Relation between Postural Stability and Plantar Flexors Muscle Volume in Young Males

Effects of Occasional and Habitual Wearing of High-Heeled Shoes on Static Balance in Young Women

The purpose of this study was to examine the effects of occasional and habitual wearing of high-heeled shoes on static balance in young women. Groups of habitual high-heel wearers and non-wearers (n = 7 in both groups) were asked to stand quietly on a force platform without shoes (WS condition) or with high heels (heel area 1 cm², heel height 7 cm) (HH condition). During the trials, the center-of-pressure (CoP) position in the anterior-posterior direction was measured, and its root mean square (as a measure of postural sway magnitude, CoP_RMS) and mean velocity (as a measure of regulatory activity, CoP_MV) were calculated. To further examine the effect of high-heel wearing on the temporal aspects of slow and fast processes in static balance, the CoP sway was decomposed into low- (below 0.5 Hz) and high- (above 0.5 Hz) frequency components, and then spectral analysis was performed. Results showed that the CoP_RMS was not significantly different between the groups or between the shoe conditions, indicating that wearing high heels with a heel height of 7 cm did not increase the magnitude of postural sway, irrespective of high-heel experience. The CoP_MV was significantly larger in the HH condition than in the WS condition, whereas it was not significantly different between the groups. This result indicates that wearing high heels increased the amount of regulatory activity in both habitual wearers and non-wearers. The spectral analysis further showed that habitual high-heel wearers showed significantly decreased rate of regulatory activity than non-wearers, both while standing with and without high heels. These results suggest that use-dependent changes in static balance control are evident in both high-heeled and without shoes conditions.

Muscle size-strength relationship including ultrasonographic echo intensity and voluntary activation level of a muscle group

This study aimed to investigate the relationship between muscle volume (MV) and joint torque for the plantar flexors (PF) in 40 young (20 men and 20 women) and 33 elderly (19 men and 14 women) individuals in consideration of the voluntary activation (VA) of PF and ratio of intramuscular adipose tissue within PF assessed by ultrasonographic echo intensity (EI). MV was estimated from the thickness of PF on ultrasonography and the lower leg length using a prediction equation previously reported. The maximal voluntary contraction torque of isometric plantar flexion was measured as TQ_MVC. VA (%) was assessed using the twitch interpolation technique, and maximal joint torque calculated by TQ_MVC/VA × 100 was adopted as TQ_100%. The correlation coefficients between MV and TQ_MVC (r = 0.518) and between MV and TQ_100% (r = 0.602) were both significant, with the latter being significantly higher than the former. When a stepwise multiple regression analysis using MV and EI as independent variables and TQ_100% as the dependent variable was performed, MV (β = 0.554) and EI (β = -0.203) were both selected as significant contributors for estimating TQ_100%. Additionally, the residual errors of TQ_100% using the multiple regression equation (independent variables: MV and EI; 18.6 ± 14.4 Nm) were significantly lower than those using the simple regression equation (independent variable: MV; 36.6 ± 28.0 Nm). These results suggest that the consideration of VA and EI with muscle size results in a closer muscle size-strength relationship than previously achieved.

Sequencing Effects of Balance and Plyometric Training on Physical Performance in Youth Soccer Athletes

Hammami, R, Granacher, U, Makhlouf, I, Behm, DG, and Chaouachi, A. Sequencing effects of balance and plyometric training on physical performance in youth soccer athletes. J Strength Cond Res 30(12): 3278-3289, 2016-Balance training may have a preconditioning effect on subsequent power training with youth. There are no studies examining whether the sequencing of balance and plyometric training has additional training benefits. The objective was to examine the effect of sequencing balance and plyometric training on the performance of 12- to 13-year-old athletes. Twenty-four young elite soccer players trained twice per week for 8 weeks either with an initial 4 weeks of balance training followed by 4 weeks of plyometric training (BPT) or 4 weeks of plyometric training proceeded by 4 weeks of balance training (PBT). Testing was conducted pre- and posttraining and included medicine ball throw; horizontal and vertical jumps; reactive strength; leg stiffness; agility; 10-, 20-, and 30-m sprints; Standing Stork balance test; and Y-Balance test. Results indicated that BPT provided significantly greater improvements with reactive strength index, absolute and relative leg stiffness, triple hop test, and a trend for the Y-Balance test (p = 0.054) compared with PBT. Although all other measures had similar changes for both groups, the average relative improvement for the BPT was 22.4% (d = 1.5) vs. 15.0% (d = 1.1) for the PBT. BPT effect sizes were greater with 8 of 13 measures. In conclusion, although either sequence of BPT or PBT improved jumping, hopping, sprint acceleration, and Standing Stork and Y-Balance, BPT initiated greater training improvements in reactive strength index, absolute and relative leg stiffness, triple hop test, and the Y-Balance test. BPT may provide either similar or superior performance enhancements compared with PBT.

Age-Related Differences in Muscle Shear Moduli in the Lower Extremity

This study investigated the age-related differences in shear moduli of the rectus femoris muscle (RF), the lateral head of the gastrocnemius muscle (LG) and the soleus muscle (SOL) using shear wave ultrasound elastography. Thirty-one young individuals and 49 elderly individuals volunteered for this study. The shear modulus of RF was determined at 50% of the thigh length, and those of LG and SOL were determined at 30% of the lower leg length. RF and LG shear moduli were significantly higher in young individuals than in elderly individuals, but there was no age-related difference in SOL shear modulus. From the standpoint of an index reflecting muscle mechanical properties, it is suggested that the lower muscle shear moduli of RF and LG are the reason for the decreased explosive muscle strength in the lower extremity and the increased risk of falls for elderly individuals.