Nat Benjanuvatra

Comparison of buoyancy, passive and net active drag forces between Fastskin™ and standard swimsuits

A cross-sectional comparison between the buoyancy, passive and net active drag force characteristics of full-length, Fastskin swimsuits with that of standard swimsuits was completed with nine Open National level swimmers (5 males and 4 females). Subjects were weighed in a hydrostatic tank and then towed via a mechanical winch on the surface and 0.4 m deep at 1.6, 2.2 and 2.8 m/s. The subjects performed a prone streamlined glide and maximum effort flutter kick at each towing velocity and depth. Hydrostatic weight differences between swimsuit types were not significant (p> 0.05. Fastskin passive drag values were significantly less than normal swimsuits during surface towing at 1.6 and 2.8 m/s: and at 0.4 m deep towing at 1.6, 2.2 and 2.8 m/s. Net active drag force values also were lower for the Fastskin suits when compared with those of normal swimsuits and a significant difference existed for surface towing at all three velocities of 1.6, 2.2 and 2.8 m/s. The full-length, Fastskin swimsuits created less total hydrodynamic resistance than normal swimsuits while providing no additional buoyancy benefits.

Comparison of ground reaction force asymmetry in one- and two-legged countermovement jumps

Abstract Benjanuvatra, N, Lay, BS, Alderson, JA, and Blanksby, BA. Comparison of ground reaction force asymmetry in one- and two-legged countermovement jumps. J Strength Cond Res 27(10): 2700–2707, 2013—This study examined whether ground reaction force (GRF) asymmetry of 2-legged countermovement jumps (CMJ) is related to 1-legged CMJ asymmetry. The GRF asymmetry of a 2-legged CMJ has been suggested as a preferred test to the 1-legged CMJ for functional strength and power deficit assessment. Twenty-eight men and 30 women performed 5 trials each of a 1-legged CMJ with the right limband the left limb, and a 2-legged CMJ. Vertical GRFs were collected from each lower limb using 2 force platforms. Although several GRF variables were calculated, vertical impulse correlated most strongly with jump height in all conditions (p < 0.05), and they were used in subsequent analyses. A moderate correlation was found for impulse asymmetry between the 1- and 2-legged CMJs for women (r = 0.45, p < 0.05), but not for men (r = 0.06, p = 0.76). In contrast, cross-tabulation analyses of subjects presented with the same dominant characteristics in the 1- and 2-legged CMJs revealed poor associations for both men (Freeman-Halton exact p = 0.61) and women (Freeman-Halton exact p = 0.19). Only 11 women recorded the same dominant limb for both 1- and 2-legged CMJs. This suggests that impulse asymmetries found in the 1- and 2-legged CMJ were unrelated. As the 1-legged CMJ relies on the extension forces generated entirely from 1 limb, variations in jump heights and GRF impulses by left and right limbs separately were more indicative of functional strength differences between sides. Hence, it is recommended that the 1-legged CMJ is used when examining functional strength asymmetry in the lower limbs. In contrast, factors causing asymmetry in GRF impulses during 2-legged CMJs are more complicated and require further investigation.

Do footedness and strength asymmetry relate to the dominant stance in swimming track start

Abstract This study explored the relationship between lower limb asymmetry and stance preference in the swimming track start. Track start performances and asymmetry measures were collected from 11 male and 11 female competitive age group swimmers. The track start performance was defined as the time taken to reach the 5-m mark. Asymmetry measures included assessment of footedness using the revised version of the Waterloo Footedness Questionnaire and assessment of performance asymmetry in the one-legged countermovement jump. Participants performed five trials on each side of both the one-legged countermovement jump and the track start, and the best three trials of each were compared. Asymmetry was declared when at least two trials from one side were better than the contralateral side. While the majority of the participants produced better performances using the preferred track start stance, it was not related to footedness or the dominant limb for the one-legged countermovement jump. Further investigation is required to identify factors that predict the lateralised behaviour of the track start, and determine whether changing the stance would provide significant advantage.