require high levels of muscular power and coordination and are often used to generate momentum or change direction quickly.

Guided Movement

Guided movement occurs when both the agonist and antagonist muscles contract simultaneously to control a movement. This type of movement is frequently observed in fine motor skills, such as writing or drawing, where precision and control are essential.

Dynamic Balance Movements

Dynamic balance movements involve continuous agonist-antagonist muscle contractions to maintain a specific position or posture. These movements constantly adjust to provide stability and balance. For example, when standing on one leg, the body makes constant, subtle corrective movements to maintain balance, as it is impossible to remain perfectly still.

4.1.5 Planes of motion

Daily, we navigate a three-dimensional (3D) world and engage in various 3D movements. To effectively describe these complex movements, a unified system is required. The planes of motion offer a comprehensive framework that allows for a more precise description of the human body’s movements within 3D space (Levangie et al., 2005).

Understanding the planes allows you to define and categorize movements essential for knowing where the exercise is performed in space. This knowledge enables us to design targeted and efficient exercise programs that consider human movement’s complexity.

There are three primary planes of motion:

1-Sagittal Plane:

  • Vertical plane dividing the body into left and right sections
  • Includes movements such as flexion and extension
  • Examples: walking, running, bicep curls, and squats

 

2-Frontal Plane:

  • Vertical plane dividing the body into front and back sections
  • Includes movements such as abduction and adduction
  • Examples: lateral raises, jumping jacks, and side lunges

 

3-Transverse Plane:

  • A horizontal plane dividing the body into upper and lower sections
  • Includes rotational and twisting movements
  • Examples: trunk rotations, horizontal shoulder abduction, and Russian twists

You will notice that there is often a fourth plane of human motion mentioned in the literature, the median plane. The frequent question arises if the median and the sagittal plane are the same.

The sagittal plane is a vertical plane that divides the body into left and right sections, while the median plane (also known as the mid-sagittal plane) is a specific sagittal plane that divides the body into equal left and right halves. The median plane passes through the body’s center, whereas other sagittal planes may not be exactly centered.

 

Single Plane vs. Multiplanar Movements

Single-plane movements involve motion in only one plane. It means that the motion is executed only through the imaginary surface of one plane.

Here are some examples of single-plane exercises:

  • Sagittal plane: Bicep curls and squats
  • Frontal plane: Lateral raises and side lunges
  • Transverse plane: Trunk rotations and Russian twists

Multiplanar movements, on the other hand, involve motion across two or more planes. These complex movements often resemble real-life actions and require greater coordination and control.

Here are some examples of exercises:

  • Throwing a ball: Involves motion in the sagittal, frontal, and transverse planes
  • Swimming: Combines movements from all three planes for various strokes
  • Jumping and landing: Requires a combination of sagittal and frontal plane movements

By recognizing these planes of motion and understanding the differences between the single-plane and multiplanar movements, we can create effective exercise programs that target specific muscles, improve overall movement quality, and reduce the risk of injury. This understanding also facilitates better communication between fitness professionals and their clients, enabling them to work together to achieve optimal results.

Movement, with the exception of multiplanar movement, occurs within a plane of motion and around an axis that is perpendicular to the plane of motion. 

For example: biceps curl is the concentric contraction of the biceps that occurs in the sagittal plane. Lateral dumbbell raise is the abduction of the arm that occurs in the frontal plane. The standarised reference position for which the movements of the body are described, in which the body is facing forward, arms at sides and palms forward.

Table: Fundamental anatomical movement in each plane of motion

4.1.6 Fundamental movement of major body segments

A multitude of movements is facilitated by the numerous joints in the human body. Six primary movements transpire at the joints connecting body segments: flexion, extension, abduction, adduction, rotation, and circumduction (Neumann, 2017).

Flexion involves a decrease in the angle between two body segments, occurring at the shoulder, elbow, hip, and knee joints. Examples include bending the elbow, bending the knee, and curling the toes.

Extension refers to an increase in the angle between two body segments or the return from flexion. It can occur in the arms, legs, and spine. 

Hyperextension, an increase in the angle beyond the normal joint movement, can be observed when the leg is lifted behind the body (hip joint) on a standing hip machine.

Abduction is the movement of a body segment away from the midline, involving a limb moving away from the body’s center or one limb moving away from another. Examples include lifting the arm away from the side of the body or moving the leg away from the midline while walking.

Adduction is the movement of a body segment toward the midline or the return from abduction, commonly seen in the shoulder and hip joints, such as when legs come together on a hip adductor machine.

Rotation entails the circular movement of a body segment around a long axis, with inward rotation moving towards the body’s midline and outward rotation moving away. Right and left rotations describe the directional rotation of the head and trunk.

Special rotations occur in the forearms and feet:

  • Pronation refers to the rotation of the forearm to a palms-down position
  • Supination involves the rotation of the forearm segment to a palms-up position
  • Eversion, or foot pronation, is the outward tilting of the foot’s sole
  • Inversion, or foot supination, is the inward tilting of the foot’s sole

Circumduction is the sequential combination of movements that outline a geometric cone, such as circles made by the trunk, shoulder, hip, ankle, or thumb.