Residual force enhancement (RFE) is the increase in steady-state force after active stretch relative to the force during isometric contraction at the same final length. The muscular dystrophy with ...myositis (mdm) mutation in mice, characterized by a small deletion in N2A titin, has been proposed to prevent N2A titin-actin interactions so that active mdm muscles are more compliant than wild type (WT). This decrease in active muscle stiffness is associated with reduced RFE. We investigated RFE in permeabilized soleus (SOL) and extensor digitorum longus (EDL) fiber bundles from WT and mdm mice. On each fiber bundle, we performed active and passive stretches from an average sarcomere length of 2.6-3.0 µm at a slow rate of 0.04 µm s-1, as well as isometric contractions at the initial and final lengths. One-way ANOVA showed that SOL and EDL fiber bundles from mdm mice exhibited significantly lower RFE than WT mice (P<0.0001). This result is consistent with previous observations in single myofibrils and intact muscles. However, it contradicts the results from a previous study that appeared to show that compensatory mechanisms could restore titin force enhancement in single fibers from mdm psoas. We suggest that RFE measured previously in mdm single fibers was an artifact of the high variability in passive tension found in degenerating fibers, which begins after ∼24 days of age. The results are consistent with the hypothesis that RFE is reduced in mdm skeletal muscles owing to impaired Ca2+-dependent titin-actin interactions resulting from the small deletion in N2A titin.
Pichardo, AW, Neville, J, Tinwala, F, Cronin, JB, and Brown, SR. Validity and reliability of force-time characteristics using a portable load cell for the isometric midthigh pull. J Strength Cond Res ...38(1): 185-191, 2024-Many practitioners use the isometric midthigh pull (IMTP) to assess maximal strength in a safe, time-effective manner. However, expensive, stationary force plates are not always practical in a large team setting. Therefore, the purpose of this study was to establish the validity and between-session reliability of peak force, rate of force development (RFD), and impulse during an IMTP using 2 experimental protocols: a traditional fixed bar with a force plate (BarFP) and a flexible chain measured with a force plate (ChainFP) and a load cell (ChainLC). After a familiarization session, 13 resistance-trained men performed 3 trials of the BarFP condition and 3 trials of the chain-based conditions. The identical procedures were replicated twice more, with a week between each testing session. The main findings were (a) no RFD or impulse measures were found to achieve acceptable reliability across all methodological approaches and testing occasions; (b) peak force was reliable across all methods, with coefficient of variation ranging from 4.6 to 8.3%, intraclass correlation coefficient ranging from 0.94 to 0.98, and the least variability associated with the ChainLC condition; and (c) the ChainFP method was found to significantly underrepresent peak force by 4.8% (p < 0.05), with no significant differences between the ChainLC and BarFP methods. Therefore, the ChainLC would seem a valid, reliable, portable, and cost-effective alternative to force plates when assessing maximal isometric strength in the IMTP.
For a positive integer m, a bounded linear operator T on a Hilbert space is called an exponentially m-isometric operator if ∑k=0m(−1)m−k(mk)ekT⁎ekT=0. For 1≤n≤m, skew-n-selfadjoint operators, ...nilpotent operators of order less than or equal to m+12, the greatest integer not greater than m+12, and 2πi multiples of idempotents are main examples of such operators. We establish a decomposition theorem for strict exponentially m-isometric operators with finite spectrum and prove that they are exponentially isometric m-Jordan. Finally, the dynamics of this operator will be considered. We will show that there is no N-supercyclic exponentially m-isometric operator on an infinite-dimensional Hilbert space.
Hypertension is a condition when the systolic blood pressure (BP) is greater than 140 mmHg and the diastolic blood pressure is greater or above 90 mmHg. According to the America Heart Association ...(AHA), the America population aged over 20 years who hypertension has reached 74.5 milion people, but almost 90-95% of cases have no known cause. Hypertension has the potential to cause fatal complications end opens up greater opportunities for patients to suffer from storke, coronary heart disease, have a high risk of kidney failure, heart failure, and eye damage. Physical activity that used to lower blood pressure is the Isometric Handgrip Exercise which done with static exercises on contracting muscles, without any changes in muscle length or hand joint movement. Objective : This study aims to determine the effect of isometric handgrip therapy on blood pressure in patients with hypertension in the working area Batang Kuis Health Center. Method : This study uses a quasi-experimental quantitative method using a pre-test post-test design with a sample 29 people. The measuring instrument used in this research is the observation sheet. Data analysis was carried out using the paired t-test sample. Result: It seen the paired t-test of blood pressure before and after giving of isometric handgrip therapy, the mean value is 4.034 with std. Devitation 1.267 with a 95% confidence level with a value of 0.05 from a significant value of 2 tiles 0.000 or 0.000 < 0.05. Thus, it concluded that there is an effect of giving isometric handgrip therapy on reducing blood pressuer in hypertension patients in the Batang Kuis Health Center.
Lower limb injury rates have increased dramatically in line with increased female sport participation levels. Muscle strength is a modifiable lower limb injury risk factor, guiding performance ...monitoring and rehabilitation.
The aim of this study was to investigate the test-retest reliability of isokinetic and isometric lower limb peak torque to body mass of muscles acting on the hip, knee, and ankle in female team sport athletes. It was hypothesised the test-retest reliability would be good (intraclass correlation coefficients (ICC) ≥ 0.75).
Thirty-eight female athletes (Australian Rules Football = 18, netball = 12, soccer = 8) aged 16–35 years participated in this study. Participants performed isokinetic (60°/s and 120°/s) and isometric testing on a Biodex Isokinetic Dynamometer on three separate days.
Poor to good reliability was demonstrated for all joint movements (ICC = 0.38–0.88) with small to moderate effect sizes (0.00–0.43) and typical errors (5.65–24.49).
Differences in peak torque to body mass were observed between sessions one and two and/or one and three, demonstrating a learning effect. Therefore, three testing sessions, and/or the inclusion of a familiarisation session, is recommended for future assessments in populations unfamiliar with dynamometry.
•Lower limb strength does not comprise of just a single joint (hip, knee and ankle).•Differences in peak torque between sessions demonstrate potential learning effects.•In future, a familiarisation session or three testing sessions are recommended.
Abstract
Ben-Zeev, T, Sadres, E, and Hoffman, JR. Comparison of force measures between start position, transition phase, and midthigh pull with weightlifting performance during Israel National ...Competition.
J Strength Cond Res
37(11): 2200–2205, 2023—This study compared the relationship between peak force (PKF) and rate of force development (RFD) at isometric start position pull (ISPP), isometric transition position pull (ITPP), and isometric midthigh pull (IMTP) with the snatch (SN), clean and jerk (C&J), and total score (TOT) in 30 national and international Israeli weightlifters (18 men and 12 women). All measures were collected either 1 week before or 1 week after the Israel weightlifting championship. A significant correlation was observed between peak force at all pull positions and performance in the SN, C&J, and TOT for men, women, and both sexes combined (
p
< 0.001). The correlations were all very strong (e.g.,
r
values all above 0.90) for both ISPP and ITPP, and all weightlifting performance variables, whereas the correlation between IMTP and weightlifting performance ranged from moderate (
r
= 0.69) to strong (
r
= 0.89). In addition, significant differences were observed between the correlation coefficient value in ISPP and ITPP with the TOT score compared with the correlations observed in IMTP (
z
= 0.7,
p
= 0.046, and
z
= 1.7,
p
= 0.049, respectively). Significant differences were also observed in the women group for ISPP for the SN and TOT score compared with the correlation in IMTP (
z
= 1.72,
p
= 0.043, and
z
= 1.75,
p
= 0.040, respectively). Rate of force development at 250 milliseconds significantly (
p
values <0.05) correlated with the SN, C&J, and TOT in women (
r
's = 0.65, 0.68, and 0.67, respectively), and when both sexes were combined (
r
's = 0.59, 0.61, and 0.60, respectively), but not for the men. Results of this investigation indicated the importance of isometric force capabilities at ISPP and ITPP for weightlifting performance.
Isometric mid-thigh pull (IMTP) is used to measure and monitor the peak force and the rate of force development. However, current IMTP implementation is costly and time-consuming. Thus, a quick, ...lowcost, and easy method is needed to monitor muscle strength. This case series study aimed to examine the relationship between IMTP assessed using a back strength dynamometer and jumping abilities and determine whether relative strength (N/body weight BW) can indicate jumping abilities. Eleven female collegiate basketball players in division III female Tokai Student Basketball League participated in this study. A back strength dynamometer was used to measure IMTP. The starting posture was a 145 relative angle at the knee and hip joints with the chain extended. Jumping measurements were performed for squat jump (SJ), countermovement jump (CMJ), and rebound jump (RJ) using a jump mat.
Additionally, the highest rebound jump index (RJI), jump height, and ground contact time for the highest RJI were used in the statistical analysis. Participants were divided into high (HG) and low (LG) groups based on the median value of relative strength. Cohen’s d as an effect size (ES) with a 95% confidence interval was used to compare the jumping abilities between the groups. The relationship between relative strength and jumping abilities was determined using Pearson’s correlation coefficient. The HG showed significantly moderate ES for SJ height (d=1.19), CMJ height (d=1.08), RJ height (d=1.19), and ground contact time (d=0.83) and significantly larger ES for RJI (d=1.36) relative to those of the LG. In addition, no significant correlations were observed between relative strength and any of the jump measures. However, relative strength exhibited a moderate correlation coefficient for the correlation between RJI and ground contact time. Therefore, IMTP assessed using a back strength dynamometer can be used to monitor muscle variables related to jumping abilities at a lower cost and training time than those of conventional methods.
ABSTRACTKontochristopoulos, N, Bogdanis, GC, Paradisis, G, and Tsolakis, C. Effect of a supplementary periodized complex strength training and tapering period on postactivation potentiation of ...sport-specific explosive performance in adolescent national-level fencers. J Strength Cond Res XX(X)000–000, 2018—This study examined the effects of strength training and tapering on countermovement jump (CMJ), change of direction (COD), and step-lunge (SL) after a conditioning activity in adolescent fencers. Twenty fencers (age15.8 ± 1.2 years) were randomly assigned to experimental (EXP, n = 10) group and control (CON, n = 10) group. EXP and CON groups performed 8 weeks of fencing training (4 times per week), while EXP group performed a supplementary strength training program twice per week, including a hypertrophy (first 2 weeks) and a complex strength training period (6 weeks). A 14-day tapering period with reduced training volume was then applied in both groups. Conditioning activity consisted of 3 × 3 seconds of maximal voluntary isometric contraction (MVIC; half-squat; knee angle = 90°), followed by either CMJ or COD or SL performance measurements in 3 different testing sessions 24 hours apart. There was no performance enhancement in all tests for both EXP and CON groups, after the conditioning MVIC before training (p > 0.05). After training, half-squat dynamic strength (1 repetition maximum 1RM) was significantly increased only in the EXP group (from 74.8 ± 20.0 to 127.0 ± 28.9 kg, p = 0.001) and maintained after tapering. After tapering, baseline CMJ height was significantly increased only in the EXP group (from 27.2 ± 4.6 to 30.9 ± 3.8 cm, p = 0.003). Contrary to our hypothesis, the increase in 1RM and CMJ was not followed by a postactivation potentiation enhancement in all tests (p > 0.05), possibly because of the relatively low strength and jumping performance of fencers. Thus, adolescent high-level fencers do not exhibit a performance increase after MVIC, and this was not modified by the supplementary strength training protocol used.
A sparse and low-rank near-isometric linear embedding (SLRNILE) method has been proposed to make dimensionality reduction and extract proper features for hyperspectral imagery (HSI) classification. ...The SLRNILE stands on the theory of the John-Lindenstrauss lemma, and tries to estimate a sparse and low-rank projection matrix that satisfies the restricted isometric property (RIP) condition on all secants of the HSI data. The RIP condition guarantees that the desired linear mapping near-isometrically preserves nearest neighbor points of all HSI pixels. Seeking the desired mapping is then modeled into minimizing a Lagrange multipliers formulation. The alternating direction method of multipliers framework is utilized to solve the above convex program, and column generation techniques are adopted to alleviate the computation memory burden during the optimization procedure. Five experiments on three widely used HSI data sets are designed to completely test the performance of SLRNILE, and experimental results are compared against those of six state-of-the-art feature extraction methods, including principal component analysis, Laplacian eigenmaps, locality preserving projections, neighborhood preserving embedding, sparse nonnegative matrix underapproximation, and random projections. The results show that SLRNILE performs best among all the seven methods, and its computational time is longest of all but still bearable for regular users. Therefore, the SLRNILE can be a good choice for feature extraction in HSI classification.
The purpose of this study was to test the validity of hamstring muscle strength of handball athletes. A total of 30 handball athletes with categories of 15 male athletes (18.0 ± 5.1 years, weight ...62.6 ± 20.7 kg, height 173.6 ± 5.0 cm, BMI 22.1 ± 4.0 kg / m2) and female (18.0 ± 5.1 years, weight 54.6 ± 17.4 kg, height 164.7 ± 6.9 cm, BMI 21.4 ± 2.2 kg/m2). No history of lower extremity injuries participated in a hamstring strength test. Hamstring strength tests are performed isometrically with ISO Prone and ISO 60 tests using nordbord tools and load cells tied using hooks called pabletest. From the test results there is a validity level of 0.000 with reliability of 0.8, so that the data can be said to be valid on both tests, namely ISO Prone and ISO 60. Load cells on pabletes are able to measure hamstring muscle strength in handball athletes. The advantages of load cells on pabletes can be made simply but not everyone can make arrangements so as to output data that can be interpreted. Subsequent research can be done using different contractions such as eccentrics and increasing the number of research subjects more by developing better software.
Keywords: validity, hamstring, muscle, strength, isometric
