This is an attempt to find a concise definition of "strength" among both sport scientists and coaches. Introduction : Ask any six coaches or sports scientists for a definition of strength and chances are you will likely get four or five different ideas. Indeed, many coaches and athletes have used the term strength as meaning "to have powers of resistance" or being tough. It is not uncommon for runners to discuss training for "strength" as a term used to denote endurance. On the other hand throwers or weightlifters may use the term "strength" to denote the ability to lift heavy weights. These examples point out the need for a concise definition of "strength" among both sport scientists and coaches. In the scientific literature several definitions have been used over the years. Steindler (1935) defined strength as the "maximum display of power". However, as pointed out by Atha (1981) this definition simply substitutes one unexplained term (power) for another (strength). Later definitions began to consider strength and force as being linked, for example Muller (1970) indicated strength should be defined as the " maximum force that can be exerted against an immovable resistance by a single contraction". However, Muller's (1970) definition implies that all strength is a "maximum isometric effort". Not all scientist or practitioners have agreed with this definition, pointing out that force production is important in "muscular endurance" (Jones 1974), speed of movement (McCloy 1936, Nelson and Fahrney 1965; Nelson and Jorden 1969) and that force is particularly important to power production (Berger and Henderson 1966). Furthermore, it has been noted that measures of maximum force production including 1 RM 's have been associated with maximum power production. ( Moss et al. 1997; Robinson 1995). The implications are that if force and strength are linked then strength must be related in some manner to endurance, speed and power. Thus, a definition of strength being a maximal isometric contraction may be too simplistic and does not adequately define strength under all conditions. Perhaps a better way to begin to understand the concept of "strength" is to consider it as an ability. Thus, strength can be simply defined as: Strength = the ability of the neuromuscular system to produce force Using this definition essentially makes strength and force synonymous. Furthermore, use of this definition removes the limitations of isometric conditions imposed previously and allows the further use descriptive limitations (i.e. a given set of conditions). For example: force is a vector quantity and has a magnitude and direction; additionally we can describe force in static or dynamic terms. Thus strength will have a magnitude ranging from 0 to 100% (maximum), have a direction which results from the muscles being activated and will result in a speed of movement ranging from 0 - 100%. Measurement of Strength (force): Strength can be expressed and measured in a number of different manners. There is a high degree of mechanical specificity involved in appropriate strength (and other parameters such as power and endurance) measurement. This means that not just any test will suffice. Proper strength measurement for sport application depends upon many factors including movement patterns, or positional considerations for isometric tesing, velocity, rate of force development or the type of muscle action (contraction ) involved. Different types of muscle actions include: 1 Isometric - muscle gains tension but does not change length 2 Concentric - muscle gains tension and shortens 3 Eccentric - muscle gains tension and lengthens 4 Plyometric - concentric action immediately preceded by an eccentric action Types 2-4 are dynamic and can be applied in a variety of different movement patterns and at different speeds. Type 1 is an expression of static strength that can be applied in a number of positional patterns and at different rates of force development. All of these factors can make strength testing a confusing issue. Selecting the correct tests for your sport is of paramount importance - Future articles will begin to address some of the factors which have been associated with the effectiveness of strength testing procedures.