Incremental Loading Test Research Articles

Fatigue behavior and prediction model of self-compacting concrete under constant amplitude load and incremental amplitude load

To explore the fatigue fracture behavior of self-compacting concrete (SCC), constant amplitude loading tests and incremental amplitude loading tests were carried out. The experimental results of SCC were obtained and analyzed, including P-CMOD curve, fatigue life, effective crack length, fatigue crack growth (FCG) rate, stress intensity factor (SIF). The results show that the P-CMOD curves of SCC beams follow the unique envelope theory. The fatigue damage of SCC under constant amplitude load can be divided into three stages. In the second stage, cracks grow steadily. The critical SIF is the boundary point between the second and the third stages of fatigue damage. When SIF exceeds the critical SIF, cracks develop rapidly. The first stage of fatigue damage is not obvious for incremental amplitude loading tests. With the increase of load amplitude, there are obvious second and third stages of damage. Except for the maximum load stage, the crack opening rate keeps constant generally. Combined with damage mechanics and fracture mechanics, damage evolution equations of SCC under constant amplitude load and incremental amplitude load were established. The parameters of fatigue damage model based on continuous damage mechanics (CDM) were calibrated by test data, and the predicted results were compared with the experimental results. The results show that the model is sensitive to the first stage of damage. The fatigue damage model based on CDM is more suitable to predict fatigue life for incremental amplitude tests and constant amplitude tests with high cycle. The advantage of this model is that it can be applied to predict fatigue life for different load levels.

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.

Group versus Individualised Minimum Velocity Thresholds in the Prediction of Maximal Strength in Trained Female Athletes.

This study examined the accuracy of different velocity-based methods in the prediction of bench press and squat one-repetition maximum (1RM) in female athletes. Seventeen trained females (age 17.8 ± 1.3 years) performed an incremental loading test to 1RM on bench press and squat with the mean velocity being recorded. The 1RM was estimated from the load–velocity relationship using the multiple- (8 loads) and two-point (2 loads) methods and group and individual minimum velocity thresholds (MVT). No significant effect of method, MVT or interaction was observed for the two exercises (p > 0.05). For bench press and squat, all prediction methods demonstrated very large to nearly perfect correlations with respect to the actual 1RM (r range = 0.76 to 0.97). The absolute error (range = 2.1 to 3.8 kg) for bench press demonstrated low errors that were independent of the method and MVT used. For squat, the favorable group MVT errors for the multiple- and two-point methods (absolute error = 7.8 and 9.7 kg, respectively) were greater than the individual MVT errors (absolute error = 4.9 and 6.3 kg, respectively). The 1RM can be accurately predicted from the load–velocity relationship in trained females, with the two-point method offering a quick and less fatiguing alternative to the multiple-point method.

The Use of Lifting Straps Alters the Entire Load-Velocity Profile During the Deadlift Exercise.

Jukic, I, García-Ramos, A, Malecek, J, Omcirk, D, and Tufano, JJ. The use of lifting straps alters the entire load-velocity profile during the deadlift exercise. J Strength Cond Res 34(12): 3331-3337, 2020-This study aimed to compare the one repetition maximum (1RM) and load-velocity (LV) profile between deadlifts performed with (DLw) and without (DLn) lifting straps. The full individual LV relationship of 20 men (age: 24.3 ± 2.4 years; body height: 180.6 ± 6.9 cm; body mass: 85.8 ± 8.0 kg) was randomly evaluated during 2 separate sessions for the DLw and DLn via an incremental loading test. One repetition maximum was greater (p < 0.001; g = 0.56, 95% confidence interval = [0.32, 0.79]) for DLw (177.0 ± 28.9 kg) compared with DLn (160.6 ± 26.0 kg). A highly linear relationship between mean velocity (MV) and %1RM was observed for both conditions (R > 0.95; SEE < 6.18 %1RM for pooled data and R > 0.98; SEE < 3.6 %1RM for individual data). However, MV associated with each %1RM was greater for DLn, and these differences were accentuated as the loading magnitude increased (g = 0.30-1.18). One repetition maximum was strongly associated between both conditions (r = 0.875 [0.71, 0.95]), whereas MV at 1RM (r = 0.21 [-0.25, 0.60]) was unrelated between conditions. The slope of the LV profiles (r = 0.845 [0.64, 0.94]) was correlated, but differed (g = 0.41 [0.16, 0.66]) between DLw and DLn, whereas the mean test velocity of all loads was unrelated (r = 0.270 [-0.20, 0.64]). An individual LV profile should be created for each athlete in the same condition that are going to be used in training to obtain a more precise estimation of the submaximal relative loads.

Effect of Rolling after Heat Treatment on Hydrogen Embrittlement Susceptibility for High Strength Steel Fasteners

Abstract Steel fasteners comprising two different metallurgical structures were investigated for hydrogen embrittlement (HE) susceptibility by incremental step load testing. The metallurgical structures examined consisted of tempered martensite obtained by quenching and tempering and lower bainite obtained by austempering. It has been shown that lower bainite exhibits marginally lower HE susceptibility when tested under moderate hydrogen charging conditions (e.g., −1.0 V). At the most severe hydrogen charging potential of −1.2 V, both microstructures are equally embrittled. The current paper examines the effect of the sequence of the fabrication process, specifically the effect of rolling the threads before and after heat treatment (i.e., quenching and tempering or austempering). The results show irrespective of the metallurgical structure, rolling the threads after heat treatment causes a significant decrease in HE susceptibility. These findings are attributed to the presence of high dislocation density when thread rolling is performed on hardened parts as a final manufacturing step.

Changes in the Load–Velocity Profile Following Power- and Strength-Oriented Resistance-Training Programs

To compare the short-term effect of power- and strength-oriented resistance-training programs on the individualized load-velocity profiles obtained during the squat (SQ) and bench-press (BP) exercises. Thirty physically active men (age = 23.4[3.5]y; SQ 1-repetition maximum [1RM] = 126.5 [26.7]kg; BP 1RM = 81.6 [16.7]kg) were randomly assigned to a power- (exercises: countermovement jump and BP throw; sets per exercise: 4-6; repetitions per set: 5-6; load: 40% 1RM) or strength-training group (exercises: SQ and BP; sets per exercise: 4-6; repetitions per set: 2-8; load: 70%-90% 1RM). The training program lasted 4 wk (2sessions/wk). The individualized load-velocity profiles (ie,velocity associated with the 30%-60%-90% 1RM) were assessed before and after training through an incremental loading test during the SQ and BP exercises. The power-training group moderately increased the velocity associated with the full spectrum of % 1RM for the SQ (effect size [ES] range: 0.70 to 0.93) and with the 30% 1RM for the BP (ES: 0.67), while the strength-training group reported trivial/small changes across the load-velocity spectrum for both the SQ (ES range: 0.00 to 0.35) and BP (ES range: -0.06 to -0.33). The power-training group showed a higher increase in the mean velocity associated with all % 1RM compared with the strength-training group for both the SQ (ES range: 0.54 to 0.63) and BP (ES range: 0.25 to 0.53). The individualized load-velocity profile (ie,velocity associated with different % 1RM) of lower-body and upper-body exercises can be modified after a 4-wk resistance-training program.

Movement Velocity as A Measure of Exercise Intensity in Persons with Multiple Sclerosis: A Validity Study.

Objectives: This study aims to analyse the validity (agreement between two methods) of the movement propulsive velocity (MPV) as an indicator of relative load in leg press (LP) and bench press (BP) exercises in persons with multiple sclerosis (MS). Methods: 18 persons with MS (sex = 55% male; age (mean ± SD) = 44.88 ± 10.62 years; body mass = 67.19 ± 10.63 kg; height = 1.66 ± 0.07 m; Expanded Disability Status Scale (EDSS) = 3.12 ± 1.73) performed an incremental loading test in BP and LP exercises in two separate sessions. Individual determination of the one-repetition maximum (1RM) and full load-velocity profile were obtained for each participant. Results: a significant linear relationship was observed between the %1RM load and the MPV in LP (%1RM = −133.58 × MPV + 117.44; r2 = 0.84; standard error of the estimate (SEE) = 9.38%1RM) and BP (%1RM = −95.66 × MPV + 115.26; r2 = 0.86; SEE = 9.82%1RM). In addition, no significant differences were found between the %1RM achieved directly and the %1RM obtained by the equation calculated from the linear regression (LP, p = 0.996; BP, p = 0.749). Conclusions: these results indicate that movement velocity can estimate the relative load in bench press and leg press exercises in persons MS.

1D Compressibility of High Moisture Content Clays Solidified with Small Cement Dosages

Soft soil is normally associated with high moisture content and fine content which result in high compressibility and low strength. However, a proper treatment such as solidification by means of hydraulic binders is required in order to be usable for beneficial purposes (e.i backfilling). This paper experiments the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a high moisture content (MC) soil (twice liquid limit), based incremental loading test. The effects of Portland cement addition are evaluated for dosages ranging from 0 % to 15% by dry mass of soil. After curing, it was found that 10 % cement was required to make meaningful reduction in MC for kaolin while no major difference was noted between after mixing and after curing for DMS. In kaolin the moisture content decreased by 6.5 % for each 5 % increment of cement. Similarly, the MC of DMS reduced by 10 % for each 5 % increment. Thus, the reduction, immediately after mixing, in DMS was higher by 3.5 % compared to kaolin. The most evident effect of the treatment feasibility is the development of a cementation-induced yield stress after 7 days of curing: the bigger the cement dosage, the greater the yield stress and the greater the vertical effective stress that can be sustained at any void ratio. The maximum yield stress at 15 % cement content was found 30 kPa and 70 kPa for DMS and kaolin respectively. The highest void ratio values were found in the control specimens (3.77) in kaolin and DMS (5.66) whereas the lowest void ratio was corresponded to 15 % cement 3.35 and 4.65 for kaolin and DMS respectively. The control specimens decreased dramatically from 38.93 m2 / KN - 0.13 m2 / KN and 36.03 m2 / KN - 0.19 m2 / KN for kaolin and DMS specimens respectively. The results correspondingly provide a consistent depiction of the effects of cement treatment on MC, void ratio and coefficient of volume compressibility. The effectiveness of the treatment is obvious compared to the untreated soil.

Physiological Predictors of Competition Performance in CrossFit Athletes.

The aim of this study was to determine the physiological variables that predict competition performance during a CrossFit competition. Fifteen male amateur CrossFit athletes (age, 35 ± 9 years; CrossFit experience, 40 ± 27 months) performed a series of laboratory-based tests (incremental load test for deep full squat and bench press; squat, countermovement and drop jump tests; and incremental running and Wingate tests) that were studied as potential predictors of CrossFit performance. Thereafter, they performed the five Workouts of the Day (WODs) corresponding to the CrossFit Games Open 2019, and we assessed the relationship between the laboratory-based markers and CrossFit performance with regression analyses. Overall CrossFit performance (i.e., final ranking considering the sum of all WODs, as assessed by number of repetitions, time spent in exercises or weight lifted) was significantly related to jump ability, mean and peak power output during the Wingate test, relative maximum strength for the deep full squat and the bench press, and maximum oxygen uptake (VO2max) and speed during the incremental test (all p < 0.05, r = 0.58–0.75). However, the relationship between CrossFit Performance and most laboratory markers varied depending on the analyzed WOD. Multiple linear regression analysis indicated that measures of lower-body muscle power (particularly jump ability) and VO2max explained together most of the variance (R2 = 81%, p < 0.001) in overall CrossFit performance. CrossFit performance is therefore associated with different power-, strength-, and aerobic-related markers.

Validity of Load-Velocity Relationship to Predict 1 Repetition Maximum During Deadlifts Performed With and Without Lifting Straps: The Accuracy of Six Prediction Models.

Jukic, I, García-Ramos, A, Malecek, J, Omcirk, D, and Tufano, JJ. Validity of load-velocity relationship to predict 1 repetition maximum during deadlifts performed with and without lifting straps: The accuracy of six prediction models. J Strength Cond Res 36(4): 902-910, 2022-This study aimed to compare the accuracy of six 1 repetition maximum (1RM) prediction models during deadlifts performed with (DLw) and without (DLn) lifting straps. In a counterbalanced order, 18 resistance-trained men performed 2 sessions that consisted of an incremental loading test (20-40-60-80-90% of 1RM) followed by 1RM attempts during the DLn (1RM = 162.0 ± 26.9 kg) and DLw (1RM = 179.0 ± 29.9 kg). Predicted 1RMs were calculated by entering both group and individualized mean concentric velocity of the 1RM (V1RM) into an individualized linear and polynomial regression equations, which were derived from the load-velocity relationship of 5 ([20-40-60-80-90% of 1RM], i.e., multiple-point method) or 2 ([40 and 90% of 1RM] i.e., 2-point method) incremental warm-up sets. The predicted 1RMs were deemed highly valid if the following criteria were met: trivial to small effect size, practically perfect r, and low absolute errors (<5 kg). The main findings revealed that although prediction models were more accurate during the DLn than DLw, none of the models provided an accurate estimation of the 1RM during both DLn (r = 0.92-0.98; absolute errors: 6.6-8.1 kg) and DLw (r = 0.80-0.93; absolute errors: 12.4-16.3 kg) according to our criteria. Therefore, these results suggest that the 1RM for both DLn and DLw should not be estimated through the recording of movement velocity if sport professionals are not willing to accept more than 5 kg of absolute errors.

Velocity Performance Feedback During the Free-Weight Bench Press Testing Procedure: An Effective Strategy to Increase the Reliability and One Repetition Maximum Accuracy Prediction.

Jiménez-Alonso, A, García-Ramos, A, Cepero, M, Miras-Moreno, S, Rojas, FJ, and Pérez-Castilla, A. Velocity performance feedback during the free-weight bench press testing procedure: An effective strategy to increase the reliability and one repetition maximum accuracy prediction. J Strength Cond Res 36(4): 1077-1083, 2022-This study aimed to determine whether the verbal provision of velocity performance feedback during the free-weight bench press (BP) exercise influences (a) the within-session reliability and magnitude of mean concentric velocity (MCV) values recorded against a range of submaximal loads and (b) the accuracy of the individualized load-velocity profile to estimate the BP 1 repetition maximum (1RM). Fifteen men (BP 1RM relative to body mass = 1.08 ± 0.22) performed an incremental loading test until reaching the 1RM on 2 separate sessions. Subjects received verbal velocity performance feedback in 1 session (knowledge of results [KR]), and no KR was provided in another session (Control). A linear velocity transducer was used to collect the MCV against 4 loads (40-55-70-85% 1RM), and the BP 1RM was estimated from the individualized load-velocity relationship modeled through the multiple-point (40-55-70-85% 1RM) and 2-point methods (40-85% 1RM). The KR condition provided a higher reliability (coefficient of variation [CV]: KR = 2.41%, Control = 3.54%; CV ratio = 1.47) and magnitude (p = 0.001; effect size [ES] = 0.78) of MCV for the 40% 1RM, but no significant differences in reliability (CV ratio ≤1.15) nor in the magnitude (p ≥ 0.058; ES range = 0.00-0.32) were observed for higher loads. The accuracy in the estimation of the 1RM was higher for the KR (absolute errors: multiple-point = 3.1 ± 2.3 kg; 2-point = 3.5 ± 2.1 kg) compared with the Control condition (absolute errors: 4.1 ± 1.9 kg for both multiple-point and 2-point methods). These results encourage the provision of verbal velocity performance feedback during BP testing procedures.

Influence of Grip Width and Anthropometric Characteristics on the Bench-Press Load-Velocity Relationship.

To compare the load-velocity (L-V) relationship between bench-press exercises performed using 4 different grip widths, to determine the association between the anthropometric characteristics and L-V profile, and to explore whether a multiple linear-regression model with movement velocity and subjects' anthropometric characteristics as predictor variables could increase the goodness of fit of the individualized L-V relationship. The individual L-V relationship of 20 men was evaluated by means of an incremental loading test during the bench-press exercise performed on a Smith machine using narrow, medium, wide, and self-selected grip widths. Simple and multiple linear-regression models were performed. The mean velocity associated with each relative load did not differ among the 4 grip widths (P ≥ .130). Only body height and total arm length were correlated with the mean velocity associated with light and medium loads (r ≥ .464). A slightly higher variance of the velocity attained at each relative load was explained when some anthropometric characteristics were used as predictor variables along with the movement velocity (r2 = .969 [.965-.973]) in comparison with the movement velocity alone (r2 = .966 [.955-.968]). However, the amount of variance explained by the individual L-V relationships was always higher than with the multiple linear-regression models (r2 = .995 [.985-1.000]). These results indicate that the individual determination of the L-V relationship using a self-selected grip width could be recommended to monitor relative loads in the Smith machine bench-press exercise.

Comparison of the bench press one-repetition maximum obtained by different procedures: Direct assessment vs. lifts-to-failure equations vs. two-point method

This study examined the differences in the bench press one-repetition maximum obtained by three different methods (direct method, lifts-to-failure method, and two-point method). Twenty young men were tested in four different sessions. A single grip width (close, medium, wide, or self-selected) was randomly used on each session. Each session consisted of an incremental loading test until reaching the one-repetition maximum, followed by a single set of lifts-to-failure against the 75% one-repetition maximum load. The last load lifted during the incremental loading test was considered the actual one-repetition maximum (direct method). The one-repetition maximum was also predicted using the Mayhew’s equation (lifts-to-failure method) and the individual load–velocity relationship modeled from two data points (two-point method). The actual one-repetition maximum was underestimated by the lifts-to-failure method (range: 1–2 kg) and overestimated by the two-point method (range: –3 to –1 kg), being these differences accentuated using closer grip widths. All predicted one-repetition maximums were practically perfectly correlated with the actual one-repetition maximum ( r ≥ 0.95; standard error of the estimate ≤ 4 kg). The one-repetition maximum was higher using the medium grip width (83 ± 3 kg) compared to the close (80 ± 3 kg) and wide (79 ± 3 kg) grip widths ( P ≤ 0.025), while no significant differences were observed between the medium and self-selected (81 ± 3 kg) grip widths ( P = 1.000). In conclusion, although both the Mayhew’s equation and the two-point method are able to predict the actual one-repetition maximum with an acceptable precision, the differences between the actual and predicted one-repetition maximums seem to increase when using close grip widths.

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

BackgroundThis 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.MethodsA 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.ResultsThe 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).ConclusionsAlthough 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.

Excessive Treadmill Training Enhances Brain-Specific MicroRNA-34a in the Mouse Hippocampus.

Background: An imbalance between total training load and total recovery may cause overtraining (OT). The purpose of the present study was to verify the effects of OT on the expression of brain-derived neurotrophic factor (BDNF), its receptor tropomyosin receptor kinase B (TrkB) and p75 and the dynamic expression patterns of brain-specific miR-34a and miR-124 or inflammation-related miR-21 and miR-132 in the mouse hippocampus.Method: Eight weeks old C57BL/6J mice were randomly assigned to the control (CON), normal training (NT) and OT groups. An 8-week OT training protocol was applied to evaluate the phenotype of mice endurance (incremental load test, ILT) and cognitive capacity (Morris water maze test). We used qRT-PCR and immunoblotting to detect changes in the molecular level of hippocampal samples.Result: Compared with the CON, both NT and OT decreased bodyweight after 8-week training. After 8-week of training, NT increased the exhaustion velocity (EV) while the EV of OT was lower than NT. Mice in NT decreased the escape latency than CON. The percentage of time spent in the probe quadrant and the number of crossing platform times in NT were higher than CON and OT. The BDNF, p75 and TrkB mRNA levels were increased in NT than CON, only the p75 mRNA was increased in OT. The NT exhibited increased protein levels of BDNF and TrkB compared to CON. The protein expression of BDNF was decreased in OT than NT and CON. The protein level of p75 in the OT was higher than in NT and CON. In addition, the phosphorylation level of TrkB in OT was higher than CON and NT. Only the miR-34a level was increased in the OT. Moreover, the expression of miR-34a was found to be negatively correlated with the expression of BDNF, and the increase in miR-34a level was accompanied by a decrease in performance.Conclusion: In summary, the training-evoked increase in the BDNF level may help to improve performance, whereas this conditioning is lost after OT. Moreover, miR-34a potentially mediated changes in the expression of BDNF and may reflect the decrease in performance after OT.

Aerobic exercise has an anxiolytic effect on streptozotocin-induced diabetic rats

Diabetes is a metabolic disorder characterized by hyperglycemia and impaired insulin secretion or action. Psychological comorbidities, such as depression and anxiety, are more common in people with diabetes. Exercise results in anxiolytic effects, as demonstrated in numerous studies. This study aims to evaluate potential anxiolytic effects of aerobic exercise in streptozotocin (STZ)‑induced diabetes. Male Wistar albino rats (n=40) were randomly divided into four groups of control, exercise, diabetes, and diabetes + exercise. Diabetes was induced with a single i.p. injection of STZ. The incremental load test was applied to exercise groups to determine maximal exercise capacity. Rats exercised on a treadmill at 70% of their maximal capacity for 45 min, five days per week for 12 weeks. On the day after the last exercise session the open field test and elevated plus maze test were carried out. Diabetes caused an increase in anxiety level, reflected in stretch‑attend posture, self‑grooming behaviors, and freezing time, with no significant changes for other behavioral parameters. Training normalized diabetes‑induced deteriorations and also induced a significant anxiolytic effect both on diabetic and non‑diabetic rats. This effect was observed for all behavioral parameters. The results of the open field test and elevated plus maze were consistent. The current results demonstrated a slight increase in anxiety with diabetes and a prominent anxiolytic effect of aerobic exercise. Considering the conflicting results in exercise‑anxiety studies, this study hig hlights the importance of individually designed exercise protocols.

Evaluation of material susceptibility to hydrogen embrittlement (HE): An approach based on experimental and finite element (FE) analyses

A stress coupled hydrogen diffusion finite element model has been developed to simulate incremental step load (ISL) test. It is further integrated with a cohesive zone model (CZM) based on a stiffness-separation law. The influence of hydrogen on the cohesive law has been implemented through a newly proposed approach rooted in the hydrogen enhanced decohesion (HEDE) mechanism. Finally, this coupled model has been utilized to assess hydrogen embrittlement (HE) susceptibility of materials through the prediction of crack initiation time. The crack initiation time decreases with the increase of initial hydrogen concentration in a quench and tempered 36NiCrMo4 (4340) steel showing a ductile-brittle transition behavior. Similar observations were done from ISL experiments. In addition to initial hydrogen concentration, the influence of yield strength, fracture toughness and hydrogen diffusivity on material susceptibility was also studied. Three different materials-iron, niobium, 304 stainless steel in addition to 36NiCrMo4 (4340) steel were selected for the study. Iron shows better resistance to HE failure owing to its low yield strength and high fracture toughness while 304 austenitic stainless steel reveals least susceptibility to hydrogen induced cracking. This is largely attributed to the lower diffusivity of hydrogen in 304 stainless steel.

A Repeated Power Training Enhances Fatigue Resistance While Reducing Intraset Fluctuations.

Oliver, GS, Julio, TF, Moras, G, José Luis, AS, and Alberto, MV. A repeated power training enhances fatigue resistance while reducing intraset fluctuations. J Strength Cond Res 33(10): 2711-2721, 2019-The present study analyzed the effects of adding upper-body repeated power ability (RPA) training to habitual strength training sessions. Twenty young elite male basketball players were randomly allocated into a control group (CON, n = 10) or repeated power group (RPG, n = 10) and evaluated by 1 repetition maximum (1RM), incremental load, and RPA tests in the bench press exercise before and after a 7-week period and a 4-week cessation period. Repeated power group performed 1-3 blocks of 5 sets of 5 repetitions using the load that maximized power output with 30 seconds and 3 minute of passive recovery between sets and blocks, respectively. Between-group analysis showed substantial greater improvements in RPG compared with CON in: best set (APB), last set (APL), mean power over 5 sets (APM), percentage of decrement, fluctuation decrease during APL and RPA index (APLpost/APBpre) during the RPA test (effect size [ES] = 0.64-1.86), and 1RM (ES = 0.48) and average power at 80% of 1RM (ES = 1.11) in the incremental load test. The improvements of APB and APM were almost perfectly correlated. In conclusion, RPA training represents an effective method to mainly improve fatigue resistance together with the novel finding of a better consistency in performance (measured as reduced intraset power fluctuations) at the end of a dynamic repeated effort.

Experimental and numerical investigations on the impact resistance of SHCC-strengthened RC slabs subjected to drop weight loading

In this paper, a thin layer of Strain-Hardening Cementitious Composites (SHCC) is provided in either tension or compression side of RC slabs aiming to improve their impact resistance under the effect of drop weight loading. The main parameter of the current study is the condition of the contact surface between the substrate slab and the SHCC overlay that was prepared by grinding, grinding plus steel dowels or grinding plus epoxy adhesive. Accordingly, 63 RC slabs were prepared and tested under the effect of drop weight falling from three different heights; 1, 1.5 and 2 m. It was found that the SHCC strengthening layer enhanced the impact resistance of the strengthened slab when added at either tension or compression side. However, in order to attain the outermost impact resistance showing ductile performance, it is better to provide a thin layer of the SHCC at the tension side of the slab connected to the substrate slab by epoxy resin applied on pre-prepared grinded surface. Furthermore, numerical simulations based on ABAQUS software package were performed on the strengthened slabs. Their results showed good agreement with the experimental findings from the viewpoint of the kinetic energy. Besides, the impact failure loads were determined numerically for the studied slabs and compared with those obtained from incremental static loading tests.

Movement velocity can be used to estimate the relative load during the bench press and leg press exercises in older women.

BackgroundMovement velocity has been proposed as an effective tool to prescribe the load during resistance training in young healthy adults. This study aimed to elucidate whether movement velocity could also be used to estimate the relative load (i.e., % of the one-repetition maximum (1RM)) in older women.MethodsA total of 22 older women (age = 68.2 ± 3.6 years, bench press 1RM = 22.3 ± 4.7 kg, leg press 1RM = 114.6 ± 15.9 kg) performed an incremental loading test during the free-weight bench press and the leg press exercises on two separate sessions. The mean velocity (MV) was collected with a linear position transducer.ResultsA strong linear relationship between MV and the relative load was observed for the bench press (%1RM = −130.4 MV + 119.3; r2 = 0.827, standard error of the estimate (SEE) = 6.10%1RM, p < 0.001) and leg press exercises (%1RM = −158.3 MV + 131.4; r2 = 0.913, SEE = 5.63%1RM, p < 0.001). No significant differences were observed between the bench press and leg press exercises for the MV attained against light-medium relative loads (≤70%1RM), while the MV associated with heavy loads (≥80%1RM) was significantly higher for the leg press.ConclusionsThese results suggest that the monitoring of MV could be useful to prescribe the loads during resistance training in older women. However, it should be noted that the MV associated with a given %1RM is significantly lower in older women compared to young healthy individuals.