Electromyographic evaluation of the rectus femoris muscle during exercises performed on the leg press

The rectus femoris was analysed in 10 volunteers during knee flexion and extension with the feet in normal, plantar flexion and dorsal flexion positions. Hewlett-Packard surface electrodes, an electromyographic signal amplifier, a computer equipped with an A/D conversion plaque (Model CAD 10/26), software specially designed to record and analyse the signals, Horizontal Leg Press, and electrogoniometers were used. The rectus femoris muscle showed strong potentials at the beginning of knee extension. In the simultaneous bendings of the knee and hip the activity was strong toward the end of the movement. The rectus femoris showed a similar activity both in the upper and lower platforms. As for foot positions, the rectus femoris showed the smallest potentials with the foot in plantar flexion and the largest ones with the foot in dorsal flexion.

Dynamic and isometric protocols of knee extension: Effect of fatigue on the EMG signal

The objective of this study was to analyze the electromyographic (EMG) signal behavior of rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL) and biceps femoris (caput longum) (BFCL) from nine women during fatiguing dynamic and isometric knee extensions tests and to determine their EMGFT (Electromyographic Fatigue Threshold). Surface electrodes, biological signal acquisition module, analogical-digital converter board and specific software were used. The RMS (Root Mean Square) values obtained from concentric phase (80 to 30 degrees) of the dynamic knee extension andfrom isometric contraction were correlated with time on each load by linear regression analysis. The respective slopes were correlated with the correspondent load to determine the EMGFT. Force (Kgf) and median frequency - MF (Hz) obtained during MIVC (Maximal Isometric Voluntary Contraction) performed before and after the fatiguing tests were calculated in Matlab environment. The results demonstrated that the endurance time decreases with higher loads the EMG amplitude increase with time and was greater at higher loads, between muscles in dynamic exercise the RF and VL showed higher slopes, and in isometric exercise the VL showed the same behavior The EMGFT values were similar in both exercises; the force values predominantly decreased after fatiguing tests; however the MF only decreased after some loads. The protocols proposed allowed standardizing protocols at least to induce the fatigue process and to determine the EMGFT as an endurance indicative, which may be used to evaluate the effectiveness of rehabilitative or training interventions indicated to reduce muscle weakness and fatigue.

Arterial O2 content and tension in regulation of cardiac output and leg blood flow during exercise in humans

[EN] A universal O2 sensor presumes that compensation for impaired O2 delivery is triggered by low O2 tension, but in humans, comparisons of compensatory responses to altered arterial O2 content (CaO2) or tension (PaO2) have not been reported. To directly compare cardiac output (QTOT) and leg blood flow (LBF) responses to a range of CaO2 and PaO2, seven healthy young men were studied during two-legged knee extension exercise with control hemoglobin concentration ([Hb] = 144.4 +/- 4 g/l) and at least 1 wk later after isovolemic hemodilution ([Hb] = 115 +/- 2 g/l). On each study day, subjects exercised twice at 30 W and on to voluntary exhaustion with an FIO2 of 0.21 or 0.11. The interventions resulted in two conditions with matched CaO2 but markedly different PaO2 (hypoxia and anemia) and two conditions with matched PaO2 and different CaO2 (hypoxia and anemia + hypoxia). PaO2 varied from 46 +/- 3 Torr in hypoxia to 95 +/- 3 Torr (range 37 to >100) in anemia (P < 0.001), yet LBF at exercise was nearly identical. However, as CaO2 dropped from 190 +/- 5 ml/l in control to 132 +/- 2 ml/l in anemia + hypoxia (P < 0.001), QTOT and LBF at 30 W rose to 12.8 +/- 0.8 and 7.2 +/- 0.3 l/min, respectively, values 23 and 47% above control (P < 0.01). Thus regulation of QTOT, LBF, and arterial O2 delivery to contracting intact human skeletal muscle is dependent for signaling primarily on CaO2, not PaO2. This finding suggests that factors related to CaO2 or [Hb] may play an important role in the regulation of blood flow during exercise in humans.

Mineralogy and structural specification of ODP Leg 125 peridotite samples

Abundant serpentinite seamounts are found along the outer high of the Mariana forearc at the top of the inner slope of the trench. One of them, Conical Seamount, was drilled at Sites 778, 779, and 780 during Leg 125. The rocks recovered at Holes 779A and 780C, respectively, on the flanks and at the summit of the seamount, include moderately serpentinized depleted harzburgites and some dunites. These rocks exhibit evidence of resorption of the orthopyroxene, when present, and the local presence of very calcic-rich diopside in veins oblique to the main high-temperature foliation of the rock. The peridotites, initially well-foliated with locally poikiloblastic textures, show overprints of a two-stage deformation history: (1) a high-temperature (>1000°C), low-stress (0.02 GPa), homogeneous deformation that has led to the present Porphyroclastic textures displayed by the rocks and (2) heterogeneous ductile shearing at a much higher stress (0.05 GPa). This heterogeneous shearing probably describes a single tectonic event because it began at high temperatures, producing dynamic recrystallization of olivine in the shear zone, and ended at low temperatures in the stability field of chlorite and serpentine. In a few samples, olivine shows evidence of quasi-hydrostatic recrystallization at a very high temperature. Here, we propose that this recrystallization was related to fluid/magma percolation, a process that can also account for the resorption of the orthopyroxene and for the late crystallization of diopside veins in the rock. The impregnation by fluid or magma, development of the main high-temperature, low-stress deformation, and subsequent migration recrystallization of olivine probably occurred in a mantle fragment involved in the arc formation. In addition, this mantle has preserved structures that may have formed earlier in the oceanic lithosphere upon which the arc formed. Heterogeneous ductile shear zones in the peridotites may have developed during uplift. The "cold" deformation may have taken place during diapiric rise of hot mantle that underwent subsequent serpentinization or gliding along normal faults associated with the extension of the eastern margin of the forearc.

Argon ratios, 40Ar/39Ar datings and biostratigraphic ages of ODP Leg 165 sites

Drilling in the Caribbean Sea during Ocean Drilling Program Leg 165 has recovered a large number of silicic tephra layers and led to the discovery of three major episodes of explosive volcanism that occurred during the last 55 m.y. on the margins of this evolving ocean basin. The earliest episode is marked by Paleocene to early Eocene explosive volcanism on the Cayman Rise, associated with activity of the Cayman arc, an island arc that was the westward extension of the Sierra Maestra volcanic arc in southern Cuba. Caribbean sediments also document a major mid- to late Eocene explosive volcanic episode that is attributed to ignimbrite-forming eruptions on the Chortis Block in Central America to the west. This event is contemporaneous with the first phase of activity of the Sierra Madre volcanic episode in Mexico, the largest ignimbrite province on Earth. In the Caribbean sediments, a Miocene episode of explosive volcanism is comparable to the Eocene event, and also attributed to sources in the Central American arc to the west. Radiometric 40Ar/39Ar dates have been obtained for biotites and sanidines from 27 tephra layers, providing absolute ages for the volcanic episodes and further constraining the geochronology of Caribbean sediments. Volcanic activity of the Cayman arc is attributed to the northward subduction of the leading edge of the oceanic plate that carried the Caribbean oceanic plateau. Although the factors generating the large episodes of Central American explosive volcanism are unclear, we propose that they are related to contemporary major readjustments of plate tectonic configuration in the Pacific.

Geochemistry of ODP Leg 125 peridotites

Trace element analyses (first-series transition elements, Ti, Rb, Sr, Zr, Y, Nb, and REE) were carried out on whole rocks and minerals from 10 peridotite samples from both Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc using a combination of XRF, ID-MS, ICP-MS, and ion microprobe. The concentrations of incompatible trace elements are generally low, reflecting the highly residual nature of the peridotites and their low clinopyroxene content (<2%). Chondrite-normalized REE patterns show extreme U shapes with (La/Sm)n ratios in the range of 5.03-250.0 and (Sm/Yb)n ratios in the range of 0.05-0.25; several samples show possible small positive Eu anomalies. LREE enrichment is common to both seamounts, although the peridotites from Conical Seamount have higher (La/Ce)n ratios on extended chondrite-normalized plots, in which both REEs and other trace elements are organized according to their incompatibility with respect to a harzburgitic mantle. Comparison with abyssal peridotite patterns suggests that the LREEs, Rb, Nb, Sr, Sm, and Eu are all enriched in the Leg 125 peridotites, but Ti and the HREEs exhibit no obvious enrichment. The peridotites also give positive anomalies for Zr and Sr relative to their neighboring REEs. Covariation diagrams based on clinopyroxene data show that Ti and the HREEs plot on an extension of an abyssal peridotite trend to more residual compositions. However, the LREEs, Rb, Sr, Sm, and Eu are displaced off this trend toward higher values, suggesting that these elements were introduced during an enrichment event. The axis of dispersion on these plots further suggests that enrichment took place during or after melting and thus was not a characteristic of the lithosphere before subduction. Compared with boninites sampled from the Izu-Bonin-Mariana forearc, the peridotites are significantly more enriched in LREEs. Modeling of the melting process indicates that if they represent the most depleted residues of the melting events that generated forearc boninites they must have experienced subsolidus enrichment in these elements, as well as in Rb, Sr, Zr, Nb, Sm, and Eu. The lack of any correlation with the degree of serpentinization suggests that low-temperature fluids were not the prime cause of enrichment. The enrichment in the high-field-strength elements also suggests that at least some of this enrichment may have involved melts rather than aqueous fluids. Moreover, the presence of the hydrous minerals magnesio-hornblende and tremolite and the common resorption of orthopyroxene indicate that this high-temperature peridotite-fluid interaction may have taken place in a water-rich environment in the forearc following the melting event that produced the boninites. The peridotites from Leg 125 may therefore contain a record of an important flux of elements into the mantle wedge during the initial formation of forearc lithosphere. Ophiolitic peridotites with these characteristics have not yet been reported, perhaps because the precise equivalents to the serpentinite seamounts have not been analyzed.

Strength and deformation behavior of ODP Leg 110 sediments

The shape and morphology of the northern Barbados Ridge complex is largely controlled by the sediment yield and failure behavior in response to high lateral loads imposed by convergence. Loads in excess of sediment yield strength result in nonrecoverable deformations within the wedge, and failure strength acts as an upper limit beyond which stresses are released through thrust faults. Relatively high loading rates lead to delayed consolidation and in-situ pore pressures greater than hydrostatic. The sediment yield and failure behavior is described for any stress path by a generalized constitutive model. A yield locus delineates the onset of plastic (non-recoverable) deformation, as defined from the isotropic and anisotropic consolidation responses of high-quality 38-mm triaxial specimens; a failure envelope was obtained by shearing the same specimens in both triaxial compression and extension. The yield locus is shown to be rotated into extension space and is centered about a K-line greater than unity, suggesting that the in-situ major principal stress has rotated into the horizontal plane, and that the sediment wedge is being subjected to extensional effective stress paths.

Automated composite depth scale reconstruction of ODP Leg 138 and 154 sites

A composite section, which reconstructs a continuous stratigraphic record from cores of multiple nearby holes, and its associated composite depth scale are important tools for analyzing sediment recovered from a drilling site. However, the standard technique for creating composite depth scales on drilling cruises does not correct for depth distortion within each core. Additionally, the splicing technique used to create composite sections often results in a 10-15% offset between composite depths and measured drill depths. We present a new automated compositing technique that better aligns stratigraphy across holes, corrects depth offsets, and could be performed aboard ship. By analyzing 618 cores from seven Ocean Drilling Program (ODP) sites, we estimate that ?80% of the depth offset in traditional composite depth scales results from core extension during drilling and extraction. Average rates of extension are 12.4 ± 1.5% for calcareous and siliceous cores from ODP Leg 138 and 8.1 ± 1.1% for calcareous and clay-rich cores from ODP Leg 154. Also, average extension decreases as a function of depth in the sediment column, suggesting that elastic rebound is not the dominant extension mechanism.

Geochemistry of ODP Leg 127 igneous rocks

Legs 127 and 128 of the Ocean Drilling Program cored basement samples from two sites in the Yamato Basin (Sites 794 and 797) and one site in the Japan Basin (Site 795) of the Japan Sea. These samples represent sills and lava flows erupted or shallowly intruded in a marine environment during backarc extension and spreading in the middle Miocene. In this paper, we describe the geochemical characteristics of these igneous units using 52 new instrumental neutron activation analyses (INAA), 8 new X-ray fluorescence (XRF) analyses, and previous shipboard XRF analyses. The sills intruded into soft sediment at Sites 794 and 797 were subject to extensive hydrothermal activity, estimated at <230° C under subgreenschist facies conditions, which heavily to totally altered the fine-grained unit margins and moderately to heavily altered the coarse-grained unit interiors. Diagenesis further altered the composition of these igneous bodies and lava flows at Sites 794, 795, and 797, most intensely at unit margins. Our study of two well-sampled units shows that Mg, Ca, Sr, and the large-ion lithophile elements (LILE) mobilized during alteration, and that the concentrations of Y, Yb, and Lu decreased and Ce increased in the most severely altered samples. Nevertheless, our study shows that the rare-earth elements (REE) were relatively immobile in the majority of the samples, even where secondary mixed-layer clays comprised the great majority of the rock. Fresher Yamato Basin samples are compositionally heterogenous tholeiitic basalts and dolerites. At Site 794 in the north-central portion of the basin, Units 1 to 5 (upper basement) comprise mildly light rare-earth element (LREE) enriched basalts and dolerites (chondrite-normalized La/Sm of 1.4-1.8), while the stratigraphically lower Units 6 to 9 are less enriched dolerites with (La/Sm)N of 0.7-1.3. All Site 794 samples lack Nb and Ta depletions and LILE enrichments, lacking a strong subduction-related incompatible element geochemical signature. At Site 797 in the western margin of the basin, two stratigraphically-definable unit groups also occur. The upper nine units are incompatible-element depleted tholeiitic sills and flows with strong depletions of Nb and Ta relative to normal mid-ocean ridge basalt (N-MORB). The lower twelve sills represent LREE-enriched tholeiites (normalized La/Sm ranges from 1.1 to 1.8), with distinctly higher LILE and high field-strength element (HFSE) contents. At Site 795 at the northern margin of the Japan Sea, three eruptive units consist of basaltic andesite to calc-alkaline basalt (normalized La/Sm of 1.1 to 1.5) containing moderate depletions of the HFSE relative to N-MORB. The LILE-depleted nature of these samples precludes their origin in a continental arc, indicating that they more likely erupted within a rifting oceanic arc system. The heterogenous nature of the Japan Sea rocks indicate that they were derived at each site from multiple parental magmas generated from a compositionally heterogenous mantle source. Their chemistry is intermediate in character between arc basalts, MORB, and intraplate basalts, and implies little involvement of continental crust at any point in their genesis. Their flat chondrite-normalized, medium-to-heavy rare earth patterns indicate that the primary magmas which produced them last equilibrated with and segregated from spinel lherzolite at shallow depths (<30 kbar). In strong contrast to their isotopic compositional arrays, subduction-related geochemical signatures are usually poorly defined. No basin-wide temporal or geographic systematics of rock chemistry may be confidently detailed; instead, the data show both intimate (site-specific) and widespread backarc mantle heterogeneity over a narrow (2 Ma or so) range in time, with mantle heterogeneity most closely resembling a "plum-pudding" model.

Magnetic susceptibility anisotropy in deformed sediments of ODP Leg 110

The anisotropy of magnetic susceptibility documents the generation of tectonically produced fabrics in sediments that macroscopically show no evidence of this disruption. The fabric observed in initial accretion is largely produced by overprinting of the original sedimentary susceptibility anisotropy by an E-W horizontal tectonic shortening and vertical extension. The response of the sediments to stress during initial accretion is variable, particularly near the sediment surface, and appears to reflect the inhomogeneous distribution of strain rate in the overthrust sequence. The susceptibility anisotropy of sediments possessing scaly fabric is consistent with the strong orientation of Phyllosilicates seen in thin section, producing a Kmin normal to the scalyness. The slope sediments deposited on the accreted sequence are also affected by tectonic shortening. The accreted sequences at Sites 673 and 674 show a complex history of fabric modification, with previous tectonic fabrics overprinted by later fabric modifications, pointing to continued tectonic shortening during the accretion process. The form of the susceptibility anisotropy axes at Sites 673 and 674 is consistent with NESW shortening, probably reflected in the NW-SE surface expression of the out-of-sequence thrusts. The susceptibility anisotropy appears to document a downhole change in the trend of shortening from E to W at the surface to more NESW at depth, probably as a result of the obliquely trending basement ridge, the Tiburon Rise.

Magnetic stratigraphy of ODP Leg 133 sites

This study is a synthesis of paleomagnetic and mineral magnetic results for Sites 819 through 823 of Ocean Drilling Program (ODP) Leg 133, which lie on a transect from the outer edge of the Great Barrier Reef (GBR) down the continental slope to the bottom of the Queensland Trough. Because of viscous remagnetization and pervasive overprinting, few reversal boundaries can be identified in these extremely high-resolution Quaternary sequences. Some of the magnetic instability, and the differences in the quality of the paleomagnetic signal among sites, can be explained in terms of the dissolution of primary iron oxides in the high near-surface geochemical gradients. Well-defined changes in magnetic properties, notably susceptibility, reflect responses to glacio-eustatic sea-level fluctuations and changes in slope sedimentation processes resulting from formation of the GBR. Susceptibility can be used to correlate between adjacent holes at a given site to an accuracy of about 20 cm. Among-site correlation of susceptibility is also possible for certain parts of the sequences and permits (tentative) extension of the reversal chronology. The reversal boundaries that can be identified are generally compatible with the calcareous nannofossil biostratigraphy and demonstrate a high level of biostratigraphic consistency among sites. A revised chronology based on an optimum match with the susceptibility stratigraphy is presented. Throughout most of the sequences there is a strong inverse correlation both between magnetic susceptibility and calcium carbonate content, and between susceptibility and d18O. In the upper, post-GBR, sections a more complicated type of magnetic response occurs during glacial maxima and subsequent transgressions, resulting in a positive correlation between susceptibility and d18O. Prior to and during formation of the outer-reef barrier, the sediments have relatively uniform magnetic properties showing multidomain behavior and displaying cyclic variations in susceptibility related to sea-level change. The susceptibility oscillations are controlled more by carbonate dilution than by variation in terrigenous influx. Establishment of the outer reef between 1.01 and 0.76 Ma restricted the supply of sediment to the slope, causing a four-fold reduction in sedimentation rates and a transition from prograding to aggrading seismic geometries (see other chapters in this volume). The Brunhes/Matuyama boundary and the end of the transition period mark a change to lower and more subdued susceptibility oscillations with higher carbonate contents. The major change in magnetic properties comes at about 0.4 Ma in the aggrading sequence, which contains prominent sharp susceptibility peaks associated with glacial cycles, with distinctive single-domain magnetite and mixed single-domain/superparamagnetic characteristics. Bacterial magnetite has been found in the sediments, particularly where there are high susceptibility peaks, but its importance has not yet been assessed. A possible explanation for the characteristic pattern of magnetic properties in the post-GBR glacial cycles can be found in terms of fluvio-deltaic processes and inter-reefal lagoonal reservoirs that develop when the shelf becomes exposed at low sea-level.

(Table T1) Porosity and permeability of samples from ODP Leg 180 sites

Woodlark Basin, an area of continental extension, is an ideal location to study the evolution of permeability and the development of overpressures within an active rift basin. In this investigation, we measured sediment permeabilities of cores from Woodlark Basin and used numerical modeling to determine if pore fluid overpressures are likely at the base of the rift basin. Constant-rate flow tests were conducted on cores from Site 1108, located in the rift basin, and Sites 1115 and 1118, located on the northern margin of the basin. Results of the laboratory tests indicated permeabilities that range from 1.5 x 10**-18 to 1 x 10**-16 m**2. Results of the numerical modeling of Site 1108 suggest that overpressures due to sedimentation are unlikely.

Particel size distribution and microstructures of sediments from ODP Leg 205 sites (Table 1)

Ocean Drilling Program Legs 170 and 205 offshore Costa Rica provide structural observations which support a new model for the geometry and deformation response to the seismic cycle of the frontal sedimentary prism and decollement. The model is based on drillcore, thin section, and electron microscope observations. The decollement damage zone is a few tens of meters in width, it develops mainly within the frontal prism. A clear cm-thick fault core is observed 1.6 km from the trench. The lower boundary of the fault core is coincident with the lithological boundary between the frontal prism and the hemipelagic and pelagic sediment of the Cocos plate. Breccia clast distributions in the upper portion of the decollement damage zone were studied through fractal analysis. This analysis shows that the fractal dimension changes with brecciated fragment size, implying that deformation was not accommodated by self-similar fracturing. A higher fractal dimensionality correlates with smaller particle size, which indicates that different or additional grain-size reduction processes operated during shearing. The co-existence of two distinct fracturing processes is also confirmed by microscopic analysis in which extension fracturing in the upper part of the damage zone farthest from the fault core is frequent, while both extension and shear fracturing occur approaching the fault core. The coexistence of extensional and shear fracturing seems to be best explained by fluid pressure variations in response to variations of the compressional regime during the seismic cycle. During the co-seismic event, sub-horizontal compression and fluid pressure increase, triggering shear fracturing and fluid expulsion. Fractures migrate upward with fluids, contributing to the asymmetric shape of the decollement, while slip propagates. In the inter-seismic interval the frontal prismrelaxes and fluid pressure drops. The frontal prismgoes into diffuse extension during the intervalwhen plate convergence is accommodated by creep along the ductile fault core. The fault core is typically a barrier to deformation, which is explained by its weak, but impermeable, nature. The localized development of a damage zone beneath the fault core is characterized by shear fracturing that appears as the result of local strengthening of the detachment.

Grain counts and relative abundances of volcaniclastic sands and sandstones of ODP Leg 180 sites

Modal analysis of middle Miocene to Pleistocene volcaniclastic sands and sandstones recovered from Sites 1108, 1109, 1118, 1112, 1115, 1116, and 1114 within the Woodlark Basin during Leg 180 of the Ocean Drilling Program indicates a complex source history for sand-sized detritus deposited within the basin. Volcaniclastic detritus (i.e., feldspar, ferromagnesian minerals, and volcanic rock fragments) varies substantially throughout the Woodlark Basin. Miocene sandstones of the inferred Trobriand forearc succession contain mafic and subordinate silicic volcanic grains, probably derived from the contemporary Trobriand arc. During the late Miocene, the Trobriand outerarc/forearc (including Paleogene ophiolitic rocks) was subaerially exposed and eroded, yielding sandstones of dominantly mafic composition. Rift-related extension during the late Miocene-late Pliocene led to a transition from terrestrial to neritic and finally bathyal deposition. The sandstones deposited during this period are composed dominantly of silicic volcanic detritus, probably derived from the Amphlett Islands and surrounding areas where volcanic rocks of Pliocene-Pleistocene age occur. During this time terrigenous and metamorphic detritus derived from the Papua New Guinea mainland reached the single turbiditic Woodlark rift basin (or several subbasins) as fine-grained sediments. At Sites 1108, 1109, 1118, 1116, and 1114, serpentinite and metamorphic grains (schist and gneiss) appear as detritus in sandstones younger than ~3 Ma. This is thought to reflect a major pulse of rifting that resulted in the deepening of the Woodlark rift basin and the prevention of terrigenous and metamorphic detritus from reaching the northern rift margin (Site 1115). The Paleogene Papuan ophiolite belt and the Owen Stanley metamorphics were unroofed as the southern margin of the rift was exhumed (e.g., Moresby Seamount) and, in places, subaerially exposed (e.g., D'Entrecasteaux Islands and onshore Cape Vogel Basin), resulting in new and more proximal sources of metamorphic, igneous, and ophiolitic detritus. Continued emergence of the Moresby Seamount during the late Pliocene-early Pleistocene bounded by a major inclined fault scarp yielded talus deposits of similar composition to the above sandstones. Upper Pliocene-Pleistocene sandstones were deposited at bathyal depths by turbidity currents and as subordinate air-fall ash. Silicic glassy (high-K calc-alkaline) volcanic fragments, probably derived from volcanic centers located in Dawson and Moresby Straits, dominated these sandstones.