Eccentric exercise ≠ eccentric contraction.

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact of changing the activation timing and level (i.e., preactivation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were used to assess muscle fascicle kinematics and muscle activity levels, respectively. Although joint kinematics were similar among MTU-stretch-hold contractions (∼40° rotation amplitude), increasing preactivation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, P ≤ 0.015). This led to increasing positive and negative fascicle work with increasing preactivation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of preactivation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, P = 0.559) by preactivation, but rFE was strongly correlated with peak fascicle force during stretch (rrm = 0.62, P = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series compliance to better understand the mechanical drivers of adaptation to exercise.NEW & NOTEWORTHY Apparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depends on the preactivation during the exercise and cannot be estimated from the muscle-tendon unit (MTU) or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series compliance and muscle preactivation need to be considered when eccentric exercise protocols are designed.

The interplay between gastrocnemius medialis force-length and force-velocity potentials, cumulative EMG activity and energy cost at speeds above and below the walk to run transition speed.

NEW FINDINGS: What is the central question of the study? Are the changes in force potentials (at the muscle level) related with metabolic changes at speeds above and below the walk-to-run transition? What is the main finding and its importance? The force-length and force-velocity potentials of gastrocnemius medialis during human walking decrease as a function of speed; this decrease is associated with an increase in cumulative EMG activity and in the energy cost of locomotion. Switching from fast walking to running is associated to an increase in the force potentials, supporting the idea that the 'metabolic trigger' that determines the transition from walking to running is ultimately driven by a reduction of the muscle's contractile capacity. ABSTRACT: The aim of this study was to investigate the interplay between the force-length (F-L) and force-velocity (F-V) potentials of gastrocnemius medialis (GM) muscle fascicles, the cumulative muscle activity per distance travelled (CMAPD) of the lower limb muscles (GM, vastus lateralis, biceps femori, tibialis anterior) and net energy cost (Cnet ) during walking and running at speeds above and below the walk-to-run transition speed (walking: 2-8 km h-1 ; running: 6-10 km h-1 ). A strong association was observed between Cnet and CMAPD: both changed significantly with walking speed but were unaffected by speed in running. The F-L and F-V potentials decreased with speed in both gaits and, at 6-8 km h-1 , were significantly larger in running. At low to moderate walking speeds (2-6 km h-1 ), the changes in GM force potentials were not associated with substantial changes in CMAPD (and Cnet ), whereas at walking speeds of 7-8 km h-1 , even small changes in force potentials were associated with steep increases in CMAPD (and Cnet ). These data suggest that: (i) the walk to run transition could be explained by an abrupt increase in Cnet driven by an upregulation of the EMG activity (e.g., in CMAPD) at sustained walking speeds (>7 km h-1 ) and (ii) the reduction in the muscle's ability to produce force (e.g., in the F-L and F-V potentials) contributes to the increase in CMAPD (and Cnet ). Switching to running allows regaining of high force potentials, thus limiting the increase in CMAPD (and Cnet ) that would otherwise occur to sustain the increase in locomotion speed.

Achilles Tendon Mechanical Behavior and Ankle Joint Function at the Walk-to-Run Transition.

Walking at speeds higher than transition speed is associated with a decrease in the plantar-flexor muscle fibres' ability to produce force and, potentially, to an impaired behaviour of the muscle−tendon unit (MTU) elastic components. This study aimed to investigate the ankle joint functional indexes and the Achilles tendon mechanical behaviour (changes in AT force and power) to better elucidate the mechanical determinants of the walk-to-run transition. Kinematics, kinetic and ultrasound data of the gastrocnemius medialis (GM) were investigated during overground walking and running at speeds ranging from 5−9 km·h−1. AT and GM MTU force and power were calculated during the propulsive phase; the ankle joint function indexes (damper, strut, spring and motor) were obtained using a combination of kinetic and kinematic data. AT force was larger in running at speeds > 6.5 km/h. The contribution of AT to the total power provided by the GM MTU was significantly larger in running at speeds > 7.5 km/h. The spring and strut indexes of the ankle were significantly larger in running at speeds > 7.5 km/h. These data suggest that the walk-to-run transition could (at least partially) be explained by the need to preserve AT mechanical behaviour and the ankle spring function.

Achilles tendon mechanical properties during walking and running are underestimated when its curvature is not accounted for.

Achilles tendon (AT) mechanical properties can be estimated using an inverse dynamic approach, taking into account the tendon internal moment arm (IMA) and its kinematic behavior. Although AT presents a curvilinear line of action, a straight-line function to estimate IMA and AT length is often utilized in the literature. In this study, we combined kinetic, kinematic and ultrasound data to understand the impact of two different approaches (straight-line vs. curvilinear) in determining AT mechanical properties in vivo (during walking and running at the self-selected speed). AT force and power were calculated based on data of AT IMA and AT length derived by both respective methods. All investigated parameters were significantly affected by the method utilized (paired t-test; p < 0.05): when using the curvilinear method IMA was about 5% lower and AT length about 1.2% higher, whereas peak and mean values of AT force and power were 5% higher when compared to the straight-line method (both in walking and running). Statistic-parametric mapping (SMP) analysis revealed significant differences in IMA during the early and the late stance phase of walking and during the late stance phase of running (p < 0.01); SPM revealed significant differences also in AT length during the entire stance phase in both locomotion modes (p < 0.01). These results confirm and extend previous findings to human locomotion: neglecting the AT curvature might be a source of error, resulting in underestimates not only of internal moment arm and tendon length, but also of tendon force and power.

Influence of muscle-belly and tendon gearing on the energy cost of human walking.

This study combines metabolic and kinematic measurements at the whole-body level, with EMG and ultrasound measurements to investigate the influence of muscle-tendon mechanical behavior on the energy cost (Cnet ) of walking (from 2 to 8 km·h-1 ). Belly gearing (Gb = Δmuscle-belly length/Δfascicles length) and tendon gearing (Gt = ∆muscle-tendon unit length/∆muscle-belly length) of vastus lateralis (VL) and gastrocnemius medialis (GM) were calculated based on ultrasound data. Pendular energy recovery (%R) was calculated based on kinematic data, whereas the cumulative activity per distance travelled (CMAPD) was calculated for the VL, GM, tibialis anterior, and biceps femoris as the ratio between their EMG activity and walking speed. Finally, total CAMPD (CMAPDTOT ) was calculated as the sum of the CMAPD of all the investigate muscles. Cnet and CMAPDTOT showed a U-shaped behavior with a minimum at 4.2 and 4.1 km·h-1 , respectively; while %R, VL, and GM belly gearing showed an opposite trend, reaching a maximum (60% ± 5%, 1.1 ± 0.1 and 1.5 ± 0.1, respectively), between 4.7 and 5 km·h-1 . Gt was unaffected by speed in GM (3.5 ± 0.1) and decreased as a function of it in VL. A multiple stepwise linear regression indicated that %R has the greatest influence on Cnet, followed by CMAPDTOT and GM belly gearing. The role of Gb on Cnet could be attributed to its role in determining muscle work: when Gb increases, fascicles shortening decreases compared with that of the muscle-belly, thereby reducing the energy cost of contraction.

The influence of in vivo mechanical behaviour of the Achilles tendon on the mechanics, energetics and apparent efficiency of bouncing gaits.

In this study, we used kinematic, kinetic, metabolic and ultrasound analysis to investigate the role of elastic energy utilization on the mechanical and physiological demands of a movement task (hopping) that primarily involves the plantar-flexor muscles to determine the contribution of tendon work to total mechanical work and its relationship with apparent efficiency (AE) in bouncing gaits. Metabolic power (PMET) and (positive) mechanical power at the whole-body level (PMEC) were measured during hopping at different frequencies (2, 2.5, 3 and 3.5 Hz). The (positive) mechanical power produced during the Achilles tendon recoil phase (PTEN) was obtained by integrating ultrasound data with an inverse dynamic approach. As a function of hopping frequency, PMEC decreased steadily and PMET exhibited a U-shape behaviour, with a minimum at about 3 Hz. AE (PMEC/PMET) showed an opposite trend and was maximal (about 0.50) at the same frequency when PTEN was also highest. Positive correlations were observed: (i) between PTEN and AE (AE=0.22+0.15PTEN, R2=0.67, P<0.001) and the intercept of this relationship indicates the value of AE that should be expected when tendon work is nil; (ii) between AE and tendon gearing (Gt=Δmuscle-tendon unit length/Δmuscle belly length; R2=0.50, P<0.001), where a high Gt indicates that the muscle is contracting more isometrically, thus allowing the movement to be more economical (and efficient); (iii) between Gt and PTEN (R2=0.73, P<0.001), which indicates that Gt could play an important role in the tendon's capability to store and release mechanical power.

Low-cost electromyography: validity against a commercial system depends on exercise type and intensity.

The aim of this study was to assess the validity of a custom-made low cost (LC) and a commercial surface EMG apparatus in controlled experimental conditions and different exercise types: maximal voluntary contractions (MVC) at 105, 90, 75, 60, 45 and 30° knee angle and explosive fix-end contractions of the knee extensors (75°) at an isometric dynamometer. sEMG of vastus lateralis was recorded from the same electrodes simultaneously, then analyzed in the same way; sEMG were finally expressed in percentage of those collected at 75°MVC. LC underestimated the sEMG signal at the more extended knee angles (30-60°), significant difference was observed only at 30°. In the explosive contractions no differences between devices were observed in average and peak sEMG, as well as in the time to peak and the activation time. Bland-Altman tests and correlation parameters indicate the LC device is not sensible enough to detect the time to peak and the peak values of the sEMG signal properly. Results suggest low-cost systems might be a valid alternative to commercial ones, but attention must be paid when analyzing rapid events.

Understanding lifetimes and failure modes of defective washing machines and dishwashers.

The available literature on average lifetimes and failure modes of household appliances is mainly based on results of surveys conducted among end-users, but very little precise information can be found on specific failure modes and repair rates. The main objective of this study is to provide quantitative data about frequent failures and average service lifetimes of two household appliances, through the analysis of repair services performed by professional repair operators. We based our analysis on available datasets provided by a representative independent repair centre based in Europe, and we focused on the failures most frequently occurring and the potential repair or discard of the appliances. A database of about 11,000 diagnoses on defective washing machines and dishwashers was analysed, and frequent failure modes and repair rates were identified. The analysis was supported by a tailored visualisation of results. Concerning washing machines, recurring failures diagnosed by the repair operator regarded the electronics, shock absorbers and bearings, doors, carbon brushes and pumps. While the highest repair rates (repaired devices over total diagnosed devices with a specific failure mode) were observed for doors, carbon brushes and removal of foreign objects, the lowest rates were observed for bearings, drums and tubs, circulation pumps and electronics. Regarding dishwashers, recurring failures involved pumps, electronics, aquastop and valves, foreign objects and doors. The lowest repair rates, however, were again observed for circulation pumps and electronics. We also observed that the average service lifetime of an appliance not repaired by repair centre operators is 12.6 years for washing machines and 12 years for dishwashers. This work brings important knowledge on lifetimes and failure modes of defective washing machines and dishwashers, concerning in particular weak and critical components, but also age of appliances to be repaired. Based on the exercise on the two appliances, we discuss a possible classification scheme for repair services of household appliances, including both information retrieved by professional repair operators and information retrieved through interviews with end-users.

Ease of disassembly of products to support circular economy strategies.

Circular economy strategies encourage, among others, concrete actions to extend the product lifetime. Product's repair and reuse, and component harvesting for reuse, all require the facilitated access to product components. Consequently, a reduction of the disassembly time and the related costs will increase the economic feasibility of product lifetime extension and therefore increase the viability of a circular economy in industrialised regions. Furthermore, disassembly has the potential to significantly increase the recycling yield and purity for precious metals, critical metals and plastics. For this reason, the European Commission and several ecolabels have considered to include design for disassembly requirements in legislation or voluntary environmental instruments. However, up to date, there is no standardised method to evaluate the ease of disassembly in an unambiguous manner with a good trade-off between the efforts required to apply the method and the accuracy of the determined disassembly time. The article proposes a robust method "eDiM" (ease of Disassembly Metric), to calculate the disassembly time based on the Maynard operation sequence technique (MOST). A straightforward calculation sheet is employed in eDiM to calculate the disassembly time given the sequence of actions and basic product information. This makes the results fully verifiable in an unambiguous manner, which makes eDiM suited to be used in policy measures in contrast to the results of prior developed methods One of the innovative aspects of eDiM is the categorization of disassembly tasks in six categories, which provides better insights on which disassembly tasks are the most time consuming and how the product design could be improved. The proposed method is illustrated by means of a case study of an LCD monitor. The presented case study demonstrates how the proposed method can be used in a policy context and how the calculated disassembly times per category can provide insights to manufacturers to improve the disassemblability of their products. The results also demonstrate how the proposed method can produce realistic results with only limited detail of input data.

Towards a durability test for washing-machines.

Durability plays a key role in enhancing resource conservation and contributing to waste minimization. The washing-machine product group represents a relevant case study for the development of a durability test and as a potential trigger to systematically address durability in the design of products. We developed a procedure to test the durability performance of washing-machines as a main objective of this research. The research method consisted of an analysis of available durability standards and procedures to test products and components, followed by an analysis of relevant references related to frequent failures. Finally, we defined the criteria and the conditions for a repeatable, relatively fast and relevant endurance test. The durability test considered the whole product tested under conditions of stress. A series of spinning cycles with fixed imbalanced loads was run on two washing-machines to observe failures and performance changes during the test. Even though no hard failures occurred, results clearly showed that not all washing-machines can sustain such a test without abrasion or performance deterioration. However, the attempt to reproduce the stress induced on a washing-machine by carrying out a high number of pure spinning cycles with fixed loads did not allow equal testing conditions: the actions of the control procedure regarding imbalanced loads differ from machine to machine. The outcomes of this research can be used as grounds to develop standardised durability tests and to, hence, contribute to the development of future product policy measures.

In search of standards to support circularity in product policies: A systematic approach.

The aspiration of a circular economy is to shift material flows toward a zero waste and pollution production system. The process of shifting to a circular economy has been initiated by the European Commission in their action plan for the circular economy. The EU Ecodesign Directive is a key policy in this transition. However, to date the focus of access to market requirements on products has primarily been upon energy efficiency. The absence of adequate metrics and standards has been a key barrier to the inclusion of resource efficiency requirements. This paper proposes a framework to boost sustainable engineering and resource use by systematically identifying standardization needs and features. Standards can then support the setting of appropriate material efficiency requirements in EU product policy. Three high-level policy goals concerning material efficiency of products were identified: embodied impact reduction, lifetime extension and residual waste reduction. Through a lifecycle perspective, a matrix of interactions among material efficiency topics (recycled content, re-used content, relevant material content, durability, upgradability, reparability, re-manufacturability, reusability, recyclability, recoverability, relevant material separability) and policy goals was created. The framework was tested on case studies for electronic displays and washing machines. For potential material efficiency requirements, specific standardization needs were identified, such as adequate metrics for performance measurements, reliable and repeatable tests, and calculation procedures. The proposed novel framework aims to provide a method by which to identify key material efficiency considerations within the policy context, and to map out the generic and product-specific standardisation needs to support ecodesign. Via such an approach, many different stakeholders (industry, academics, policy makers, non-governmental organizations etc.) can be involved in material efficiency standards and regulations. Requirements and standards concerning material efficiency would compel product manufacturers, but also help designers and interested parties in addressing the sustainable resource use issue.