Particular joint movement
The term strength will be employed to identify the maximal force or torque that can be developed by the muscles performing a particular joint movement (e.g. elbow flexion, knee extension). However, the muscles may perform at maximal effort as either isometric, concentric or eccentric actions and the two dynamic actions may be performed at a wide range of velocities.
An infinite number of values for the strength of muscle(s) may be obtained either for an isolated muscle preparation or for a human movement as related to the type of action, the velocity of the action, and the length of the muscle(s) when the measurement is accomplished.
Performance of sport
Therefore, strength is not the result of an assessment performed under a single set of conditions. Because of the number of variables or conditions involved, strength of a muscle or muscle group must be defined as the maximal force generated at a specified or determined velocity (Knuttgen & Kraemer 1987).
For a particular exercise performance with free weights (e.g. military press in power lifting, clean and jerk in Olympic weightlifting), the combination of strengths employed to complete the man oeuvre is assessed as the largest mass lifted. The performance of sport and all exercise can be assessed and described in terms of force, work, torque, power and endurance time, and presented in the units of the International System of Measurement (the SI).
The human body is capable of power production over a wide range from low-intensity aerobic exercise, to exercise eliciting peak oxygen uptake for the muscles involved, high-intensity anaerobic exercise emphasizing anaerobic glycolysis as the main energy source, and the highest power productions which rely solely on the high-energy phosphates as the energy source.
The chapters of this volume will concentrate on the highest expressions of power which involve predominantly the high-energy phosphates, with the possible contribution of anaerobic glycolysis when the short, intense exercise performance lasts for periods somewhat longer than a few seconds.