Showing papers by "Marco Narici published in 1997"

The interplay of central and peripheral factors in limiting maximal O2 consumption in man after prolonged bed rest

Abstract: 1. The effects of bed rest on the cardiovascular and muscular parameters which affect maximal O2 consumption (VO2,max) were studied. The fractional limitation of VO2,max imposed by these parameters after bed rest was analysed. 2. The VO2,max, by standard procedure, and the maximal cardiac output (Qmax), by the pulse contour method, were measured during graded cyclo-ergometric exercise on seven subjects before and after a 42-day head-down tilt bed rest. Blood haemoglobin concentration ([Hb]) and arterialized blood gas analysis were determined at the highest work load. 3. Muscle fibre types, oxidative enzyme activities, and capillary and mitochondrial densities were measured on biopsy samples from the vastus lateralis muscle before and at the end of bed rest. The measure of muscle cross-sectional area (CSA) by NMR imaging at the level of biopsy site allowed computation of muscle oxidative capacity and capillary length. 4. The VO2,max was reduced after bed rest (-16.6%). The concomitant decreases in Qmax (-30.8%), essentially due to a change in stroke volume, and in [Hb] led to a huge decrease in O2 delivery (-39.7%). 5. Fibre type distribution was unaffected by bed rest. The decrease in fibre area corresponded to the significant reduction in muscle CSA (-17%). The volume density of mitochondria was reduced after bed rest (-16.6%), as were the oxidative enzyme activities (-11%). The total mitochondrial volume was reduced by 28.5%. Capillary density was unchanged. Total capillary length was 22.2% lower after bed rest, due to muscle atrophy. 6. The interaction between these muscular and cardiovascular changes led to a smaller reduction in VO2,max than in cardiovascular O2 transport. Yet the latter appears to play the greatest role in limiting VO2,max after bed rest (> 70% of overall limitation), the remaining fraction being shared between peripheral O2 diffusion and utilization.

Body composition analysis by dual energy x-ray absorptiometry and anthropometry in adults with childhood-onset growth hormone (GH) deficiency before and after six months of recombinant GH therapy.

Abstract: Measurements of total body fat (BF) and fat free mass (FFM) obtained by anthropometry, using the Durnin and Womersley (DW) equations, and by total body dual energy x-ray absorptiometry (DXA) were compared in 8 adults with childhood-onset GH deficiency (GHD) and in 9 healthy subjects. The sensitivity of these two methods in detecting the changes in body composition produced by six months of GH therapy in patients with GHD was also compared. Anthropometric determination of percent BF was calculated from the sum of biceps, triceps, subscapular and suprailiac skinfolds, using the appropriate DW and Siri equations for body density and percent fat estimation. FFM was calculated by subtracting BF from body mass (BM). BF and FFM were also determined by DXA (QDR 1000W, Hologic Inc). The data obtained from the GHD patients were compared with those recorded in a control group of healthy males, matched for sex, age and physical activity. Body composition obtained by anthropometry: before GH treatment, significant differences existed between patients and controls in terms of BM (mean±SD: 45.8±10.0 vs 71.7±6.6 kg), percent BF (21.0±3.2 vs 17.1±3.7%) and FFM (36.0±6.5 vs 59.3±3.7 kg), while body mass index (BMI, kg/m2) values were similar in the two groups. Six months of GH therapy did not change BM and BMI, but caused a significant reduction of percent BF (from 21.0±3.2 to 18.6±4.0%) and a rise of FFM (from 36.0±6.5 to 38.0α6.7 kg). After treatment, no significant differences were found between percent BF values of patients and controls. Body composition obtained by DXA: BF (22.0±3.9 %) and FFM (37.2±8.0 kg) of patients significantly differed from those of controls (16.8±3.7% and 59.8±3.7 kg) before treatment; after GH treatment, percent BF values (17.7±4.9%) of patients were similar to those of controls. Anthropometry vs DXA: high correlation (p<0.001–0.0001, R2= 0.784–0.988) was found between the percent BF and FFM determined by anthropometry and by DXA for both patients, before and after treatment, and controls. It is noteworthy that, for both BF and FFM, most values were evenly distributed along the identity line, showing no systematic overestimation or underestimation by anthropometry. The relation between DXA and anthropometry was maintained even after GH treatment. These results indicate that body fat and FFM assessment by anthropometry are comparable to those by DXA. GH-induced changes in body composition in hypopituitary adults are detected with the same level of accuracy by the two techniques. The reliability, practicality and low cost of anthropometry favour its use for the assessment of body composition even in GHD patients.

Comments on the Role of Elastic Energy in Jumping Performance

Abstract: Heglund, N.C., Fedak, M.A., Taylor, C.R., & Cavagna, G.A. (1982). Energetics and mechanics of terrestrial locomotion: IV. Total mechanical energy changes as a function of speed and body size in birds and mammals. Journal of Experimental Biology, 97,5746. Ingen Schenau, G.J. van, Bobbert, M.F., & Haan, A. de. (1997). Does elastic energy enhance work and efficiency in the stretch-shortening cycle? Journal of Applied Biomechanics, 13,389-415. Kushmerick, M.J., & Paul, R.J. (1976). Relationship between initial chemical reactions and oxidative recovery metabolism for single isometric contractions of frog sartorius at 0 degrees C. Journal of Physiology, 254,711-727. K r w R., &Taylor, C.R. (1990). The cost of generating force: A new perspective. Nature, 346,265-267. Marsh, R.L., & Olson, J.M. (1994). Power output of scallop adductor muscle during contractions replicating the in vivo mechanical cycle. Journal of Experimental Biology, 193, 139-156. Rall, R.J. (1985). Energetic aspects of skeletal muscle contraction: Implication of fiber types. Exercise and Sport Sciences Reviews, 13,33-74. Roberts, T.J., Marsh, R.L., Weyand, P.G., &Taylor, C.R. (1997). Muscular force in running turkeys: The economy of minimizing work. Science, 275,1113-1 115.