Stretch-shorten cycle compared with isometric preload: contributions to enhanced muscular performance.

To isolate any difference muscular contraction history may have on concentric work output, 40 trained male subjects performed three separate isokinetic concentric squats that involved differing contraction histories, 1) a concentric-only (CO) squat, 2) a concentric squat preceded by an isometric preload (IS), and 3) a stretch-shorten cycle (SSC) squat. Over the first 300 ms of the concentric movement, work output for both the SSC and IS conditions was significantly greater (154.8 +/- 39.8 and 147.9 +/- 34.7 J, respectively; P < 0.001) compared with the CO squat (129.7 +/- 34.4 J). In addition, work output after the SSC test over the first 300 ms was also significantly larger than that for the corresponding period after the IS protocol (P < 0.05). There was no difference in normalized, integrated electromyogram among any of the conditions. It was concluded that concentric performance enhancement derived from a preceding stretch of the muscle-tendon complex was largely due to the attainment of a higher active muscle state before the start of the concentric movement. However, it was also hypothesized that contractile element potentiation was a significant contributor to stretch-induced muscular performance under these conditions.

The influence of musculotendinous stiffness on drop jump performance.

This study investigated the relationship between musculotendinous stiffness and the ability to perform dynamic stretch-shorten cycle actions involving a range of eccentric loads. Twenty trained male subjects 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 allowed the estimation of each subject's maximal musculotendinous stiffness (k) for the lower body musculature. All subjects also performed a countermovement jump (CMJ) and a series of drop jumps (DJs) from heights of 20, 40, 60, 80, and 100 cm. When the jump heights of the nine most compliant (mean k = 11.4 +/- 2.7 kNxm-1) and nine stiffest (mean k = 20.5 +/- 2.5 kNxm-1) subjects were compared the stiff subjects demonstrated significantly poorer capacity to perform under the highest (DJ80 and DJ100) eccentric loading conditions. It was hypothesised that the relatively greater forces transmitted from the skeletal system to the musculature of the stiff subjects reduced their ability to attenuate the higher eccentric loads due to less effective contractile dynamics and greater levels of reflex induced inhibition.

The development of an isokinetic squat device: reliability and relationship to functional performance.

This study was performed to determine the reliability and validity of a new isokinetic squat device in comparison to knee-extension tests performed using a Cybex. Athletic male subjects (n = 29) performed a series of isokinetic squat tests at 0.4 m.s-1, knee-extension tests at 1.05, 2.09 and 3.14 rad.s-1, and a 6-s stationary cycle test which was used as the measure of functional performance. The squat tests included a purely concentric squat without pre-load, a test with pre-load and a stretch-shorten cycle test. Two trials of each test were performed on one testing occasion. Intraclass correlation co-efficients (r = 0.89-0.96) and co-efficients of variation (3.1-8.7%) were determined between trials, and these indicated that all of the tests were highly reliable. The velocity characteristics of the newly developed system demonstrated that it was an effective isokinetic device, with the mean velocity of 0.41 m.s-1 varying within narrow limits, a relatively small velocity overshoot and an isokinetic portion of movement of approximately 80%. The squat tests demonstrated a higher relationship to cycling performance (r = 0.57-0.65) as compared to the knee-extension tests (r = 0.45-0.51). This difference was amplified when a more homogeneous group of subjects was examined. Further, the squat tests were superior to the knee-extension tests in discriminating between differing levels of cycling performance ability. These differences were believed to be due to the greater specificity of the squat movement, in comparison to the knee extension, to the performance of interest.

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.

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.

An audit of the clinical investigation of pleural effusion.

BACKGROUND: Pleural aspiration with pleural biopsy is advised for the investigation of pleural effusion. The clinical investigation of pleural effusion in a group of teaching hospitals was audited with reference to adequacy and diagnostic value of sampling procedures. METHODS: A retrospective review of case records of all patients investigated for pleural effusion during an eight month period was performed. The records of 112 patients, age range 16-91 years, who underwent 150 procedures were reviewed. RESULTS: Microbiology samples were obtained from 137 procedures, of which five provided a positive culture, including one for mycobacteria. Cytology samples were obtained from 145 procedures though approximately two thirds of samples were less than the recommended 30 ml. The pleural biopsy rate was 30%, varying from 0% in general or thoracic surgery to 68% in thoracic medicine (thoracic surgeons carried out thoracoscopy). Twenty nine per cent of pleural biopsy samples were of poor quality. The complication rate was 2% for aspiration alone, and 4% for aspiration plus biopsy. The sensitivity of the first diagnostic procedure for a diagnosis of malignancy or tuberculosis was 53% for cytology alone, 50% for biopsy alone and 72% for cytology plus biopsy. CONCLUSION: The samples obtained from pleural aspiration and biopsy in the initial investigation of pleural effusion are often inadequate. Further education is necessary to improve the quantity and quality of specimens submitted for histological and cytological examination.