Stroke Cycle Research Articles

Development of a Kinematical Model to Study the Aerodynamics of Flapping-Wings

The kinematics that characterizes the “natural flight” of insects is quite complex. It involves simultaneous rotations, oscillations and significant changes in the angle of attack. All this permits the wings to follow an extremely complex trajectory producing different flight mechanisms that are efficient at low to moderate Reynolds numbers. Some of these mechanisms, such as the delayed stall, the additional circulation generated by the rotation of the wing, and the wake capture amongst others, offer unique advantages with respect to the well-known fixed-wing aerial vehicles. Such advantages are better lift and thrust generation without the need to increase weight. This paper presents a general kinematical model that permits studying the movements of the wings of a scale robot of a house fly, the ‘RoboFly’, built at UC Berkeley, USA. Additionally, this general kinematical model allows studying the kinematics of the wings of a flying insect considering both the body orientation and the stroke plane orientation of the creature in the 3D space. This work provides a nexus between the descriptive language used by biologists and the predictive language used by engineers. This connection between scientific disciplines allows one to study and characterize the principal kinematic parameters that intervene in a stroke cycle, as well as to determine how these variables modify the trajectories of the material points on the wings.

The force–time profile of elite front crawl swimmers

In this study, we used recently developed technology to determine the force–time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force–time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92 ± 0.06 m · s−1, the mean passive drag for the swimmers was 80.3 ± 4.0 N, and the mean net force was 262.4 ± 33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force–time profile also identified any stroke asymmetry.

The effect of critical speed and exercise intensity on stroke phase duration and bilateral asymmetry in 200-m front crawl swimming

The main aim of this study was to determine the absolute temporal relationship between the power and recovery phases of the stroke cycle in front crawl swimming in response to progressive changes in exercise intensity that occurred before and after critical speed. A second objective was to determine whether intensity-related changes in the power/recovery phase relationship affects the bilateral symmetry of the stroke. Stroke parameters were recorded for each 25-m length during a progressive 200-m interval training set, in which eight (2 males, 6 females) national-level swimmers swam at intensities below, above, and at critical speed. The results demonstrated that substantial increases in stroke rate (P < 0.01) occurred at critical speed, and that these increases were related to a greater decrease in the duration of the power phase than the recovery phase (P < 0.01). The results also show that the degree of bilateral asymmetry was greater for the power phase than the recovery phase, and was inversely related to intensity in both phases of the stroke cycle. The findings of this study suggest that critical speed-related increases in stroke rate are an indirect consequence of increased force production in the power phase of the stroke, and that bilateral asymmetry is both intensity- and stroke-phase dependent.

B24 スイマーの筋力特性を考慮したクロール泳ストロークの最適化(泳動作におけるマッチング)

In this study, the optimal arm strokes in crawl swimming which maximize the swimming speed and propulsive efficiency were solved computationally. For this objective, an optimizing method which consisted of the random search and the PSO (Particle Swarm Optimization) algorithm was constructed. In order to consider the muscle strength characteristics of the swimmer as the constraint condition of the optimization, an experiment to measure the maximum joint torques was carried out for various joint angles and angular speeds. Using the measured experimental data as the reference values, a musculoskeletal simulation model was constructed. By the constructed musculoskeletal model, muscle strength characteristics in various conditions were investigated and used to create a database. Using this database, the optimizing calculation was finally conducted and the following results were obtained: In the optimization maximizing the swimming speed, the swimming speed became maximum when the stroke cycle was 0.9 s. A relatively I-shaped stroke was obtained in this case. In the optimization maximizing the propulsive efficiency, the propulsive efficiency became maximum when the stroke cycle was 1.3 s. A relatively S-shaped stroke was obtained in this case. Two strokes which respectively maximized the swimming speed and propulsive efficiency were very similar to each other when the stroke cycles were the same. The swimming speeds and stroke cycles obtained in the optimizing calculation were within reasonable ranges compared to the actual races.

Kinematic differences between front crawl sprint and distance swimmers at sprint pace

The purpose of this study was to use three-dimensional methods to determine whether there are distinct kinematic differences between sprint and distance front crawl swimmers when swimming at a sprint pace. Seven sprint and eight distance specialists performed four 25-m sprints through a 6.75-m3 calibrated space recorded by six gen-locked cameras. The variables of interest were: average swim velocity, stroke length, stroke frequency, upper limb and foot displacement, elbow angle, shoulder and hip roll angles, duration of stroke phases, and the time corresponding to particular events within the stroke cycle relative to hand entry. Differences between sprint and distance swimmers were assessed with an independent t-test for each variable, in addition to effect size calculations. Differences between sprint and distance front crawl swimmers were generally small and not significant when swimming at a sprint pace. Differences were limited to temporal aspects of the stroke cycle. These findings suggest that coaches should not train sprint and distance specialists differently in terms of technique development.

The Effect of Retrofit Technologies on Formaldehyde Emissions from a Large Bore Natural Gas Engine

Formaldehyde is an air toxic that is typically emitted from natural gas-fired internal combustion engines as a product of incomplete combustion. The United States Environmental Protection Agency (EPA) regulates air toxic emissions, including formaldehyde, from stationary reciprocating internal combustion engines. National air toxic standards are required under the 1990 Clean Air Act Amendments. This work investigates the effect that hardware modifications, or retrofit technologies, have on formaldehyde emissions from a large bore natural gas engine. The test engine is a Cooper-Bessemer GMV-4TF two stroke cycle engine with a 14” (35.6 cm) bore and a 14” (35.6 cm) stroke. The impact of modifications to the fuel injection and ignition systems are investigated. Data analysis and discussion is performed with reference to possible formaldehyde formation mechanisms and in-cylinder phenomena. The results show that high pressure fuel injection (HPFI) and precombustion chamber (PCC) ignition significantly reduce formaldehyde emissions

Influence of swimming speed on inter-arm coordination in competitive unilateral arm amputee front crawl swimmers

This study examined the effect of swimming speed on inter-arm coordination and the inter-relationships between swimming speed, inter-arm coordination, and other stroke parameters, in a group of competitive unilateral arm amputee front crawl swimmers. Thirteen highly-trained swimmers were filmed underwater during a series of 25-m front crawl trials of increasing speed. Arm coordination for both arms was quantified using an adapted version of the Index of Coordination. Inter-arm coordination of the amputee swimmers did not change as swimming speed was increased up to maximum. Swimmers showed significantly more catch-up coordination of their affected-arm compared to their unaffected-arm. When sprinting, the fastest swimmers used higher stroke frequencies and less catch-up of their affected-arm than the slower swimmers. Unilateral arm-amputees used an asymmetrical strategy for coordinating their affected-arm relative to their unaffected-arm to maintain the stable repetition of their overall arm stroke cycle. When sprinting, the attainment of a high stroke frequency is influenced mainly by the length of time the affected-arm is held in a stationary position in front of the body before pulling. Reducing this time delay appears to be beneficial for successful swimming performance.

Assessment of individual anaerobic threshold and stroking parameters in swimmers aged 10–11 years

The assessment of blood lactate concentration is considered essential for the physiological diagnosis of swimming performance. But for a more detailed and complete analysis of a swimmer's strengths and weaknesses, it is also important to examine his or her technical characteristics. However, few studies have combined physiological and technical evaluation in child swimmers. The aim of the present study was to assess the metabolic anaerobic threshold (blood lactate concentration and corresponding swimming velocity) of 10- to 11-year-old swimmers (n=15) using an individualized intermittent incremental protocol. Comparison was made with the traditionally used 4 mmol · l−1 lactate threshold. In addition, stroke rate, stroke length, and stroke index were measured throughout the experimental protocol for assessment of the anaerobic threshold. Each swimmer performed a front crawl 5×200 m test, in which the swimming velocity was controlled by an acoustic signal each 50 m. Blood samples were collected from the ear lobe (Lactate Pro, Arkay, Inc., Kyoto, Japan), at rest and after each step. Stroke rate was registered by a Seiko base 3 chronofrequencemeter; stroke length, stroke index, and velocity were calculated at the end of each 200 m. The individual anaerobic threshold occurred at 2.3 mmol · l−1 (s=0.59), and the corresponding velocity was 1.026 m · s−1 (s=0.053), much lower than the traditionally used 4 mmol · l−1 value (or even 3.5 mmol · l−1). The velocity corresponding to 4 mmol · l−1 and 3.5 mmol · l−1 was 1.081 m · s−1 (s=0.056) and 1.067 m · s−1 (s=0.055), respectively. Stroke rate increased and stroke length decreased throughout the incremental protocol (i.e. with increasing velocity). The stroke index showed a tendency to increase throughout the protocol, with a significant difference from the first to the second step. The velocity corresponding to 4 mmol · l−1 (and 3.5 mmol · l−1) does not represent the metabolic individual anaerobic threshold in trained swimmers, independently of their age, and age-group swimmers prefer to increase their velocity through an increase in stroke rate. Thus, given the importance of developing swimming technique in age-group swimmers, coaches should implement the lengthening of swimmers' stroke cycles in their training practice routines, so that they limit the effects of reduced stroke length when velocity increases.

Acquisition of gliding skills by Weddell seal (Leptonychotes weddellii) pups during lactation

Pinnipeds give birth to their pups ashore or on ice and forage in water. Therefore, neonates initially lack the adaptations to sustain prolonged underwater diving activity. Although the physiological development for breath-holding during diving has been investigated in seal pups, little is known about the concurrent development of behavioral adaptations during lactation. In this study, multisensor data loggers were used to record diving behavior and swimming gaits of pre-weaned Weddell seal (Leptonychotes weddellii) pups. Experiments were conducted in 16 pups at the Syowa Station, Antarctica, from November to December 1999 and 2004. Swimming speeds, dive depths and flipper stroking rates were recorded for each individual for about 24 h. We found that the glide index during ascending was increased with body length, whereas the dominant stroke cycle frequency were not affected by body length, dive depth and descent or ascent phase. All pups had significantly higher stroke rates in descent than in ascent, but there was no difference between swimming speed. As we found a positive relationship between the body length and age, we considered body length as an index of growth. Therefore, we conclude that pups gradually acquire the ability to glide with utilizing positive buoyancy during ascending toward the end of lactation.

Kinematical changes in swimming front Crawl and Breaststroke with the AquaTrainer® snorkel

The aim of the present study was to assess the kinematical changes when swimming maximal bouts in Front Crawl and Breaststroke with the AquaTrainer snorkel. Thirteen male swimmers (7 at Breaststroke and 6 at Front Crawl) of national level performed randomly two maximal bouts of 100-m swims: one bout using the AquaTrainer snorkel (snorkel swim) and another one without the snorkel (free swim). The swims were videotaped in sagittal plane with a pair of cameras providing 2D kinematics evaluation. The following measures were assessed: swimming performance (T100), stroke cycle period (P), stroke rate (SR), stroke length (SL), swimming velocity (v), swimming efficiency as estimated by the stroke index (SI), speed fluctuation (dv) and the mathematical characterisation of dv. T100 was significantly higher when swimming with the snorkel than in free swimming at Breaststroke (Delta = 6.26%) and at Front Crawl (Delta = 4.75%). P, SR and SL, as well as SI and dv did not present significant differences. The main finding of the study was that changes in the swimming velocity imposed by the use of the Aquatrainer do not seem due to changes in general kinematics or swimming efficiency.

Data-processing artefacts in three-dimensional dive path reconstruction from geomagnetic and acceleration data

ABSTRACT: Tri-axis magnetism and acceleration data loggers have recently been used to obtaintime-series headings and, consequently, the 3-dimensional dive paths of aquatic animals. However,problems may arise in the resulting calculation process with multiple parameters. In this study, thedive paths of loggerhead turtles and emperor penguins were reconstructed. For both species, appar-ently unrealistic movements were found. Time-series heading data of turtles showed small regularfluctuations synchronous with stroking. In the dive paths of penguins, infrequent abrupt changes inheading were observed during stroke cycles. These were unlikely to represent true behavioursaccording to observations of underwater behaviour and tri-axis magnetism and acceleration data.Based on the relationship between sampling frequency and frequency of body posture change, wesuggest that (1) the changes in the animals’ posture concurrent with strokes and (2) the mismatchedtreatment (i.e. filtering and non-filtering) of the acceleration and magnetism data caused the arte-facts. These inferences are supported by the results of simulations. For data sets obtained at a givensampling frequency, the error pattern in calculated dive paths is likely to differ depending on the fre-quency and amplitude of body posture changes and in swim speed. In order to avoid misinterpreta-tion, it is necessary to understand the assumptions and inherent problems of the calculation methodsas well as the behavioural characteristics of the study animals.KEY WORDS: 3D dive path · Low-pass filter · Sampling frequency · Stroke activity · Data logger ·Dead-reckoning

Body roll in swimming: A review

In this article, we present a critical review of the swimming literature on body roll, for the purposes of summarizing and highlighting existing knowledge, identifying the gaps and limitations, and stimulating further research. The main research findings can be summarized as follows: swimmers roll their shoulders significantly more than their hips; swimmers increase hip roll but maintain shoulder roll when fatigued; faster swimmers roll their shoulders less than slower swimmers during a 200-m swim; roll asymmetries, temporal differences in shoulder roll and hip roll, and shoulder roll side dominance exist in front crawl swimming, but there is no evidence to suggest that they affect swimming performance; and buoyancy contributes strongly to generating body roll in front crawl swimming. Based on and stimulated by current knowledge, future research should focus on the following areas: calculation of body roll for female swimmers and for backstroke swimming; differences in body roll between breathing and non-breathing cycles; causes of body roll asymmetries and their relation to motor laterality; body roll analysis across a wide range of velocities and swimming distances; exploration of the association between body roll and the magnitude and direction of propulsive/resistive forces developed during the stroke cycle; and the influence of kicking actions on the generation of body roll.

Three‐dimensional analysis of intracycle velocity fluctuations in frontcrawl swimming

The purpose of this study was to determine accurately the magnitude and changes of intra-cycle velocity fluctuation (Vfluc), maximum (Vmax) and minimum velocity (Vmin) of the center of mass during a maximum 200 m frontcrawl swim, and to examine whether they are associated with performance. Performance was indicated by the mean velocity (Vmean) of the stroke cycle (SC) in the swimming direction. The relative Vfluc, Vmax and Vmin were also calculated as a percentage of Vmean, while Vfluc was calculated for all three directions. Eleven male swimmers of national/international level participated in this study and their performance was recorded with four below- and two above-water-synchronized cameras. Four SCs were analyzed for the 200 m swim (one for each 50 m). Anthropometric data were calculated by the elliptical zone method. Vmean generally decreased throughout the test. Vmax and Vmin were positively correlated to performance and were significantly higher in SC1 than in the other SCs. However, the relative Vmax and Vmin values were remarkably consistent during the 200 m and not associated with performance. Despite the noteworthy magnitude of Vfluc in all directions, they were in general not correlated with performance and there were no significant changes during the test.

21101 高速ディーゼル機関におけるバイオ燃料の燃焼及び排ガス特性(OS11 環境に優しいエンジン技術(2),オーガナイズドセッション)

With regard to global wanning, reduction of carbon dioxide (CO_2) emission is a problem of great urgency. The thermal efficiency of a marine diesel engine is high. Therefore it is difficult to reduce CO_2 emission by improvement of the thermal efficiency. For such a reason, it is realistic to restrain the use of fossil fuel by using bio-fuel (raw vegetable oil, waste cooking oil) as a countermeasure against global warming, hi this paper, we studied on the emission characteristics of the high speed, naturally aspirated, 4 stroke cycle diesel engine using gas oil, marine diesel fuel (MDF), raw rapeseed oil, raw palm oil and waste cooking oil. The followings were found: Emission of CO of bio fuels is higher than that of gas oil or MDF. Smoke of bio fuels is lower than that of gas oil or MDF.

Boat acceleration, temporal structure of the stroke cycle, and effectiveness in rowing

The purposes of the study were to explain the double peak in the boat acceleration during the drive phase, to analyse the temporal structure of the stroke cycle, and to find correlations between the temporal structure and the boat type, rower gender, stroke rate, force profile, and effectiveness of rowing. Measurements of the boat acceleration, boat velocity, handle force, oar angle, and velocity of body segments were made in competitive rowing boats using a telemetry system. The accelerations of the whole system and of the rower's centre of mass (CM) were derived and used to define the temporal structure of the stroke cycle. Six microphases were defined during the drive phase, and three microphases were defined during the recovery phase. The relative magnitudes of the accelerations of the boat and of the rower's CM switched twice during the drive phase. During the ‘initial rower's acceleration’ and the ‘rower's acceleration’ microphases, the acceleration of the rower's CM was higher and, during the ‘initial boat acceleration’ and ‘boat acceleration’ microphases, the acceleration of the boat was higher. The presence of the initial boat acceleration microphase is an important indicator of the effectiveness of a rower's technique.

Inter-limb coordination in swimming: Effect of speed and skill level

The aim of this study was to examine the effects of swimming speed and skill level on inter-limb coordination and its intra-cyclic variability. The elbow–knee continuous relative phase (CRP) was used as the order parameter to analyze upper–lower limbs coupling during a complete breaststroke cycle. Twelve recreational and 12 competitive female swimmers swam 25 m at a slow speed and 25 m at maximal speed. Underwater and aerial side views were mixed and genlocked with an underwater frontal view. The angle, angular velocity, and phase were calculated for the knee and elbow by digitizing body marks on the side view. Three cycles were analyzed, filtered, averaged, and normalized in percentage of the total cycle duration. The competitive swimmers showed greater intra-cyclic CRP variability, indicating a combination of intermediate phase and in-phase knee–elbow coupling within a cycle. This characteristic was more marked at slow speed because more time was spent in the glide period of the stroke cycle, with the body completely extended. Conversely, because they spent less time in the glide, the recreational swimmers showed lower intra-cyclic CRP variability (which is mostly in the in-phase coordination mode), resulting in superposition of contradictory actions (propulsion of one limb during the recovery of the other limb).

Does the Hip Reflect the Centre of Mass Swimming Kinematics?

The purpose of this study was to determine the relationship between the hip point and the centre of mass for kinematical parameters (displacement, velocity and acceleration) in the three axes of motion. One complete stroke cycle was analyzed in eight swimmers performing a 25 m front crawl swim test at high intensity. Within-subject correlation coefficients were computed between the centre of mass and both hips, as well as mean of the errors, RMS error and a paired sample t-test. High correlation coefficients were found for the displacement in the horizontal direction (r=1.00 for both hips) and low to moderate correlation coefficients (r=-0.01 to r=0.54) were found for all other studied variables. Moreover, moderate to large RMS errors were observed: (i) between 0.05 and 0.15 for the displacement; (ii) between 0.16 and 0.30 for the velocity and (iii) between 5.28 and 7.86 for the acceleration. Complementarily, RMS errors for the intracyclic velocity variation were between 0.07 and 0.18. Considering the centre of mass and hip values statistical differences were found in velocity in x, acceleration in x and y, and intracyclic velocity variation in y axes. Therefore, results suggest that the hip point does not represent most kinematical parameters of the estimated centre of mass in front crawl swimming.

Details of Insect Wing Design and Deformation Enhance Aerodynamic Function and Flight Efficiency

Insect wings are complex structures that deform dramatically in flight. We analyzed the aerodynamic consequences of wing deformation in locusts using a three-dimensional computational fluid dynamics simulation based on detailed wing kinematics. We validated the simulation against smoke visualizations and digital particle image velocimetry on real locusts. We then used the validated model to explore the effects of wing topography and deformation, first by removing camber while keeping the same time-varying twist distribution, and second by removing camber and spanwise twist. The full-fidelity model achieved greater power economy than the uncambered model, which performed better than the untwisted model, showing that the details of insect wing topography and deformation are important aerodynamically. Such details are likely to be important in engineering applications of flapping flight.

Myths of orthodontic gnathology

D r Beverly McCollum established the Gnathologic Society in 1926. Gnathology is defined as ‘‘the science that treats the biology of the masticatory mechanism as a whole: that is, the morphology, anatomy, histology, physiology, and the therapeutics of the jaws or masticatory system and the teeth as they relate to the health of the whole body, including applicable diagnostic, therapeutic, and rehabilitation procedures.’’ Many gnathologic research endeavors have added much to our knowledge and understanding of the stomatognathic system, particularly those involving chewing (masticatory) kinematics and the early intraoral telemetry studies (to cite only a few). Although originally founded on scientific principles, the application of the valid gnathologic research to clinical practice has moved away from these founding tenets. Modern clinical gnathology (vs university-based gnathologic research) has become, for the most part, a pseudo-science based on mechanistic, perfunctory procedures, and instrumentation. There are many contemporary occlusal institutes that clearly have perverse views on gnathology that are not evidence-based. Dr Lysle Johnston sarcastically stated that ‘‘gnathology is the science of how articulators chew.’’ In the 1970s, Roth formally introduced the classic principles of clinical gnathology to orthodontics (orthodontic gnathology). The notions and considerations of modern orthodontic gnathology are not based on principles of science and do not correspond to contemporary evidence-based thinking. There might not be a unified orthodontic gnathologic view, but it seems that the one established by Roth is by far the most notable.

Intra-cyclic Stroke Parameter Changes Associated With Increased Speed In Competitive Front-crawl Swimming

Studies of stroke parameter relationships in swimming have shown that the basic strategy used by elite swimmers to increase speed is to increase stroke rate (SR) while attempting to maintain stroke length (SL). Recently, it has been shown that non-linear changes in SR and SL occur immediately after a swimmer reaches critical speed. The specific intra-cyclic mechanisms responsible for producing these changes, namely the duration of the propulsive and recovery phases of the stroke cycle, have not been investigated. PURPOSE: To determine temporal changes in the propulsion and recovery time associated with increased SR in front-crawl swimming. METHODS: Eight elite competitive swimmers (6 female, 2 male; 17.9 ± 0.86 yrs) performed a 4 x 200 m interval training set (60 s rest) in a 25 m pool according to target times that were based on a critical speed test (1 = submax. intensity, 2 = max. lactate steady state, 3 = critical speed, 4 = VO2 max.). Velocity, SR, SL, propulsion time and recovery time were recorded for each 25 m length of each 200 m repetition. The data were normalized (1st length %) to compare the relative stroke parameter changes between the 4 x 200s using repeated measures ANOVA. RESULTS: As speed increased, SR increased significantly (p < 0.05) for each repetition (+26.5 ± 7.8% from 1st to last repetition), whereas SL decreased significantly (p < 0.05) for the 3rd and 4th repetitions (-2.6 ± 1.6% & -4.8 ± 2.8%, respectively). In addition, SR increased markedly during the 3rd (critical speed) 200 (+12.0% vs. the previous increase of +3.4%). Changes in SR were associated with significant decreases (p < 0.01) in the propulsion time for each repetition (-25.6 ± 8.1% from the 1st to 4th repetition) as well as the recovery time (p < 0.05) for the 3rd and 4th repetitions (-6.9 ± 4.9% & -13.2 ± 5.7%, respectively). An asymmetric change in the stroke cycle was shown by a significant drop (p < 0.05) in the propulsion/recovery ratio from the 1st to 4th repetition (-9.3 ± 11.2%). CONCLUSION: Progressive speed related increases in SR are associated with simultaneous decreases in the duration of the propulsion and recovery phases of the stroke cycle, such that propulsion time decreases more than recovery time. This suggests that pulling/pushing the arm through the water faster contributes more to the elevation of SR than increasing the tempo of the recovery.