Drag-Based ‘Hovering’ in Ducks: The Hydrodynamics and Energetic Cost of Bottom Feeding

Diving ducks use their webbed feet to provide the propulsive force that moves them underwater. To hold position near the bottom while feeding, ducks paddle constantly to resist the buoyant force of the body. Using video sequences from two orthogonal cameras we reconstructed the 3-dimensional motion of the feet through water and estimated the forces involved with a quasi-steady blade-element model. We found that during station holding, near the bottom, ducks use drag based propulsion with the webbed area of the foot moving perpendicular to the trajectory of the foot. The body was pitched at 76±3.47° below the horizon and the propulsive force was directed 26±1.9° ventral to the body so that 98% of the propulsive force in the sagittal plane of the duck worked to oppose buoyancy. The mechanical work done by moving both feet through a paddling cycle was 1.1±0.2 J which was equivalent to an energy expenditure of 3.7±0.5 W to hold position while feeding at 1.5 m depth. We conclude that in shallow water the high energetic cost of feeding in ducks is due to the need to paddle constantly against buoyancy even after reaching the bottom. The mechanical energy spent on holding position near the bottom, while feeding, is approximately 2 fold higher than previous estimates that were made for similar bottom depths but based on the presumed motion of the body instead of motion of the feet.     

THE EFFECTS OF THREE DIFFERENT REAR KNEE ANGLES ON KINEMATICS IN THE SPRINT START

The purpose of this study was to investigate the rear knee angle range in the set position that allows sprinters to reach greater propulsion on the rear block during the sprint start. Eleven university-track team sprinters performed the sprint start using three rear knee angle conditions: 90°, 115° and 135°. A motion capture system consisting of 8 digital cameras (250 Hz) was used to record kinematic parameters at the starting block phase and the acceleration phase. The following variables were considered: horizontal velocity of the centre of mass (COM), COM height, block time, pushing time on the rear block, percentage of pushing time on the rear block, force impulse, push-off angle and length of the first two strides. The main results show that first, horizontal block velocity is significantly greater at 90° vs 115° and 135° rear knee angle (p<0.05 and p<0.001 respectively) at block clearance and the first two strides; second, during the pushing phase, the percentage of pushing time of the rear leg is significantly greater at 90° vs 135° rear knee angle (p<0.01). No significant difference was found for block time among the conditions. These results indicate that block velocity is the main kinematic parameter affected by rear knee angle during the starting block phase and acceleration phase. Furthermore, the 90° rear knee angle allows for a better push-off of the rear leg than larger angles at the set position. The findings of this study provide some direction and useful practical advice in defining an efficient rear leg biomechanical configuration at the set position.     

Torsion and Antero-Posterior Bending in the In Vivo Human Tibia Loading Regimes during Walking and Running

Bending, in addition to compression, is recognized to be a common loading pattern in long bones in animals. However, due to the technical difficulty of measuring bone deformation in humans, our current understanding of bone loading patterns in humans is very limited. In the present study, we hypothesized that bending and torsion are important loading regimes in the human tibia. In vivo tibia segment deformation in humans was assessed during walking and running utilizing a novel optical approach. Results suggest that the proximal tibia primarily bends to the posterior (bending angle: 0.15°–1.30°) and medial aspect (bending angle: 0.38°–0.90°) and that it twists externally (torsion angle: 0.67°–1.66°) in relation to the distal tibia during the stance phase of overground walking at a speed between 2.5 and 6.1 km/h. Peak posterior bending and peak torsion occurred during the first and second half of stance phase, respectively. The peak-to-peak antero-posterior (AP) bending angles increased linearly with vertical ground reaction force and speed. Similarly, peak-to-peak torsion angles increased with the vertical free moment in four of the five test subjects and with the speed in three of the test subjects. There was no correlation between peak-to-peak medio-lateral (ML) bending angles and ground reaction force or speed. On the treadmill, peak-to-peak AP bending angles increased with walking and running speed, but peak-to-peak torsion angles and peak-to-peak ML bending angles remained constant during walking. Peak-to-peak AP bending angle during treadmill running was speed-dependent and larger than that observed during walking. In contrast, peak-to-peak tibia torsion angle was smaller during treadmill running than during walking. To conclude, bending and torsion of substantial magnitude were observed in the human tibia during walking and running. A systematic distribution of peak amplitude was found during the first and second parts of the stance phase.     

Influence of Passive Muscle Tension on Electromechanical Delay in Humans

Background

Electromechanical delay is the time lag between onsets of muscle activation and muscle force production and reflects both electro-chemical processes and mechanical processes. The aims of the present study were two-fold: to experimentally determine the slack length of each head of the biceps brachii using elastography and to determine the influence of the length of biceps brachii on electromechanical delay and its electro-chemical/mechanical processes using very high frame rate ultrasound.

Methods/Results

First, 12 participants performed two passive stretches to evaluate the change in passive tension for each head of the biceps brachii. Then, they underwent two electrically evoked contractions from 120 to 20° of elbow flexion (0°: full extension), with the echographic probe maintained over the muscle belly and the myotendinous junction of biceps brachii. The slack length was found to occur at 95.5 ± 6.3° and 95.3 ± 8.2° of the elbow joint angle for the long and short heads of the biceps brachii, respectively. The electromechanical delay was significantly longer at 120° (16.9 ± 3.1 ms; p<0.001), 110° (15.0 ± 3.1 ms; p<0.001) and 100° (12.7 ± 2.5 ms; p = 0.01) of elbow joint angle compared to 90° (11.1 ± 1.7 ms). However, the delay between the onset of electrical stimulation and the onset of both muscle fascicles (3.9 ± 0.2 ms) and myotendinous junction (3.7 ± 0.3 ms) motion was not significantly affected by the joint angle (p>0.95).

Conclusion

In contrast to previous observations on gastrocnemius medialis, the onset of muscle motion and the onset of myotendinous junction motion occurred simultaneously regardless of the length of the biceps brachii. That suggests that the between-muscles differences reported in the literature cannot be explained by different muscle passive tension but instead may be attributable to muscle architectural differences.     

Optic Disc - Fovea Angle: The Beijing Eye Study 2011

Purpose

To determine the optic disc-fovea angle (defined as angle between the horizontal and the line between the optic disc center and the fovea) and to assess its relationships with ocular and systemic parameters.

Methods

The population-based cross-sectional Beijing Eye Study 2011 included 3468 individuals. A detailed ophthalmic examination was carried out. Using fundus photographs, we measured the disc-fovea angle.

Results

Readable fundus photographs were available for 6043 eyes of 3052 (88.0%) individuals with a mean age of 63.6±9.3 years (range: 50–91 years) and a mean axial length of 23.2±1.0 mm (range: 18.96–28.87 mm). Mean disc-fovea angle was 7.76 ± 3.63° (median: 7.65°; range: -6.3° to 28.9°). The mean inter-eye difference was 4.01 ± 2.94° (median: 3.49°; range: 0.00–22.3°). In multivariate analysis, larger disc-fovea angle was associated (regression coefficient r²: 0.08) with older age (P = 0.009; standardized regression coefficient beta: 0.05), thinner RNFL in the nasal superior sector (P<0.001; beta: -0.17), superior sector (P<0.001; beta: -0.10) and temporal superior sector (P<0.001; beta: -0.11) and thicker RNFL in the inferior sector (P<001; beta: 0.13), nasal inferior sector (P<001; beta: 0.13) and nasal sector (P = 0.007; beta: 0.06), higher prevalence of retinal vein occlusion (P = 0.02; beta: 0.04), and with larger cylindrical refractive error (P = 0.04; beta: 0.04).

Conclusions

The optic disc-fovea angle markedly influences the regional distribution of the RNFL thickness pattern. The disc-fovea angle may routinely be taken into account in the morphological glaucoma diagnosis and in the assessment of structure-function relationship in optic nerve diseases. Future studies may address potential associations between a larger disc-fovea angle and retinal vein occlusions and between the disc-fovea angle and the neuroretinal rim shape.     

Factors of Force Potentiation Induced by Stretch-Shortening Cycle in Plantarflexors

Muscle force is potentiated by countermovement; this phenomenon is called stretch-shortening cycle (SSC) effect. In this study, we examined the factors strongly related to SSC effect in vivo, focusing on tendon elongation, preactivation, and residual force enhancement. Twelve healthy men participated in this study. Ankle joint angle was passively moved by a dynamometer, with a range of motion from 15° dorsiflexion (DF) to 15° plantarflexion (PF). Muscle contraction was evoked by electrical stimulation, with stimulation timing adjusted to elicit three types of contraction: (1) concentric contraction without preliminary contraction (CON), (2) concentric contraction after preliminary eccentric contraction (ECC), and (3) concentric contraction after preliminary isometric contraction (ISO). Joint torque was recorded at DF5°, PF0°, and PF5°, respectively. SSC effect was calculated as the ratio of joint torque obtained in ECC or ISO with respect to that obtained in CON at the aforementioned three joint angles. SSC effect was prominent in the first half of movement in both ECC (DF5°, 329.3 ± 101.2%; PF0°, 159.2 ± 29.4%; PF5°, 125.5 ± 20.8%) and ISO (DF5°, 276.4 ± 87.0%; PF0°, 134.5 ± 24.5%; PF5°, 106.8 ± 18.0%) conditions. SSC effect was significantly larger in ECC than in ISO at all joint angles (P < 0.001). Even without preliminary eccentric contraction (i.e., ISO condition), SSC effect was clearly large, indicating that a significant part of SSC effect is derived from preactivation. However, the active lengthening-induced force potentiation mechanism (residual force enhancement) also contributes to SSC effect.     

KINEMATICS THAT DIFFERENTIATE THE BEACH FLAGS START BETWEEN ELITE AND NON-ELITE SPRINTERS

This study differentiated the kinematics of the beach flags sprint start between five elite (three males, two females; age = 21.2 ± 2.6 years; height = 1.71 ± 0.04 m; mass = 66.2 ± 5.9 kg) and five non-elite (three males, two females; age = 20.4 ± 1.7 years; height = 1.69 ± 0.08 meters [m]; mass = 61.6 ± 5.7 kilograms) sprinters. A high-speed camera filmed the start. Timing gates recorded the 0-2, 0-5, and 0-20 m intervals. Data included body position during the start and at take-off; start time; first step length; and sprint times. A Mann-Whitney U-test determined significant (p < 0.05) between-group differences; effect sizes (ES) were also calculated. Elite sprinters had a greater take-off trajectory angle (p = 0.01; ES = 2.57), and were faster over the 0-2 (p = 0.02; ES = 1.77), 0-5 (p = 0.05; ES = 1.20), and 0-20 m (p = 0.02; ES = 1.83) intervals. Large effects were found for: greater take-off swing leg hip flexion (ES = 1.13) and trunk lean (ES = 1.37); longer duration start time (ES = 1.33); and longer first step length (ES = 1.23) in elite sprinters. A longer start time assists with force generation, which in conjunction with increased hip flexion, could translate to a longer first step. Increased trunk lean shifts the take-off trajectory angle towards the horizontal. A greater trajectory angle at start take-off, which could be advantageous for force production during sprint performance, is likely necessary for beach flags.     

Passive Flexion and Femoral Vein Flow: A Study Using a Motorized Foot Mover

The effect of rhythmic passive flexion of the foot on femoral vein blood volume flow rate has been investigated in 11 patients undergoing surgery for varicose veins. With rates of flexion varying from 24 to 50 per minute and with amplitudes varying from 20° to 50° it has been shown that the peak femoral vein flow can be increased to twice its normal value and that its pulsatility can be increased elevenfold. These increases are proportional to both the rate and the amplitude of the flexion, the maximum occurring, theoretically, when the foot is flexed ±28° about a line perpendicular to the leg.The investigation has further shown that the effects of sustained passive flexion are maintained, without appreciable dimunition, for 30 minutes and that the maximum increases are produced in those patients who have the lowest resting flows. It is suggested that per-operative passive flexion of the feet may be a good prophylactic against postoperative deep vein thrombosis.     

Modulation of Force below 1 Hz: Age-Associated Differences and the Effect of Magnified Visual Feedback

Oscillations in force output change in specific frequency bins and have important implications for understanding aging and pathological motor control. Although previous studies have demonstrated that oscillations from 0–1 Hz can be influenced by aging and visuomotor processing, these studies have averaged power within this bandwidth and not examined power in specific frequencies below 1 Hz. The purpose was to determine whether a differential modulation of force below 1 Hz contributes to changes in force control related to manipulation of visual feedback and aging. Ten young adults (25±4 yrs, 5 men) and ten older adults (71±5 yrs, 4 men) were instructed to accurately match a target force at 2% of their maximal isometric force for 35 s with abduction of the index finger. Visual feedback was manipulated by changing the visual angle (0.05°, 0.5°, 1.5°) or removing it after 15 s. Modulation of force below 1 Hz was quantified by examining the absolute and normalized power in seven frequency bins. Removal of visual feedback increased normalized power from 0–0.33 Hz and decreased normalized power from 0.66–1.0 Hz. In contrast, magnification of visual feedback (visual angles of 0.5° and 1.5°) decreased normalized power from 0–0.16 Hz and increased normalized power from 0.66–1.0 Hz. Older adults demonstrated a greater increase in the variability of force with magnification of visual feedback compared with young adults (P = 0.05). Furthermore, older adults exhibited differential force modulation of frequencies below 1 Hz compared with young adults (P<0.05). Specifically, older adults exhibited greater normalized power from 0–0.16 Hz and lesser normalized power from 0.66–0.83 Hz. The changes in force modulation predicted the changes in the variability of force with magnification of visual feedback (R² = 0.80). Our findings indicate that force oscillations below 1 Hz are associated with force control and are modified by aging and visual feedback.     

Defining Optimal Head-Tilt Position of Resuscitation in Neonates and Young Infants Using Magnetic Resonance Imaging Data

Head-tilt maneuver assists with achieving airway patency during resuscitation. However, the relationship between angle of head-tilt and airway patency has not been defined. Our objective was to define an optimal head-tilt position for airway patency in neonates (age: 0–28 days) and young infants (age: 29 days–4 months). We performed a retrospective study of head and neck magnetic resonance imaging (MRI) of neonates and infants to define the angle of head-tilt for airway patency. We excluded those with an artificial airway or an airway malformation. We defined head-tilt angle a priori as the angle between occipito-ophisthion line and ophisthion-C7 spinous process line on the sagittal MR images. We evaluated medical records for Hypoxic Ischemic Encephalopathy (HIE) and exposure to sedation during MRI. We analyzed MRI of head and neck regions of 63 children (53 neonates and 10 young infants). Of these 63 children, 17 had evidence of airway obstruction and 46 had a patent airway on MRI. Also, 16/63 had underlying HIE and 47/63 newborn infants had exposure to sedative medications during MRI. In spontaneously breathing and neurologically depressed newborn infants, the head-tilt angle (median ± SD) associated with patent airway (125.3° ± 11.9°) was significantly different from that of blocked airway (108.2° ± 17.1°) (Mann Whitney U-test, p = 0.0045). The logistic regression analysis showed that the proportion of patent airways progressively increased with an increasing head-tilt angle, with > 95% probability of a patent airway at head-tilt angle 144–150°.     

Does a linear position transducer placed on a stick and belt provide sufficient validity and reliability of countermovement jump performance outcomes?

Manufacturers recommend that linear position transducers (LPTs) should be placed on the side of a barbell (or wooden dowel) to measure countermovement jump (CMJ) height, but the validity and reliability of this placement have not been compared to other attachment sites. Since this recommended attachment site is far from the centre of mass, a belt attachment where the LPT is placed between the feet may increase the validity and reliability of CMJ data. Thirty-six physical education students participated in the study (24.6 ± 4.3 years; 177.0 ± 7.7 cm; 77.2 ± 9.0 kg). Parameters from the two LPT attachments (barbell and belt) were simultaneously validated to force plate data, where the nature of bias was analysed (systematic vs random). The within-session and between-session reliability of both attachment sites were compared to force plate data using a test-retest protocol of two sets of 5 CMJs separated by 7 days. The LPT provided highly reliable and valid measures of peak force, mean force, mean power, and jump height, where the bias was mostly systematic (r² > 0.7; ICC > 0.9). Peak velocity, mean velocity, and peak power were in very good agreement with the force plate and were highly reliable (r² > 0.5; ICC > 0.7). Therefore, both attachment sites produced similar results with a systematic bias compared to force plate data. Thus, both attachment sites seem to be valid for assessing CMJs when the measuring tool and site remain consistent across measurements. However, if LPT data are to be compared to force plate data, recalculation equations should be used.     

Feeding Kinematics,Suction, and Hydraulic Jetting Performance of Harbor Seals (Phoca vitulina)

The feeding kinematics, suction and hydraulic jetting capabilities of captive harbor seals (Phoca vitulina) were characterized during controlled feeding trials. Feeding trials were conducted using a feeding apparatus that allowed a choice between biting and suction, but also presented food that could be ingested only by suction. Subambient pressure exerted during suction feeding behaviors was directly measured using pressure transducers. The mean feeding cycle duration for suction-feeding events was significantly shorter (0.15±0.09 s; P<0.01) than biting feeding events (0.18±0.08 s). Subjects feeding in-water used both a suction and a biting feeding mode. Suction was the favored feeding mode (84% of all feeding events) compared to biting, but biting comprised 16% of feeding events. In addition, seals occasionally alternated suction with hydraulic jetting, or used hydraulic jetting independently, to remove fish from the apparatus. Suction and biting feeding modes were kinematically distinct regardless of feeding location (in-water vs. on-land). Suction was characterized by a significantly smaller gape (1.3±0.23 cm; P<0.001) and gape angle (12.9±2.02°), pursing of the rostral lips to form a circular aperture, and pursing of the lateral lips to occlude lateral gape. Biting was characterized by a large gape (3.63±0.21 cm) and gape angle (28.8±1.80°; P<0.001) and lip curling to expose teeth. The maximum subambient pressure recorded was 48.8 kPa. In addition, harbor seals were able to jet water at food items using suprambient pressure, also known as hydraulic jetting. The maximum hydraulic jetting force recorded was 53.9 kPa. Suction and hydraulic jetting where employed 90.5% and 9.5%, respectively, during underwater feeding events. Harbor seals displayed a wide repertoire of behaviorally flexible feeding strategies to ingest fish from the feeding apparatus. Such flexibility of feeding strategies and biomechanics likely forms the basis of their opportunistic, generalized feeding ecology and concomitant breadth of diet.     

Experimental Induction of Pulmonary Fibrosis in Horses with the Gammaherpesvirus Equine Herpesvirus 5

Gammaherpesviruses (γHV) are implicated in the pathogenesis of pulmonary fibrosis in humans and murine models of lung fibrosis, however there is little direct experimental evidence that such viruses induce lung fibrosis in the natural host. The equine γHV EHV 5 is associated with equine multinodular pulmonary fibrosis (EMPF), a progressive fibrosing lung disease in its natural host, the horse. Experimental reproduction of EMPF has not been attempted to date. We hypothesized that inoculation of EHV 5 isolated from cases of EMPF into the lungs of clinically normal horses would induce lung fibrosis similar to EMPF. Neutralizing antibody titers were measured in the horses before and after inoculation with EHV 5. PCR and virus isolation was used to detect EHV 5 in antemortem blood and BAL samples, and in tissues collected postmortem. Nodular pulmonary fibrosis and induction of myofibroblasts occurred in EHV 5 inoculated horses. Mean lung collagen in EHV 5 inoculated horses (80 µg/mg) was significantly increased compared to control horses (26 µg/mg) (p < 0.5), as was interstitial collagen (32.6% ± 1.2% vs 23% ± 1.4%) (mean ± SEM; p < 0.001). Virus was difficult to detect in infected horses throughout the experiment, although EHV 5 antigen was detected in the lung by immunohistochemistry. We conclude that the γHV EHV 5 can induce lung fibrosis in the horse, and hypothesize that induction of fibrosis occurs while the virus is latent within the lung. This is the first example of a γHV inducing lung fibrosis in the natural host.     

Force platform for rats measures fore and hind forces concurrently

Animal models are commonly used to test the efficacy of impact loading regimens on bone strength. We designed an inexpensive force platform to concurrently measure the separate peak vertical impact forces produced by the fore and hindfeet of immature F-344 rats when dropped onto the platform. The force platform consisted of three load cells placed in a triangular pattern under a flat plate. Rats were dropped from heights of 30, 45 and 60 cm onto the platform so that they landed on all four feet concurrently. The peak vertical impact forces produced by the feet of the rats were measured using a sampling frequency of 100 kHz. The location of each foot at landing relative to the load cells, and the force received by each load cell were combined in a series of static equations to solve for the vertical impact forces produced by the fore and hindfeet. The forces produced by feet when rats stood on the single platform were similarly determined. The forces exerted separately by the fore and hindfeet of young rats when landing on the plate as a ratio to standing forces were then calculated. Rats when standing bore more weight on their hindfeet but landed with more weight on their forefeet, which provides rationale for the greater response to landing forces of bones in the forelimbs than those in the hindlimbs. This system provided a useful method to simultaneously measure peak vertical impact forces in fore and hindfeet in rats.     

In Vivo Open-Bore MRI Reveals Region- and Sub-Arc-Specific Lengthening of the Unloaded Human Posterior Cruciate Ligament

Open-bore MRI scanners allow joint soft tissue to be imaged over a large, uninterrupted range of flexion. Using an open-bore scanner, 3D para-sagittal images of the posterior cruciate ligament (PCL) were collected from seven healthy subjects in unloaded, recumbent knee extension and flexion. PCL length was measured from one 2D MRI slice partition per flexion angle, per subject. The anterior surface of the PCL lengthened significantly between extension and flexion (p<0.001). Conversely, the posterior surface did not. Changes were not due to the PCL moving relative to the 2D slice partition; measurements made from 3D reconstructions, which compensated for PCL movement, did not differ significantly from measurements made from 2D slice partitions. In a second experiment, videos of knee flexion were made by imaging two subjects at several flexion angles. Videos allowed soft tissue tracking; examples are included. In a third experiment, unloaded knees of seven healthy, recumbent subjects were imaged at extension and at 40°, 70°, 90°, 100°, 110° and 120° flexion. The distance between PCL attachments increased between extension and 100°, and then decreased (p<0.001). The anterior surface of the PCL lengthened over the flexion angles measured (p<0.01). The posterior surface of the PCL lengthened between extension and 40° and then shortened (p<0.001). Both attachment separation and anterior surface length increased dramatically between extension and 40°, but varied less afterwards. Results indicate that PCL dynamics differ between terminal extension and active function sub-arcs. Also, attachment separation cannot predict the lengthening of all parts of the PCL, nor can lengthening of one part of the PCL predict the lengthening of another part. A potential connection between lengthening and loading is discussed. We conclude that low-field MRI can assess ligament lengthening during flexion, and that the dynamics of the PCL for any given region and sub-arc should be measured directly.     

Stereoscopic Analysis of Optic Nerve Head Parameters in Primary Open Angle Glaucoma: The Glaucoma Stereo Analysis Study

PurposeThe Glaucoma Stereo Analysis Study (GSAS), a cross sectional multicenter collaborative study, used a stereo fundus camera to assess various morphological parameters of the optic nerve head (ONH) in glaucoma patients and investigated the relationships between these parameters and patient characteristics.ResultsPatient characteristics included refractive error of −3.38±3.75 diopters, intraocular pressure (IOP) of 13.6±2.6 mmHg, and visual field mean deviation (MD) of −4.71±3.26 dB. Representative ONH parameters included a horizontal disc width of 1.66±0.28 mm, vertical disc width of 1.86±0.23 mm, disc area of 2.42±0.63 mm², cup area of 1.45±0.57 mm², and cup volume of 0.31±0.22 mm³. Correlation analysis revealed significant negative associations between vertical cup-to-disc ratio (0.82±0.08) and MD (r = −0.40, P<0.01) and between disc tilt angle (10.5±12.5 degrees) and refractive error (r = −0.36, P<0.01). Seventy-five percent of the eyes had a positive value for rim decentering (0.30±0.42), indicating that rim thinning manifested more often as an inferior lesion than a superior lesion.ConclusionWe used stereoscopic analysis to establish a database of ONH parameters, which may facilitate future studies of glaucomatous changes in ONH morphology.     

The Principal Components of Adult Female Insole Shape Align Closely with Two of Its Classic Indicators

The plantar surface of the human foot transmits the weight and dynamic force of the owner’s lower limbs to the ground and the reaction forces back to the musculoskeletal system. Its anatomical variation is intensely studied in such fields as sports medicine and orthopedic dysmorphology. Yet, strangely, the shape of the insole that accommodates this surface and elastically buffers these forces is neither an aspect of the conventional anthropometrics of feet nor an informative label on the packet that markets supplementary insoles. In this paper we pursue an earlier suggestion that insole form in vertical view be quantified in terms of the shape of the foot not at the plane of support (the “footprint”) but some two millimeters above that level. Using such sections extracted from laser scans of 158 feet of adult women from the University of Zagreb, in conjunction with an appropriate modification of today’s standard geometric morphometrics (GMM), we find that the sectioned form can be described by its size together with two meaningful relative warps of shape. The pattern of this shape variation is not novel. It is closely aligned with two of the standard footprint measurements, the Chippaux-Šmiřák arch index and the Clarke arch angle, whose geometrical foci (the former in the ball of the foot, the latter in the arch) it apparently combines. Thus a strong contemporary analysis complements but does not supplant the simpler anthropometric analyses of half a century ago, with implications for applied anthropology.     

Juxtaposition of the changes in intracellular calcium and force during staircase potentiation at 30 and 37°C

Ca²⁺ entry during the action potential stimulates muscle contraction. During repetitive low frequency stimulation, skeletal muscle undergoes staircase potentiation (SP), a progressive increase in the peak twitch force induced by each successive stimulus. Multiple mechanisms, including myosin regulatory light chain phosphorylation, likely contribute to SP, a temperature-dependent process. Here, we used the Ca²⁺-sensitive fluorescence indicators acetoxymethyl (AM)-furaptra and AM-fura-2 to examine the intracellular Ca²⁺ transient (ICT) and the baseline Ca²⁺ level at the onset of each ICT during SP at 30 and 37°C in mouse lumbrical muscle. The stimulation protocol, 8 Hz for 8 s, resulted in a 27 ± 3% increase in twitch force at 37°C and a 7 ± 2% decrease in twitch force at 30°C (P < 0.05). Regardless of temperature, the peak rate of force production (+df/dt) was higher in all twitches relative to the first twitch (P < 0.05). Consistent with the differential effects of stimulation on twitch force at the two temperatures, raw ICT amplitude decreased during repetitive stimulation at 30°C (P < 0.05) but not at 37°C. Cytosolic Ca²⁺ accumulated during SP such that baseline Ca²⁺ at the onset of ICTs occurring late in the train was higher (P < 0.05) than that of those occurring early in the train. ICT duration increased progressively at both temperatures. This effect was not entirely proportional to the changes in twitch duration, as twitch duration characteristically decreased before increasing late in the protocol. This is the first study identifying a changing ICT as an important, and temperature-sensitive, modulator of muscle force during repetitive stimulation. Moreover, we extend previous observations by demonstrating that contraction-induced increases in baseline Ca²⁺ coincide with greater +df/dt but not necessarily with higher twitch force.     

Predictive Thermal Inactivation Model for Effects of Temperature, Sodium Lactate, NaCl, and Sodium Pyrophosphate on Salmonella Serotypes in Ground Beef

Analyses of survival data of a mixture of Salmonella spp. at fixed temperatures between 55°C (131°F) and 71.1°C (160°F) in ground beef matrices containing concentrations of salt between 0 and 4.5%, concentrations of sodium pyrophosphate (SPP) between 0 and 0.5%, and concentrations of sodium lactate (NaL) between 0 and 4.5% indicated that heat resistance of Salmonella increases with increasing levels of SPP and salt, except that, for salt, for larger lethalities close to 6.5, the effect of salt was evident only at low temperatures (<64°C). NaL did not seem to affect the heat resistance of Salmonella as much as the effects induced by the other variables studied. An omnibus model for predicting the lethality for given times and temperatures for ground beef matrices within the range studied was developed that reflects the convex survival curves that were observed. However, the standard errors of the predicted lethalities from this models are large, so consequently, a model, specific for predicting the times needed to obtained a lethality of 6.5 log₁₀, was developed, using estimated results of times derived from the individual survival curves. For the latter model, the coefficient of variation (CV) of predicted times range from about 6 to 25%. For example, at 60°C, when increasing the concentration of salt from 0 to 4.5%, and assuming that the concentration of SPP is 0%, the time to reach a 6.5-log₁₀ relative reduction is predicted to increase from 20 min (CV = 11%) to 48 min (CV = 15%), a 2.4 factor (CV = 19%). At 71.1°C (160°F) the model predicts that more than 0.5 min is needed to achieve a 6.5-log₁₀ relative reduction.