We measured diffusing capacity (DLCO), alveolar membrane properties (D (m)), capillary lung volume (V (c)), and alveolar volume (V (A) ) in 20 healthy subjects (12 males; age 32.4 +/- 13 (SD); BMI 21.7 +/- 3; non smokers) at total lung capacity (TLC) and at approximately 80, 60, and 40% TLC. In all subjects, D (m) increased with lung volume, the increase being significantly greater for higher values of D (m)(TLC): the inter-individual differences can be interpreted by a greater number of alveolar units coupled to a lower thickness of the air-blood barrier (thus a higher alveolar surface to thickness ratio S (A)/tau). On the average, the volume-dependent increase of D (m) from approximately 40 to 100% TLC is less than expected based on geometrical increase of S (A) /tau. In fact, up to approximately 80% TLC, the increase in D (m) closely reflects only the increase of S (A), suggesting "unfolding" of the septa with no appreciable decrease in tau. Conversely, above 80% TLC, the decrease in tau due to parenchymal stretching becomes the main factor affecting D (m). In all subjects, V (c) decreased with increasing lung volume, in line with an increase in parenchymal stretching; the decrease was significantly larger for higher values of V (c) (40% TLC). Possibly reflecting differences in alveolar capillary density. No correlation was found between D (m)(TLC) and V (c)(40%TLC). The individual specificity in the lung volume dependence of V (c) and D (m) can be reasonably described by evaluating the V (c)/D (m) ratio at TLC and at approximately 40%TLC.

Our aim was to investigate the relationship between physiological variables (not previously studied) and performance in elite 1,500-m runners. We assessed eight male athletes with an average personal best time of 233.3 ± 6.9 s (110% of the world record) for the 1,500-m race. Ventilatory measurements, maximal oxygen consumption VO2max maximal vastus lateralis muscle deoxygenation (∆[deoxy(Hb+Mb)])max via near-infrared spectroscopy (NIRS), and maximal velocity (V (max)) were obtained during an incremental treadmill test. During subsequent constant-speed exercise at Vmax, we determined the time to exhaustion (Tlim), end-exercise blood lactate concentration ([La]b(max)), VO2 and ∆[deoxy(Hb+Mb)] kinetics parameters. The mean VO2max, [La]b(max) and Vmax were 70.2 ± 3.9 mL kg(-1) min(-1), 12.7 ± 2.4 mmol L(-1), 21.5 ± 0.5 km h(-1), respectively. VO2 at Vmax showed a significant negative correlation with Tlim, whereas [La]b(max) was positively correlated with Tlim. Race speed was found to significantly correlate with ∆[deoxy(Hb+Mb)](max) (79% of maximal value obtained during a transient limb ischemia), ∆[deoxy(Hb+Mb)] slow component (22.9 ± 9.3% of total amplitude) and [La]b(max) at Vmax. [La]b(max) at Vmax was also significantly correlated with ∆[deoxy(Hb+Mb)] slow component, suggesting a greater release of oxygen from the hemoglobin due to the Bohr effect. We conclude that both the maximal capacity of muscle to extract O2 from the blood and the end-exercise blood lactate accumulation are important predictors of best performance in 1,500-m runners.

During exercises with relatively small muscle masses, limitations to exercise performance by the cardiovascular system should be significantly reduced, allowing one to fully-test the "oxidative potential" of the investigated muscles. Ten elderly males (E, 77.8 +/- 2.9 years [x +/- SD]) and eight young controls (Y, 26.6 +/- 3.0) underwent incremental exercises to voluntary exhaustion on a dynamic leg-extension (dominant limb) machine (knee-extension, KE) and on a cycloergometer (CYCLO). During KE the load was increased every 3 min to loads corresponding to 20, 40 and 60% of the force of one-repetition maximum (1RM). The following variables were determined (vastus lateralis muscle): concentration changes of deoxygenated haemoglobin and myoglobin (Delta[deoxy(Hb + Mb)]) by near-infrared spectroscopy (NIRS), expressed as percentage of the maximal value obtained during transient limb ischemia, and taken as an index of O2 extraction; root mean square (RMS) and median power frequency (MDF) by electromyography. The total lifted load during KE and peak workload during CYCLO were lower in E versus Y (620.4 +/- 321.9 kg vs. 1347.4 +/- 458.7; 113.5 +/- 23.9 W vs. 224.3 +/- 41.0, respectively). During CYCLO Delta[deoxy(Hb + Mb)] peak (i.e. the value determined at exhaustion) was lower in E (44.5 +/- 17.7%) versus Y (67.1 +/- 22.9), whereas during KE Delta[deoxy(Hb + Mb)] peak was higher in E (56.8 +/- 20.9%) versus Y (38.6 +/- 15.8). "Thresholds", that is abrupt increases in RMS slopes, were detected in Y but not in E, suggesting less recruitment or a preferential atrophy of type 2 fibers in the elderly. These findings, associated with the preserved capacity of O2 extraction, suggest a shift towards oxidative metabolism in skeletal muscles of 78 year-old subjects, which could preserve, at least in part, their capacity to carry out exercise.

-A recent study has demonstrated that neuromuscular electrical stimulation (NMES) determines, in vitro, a fast-to-slow shift in the metabolic profile of muscle fibers. The aim of the present study was to evaluate if, in the same subjects, these changes would translate, in vivo, into an enhanced skeletal muscle oxidative metabolism. Seven young men were tested (cycle ergometer) during incremental exercises up to voluntary exhaustion and moderate and heavy constant-load exercises (CLE). Measurements were carried out before and after an 8-wk training program by isometric bilateral NMES (quadriceps muscles), which induced an ϳ25% increase in maximal isometric force. Breathby-breath pulmonary O2 uptake (V O2) and vastus lateralis oxygenation indexes (by near-infrared spectroscopy) were determined. Skeletal muscle fractional O2 extraction was estimated by near-infrared spectroscopy on the basis of changes in concentration of deoxygenated hemoglobin ϩ myoglobin. Values obtained at exhaustion were considered "peak" values. The following functional evaluation variables were unaffected by NMES: peak V O2; gas exchange threshold; the V O2 vs. work rate relationship (O2 cost of cycling); changes in concentration of deoxygenated hemoglobin ϩ myoglobin vs. work rate relationship (related to the matching between O2 delivery and V O2); peak fractional O2 extraction; V O2 kinetics (during moderate and heavy CLE) and the amplitude of its slow component (during heavy CLE). Thus NMES did not affect several variables of functional evaluation of skeletal muscle oxidative metabolism. Muscle hypertrophy induced by NMES could impair peripheral O2 diffusion, possibly counterbalancing, in vivo, the fast-to-slow phenotypic changes that were observed in vitro, in a previous work, in the same subjects of the present study. strength training; muscle hypertrophy; near-infrared spectroscopy; gas exchange kinetics NEUROMUSCULAR ELECTRICAL STIMULATION (NMES) (26, 28) is widely utilized as a complement to voluntary exercise in athletes (27) and in patients, such as those with heart failure (46), chronic obstructive pulmonary disease (34), or cancer (6). NMES represents an obligatory choice for training in patients who cannot perform voluntary contractions, such as those with spinal cord lesions (10), or in patients immobilized for fractures or following ligament reconstruction surgery (42). It is well established that NMES leads to significant increases in muscle mass and maximal voluntary strength (13,26,39).The effects of NMES on oxidative metabolism appear rather controversial. At molecular level, Perez et al. (36) reported a higher succinic dehydrogenase activity after NMES training, whereas both citrate synthase and phosphofructokinase activities were unchanged. Kim et al. (21) reported, after a NMES training program, no changes in citrate synthase activity and number of capillaries. Nuhr et al. (35) showed an increase in the activity of citrate synthase associated with a decrease in the activity of glyceraldehyde phosphate dehydrogenase. Int...