Increasing Cycle Frequency Research Articles

Perceptions of Bicycle Signal Faces and Associated Compliance: Results of an Online Survey

Across the U.S.A., cities are increasingly prioritizing the implementation and enhancement of cycle facilities and networks. One of the goals of this effort is to enhance the safety and comfort of the urban cycling experience. Some of the implemented and planned facility improvements include protected cycle lanes, turning boxes, and newer control devices such as bicycle signal faces. The introduction of the bicycle signal face increases intersection complexity and can influence people’s perceptions of safety and comfort. Often, the bicycle signal symbol is the only distinguishing feature of a bicycle signal, and this could lead to user confusion. This paper describes the results of an online survey conducted in Austin, Texas, which aimed to understand people’s perceptions of bicycle signal faces. The survey was conducted after the installation of experimental bicycle signal faces at 12 intersections throughout the city. The paper also presents the results from a combination of stated and revealed preferences to compare people’s perceptions with their real-life experience of dedicated bicycle signals with bicycle signal faces. In general, perceptions of satisfaction, comfort, compliance, and safety in relation to bicycle signals are positive. For many of the questions, positive perceptions improved with decreasing age, increasing cycling frequency, access to a bicycle, or an encounter with experimental bicycle signals. The most polarizing respondent characteristics are access to a bicycle, cycling frequency, and level of cycling comfort.

Cyclic oxidation behaviour of TP446, TP310, and IN617 in air at 871°C and 982°C

ABSTRACT The influence of frequency of thermal cycling on the oxidation behaviour of alloys TP446, TP310, and Inconel 617 in dry air at very high temperatures (871°C and 982°C) is reported. The effects on the iron-basedalloys were complex, whereas that of the Ni-based alloy was not greatly affected by cycling frequency. Unexpected trends were increased oxidation rates of TP310 and Inconel 617 with increased cycle frequency at 871°C, whereas those of TP446 decreased. At 982°C, the oxidation rates of TP310 and TP446 decreased with increasing cycle frequency, though less so for TP310. While the scales formed on the iron-based alloys consisted of a basal layer corresponding to chromia containing Mn, and an outer layer corresponding to manganese chromate, differences in the rates of transport of Cr, Mn and Si in the alloys at the different temperatures appeared to account in large measure for the differences in response to thermal cycling.

Thermal Boundary Evolution of Molten Pool During Wire and Arc Additive Manufacturing of Single Walls of 5A06 Aluminum Alloy

Molten pool uniformity is a prerequisite for wire and arc additive manufacture to achieve a uniform surface appearance. The thermal boundary is a key indicator to evaluate the thermodynamic state of the molten pool. This paper focuses on thermal analysis through finite element simulation and characterizes the thermal evolution of a molten pool during bottom-up deposition. The peak temperature of the substrate plate increases from 375.7 °C to 623.1 °C when peak current increases from 120 A to 180 A. The temperature gradient decreases from 40 °C/mm to 30 °C/mm. Weld speed increases from 0.15 m/min to 0.25 m/min; the temperature gradient is kept at about 30 °C/mm. Dimensionless thermal conductivity, Ge number, is proposed and defined as the criteria to estimate layer size variation. For Ip = 140 A, the average value of the Ge number is 87.7, and it shows the best numerical stability. Dimensionless thermal conductivity, Ge, is proposed and defined as the criteria to estimate the occurrence of layer size variation. Prolonging heating time and increasing cycle frequency, Ge number shows favorable stability during bottom-up deposition. The experimental results are consistent with analytical conclusions, which proves the validity of the Ge number as an indicator of deposition stability.

Cycling exposure and infrastructural correlates in a Flemish adolescent population

IntroductionInfrastructure adjusted to cyclists can be used as a tool to reduce cycling crashes and injuries. To increase cycling frequency and safety, a population's cycling exposure to different infrastructure needs to be known. Since cycling behavior of adolescents cannot be compared to adults, the objective of this study is to describe the cycling exposure and the characteristics of routes used by adolescents for bicycle commuting. MethodsWe used an online travel diary to collect bicycle route information and an exposure matrix to collect cycling frequency data. Data were collected in Flanders (Belgium) from an adolescent population (15–18 years). ResultsFrom the 1345 participating adolescents, 47% used their bicycle at least once a week. Infrastructural correlates were based on 467,000 km of cycled roads with a mean trip distance of 5.7 ± 4.5 km; 91% of cycling exposure is on infrastructure with speed limits of 50 km/h or more and 32.7% on dedicated cycle lanes. Lower motorized traffic density was related to higher odds of daily bicycle commuting. Higher traffic densities or speed limits were related to lower odds of daily bicycle commuting, but this relationship disappeared after adjusting for presence of a dedicated cycle lane. ConclusionsMany adolescents who commute by bicycle cycle along streets with high speed limits and no dedicated cycle lanes probably because of the low motorized traffic densities on these roads. Adolescents should avoid roads without dedicated cycling infrastructure and high speed limits since these roads have been identified as high risk. The results are region specific and therefore this study should be replicated in other contexts.

Effect of Temperature Cycling on Ostwald Ripening.

We study the effect of temperature cycling on the rate of Ostwald ripening (or coarsening) of spherical particles dispersed in a binary solution. A widespread view, which states a temperature cycle generally enhances the rate of Ostwald ripening by first dissolving the smallest particles (heating) and then regrowing the dissolved amount of material on the remaining particles (cooling), is shown to be inadequate as it does not include transient effects. On the basis of a simulation method that assumes mass transfer as the limiting growth mechanism, we show that each temperature cycle is followed by a significant relaxation of the particle-size distribution, during which the number of particles remains constant, and the average particle size decreases. The relaxation is shown to be crucial to obtain a linear scaling of the average particle radius cubed with the number of cycles applied (or time), which is the behavior generally observed for the evolution of ice crystals in cycling experiments on frozen aqueous solutions or frozen foods. We show the experimentally observed increase in the proportionality constant (or “coarsening rate”) as compared to isothermal ripening, or the increase of the coarsening rate with increasing cycle frequency, can be reproduced convincingly only if some (transient) ripening is allowed to take place at the elevated temperature of each cycle. Our results thus suggest the effect of temperature cycling on Ostwald ripening is governed by a dissolution–ripening–regrowth–relaxation mechanism.

Fast cycling in a non-isothermal monolithic lean NOx trap using H2 as reductant: Experiments and modeling

A combined experimental and modeling study of fast cycling NOx storage and reduction with H2 for emissions control of lean burn gasoline and diesel vehicles is conducted to provide mechanistic insight and detailed understanding to Toyota’s Di-Air technology. Experiments reveal NOx conversion enhancement over a model Pt/Rh/BaO/CeO2/Al2O3 lean NOx trap (LNT) catalyst for cycle times less than 10s (fast cycling) compared to the longer cycle times typical of conventional NSR. Increased cycle frequency results in the increase (decrease) of the cycle-averaged NOx conversion (NH3 selectivity) over a wide temperature range. The more frequent storage and regeneration of fast cycling increases the utilization of stored NOx capacity by decreasing NOx breakthrough during the lean phase. The decreased NH3 selectivity is in part a result of a combination of increased efficiency of the NH3 oxidation by oxygen stored on the ceria component and of the adsorption of NH3 on the support. A global kinetic model incorporated into a non-isothermal 1-D monolith reactor model is effective in capturing most of the experimental trends. Quantitative agreement requires treatment of the extent of mixing of the lean and rich feeds upstream of the reactor, as well as of mixing of the product stream in the downstream FTIR cell. The predicted axial temperature profile shows a front-monolith temperature rise as high as twice that measured in the middle-monolith under slower cycling. Under faster cycling a predicted 100°C front-monolith temperature rise contrasts to a measured near-constant middle-monolith temperature. Non-isothermal effects are especially important when catalyst temperatures exceed 450°C, which lowers the NOx storage capacity, resulting in an increased amount of slipped NOx during early lean phase.

Age and attitude: Changes in cycling patterns of different e-bike user segments

ABSTRACTThe use and purchase of electric bicycles (e-bikes) is emerging in many countries. Existing knowledge about changes in cycling patterns and car replacement after gaining e-bike access is limited and partly contradictory. Based on an online survey among e-bike users in Denmark (n = 427), this study looked into these effects by differentiating between different segments of e-bike users. We distinguished four age groups as well as three segments based on cycling attitudes and motives for the use and purchase of e-bikes: (1) enthusiastic e-bikers showed the most positive attitudes toward e-bikes and mainly bought an e-bike to increase cycling frequency; (2) utilitarian e-bikers already cycled regularly before having access to an e-bike and used the e-bike particularly for practical purposes and to reduce travel time; (3) recreational e-bikers were very positive about e-bike use but used it less regularly and mainly for long-distance recreational trips. Enthusiastic e-bikers reported the highest increase in overall cycling. Half of the enthusiastic e-bikers agreed that they bought the e-bike to replace a car. Differences between the four age groups were less pronounced. Nevertheless, we found that e-bike access decreased age differences in self-reported cycling frequency, whereas it increased differences in self-reported distances. Measures to increase e-bike use should primarily focus on potential enthusiastic e-bikers. Possible interventions include promotional campaigns at workplaces, intended to address not only instrumental but also affective motives of e-bike use.

On the strengthening effect of increasing cycling frequency on fatigue behavior of some polymers and their composites: Experiments and modeling

Effect of cycling frequency on fatigue behavior of neat, talc filled, and short glass fiber reinforced injection molded polymer composites was investigated by conducting load-controlled fatigue tests at several stress ratios (R=−1, 0.1, and 0.3) and at several temperatures (T=23, 85 and 120°C). A beneficial or strengthening effect of increasing frequency was observed for some of the studied materials, before self-heating became dominant at higher frequencies. A reduction in loss tangent (viscoelastic damping factor), width of hysteresis loop, and displacement amplitude, measured in load-controlled fatigue tests, was observed by increasing frequency for frequency sensitive materials. Reduction in loss tangent was also observed for frequency sensitive materials in DMA tests. It was concluded that the fatigue behavior is also time-dependent for frequency sensitive materials. A Larson–Miller type parameter was used to correlate experimental fatigue data and relate stress amplitude, frequency, cycles to failure, and temperature together. An analytical fatigue life estimation model was also used to consider the strengthening effect of frequency in addition to mean stress, fiber orientation, and temperature effects on fatigue life.

Shoulder joint contact force during lever-propelled wheelchair propulsion

The aim of this study was to obtain quantitative results about shoulder contact force during wheelchair lever propulsion when the gear ratio of the lever propulsion mechanism is changing. The effect of the gear ratio on the shoulder contact force was investigated for few different wheelchair loading. For the experiments we designed a special mechatronic wheelchair simulator that allowed the simulation of different gear ratios of the wheelchair lever propulsion mechanism and simulation of different road inclinations. The same simulator was also used for simulation of a hand rim propelled wheelchair. We conducted also a handrim propulsion experiment and used the results from it for comparison with the lever propulsion data. Four nondisabled male adults with no prior wheeling experience participated in the experiment. In the first tests, a lever propelled wheelchair was simulated with the simulator. The target speed of the wheelchair was set to 2 km/h. For the test, the gear ratio was varied from 1.5 to 1/1.5. A load torque was applied to the rear wheels to imitate road inclinations of 0°, 2° and 4°. In the second part of the test, the simulator was structured to simulate a handrim propelled wheelchair. The participants were asked to keep the same speed (2 km/h) and the simulator was set sequentially to imitate climbing a ramp inclined on 0°, 2° and 4°. Kinematic data of the body were collected by a motion capture system. Kinetic data such as hand force and driving torque, were measured by instrumented wheels with incorporated six-axis force sensor. The intersegmental joint forces and moments were calculated from the obtained kinematic and kinetic data via inverse dynamics analysis procedure. Muscle forces were computed from the measured joint moments by using an optimization approach. Shoulder joint contact force, which indicates the joint surface loading, was computed as a synthetic vector of the intersegmental force for shoulder joint acquired from the inverse dynamics analysis and the compressive forces from muscles, tendons, ligaments and cartilages crossing the shoulder joint. It was observed that the decrease of the gear ratio causes increased cycle frequency and reduces the shoulder joint contact force. Result showed that the shoulder joint contact force during lever propulsion with a gear ratio 1/1.5 was up to 70 % lower than the shoulder joint contact force during handrim propulsion. The results from this study could be used in the design of new lever propulsion mechanisms that reduce the risks of secondary shoulder disorders and increase user’s comfort.

A48 Short term impacts of new cycling infrastructure in Sydney, Australia

Abstract Background A natural experiment to evaluate a new separated bicycle path became possible in Sydney, with the City of Sydney building a new 3.7 km separated bicycle path in the inner city in early 2014. We describe the users of the new bicycle path, and examine its short term impacts. Methods The Sydney Transport and Health Study is designed to evaluate the cycling and health impacts of a new separated bicycle path in inner Sydney, with six monthly bike counts at two intersections, plus individual resident data collection in the intervention area plus a similar comparison area before the bicycle path was built, and at 12 and 24 months. From the 865 baseline study participants, 675 agreed to be re-contacted, and were invited to complete the 12 month on-line questionnaire in September/October 2014 (513 agreed, 76%). Respondents were asked at baseline to identify the type of cyclist they most identified with (high/low intensity recreational/transport rider), cycling frequency (weekly or less than weekly) plus demographic information. At 12 month follow-up cycling frequency and perceptions of changes in the environment were asked. Chi square tests were used to compare cycling frequencies, and perceptions of the environment. Logistic regression was used to identify factors associated with use of the new bicycle path, with rider type, cycling frequency, age, sex and education in the model. Results Bike counts reported a 12 month increase of 23% and 97%. There was no change in the self-reported weekly frequency of cycling. One in five (15%) residents had used the new bicycle path, with most (76%) living in the intervention area. Bicycle path users were most likely to be high intensity recreational rider (adjusted odds ratio (AOR) 3.00, 95% confidence interval (CI) 1.16-7.80) or a low intensity transport rider (AOR=2.78, 95%CI 1.44-5.39) had ridden their bicycle in the past week (AOR=5.29, 95% CI 2.96-9.45) and less likely to be older (AOR 0.97, 95% CI 0.95-0.99). Perceptions that the neighbourhood was more pleasant, that there were more people walking and cycling were significantly higher in the intervention area (p Conclusions Increases in resident cycling frequency may require some time, or additional promotional activities. Perceptions of increased cycling may be due to increased cyclists from outside the study area using the new path. Better connectivity of the new path with the City of Sydney bicycle path network may increase cycling frequency.

Who cycles more? Determining cycling frequency through a segmentation approach in Montreal, Canada

The decision to cycle frequently in an urban setting is a complex process and is affected by a variety of factors. This study analyzed the various factors influencing cycling frequency among 1707 cyclists from Montreal, Canada using an ordinal logistic regression. A segmentation of cyclists is used in a series of ordinal logistic models to better understand the different impacts of variables on the frequency of cycling among each group of cyclists for commute and for utilitarian purposes. Our models show a variation in the impacts of each dependent variable on frequency of cycling across the various segments of cyclists. Mainly making cyclists feel safe not only on bicycle specific infrastructure but also on regular streets, emphasizing the low cost, convenience and improving the opinion on cycling in the population are effective interventions to increase bicycle usage. Also, it was shown that women were less likely to cycle to work than men, but more likely to cycle for other utilitarian trips, pointing at the presence of specific barriers to commuting for woman. Although the findings from this study are specific to Montreal, they can be of interest to transportation planners and engineers working toward increasing cycling frequency in other regions.

The dopaminergic system in upper limb motor blocks (ULMB) investigated during bimanual coordination in Parkinson's disease (PD).

Upper limb motor blocks (ULMB) (inability to initiate or sudden discontinue in voluntary movements) have been identified in both unimanual and bimanual tasks in individuals with Parkinson's disease (PD). In particular, ULMB have been observed during rhythmic bimanual coordination when switching between phase patterns which is required (e.g. between in-phase and anti-phase). While sensory-perceptual mechanisms have recently been suggested to be involved in lower limb freezing, there has been no consensus on the mechanism that evokes ULMB or whether motor blocks respond to dopamine replacement like other motor symptoms of PD. The current study investigated the occurrence of ULMB in PD participants without ('off') and with ('on') dopamine replacement using bimanual wrist flexion-extension with external auditory cues. In Experiment 1, coordination was performed in either in-phase (simultaneous flexion and extension) or anti-phase (asymmetrical flexion and extension between the limbs) in one of three sensory conditions: no vision, normal vision or augmented vision. Cycle frequency was increased within each trial across seven cycle frequencies (0.75-2 Hz). In Experiment 2, coordination was initiated in either phase pattern and participants were cued to make an intentional switch between phases in the middle of trials. Trials were performed at one of two cycle frequencies (1 or 2 Hz) and one of two sensory conditions: no vision or normal vision. Healthy age-matched control participants were also investigated in both experiments for the occurrence of motor blocks that were measured using automated detection from a computer algorithm. The results from Experiment 1 indicated that increasing cycle frequency resulted in more ULMB in individuals with PD during continuous coordinated movement, regardless of dopaminergic status, phase pattern or sensory condition. Experiment 2 also confirmed an increased occurrence of ULMB with increased cycle frequency. Furthermore, a large amount of ULMB were observed when initiating anti-phase coordination at 2 Hz, as well as after both externally-cued switches and in 'catch trials' with distracting auditory cues when no switch was required. Dopamine replacement was not found to influence the frequency of ULMB in either experiment. Therefore, ULMB likely result from non-hypodopaminergic impairments associated with PD. Specifically, ULMB may be caused by an inability to shift attentional control under increased cognitive demand that could be associated with hypoactivation in motor and prefrontal areas.

A novel thermally biased mechanical energy conversion cycle

This paper demonstrates a new power cycle for direct conversion of mechanical energy into electrical energy under a thermal bias. The cycle consisted sequentially of (i) an electric poling process under zero stress, (ii) an isoelectric process consisting of applying a uniaxial compressive stress σH followed by (iii) an electric de-poling process under constant compressive stress, and finally (iv) an isoelectric process consisting of removing the compressive stress. The new cycle was performed at constant bias-temperature Tb. It was demonstrated on [001]-poled 0.72PbMg1∕3Nb2∕3O3-0.28PbTiO3 single crystals. The power density increased with increasing cycle frequency and compressive stress for frequency up to 1 Hz. Maximum energy and power densities of 44 J/l/cycle and 44 W/l were achieved at 1 Hz for bias-temperature Tb of 80 °C and electric field cycled between 0.2 and 0.8 MV/m with compressive stress σH = 25.13 MPa. This was attributed to a tetragonal-monoclinic-orthorhombic phase transition sequence. The material efficiency reached up to 87% and exceeded that of a similar thermomechanical power cycle performed on pyroelectric material. Finally, a physical model predicting the power density was derived and yielded accurate predictions of experimental data for all bias-temperatures considered and cycle frequency up to 1 Hz.

Exploring the efficacy of cyclic vs static aspiration in a cerebral thrombectomy model: an initial proof of concept study

Background and purposeCurrent technology for endovascular thrombectomy in ischemic stroke utilizes static loading and is successful in approximately 85% of cases. Existing technology uses either static suction (applied via a...

Bipolar Disorder Maintenance Treatment

Bipolar disorder is a chronic illness that requires long-term treatment, the goal of which is to shorten or prevent mood episodes without increasing cycle frequency, thereby increasing the length of well periods. Treatment guidelines recommend mood stabilizers as first-line medications, and several atypical antipsychotics are also approved as monotherapy or as adjuncts to mood stabilizers for maintenance treatment. Combination therapy with 2 mood stabilizers or with a mood stabilizer and an antipsychotic may be necessary to achieve or maintain remission of the patient's symptoms. When treating patients with mood stabilizers and atypical antipsychotics during the maintenance phase, physicians should systematically monitor for adverse effects, particularly weight gain, and tolerability issues, and address those issues in a timely manner in order to enhance treatment adherence and improve patient outcomes.

Waste heat energy harvesting using the Olsen cycle on 0.945Pb(Zn1/3Nb2/3)O3– 0.055PbTiO3 single crystals

This paper reports on direct thermal to electrical energy conversion by performing the Olsen (or Ericsson) cycle on [001]-poled 0.945PbZn1/3Nb2/3O3–0.055PbTiO3 (PZN-5.5PT) single crystals. The cycle consists of two isothermal and two constant electric field processes. The energy density was found to decrease with increasing cycle frequency while the power density increased. The maximum energy density obtained was 150 J/l/cycle for temperatures between 100 and 190 °C and electric field between 0 and 1.2 MV m−1 at frequency 0.034 Hz. The maximum power density reached 11.7 W l−1 at 0.1 Hz for temperatures between 100 and 190 °C and electric fields between 0.2 and 1.5 MV m−1. Moreover, the dielectric constant and saturation polarization of PZN-5.5PT are reported for the first time at 0.1 Hz for temperatures between 100 and 190 °C. Finally, the experimental results agree relatively well with predictions by a recently developed temperature-dependent property model already validated with PMN-32PT. Inter-sample variability and sample durability are also discussed.

The search for stability on narrow supports: an experimental study in cats and dogs

Kinematic and coordination variables were studied in two carnivorans, one with known locomotor capabilities in arboreal substrates (cat), and the other a completely terrestrial species (dog). Two horizontal substrates were used: a flat trackway on the ground (overground locomotion) and an elevated and narrow runway (narrow-support locomotion). Despite their different degree of familiarity with the ‘arboreal’ situation, both species developed a strategy to adapt to narrow supports. The strategy of cats was based on using slower speeds, coupled with modifications to swing phase duration, to keep balance on narrow supports. The strategy of dogs relied on high speeds to gain in dynamic stability, and they increased cycle frequency by reducing swing phase duration. Furthermore, dogs showed a high variability in limb coordination, although a tendency to canter-like coordination was observed, and also avoided whole-body aerial phases. In different ways, both strategies suggested a reduction of peak vertical forces, and hence a reduction of the vertical oscillations of the centre of mass. Finally, lateral oscillation was reduced by the use of a crouched posture.

Coordination of complex bimanual multijoint movements under increasing cycling frequencies: The prevalence of mirror-image and translational symmetry

The present study examined the principles underlying inter and intralimb coordination constraints during performance of bimanual elbow–wrist movements at different cycling frequencies (from 0.75 Hz to 2.50 Hz). Participants performed eight coordination tasks that consisted of a combination of in-phase (IN) and/or anti-phase (AN) coordination modes between both elbows and wrists (interlimb), with isodirectional (Iso) or non-isodirectional (NonI) coordination modes within each limb (intralimb). As expected, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the mid-sagittal plane, had a powerful influence on the quality of global coordinative behavior both between and within limbs. When this principle was violated (i.e., when the anti-phase mode was introduced in one or both joint pairs), the non-isodirectional intralimb mode exhibited a (de)stabilizing role in coordination, which became more pronounced at higher cycling frequencies. However, pattern loss with increasing cycling frequency resulted not only in convergence toward the more stable in-phase patterns with the elbows and wrists but also to the anti-phase patterns (which were associated with directional compatibility of within-limb motions). Moreover, participants generally preserved their initial mode of coordination (either in-phase or anti-phase) in the proximal joints (i.e., elbows) while shifting from anti-phase to in-phase (or vice versa) with their distal joint pair (i.e., wrists). Taken together, these findings reflect the impact of two immanent types of symmetry in bimanual coordination: mirror-image and translational symmetry.

Analysis and Interpretation of Stress Fiber Organization in Cells Subject to Cyclic Stretch

Numerical simulations that incorporate a biochemomechanical model for the contractility of the cytoskeleton have been used to rationalize the following observations. Uniaxial cyclic stretching of cells causes stress fibers to align perpendicular to the stretch direction, with degree of alignment dependent on the stretch strain magnitude, as well as the frequency and the transverse contraction of the substrate. Conversely, equibiaxial cyclic stretching induces a uniform distribution of stress fiber orientations. Demonstrations that the model successfully predicts the alignments experimentally found are followed by a parameter study to investigate the influence of a range of key variables including the stretch magnitude, the intrinsic rate sensitivity of the stress fibers, the straining frequency, and the transverse contraction of the substrate. The primary predictions are as follows. The rate sensitivity has a strong influence on alignment, equivalent to that attained by a few percent of additional stretch. The fiber alignment increases with increasing cycling frequency. Transverse contraction of the substrate causes the stress fibers to organize into two symmetrical orientations with respect to the primary stretch direction.

Thermal dependence of contractile properties of the aerobic locomotor muscle in the leopard shark and shortfin mako shark

The work loop technique was used to examine contractile properties of the red aerobic locomotor muscle (RM) in the ectothermic leopard shark Triakis semifasciata and endothermic shortfin mako shark Isurus oxyrinchus. The effects of axial position and temperature on the twitch kinetics, and the stimulus duration and phase producing maximum net positive work and power output were investigated. Contractile performance was measured over the temperature range of 15 to 25 degrees C for Triakis and 15 to 28 degrees C for Isurus at cycle frequencies (analogous to tailbeat frequencies) ranging from 0.25 to 3 Hz using muscle bundles isolated from anterior (0.4 L where L is total body length) and posterior (0.6-0.65 L) axial positions. Pairwise comparisons of twitch times for anterior and posterior muscle samples indicated that there were no significant differences related to body position, except in mako sharks at unphysiologically cool temperatures (<20 degrees C). We found no significant differences in optimal stimulus duration, phase, net work or power output between anterior and posterior bundles in each species. With increasing cycle frequency the stimulus duration yielding maximum power decreased while optimal phase occurred earlier. The cycle frequency at which peak power was generated in leopard shark RM was only affected slightly by temperature, increasing from about 0.6 to 1.0 Hz between 15 and 25 degrees C. In contrast, mako RM showed a much more dramatic temperature sensitivity, with the peak power frequency rising from <0.25 to 2.25 Hz between 15 and 28 degrees C. These data support the hypothesis that the contractile properties of RM are functionally similar along the body in both species. In addition, our data identify a significant difference in the effect of temperature on net work and power output between these two shark species; at 15 degrees C muscle from the ectothermic leopard shark performs relatively well in comparison with mako, while at higher temperatures, which reflect those normally experienced by the mako, the optimal cycle frequency for power is nearly double that of the leopard shark, suggesting that the mako may be able to maintain greater aerobic swimming speeds.