Maximal Strength
The peak force or torque the neuromuscular system is capable of producing in a single maximal voluntary contraction, irrespective of the time element. Maximal strength plays a major role in sports where great external resistance must be overcome, such as hammer throwing, shot-putting and weightlifting. Its importance as a determinant of athletic performance diminishes as the duration of the event increases. For example a 60m indoor sprinter requires more maximal strength than a 1500m runner. Sports of an intermittent nature such as squash and tennis, which require intense burst of power interspaced with recovery periods, are also dependant on high levels of maximal strength. 

Speed strength
The ability of the neuromuscular system to produce the greatest possible force in the shortest possible time frame. It is the capacity of the neuromuscular system to overcome resistance with the greatest contraction speed possible. Speed-strength is a high priority in the field events, in the sprinting, kicking, jumping and throwing activities of team sports, and in the starts and acceleration phases of sprinting, cycling, rowing, ice skating and kayaking. 

Speed-strength encompasses three other strength qualities: starting strength, explosive strength and reactive strength.

Starting strength
The capacity to generate maximal force at the beginning of a muscular contraction; the capacity to overcome resistance and initiate movement. Starting strength is of importance in movements that require great initial speed, such as boxing blows and squash thrusts. Starting strength is a key determinant of performance in sports where the resistance to overcome is relatively light. It is dependant on the number of motor units accessed at the beginning of the contraction. 

Explosive strength
The capacity to develop a vertical rise in force once movement has been initiated, measured in terms of the increase in force per unit of time; the ability of the neuromuscular system to continue developing the already initiated force as quickly as possible; the rate at which one can develop maximal or peak force. 

Explosive strength is a key determinant of performance in sports where the resistance to overcome is relatively great, such as judo, hammer throwing and shot putting. 

Reactive strength
The ability to quickly switch from an eccentric contraction to a concentric contraction. This is also known as the stretch-shortening cycle. Reactive strength regulates performance in sports where stretch-shortening activity of the musculature is great. For example, in volleyball, in basketball and in weightlifting. In addition, the ability to quickly switch from an eccentric contraction to a concentric contraction is an important contributor to performance in jumping, throwing and sprinting. It is also an important factor for improving the efficiency of endurance runners, as it can assist in reducing ground contact times. 

Strength endurance
It is the capacity of muscles to resist fatigue while generating force over a period of time. Strength Endurance is characterised by high strength levels coupled with high levels of endurance. It is of particular importance in cyclical endurance events, such as rowing, swimming, canoeing and kayaking, where the ability to overcome exceptional resistance must be maintained over long periods. It also plays a key role in gymnastics, wrestling, boxing, judo and in many team sports. 

Relative strength
Strictly speaking, relative strength is not actually a specific type of strength but rather a way to measure strength in relation to an athletes body mass. It is the maximum force an athlete can generate per unit of bodyweight. It is affected by factors such as changes in body mass and neural drive. High relative strength is of critical importance to performance in sports in which athletes have to move their entire bodyweight, e.g. jumps, gymnastics, and sports that involve weight classes, such as judo and boxing. 

Concentric contraction
The muscle develops tension and shortens, causing movement to occur. 

The muscle lengthens while producing tension, thus braking or controlling the speed of movement. 

Eccentric contraction
When lifting the barbell overhead during the positive phase of an overhead press, the triceps shorten (concentric contraction). When lowering the barbell from overhead to under the chin during the negative phase of the overhead press, the triceps lengthen (eccentric contraction). 

When pulling the body up during the positive phase of a chin-up, the biceps shorten (concentric contraction) resulting in an elevation of the body. During the negative phase of the chin up, when lowering the body from the elevated chin-up position, the biceps lengthen (eccentric contraction). 

Isometric contraction
A muscle develops tension while its length remains unchanged, thus producing no external movement. However, when isometric tension is developed, the muscle belly and fascia do shorten internally, but a shortening in the agonist muscles is countered equally by a shortening in the antagonist muscles. Having the ability to perform adequate isometric tension is paramount in sports, for both performance optimisation and the avoidance of injury.

Strength qualities and their importance in athletic performance