Moderate-intensity resistance exercise training in patients with chronic heart failure improves strength, endurance, heart rate variability, and forearm blood flow

Thirty-nine CHF patients (New York Heart Association Functional Class = 2.3±0.5; left ventricular ejection fraction 28%±7%; age 65±11 years; 33:6 male:female) underwent 2 identical series of tests, 1 week apart, for strength and endurance of the knee and elbow extensors and flexors, VO_2peak, HRV, FBF at rest, and FBF activated by forearm exercise or limb ischemia. Patients were then randomized to 3 months of resistance training (EX, n = 19), consisting of mainly isokinetic (hydraulic) ergometry, interspersed with rest intervals, or continuance with usual care (CON, n = 20), after which they underwent repeat endpoint testing. Combining all 4 movement patterns, strength increased for EX by 21±30% (mean±SD, P<.01) after training, whereas endurance improved 21±21% (P<.01). Corresponding data for CON remained almost unchanged (strength P<.005, endurance P<.003 EX versus CON). VO_2peak improved in EX by 11±15% (P<.01), whereas it decreased by 10±18% (P<.05) in CON (P<.001 EX versus CON). The ratio of low-frequency to high-frequency spectral power fell after resistance training in EX by 44±53% (P<.01), but was unchanged in CON (P<.05 EX versus CON). FBF increased at rest by 20±32% (P<.01), and when stimulated by submaximal exercise (24±32%, P<.01) or limb ischemia (26±45%, P<.01) in EX, but not in CON (P<.01 EX versus CON).

Differentiated mTOR but not AMPK signaling after strength vs endurance exercise in training-accustomed individuals

The influence of adenosine mono phosphate (AMP)-activated protein kinase (AMPK) vs Akt-mammalian target of rapamycin C1 (mTORC1) protein signaling mechanisms on converting differentiated exercise into training specific adaptations is not well-established. To investigate this, human subjects were divided into endurance, strength, and non-exercise control groups. Data were obtained before and during post-exercise recovery from single-bout exercise, conducted with an exercise mode to which the exercise subjects were accustomed through 10 weeks of prior training. Blood and muscle samples were analyzed for plasma substrates and hormones and for muscle markers of AMPK and Akt-mTORC1 protein signaling. Increases in plasma glucose, insulin, growth hormone (GH), and insulin-like growth factor (IGF)-1, and in phosphorylated muscle phospho-Akt substrate (PAS) of 160 kDa, mTOR, 70 kDa ribosomal protein S6 kinase, eukaryotic initiation factor 4E, and glycogen synthase kinase 3α were observed after strength exercise. Increased phosphorylation of AMPK, histone deacetylase5 (HDAC5), cAMP response element-binding protein, and acetyl-CoA carboxylase (ACC) was observed after endurance exercise, but not differently from after strength exercise. No changes in protein phosphorylation were observed in non-exercise controls. Endurance training produced an increase in maximal oxygen uptake and a decrease in submaximal exercise heart rate, while strength training produced increases in muscle cross-sectional area and strength. No changes in basal levels of signaling proteins were observed in response to training. The results support that in training-accustomed individuals, mTORC1 signaling is preferentially activated after hypertrophy-inducing exercise, while AMPK signaling is less specific for differentiated exercise.

The relationship between lower body strength and obstructed gait in community-dwelling older adults

OBJECTIVES: To determine the relationship between lower body strength of community-dwelling older adults and the time to negotiate obstructed gait tasks.

DESIGN: A correlational study.

SETTING: The Biomechanics Laboratory, Deakin University, Australia.

PARTICIPANTS: Twenty-nine women and 16 men aged 62 to 88 were recruited using advertisements placed in local newspapers. The participants were independent community dwellers, healthy and functionally mobile.

MEASUREMENTS: Maximal isometric strength of the knee extensors and dynamic strength of the hip extensors, hip flexors, hip adductors, hip abductors, knee extensors, knee flexors, and ankle plantar flexors were assessed. The times to negotiate four obstructed gait tasks at three progressively challenging levels on an obstacle course and to complete the course were recorded. The relationship between strength and the crossing times was explored using linear regression models.

RESULTS: Significant associations between the seven strength measures and the times to negotiate each gait task and to walk the entire course at each level were obtained (r = -0.38 to -0.55; P < .05). In addition, the percentage of the variance explained by strength (R2), consistently increased as a function of the progressively challenging level. This increase was particularly marked for the stepping over task (R2 = 19.3%,25.0%, and 27.2%, for levels 1, 2, and 3, respectively) and the raised surface condition (R2 = 17.1%,21.1%, and 30.8%, for levels 1,2, and 3, respectively) .

CONCLUSION: The findings of the study showed that strength is a critical requirement for obstructed locomotion. That the magnitude of the association increased as a function of the challenging levels suggests that intervention programs aimed at improving strength would potentially be effective in helping community-dwelling older adults negotiate environmental gait challenges.

The effects of improved strength on obstacle negotiation in community-living older adults

Poor mobility has been associated with age-related deterioration in muscle strength. While previous work has examined the effects of improved strength on level walking, we have quantified the effects of a resistance-training program on obstructed gait tasks using biomechanical-dependent measures. Forty-five community-dwelling participants aged 62 years or older were randomised to either a control (n=16) or experimental group (n=29). The experimental subjects exercised for 24 weeks on a progressive resistance-training program designed to improve lower body strength. Dynamic strength was assessed at weeks 0 and 24 as well as specific laboratory gait kinetics and kinematics during stepping over an obstacle and negotiation of a raised surface set at 10, 20 and 30% of each subject's leg length.

The mechanical characterization of low work hardening, high strength steel

One of the major challenges in assessing the mechanical properties of recovery annealed steel is the strain localization that occurs almost immediately on the formation of the first Lüders band, such that no or limited propagation of the Lüders band occurs along the tensile coupon. The stress raiser associated with the geometry of the standard tensile coupon means that this plastic deformation is often completely outside the standard extensometers on the coupon. Hence, no strain is measured during the test. While this is not important for assessing the tensile strength of the steel, it does mean that the strain related properties, such as the elastic limit of the steel, cannot be measured using standard testing techniques.This work addresses this issue by examining three techniques for ensuring that the strain occurs inside the extensometer. It is shown that the best technique is the extended extensometer, where the gauge length covers slightly more than the tensile coupon parallel length. While this leads to some variation in the width of the material being measured, compensation can be be made by adjusting the strain to correct the Young's Modulus.This technique has direct implications not just for recovery annealed steels, but for other high strength, low work hardening materials such as ultrafine ferrite. A particular requirement of these high strength steels in structural applications is a high elastic limit; hence, measurement of the strain related properties for these high strength materials must be considered vital in their mechanical assessment.

Lifetime sport and leisure activity participation is associated with greater bone size, quality and strength in older men

Introduction: It remains uncertain whether long-term participation in regular weight-bearing exercise confers an advantage to bone structure and strength in old age. The aim of this study was to investigate the relationship between lifetime sport and leisure activity participation on bone material and structural properties at the axial and appendicular skeleton in older men (>50 years).

Methods: We used dual-energy X-ray absorptiometry (DXA) to assess hip, spine and ultradistal (UD) radius areal bone mineral density (aBMD) (n=161), quantitative ultrasound (QUS) to measure heel bone quality (n=161), and quantitative computed tomography (QCT) to assess volumetric BMD, bone geometry and strength at the spine (L₁–L₃) and mid-femur (n=111). Current (>50+ years) and past hours of sport and leisure activity participation during adolescence (13–18 years) and adulthood (19–50 years) were assessed by questionnaire. This information was used to calculate the total time (min) spent participating in sport and leisure activities and an osteogenic index (OI) score for each participant, which provides a measure of participation in weight-bearing activities.

Results: Regression analysis revealed that a greater lifetime (13–50+ years) and mid-adulthood (19–50 years) OI, but not total time (min), was associated with a greater mid-femur total and cortical area, cortical bone mineral content (BMC), and the polar moment of inertia (I _p) and heel VOS (p ranging from <0.05 to <0.01). These results were independent of age, height (or femoral length) and weight (or muscle cross-sectional area). Adolescent OI scores were not found to be significant predictors of bone structure or strength. Furthermore, no significant relationships were detected with areal or volumetric BMD at any site. Subjects were then categorized into either a high (H) or low/non-impact (L) group during adolescence (13–18 years) and adulthood (19–50+ years) according to their OI scores during each of these periods. Three groups were subsequently formed to reflect weight-bearing impact categories during adolescence and then adulthood: LL, HL and HH. Compared to the LL group, mid-femur total and cortical area, cortical BMC and I _p were 6.5–14.2% higher in the HH group. No differences were detected between the LL and HL groups.

Conclusions: In conclusion, these findings indicate that long-term regular participation in sport and leisure activities categorized according to an osteogenic index [but not the total time (min) spent participating in all sport and leisure activities] was an important determinant of bone size, quality and strength, but not BMD, at loaded sites in older men. Furthermore, continued participation in weight-bearing exercise in early to mid-adulthood appears to be important for reducing the risk of low bone strength in old age.

Long-term effects of calcium-vitamin-D3-fortified milk on bone geometry and strength in older men

The long-term effects of calcium and vitamin D supplementation on bone material and structural properties in older men are not known. The aim of this study was to examine the effects of high calcium (1000 mg/day)- and vitamin-D3 (800 IU/day)-fortified milk on cortical and trabecular volumetric BMD (vBMD) and bone geometry at the axial and appendicular skeleton in men aged over 50 years. One hundred and eleven men who were part of a larger 2-year randomized controlled trial had QCT scans of the mid-femur and lumbar spine (L1–L3) to assess vBMD, bone geometry and indices of bone strength [polar moment of inertia (Ipolar)]. After 2 years, there were no significant differences between the milk supplementation and control group for the change in any mid-femur or L1–L3 bone parameters for all men aged over 50 years. However, the mid-femur skeletal responses to the fortified milk varied according to age, with a split of ≤62 versus >62 years being the most significant for discriminating the changes between the two groups. Subsequent analysis revealed that, in the older men (>62 years), the expansion in mid-femur medullary area was 2.8% (P < 0.01) less in the milk supplementation compared to control group, which helped to preserve cortical area in the milk supplementation group (between group difference 1.1%, P < 0.01). Similarly, for mid-femur cortical vBMD and Ipolar, the net loss was 2.3 and 2.8% less in the milk supplementation compared to control group (P < 0.01 and <0.001, respectively). In conclusion, calcium–vitamin-D3-fortified milk may represent an effective strategy to maintain bone strength by preventing endocortical bone loss and slowing the loss in cortical vBMD in elderly men.

Motor unit synchronization measured by cross-correlation is not influenced by short-term strength training of a hand muscle

The purpose of the study was to quantify the strength of motor unit synchronization and coherence from pairs of concurrently active motor units before and after short-term (4–8 weeks) strength training of the left first dorsal interosseous (FDI) muscle. Five subjects (age 24.8 ± 4.3 years) performed a training protocol three times/week that consisted of six sets of ten maximal isometric index finger abductions, whereas three subjects (age 27.3 ± 6.7 years) acted as controls. Motor unit activity was recorded from pairs of intramuscular electrodes in the FDI muscle with two separate motor unit recording sessions obtained before and after strength training (trained group) or after 4 weeks of normal daily activities that did not involve training (control group). The training intervention resulted in a 54% (45.2 ± 8.3 to 69.5 ± 13.8 N, P = 0.001) increase in maximal index finger abduction force, whereas there was no change in strength in the control group. A total of 163 motor unit pairs (198 single motor units) were examined in both subject groups, with 52 motor unit pairs obtained from 10 recording sessions before training and 51 motor unit pairs from 10 recording sessions after training. Using the cross-correlation procedure, there was no change in the strength of motor unit synchronization following strength training (common input strength index; 0.71 ± 0.41 to 0.67 ± 0.43 pulses/s). Furthermore, motor unit coherence z scores at low (0–10 Hz; 3.9 ± 0.3 before to 4.4 ± 0.4 after) or high (10–30 Hz; 1.7 ± 0.1 before to 1.9 ± 0.1 after) frequencies were not influenced by strength training. These motor unit data indicate that increases in strength following several weeks of training a hand muscle are not accompanied by changes in motor unit synchronization or coherence, suggesting that these features of correlated motor unit activity are not important in the expression of muscle strength.

Are unilateral and bilateral patellar tendinopathy distinguished by differences in anthropometry, body composition, or muscle strength in elite female basketball players?

Background: Overuse injury to the patellar tendon (patellar tendinopathy) is a major reason for interrupted training and competition for elite athletes. In both sexes, the prevalence of unilateral and bilateral tendinopathy has been shown to differ. It has been proposed that bilateral pathology may have a different aetiology from unilateral pathology. Investigation of risk factors that may be unique to unilateral and bilateral patellar tendinopathy in female athletes may reveal insights into the aetiology of this condition.
Objectives: To examine whether anthropometry, body composition, or muscle strength distinguished elite female basketball players with unilateral or bilateral patellar tendinopathy.
Methods: Body composition, anthropometry, and muscle strength were compared in elite female basketball players with unilateral (n = 8), bilateral (n = 7), or no (n = 24) patellar tendinopathy. Body composition was analysed using a dual energy x ray absorptiometer. Anthropometric measures were assessed using standard techniques. Knee extensor strength was measured at 180°/s using an isokinetic dynamometer. z scores were calculated for the unilateral and bilateral groups (using the no tendinopathy group as controls). z scores were tested against zero.
Results: The tibia length to stature ratio was approximately 1.3 (1.3) SDs above zero in both the affected and non-affected legs in the unilateral group (p<0.05). The waist to hip ratio was 0.66 (0.78) SD above zero in the unilateral group (p<0.05). In the unilateral group, leg lean to total lean ratio was 0.42 (0.55) SD above zero (p<0.07), the trunk lean to total lean ratio was 0.63 (0.68) SD below zero (p<0.05), and leg fat relative to total fat was 0.47 (0.65) SD below zero (p<0.09). In the unilateral group, the leg with pathology was 0.78 (1.03) SD weaker during eccentric contractions (p<0.07).
Conclusions: Unilateral patellar tendinopathy has identifiable risk factors whereas bilateral patellar tendinopathy may not. This suggests that the aetiology of these conditions may be different. However, interpretation must respect the limitation of small subject numbers.

Precipitate characterisation of an advanced high-strength low-alloy (HSLA) steel using atom probe tomography

Increased fuel economy, combined with the need for the improved safety has generated the development of new hot-rolled high-strength low-alloy (HSLA) and multiphase steels such as dual-phase or transformation-induced plasticity steels with improved ductility without sacrificing strength and crash resistance. However, the modern multiphase steels with good strength-ductility balance showed deteriorated stretch-flangeability due to the stress concentration region between the soft ferrite and hard martensite phases [1]. Ferritic, hot-rolled steels can provide good local elongation and, in turn, good stretch-flangeability [2]. However, conventional HSLA ferritic steels only have a tensile strength of not, vert, similar600 MPa, while steels for the automotive industry are now required to have a high tensile strength of not, vert, similar780 MPa, with excellent elongation and stretch-flangeability [1]. This level of strength and stretch-flangeability can only be achieved by precipitation hardening of the ferrite matrix with very fine precipitates and by ferrite grain refinement. It has been suggested that Mo [3] and Ti [4] should be added to form carbides and decrease the coiling temperature to 650 °C since only a low precipitation temperature can provide the precipitation refinement [4]. These particles appeared to be (Ti, Mo)C, with a cubic lattice and a parameter of 0.433 nm, and they were aligned in rows [4]. It was reported [4] that the formation of these very fine carbides led to an increase in strength of not, vert, similar300 MPa. However, the detailed analysis of these particles has not been performed to date due to their nanoscale size. The aim of this work was to carry out a detailed investigation using atom probe tomography (APT) of precipitates formed in hot-rolled low-carbon steel containing additions Ti and Mo.

The investigated low-carbon steel, containing Fe–0.1C–1.24Mn–0.03Si–0.11Cr–0.11Mo–0.09Ti–0.091Al at.%, was produced by hot rolling. The processing route has been described in detail elsewhere [5] European Patent Application, 1616970 A1, 18.01.2006.[5]. The microstructure was characterised by transmission electron microscopy (TEM) on a Philips CM 20, operated at 200 kV using thin foil and carbon replica techniques. Qualitative energy dispersive X-ray spectroscopy (EDXS) was used to analyse the chemical composition of particles. The atomic level of particle characterisation was performed at the University of Sydney using a local electrode atom probe [6]. APT was carried out using a pulse repetition rate of 200 kHz and a 20% pulse fraction on the sample with temperature of 80 K. The extent of solute-enriched regions (radius of gyration) and the local solute concentrations in these regions were estimated using the maximum separation envelope method with a grid spacing of 0.1 nm [7]. A maximum separation distance between the atoms of interest of dmax = 1 nm was used.

The microstructure of the steel consisted of two types of fine ferrite grains: (i) small recrystallised grains with an average grain size of 1.4 ± 0.2 μm; and (ii) grains with a high dislocation density (5.8 ± 1.4 × 1014 m−2) and an average grain size of 1.9 ± 0.1 μm in thickness and 2.7 ± 0.1 μm in length (Fig. 1a). Some grains with high dislocation density displayed an elongated shape with Widmanstätten side plates and also the formation of cells and subgrains (Fig. 1a). The volume fraction of recrystallised grains was 34 ± 8%.

Characterization of nano-scale particles in hot-rolled, high strength low alloy steels (HSLA)

The contribution of nano-scale particles observed using Atom Probe Tomography in an increase of yield strength of conventional and advanced HSLA steels was studied. The advanced HSLA steel showed higher yield strength than conventional HSLA steel. There were two types of carbides, which primarily contribute to an increase in yield strength of conventional HSLA steel: (i) coarse TiC with average size of 25±5nm and (ii) fine TiC with average radius of 3±1.2nm. The presence of two types of carbides was found in the microstructure of advanced HSLA steel: (i)
nano-scale Ti0.98Mo0.02C0.6 carbides with average radius of 2.2±0.5nm, and (ii) C19Cr7Mo24 particles with an average radius of 1.5±0.3nm. The contribution of precipitation hardening in the yield strength of advanced HSLA steel due to the nano-scale particles was 174MPa, while this value in the conventional HSLA steel was 128MPa.

Effect of susceptibility to interfacial fracture on fatigue properties of spot-welded high strength sheet steel

While advanced high strength steels (AHSS) have numerous advantages for the automotive industry, they can be susceptible to interfacial fracture when spot-welded. In this study, the susceptibility of interfacial fracture to spot-weld microstructure and hardness is examined, as well as the corresponding relationships between fatigue, overload performance, and interfacial fracture for a TRIP (transformation induced plasticity) steel. Simple post-weld heat-treatments were used to alter the weld microstructure. The effect on interfacial fracture of diluting the weld pool by welding the TRIP material to non-TRIP steel was examined, along with the effect of altering the base material microstructure. Results show that weld hardness is not a good indicator of either the susceptibility to interfacial fracture, or the strength of the joint, and that interfacial fracture does not necessarily lead to a decrease in strength compared to conventional weld-failure mechanisms, i.e. button pullout. It was also found that while interfacial fracture does affect low cycle to failure behavior, there was no effect on high cycle fatigue.

Influence of low-strain deformation characteristics of high strength sheet steel on curl and springback in bend-under-tension tests

The influence of low-strain deformation behavior on curl and springback in advanced high strength steels (AHSS) was assessed using a bend-under-tension test. The effect of yielding behavior on curl and springback was examined by heat-treating two dual-phase steels to induce yield point elongation, while keeping a relatively constant tensile strength and a constant sheet thickness. A dual-phase and TRIP steel with similar initial thickness and tensile strengths were also examined to investigate the effect of work-hardening on curl and springback. It is shown that while current understanding limits prediction of curl and springback in bending under tension using only the initial sheet thickness and tensile strength, both the yielding and work-hardening behavior can affect the results. Explanations for these effects are proposed in terms of the discontinuous yielding and flow stress in the materials.