The effect of an on-body personal lift assist device (PLAD) on fatigue during a repetitive lifting task

Occupations demanding frequent and heavy lifting are associated with an increased risk of injury. A personal lift assist device (PLAD) was designed to assist human muscles through the use of elastic elements. This study was designed to determine if the PLAD could reduce the level of general and local back muscle fatigue during a cyclical lifting task. Electromyography of two erector spinae sites (T9 and L3) was recorded during a 45-min lifting session at six lifts/lowers per minute in which male participants (n = 10) lifted a box scaled to represent 20% of their maximum back extensor strength. The PLAD device reduced the severity of muscular fatigue at both muscle sites. RMS amplitude increased minimally (22% and 26%) compared to the no-PLAD condition (104% and 88%). Minimal median frequency decreases (0.33% and 0.41%) were observed in the PLAD condition compared to drops of 12% and 20% in the no-PLAD condition. The PLAD had an additional benefit of minimizing pre–post changes in muscular strength and endurance. The PLAD also resulted in a significantly lower rate of perceived exertion across the lifting session. It was concluded that the PLAD was effective at decreasing the level of back muscular fatigue.     

Mathematical and empirical proof of principle for an on-body personal lift augmentation device (PLAD)

In our laboratory, we have developed a prototype of a personal lift augmentation device (PLAD) that can be worn by workers during manual handling tasks involving lifting or lowering or static holding in symmetric and asymmetric postures. Our concept was to develop a human-speed on-body assistive device that would reduce the required lumbar moment by 20-30% without negative consequences on other joints or lifting kinematics. This paper provides mathematical proof using simplified free body diagrams and two-dimensional moment balance equations. Empirical proof is also provided based on lifting trials with nine male subjects who executed sagittal plane lifts using three lifting styles (stoop, squat, free) and three different loads (5, 15, and 25kg) under two conditions (PLAD, No-PLAD). Nine Fastrak sensors and six in-line strap force sensors were used to estimate the reduction of compressive and shear forces on L4/L5 as well as estimate the forces transferred to the shoulders and knees. Depending on lifting technique, the PLAD applied an added 23-36Nm of torque to assist the back muscles during lifting tasks. The peak pelvic girdle contact forces were estimated and their magnitudes ranged from 221.3+/-11.2N for stoop lifting, 324.3+/-17.2N for freestyle lifts to 468.47+/-23.2N for squat lifting. The PLAD was able to reduce the compression and shear forces about 23-29% and 7.9-8.5%, respectively.     

Estimating the L5S1 flexion/extension moment in symmetrical lifting using a simplified ambulatory measurement system

Mechanical loading of the spine has been shown to be an important risk factor for the development of low-back pain. Inertial motion capture (IMC) systems might allow measuring lumbar moments in realistic working conditions, and thus support evaluation of measures to reduce mechanical loading. As the number of sensors limits applicability, the objective of this study was to investigate the effect of the number of sensors on estimates of L5S1 moments.Hand forces, ground reaction forces (GRF) and full-body kinematics were measured using a gold standard (GS) laboratory setup. In the ambulatory setup, hand forces were estimated based on the force plates measured GRF and body kinematics that were measured using (subsets of) an IMC system. Using top-down inverse dynamics, L5S1 flexion/extension moments were calculated.RMSerrors (Nm) were lowest (16.6) with the full set of 17 sensors and increased to 20.5, 22 and 30.6, for 8, 6 and 4 sensors. Absolute errors in peak moments (Nm) ranged from 17.7 to 16.4, 16.9 and 49.3 Nm, for IMC setup’s with 17, 8, 6 and 4 sensors, respectively. When horizontal GRF were neglected for 6 sensors, RMSerrors and peak moment errors decreased from 22 to 17.3 and from 16.9 to 13 Nm, respectively.In conclusion, while reasonable moment estimates can be obtained with 6 sensors, omitting the forearm sensors led to unacceptable errors. Furthermore, vertical GRF information is sufficient to estimate L5S1 moments in lifting.     

Activation of human arm muscles during flexion/extension and supination/pronation tasks: A theory on muscle coordination

Generally the number of muscles acting across a joint exceeds the number of degrees of freedom available to the joint. This redundancy raises a problem regarding the ratio in which these muscles are activated during a particular motor task. In this paper we present a theory to explain the activation patterns of muscles used during voluntary and reflex induced contractions. The basic assumptions underlying the theory are that 1) coordination of muscles is based on synergistic muscle activities, 2) the synergisms involved satisfy certain transformations of muscle spindle signals to muscle activation signals and 3) muscle spindle output is proportional to the ratio of muscle stretch and muscle length in lengthening muscles, and is zero in shortening muscles. The theory is used to predict the recruitment threshold of motor units in six arm muscles during voluntary isometric contractions. All theoretical predictions are in reasonable agreement with the experimentally observed behavior of a large population of motor units within each muscle. However, within a single muscle sometimes motor-unit populations have been found to have different types of recruitment behavior. This deviating behavior is discussed in the light of the theory presented here.     

Comparing polynomial and cubic spline interpolation of segment angles for estimating L5/S1 net moment during symmetric lifting tasks

Simple video-based methods previously proposed for field research to estimate L5/S1 net moments during real-world manual materials handling rely on polynomial interpolation on the joint angles from key frames extracted from video recordings; however, polynomial interpolations may not converge as the number of interpolation points increases. Therefore, we compared L5/S1 net moments calculated from continuous kinematic measurements to those calculated from both polynomial and cubic spline interpolation on body segments angles during lifting tasks. For small number of interpolation points (<6) the error in the predicted moment from both the spline and polynomial fits decreased with the increase in the number of interpolation points; however, above 6 interpolation points error for the polynomial fits started to increase while the error from the spline fit continued to decrease. These results suggest that cubic spline interpolation on body segments angles provides a more robust basis for calculating L5/S1 net moment from a few key video frames.     

Spatial cognition and memory: a reversible lesion with lidocaine into the anteromedial/posterior parietal cortex (AM/PPC) affects differently working and long-term memory on two foraging tasks

Place memory is relevant for exploration and forage behaviour. When food supply is dispersed, a win-shift has advantage over a win-stay strategy. In the Olton Octagonal Maze, the rat follows a win-shift strategy using working memory. However, in the Olton 4x4 version, the rat follows a win-stay strategy, using both working and long-term memories. It has been suggested that the neocortex is required for the resolution of tasks demanding long-term, but not for that demanding working memory alone. The role of anteromedial/posterior parietal cortex (AM/PPC) was investigated here, using a reversible lesion induced by intracerebral lidocaine infusion. Long-Evans rats were implanted with guide cannulae into the AM/PPC and trained in an Olton 4x4 maze, counting working and long-term memory errors after a delay. Then, the animals were infused with lidocaine or saline during the delay phase and tested for three days. Another series of animals, treated as before, was tested in an Olton Octagonal Maze and subjected to the same injection schedule. In the Olton 4x4 Maze, lidocaine produced a significant increase in working and long-term memory errors, compared to saline and post-lidocaine conditions. In contrast, in the Olton Octagonal Maze, lidocaine did not induce any effect on working memory errors. Thus, AM/PPC is required when both working with previous information and long-term memories are needed, but not when only working memory is required, as it happens under ethological conditions. Whenever food supply is dispersed, a win-shift strategy is preferable.     

Whole-body lift and ground effect during pectoral fin locomotion in the northern spearnose poacher (Agonopsis vulsa)

The northern spearnose poacher, Agonopsis vulsa, is a benthic, heavily armored fish that swims primarily using pectoral fins. High-speed kinematics, whole-body lift measurements, and flow visualization were used to study how A. vulsa overcomes substantial negative buoyancy while generating forward thrust. Kinematics for five freely swimming poachers indicate that individuals tend to swim near the bottom (within 1 cm) with a consistently small (less than 1°) pitch angle of the body. When the poachers swam more than 1 cm above the bottom, however, body pitch angles were higher and varied inversely with speed, suggesting that lift may help overcome negative buoyancy. To determine the contribution of the body to total lift, fins were removed from euthanized fish (n=3) and the lift and drag from the body were measured in a flume. Lift and drag were found to increase with increasing flow velocity and angle of attack (ANCOVA, p<0.0001 for both effects). Lift force from the body was found to supply approximately half of the force necessary to overcome negative buoyancy when the fish were swimming more than 1 cm above the bottom. Lastly, flow visualization experiments were performed to examine the mechanism of lift generation for near-bottom swimming. A vortex in the wake of the pectoral fins was observed to interact strongly with the substratum when the animals approached the bottom. These flow patterns suggest that, when swimming within 1 cm of the bottom, poachers may use hydrodynamic ground effect to augment lift, thereby counteracting negative buoyancy.     

Jaw movement kinematics and jaw muscle (EMG) activity during drinking in the pigeon (Columba livia)

Summary Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - GENIO geniohyoideus muscle - LB lower beak - LED light-emitting diode - PQP protractor quadrati et pterygoidei muscle - PVL pterygoideus ventralis muscle, pars lateralis - SeH/StH serpihyoideus or stylohyoideus muscle - UB upper beak     

中国石龙子母体孕期调温诱导幼体表型: 母体操纵假说的实验检测

卵胎生是由卵生繁殖模式通过逐渐增加卵滞留和胚胎在母体子宫内发育的时间进化而来的繁殖模式。有鳞类爬行动物(蜥蜴和蛇)有着较高的繁殖模式多样性,因而是研究卵胎生繁殖模式进化及其适应意义的理想动物模型。至今对于卵胎生进化的选择压力尚无定论,目前有3种关于卵胎生进化的假说受到学者的关注,其中母体操纵假说最受关注但尚未得到充分的检测。研究继1995年母体操纵假说提出之后,以栖息于温带气候环境下的卵生中国石龙子(Eumeces chinensis)为模型动物检测该假说。37条中国石龙子怀卵母体采自浙江丽水市郊。将怀卵母体分置于3个热处理中,其中12条母体提供每日14 h光照时间,13条母体提供10 h光照,其余12条母体没有任何调温机会(体温随室内环境温度而改变)。结果显示:怀卵母体选择体温向下漂移。3种处理下的雌体繁殖特征没有显著差异。长、短调温组下母体产卵时间要早于非调温组母体,但新生卵的胚胎历期没有显著差异。用5种热处理孵化卵,孵化温度分别为:1=室内波动温度孵化;2=27℃;3=24—30℃;4=22—32℃(3和4孵化处理中,孵化箱内的温度每隔1d改变1次,即卵分别在22和24℃孵化24 h,随后在32和30℃孵化24 h,每2d循环1次直至孵出);5=在实验室后院内模拟石龙子野外巢址孵化。结果显示:孵出幼体的体长、腹长和头部大小(头长和头宽)在3个母体热处理间存在显著差异,其他形态学特征不存在母体热处理间的显著差异;孵化温度以及孵化温度和母体热处理的交互作用对所有的幼体形态学特征均无显著影响。孵化温度以及孵化温度和母体热处理的交互作用对幼体疾跑速和最大持续运动距离无显著影响;但不同的母体热处理显著影响幼体疾跑速和最大持续运动距离。研究结果不仅为"热变异对在一定孵化温度范围内表型无显著变化的物种的幼体表型没有重要的修饰作用"这一假说提供了有力证据,并且支持母体操纵假说的两个主要预测:雌体在孕期通过体温漂变行为提供体内胚胎发育的最适热环境,而由母体调温行为诱导的后代表型的变异将增强后代的适合度。     

Altered HBK3 expression affects glutathione and ascorbate metabolism during the early phases of Norway spruce (Picea abies) somatic embryogenesis

Plant homeobox genes play an important role in plant development, including embryogenesis. Recently, the function of a class I homeobox of knox 3 gene, HBK3, has been characterized in the conifer Picea abies (L.) Karst (Norway spruce) [8]. During somatic embryogenesis, expression of HBK3 is required for the proper differentiation of proembryogenic masses into somatic embryos. This transition, fundamental for the overall embryogenic process, is accelerated in sense lines over-expressing HBK3 (HBK3-S) but precluded in antisense lines (HBK3-AS) where the expression of this gene is experimentally reduced. Altered HBK3 expression resulted in major changes of ascorbate and glutathione metabolism. During the initial phases of embryogeny the level of reduced GSH was higher in the HBK3-S lines compared to their control counterpart. An opposite profile was observed for the HBK3-AS lines where the glutathione redox state, i.e. GSH/GSH + GSSG, switched towards its oxidized form, i.e. GSSG. Very similar metabolic fluctuations were also measured for ascorbate, especially during the transition of proembryogenic masses into somatic embryos (7 days into hormone-free medium). At this stage the level of reduced ascorbate (ASC) in the HBK3-AS lines was about 75% lower compare to the untransformed line causing a switch of the ascorbate redox state, i.e. ASC/ASC + DHA + AFR, towards its oxidized forms, i.e. DHA + AFR. Changes in activities of several ascorbate and glutathione redox enzymes, including dehydroascorbate reductase (EC 1.8.5.1), ascorbate free radical reductase (EC 1.6.5.4) and glutathione reductase (GR; EC 1.6.4.2) were responsible for these metabolic differences. Data presented here suggest that HBK3 expression might regulate somatic embryo yield through alterations in glutathione and ascorbate metabolism, which have been previously implicated in controlling embryo development and maturation both in vivo and in vitro.     

Avena phytochrome a overexpressed in transgenic tobacco seedlings differentially affects red/far-red reversible and very-low-fluence responses (cotyledon unfolding) during de-etiolation

Etiolated seedlings of tobacco (Nicotiana tabacum L.) were exposed to single light pulses predicted to establish different proportions of phytochrome in its far-red absorbing form (Pfr/P). The angle between the cotyledons was compared in wild-type and transgenic seedling overexpressing Avena phytochrome A over the range of both very low-fluence responses (VLFR) and low-fluence responses (LFR). The unfolding of the cotyledons increased linearly for 24 h after the light pulse. At this time the Pfr/P-response curve showed two linear segments. The segment below a calculated Pfr/P = 3% (i.e. VLFR) was steeper than the segment above 3% (i.e. LFR). In the VLFR range the slope was almost threefold higher in transgenic than wild-type seedlings. However, in the LFR range the difference was less than 50%. From these data we propose that Avena phytochrome A makes a higher contribution to VLFR than LFR in etiolated tobacco seedlings.Abbreviations FR far-red light - LFR low-fluence response - Pfr/P proportion of phytochrome (P) in its FR-absorbing form (Pfr) - R red light - VLFR very low-fluence response Financial support was provided by the University of Buenos Aires and Fundación Antorchas (Argentina) to J.J.C., CONICET (Argentina) to R.A.S. and the U.S. Department of Energy (DE-FG02-88ER13968) to R.D.V.     

Characteristics of EEG reactivity changes during the performance of dual tasks in healthy subjects (voluntary postural control and calculation)

Comprehensive EEG and stabilography investigation with separate and simultaneous performance of motor (voluntary postural control) and cognitive (calculation) tasks has been performed in 20 healthy subjects (22 ± 0.7 years). Specific spatial and frequency reactive changes have been found during motor task performance. These included an increase in coherence in the EEG α band for distant derivation pairs in the right hemisphere, as well as in symmetric parietal-occipital areas in both hemispheres. Cognitive task performance was accompanied by an increase in coherence for the slow bands (δ and θ) with a higher activation in the left hemisphere and frontal cortex areas. In performing the dual task, one could observe activation of spatial and frequency changes including both motor and cognitive tasks. In the dual tasks where both components were performed worse as compared to the control, reactive reorganization of EEG coherence was less pronounced than during the performance of separate tasks. A decrease in the coherence of the α₁ band in the frontal areas appeared as a zone of “conflict of interest” or interference. In dual tasks with better performance of each component as compared to the control, EEG coherence increased in each specific area, as well as in the areas of “conflict of interests.”     

Altered gravity affects ventral root activity during fictive swimming and the static vestibuloocular reflex in young tadpoles (Xenopus laevis)

During early periods of life, modifications of the gravitational environment affect the development of sensory, neuronal and motor systems. The vestibular system exerts significant effects on motor networks that control eye and body posture as well as swimming. The objective of the present study was to study whether altered gravity (AG) affects vestibuloocular and spinal motor systems in a correlated manner. During the French Soyuz taxi flight Andromède to the International Space Station ISS (launch: October 21, 2001; landing: October 31, 2001) Xenopus laevis embryos were exposed for 10 days to microgravity (microg). In addition, a similar experiment with 3g-hypergravity (3g) was performed in the laboratory. At onset of AG, embryos had reached developmental stages 24 to 27. After exposure to AG, each tadpole was tested for its roll-induced vestibuloocular reflex (rVOR) and 3 hours later it was tested for the neuronal activity recorded from the ventral roots (VR) during fictive swimming. During the post-AG recording periods tadpoles had reached developmental stages 45 to 47. It was observed that microgravity affected VR activity during fictive swimming and rVOR. In particular, VR activity changes included a significant decrease of the rostrocaudal delay and a significant increase of episode duration. The rVOR-amplitude was transiently depressed. Hypergravity was less effective on the locomotor pattern; occurring effects on fictive swimming were the opposite of microg effects. As after microgravity, the rVOR was depressed after 3g-exposure. All modifications of the rVOR and VR-activity recovered to normal levels within 4 to 7 days after termination of AG. Significant correlations between the rVOR amplitude and VR activity of respective tadpoles during the recording period have been observed in both tadpoles with or without AG experience. The data are consistent with the assumptions that during this period of life which is characterized by a progressive development of vestibuloocular and vestibulospinal projections (i) microgravity retards the development of VR activity while hypergravity weakly accelerates it; (ii) that microgravity retards the rVOR development while hypergravity caused a sensitization, and that (iii) AG-induced changes of VR activity during fictive swimming have a vestibular origin.     

Sodium nitroprusside affects the level of photosynthetic enzymes and glucose metabolism in Phaseolus aureus (mung bean)

Nitric oxide (NO) is an important signaling molecule in plants. The present study aims to investigate the downstream signaling pathways of NO in plants using a proteomic approach. Phaseolus aureus (mung bean) leaf was treated with sodium nitroprusside (SNP), which releases nitric oxide in the form of nitrosonium cation (NO+) upon light irradiation. Changes in protein expression profiles of the SNP treated mung bean leaf were analyzed by two-dimensional gel electrophoresis (2-DE). Comparison of 2-DE electropherograms revealed seven down-regulated and two up-regulated proteins after treatment with 0.5 mM SNP for 6 h. The identities of these proteins were analyzed by a combination of peptide mass fingerprinting and post-source decay using a matrix-assisted-laser-desorption-ionisation-time-of-flight (MALDI-TOF) mass spectrometer. Six out of these nine proteins found are involved in either photosynthesis or cellular metabolism. We have taken our investigation further by studying the effect of NO+ on glucose contents in mung bean leaves. Our results clearly demonstrated that NO+ rapidly and drastically decrease the amount of glucose in mung bean leaves. Moreover, four out of nine of these proteins are chloroplastic isoforms. These results suggested that chloroplasts might be one of the main sub-cellular targets of NO in plants.     

Changes in fatty chain compositions of lipid classes during frozen storage of the adductor muscle of giant ezo scallop (Patinopecten yessoensis)

Changes in lipid components, particularly glycerophospholipids in the adductor muscle of giant ezo scallop during storage at −20°C, were investigated. During storage, the contents of total lipid (TL) and polar lipid (PL) decreased but that of non-polar lipid (NL) increased. Glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE) decreased by 50 and 15% of the each initial content, while lyso-GPC and free fatty acids increased. The percentages of polyunsaturated fatty acids such as 20:5n-3 and 22:6n-3 in the TL and PL fractions decreased during storage, but those of the polyunsaturated fatty acids in the NL increased. In the alkenylacyl-GPE and diacyl-GPC, the percentages of relatively longer acids in the sn-1 positions of glycerol moieties decreased at higher rates than did the shorter chains, whereas the results for diacyl-GPE were opposite to those of alkenylacyl-GPE and diacyl-GPC. In the prominent fatty acids in the sn-2 positions of alkenylacyl-GPE and diacyl-GPC, the percentage of 22:6n-3 decreased from compared to the high level of 20:5n-3, while that of diacyl-GPE increased.     

Truncation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from Rhodospirillum rubrum affects the holoenzyme assembly and activity.

Truncations of the subunit of ribulose bisphosphate carboxylase/oxygenase (Rubisco) from Rhodospirillum rubrum were generated by site-directed mutagenesis to examine the role of the C-terminal tail section. Removal of the last and the penultimate alpha-helices in the tail section changes the quaternary structure of the protein. Electrophoretic and electron microscope analysis revealed that the truncated subunits assemble into an octamer, whereas the wild-type enzyme has a dimeric structure. The octomerization of the mutant protein is due to a hydrophobic patch exposed to the solvent by truncation of the subunit. The mutant protein thus consists of four dimers, bound end-to-end by hydrophobic interactions. Insertion of a polar amino acid in the hydrophobic patch by a L424 to N424 substitution restores the familiar dimeric structure. Truncation of the subunit is associated with a considerable decrease in catalytic activity. The mutants undergo carbamylation but bind the reaction intermediate analog, 2-carboxy arabinitol-1,5-bisphosphate, poorly. This indicates that loss of activity in the mutant is due to weakened substrate binding. These findings suggest that the mutations in the tail section of the subunit are transmitted to the active site, although the C-terminal region is far from the active site. On the basis of the crystal structure of Rubisco, we propose a model for how the truncations of the enzyme subunit induce conformational changes in one of the two phosphate binding sites.     

Ultrastructural changes of the anterior and posterior sternal integument of the terrestrial isopod Porcellio scaber Latr. (Crustacea) during the moult cycle

The ultrastructure of the anterior (ASE) and posterior sternal epithelium (PSE) was investigated during the biphasic moult cycle. During early premoult the sternal epithelial cells increase in size, accumulate huge amounts of glycogen, and increase the abundance of cellular organelles. CaCO(3) deposit formation begins before the secretion of the epicuticle in the anterior sternal integument and continues through the secretion of the first exocuticular layers. The deposition of cuticle is delayed in the ASE until the CaCO(3) deposit is fully resorbed between the anterior and posterior moult. The development of the interstitial network (IN), which enormously increases the basolateral compartment of the plasma membrane, starts at the beginning of the exocuticle deposition. During CaCO(3) deposit formation and resorption the volume fraction of the mitochondria is much larger in the ASE than in the PSE, although the cuticle is secreted faster in the posterior integument. The results suggest that the exocuticular and epicuticular layers are permeable to calcium and probably also carbonate ions; that the IN is required during late premoult, when CaCO(3) deposition is accelerated, but not during early CaCO(3) deposition; and that active mechanisms contribute to transepithelial ion transport during CaCO(3) deposit formation and resorption.     

Test-retest reliability of wavelet - and Fourier based EMG (instantaneous) median frequencies in the evaluation of back and hip muscle fatigue during isometric back extensions.

The present study aimed at assessing the test–retest reliability of wavelet – and Fourier derived (instantaneous) median frequencies of surface electromyographic (EMG) measurements of back and hip muscles during isometric back extensions. Twenty healthy subjects (10 males and 10 females) performed a modified Biering-Sørensen test on two separate days, with a 1-week interval between the two tests. Surface EMG measurements were bilaterally performed from the latissimus dorsi, the thoracic and lumbar parts of the longissimus thoracis, the thoracic and lumbar parts of the iliocostalis lumborum, the multifidus, the gluteus maximus and the biceps femoris. In addition, three-dimensional kinematic data were recorded of the subjects’ lumbar vertebrae. The (instantaneous) median frequencies were calculated from the EMG signals using continuous wavelet (IMDF) – and short-time Fourier transforms (MDF). Linear regressions performed on the IMDF and MDF data as a function of time yielded slopes (IMDF_slope and MDF_slope) and intercepts (IMDF_init and MDF_init) of the regression lines. Test–retest reliability was assessed on the normalized slopes and intercept parameters by means of intraclass correlation coefficients (ICC) and standard errors of measurements expressed as percentages of the mean values (% SEM). The results of IMDF_slope and MDF_slope parameters indicated ICCs for back and hip muscles between .443 and .727 for IMDF_slope, values between .273 and .734 for MDF_slope, % SEM between 7.6% and 58.9% for IMDF_slope and % SEM between 8.2% and 25.3% for MDF_slope, respectively. The ICCs for IMDF_init and MDF_init parameters varied between .376 and .907 for IMDF_init and between .383 and .883 for MDF_init, and % SEM ranged from 2.7% to 6.3% for IMDF_init and from 2.6% to 4.7% for MDF_init, respectively. These results indicate that both wavelet – and Fourier based (instantaneous) median frequency parameters generally are reliable in the analysis of back and hip muscle fatigue during a modified Biering-Sørensen test.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured V˙o₂ during digging and resting at ambient temperature (T_a) below, within, and above thermoneutrality. Digging metabolic rate was lowest at T_a within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (T_b) remained constant at all T_as. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant T_b during digging.