Validity of the bench press one-repetition maximum test predicted through individualized load-velocity relationship using different repetition criteria and minimal velocity thresholds

BACKGROUND: More practical and less fatiguing strategies have been developed to accurately predict the one-repetition maximum (1RM). OBJETIVE: To compare the accuracy of the estimation of the free-weight bench press 1RM between six velocity-based 1RM prediction methods. METHODS: Sixteen men performed an incremental loading test until 1RM on two separate occasions. The first session served to determine the minimal velocity threshold (MVT). The second session was used to determine the validity of the six 1RM prediction methods based on 2 repetition criteria (fastest or average velocity) and 3 MVTs (general MVT of 0.17 m⋅s-1, individual MVT of the preliminary session, and individual MVT of the validity session). Five loads (≈ 2540557085% of 1RM) were used to assess the individualized load-velocity relationships. RESULTS: The absolute difference between the actual and predicted 1RM were low (range = 2.7–3.7%) and did not reveal a significant main effect for repetition criterion (P= 0.402), MVT (P= 0.173) or their two-way interaction (P= 0.354). Furthermore, all 1RM prediction methods accurately estimated bench press 1RM (P⩾ 0.556; ES ⩽ 0.02; r⩾ 0.99). CONCLUSIONS: The individualized load-velocity relationship provides an accurate prediction of the 1RM during the free-weight bench press exercise, while the repetition criteria and MVT do not appear to meaningfully affect the prediction accuracy.

Numerical Analysis of the Influence of Porosity and Pore Geometry on Functionality of Scaffolds Designated for Orthopedic Regenerative Medicine

Background: Scaffolds are vital for orthopedic regenerative medicine. Therefore, comprehensive studies evaluating their functionality with consideration of variable parameters are needed. The research aim was to evaluate pore geometry and scaffold porosity influence on first, cell culture efficiency in a perfusion bioreactor and second, osteogenic cell diffusion after its implantation. Methods: For the studies, five pore geometries were selected (triangular prism with a rounded and a flat profile, cube, octagonal prism, sphere) and seven porosities (up to 80%), on the basis of which 70 models were created for finite element analyses. First, scaffolds were placed inside a flow channel to estimate growth medium velocity and wall shear stress. Secondly, scaffolds were placed in a bone to evaluate osteogenic cell diffusion. Results: In terms of fluid minimal velocity (0.005 m/s) and maximal wall shear stress (100 mPa), only cubic and octagonal pores with 30% porosity and spherical pores with 20% porosity fulfilled the requirements. Spherical pores had the highest osteogenic cell diffusion efficiency for porosities up to 30%. For higher porosities, the octagonal prism’s pores gave the best results up to 80%, where no differences were noted. Conclusions: The data obtained allows for the appropriate selection of pore geometry and scaffold porosity for orthopedic regenerative medicine.

Abstract 14595: The Clinical Impact of Portal Vein Pulsatility on the Prognosis of Hospitalized Acute Heart Failure Patients

Introduction: Heart failure (HF) especially right-heart failure causes hepatic portal system congestion. The Portal vein (PV) pulsatility can be influenced by right atrial pressure (RAP). However, the association between PV pulsatility and the condition of HF remains unclear. Hypothesis: In this study, we aim to evaluate usefulness of PV pulsatility as a prognostic marker as well as a therapeutic indicator for hospitalized acute HF patients. Methods: We enrolled 54 patients with acute HF and 17 patients without HF served as controls. PV flow velocity was measured by ultrasonography at admission and discharge phase. PV pulsatility ratio (PVPR) was calculated by dividing minimal velocity by peak velocity. The primary endpoint for prognostic analysis was cardiac death and unexpected re-hospitalization for recurrent HF. The observation period was one year from first hospitalization for HF. Results: On admission, PVPR was significantly higher in controls compared to acute HF patients (0.91±0.08 vs. 0.71±0.04, p&lt0.01).PVPR did not change during the hospitalization in controls (admission 0.91±0.08 vs discharge 0.93±0.06, p=0.31). However, in acute HF patients, PVPR was significantly elevated after the improvement of HF (admission 0.71±0.04 vs discharge 0.82±0.02, p&lt0.05) due to the increase in minimal velocity (admission 12.6±4.5 cm/s vs. discharge 14.6±4.6 cm/sec, p&lt0.05), indicating the decrease in RAP. To elucidate the association between PVPR and primary endpoint, the patients were divided into three groups according to the tertile of PVPR at discharge (PVPR-Q1:0.92&ltPVPR&lt1, PVPR-Q2: 0.73&ltPVPR&lt0.92, PVPR-Q3:PVPR&lt0.73). Kaplan-Meier analysis found that the patients with higher PV pulsatility at discharge had significantly higher event rate among the groups (Figure). Conclusions: PVPR at discharge would reflect the condition of HF. It also can be a novel prognostic marker for hospitalized acute HF patients.

Reliability of the velocity achieved during the last repetition of sets to failure and its association with the velocity of the 1-repetition maximum

Background This study aimed to determine the reliability of the velocity achieved during the last repetition of sets to failure (Vlast) and the association of Vlast with the velocity of the 1-repetition maximum (V1RM) during the paused and touch-and-go bench press (BP) exercises performed in a Smith machine. Methods A total of 96 healthy men participated in this study that consisted of two testing sessions. A single BP variant (paused BP or touch-and-go BP) was evaluated on each session in a randomized order. Each session consisted of an incremental loading test until reaching the 1RM, followed by two sets of repetitions to failure against a load ranging from 75% to 90% of 1RM. Results The reliability of Vlast was unacceptable for both BP variants (CV > 18.3%, ICC < 0.60). The correlations between V1RM and Vlast were small for the paused BP (r = 0.18) and moderate for the touch-and-go BP (r = 0.37). Conclusions Although these results suggest that Vlast could be a better indicator of the minimal velocity threshold than V1RM, the low reliability of Vlast and the similar values of Vlast for both BP variants suggest that a standard V1RM should be used to estimate the 1RM from the individualized load-velocity relationship.

Bench Press 1-Repetition Maximum Estimation Through the Individualized Load–Velocity Relationship: Comparison of Different Regression Models and Minimal Velocity Thresholds

Purpose: To compare the accuracy of nine 1-repetition maximum (1RM) prediction methods during the paused and touch-and-go bench press exercises performed in a Smith machine. Method: A total of 86 men performed 2 identical sessions (incremental loading test until reaching the 1RM followed by a set to failure) in a randomized order during the paused and touch-and-go bench press exercises. Individualized load–velocity relationships were modeled by linear and polynomial regression models considering 4 loads (45%–60%–75%–90% of 1RM) (multiple-point methods) and considering only 2 loads (45%–90% of 1RM) by a linear regression (2-point method). Three minimal velocity thresholds were used: the general velocity of 0.17 m·s−1 (general velocity of the 1RM [V1RM]), the velocity obtained when lifting the 1RM load (individual V1RM), and the velocity obtained during the last repetition of a set to failure. Results: The 1RM prediction methods were generally valid (range: r = .96–.99, standard error of the estimate = 2.8–4.9 kg or 4.6%–8.0% of 1RM). The multiple-point linear method (2.79 [2.29] kg) was more precise than the multiple-point polynomial method (3.54 [3.31] kg; P = .013), but no significant differences were observed when compared with the 2-point method (3.09 [2.66] kg, P = .136). The velocity of the last repetition of a set to failure (3.47 [2.97] kg) was significantly less precise than the individual V1RM (2.91 [2.75] kg, P = .009) and general V1RM (3.00 [2.65] kg, P = .010). Conclusions: Linear regression models and a general minimal velocity threshold of 0.17 m·s−1 should be recommended to obtain a quick and precise estimation of the 1RM during the bench press exercise performed in a Smith machine.

Minimal velocity surface in the restricted circular Three-Body-Problem

In the framework of the restricted circular Three-Body-Problem, the concept of the minimum velocity surface S is introduced, which is a modification of the zero-velocity surface (Hill surface). The existence of Hill surface requires occurrence of the Jacobi integral. The minimum velocity surface, other than the Jacobi integral, requires conservation of the sector velocity of a zero-mass body in the projection on the plane of the main bodies motion. In other words, there must exist one of the three angular momentum integrals. It is shown that this integral exists for a dynamic system obtained after a single averaging of the original system by longitude of the main bodies. Properties of S are investigated. Here is the most significant. The set of possible motions of the zero-mass body bounded by the surface S is compact. As an example the surfaces S for four small moons of Pluto are considered in the framework of the averaged problem Pluto — Charon — small satellite. In all four cases, S represents a topological torus with small cross section, having a circumference in the plane of motion of the main bodies as the center line.

NUMERICAL ESTIMATION OF SHAPED CHARGES EFFICIENCY

The paper shows the estimations of maximal penetration depths of shaped charge jets in a steel armour as a function of stand-off distance to the liner base. The data – in-stantaneous coordinates of positions, masses, and velocities of jet elements were received as results of numerical calculations for selected examples of designs of shaped charges. It was shown that the crater’s depth is a function of acceptable maximal extension of jet elements and their minimal velocity. The results were compared with experimental data.

Impact of the reduced speed of light approximation on ionization front velocities in cosmological simulations of the epoch of reionization

Context. Coupled radiative-hydrodynamics simulations of the epoch of reionization aim to reproduce the propagation of ionization fronts during the transition before the overlap of HII regions. Many of these simulations use moment-based methods to track radiative transfer processes using explicit solvers and are therefore subject to strict stability conditions regarding the speed of light, which implies a great computational cost. The cost can be reduced by assuming a reduced speed of light, and this approximation is now widely used to produce large-scale simulations of reionization. Aims. We measure how ionization fronts propagate in simulations of the epoch of reionization. In particular, we want to distinguish between the different stages of the fronts’ progression into the intergalactic medium. We also investigate how these stages and their properties are impacted by the choice of a reduced speed of light. Methods. We introduce a new method for estimating and comparing the ionization front speeds based on maps of the reionization redshifts. We applied it to a set of cosmological simulations of the reionization using a set of reduced speeds of light, and measured the evolution of the ionization front speeds during the reionization process. We only considered models where the reionization is driven by the sources created within the simulations, without potential contributions of an external homogeneous ionizing background. Results. We find that ionization fronts progress via a two-stage process, the first stage at low velocity as the fronts emerge from high density regions and a second later stage just before the overlap, during which front speeds increase close to the speed of light. For example, using a set of small 8 Mpc h−3 simulations, we find that a minimal velocity of 0.3c is able to model these two stages in this specific context without significant impact. Values as low as 0.05c can model the first low velocity stage, but limit the acceleration at later times. Lower values modify the distribution of front speeds at all times. Using another set of simulations with larger 64 Mpc h−3 volumes that better account for distant sources, we find that reduced speed of light has a greater impact on reionization times and front speeds in underdense regions that are reionized at late times and swept by radiation produced by distant sources. Conversely, the same quantities measured in dense regions with slow fronts are less sensitive to c∼ values. While the discrepancies introduced by reduced speed of light could be reduced by the inclusion of an additional UV background, we expect these conclusions to be robust in the case of simulations with reionizations driven by inner sources.

Effect of Descent Velocity upon Muscle Activation and Performance in Two-Legged Free Weight Back Squats

Background: The aim of this study was to investigate the effect of descent velocity during two-legged full back squats upon muscle activation and squat ascent performance. Methods: Eleven healthy resistance-training males (age: 24 ± 6 years, body mass: 89.5 ± 21.5 kg, height: 1.84 ± 0.10 m) performed 4-repetition maximum (4-RM) two-legged full squats with slow, normal, and fast descent phases. Kinematics and muscle activity of ten muscles divided into five regions were measured. Results: The main findings were that maximal and minimal velocity were lower and maximal velocity occurred later in the slow condition, while there was no difference in second peak velocity or ascent displacement when compared with the normal and fast conditions. Furthermore, no differences in muscle activation were found as an effect of the descent velocity. Conclusion: It was concluded that the slow descent velocity had a negative effect upon the ascent phase, because of the lower peak velocity and peak force increasing the chance of failure. The lower velocities were not caused by lower pre-activation of the muscles but were probably a result of potentiation and/or utilization of stored elastic energy and/or the stretch reflex.