Aerobic and anaerobic energy during a 2-km race simulation in female rowers

The maximal aerobic power (VO2max) and maximal anaerobic capacity (AODmax) of 16 female rowers were compared to their peak aerobic power (VO2peak) and peak anaerobic capacity (AODpeak, respectively) during a simulated 2-km race on a rowing ergometer. Each subject completed three tests, which included a 2-min maximal effort bout to determine the AODmax, a series of four, 4-min submaximal stages with subsequent progression to VO2max and a simulated 2-km race. Aerobic power was determined using an open-circuit system, and the accumulated oxygen deficit method was used to calculate anaerobic capacities from recorded mechanical power on a rowing ergometer. The average VO2peak (3.58 l min(-1)), which usually occurred during the last minute of the race simulation, was not significantly different (P > 0.05) from the VO2max (3.55 l min(-1)). In addition, the rowers' AODmax (3.40 l) was not significantly different (P > 0.05) from their AODpeak (3.50 1). The average time taken for the rowers to complete the 2-km race simulation was 7.5 min, and the anaerobic system (AODpeak) accounted for 12% of the rowers' total energy production during the race.     

The optimum finger spacing in human swimming

Competitive swimmers spread fingers during the propulsive stroke. Due to the inherent inefficiency of human swimming, the question is: does this strategy enhance performance or is it just a more comfortable hand posture? Here we show, through computational fluid dynamics (CFD) of a 3D model of the hand, that an optimal finger spacing (12°, roughly corresponding to the resting hand posture) increases the drag coefficient (+8.8%), which is ‘functionally equivalent’ to a greater hand palm area, thus a lower stroke frequency can produce the same thrust, with benefits to muscle, hydraulic and propulsive efficiencies. CFD, through flow visualization, provides an explanation for the increased drag associated with the optimum finger spacing.     

Validated biomechanical model for efficiency and speed of rowing

The speed of a competitive rowing crew depends on the number of crew members, their body mass, sex and the type of rowing—sweep rowing or sculling. The time-averaged speed is proportional to the rower?s body mass to the 1/36^th power, to the number of crew members to the1/9^th power and to the physiological efficiency (accounted for by the rower?s sex) to the 1/3^rd power. The quality of the rowing shell and propulsion system is captured by one dimensionless parameter that takes the mechanical efficiency, the shape and drag coefficient of the shell and the Froude propulsion efficiency into account. We derive the biomechanical equation for the speed of rowing by two independent methods and further validate it by successfully predicting race times. We derive the theoretical upper limit of the Froude propulsion efficiency for low viscous flows. This upper limit is shown to be a function solely of the velocity ratio of blade to boat speed (i.e., it is completely independent of the blade shape), a result that may also be of interest for other repetitive propulsion systems.     

Evolution of water surface locomotion by spiders: a comparative approach

Spiders vary enormously in their behaviour when placed on the surface of fresh water. In some families (e.g. Theridiidae), the spider typically becomes wet and either sinks or is incapacitated by adhesion to the water. In other families (e.g. Agelenidae), the spider remains dry and moves across the water using its legs in much the same way it does on land, with the members of each leg pair moving in alternation with each other. In at least one family (Pisauridae), the spider remains dry and moves across the water using a rowing or galloping gait in which the members of each propulsive pair of legs move in synchrony with each other. While some degree of hydrophobicity is widespread among spiders, the ability to move on water by rowing occurs rarely; it is common only among families in the Lycosoidea, which is a subset of the GST (Grate-Shaped Tapetum) clade. Our mapping of water surface locomotion behaviour of representatives of 42 families of spiders onto cladograms of the Araneae suggests that the ability to row evolved at the base of the clade that includes Trechaleidae, Pisauridae and Lycosidae and evolved independently in some members of the family Ctenidae. Rowing behaviour is seen in all subfamilies of Lycosidae but, unlike in the Pisauridae in which all animals tested showed the rowing behaviour, many individuals that could row did not do so all of the time. Among the 166 non-lycosoid species we have tested, we have found one species of Araneidae and two species of Salticidae that can row. It is evident from our data that, in most spiders, phylogeny trumps recent selection (based on habitat preference) in determining the spiders' locomotor behaviour on the water surface.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 63–78.     

Predicting muscle forces in gait from EMG signals and musculotendon kinematics

An EMG-driven muscle model for determining muscle force-time histories during gait is presented. The model, based on Hill's equation (1938), incorporates morphological data and accounts for changes in musculotendon length, velocity, and the level of muscle excitation for both concentric and eccentric contractions. Musculotendon kinematics were calculated using three-dimensional cinematography with a model of the musculoskeletal system. Muscle force-length-EMG relations were established from slow isokinetic calibrations. Walking muscle force-time histories were determined for two subjects. Joint moments calculated from the predicted muscle forces were compared with moments calculated using a linked segment, inverse dynamics approach. Moment curve correlations ranged from r = 0.72 to R = 0.97 and the root mean square (RMS) differences were from 10 to 20 Nm. Expressed as a relative RMS, the moment differences ranged from a low of 23% at the ankle to a high of 72% at the hip. No single reason for the differences between the two moment curves could be identified. Possible explanations discussed include the linear EMG-to-force assumption and how well the EMG-to-force calibration represented excitation for the whole muscle during gait, assumptions incorporated in the muscle modeling procedure, and errors inherent in validating joint moments predicted from the model to moments calculated using linked segment, inverse dynamics. The closeness with which the joint moment curves matched in the present study supports using the modeling approach proposed to determine muscle forces in gait.     

Ontogenetic changes in the bell morphology and kinematics and swimming behavior of rowing medusae: the special case of the limnomedusa Liriope tetraphylla

Swimming animals may experience significant changes in the Reynolds number (Re) of their surrounding fluid flows throughout ontogeny. Many medusae experience Re environments with significant viscous forces as small juveniles but inertially dominated Re environments as adults. These different environments may affect their propulsive strategies. In particular, rowing, a propulsive strategy with ecological advantages for large adults, may be constrained by viscosity for small juvenile medusae. We examined changes in the bell morphology and swimming kinematics of the limnomedusa Liriope tetraphylla at different stages of development. L. tetraphylla maintained an oblate bell (fineness ratio ≈ 0.5-0.6), large velar aperture ratio (R(v) ≈ 0.5-0.8), and rapid bell kinematics throughout development. These traits enabled it to use rowing propulsion at all stages except the very smallest sizes observed (diameter = 0.14 cm). During the juvenile stage, very rapid bell kinematics served to increase Re sufficiently for rowing propulsion. Other taxa that use rowing propulsion as adults, such as leptomedusae and scyphomedusae, typically utilize different propulsive strategies as small juveniles to function in low Re environments. We compared the performance values of the different propulsive modes observed among juvenile medusae.     

Measurement of propulsive power and evaluation of propulsive performance from the wake of a self-propelled vehicle

Propulsive efficiency is a key indicator of propulsive performance, but it can be difficult to measure when the propulsion system is integrated into the vehicle body because the average rate of useful work done propelling the vehicle (Wu) and/or the average mechanical power expended propelling the vehicle (Pmech) is not known directly. A general approach would be to determine either or both of (Wu) and (Pmech) from the vehicle wake. The present discussion demonstrates that only (Pmech) can be determined from the flow crossing a plane a fixed (average) distance downstream of the vehicle. A method for measuring (Pmech) is presented using the observation that the power required to tow a permeable obstruction behind the vehicle depends on (Pmech). Several methods for evaluating propulsive performance using [Formula: see text] are proposed, including the definition of an equivalent jet velocity and corresponding Froude efficiency if the time-averaged mass flow rate through the propulsion system is known. If only (Pmech) is known, the recommended measure of propulsive performance is a power coefficient defined analogous to a drag coefficient.     

Numerical Study of Propulsion Mechanism for Oscillating Rigid and Flexible Tuna-Tails

Numerical study on the unsteady hydrodynamic characteristics of oscillating rigid and flexible tuna-tails in viscous flow-field is performed.Investigations are conducted using Reynolds-Averaged Navier-Stokes (RANS) equations with a moving adaptive mesh.The effect of swimming speed,flapping amplitude,frequency and flexure amplitude on the propulsion performance of the rigid and flexible tuna-tails are investigated.Computational results reveal that a pair of leading edge vortices develop along the tail surface as it undergoes an oscillating motion.The propulsive efficiency has a strong correlation with various locomotive parameters.Peak propulsive efficiency can be obtained by adjusting these parameters.Particularly,when input power coefficient is less than 2.8,the rigid tail generates larger thrust force and higher propulsive efficiency than flexible tail.However,when input power coefficient is larger than 2.8,flexible tail is superior to rigid tail.     

Computation of Unsteady Flow Past a Biomimetic Fin

The unsteady hydrodynamics of a biomimetic fin attached to a cylindrical body has been studied numerically using a computational fluid dynamic (CFD) simulator based on an in-house solver of the Navier-Stokes equations, combined with a recently developed multi-block, overset grid method. The fin-body CFD model is based on a mechanical pectoral fin device, which consists of a cylindrical body and an asymmetric fin and can mimic flapping, rowing and feathering motions of the pectoral fins in fishes. First the multi-block, overset grid method incorporated into the NS solver was verified through an extensive study of unsteady flows past a single fin undergoing rowing and feathering motion. Then unsteady flows past the biomimetic fin-body model undergoing the same motions were computed and compared with the measurements of forces of the mechanical pectoral fin, which shows good agreement in both time-varying and time-averaged hydrodynamic forces. The relationship between force generation and vortex dynamics points to the importance of the match in fin kinematics between power and recovery strokes and implies that an optimal selection of parameters of phase lags between and amplitudes of rowing and feathering motions can improve the performance of labriform propulsion in terms of either maximum force generation or minimum mechanical power.     

No evidence of expertise-related changes in muscle synergies during rowing

The purpose of the present study was to determine whether expertise in rowing is driven by a specific structure in muscular coordination. We compared seven experienced rowers and eight untrained (i.e., inexperienced) subjects during rowing on an ergometer. Both surface electromyography activity and mechanical patterns (forces exerted at the handle and the foot-stretcher) were recorded during a high intensity rowing exercise. A non-negative matrix factorization was applied to 23 electromyographic patterns to differentiate muscle synergies. Results showed that expertise was not associated with different dimensionality in the electromyographic data and that three muscle synergies were sufficient to explain the majority of the variance accounted for (i.e., >90% of the total variance) in the two populations. The synergies extracted were similar in the two populations, with identical functional roles. While the temporal organization of the propulsive synergies was very similar, slight differences were found in the composition of the muscle synergies (muscle synergy vectors) between the two populations. The results suggests that rowing expertise would not require the development of novel muscle synergies but would imply intrinsic synergies already used in different behaviors. Performance in rowing is more probably linked to adjustments in the mechanical output of the muscle synergies rather than to differences in the shape and timing of their activations.     

Are powerful females powerful enough? Acceleration in gravid green iguanas (Iguana iguana)

One demand placed exclusively on the musculoskeletal systemof females is maintaining locomotor performance with an increasingload over the reproductive cycle. Here, we examine whether gravid(i.e., "pregnant") iguanas can increase their force and powerproduction to support, stabilize, and accelerate the additionalmass of a clutch of eggs. At any acceleration, gravid iguanasproduced very high mechanical power (average total power = 673w/kg; total peak power = 1175 w/kg). While the increase in totalpower was partly a result of greater propulsive power (averagepropulsive power = 25% higher, peak propulsive power = 38% higher),increased vertical power (roughly 200% increase) was the maincontributor. Gravid iguanas were also able to increase peakforces (propulsive = 23%, mediolateral = 44%, vertical = 42%),and step duration (44%) resulting in greater impulses (i.e.,the sum of force produced during a step) to accelerate, balance,and support their increased mass. The increase in step durationand smaller increase in peak propulsive force suggests thatgravid iguanas may be force-limited in the direction of motion.We discuss how biomechanical constraints due to females’reproductive role may influence the evolution of the femalemusculoskeletal systems and contribute to the evolution andmaintenance of ecological dimorphism in lizards.     

Power equations in endurance sports

This paper attempts to clarify the formulation of power equations applicable to a variety of endurance activities. An accurate accounting of the relationship between the metabolic power input and the mechanical power output is still elusive, due to such issues as storage and recovery of strain energy and the differing energy costs of concentric and eccentric muscle actions. Nevertheless, an instantaneous approach is presented which is based upon the application of conventional Newtonian mechanics to a rigid segment model of the body, and does not contain assumptions regarding the exact nature of segmental interactions--such as energy transfer, etc. The application of the equation to running, cycling, speed skating, swimming and rowing is discussed and definitions of power, efficiency, and economy are presented.     

A test of the endogenous and exogenous selection hypotheses for the maintenance of a narrow avian hybrid zone

The contributions of genetic and environmental factors to differential reproductive success across hybrid zones have rarely been tested. Here, we report a manipulative experiment that simultaneously tested endogenous (genetic-based) and exogenous (environmental-based) selection within a hybrid zone. We transplanted mated pairs of two chickadee species (Poecile atricapilla and P. carolinensis) and their hybrids into isolated woodlots within their hybrid zone and monitored their reproductive success. Although clutch sizes were similar, based on an estimate of the genetic compatibility of a pair, hybrid pairs produced fewer nestlings and fledglings than did pairs of either parental species. According to a linear model generated from the data, a pure pair of either parental species would be expected to produce 1.91-2.48 times more fledglings per nesting attempt, respectively, than the average or least compatible pair in the experiment. Our result of decreased reproduction for hybrid pairs relative to parental species pairs within same environment (the hybrid zone in this experiment) support the endogenous selection hypothesis for maintenance of this hybrid zone. Because the experiment was conducted entirely within the hybrid zone (i.e., the same environment for parental and hybrid pairings), our data do not support the exogenous selection hypothesis as it predicts either all pairings doing poorly or the hybrid pairs more successful than the parental pairs.     

An estimation of drag in front crawl swimming

Propulsive arm forces of twelve elite male swimmers during a front crawl swimming-like activity were measured. The swimmers pushed off against grips which are attached to a 23 m tube at 0.8 m under the water surface. The tube was fixed to a force transducer. Since at constant speed, mean propulsive force equals mean drag force this method also provides the mean active drag on a moving swimmer. The mean propulsive force at a speed of v = 1.48 m s-1 appeared to be 53.2 +/- 5.8 N which is two to three times smaller than what is reported by other authors for active drag but which is in agreement with values reported for passive drag on a (towed) swimmer who is not moving. Discrepancies with indirect active drag measurements are discussed.     

On hydrodynamics of drag and lift of the human arm

The work presents results on drag and lift measurement conducted in a low speed wind tunnel on a replica of the entire human arm. The selected model positions were identical to those during purely rotational front crawl stroke in quasi-static conditions. A computational fluid dynamics model using Fluent showed close correspondence with the experimental results and confirmed the suitability of low speed wind tunnel for the drag and lift measurement in quasi-static conditions. The obtained profiles of the hydrodynamic forces were similar to the dynamic data presented in an earlier study suggesting that shape drag is a major contributing factor in propulsive force generation. The aim of this study was to underline the importance of the entire arm analysis, the elbow angle and a newly defined angle of attack representing the angle of shoulder rotation. It was found that both the maximum value of the drag force at 160 degrees elbow flexion angle and the momentum generated by it exceed the respective magnitudes for the fully extended arm. The latter is underlined by a prolonged plateau of near maximum drag that was obtained at shoulder angle range of 50-140 degrees suggesting that optimal arm configuration in terms of propulsive force generation requires elbow flexion. Furthermore it was found that drag trend is not consistent with the widely assumed and used sinus wave profile. A gap in the existing experimental research was filled as for the first time the entire arm lift and drag was measured across the entire stroke range.     

Active drag related to velocity in male and female swimmers

Propulsive arm forces of 32 male and 9 female swimmers were measured during front crawl swimming using arms only, in a velocity range between 1.0 m s-1 and 1.8 m s-1. At constant velocity, the measured mean propulsive force Fp equals the mean active drag force (Fd). It was found that Fd is related to the swimming velocity v raised to the power 2.12 +/- 0.20 (males) or 2.28 +/- 0.35 (females). Although many subjects showed rather constant values of Fd/v2, 12 subjects gave significantly (p less than 0.01) stronger or weaker quadratic relationships. Differences in drag force and coefficient of drag between males and females (drag: 28.9 +/- 5.1 N, 20.4 +/- 1.9 N, drag coefficient: 0.64 +/- 0.09, 0.54 +/- 0.07 respectively) are especially apparent at the lowest swimming velocity (1 m s-1), which become less at higher swimming velocities. Possible explanations for the deviation of the power of the velocity from the ideal quadratic dependency are discussed.     

Propulsion of micro-organisms by three-dimensional flagellar waves

The hydrodynamic effects of non-uniformities in cross-section and wavelength of three-dimensional flagellar waveforms are investigated. Estimates of propulsive velocity obtained by the use of mean constant wave parameters are close to the more precise calculations except where the wavelength varies more than twofold during wave propagation. Energy expenditures against external viscous forces are appreciably greater than the estimates based on mean wave parameter assumptions. Rotation of an inert head attached to a flagellum contributes a significant proportion of the total power dissipation. Energy requirements of an individual bull spermatozoon are greater than previous estimates. There is little difference between the energy supplies necessary to propel bacteria by rotating rigid flagellar helices or by propagation of helical waves.     

vProtein: identifying optimal amino acid complements from plant-based foods

Background

Indispensible amino acids (IAAs) are used by the body in different proportions. Most animal-based foods provide these IAAs in roughly the needed proportions, but many plant-based foods provide different proportions of IAAs. To explore how these plant-based foods can be better used in human nutrition, we have created the computational tool vProtein to identify optimal food complements to satisfy human protein needs.

Methods

vProtein uses 1251 plant-based foods listed in the United States Department of Agriculture standard release 22 database to determine the quantity of each food or pair of foods required to satisfy human IAA needs as determined by the 2005 daily recommended intake. The quantity of food in a pair is found using a linear programming approach that minimizes total calories, total excess IAAs, or the total weight of the combination.

Results

For single foods, vProtein identifies foods with particularly balanced IAA patterns such as wheat germ, quinoa, and cauliflower. vProtein also identifies foods with particularly unbalanced IAA patterns such as macadamia nuts, degermed corn products, and wakame seaweed. Although less useful alone, some unbalanced foods provide unusually good complements, such as Brazil nuts to legumes.Interestingly, vProtein finds no statistically significant bias toward grain/legume pairings for protein complementation. These analyses suggest that pairings of plant-based foods should be based on the individual foods themselves instead of based on broader food group-food group pairings. Overall, the most efficient pairings include sweet corn/tomatoes, apple/coconut, and sweet corn/cherry. The top pairings also highlight the utility of less common protein sources such as the seaweeds laver and spirulina, pumpkin leaves, and lambsquarters. From a public health perspective, many of the food pairings represent novel, low cost food sources to combat malnutrition. Full analysis results are available online at http://www.foodwiki.com/vprotein.     

Drag from fishing gear entangling North Atlantic right whales

Lethal and sublethal fishing gear entanglement is pervasive in North Atlantic right whales (Eubalaena glacialis). Entanglement can lead to direct injury and is likely to incur substantial energetic costs. This study (1) evaluates drag characteristics of entangled right whales, (2) contextualizes gear drag measurements for individual whales, and (3) quantifies the benefits of partial disentanglement. A load cell measured drag forces on 15 sets of fishing gear removed from entangled right whales, a towed satellite telemetry buoy, and 200 m of polypropylene line as it was shortened to 25 m, as they were towed behind a vessel at ~0.77, 1.3, and 2.1 m/s (~1.5, 2.5, and 4 knots) and ~0, 3, and 6 m depth. Mean drag ranges from 8.5 N to 315 N, and can be predicted from the dry weight or length of the gear. Combining gear drag measurements with theoretical estimates of drag on whales' bodies suggests that on average, entanglement increases drag and propulsive power by 1.47 fold. Reducing trailing line length by 75% can reduce parasitic gear drag by 85%, reinforcing current disentanglement response practices. These drag measurements can be incorporated into disentanglement response, serious injury determination, and evaluation of sublethal effects on population dynamics.