Lean Production and Its Impact on Worker Health

Lean is currently applied successfully in many industrial sectors. However, its value and impact on human health is not fully understood. To gain a better understanding, this chapter explores how ergonomics force and fatigue evaluation methods can be applied in a manner to enhance lean initiatives. These methods incorporate ergonomic-related variables of force type, force duration, force frequency, and degree of awkward posture, and incorporate the recommended cumulative rest allowance (RCRA) model as a practical fatigue-based metric. These methods and their application are discussed.

Angiotensin 1–7 prevents the excessive force loss resulting from 14- and 28-day denervation in mouse EDL and soleus muscle

Denervation leads to muscle atrophy, which is described as muscle mass and force loss, the latter exceeding expectation from mass loss. The objective of this study was to determine the efficiency of angiotensin (Ang) 1–7 at reducing muscle atrophy in mouse extensor digitorum longus (EDL) and soleus following 14- and 28-d denervation periods. Some denervated mice were treated with Ang 1–7 or diminazene aceturate (DIZE), an ACE2 activator, to increase Ang 1–7 levels. Ang 1–7/DIZE treatment had little effect on muscle mass loss and fiber cross-sectional area reduction. Ang 1–7 and DIZE fully prevented the loss of tetanic force normalized to cross-sectional area and accentuated the increase in twitch force in denervated muscle. However, they did not prevent the shift of the force–frequency relationship toward lower stimulation frequencies. The Ang 1–7/DIZE effects on twitch and tetanic force were completely blocked by A779, a MasR antagonist, and were not observed in MasR−/− muscles. Ang 1–7 reduced the extent of membrane depolarization, fully prevented the loss of membrane excitability, and maintained the action potential overshoot in denervated muscles. Ang 1–7 had no effect on the changes in α-actin, myosin, or MuRF-1, atrogin-1 protein content or the content of total or phosphorylated Akt, S6, and 4EPB. This is the first study that provides evidence that Ang 1–7 maintains normal muscle function in terms of maximum force and membrane excitability during 14- and 28-d periods after denervation.

Frequency characteristics of dissipative and generative fractional RLC circuits

Equations governing the transient and steady-state regimes of the fractional series RLC circuits containing dissipative and/or generative capacitor and inductor are posed by considering the electric current as a response to electromotive force. Further, fractional RLC circuits are analyzed in the steady-state regime and their energy consumption/production properties are established depending on the angular frequency of electromotive force. Frequency characteristics of the modulus and argument of transfer function, i.e., of circuit's equivalent admittance, are analyzed through the Bode diagrams for the whole frequency range, as well as for low and high frequencies as the asymptotic expansions of transfer function modulus and argument.

Virial and Energy Dissipation in Measurement of Dynamic Acoustic Forces Using Bimodal-frequency Excitation of Micro-cantilever Array

Virial and energy dissipation, related to oscillation observable responses, possess complementary information regarding acoustic force measurements. In this paper, we introduce a mathematical framework describing the analytic relationship between oscillation observables and energy quantities at the second eigenmode in the measurement of dynamic acoustic forces. We utilize a bimodal-frequency excitation scheme for actuation of the micro-cantilever array to obtain high-sensitivity frequency bands. Herein, we analyze the virials of acoustic force interaction and the energy dissipation levels on the domain of acoustic force frequency. For our case, we obtain the high-frequency bands of around 200-270 kHz and 440-570 kHz for the force strengths in the range of 4.0-36.0 pN. In addition, results of virials and dissipated power with respect to acoustic force strengths are introduced for low- and high-sensitivity frequency regions. Therefore, the energy quantities can be robustly utilized to determine high-sensitivity frequency windows in the measurement of dynamic acoustic forces.

Effects of alcohol on skeletal muscle contractile performance in male and female mice

Background Acute and chronic alcohol use can cause skeletal muscle myopathy in concert with impairments in skeletal muscle strength, function and fatigue resistance. However, the fundamental contractile deficits induced in the presence of alcohol versus those observed in the recovery period following the clearance of alcohol have not yet been characterized nor is it known whether sex influences these outcomes. Methods Male and female mice received an intraperitoneal injection of either saline (Control) or ethanol (EtOH; 5g/kg body weight). Muscle force, fatigue, fatigue recovery and twitch characteristics of the posterior crural muscle complex were measured in situ 1 hour and 24 hours post alcohol. Results In the presence of alcohol (1-hour post treatment) absolute and normalized force generated at 80–150 Hertz was decreased in male and female mice with concurrent reductions in the rate of force development and increases in ½ relaxation time. When expressed as a percentage of maximum force, both males and females also displayed an alcohol-induced leftward shift in the force frequency curve indicative of a type I contractile phenotype. Alcohol enhanced fatigue in both males and females but had no effect on force recovery. Following clearance of alcohol (24-hour post treatment), contractile function was completely restored in females while alcohol treated males experienced sustained reductions in absolute force and had enhanced fatigue compared with male controls. Conclusions In the presence of alcohol, both males and females exhibited significant declines in muscle force production and enhanced fatigue; however, following complete clearance of the alcohol, females recovered all functional parameters, while males did not.

Skeletal Muscle Specific Calpastatin Overexpression Mitigates Muscle Weakness in Aging and Extends Lifespan

Calpain activation has been postulated as a potential contributor to the loss of muscle mass and function associated with both aging and disease but limitations of previous experimental approaches have failed to completely examine this issue. We hypothesized that mice overexpressing calpastatin, an endogenous inhibitor of calpain (CalpOX), solely in skeletal muscle would show an amelioration of the aging muscle phenotype. We assessed 4 groups of mice (age in months): (1) young wild type (5.71±0.43) (WT); (2) young CalpOX (5.6±0.5); (3) old WT (25.81±0.56); and (4) old CalpOX (25.91±0.60) for diaphragm and limb muscle (extensor digitorum longus, EDL) force frequency relations. Aging significantly reduced diaphragm and EDL peak force in old WT mice, and decreased the force-time integral during a fatiguing protocol by 48% and 23% in aged WT diaphragm and EDL, respectively. In contrast, we found that CalpOX mice had significantly increased diaphragm and EDL peak force in old mice, similar to that observed in young mice. The impact of aging on the force-time integral during a fatiguing protocol was abolished in the diaphragm and EDL of old CalpOX animals. Surprisingly, we found that CalpOX had a significant impact on longevity, increasing median survival from 20.55 months in WT mice to 24 months in CalpOX mice (p = 0.0006).