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Background: The hyperbolic torque-duration curve depicts critical torque (CT) and W prime (W′), with the curve's asymptote representing CT as the boundary between heavy- and severe-intensity domains. W′, the curvature constant, indicates cumulative work beyond CT. This study investigated age-related reductions in W′, CT, and gait speed, and whether W′ and CT predict gait speed independently of muscle torque. Methods: three groups (adults, middle-aged, older) totaling 131 women were studied. W′ and CT were determined using 60 maximal isometric voluntary contractions of knee extensors. The fast gait speed was calculated in walking tests at 10 m, 400 m, and six minutes (6 MWT). Results: gait speed decreased (p < 0.05) with age, as did W′ and CT. Both W′ and CT correlated positively with gait speed at different distances (10 m, 400 m, 6 MWT). Adjusted for maximum muscle torque, only W′ maintained a positive association (p < 0.05) with all gait speed tests (10 m: β = 0.201, SE = 0.086; 400 m: β = 0.262, SE = 0.085; 6 MWT: β = 0.187, SE = 0.086). Conclusions: aging led to declines in W′, CT, and gait speed. W′, not CT, remained a significant predictor of gait speed, indicating its importance for older women's mobility. [ABSTRACT FROM AUTHOR]

Problem statement: Center-of-mass (CoM) analysis of takeoff speeds in jumps preceded by run-ups (such as volleyball spike jumps), using a force platform, requires prior information on CoM speed at touchdown. This, however, can only be evaluated through kinematic methods (KIN). To this end, KINs must be evaluated for accuracy and concurrent validity. An example is a double integration of force (DIF) method for jumps in which the initial CoM speed is zero in countermovement jumps with and without arm swing. Aim: To evaluate the reliability and accuracy of three methods for calculating takeoff velocity and their concurrent validity during vertical jumps. Material and methods: Fifteen female volleyball players performed 10 vertical countermovement jumps (CMJ), and 10 countermovement jumps with arm swing (CMJa). Two methods were used to measure CoM takeoff velocity: (1) numerical DIF and (2) full-body 3D model (KIN). The latter was implemented using two minimalist marker setups between the right anterior and posterior iliac spines (RASI) and (RPSI), respectively. Results: KIN and DIF were more reliable in all jumps (ICC: 0.93-0.96) than minimalistic methods (ICC: 0.87-0.93). The standard error of measurement was lower in KIN and DIF (SEM mean= 1.9) than in minimalistic methods (SEM mean= 3.1). KIN was valid regarding DIF in CMJ, with bias equal to zero, no proportional bias (p=0.514), and narrow limits of agreement (LoA) (0.1 m/s). KIN was also valid in CMJa (bias = 0.01 m/s), with no proportional bias (p=0.244), LoA =0.21 m/s. The minimalist RPSI method was valid only in CMJ (bias= -0.12m/s), with no proportional bias (p=0.27), LoA=0.31 m/s. The RASI method showed a bias difference compared to DIF (p=0.001) and was not valid with either jump types. A large displacement of the pelvis may lead to increased errors using a single marker. Conclusions: All procedures were reliable and accurate, but minimalist marker setups decreased the values. The KIN method using a Plug-in-Gait model was valid in both jumps. Minimalist marker setups with a single marker at RPSI may be applied only in CMJ. Minimalist marker setups with a single marker may also lead to controversial results depending on the pelvis's jump type and marker position. These possibilities should be considered to calculate takeoff and touchdown velocities during volleyball spike jumps. [ABSTRACT FROM AUTHOR]

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The current investigation aimed to find the difference between right and left lower limb strength of quadriceps and hamstring muscles and describe young futsal players' explosive strength and anaerobic power. The study comprised 12 university male U-20 futsal players (74.5 ± 9.7 kg;173.2 ± 7.2 cm; 18.7 ± 1.2 yrs.). Isometric strength was measured using an isometric dynamometer, lower limb explosive strength was assessed through the Countermovement Jump and anaerobic power was estimated with the Wingate test. Initially, results were displayed through descriptive statistics. Magnitude-based inference with respective Confidence Intervals (CI=90%) and effect size were used to compare inter-lower limb strength. No substantial differences were found between right and left lower limb, to knee extension and flexion. Team's explosive strength and anaerobic power were 36.7 ± 7 cm and 998.3 ± 125.9 W, respectively. These findings suggest that young futsal players' performance may be less affected due to inter-lower limb asymmetries. [ABSTRACT FROM AUTHOR]

BACKGROUND AND OBJECTIVE: Muscle strength imbalance can be an important factor in hamstrings muscle strain. The main purpose of this study was to investigate the effects of downhill running on hamstrings/quadriceps torque (H/Qtorque) and the electromechanical delay (H/QEMD) ratios. METHODS: Fifteen active male individuals performed two maximal voluntary isometric contractions of the knee extensors and knee flexors, from which the maximal muscle torque, EMD and H/Qtorque and H/QEMD ratios were extracted. Thereafter, the participants performed a 30-minute downhill run (−16%) at 70% VO2max. Dependent variables were assessed immediately before, immediately following and 48 hours after the effort. RESULTS: Maximal isometric torque decreased significantly immediately after the downhill run for both the extensors (pre: 271.8 ±45.9 N•m; post: 235.5 ± 55.7 N•m) and flexors (pre: 112.2 ±26.3 N•m; post: 97.7 ±27.2 N•m). No significant difference was identified over time for the EMD of the vastus lateralis and biceps femoris muscles. The H/Qtorque and H/QEMD ratios were not influenced by the downhill run. CONCLUSION: We have demonstrated that moderate intensity and volume downhill run does not impair knee joint stability at early (H/QEMD) and late phases (H/Qtorque) of quadriceps/hamstrings contraction. [ABSTRACT FROM AUTHOR]

Background: The rest interval between sets can affect the responses to resistance training. Thus, the purpose of this study was to compare the effects of different rest intervals (RI) on volume, density, and rating of perceived exertion (RPE) when adopting a crescent pyramid (CP) system., Methods: Twenty young women (21.1±2.6 years, 1.59±0.06 m, 58.5±9.3 kg) participated in this study. All participants performed three experimental sessions of the leg press exercise in 5 sets until voluntary muscular failure at 60%, 65%, 70%, 75%, and 80% of one-repetition maximum (1RM). A randomized and crossover design was used so that in each session one of three RI (RI-1 = 1 min, RI-2 = 2 min, and RI-3 = 3 min) was tested., Results: The participants performed a significantly larger volume in the RI-3 (12820±3134 kg) when compared to RI-1 (10367±3053 kg) condition (P<0.05). The volume did not differ between RI-2 and RI-3 (P>0.05). The density was higher (P<0.05) in RI-1 (43.1±12.7 kg/s) when compared RI-2 (25.6±5.8 kg/s) and RI-3 (17.7±4.3 kg/s). The RI-2 presented higher density compared to RI-3 condition (P<0.05). The RPE was not different between the three conditions (P>0.05)., Conclusions: The use of 2 minutes of rest between sets allowed the performance of a high volume-load and density of the session in young women. In addition, the three experimental sessions provided a high perception of effort.

The aim of this study was to evaluate the impact of creatine supplementation (CS) on renal function in young, healthy, and active subjects. We used a randomized, double-blind, placebo-controlled clinical trial as the study design. Thirty-six healthy male university students were recruited and divided into three groups: group placebo, group G3 (3 g/day of CS), and group G5 (5 g/day of CS). To assess renal function, new kidney biomarkers, kidney injury molecule-1 (KIM-1) and monocyte chemoattractant protein-1 (MCP-1), were quantified. Serum albumin, serum creatinine, serum urea, estimated glomerular filtration rate (eGFR), proteinuria, and albuminuria were also measured. All groups were evaluated at two times: prior CS or placebo (pre) and after 35 days on CS or placebo (post). After 35 days of intervention, all characteristics were maintained without significant difference ( P  > 0.05) between the groups, including serum creatinine, eGFR, and more sensitive kidney biomarker concentrations (KIM-1 and MCP-1). The paired analysis showed that the supplemented groups (G3 and 5G) had increased serum creatinine and decreased eGFR levels ( P  < 0.05). However, the values were still within the normal reference range. In conclusion, the results of renal function evaluation did not show any difference between the evaluated groups. Increased serum creatinine and decreased eGFR levels in CS groups can be explained by increased creatine stores and metabolism, since creatinine is a by-product of creatine metabolism. These findings indicate that the use of CS at doses of 3 g and 5 g/day for a short period (35 days) is safe and did not impair the kidneys or renal function in young healthy subjects., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)