Functional assessment of the muscle-bone unit in the lower leg.

Based on the mechanostat theory and the muscle-bone hypothesis, a methodological assessment of the musculoskeletal status in health and disease should relate maximum muscle force in relation to bone mass and geometry. While useful (i.e. three-dimensional) measures of tibial bone parameters can be obtained by peripheral quantitative computed tomography (pQCT), intrinsic plantarflexor muscle force cannot be directly measured under in vivo condition in humans. Instead, tissue size, torque and ground reaction force have been used as proxy markers of intrinsic muscle force. However, most of these proxy markers are not or insufficiently representative of maximum force. Based on our recent research, we describe a novel approach for the assessment of the lower leg muscle-bone unit in health and disease. It incorporates multiple one-legged hopping (m1LH) to assess maximum voluntary ground reaction force acting on the forefoot (F(m1LH)) and bone mineral content at the 14%-site of tibia length (vBMC(14%)) as assessed by pQCT. Using the quantitative relationship between these two variables in conjunction with F(m1LH) per body weight, we present a two-step quantitative diagnostic algorithm to discriminate between primary and secondary bone disorders in children and adults.

Effects of jumping exercise on maximum ground reaction force and bone in 8- to 12-year-old boys and girls: a 9-month randomized controlled trial.

OBJECTIVES: To assess adaptations of the lower leg muscle-bone unit in 8- to 12-year-old children following a randomized controlled jumping exercise intervention for 9 months. METHODS: Twelve boys and 10 girls (INT) performed a supervised jumping protocol during the first 10 min of their regularly scheduled physical education class twice a week, while 11 boys and 12 girls (CON) completed the regular curriculum. We assessed maximum voluntary ground reaction force during multiple one-legged hopping (F(m1LH)), and tibial bone strength/geometry by peripheral quantitative computed tomography (pQCT) at the 4-, 14-, 38- and 66%-site pre, intermediate, and post intervention. RESULTS: Whether increases in F(m1LH) (+2.1% points, P= 0.752), nor changes in bone strength/geometry (+1 to +3% points, 0.169

Uptake of selenate and selenite by isolated intestinal brush border membrane vesicles from pig, sheep, and rat.

Selenate and selenite uptakes by isolated intestinal brush border membrane vesicles (BBMV) from pig, sheep, and rat were investigated. Selenate uptake into jejunal and ileal, but not duodenal, BBMV from pig was stimulated by an inwardly directed transmembrane Na(+) gradient (Na out (+) >Na in (+) ). Selenate transport into rat ileal and sheep jejunal BBMV was also enhanced in the presence of a Na(+) gradient. Unlike selenate uptake, selenite uptake was not Na(+) dependent, neither in pig small intestine nor in sheep jejunum and rat ileum. Uptake of selenate represented real uptake into the vesicular lumen, whereas selenite uptake was a result of an extensive binding of(75)Se to the membranes. Thiosulfate at a 250-fold concentration of selenate completely inhibited Na(+)-dependent selenate uptake into pig jejunal BBMV. Furthermore, Na(+)-dependent sulfate uptake was totally inhibited in the presence of a 250-fold selenate concentration. The results clearly show that selenate transport across the BBM of pig jejunum and ileum, sheep jejunum, and rat ileum is partially energized by a transmembrane Na(+) gradient. Moreover, it is concluded from the results that there exists a common transport mechanism for sulfate and selenate in the BBM. The extensive binding of(75)Se from(75)Se-labeled selenite to the membranes could be from a spontaneous reaction of selenite with membrane-associated SH groups.