STRENGTH AND POWER TESTING (DYNAMOMETRY)
Abernethy, P., Wilson, G., & Logan, P. (1995). Strength and power assessment. Sports Medicine, 19, 401-417.
This review article considers the factors associated with strength and power testing. It highlights shortcomings and problems associated with this form of assessment. An underlying theme that is verified by its exhaustive review is that much strength and power testing is invalid and unreliable. The reasons for this status are primarily a failure to scientifically develop testing protocols and validities and then to cross-validate the utility of tests with each sport and level of participant.
Generally, there is little consistency between laboratories in terms of the rationale for, or execution of, strength and power assessments. This means that results will be dependent upon who does the testing. The tenuousness of those results is compounded further when unsubstantiated validity, reliability, and accuracy are considered.
Strength and power are assessed for four main purposes:
Current methods of dynamometry can measure power associated with tasks in which either the load or movement velocity are held constant. This contrasts with the dynamic nature of sporting activities. This discrepancy between sports and laboratory activities is one of the major challenges for sport scientists.
Testing is further confounded when the type of contractions, movement paths, and nature of the testing activity are at variance with what occurs in the sporting situation. These problems create difficulties in mimicking sporting movements. Consequently, many testing protocols are limited to nonspecific tasks. The difficulty presented with "general" tests is their lack of sensitivity to the requirements of and changes in specific sporting activities. Important movement, capacity, and adaptive subtleties are likely to be lost in nonspecific tests.
The failure to address these problems because of expediency and the "need" for testing does not make testing any more valuable or useful. It serves to perpetuate problems and increases the likelihood of inappropriate information being used to make coaching decisions. The current trend to perform testing for testing sake is the symptom of this expediency.
There are three modes of dynamometry:
Isometric dynamometry measures the amount of strength that can be exerted against an immovable object (MVC - maximal voluntary contraction). The important characteristic of isometric contractions is the rapidity with which maximum force can be developed (RFD - rate of force development). Proponents of this form of testing assert there is a high level of assessment control. Detractors assert that isometric tests bear little semblance to the dynamic nature of sporting tasks.
Isometric assessments usually display high test-retest reliabilities. However, reliability varies between the muscle groups and the parameter (RFD or MVC) being assessed. Different tests are appropriate for athletes, nonathletes, women, men, and children. Differences in the posture of actions also change reliabilities.
To achieve some potential for acceptable reliability, it is suggested that:
Isoinertial dynamometry involves natural activities. Previously this was called isotonic (constant tension) work, but the nature of dynamic work is hardly that and so the "new" label is more appropriate. Isoinertial means constantly resistant to motion, and in most activities resistances such as gravity, water, air, and equipment are always impeding progress and performance. Maximum successful exertion for one repetition of a task (1RM) is the usual measure of maximum isoinertial strength and is used commonly in sport profiling.
However, isoinertial movements also bear little resemblance to sporting activities. They are usually performed relatively slowly and are trained by a low number of repetitions. This nonspecific measure and training mode is questionable for its relevance and transfer value to actual sporting movements. Some argue that the dynamic accelerative motion associated with these tests more closely approximates movements in many sports. Those who argue against this form of assessment emphasize the potential for athlete injury and poor reliability and objectivity due to intertrial, interathlete, and interlaboratory variations. Much of the gains in these forms of tests results from learning to do the movements of the tests rather than reflecting training effects from sporting participation.
There may be a load threshold beyond which reductions in reliability of this form of movement seriously compromise its validity. For example, several acute variables, including preloading and recovery between 1RM efforts, may affect 1RM strength. The number of trials to achieve maximum and the type of movement will also affect reliability. Further, it is also very possible that maximum values of exertion may not be the best measure of a strength and power capacity in a number of sports.
Isokinetic dynamometry is perceived to be the easiest assessment over which to achieve reliability and objectivity. However, the movement loading pattern bears little relationship to most sporting activities. That weakness makes inferences from results to actual activity tenuous at best.
Reliability is affected by the selected speed of the movement. Usually fewer trials are needed for slow movements while more are needed for fast movements. The order of testing also influences results. It has been shown that reliability of eccentric and concentric assessments is reduced when tests for highest speed precede those of lower speeds. Further, results for one joint should not be considered characteristic of other untested joints. It is incorrect to infer strength status between joints and movements, particularly in highly trained athletes. As with other forms of strength assessment, test positioning and stabilization affect reliability.
With all forms of dynamometry, there are weaknesses that often make results unreliable and therefore, unrelated to sporting pursuits. Poor generalization, particularly in light of strong support for the specificity of training effect, is further compounded by non-standardized and poorly constructed testing protocols. The validity, reliability, and objectivity of strength and power testing procedures has to be established before any credence can be placed in results so that better coaching decisions can be made.
Most assessment procedures offered by sports science services display discrepancies in the logic and practices of their proponents because they are generally governed by belief, preference and/or expediency, rather than objectively verified fact and practice. As such, strength and power testing rarely deserves the status of acceptable sports "science." The following are worthy of note.
1. Factors which modify strength and power test results.
2. Correlations between test measures and athletic performance.
3. Discriminations between groups of individuals.
4. Sensitivity of testing to training effects.
5. Assumptions of strength and power assessment.
Implications. Practical situations often determine the limits of testing and training. Assessments quite often are restricted to available equipment, whether or not the modality of testing is appropriate for a sport. When this situation exists, a coach or athlete should ask for objective verification of claims of benefit before participating in testing or training. Given the state of scientific knowledge and demonstrations in this field, it would be more prudent for a coach to graciously refuse to accept assistance from "strength and power trainers" if no substantiating evidence can be provided.
Until this area of sports conditioning and assessment is clarified by acceptable research, its claims must be viewed with skepticism. There are too many advocates making too many uncorroborated claims about the value of inferring strength and power assessment results to program presumptions and consequential athlete benefits.
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