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Biomedical subjects

A J Murphy

Publications and source records attributed to A J Murphy.

At least 37 records · Page 2Linked to original sources
PubMed1997

The ability of tests of muscular function to reflect training-induced changes in performance.

We examined the ability of isokinetic and isoinertial tests of muscular function to track training-induced changes in performance. Subjects completed the following tests before and after training: (1) two isoinertial tests using concentric and eccentric actions; (2) isokinetic knee extension at two velocities; and (3) a one-repetition maximum squat. Further, a 40 m sprint and 6 s cycle test were conducted as measures of athletic performance. The subjects were split into a weights group, which performed heavy squats, and a control group. The results showed that training significantly enhanced sprint time by 2.2%, and the improvement in cycle performance (9%) approached significance (P = 0.09). However, apart from the squat, no measure of muscular function significantly changed because of training. 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 tests of muscular function cannot be used to monitor training-induced changes in performance. We considered this to be due to the large degree of variance unaccounted for in the relationship between the scores on tests of muscle function and performance. Therefore, the effectiveness of training should be based on changes in performance rather than changes in test scores of muscle function.

Adult↗
PubMed1996

The validity and reliability of a test of lower body musculotendinous stiffness.

The aim of this study was to investigate the validity and reliability of an in vivo test of lower body musculotendinous stiffness. Male subjects (n = 23) with at least 12 months of weight training experience performed a series of quasi-static muscular actions in a supine leg press position during which a brief perturbation was applied. The resulting damped oscillations enabled each subject's maximal musculotendinous stiffness for the lower body musculature to be estimated. To assess the individual's capacity to benefit from active stretch, subjects also performed both a static jump and a countermovement jump. Statistical analysis revealed no significant different between day 1 and day 2 stiffness values (P < 0.01), an interday reliability of r = 0.94 and a coefficient of variance of 8%. It was further demonstrated that maximal stiffness was significantly correlated to both isometric and concentric rate of force development (r = 0.50 and r = 0.54, respectively), and inversely related to the percentage difference between vertical jumps with and without prior stretch (r = -0.54). Such results tend to suggest that the test is valid and are discussed with reference to the restitution of elastic strain energy, muscle potentiation and the interaction effects of elastic recoil on dynamic muscular function. It was concluded that the assessment of stiffness of the lower body using the oscillation technique is a valid and reliable in vivo measure of musculotendinous stiffness.

Adolescent↗
PubMed1996

The specificity of strength training: the effect of posture.

There is a paucity of research into the importance of performing strength training exercises in postures specific to the movements they are attempting to facilitate. In addressing this question, 27 previously trained subjects were randomly allocated into heavy weight training and control groups. The weight training group performed 4-6 sets of 6-10 repetitions of the squat and bench press lifts twice a week for 8 weeks. Prior to and after the training period the following tests were conducted: bench press throw at 30% of maximal load, vertical jump, maximal squat and bench press lifts, push-up test performed over a force platform, 40-m sprint, 6-s cycle, and isokinetic tests assessing upper and lower body musculature in varying actions. The results supported the concept that posture is important in training as those exercises conducted in similar postures to the training recorded the greatest improvement in performance. For example, after completion of the training the weight training subjects significantly increased by approximately 12% the maximal load lifted in the bench press exercise and the peak torque in the isokinetic bench press test. However, performance in the isokinetic horizontal arm adduction test was not significantly changed. We speculate that the phenomenon of posture specificity may, at least in part, be caused by the differing postures altering the neural input to the musculature. The results stress the importance of selecting exercises in which the posture closely resembles that of the movements they are attempting to facilitate.

Adolescent↗
PubMed1996

Poor correlations between isometric tests and dynamic performance: relationship to muscle activation.

The purpose of this research was to perform isometric tests at two joint angles and examine their relationship to dynamic performance. In addition, electromyograph data were collected from the triceps brachii and pectoralis major muscles to compare underlying neural characteristics between the isometric tests and dynamic movement. A group of 24 healthy male subjects performed two isometric tests in a bench press position, at elbow angles of 90 and 120 degrees. From these data, the maximal force and rate of force development were determined. In addition, each subject performed a seated medicine ball throw as a measure of dynamic upper body performance. Correlations showed that isometric measurements of force (r = 0.47-0.55) and rate of force development (r = 0.08-0.31) were poor predictors of dynamic performance. The angle of isometric assessment had little effect on the relationship between the tests and measurements of performance. The myo-electric data was processed in terms of the integrated electromyogram and the Fourier transformed frequency spectrum. These data demonstrated differences in the neural activation patterns of the musculature, between the isometric 90 degrees test and the medicine ball throw. The poor relationship between isometric tests and medicine ball performance was consequently, at least partially, attributed to differing motor unit activation patterns between isometric and dynamic movement. The results of this research strongly suggest that isometric tests have limited value when assessing dynamic upper body performance.

Adult↗
PubMed1996

Strength diagnosis: the use of test data to determine specific strength training.

The aim of this study was to determine if pre-training strength and power tests could provide data that effectively discriminated between subjects whose cycling performance improved considerably from training, from those who did not. Twenty active healthy male subjects performed 10 weeks of plyometric or weight training. Prior to and at the completion of the training, the following tests were performed: (1) a 6-s cycle ride; (2) isokinetic leg extension at 1.05 and 5.24 rads s-1; and (3) a maximum isometric squat. The subjects in the two training groups were separated into those whose cycling performance improved significantly as a result of the training (good) and those who did not (poor). The pre-training muscular function tests of the good versus poor achievers were then compared, individually for each form of training, to determine if they could be used to discriminate between the two subject groups. The pre-training isometric data effectively discriminated between those individuals who improved their cycling performance significantly as a consequence of training and those who did not. While this finding has practical implications for the exercise science field, further research is required before generally useful normative data can be used with confidence to prescribe individual specific training programmes.

Adult↗
PubMed1996

Stretch shorten cycle performance: detrimental effects of not equating the natural and movement frequencies.

This study aimed to assess whether the benefits associated with stretch shorten cycle (SSC) movements required the movement frequency to be in resonance with the natural frequency of the elastic structures. Seventeen untrained participants performed SSC and concentric bench press throws. Further, quasi-static muscular actions were also performed in which a brief perturbation was applied to the bar with the resulting damped oscillations providing natural frequency data. It was observed that prior stretch did not facilitate concentric performance. Further, there were large significant differences between the natural frequency of the musculo-tendinous system and the frequency of the SSC movements. The authors hypothesize that the failure to achieve resonance contributed to the poor performance achieved in the SSC actions.

Adult↗
PubMed1996

Weight and plyometric training: effects on eccentric and concentric force production.

The study was performed in an effort to gain greater insights into the adaptations invoked by plyometric and weight training. Forty-one previously trained males were randomly allocated in either a control, plyometric, or weight-training group. The experimental groups trained for 8 weeks, performing either heavy lifts or dynamic plyometric exercises. The following test items were performed prior to and at the completion of the training period: (a) vertical jump, (b) a series of isoinertial concentric and eccentric tests, (c) push-up tests, and (d) maximal bench press and squat lifts. Plyometric training significantly enhanced the rate of eccentric lower body force production. The weight-training group primarily enhanced concentric function. These results were attributed to the specific stresses imposed by the differing forms of training and are discussed with reference to methods of enhancing training induced adaptations and the types of movements such training would tend to facilitate.

Adaptation, Physiological↗
PubMed1996

The use of isometric tests of muscular function in athletic assessment.

Isometric assessment of muscular function is a popular form of testing which has been used in exercise science for over 40 years. It typically involves a maximal voluntary contraction performed at a specified joint angle against an unyielding resistance which is in series with a strain gauge, cable tensiometer, force platform or similar device whose transducer measures the applied force. Often both the maximum force and the rate of force development are recorded. These tests have generally shown high reliability in both single and multi-joint test protocols, although the maximum force is typically more reliable than rate of force development. This review outlines the reliability of isometric assessment and discusses a number of methodological considerations designed to enhance reliability and validity, including standardisation procedures, type of instructions, muscular pre-tension, testing position and joint angle. Currently, there appears to be considerable controversy as to the external validity of isometric assessment, particularly the ability of the tests to monitor changes in dynamic performance and their relationship to such performances. Indeed, a number of studies have recently shown that dynamic assessment modalities (isokinetic and isoinertial) are superior in terms of their relationship to dynamic performance and ability to discriminate between athletes of various performance levels compared with isometric assessment. This article reviews the use of isometric assessment in exercise science and consequently outlines a number of neural, mechanical and methodological factors which may have contributed to the contrasting research, and which may limit the ability of isometric assessment to relate to dynamic movement. Because of the large neural and mechanical differences between isometric and dynamic muscular actions, athletic assessment, which is dynamic in its nature, is generally most appropriately accomplished using dynamic muscular assessment methods, and in most instances isometric testing should be avoided.

Biomechanical Phenomena↗
PubMed1996

The assessment of human dynamic muscular function: a comparison of isoinertial and isokinetic tests.

This investigation compared the relationship of isokinetic and isoinertial tests of muscular function to dynamic upper body performances. The electromiyographic activity 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 test 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 deg/s while the isoinertial tests were performed at loads of 30%, 60% and 130% of the one repetition maximum. Subjects also performed the following tests of dynamic performance: a maximum one repetition bench press (1 RM), a seated shotput throw and two drop bench press throws from a height of 0.25 m at various loads. Forces/torques, displacement and electromyographic data were recorded from the isoinertial and isokinetic tests. Both the isoinertial and isokinetic parameters were related to the various measures of upper body performance (r = 0.33-0.94), however, neither was superior at predicting performance. 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 EMG signals were significantly higher in the isoinertial, as compared to the isokinetic tests. It is postulated that structural considerations, such as a specific testing position, rather than neural factors, underlie the observed results. These results support previous research which has reported the existence of a generality of strength across dynamic testing modalities.

Adult↗
PubMed1994

Use of the iso-inertial force mass relationship in the prediction of dynamic human performance.

The purpose of this investigation was to develop a new test of muscle function, termed the iso-inertial force-mass relationship, and to determine its relationship to dynamic physical performance in comparison to an isometric test. A group of 13 trained subjects performed an isometric, and a series of iso-inertial maximal upper body tests, in a bench press movement at loads of 30%, 60%, 100% (concentric) and 100%, 130% and 150% (eccentric) of maximum. Vertical forces exerted throughout the movement were recorded by a force plate. In addition, the subjects performed the following three performance tests: a maximal bench press, a seated shotput, and two drop bench-press throws from a height of 0.25 m, with loads of 10 kg and 30% of maximum. Correlation analysis demonstrated that in each instance the iso-inertial force mass tests were the best predictors of performance (r = 0.78-0.88) with both contraction type and mass specific effects apparent. Maximal isometric force and rate of force development were significantly related to some performance variables (r = 0.22-0.78). However, for all the performance movements assessed, the iso-inertial test modality recorded the highest relationship to performance. The difference in the relationship between performance and iso-inertial and isometric test modalities was particularly evident in the light load dynamic performance of the seated shotput (r = 0.86 vs r = 0.38, respectively). These results are explained in part by the neural and mechanical differences between iso-inertial and isometric muscle actions and their respective specificity to dynamic physical performance.

Adult↗
PubMed1994

Musculotendinous stiffness: its relationship to eccentric, isometric, and concentric performance.

The purpose of this study was to quantify the relationship between musculotendinous stiffness and performance in eccentric, isometric, and concentric activities. Thirteen trained subjects performed a series of maximal effort eccentric, concentric, and isometric muscular contractions in a bench press-type movement. Additionally, subjects performed a series of quasi-static muscular contractions 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. Musculotendinous stiffness was significantly related to isometric and concentric performance (r = 0.57-0.78) but not to eccentric performance. These results are interpreted as demonstrating that the optimal musculotendinous stiffness for maximum concentric and isometric activities was toward the stiff end of the elasticity continuum. A stiffer musculotendinous unit may facilitate such performances by improving the force production capabilities of the contractile component, due to a combination of improved length and rate of shortening, and additionally by enhancing initial force transmission.

Adult↗
PubMed1993

Sarcoplasmic reticulum calcium ATPase. Labeling of a putative Mg2+ site by reaction with a carbodiimide and a spin-label.

The sarcoplasmic reticulum Ca(2+)-ATPase loses hydrolytic activity and the ability to be phosphorylated by Pi following incubation with EDC [1-ethyl-3-(3-dimethylaminopropyl)carbodiimide]. 4 nmol of tempamine per mg SR protein can be coupled to either a glu or an asp side chain through the EDC reaction. Mg2+ protects against loss of activity and tempamine labeling with a mid-point of about 3 mM in the absence of Ca2+. This is similar to the Kd for a Mg2+ that serves as a cofactor in enzyme phosphorylation. The Mg2+ protection constant is lowered by an order of magnitude when Ca2+ is bound to the transport sites. It is suggested that control of the Mg2+ binding site affinity may be part of the mechanism of enzyme activation by Ca2+.

Animals↗
PubMed1993

Formation of a stable inactive complex of the sarcoplasmic reticulum calcium ATPase with magnesium, beryllium, and fluoride.

Incubation of leaky or nonionic detergent-solubilized sarcoplasmic reticulum vesicles in solutions containing magnesium, beryllium, and fluoride caused a time-dependent complete inhibition of calcium ATPase activity. The inhibited state persisted through dialysis for 2 days versus EGTA and was reversed within minutes by the presence of 0.5 mM calcium. Calcium-independent ATPase activity was unaffected. Omission of magnesium or fluoride resulted in retention of activity, while omission of beryllium produced slower inactivation, as described previously (Murphy, A. J., and Coll, R. J. (1992) J. Biol. Chem. 267, 5229-5235). Incubation of nonleaky vesicles had a similar effect, although it occurred more than 10-fold more slowly, suggesting that a component, probably beryllium, must enter the vesicles for inhibition to occur. By contrast, inhibition of nonleaky vesicles by magnesium and fluoride developed less than 2-fold more slowly. Including calcium in the incubation mixtures resulted in partial protection, so that the time course of CaATPase activity leveled off at nonzero values (for example, at 0.1 mM calcium, the activity leveled off at 43% of control). This result is most simply accounted for by a model involving simultaneous binding of calcium and a form of fluoroberyllium to the CaATPase (e.g. Ca2EMgBeFn).

Adenosine Diphosphate↗
PubMed1993

The optimal training load for the development of dynamic athletic performance.

This study was performed to determine which of three theoretically optimal resistance training modalities resulted in the greatest enhancement in the performance of a series of dynamic athletic activities. The three training modalities included 1) traditional weight training, 2) plyometric training, and 3) explosive weight training at the load that maximized mechanical power output. Sixty-four previously trained subjects were randomly allocated to four groups that included the above three training modalities and a control group. The experimental groups trained for 10 wk performing either heavy squat lifts, depth jumps, or weighted squat jumps. All subjects were tested prior to training, after 5 wk of training and at the completion of the training period. The test items included 1) 30-m sprint, 2) vertical jumps performed with and without a countermovement, 3) maximal cycle test, 4) isokinetic leg extension test, and 5) a maximal isometric test. The experimental group which trained with the load that maximized mechanical power achieved the best overall results in enhancing dynamic athletic performance recording statistically significant (P < 0.05) improvements on most test items and producing statistically superior results to the two other training modalities on the jumping and isokinetic tests.

Adult↗