Mechanical efficiency of positive work in running at different speeds

To investigate the possible role of elastic potentiation on mechanical efficiency, three male marathon runners were filmed while running on a treadmill at various steady-state speeds ranging from 7.0-22.0 km X h-1. Kinematic and mechanical energy analyses were performed from the film. Expired air was collected for energy expenditure determination. The analysis disclosed that during contact on the treadmill the knee and ankle joints initially had a phase of negative (flexion) angular velocity, followed by a positive velocity. In the hip joint the stretch-shortening cycle of the extensor muscles occurred primarily during the flight phase. The mean vertical and horizontal forces of the negative and positive phases of the contact period increased linearly with the increase in the running speed. The calculated mechanical efficiency of positive work was high but relatively constant (55.1 +/- 12.7%) across all speeds. The absolute contribution of the extra work, which comes from the stored elastic energy to the positive work, increased with running speed; however, its relative value (0.61 +/- 0.09 J X min-1 X kg-1) remained constant at all measured speeds. It is suggested, therefore, that when the flight phase is included in the mechanical energy calculations, the measured efficiency for the positive work reaches a high but constant value in running at low-to-moderate speeds.     

Effects of prestretch intensity on mechanical efficiency of positive work and on elastic behavior of skeletal muscle in stretch-shortening cycle exercise

Mechanical efficiency of positive work (eta+) and elastic behavior of human skeletal muscles were investigated on a special sledge apparatus which allowed the use of the normal stretch-shortening cycle exercises. Twenty-five young men were investigated in a total of 92 exercise situations, in which the intensity of the prestretch (eccentric contraction) was different, but the shortening phase (concentric contraction) was kept constant in all conditions. The results demonstrated that eta+ was on the average 35.8% +/- 6.4% and correlated positively with the prestretch intensity (r = 0.413; P less than 0.001), reaching a highest individual value of 51.5%. Estimation performed on the elastic characteristics of the leg extensor muscles confirmed an earlier suggestion that the pure muscle elasticity plays an important role in potentiating performance in stretch-shortening cycle exercises. The analysis of the myoelectrical activity of the leg extensor muscles showed that the nervous system plays an essential role in regulating muscle stiffness and thus utilization of muscle elasticity in ballistic exercises.     

Cerebral abscess with special reference to the angiographic changes

Summary From 1961 to 1973 forty patients with surgically confirmed intracranial abscesses had preoperative cerebral angiography. The findings were abnormal in all cases but one. In 20 patients (50%) the primary diagnosis was a space-occupying lesion. In 19 patients (47.5%) an abscess was suggested by the presence of a capsule, the only finding definitely diagnostic of an abscess. Subtraction technique provided essential information in detecting the capsule. Angiography proved indispensable in suggesting the nature of the lesion.     

Hemophilic osteoarthropathy with special reference to the elbow joint

Hemophilia is a rare disorder, whereby recurrent bleedings into the joint can result in osteoarthropathy. Radiological changes consist of osteoporosis, enlargement of the epiphyses, irregularity of the subchondral bone surface, narrowing of the joint space, cysts, erosions, joint incongruence and joint deformity. The earlier and the more frequent bleedings have occurred that have not been treated adequately, the more of the changes mentioned above are present. In children, osteoarthropathy of the elbow is present in only about 50% of cases, and in the remaining cases the degree is mostly minimal or moderate. Differential diagnosis consists of juvenile rheumatoid arthritis in children, and rheumatoid arthritis and osteoarthritis in adults.     

Imaging of osteomyelitis with special reference to children

Infection of bone in children represents a diagnostic and therapeutic challenge to the pediatrician, the surgeon, the radiologist, and the pathologist. The pattern of manifestation varies and is dependent on the site of involvement, the initiating event, the infecting organism, and the acute or chronic nature of the illness. Early diagnosis allows prompt treatment, which can prevent many of the dreaded complications of this disease. Plain radiographs remain the initial imaging modality used in the diagnosis and differential diagnosis of osteomyelitis. However, with the advent of newer imaging techniques such as scintigraphy, ultrasonography, computed tomography, and magnetic resonance imaging, a higher degree of accuracy in diagnosis and definition of the extent of the disease has been achieved. The time interval between the onset of symptoms and diagnosis has also been significantly reduced. Although magnetic resonance imaging has the additional advantage of multiplanar capability, greater anatomic detail, and excellent soft tissue resolution, it is a relatively expensive technique, which somewhat limits its use. Following a brief review of the classification and pathophysiology of osteomyelitis, we have tried to elucidate the utility of various imaging modalities in the diagnosis of osteomyelitis in children, outlining their relative strengths and weaknesses. Certain entities specific to children and a brief review of differential diagnosis are also presented.