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Original Publication Information: |
INTRODUCTION
Muscular strength is a necessary quality for achieving optimum physical performance. Although typically defined as the maximum amount of force that can be exerted against a resistance, strength can be measured several ways. The isometric technique is one of the older methods used in exercise science and requires the individual to push or pull maximally against a recording device without movement taking place.
However, most physical performances exist along a dynamic continuum. Anaerobic performance requires force to be exerted quickly, while aerobic power demands a lower force generation over a longer time period. Although isometric strength measurement has been used widely in the past, the degree to which isometric strength contributes to various performances appears to be controversial (Wilson & Murphy, 1996). The purpose of this study was to determine the relationship between commonly used isometric strength measurements and selected physical performance tests in college females
METHODS
One hundred women enrolled in a required fitness class volunteered to serve as subjects. All measurements were made prior to any training.
Anaerobic power was determined from the vertical jump (VJ), Lewis power jump (LPJ), standing long jump (SLJ), Margaria-Kalamen stair run (M-K), and 40-yd dash.
Strength was measured isometrically for right and left grip, back pull, and leg lift (Clarke, 1967). Two trials were given for each measurement, and the higher trial used for analysis. Total strength was calculated as the sum of the four measurements. Relative strength was determined by dividing total strength by body weight.
RESULTS
The physical characteristics of the subjects were typical of college females (Table 1). Most of the strength measurements had significant but moderate relationships with the power measurements (Table 2). Total strength had no greater correlations with power performances than did the individual strength measurements. Expressing strength relative to body weight increased the relationships with four of the five tests. Leg strength had lower correlations with most power tests than did the other strength measures, except with the 40-yd dash.
DISCUSSION
While the isometric strength measurements used in this study were significantly related to the power performances, they accounted for a maximum of 41% of the common variance among the tests. This was substantially higher than the maximum 24% shared variance previously noted in males (Guy et al., 1996) and somewhat higher than the value noted by Wilson and Murphy (1996) in their review of isometric testing as a predictor of dynamic performance.
Part of the explanation for why isometric testing did not account for more of the variance in dynamic performance may lie in the neuromuscular activation pattern of muscle during different forms of contraction. Recent research has shown that different neural activation patterns are present for isometric and dynamic performances (Murphy & Wilson, 1996; Ter Haar Romeny et al., 1982). Indeed, Almasbakk and Hoff (1996) have shown that coordination of movement is a more dominant factor in power performance than is strength. The low correlations between strength measurements and vertical jump may support this idea (Table 2). However, the higher correlations between isometric strength and the Margaria-Kalamen test might also indicate an association between muscular strength and dynamic performance, indicating that a minimum level of strength is required is order to achieve any degree of dynamic, coordinated performance. Furthermore, perhaps the neuro-motor recruitment pattern for static and dynamic performance are more similar in females than in males. Therefore, it is possible that females who can better synchronize their neuro-motor recruitment pattern can produce greater dynamic performances.
TABLE 1. Physical and Performance Characteristics of the Subjects (n = 100).
TABLE 2. Relationship of Strength Tests to Power Tests in College Women (n = 100).
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