Greater Propulsive Forces Research Articles

Load-Velocity Profile and Active Drag in Young Female Swimmers: An Age-Group Comparison.

The present study aimed to establish differences in load-velocity profiling, active drag (AD), and drag coefficient (Cd) between 3 age groups of female swimmers. Thirty-three swimmers (11, 13, or 16y old) were recruited. The individual load-velocity profile was determined for the 4 competitive swimming strokes. The maximal velocity (V0), maximal load (L0), L0 normalized to the body mass, AD, and Cd were compared between the groups. A 2-way analysis of variance and correlation analysis were conducted. Compared with their younger counterparts, 16-year-old swimmers generally had larger V0, L0, and AD, which was particularly evident when comparing them with 11-year-old swimmers (P ≤ .052). The exception was breaststroke, where no differences were observed in L0 and AD and Cd was smaller in the 16-year-old group than the 11-year-old group (P = .03). There was a negative correlation between Cd and V0 for all groups in backstroke (P ≤ .038) and for the 11-year-old group and 13-year-old group in breaststroke (P ≤ .022) and front crawl (P ≤ .010). For the 16-year-old group, large correlations with V0 were observed for L0, L0 normalized to the body mass, and AD (P ≤ .010) in breaststroke and for L0 and AD with V0 in front crawl (P ≤ .042). In butterfly, large negative correlations with V0 were observed in the 13-year-old group for all parameters (P ≤ .027). Greater propulsive force is likely the factor that differentiates the oldest age group from the younger groups, except for breaststroke, where a lower Cd (implying a better technique) is evident in the oldest group.

A distributed control method for flexible robotic fish based on PDE

AbstractAt present, research on flexible robotic fish has become a hot topic. Here, a novel dynamic model of flexible robotic fish is established, and a new control method for flexible robotic fish is proposed. Based on the Hamilton principle, the dynamic model of the flexible robotic fish is established by a partial differential equation, which obtains the relationship between the motion law and the force of the flexible robotic fish. The proposed control method produces the practical motion of flexible robotic fish along with any reference motion of flexible robotic fish, and it is proven that the attitude error is stable in a certain range by using the Lyapunov direct method and simulation. Control parameters are explored to reflect the influence on the control effect. For robotic fish, simulation results indicate that the proposed method can generate more than 10% greater propulsive force than some kinds of traditional control methods and improve the forward propelling efficiency of robotic fish.

Biomechanical Performance Factors in the Track and Field Sprint Start: A Systematic Review.

In athletics sprint events, the block start performance can be fundamental to the outcome of a race. This Systematic Review aims to identify biomechanical factors of critical importance to the block start and subsequent first two steps performance. A systematic search of relevant English-language articles was performed on three scientific databases (PubMed, SPORTDiscus, and Web of Science) to identify peer-reviewed articles published until June 2021. The keywords “Block Start”, “Track and Field”, “Sprint Running”, and “Kinetics and Kinematics” were paired with all possible combinations. Studies reporting biomechanical analysis of the block start and/or first two steps, with track and field sprinters and reporting PB100m were sought for inclusion and analysis. Thirty-six full-text articles were reviewed. Several biomechanical determinants of sprinters have been identified. In the “Set” position, an anthropometry-driven block setting facilitating the hip extension and a rear leg contribution should be encouraged. At the push-off, a rapid extension of both hips and greater force production seems to be important. After block exiting, shorter flight times and greater propulsive forces are the main features of best sprinters. This systematic review emphasizes important findings and recommendations that may be relevant for researchers and coaches. Future research should focus on upper limbs behavior and on the analysis of the training drills used to improve starting performance.

Discriminating features of ground reaction forces in overweight old and young adults during walking using functional principal component analysis

BackgroundLimited attention has been paid to age- or body size-related changes in the ground reaction forces (GRF) during walking despite their strong associations with lower limb injuries and pathology. Research questionDo the features of GRF during walking associate with age or body size? MethodsFifty-four participants were subdivided into four groups according to their age and body size: overweight old (n = 12), non-overweight old (n = 13), overweight young (n = 13), and non-overweight young (n = 16). Participants were asked to walk at their self-selected speeds on level ground with force plates embedded in the center of walkway. Functional principal component analysis (FPCA) was performed to extract major modes of variation and functional principal component scores (FPCs) in three-dimensional GRFs. Analysis of variance models were employed to investigate the effect of age, body size, or their interactions on the FPCs of each component of the GRF, with the adjustment to gait speed. ResultsSignificant age and body size effects were observed in FPC1 across all three-dimensional GRF. Both overweight and older groups showed greater braking force after heel-strike and greater propulsive forces during pre-swing when compared to the non-overweight and younger groups, respectively. The overweight old group displayed greater medial forces during mid-stance and the overweight young group showed prominently larger medial forces during pre-swing, while non-overweight old showed a tendency of flatter medial-lateral GRF waveforms during the entire stance phase. FPC2 revealed that only body size had an effect on three-dimensional GRF with the highest FPC2 scores in the overweight old group. SignificanceThree-dimensional GRF during walking could be altered by the body size and age, which were more pronounced in the overweight and older group. The more dynamic GRF pattern with greater and/or lower peaks could be contributing factors to the increased joint load and injury rates observed in overweight aged individuals.

Mechanisms used to increase peak propulsive force following 12-weeks of gait training in individuals poststroke

Current rehabilitation efforts for individuals poststroke focus on increasing walking speed because it is a predictor of community ambulation and participation. Greater propulsive force is required to increase walking speed. Previous studies have identified that trailing limb angle (TLA) and ankle moment are key factors to increases in propulsive force during gait. However, no studies have determined the relative contribution of these two factors to increase propulsive force following intervention. The purpose of this study was to quantify the relative contribution of ankle moment and TLA to increases in propulsive force following 12-weeks of gait training for individuals poststroke. Forty-five participants were assigned to 1 of 3 training groups: training at self-selected speeds (SS), at fastest comfortable speeds (Fast), and Fast with functional electrical stimulation (FastFES). For participants who gained paretic propulsive force following training, a biomechanical-based model previously developed for individuals poststroke was used to calculate the relative contributions of ankle moment and TLA. A two-way, mixed-model design, analysis of covariance adjusted for baseline walking speed was performed to analyze changes in TLA and ankle moment across groups. The model showed that TLA was the major contributor to increases in propulsive force following training. Although the paretic TLA increased from pre-training to post-training, no differences were observed between groups. In contrast, increases in paretic ankle moment were observed only in the FastFES group. Our findings suggested that specific targeting may be needed to increase ankle moment.

Do male secondary sexual characters correlate with testis size and sperm length in the small hairy maggot blowfly?

The phenotype-linked fertility hypothesis proposes that secondary sexual characters (SSCs) advertise a male's fertility to prospective mates. However, findings from empirical studies attempting to test this hypothesis are often ambivalent or even contradictory, and few studies have simultaneously evaluated how both morphological and behavioural SSCs relate to ejaculate characteristics. Males of the small hairy maggot blowfly, Chrysomya varipes, possess conspicuous foreleg ornaments and display highly stereotyped courtship behaviour. These traits are favoured by females during pre-copulatory mate choice, but it remains unknown whether they correlate with post-copulatory traits expected to influence male fertility. The aim of this study was to investigate whether male courtship and ornamentation correlate with testis size and sperm length in C. varipes. We found that males investing more in courtship had bigger testes, and males with more extensive foreleg ornamentation released sperm with longer tails. Based on the assumption that larger testes enable males to produce more sperm, and that sperm with longer tails have greater propulsive force, our findings suggest that more vigorous and more ornamented males may be more fertile. These findings lend support to the phenotype-linked fertility hypothesis. However, a complete test of this hypothesis will require evaluating whether testis size and sperm length influence male fertilisation ability, as well as female fecundity and/or fertility.

Effects of time-varying camber deformation on flapping foil propulsion and power extraction

Research into the effectiveness of flapping foil propulsion and power extraction systems has typically focused on the kinematic parameters defining the pitching and plunging motion, and used simple basic rigid airfoil shapes. In this paper, the effects of a time-varying deformable foil shape on the power extraction and propulsive efficiency of flapping foil systems are studied. Two-dimensional Navier–Stokes solutions using the commercial flow solver Fluent are performed with a deformable mesh to alter the camber of the foil during the flapping cycle. All simulations are assumed to be fully laminar, with a free stream Reynolds number of Re=1100 for the power extraction cases and Re=20000 for the propulsion cases, chosen to match representative cases in the existing literature. The shape of the foil is constructed by deforming the camber line via a circular arc centered at the mid-span, with the magnitude of the circular arc deformation varying sinusoidally in time. The phase angle of this sinusoidal camber variation is the primary independent variable, resulting in a broad range of foil interactions with the shed vortex flow fields as the shape varies over the flapping cycle. This camber deformation is superimposed on kinematically constrained sinusoidal motions for both the power extraction and propulsion regimes, as well as semi-passive motions for power extraction. The results show that the efficiency of these systems can be increased by judiciously deforming the foil shape to interact with the resulting leading and trailing edge vortex structures. For all cases, the power required to deform the foil surface is included in the overall efficiency calculation, and for several cases is a significant factor in the final efficiency. The performance of the power extraction cases is primarily determined by the interactions between the shed LEV and the foil horizontal surface during the plunging stroke and the interaction of the trailing edge as it passes through the vortex during the pitch reversal portion of the cycle. The semi-passive cases for power extraction are also strongly affected by the vortex interactions, and the resulting forces and moments can significantly alter the flapping frequency, further increasing their impact. The propulsion cases show a high dependence on the interaction of the leading edge vortex with the foil curvature to provide high leading suction and greater propulsive forces. For all three regimes, regions of phase angle where the efficiency is increased by the deformation of the foil are shown.

Real-time feedback enhances forward propulsion during walking in old adults

BackgroundReduced propulsive function during the push-off phase of walking plays a central role in the deterioration of walking ability with age. We used real-time propulsive feedback to test the hypothesis that old adults have an underutilized propulsive reserve available during walking. Methods8 old adults (mean [SD], age: 72.1 [3.9] years) and 11 young adults (age: 21.0 [1.5] years) participated. For our primary aim, old subjects walked: 1) normally, 2) with visual feedback of their peak propulsive ground reaction forces, and 3) with visual feedback of their medial gastrocnemius electromyographic activity during push-off. We asked those subjects to match a target set to 20% and 40% greater propulsive force or push-off muscle activity than normal walking. We tested young subjects walking normally only to provide reference ground reaction force values. FindingsWalking normally, old adults exerted 12.5% smaller peak propulsive forces than young adults (P<0.01). However, old adults significantly increased their propulsive forces and push-off muscle activities when we provided propulsive feedback. Most notably, force feedback elicited propulsive forces that were equal to or 10.5% greater than those of young adults (+20% target, P=0.87; +40% target, P=0.02). With electromyographic feedback, old adults significantly increased their push-off muscle activities but without increasing their propulsive forces. InterpretationOld adults with propulsive deficits have a considerable and underutilized propulsive reserve available during level walking. Further, real-time propulsive feedback represents a promising therapeutic strategy to improve the forward propulsion of old adults and thus maintain their walking ability and independence.

Simple Change in Initial Standing Position Enhances the Initiation of Gait

Older adults and individuals with Parkinson's disease exhibit impaired gait initiation performance with less effective anticipatory postural adjustments (APA) and less dynamic stepping characteristics. These observations may reflect impaired interactions between the postural and locomotor components of this task. The purpose of this study was to evaluate the effectiveness of altering the stance position of the initial swing limb on improving APA characteristics and stepping performance. Three groups (healthy young adults, individuals with Parkinson's disease, and age-matched older adults) of 12 participants initiated gait from three initial stance conditions: normal, backward displaced swing limb, and forward displaced swing limb. Ground reaction forces and whole body kinematics were recorded to characterize the APA and step parameters. Initiating gait from the back condition produced more forceful weight shifting (P < 0.001), greater propulsive forces (P < 0.001), and faster center-of-mass velocities throughout the stepping phases (P < 0.05). Translating the swing limb 0.5-ft-length backward seems to enhance the interaction between posture and locomotion, which may have therapeutic potential for improving gait initiation performance.

Body position determines propulsive forces in accelerated running

Rapid accelerations during running are crucial for the performance in a lot of sports. While high propulsive forces are beneficial to forward acceleration, vertical forces have to be small to attain high stride frequencies. However, propulsive and vertical force components cannot be altered independently, because the resultant force vector affects the angular momentum of the body. Therefore we hypothesized that propulsive forces in accelerated running mainly depend on body position regardless of performance level. In our cross-sectional study 28 male and 13 female physical education students performed submaximal and maximal accelerations. Ground reaction forces and whole body kinematics were recorded. Higher accelerations were generated by lower, but more forward oriented forces. The orientation of the maximum force vector strongly correlated with the forward lean of the body at toe-off ( r = 0.93 , p ≤ 0.001 ) . All subjects demonstrated similar propulsive forces at equal body positions. This indicates an external constraint of propulsive force application by the mechanical requirement of running to maintain a stable body posture. Faster subjects utilized a more posterior foot plant or a longer ground contact time. Both strategies facilitated greater forward leans of the body which finally resulted in greater propulsive forces. Consequently, maximizing forward propulsion requires optimal, not maximal force application.