A simple method for measuring stiffness during running

The spring-mass model, representing a runner as a point mass supported by a single linear leg spring, has been a widely used concept in studies on running and bouncing mechanics. However, the measurement of leg and vertical stiffness has previously required force platforms and high-speed kinematic measurement systems that are costly and difficult to handle in field conditions. We propose a new "sine-wave" method for measuring stiffness during running. Based on the modeling of the force-time curve by a sine function,this method allows leg and vertical stiffness to be estimated from just a few simple mechanical parameters: body mass, forward velocity, leg length, flight time, and contact time. We compared this method to force-platform-derived stiffness measurements for treadmill dynamometer and overground running conditions, at velocities ranging from 3.33 m.s-1 to maximal running velocity in both recreational and highly trained runners. Stiffness values calculated with the proposed method ranged from 0.67 % to 6.93 % less than the force platform method, and thus were judged to be acceptable. Furthermore, significant linear regressions (p < 0.01) close to the identity line were obtained between force platform and sine-wave model values of stiffness. Given the limits inherent in the use of the spring-mass model, it was concluded that this sine-wave method allows leg and stiffness estimates in running on the basis of a few mechanical parameters, and could be useful in further field measurements.     

Coordinate transformations for eye and arm movements in the brain

Recent work on the coding of spatial information in the brain has significantly advanced our knowledge of sensory to motor transformations on several fronts. The encoding of information referenced to the retina (eye-centered) but modulated by eye position, called a gain field representation, has proved to be very common throughout parietal and occipital cortex. The use of an eye-centered representation as a working memory of spatial location is problematic if the eyes move during the memory period. Details regarding the manner in which the brain solves this problem are beginning to emerge. Finally, the discovery of eye-centered representations of ongoing or intended arm movements has changed the way we think about the order of operations in the sensory to motor coordinate transformation.     

Fetal movements during late gestation in the pig: A longitudinal ultrasonographic study

Repeated ultrasonographic observation of fetal movements was used to distinguish movement patterns and to investigate the rate of occurrence and temporal organisation of these patterns (rest-activity cycles) during the last three weeks of gestation in the pig.By means of transabdominal ultrasonography with a 3.5 MHz linear array transducer, motility in ten different fetuses (one per sow) was studied. Six (median; range 4-6) 1 h recordings were made per fetus at 3-5 day intervals. Fifty-five 1 h recordings were available for analysis. The occurrence of fetal general movements (GM), isolated head (HM), forelimb movements (LM), and rotations (ROT) was analysed from video tapes. For each movement pattern, the trend in occurrence over time was assessed by multilevel analysis. The temporal association between different movement patterns was studied by calculation of the kappa value.ROT occurred very infrequently and showed no particular trend over time. GM, HM, and LM showed a significant decreasing trend towards parturition (P < 0.01). Total fetal activity (i.e., the sum of the four movement incidences) declined from an average of 25% of recording time to 9% over the last three weeks of pregnancy. Periods of fetal quiescence gradually increased with progressing gestation (P < 0.05). There was no evidence of concordant association between the periods of rest and activity of GM, HM, and LM or of improved temporal linkage between these movement patterns with time.Fetal bodily activity decreases towards parturition mainly due to prolonged periods of rest. Fetal movement patterns show rest-activity cycles, but each pattern appears to cycle independently from the other throughout late gestation. The present results of spontaneous fetal movements in the pig provide reference data for future studies of fetal activity under different zootechnical conditions or pharmacological interventions.     

A measurement system to detect small plant movements

A measurement system based on a photodiode array technique is presented, together with some results from recordings of phototropic responses of Avena sativa L. (cv. Seger I) coleoptiles.
A commercial photodiode array (RL-256G) was used, controlled by a likewise commercial control board RC-301. Electronic circuits were built to connect the control board to the interface card IO-801 of an Apple IIe microcomputer. The circuits constitute a fast temporary memory, which mainly contains two shift registers and two timers. Programs, which control the measurements, have been written and are presented.
Detailed recordings of blue light induced phototropic movements are presented: resolution and other features of the equipment are discussed.     

Extraction algorithms for cortical control of arm prosthetics

Now that recordings of multiple, individual action potentials are being made with chronic electrodes, it seems that previous work showing simple encoding of movement parameters in these spike trains can be used as a real-time control signal for prosthetic arms. Efficient extraction algorithms can compensate for the limited ensemble sample acquired with this emerging technology.     

Effects of ankle position during static stretching for the hamstrings on the decrease in passive stiffness

Static stretching is frequently performed to improve flexibility of the hamstrings, although the ankle position during hamstring stretching has not been fully investigated. We investigated the effects of ankle position during hamstring stretching on the decrease in passive stiffness. Fourteen healthy men performed static stretching for the hamstrings with the ankle dorsiflexed and plantar-flexed in a randomized order on different days. The hip was passively flexed to the maximum angle which could be tolerated without stretch pain with the knee fully extended; this was maintained for 5 min, with 1-min stretching performed in 5 sessions. Final angles and passive stiffness were measured before and after stretching. The final angle was defined as that formed by the tibia and horizontal plane when the knee was passively extended from hip and knee angles at 90° flexion to the maximum extension angle which could be tolerated without stretch pain. Passive stiffness was determined by the slope of torque–angle curve during the measurement of the final angle. The final angle significantly increased after stretching with the ankle dorsiflexed and plantar-flexed, whereas passive stiffness significantly decreased only after stretching with the ankle planter-flexed. The results suggest that passive stiffness decreases after stretching with the ankle planter-flexed but not after stretching with the ankle dorsiflexed, although the range of joint motion increases regardless of the ankle position during 5-min stretching for the hamstrings. These results indicate that static stretching should be performed with the ankle plantar-flexed when aiming to decrease passive stiffness of the hamstrings.     

A method for quantifying the anterior load–displacement behavior of the human knee in both the low and high stiffness regions

The anterior load–displacement behavior of the human knee with an intact ACL is characterized by a very low stiffness region initially and a high stiffness region that develops as anterior load is increased. Although this behavior has been well recognized for some time, a method for quantitatively describing the behavior in these two regions based on limits of motion at specific values of anterior/posterior force has not yet been developed. Thus, the purposes of this study were to describe and justify such a method for measuring the laxity and stiffness in both of these regions in the intact knee.

Unique to this study, low stiffness and high stiffness laxities were computed based on three limits of motion for seven cadaveric knees tested at flexion angles ranging from 0° to 90°. Defining the reference position of the tibia relative to the femur, one limit was the 0 N posterior limit which was determined using a specially designed load cycle to reduce uncertainty in establishing a reference position. Defining the upper bound of the load–displacement curve, a second limit was the 225 N anterior limit. A third intermediate limit was the 45 N anterior limit, which was the load that represented the transition from the low stiffness to the high stiffness region. Stiffnesses corresponding to each of the two regions were computed using regression analysis and also estimated based on the laxities. Comparison between the computed and estimated stiffnesses demonstrated that the stiffnesses in both the low and high stiffness regions can be estimated reasonably accurately based on the laxities. Therefore, the 0 N posterior limit and the two laxities are the three quantities needed to describe the load–displacement behavior of the normal knee.     

A method to record circadian plant movements, with application to Oxalis leaf rhythms

A transducer was developed to record the circadian movement of the individual leaflets in Oxalis regnellii Mig. The method can easily be adapted to measure other kinds of plant movements as well. It is based on the detection of the shadow each leaflet casts on the small side of a specially formed Perspex plate. The light is guided through the Perspex and collected by a phototransistor, which provides an electrical signal that is proportional to the light intensity falling onto it. The output signal can be made a linear function of the leaf angle. This equipment was used in experiments to study the coupling between the 3 leaflets in Oxalis . Pulses of 4 h of red light were given to one of the leaflets, the two others were shielded from the light. A phase response curve was determined for each leaflet, but there was no significant difference in the phase response between the 3 leaflets. Experiments were also made in which the 3 leaflets were separated physically by cuts along the petiole between the pulvini. In this case ultradian oscillations were observed.     

A new method for measuring 13carbon abundance in tracer experiments

Abstract. A new technique for the precise measurement of ¹³C-abundance and concentration is described. It is based on the differences in infra-red spectra between ¹²CO₂ and ¹³CO₂ and can be applied to gas mixtures or organic materials which have been oxidized to CO₂. The gas mixture is first dried and then passed through two infra-red gas analysers (IRGAs) connected in parallel. The two IRGAs are fitted with different optical filters so they differ in their relative sensitivities to ¹²CO₂ and ¹³CO₂. Once these sensitivities are known then simple algebra allows the concentrations of ¹²CO₂ and ¹³CO₂ to be calculated from the two readings. Two variants of this basic system have been tested. In both, one IRGA was a normal commercial instrument with a narrow band pass interference filter making it highly specific for ¹²CO₂; the second instrument was fitted with either a wide-band pass filter covering both the ¹²CO₂ and ¹³CO₂ absorption bands, or a narrow band pass filter specific for ¹³CO₂. These variations convey different advantages in operation. The wide-band system can be easily calibrated using a single natural abundance ¹²CO₂ standard but is only moderately precise at low abundances. It is particularly valuable for continuous monitoring of the relatively high abundance sources used in plant photosynthesis experiments. The narrow-band system gives high precision but requires a more complex standardization procedure. It is recommended for measurements on low-abundance samples resulting from tracer experiments. Here, its high sensitivity permits measurements on samples as small as 3 μmole C, thus enabling plant fractions and individual metabolites to be investigated. While the wide-band system can be manually operated under field conditions, it is necessary for highest precision to use computerized data collection and linearization. These processes are described, as are novel techniques for standardization, the preparation of small quantities of CO₂ of known abundance, and the transfer of gas samples from oxidizer to analyser. Determinations by the wide band system of % abundance in standard gas mixtures gave a standard error of ±0.03% but this increased to over ±0.1% for abundances below 20%. Corresponding values for the narrow-band system were ±0.01% over the whole abundance range an accuracy almost identical to that observed with an organic mass spectrometer. Two pulse-chase experiment with ¹³CO₂ are described in which the technique was used for studies on growth and metabolism of Lemna minor. The first demonstrated that ¹³C-accumulation within the plants matched closely the predictions from the net assimilation rate and measurements of ¹³C-abundance in the gas phase. The second revealed the rapid changes in the ¹³C-labelling of some plant components during pulse and chase phases. These examples demonstrate the potential of the method for studies in plant physiology and biochemistry. In view of its relative cheapness, ease of maintenance and operation, accuracy, and sensitivity, it is suggested that this new method may encourage a wider use of the safe stable ¹³C for biological and medical applications.     

Bead method for measuring the root surface area in conifers

A method of determining the surface area of mycorrhizous conifer roots is described. The roots are cleaned from soil particles by washing, slightly dried and covered with a monolayer of plastic beads. The surface area is estimated on the basis of the weight of adhered beads.The method has been tested against the surface area measurements by a photographic-planimetric method. The estimates of the surface area by both methods compare fairly well.An analysis of model root systems shows that the accuracy of the method for measuring the roots of 0.3mm diameter is about 5%.     

A method for determining lower extremity muscle-tendon lengths during flexion/extension movements

A study was conducted to examine the relationship between muscle-tendon lengths of 16 lower extremity muscles and the flexion angle(s) of the joint(s) they cross. Anthropometric data from six subjects were obtained. Various lower extremity joint flexion angle combinations were simulated for each subject using computer software. For each simulated lower extremity position, muscle origin and insertion locations were determined based on averaged cadaveric origin/insertion information and individual anthropometric parameters. Corresponding muscle-tendon lengths were computed and normalized to segment lengths. Regression equations were derived which allow normalized muscle-tendon lengths to be estimated from known joint flexion angles. The regression equations obtained for biarticular muscles fit the data quite well giving correlation coefficients greater than 0.92. The correlation coefficients for the equations describing normalized single joint muscle-tendon lengths range from 0.77 to 0.97. The equations were then validated by comparing predicted lengths to those reported by previous investigations. Confirming the utility of the equations, the comparisons were excellent for both uniarticular and biarticular muscles. Used in conjunction with velocity data (obtained by differentiating the length data) and electromyogram recordings, these equations enable a detailed analysis of muscle function.     

A model for altered neural network dynamics related to prehension movements in Parkinson disease

In this paper, we present a neural network model of the interactions between cortex and the basal ganglia during prehensile movements. Computational neuroscience methods are used to explore the hypothesis that the altered kinematic patterns observed in Parkinson’s disease patients performing prehensile movements is mainly due to an altered neuronal activity located in the networks of cholinergic (ACh) interneurons of the striatum. These striatal cells, under a strong influence of the dopaminergic system, significantly contribute to the neural processing within the striatum and in the cortico-basal ganglia loops. In order to test this hypothesis, a large-scale model of neural interactions in the basal ganglia has been integrated with previous models accounting for the cortical organization of goal directed reaching and grasping movements in normal and perturbed conditions. We carry out a discussion of the model hypothesis validation by providing a control engineering analysis and by comparing results of real experiments with our simulation results in conditions resembling these original experiments.     

Optimal spacer arm microenvironment for the immobilization of recombinant Protein A on heterofunctional amino-epoxy agarose supports

In this study, recombinant Staphylococcus Protein A (rSPA) was immobilized on three different amino-epoxy agaroses: traditional amino-epoxy, butanediol diglycidyl-amino and glycidyl-amino agarose (coded as AE, BDA and GA agarose, respectively), for obtaining affinity adsorbents to bind human immunoglobulin G (hIgG). The effects of the spacer arm microenvironment of the support on the rSPA immobilization were investigated. Compared with the AE agarose, the GA agarose presents ionized amino groups far from the support. Therefore, the rSPA immobilization efficiency of 92 % is slightly higher than that of 88 % on AE agarose due to the weak steric hindrance. Moreover, the BDA agarose exhibited the lowest immobilization efficiency of 58 %, attributing to the existence of hydrophobic butylidene groups on the BDA agarose. Ethanolamine was used as the blocking agent to obtain three affinity adsorbents. The hIgG-binding capacity from the human plasma was determined to be 18.7, 34.7 and 38.7 mg/mL for rSPA-BDA, rSPA-AE and rSPA-GA, respectively. Furthermore, the maximum hIgG-binding capacity was calculated by the Langmuir model of adsorption isotherm to be 25.1, 44.8 and 52.2 mg/mL for rSPA-BDA, rSPA-AE and rSPA-GA, respectively. Therefore, the GA agarose bears the optimal spacer arm microenvironment for preparing the rSPA adsorbent with high hIgG-binding capacity.     

A method for measuring microquantities of DNA

Quantitative analysis of DNA content represents a critical step when only very small amounts of nucleic acids are available. The DNA content of a small RNA-free sample can be measured in a simple and precise way using a two-dimensional approach. DNA samples are spotted on the surface of an agarose gel containing ethidium bromide (EtBr) and the ultraviolet-induced low-light fluorescence emitted by EtBr molecules intercalated into the DNA is evaluated. The high sensitivity and reproducibility of this quantitative method has been obtained using an advanced analysis system capable of distinguishing low-light fluorescent patterns, as in the case of DNA stained with EtBr, from the background. Use of an internal standard is necessary because the intensity of the signal is due to the aperture of camera diaphragm and to gel conditions. Using this two-dimensional analysis system it is possible to obtain rapid and precise quantitation of as little as 2ng of DNA.     

测定温度的转化糖方法及其在景观生态学研究中的应用

通过理论分析,室内实验和野外实测对测定温度的转化糖方法进行了研究,获得如下结论：①该方法的测定结果能有效地反映小尺度景观单元中和各种群落内部的平均温度特征。②调整样品ＰＨ值,能使转化糖方法适用于多种研究地区和多种观测时段;③该方法能够方便而经济地实现在大量不同景观部位和不同群落类型中实现同步测定,也能在难以设置仪器的条件中进行测定;④转化糖方法所测之“效应温度”直接反映了温度对反应过程中的作用程度,因此,对生态过程中与温度之间的关系的研究具有特殊意义。     

A simple method for measuring force, velocity and power output during squat jump

Our aim was to clarify the relationship between power output and the different mechanical parameters influencing it during squat jumps, and to further use this relationship in a new computation method to evaluate power output in field conditions. Based on fundamental laws of mechanics, computations were developed to express force, velocity and power generated during one squat jump. This computation method was validated on eleven physically active men performing two maximal squat jumps. During each trial, mean force, velocity and power were calculated during push-off from both force plate measurements and the proposed computations. Differences between the two methods were not significant and lower than 3% for force, velocity and power. The validity of the computation method was also highlighted by Bland and Altman analyses and linear regressions close to the identity line (P<0.001). The low coefficients of variation between two trials demonstrated the acceptable reliability of the proposed method. The proposed computations confirmed, from a biomechanical analysis, the positive relationship between power output, body mass and jump height, hitherto only shown by means of regression-based equations. Further, these computations pointed out that power also depends on push-off vertical distance. The accuracy and reliability of the proposed theoretical computations were in line with those observed when using laboratory ergometers such as force plates. Consequently, the proposed method, solely based on three simple parameters (body mass, jump height and push-off distance), allows to accurately evaluate force, velocity and power developed by lower limbs extensor muscles during squat jumps in field conditions.     

A non-invasive method for measuring inspiratory muscle fatigue during progressive isocapnic hyperventilation in man

Eleven normal adults each performed a ten minute progressive isocapnic hyperventilation (PIHV) test in which ventilatory levels were increased every two minutes. All subjects exhibited mechanical fatigue by failing to maintain the target of 80% of maximum voluntary ventilation (MVV). The mean ventilation at this level was 67.5 +/- 1.4% MVV. This fatigue was accompanied by a fall in transdiaphragmatic pressure. During the test the EMG of the sternomastoid (SM) was monitored by surface electrodes and was analyzed using fast-fourier transform. The centroid frequency (Fc) fell as ventilation increased, and correlated negatively with the inability to achieve target ventilation(r = -0.99, p less than 0.015). Five subjects performed the test while the diaphragmatic EMG was recorded from an oesophageal electrode (DIes) and from surface electrodes (DIs). The Fc of DIes fell with increasing ventilation levels (r = -0.95, p less than 0.05) and there was a correlation between the Fc changes of both DIes and the SM (r = -0.92, p less than 0.001). The Fc of DIs did not correlate with either mechanical performance or the Fc of DIes, because of contamination of surface signals by signals from expiratory muscles. It is concluded that the PIHV along with surface monitoring of EMG activity from the sternomastoid can serve as a non-invasive method for evaluating inspiratory muscle fatigue.     

A technical method using musculoskeletal model to analyse dynamic properties of muscles during human movement

An effective way to avoid invading or injuring the subjects is to use the musculoskeletal model when studying the dynamic properties of muscles in vivo. So, we put forward a joint coordinate system-based method, which mainly focuses on the coordinate's transformation of corresponding muscle attachment points, respectively, in the model and the subject in order to reproduce the movement of the subject on the model. As muscle moment arm is usually used to evaluate the dynamic properties of muscles, the moment arms in elbow flexion for each of the major muscles crossing the elbow in 50 healthy subjects (25 males and 25 females), ranging in height from 1.50 to 1.80 m (mean 1.6542 m) are calculated and compared with the measured data obtained from anatomical studies reported in the literature. The trends of the value basically coincide with each other. So, this novel method can be valid.     

A method for measuring mitochondrial mass and activity

Mitochondria, responsible for the energy-generating process essential for the cell metabolism, differ for the number, localization and activity in animal cells and tissues in relation to the energetic needs. Using fluorescent probes specific for mitochondria, Mitotracker Green (MTG) and Orange (MTO), and Confocal Laser-Scanning Microscope (CLSM), we elaborated a method to measure in vivo the mitochondrial mass and activity, in sea urchin Paracentrotus lividus eggs and embryos. The analysis of captured images, revealed a variation of mitochondrial distribution and an increase of activity after fertilization.     

A method for measuring radial differences in water content of intact tree stems by attenuation of gamma radiation

Abstract. A technique is described for the nondestructive measurement of water content variations in the stems of trees.
The density of intact tree stems in the forest was estimated using attenuation of gamma radiation. Water content was calculated after subsequent derivation of the volume fraction of solid matrix.
A radial sequence of such measurements was obtained by measuring a sequence of chords, and assuming homogeneity within concentric tori. Analysis of the source of errors showed that the system was a close approximation of an ideal, rigid-geometry, mono-energetic source/detector system, with basic precision dependent on the quantity of gamma radiation measured. Correlation coefficients between the gamma-attenuation technique and subsequent gravimetric estimates of water content for two field experiments reported here were 0.882 and 0.938.
The technique was shown to be capable of describing the radial and diurnal variation in water content at two heights in the stem of a 20-year-old tree of Pinus contorta .