Biomechanics In Sport
Original Editor - Naomi O'Reilly
Introduction[edit | edit source]
Biomechanics in sport incorporates a detailed analysis of sport movements in order to minimise the risk of injury and improve sports performance. Sport and exercise biomechanics encompasses the area of science concerned with the analysis of the mechanics of human movement. It refers to the description, detailed analysis and assessment of human movement during sport activities. Mechanics is a branch of physics that is concerned with the description of motion/movement and how forces create motion/movement. Therefore, sport biomechanics is the science of explaining how and why the human body moves in the way that it does. In sport and exercise, that definition is often extended to also consider the interaction between the performer, their equipment and the environment. Biomechanics is traditionally divided into the areas of kinematics and kinetics. Kinematics is the branch of mechanics that deals with the geometry of the motion of objects, including displacement, velocity, and acceleration, without taking into account the forces that produce the motion. Kinetics is the study of the relationships between the force system acting on a body and the changes it produces in body motion. In terms of this, there are skeletal, muscular and neurological considerations we need to consider when describing biomechanics.
Application [edit | edit source]
According to Knudson human movement performance can be enhanced in many ways. Effective movement encompasses anatomical factors, neuromuscular skills, physiological capacities, and psychological/cognitive abilities. Biomechanics is essentially the science of movement technique and tends to be most utilised in sports where technique is a dominant factor rather than physical structure or physiological capacities. The following are some of the areas where biomechanics is applied, to either support the performance of athletes or solve issues in sport or exercise:
- The identification of optimal technique for enhancing sports performance
- The analysis of body loading to determine the safest method for performing a particular sport or exercise task
- The assessment of muscle recruitment and loading
- The analysis of sport and exercise equipment e.g., shoes, surfaces and rackets.
Biomechanics is utilised to attempt to enhance performance or reduce the risk of injury in the sport and exercise tasks examined.
Principles of Biomechanics[edit | edit source]
It is important to know several biomechanical terms and principles when examining the role of biomechanics in sport and exercise.
Forces and Torques[edit | edit source]
A force is simply a push or pull. A force can change the motion of a body segment. Motion is created and modified by the actions of forces. When force rotates a body segment or a racket, this effect is called a torque or moment of force. Example - Muscles create a torque to rotate the body segments in all tennis strokes. In the service action internal rotation of the upper arm is the result of an internal rotation torque at the shoulder joint, caused by muscle actions (latissimus dorsi and parts of the pectoralis major and deltoid). To rotate a segment with more power a player would generally apply more muscle force.
Newton’s Laws of Motion[edit | edit source]
- Law of Inertia - Newton’s First Law of inertia states that objects tend to resist changes in their state of motion. An object in motion will tend to stay in motion and an object at rest will tend to stay at rest unless acted upon by a force. Example - A skater gliding on ice will continue gliding with the same speed and in the same direction, unless an external force acts upon the skater.
- Law of Acceleration - Newton’s Second Law explains how much motion a force creates. The acceleration (tendency of an object to change speed or direction) an object experiences is proportional to the size of the force and inversely proportional to the object’s mass (F = ma). Example - When a ball is thrown, kicked, or struck with an implement, it tends to travel in the direction of the line of action of the applied force. The greater the amount of force applied, the greater the speed the ball has. If a player improves leg strength through training while maintaining the same body mass, they will have an increased ability to accelerate the body using the legs, resulting in better agility and speed.
- Law of Reaction - The Third Law states that for every action (force) there is an equal and opposite reaction force. This means that forces do not act alone, but occur in equal and opposite pairs between interacting bodies. Example - The force created by a player's legs “pushing” against the ground results in ground reaction forces in which the ground “pushes back” and allows the runner to move across the court (As the Earth is much more massive than the player, the player accelerates and moves rapidly, while the Earth does not really accelerate or move at all). This action-reaction also occurs at impact of a racket with a ball. The force applied to the ball is matched with an equal and opposite force applied to the racket.
Momentum[edit | edit source]
Newton’ Second Law is also related to the variable momentum, which is the product of an object’s velocity and mass. Momentum is the quantity of motion an object possesses. Momentum can be transferred from one object to another. There are different types of momentum which each have a different impact on the sport.
- Linear momentum: momentum in a straight line
- Angular momentum: rotational momentum created by the rotations of the various body segments
In tennis, one of the main reasons for the increase in the power of the game today is the incorporation of angular momentum into ground stroke and serve techniques. The angular momentum developed by the coordinated action of body segments transfers to the linear momentum of the racket at impact.
Centre of Gravity[edit | edit source]
The Centre of Gravity (COG) is an imaginary point around which body weight is evenly distributed. The centre of gravity of the human body can change considerably because the segments of the body can move their masses with joint rotations. This concept is critical to understanding balance and stability and how gravity affects sport techniques.
The direction of the force of gravity through the body is downward, towards the centre of the earth, and through the COG. This line of gravity is important to understand and visualise when determining a person's ability to successfully maintain balance. When the line of gravity falls outside the Base of Support (BOS), a reaction is needed in order to stay balanced.
The centre of gravity of a squash racket is a far simpler process and can usually be found by identifying the point where the racket balances on your finger or another narrow object.
Balance[edit | edit source]
- Static balance: the ability to maintain postural stability and orientation with centre of mass over the base of support and body at rest
- Dynamic balance: the ability to maintain postural stability and orientation with centre of mass over the base of support while the body parts are in motion
Correct Biomechanics[edit | edit source]
As mentioned above, correct biomechanics provide efficient movement and may reduce the risk of injury. In sport, it is always good to consider abnormal or faulty biomechanics as a possible cause of injury. These abnormal biomechanics can be due to anatomical or functional abnormalities. Anatomical abnormalities such as leg length discrepancies cannot be changed, but the secondary effects can be addressed with, for example, a shoe insert or orthotics. An example of functional abnormalities is muscle imbalance that develops after a long period of immobilisation.
The different planes of motion and axes are often referred to in biomechanics. Have a look at this video, to refresh your memory.
Incorrect technique can cause abnormal biomechanics which can lead to injuries. Below are some examples of the relationship between faulty technique and associated injuries.
|Cricket||Mixed bowling action||Pars interarticularis stress fractures|
|Tennis||Excessive wrist action with backhand||Extensor tendinopathy of the elbow|
|Swimming||Decreased external rotation of the shoulder||Rotator cuff tendinopathy|
|Running||Anterior pelvic tilt||Hamstring injuries|
|Rowing||Change from bow side to stroke side||Rib stress fractures|
|Ballet||Poor turnout||Hip Injuries|
Lower Limb Biomechanics[edit | edit source]
As humans, ambulation is the main form of movement. When walking upright it is the lower limbs that move the body forwards. The way in which the foot strikes the ground, and the effect of this on the lower limbs has become a subject of much debate and controversy in recent years.
Lower limb biomechanics refers to a complex interplay between the joints, muscles, and nervous system which results in a certain patterning of movement, often referred to as ‘alignment’. Much of the debate centres around what is considered ‘normal’ and what is considered ‘abnormal’ in biomechanical terms, as well as the extent to which we should intervene should abnormal findings be found on assessment. This section examines the biomechanics of the lower extremity, in particular the anatomy and biomechanics of the foot and ankle, the impact of Q Angle on the mechanics of the hip and knee, and finally the implications of this on gait.
Foot and Ankle Biomechanics[edit | edit source]
The foot and ankle form a complex system which consists of 26 bones, 33 joints and more than 100 muscles, tendons and ligaments. It functions as a rigid structure for weight bearing and it can also function as a flexible structure to conform to uneven terrain. The foot and ankle provide various important functions which include supporting body weight, providing balance, shock absorption, transferring ground reaction forces, compensating for proximal malalignment, and substituting hand function in individuals with upper extremity amputation/paralysis. All these functions are key when involved with any exercise or sport involving the lower limbs. The Biomechanics of Foot and Ankle Physiopedia page examines the biomechanics of the foot and ankle and its role in locomotion.
Q Angle[edit | edit source]
An understanding of the normal anatomical and biomechanical features of the patellofemoral joint is essential to any evaluation of knee function. The Q angle formed by the vector for the combined pull of the quadriceps femoris muscle and the patellar tendon, is important because of the lateral pull it exerts on the patella.
The direction and magnitude of force produced by the quadriceps muscle have great influence on patellofemoral joint biomechanics. The line of force exerted by the quadriceps is lateral to the joint line mainly due to the large cross-sectional area and force potential of the vastus lateralis. Since there exists an association between patellofemoral pathology and excessive lateral tracking of the patella, assessing the overall lateral line of pull of the quadriceps relative to the patella is a meaningful clinical measure. Such a measure is referred to as the Quadriceps angle or Q angle. It was initially described by Brattstrom. Read more about the Q-angle here: Q Angle
Biomechanics of Gait[edit | edit source]
Sandra J. Shultz describes gait as, “...someone’s manner of ambulation or locomotion, involves the total body". Gait speed determines the contribution of each body segment. Normal walking speed primarily involves the lower extremities, with the arms and trunk providing stability and balance. The faster the speed, the more the body depends on the upper extremities and trunk for propulsion as well as balance and stability. The legs continue to do the most work as the joints produce greater ranges of motion through greater muscle responses. In the bipedal system the three major joints of the lower body and pelvis work with each other as muscles and momentum move the body forward. The degree to which the body’s centre of gravity moves during forward translation defines efficiency. The body’s centre moves both side to side and up and down during gait.” Bipedal walking is an important characteristic of humans". The Gait Physiopedia page presents information about the different phases of the gait cycle and important functions of the foot while walking.
Upper Limb Biomechanics[edit | edit source]
Correct biomechanics are as important in upper limb activities as they are in lower limb activities. The capabilities of the upper extremity are varied and impressive. With the same basic anatomical structure of the arm, forearm, hand, and fingers, major league Baseball Pitchers pitch fastballs at 40 m/s, swimmers cross the English Channel, gymnasts perform the iron cross, and Olympic boxers in weight classes ranging from flyweight to super heavyweight showed a range of 447 to 1,066 pounds of peak punching force.
The structure of the upper extremity is composed of the shoulder girdle and the upper limb. The shoulder girdle consists of the scapula and clavicle. The upper limb is composed of the arm, forearm, wrist, hand, and fingers. However, a kinematic chain extends from the cervical and upper thoracic spine to the fingertips. Only when certain multiple segments are completely fixed can these parts possibly function independently in mechanical roles.
This section reviews the anatomical structures enabling these different types of movement as well as the biomechanics or ways in which the muscles cooperate to achieve the diversity of movement of which the upper extremity is capable.
Scapulohumeral Rhythm[edit | edit source]
Scapulohumeral rhythm (also referred to as glenohumeral rhythm) is the kinematic interaction between the scapula and the humerus. This interaction is important for the optimal function of the shoulder. Scapulohumeral rhythm was first discussed by Codman in the 1930's. When there is a change of the normal position of the scapula relative to the humerus, this can cause a dysfunction of the scapulohumeral rhythm. The change of the normal position is also called scapular dyskinesia. Various studies of the mechanism of the shoulder joint have attempted to describe the global motion capacity of the shoulder. Can you evaluate the shoulder to see if the function is correct and explain the complex interactions between components involved in placing the hand in space? Read more about the Scapulohumeral Rhythm: Scapulohumeral Rhythm.
Sport Specific Biomechanics[edit | edit source]
Running Biomechanics[edit | edit source]
Running is similar to walking in terms of locomotive activity. However, there are key differences. Having the ability to walk does not mean that the individual has the ability to run. There are some differences between the gait and run cycle - the gait cycle is one third longer in time, the ground reaction force is smaller in the gait cycle (so the load is lower), and the velocity is much higher. In running, there is also just one stance phase while in stepping there are two. Shock absorption is also much larger in comparison to walking. This explains why runners have more overload injuries.
- Greater balance
- Greater muscle strength
- Greater joint range of movement
Read more about running biomechanics: Running Biomechanics
Cycling Biomechanics[edit | edit source]
Cycling was initially invented by Baron Carl von Drais in 1817, but not as we know it. Cycling consisted of a machine which initially had two wheels that were connected by a wooden plank with a rudder device for steering. It involved people running along the ground whilst sitting down; giving them the name of a 'running machine' (in all senses) or a velocipede.
A survey in 2020 estimated that over 47% of people, over the age of five, in England own or have access to a cycle. This means that a large amount of people are cycling, whether it be professional, recreational or for commuting this increase the chance of developing an injury.
Read more: Cycling Biomechanics
Baseball Pitching Biomechanics[edit | edit source]
Baseball pitching is one of the most intensely studied athletic motions. Although the focus has been more on the shoulder movement, entire body movement is required to perform baseball pitching. Throwing is also considered one of the fastest human motions performed, and maximum humeral internal rotation velocity reaches about 7000 to 7500o/second.
Read more about the biomechanics of throwing: Throwing Biomechanics
Tennis Biomechanics[edit | edit source]
Tennis biomechanics is a very complex task. Consider hitting a tennis ball. The athlete needs to see the ball coming off their opponent's racket, then they have to judge the speed, spin, trajectory and the direction of the tennis ball. The player then needs to adjust their body position quickly to move around the ball. As the player prepares to hit the ball the body is in motion, the ball is moving both in a linear and rotational direction if there is spin on the ball, and the racket is also in motion. The player must coordinate all these movements in approximately a half a second so they strike the ball as close to the centre of the racket in order to produce the desired spin, speed and direction for return of the ball. It is obvious from this that biomechanics is vitally important to a tennis player's ability to produce a stroke effectively and efficiently. Not only is good biomechanics important for stroke production, but also equally important for injury prevention.
These articles provide some more detailed information on Serve and Ground Stroke Biomechanics and also look at the implications for strength training and rehabilitation:
- Tennis Serve Biomechanics in Relation to Ball Velocity and Upper Limb Joint Injuries
- Biomechanics of the Tennis Ground Strokes: Implications for Strength Training
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