Development Of Functional Asymmetry Research Articles

Lower-Extremity Bilateral Differences During Step-Close and No-Step Countermovement Jumps With Concern for Gender

The goals of this investigation were to characterize gender differences in step-close (SC) and no-step (NS) countermovement jumps, examine biomechanical differences of the lead leg (LL) and trail leg (TL) during the SC jump, contrast the LL and TL of the SC to those of the NS jump, and determine whether bilateral asymmetries of the SC jump transfer to NS jump performance. The SC jump differs from the NS jump by a lead-in step that is continuous with the ensuing countermovement. Recreationally competitive volleyball players (12 men and 12 women) volunteered for the study. Three maximal-effort attempts in each condition were analyzed. Ground reaction forces were measured with force platforms and lower-extremity kinematics with optical capture. Ground reaction force as well as anatomical flexion and extension plane joint angle, moment, and power maximum (or minimum) and average values during the propulsion phase were analyzed with significance assessed at p < 0.05. Differences existed between the men and women in anthropometrics and jump height, as well as in many of the joint angles and body weight-normalized kinetic parameters, suggesting that women would benefit from increased strength and power at the ankle, knee, and hip. Differences also existed in many of the parameters between the LL and TL of the SC jump. Subjects jumped higher in the SC condition with greater demands placed on the LL, with the TL often acting similarly to its behavior in the NS condition. A few asymmetries of the LL and TL in the SC jump at the ankle and knee were also present in the NS jump. Strength and conditioning programs should include activities, such as plyometric jumps, that incorporate a step-close technique to optimize the development of this jump style. To minimize the development of functional asymmetries, the LL should be alternated by sets or repetitions.

Early experience influences the development of bilateral asymmetry in a lobster motoneuron

The development of functional asymmetry between a pair of homologous motoneurons of the claw closer muscles in lobsters, Homarus americanus, was studied. In juvenile lobsters, 3–5 years old, where the paired claws are highly specialized into a major (crusher) and minor (cutter) type, the fast closer excitor (FCE) motoneuron fired longer bursts of spikes in the crusher claw compared to those in its cutter counterpart. The intraburst impulse frequency was greater for the cutter FCE and its neuromuscular synapses showed greater facilitation at these high impulse frequencies compared to that of the crusher claw. However, such asymmetry in firing patterns and synaptic facilitation was absent in lobsters raised without a substrate and having paired cutter claws. In the earliest juvenile stage, synaptic facilitation was similar between the paired claws and then developed in either an asymmetric or symmetric manner depending on whether the lobsters experienced a substrate or not. In a substrate-free environment asymmetry could be produced by exercising one of the claws during development, implicating bilateral differences in the reflexive activity of the claws as a control mechanism.

On the phylogeny of asymmetry and spatial discrimination

We define and develop the fundamental experimental conditions required for an organism to demonstrate the capacity for spatial discrimination. It is then shown that concomitant with evolutionary progression in organisms, there is a corresponding increase in the dimensions of functional asymmetry, and in the quantity and dimensionality of spatial discrimination. It is also shown that the mismatch in asymmetry between the human body form and functional mechanism, and a demonstrated weakness in left-right discrimination, implies that the human organism is in transition between archetypal stages of phylogeny. Implications for the phenomena of mirror-image reversal and left-right confusion are discussed. It is further argued that the development of functional asymmetry is an inherent principle of evolution.