Effects of lower limb unloading on skeletal muscle mass and function in humans.

A model to simulate effects of microgravity on skeletal muscle mass and function in humans has been developed. Unilateral lower limb unloading that allowed ankle, knee, and hip joint mobility was conducted in six healthy men by suspending one lower limb and having the subjects walk on crutches. They performed maximal unilateral concentric or eccentric quadriceps actions at different angular velocities before and after 4 wk of suspension and after 4 days and after 7 wk of uncontrolled recovery. Peak torque (PT) and angle-specific torque (AST) were measured. Muscle cross-sectional area (CSA) and radiological density (RD) of the thigh were assessed by means of computerized tomography. Concentric and eccentric PT and AST across speeds decreased (P less than 0.05) by 22 and 16%, respectively, in response to unloading. At 4 days of recovery PT (-11%) and AST (-7%) were still lower (P less than 0.05) than before. Muscle CSA and RD decreased (P less than 0.05) by 7 and 6%, respectively. After 7 wk of recovery PT, AST, CSA, and RD had returned to normal. The control limb showed no changes over the experimental period except for a 6% decrease (P less than 0.05) in RD. It is suggested that this human model of unloading could serve to simulate effects of microgravity on skeletal muscle mass and function because reductions in muscle mass and strength were of similar magnitude to those produced by bed rest.

In vivo moment arm lengths for hip extensor muscles at different angles of hip flexion.

Moment arm lengths of three hip extensor muscles, the gluteus maximus, the hamstrings and the adductor magnus, were determined at hip flexion angles from 0 degrees to 90 degrees by combining data from ten autopsy specimens and from twenty patients, the latter examined by computed tomography. A straight-line muscle model for muscle force was used for the hamstrings and adductor magnus, and for the gluteus maximus a two-segment straight-line muscle force model was used. With the joint in its anatomical position the moment arm of the gluteus maximus to the bilateral motion axis averaged 79 mm, for the hamstrings 61 mm and for the adductor magnus 15 mm. The moment arm of gluteus maximus decreased with increasing hip flexion angle. The hamstrings showed an increase in moment arm length up to an average of 35 degrees hip flexion and then a decrease with increasing hip flexion angle. The corresponding figures for the adductor magnus moment arm showed an increase up to 75 degrees and then a decrease. Statistical analysis revealed significant differences in moment arm length between men and women.

3D-location of the L5-S1 fulcrum in relation to the hip.

The purpose of the present study was to measure the three-dimensional distance between the hips and L5-S1 joint in vivo so that this data could then be used in computer programs predicting the load at the lumbosacral joint from posture and anthropometric data. Twenty-one subjects were investigated with computed tomography; consecutive transverse slices were taken from the low-back to proximal thigh, and three-dimensional coordinates were recorded. The distance between the hips and the L5-S1 joint was 122 mm, corresponding to 6.9% and 7.5% of body height for men and women, respectively (P less than 0.05).

Moment arm lengths of trunk muscles to the lumbosacral joint obtained in vivo with computed tomography.

Computed tomography is valuable in obtaining in vivo length of muscular moment arms, which can be used in biomechanical models. Using computed tomography, the authors measured lengths of the muscular moment arms of the erector spinae, psoas, oblique abdominal, and rectus abdominis muscles to the bilateral motion axis (about which flexion/extension movements occur) and to the anteroposterior motion axis (about which lateral bending occurs), both axes running through the lumbosacral joint. The subjects were 21 patients. Examinations were performed on a General Electric CT/T 7800 scanner. The average erector spinae moment arm to the bilateral motion axis was 68 mm, which is greater than the moment arm used earlier. The results also revealed significant differences in moment arm length between men and women for several muscles. The authors conclude that for some muscles different moment arm lengths should be used for men and for women. The moment arms reported are proposed for use in biomechanical models for calculating lumbosacral joint load.

Moment arms of hip abductor and adductor muscles measured in vivo by computed tomography.

Anatomical data on the length of moment arms of hip muscles is required to evaluate the load on an endoprosthesis or a joint. We investigated 20 subjects and measured the moment arms of eight hip muscles with respect to their action in the coronal plane, i.e. in abduction or adduction. For this purpose computed tomography was used. Consecutive transverse scans were taken, three-dimensional coordinates recorded and moment arms calculated. The length of the moment arms was slightly longer in comparison with earlier data. It was also shown that several muscles produce moments in more than one plane, which probably contributes to joint stability. It is therefore concluded that one should consider contribution from muscles other than those traditionally classified as abductors, otherwise the forces at the hip will tend to be understimated.

The effect of athletic activity on the bone mass in human diaphyseal bone.

Both humeri of seven professional tennis players and seven controls were examined with x-ray spectrophotometry, and computed tomography. Both the bone mineral content and the cortical cross-sectional area were found to be larger in the dominant arm of the tennis players than in their non-dominant arm, and in comparison to both arms of the controls. The increase in cortical cross-sectional area was a result of an increased outer diameter of the diaphysis.

Percutaneous nephrolithotomy--the birth of a new technique.

Extraction of renal calculi via a percutaneous track was for the first time practised at the Karolinska Hospital in 1973. After very strict indications in the beginning because of fear of uncontrollable bleeding, the method was found to be safe and the technique was spread all over the world. Now being to a large extent replaced by extracorporeal shock wave lithotripsy (ESWL), percutaneous nephrolithotomy (PNL) has still many applications e.g. alone in obstructed kidneys or together with ESWL in staghorn calculi.