Thesis
Testing strength and power: an investigation of the reliability, validity and appropriate uses of isometric, isokinetic and isoinertial tests of muscular function
Southern Cross University, School of Exercise Science and Sports Management
Doctor of Philosophy (PhD), Southern Cross University
1996
Metrics
41 Record Views
Abstract
The series of studies conducted in this doctoral project represented a major investigation into the application of isometric, isokinetic and isThe series of studies conducted in this doctoral project represented a major investigation into the application of isometric, isokinetic and isoinertial tests of muscular function. In essence, this research was conducted to examine the reliability, validity and the usefulness of a number of new The series of studies conducted in this doctoral project represented a major investigation into the application of isometric, isokinetic and isoinertial tests of muscular function. In essence, this research was conducted to examine the reliability, validity and the usefulness of a number of new and established tests of muscular function. In so doing, the mechanical and neural responses of the human system in the varying testing modalities were determined to establish which test(s) most accurately reflected the underlying mechanisms in operation during dynamic muscle performance. Further, the question of whether a general strength component exists was pursued in studies 1 and 2. In each study, the reliability of the various parameters was determined using intra-class correlations and the co-efficient of variation. The validity of the tests was evaluated by the magnitude of the relationship between the tests and dynamic performance, and the ability of the tests to discriminate between individuals of varying performance levels.
In study 1, 13 trained subjects performed a series of isometric (at two joint angles) and isoinertial maximal upper body tests in a bench press movement. The isoinertial tests were conducted at loads of 30%, 60%, 100% (concentric) and 100%, 130% and 150% (eccentric) of the one repetition maximum. Vertical forces exerted throughout the movement were recorded by a force plate. Upper body dynamic performance was evaluated using the following tests (1) a one repetition maximum bench press; (2) a seated shot-put throw and; (3) two drop bench press throws from a height of 0.25 m, with loads of 10 kg and 30% of maximum. Additionally, in order to examine the effect that musculotendinous stiffness had on isometric, concentric and eccentric force production, subjects performed a series of quasi-static muscular actions in a bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's musculotendinous stiffness.
Correlational analysis demonstrated that in each instance the isoinertial force mass tests were the best predictors of performance (r=0.43-0.88) with both contraction type and mass specific effects apparent. Maximal isometric force and rate of force development at each joint angle were significantly related to some performance variables (r=-0.01- 0.78). However, for all the performance movements assessed, the isoinertial testing modality recorded the highest relationship to performance. The difference in the relationship between performance and isoinertial and isometric testing modalities was particularly evident in the light load dynamic performance of the seated shot-put (r=0.86 vs r=0.38, respectively). These results were partly explained by the neural and mechanical differences between isoinertial and isometric muscular actions and their respective specificity to dynamic physical performance. Interestingly, changing the isometric test from a 120° elbow angle to 90° generally improved the relationship between the isometric variable and performance by 100%. Musculo-tendinous stiffness was significantly related to isometric and concentric performance (r = 0.57-0.78), but not to eccentric performance. It was postulated that a stiffer system facilitates such isometric and concentric performance by improving the force production capabilities of the contractile component, due to a combination of improved length and rate of shortening, and additionally enhances initial force transmission.
Study 2 compared the relationship of isokinetic and isoinertial tests of muscular function to dynamic upper body performance. The neural output of each of the tests of muscular function, as recorded by surface electrodes, were examined to determine whether neural differences underlie the ability of the tests to relate to performance. Twenty four subjects performed isokinetic and isoinertial tests of muscular function in a bench press movement. The isokinetic tests were performed at velocities of 60, 90 and 120°.s-' while the isoinertial tests were performed at loads of 30%, 60% and 130% of the one repetition maximum. The same performance assessment tasks were used as in study 1. The results showed that both the isoinertial and isokinetic parameters were similarly related to the various measures of upper body performance (r=0.33-0.94), and both testing modalities were equally effective at discriminating between subjects of differing performance levels. Further, the relationship between the tests of muscular function were consistently high (r=0.75-0.88). This was the case, even though the magnitude of the myoelectric signals were significantly higher in the isoinertial, as compared to the isokinetic tests. It was postulated that mechanical and structural considerations, such as a specific testing position and muscular stiffness, rather than neural factors, may underlie the observed results between dynamic testing modalities. The results of this study strongly supported the concept of generality between dynamic testing modalities, whereby individuals will perform at a similar relative level regardless of the contraction mode of the test. However, this principle may only apply to tests conducted using similar movements.
The purpose of study 3 was primarily to examine the ability of isokinetic and isoinertial tests of muscular function to track training induced changes in performance. Twenty seven subjects completed a series of upper and lower body isoinertial and isokinetic tests of muscular function pre and post 8 weeks training. Further, a 40 m sprint, 6 s cycle test, a medicine ball throw and a plyometric pushup were conducted as measures of dynamic performance. The subjects were split into a weights group, which performed heavy squats, and a control group. Results showed that squat strength and sprint performance improved significantly for the weights group over the training period, while the 9% change in cycling performance approached statistical significance (p=0.07). However, none of the lower body tests of muscular function significantly increased pre to post training. For the upper body, the maximum bench press and the 180°.s-' isokinetic bench press test were the only variables to increase significantly as a result of the resistance training program, although the isoinertial test at 30% of maximum did approach statistical significance (p=0.06). Furthermore, there was no relationship between the training induced changes in performance and the training induced changes in the isokinetic and isoinertial tests. The results suggest that, over the time frame used in the present study, tests of muscular function cannot be used to accurately monitor training induced changes in performance. This was thought to be due to the large degree of unaccounted for variance in the relationship between tests of muscle function and performance. It was suggested that if tests are to be used to monitor training induced changes in performance, then the relationship between the tests and performance must be higher than that exhibited by tests currently used. As such, changes to training or rehabilitation programs should be based on changes in actual performance as opposed to changes in tests of muscular function.
The pre training cross-sectional data collected for study 3 was also used to examine the importance of movement specificity in isokinetic assessment. This was achieved by correlating the horizontal adduction and bench press tests to medicine ball and plyometric pushup performance. The bench press test was seen to be specific to the performance tasks, while the horizontal adduction test, a single jointed test, was relatively non specific. The results showed that the bench press tests, in every instance, were more highly related to performance than the horizontal adduction tests. The observed results were ascribed to specific neural and structural factors which may have limited the relationship between the horizontal adduction tests and performance. The results of this analysis question the usefulness of non-specific tests such as knee extension and knee flexion in isokinetic assessment batteries.
Details
- Title
- Testing strength and power: an investigation of the reliability, validity and appropriate uses of isometric, isokinetic and isoinertial tests of muscular function
- Creators
- Aron J Murphy
- Contributors
- Greg J Wilson (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University, School of Exercise Science and Sports Management
- Number of pages
- xxviii, 336
- Identifiers
- 991012959500402368
- Copyright
- © Aron J Murphy 1996
- Academic Unit
- School of Health and Human Sciences
- Resource Type
- Thesis