Muscle Metabolic Rate Research Articles

Continuous measurements of respiratory muscle blood flow and oxygen consumption using noninvasive frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy.

Prior studies of muscle blood flow and muscle-specific oxygen consumption have required invasive injection of dye and magnetic resonance imaging, respectively. Such measures have limited utility for continuous monitoring of the respiratory muscles. Frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS) can provide continuous surrogate measures of blood flow index (BFi) and metabolic rate of oxygen consumption (MRO2). This study aimed to validate sternocleidomastoid FD-NIRS & DCS outcomes against electromyography (EMG) and mouth pressure (Pm) during incremental inspiratory threshold loading (ITL). Six female and six male healthy adults (means ± SD; 30 ± 7 yr, maximum inspiratory pressure 118 ± 61 cmH2O) performed incremental ITL starting at low loads (8 ± 2 cmH2O) followed by 50-g increments every 2 min until task failure. FD-NIRS & DCS continuously measured sternocleidomastoid oxygenated and deoxygenated hemoglobin + myoglobin (oxy/deoxy[Hb + Mb]), tissue saturation of oxygen (StO2), BFi, and MRO2. Ventilatory parameters including inspiratory Pm were also evaluated. Pm increased during incremental ITL (P < 0.05), reaching -47[-74 to -34] cmH2O (median [IQR: 25%-75%]) at task failure. Ventilatory parameters were constant throughout ITL (all P > 0.05). Sternocleidomastoid BFi and MRO2 increased from the start of the ITL (both P < 0.05). Deoxy[Hb + Mb] increased close to task failure, concomitantly with a constant increase in MRO2, and decreased StO2. Sternocleidomastoid deoxy[Hb + Mb], BFi, StO2, and MRO2 obtained during ITL via FD-NIRS & DCS correlated with sternocleidomastoid EMG (all P < 0.05). In healthy adults, FD-NIRS & DCS can provide continuous surrogate measures of respiratory BFi and MRO2. Increasing sternocleidomastoid oxygen consumption near task failure was associated with increased oxygen extraction and reduced tissue saturation.NEW & NOTEWORTHY This study introduces a novel approach, frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS), for noninvasive continuous monitoring of respiratory muscle blood flow and metabolic rate of oxygen consumption. Unlike prior methods involving invasive dye injection and magnetic resonance imaging, FD-NIRS & DCS offers the advantage of continuous measurement without the need for invasive procedures. It holds promise for advancing muscle physiology understanding and opens avenues for real-time monitoring of respiratory muscles.

Impact of foam rolling with and without vibration on muscle oxidative metabolism and microvascular reactivity.

There is a growing interest in use vibration foam rolling as a warm up and recovery tool. However, whether vibration foam rolling offers additional benefits to traditional foam rolling is unclear. The current study aims to compare the effects of acute foam rolling, with and without vibration, on skeletal muscle metabolism and microvascular reactivity. Fifteen physically active young males were tested on two different days, with gastrocnemius muscle microvascular function assessed using near-infrared spectroscopy coupled with the post-occlusive reactive hyperemia technique, before and after foam rolling, performed with or without vibration. The slope of tissue saturation index (TSI) decrease during occlusion between 120 s to 150 s (TSI occlusion slope) was assessed for muscle metabolic rate. Three commonly used microvascular function indexes, including the first10s TSI slope after occlusion (TSI10), time for TSI to reach half of peak magnitude (TSI1/2), and TSI peak reactive hyperemia, were also assessed. None of the measured indexes showed significance for interaction or method (all p>0.05). However, there was a main effect for time for TSI occlusion slope, TSI1/2, and TSI peak reactive hyperemia (p=0.005, 0.034 and 0.046, respectively). No main effect for time for TSI10 was detected (p=0.963). The application of foam rolling can decrease muscle metabolism, and may improve some aspects of muscle microvascular function. However, vibration foam rolling does not seem to offer any additional benefits compared to traditional foam rolling alone.

Attenuated reactive hyperemia after prolonged sitting is associated with reduced local skeletal muscle metabolism: insight from artificial intelligence.

Blunted post-occlusive reactive hyperemia (PORH) after prolonged sitting (PS) has been used as evidence of microvascular dysfunction. However, it has not been determined if confounding variables are responsible for the reduction in PORH after PS. Therefore, the purpose of this study was to examine the PS-mediated changes in cardiovascular and metabolic factors that affect PORH using artificial intelligence (AI). We hypothesized that calf muscle metabolic rate (MMR) is attenuated after PS, which may reduce tissue hypoxia during an arterial occlusion (i.e., oxygen deficit) and PORH. Thirty-one subjects (male = 13, female = 18) sat for 2.5 h. A rapid-inflation cuff was placed around the thigh above the knee to generate an arterial occlusion. PORH was represented by the reoxygenation rate (RR) of the near-infrared spectroscopy (NIRS) tissue oxygenation index (TOI) after 5-min of arterial occlusion. An artificial intelligence model (AI) defined the stimulus-response relationship between the oxygen deficit (i.e., ΔTOI and TOI deficit), and RR with 65 previous PORH recordings. If the AI predicts the experimental RRs, then the change in RR is related to the change in the oxygen deficit. RR (Δ -0.27 ± 0.55 lnTOI%·s-1, P = 0.001), MMR (Δ -0.46 ± 0.61 lnTOI%·s-1, P < 0.001), ΔTOI (Δ -0.34 ± 0.62 lnTOI%, P < 0.001), and the TOI deficit (Δ -0.42 ± 0.68 lnTOI%·s, P < 0.001) were reduced after PS. In addition, strong linear associations were found between MMR and the TOI deficit (r2 = 0.900, P < 0.001) and ΔTOI (r2 = 0.871, P < 0.001). Furthermore, the AI accurately predicted the RRs pre- and post-PS (P = 0.471, P = 0.328, respectively). Therefore, blunted PORH after PS may be caused by attenuated MMR and not microvascular dysfunction.NEW & NOTEWORTHY Prolonged sitting reduces lower leg skeletal muscle metabolic rate in healthy individuals. Artificial intelligence revealed that impaired post-occlusive reactive hyperemia after prolonged sitting is related to a reduced stimulus for vasodilation and may not be evidence of microvascular dysfunction. Current post-occlusive reactive hyperemia protocols may be insufficient to assess micro- and macrovascular function after prolonged sitting.

Embryonic modulation through thermal manipulation and in ovo feeding to develop heat tolerance in chickens.

Healthy chickens are necessary to meet the ever-increasing demand for poultry meat. Birds are subjected to numerous stressful conditions under commercial rearing systems, including variations in the environmental temperature. However, it is difficult to counter the effects of global warming on the livestock industry. High environmental temperature is a stressful condition that has detrimental effects on growth and production performance, resulting in decreased feed intake, retarded growth, compromised gut health, enhanced oxidative stress, and altered immune responses. Traditional approaches include nutritional modification and housing management to mitigate the harmful effects of hot environments. Currently, broiler chickens are more susceptible to heat stress (HS) than layer chickens because of their high muscle mass and metabolic rate. In this review, we explored the possibility of in ovo manipulation to combat HS in broiler chickens. Given their short lifespan from hatching to market age, embryonic life is thought to be one of the critical periods for achieving these objectives. Chicken embryos can be modulated through either temperature treatment or nourishment to improve thermal tolerance during the rearing phase. We first provided a brief overview of the harmful effects of HS on poultry. An in-depth evaluation was then presented for in ovo feeding and thermal manipulation as emerging strategies to combat the negative effects of HS. Finally, we evaluated a combination of the two methods using the available data. Taken together, these investigations suggest that embryonic manipulation has the potential to confer heat resistance in chickens.

A Systematic Review on Lower-Limb Industrial Exoskeletons: Evaluation Methods, Evidence, and Future Directions.

Industrial tasks that involve frequent sitting/standing transitions and squatting activities can benefit from lower-limb industrial exoskeletons; however, their use is not as widespread as their upper-body counterparts. In this review, we examined 23 articles that evaluated the effects of using Wearable Chair (WC) and Squat-assist (SA) exoskeletons. Evaluations mainly included assessment of muscular demands in the thigh, shank, and upper/lower back regions. Both types of devices were found to lessen muscular demands in the lower body by 30-90%. WCs also reduced low-back demands (~ 37%) and plantar pressure (54-80%) but caused discomfort/unsafe feeling in participants. To generalize outcomes, we suggest standardizing approaches used for evaluating the devices. Along with addressing low adoption through design upgrades (e.g., ground and body supports/attachments), we recommend that researchers thoroughly evaluate temporal effects on muscle fatigue, metabolic rate, and stability of wearers. Although lower-limb exoskeletons were found to be beneficial, discrepancies in experimental protocols (posture/task/measures) were discovered. We also suggest simulating more realistic conditions, such as walking/sitting interchangeability for WCs and lifting loads for SA devices. The presented outcomes could help improve the design/evaluation approaches, and implementation of lower limb wearable devices across industries.

Minimum effort simulations of split-belt treadmill walking exploit asymmetry to reduce metabolic energy expenditure.

Walking on a split-belt treadmill elicits an adaptation response that changes baseline step length asymmetry. The underlying causes of this adaptation, however, are difficult to determine. It has been proposed that effort minimization may drive this adaptation, based on the idea that adopting longer steps on the fast belt, or positive step length asymmetry (SLA), can cause the treadmill to exert net-positive mechanical work on a bipedal walker. However, humans walking on split-belt treadmills have not been observed to reproduce this behavior when allowed to freely adapt. To determine if an effort-minimization motor control strategy would result in experimentally observed adaptation patterns, we conducted simulations of walking on different combinations of belt speeds with a human musculoskeletal model that minimized muscle excitations and metabolic rate. The model adopted increasing amounts of positive SLA and decreased its net metabolic rate with increasing belt speed difference, reaching +42.4% SLA and -5.7% metabolic rate relative to tied-belt walking at our maximum belt speed ratio of 3:1. These gains were primarily enabled by an increase in braking work and a reduction in propulsion work on the fast belt. The results suggest that a purely effort minimization driven split-belt walking strategy would involve substantial positive SLA, and that the lack of this characteristic in human behavior points to additional factors influencing the motor control strategy, such as aversion to excessive joint loads, asymmetry, or instability.NEW & NOTEWORTHY Behavioral observations of split-belt treadmill adaptation have been inconclusive toward its underlying causes. To estimate gait patterns when driven exclusively by one of these possible underlying causes, we simulated split-belt treadmill walking with a musculoskeletal model that minimized its summed muscle excitations. Our model took significantly longer steps on the fast belt and reduced its metabolic rate below tied-belt walking, unlike experimental observations. This suggests that asymmetry is energetically optimal, but human adaptation involves additional factors.

Anthropometric measurements and food consumption analysis of older people according to place of residence and gender: A cross-sectional study.

The older population across the world is rapidly increasing, raising the importance of a healthy and independent aging process and the factors affecting it. This study aimed to examine the food consumption habits and anthropometric measurements of older people according to their gender and the place of residence. A total of 121 healthy participants aged over 80 years who lived in rural (n:70) and urban (n:51) areas in the Aegean Region of Turkey were included in the study. A questionnaire was administered to determine the demographic data and nutritional status of the participants. Three-day food consumption was recorded and then analyzed using BeBiS 8.1. The participants' adherence to the Mediterranean diet and their Healthy Eating Index-2015 values were calculated based on their food consumption. The circumferences of the waist, hip, upper-mid arm and calf of the participants were measured by the researcher using an inelastic measuring tape. Weight, fat, muscle, water and basal metabolic rate were measured using the TANITA BC730 body impedance analyzer. The mean weight, body mass index, circumferences of waist, hip and upper-mid arm,fat-free mass and basal metabolic rate were higher in the rural men than the urban ones (p<0.05). The urban women had a higher waist-to-hip ratio than the rural ones (p<0.05). There were no significant differences in the participants' adherence to the Mediterranean diet and their Healthy Eating Index values according to gender or the region they lived in. Nutrient intake was compared with the daily recommendations in the Turkish Nutrition Guide. It was found that the urban men consumed more carbohydrates, fats, vitamins A and C, and sodium. In contrast, energy, protein, fiber, vitamins E, D, B1, B2, B6 and B12, folic acid, magnesium, calcium, iron and zinc were consumed at lower amounts than recommendations. On the other hand, the rural men consumed more carbohydrates, fats, vitamins A, C and B2, folic acid, sodium and zinc. Similarly, the urban and rural women were found to have a higher intake of carbohydrates, fats, vitamins A and B2 and sodium and lower intake of other nutrients than recommendations. Old age is one of the most sensitive periods in a person's life cycle. Place of residence during this period may physiologically affect food intake, physical activity, and therefore, anthropometric measurements. Healthcare providers should take into account that place of residence may alter older individuals' nutritional status and anthropometric measurements.

Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

PurposeJoint angle is a significant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate ({text{m}dot{text{V}}text{O}}_{{2}}) would be conserved at reduced joint angles (i.e. shorter muscle lengths).MethodsEleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of flexion (0º = extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. {text{m}dot{text{V}}text{O}}_{{2}} was determined using near-infrared spectroscopy.ResultsTime to task failure/end increased as joint angle decreased (P < 0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P < 0.001), but not 30º. {text{m}dot{text{V}}text{O}}_{{2}} increased at all joint angles (P < 0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P < 0.01). There were significant correlations between torque complexity and {text{m}dot{text{V}}text{O}}_{{2}} at 90º (ApEn, r = − 0.60, P = 0.049) and 60º (ApEn, r = − 0.64, P = 0.035; DFA α, ρ = 0.68, P = 0.015).ConclusionThe lack of correlation between {text{m}dot{text{V}}text{O}}_{{2}} and complexity at 30º was likely due to low relative task demands, given the similar kinetics of {text{m}dot{text{V}}text{O}}_{{2}} and torque complexity. An inverse correlation between {text{m}dot{text{V}}text{O}}_{{2}} and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths.

Neuromechanics and Energetics of Walking With an Ankle Exoskeleton Using Neuromuscular-Model Based Control: A Parameter Study.

Powered ankle exoskeletons that apply assistive torques with optimized timing and magnitude can reduce metabolic cost by ∼10% compared to normal walking. However, finding individualized optimal control parameters is time consuming and must be done independently for different walking modes (e.g., speeds, slopes). Thus, there is a need for exoskeleton controllers that are capable of continuously adapting torque assistance in concert with changing locomotor demands. One option is to use a biologically inspired, model-based control scheme that can capture the adaptive behavior of the human plantarflexors during natural gait. Here, based on previously demonstrated success in a powered ankle-foot prosthesis, we developed an ankle exoskeleton controller that uses a neuromuscular model (NMM) comprised of a Hill type musculotendon driven by a simple positive force feedback reflex loop. To examine the effects of NMM reflex parameter settings on (i) ankle exoskeleton mechanical performance and (ii) users’ physiological response, we recruited nine healthy, young adults to walk on a treadmill at a fixed speed of 1.25 m/s while donning bilateral tethered robotic ankle exoskeletons. To quantify exoskeleton mechanics, we measured exoskeleton torque and power output across a range of NMM controller Gain (0.8–2.0) and Delay (10–40 ms) settings, as well as a High Gain/High Delay (2.0/40 ms) combination. To quantify users’ physiological response, we compared joint kinematics and kinetics, ankle muscle electromyography and metabolic rate between powered and unpowered/zero-torque conditions. Increasing NMM controller reflex Gain caused increases in average ankle exoskeleton torque and net power output, while increasing NMM controller reflex Delay caused a decrease in net ankle exoskeleton power output. Despite systematic reduction in users’ average biological ankle moment with exoskeleton mechanical assistance, we found no NMM controller Gain or Delay settings that yielded changes in metabolic rate. Post hoc analyses revealed weak association at best between exoskeleton and biological mechanics and changes in users’ metabolic rate. Instead, changes in users’ summed ankle joint muscle activity with powered assistance correlated with changes in their metabolic energy use, highlighting the potential to utilize muscle electromyography as a target for on-line optimization in next generation adaptive exoskeleton controllers.

Exercise duration and cohort affect variability and longevity of the response to exercise training in California Yellowtail (Seriola dorsalis)

Five cohorts of cultured California Yellowtail (Seriola dorsalis) were used in exercise training experiments to assess the duration of exercise necessary to induce a positive growth and fitness response, quantify the variability and replicability of this response between cohorts, and track the longevity (persistence) of exercise-induced benefits following removal from the exercise stimulus. Custom-designed raceways were used to continuously exercise juvenile yellowtail at their optimal swimming speed for two, three, or four weeks following which several fitness metrics including measures of somatic growth, white muscle fiber area, metabolic rate, and feed conversion were tracked for up to 20 weeks post exercise in comparison to non-exercised controls. Within a cohort, the longest duration of exercise (4 weeks) generally had the largest and longest-lasting impact on growth, followed by the 3-week, and then the 2-week exercise regimes. However, all exercise treatments showed substantial variability in the magnitude and longevity of the response between cohorts. For example, the positive growth response (increase in mass above that of controls) of the 4-week swimming group ranged from 9.8% to 37.8% between cohorts. This variability in the exercise response between cohorts is similar in magnitude to that associated with other experimentally manipulated variables in the exercise regimes of previous studies, and thus highlights the need for additional species-specific experiments to quantify replicability of positive exercise results. In addition, the longevity of exercise-induced benefits was highly variable between cohorts and generally not retained for prolonged periods post exercise. Most notably, the exercise-induced growth response which may result from muscle hypertrophy (increase in white muscle fiber size) during exercise, subsided within weeks. Taken together, these results indicate that exercise can play an important role in the growth and fitness of S. dorsalis and other species, however the duration of the exercise, as well as the timing of exercise in the rearing process likely have important implications for optimizing exercise training for aquaculture enhancement.

Differences between joint-space and musculoskeletal estimations of metabolic rate time profiles.

Motion capture laboratories can measure multiple variables at high frame rates, but we can only measure the average metabolic rate of a stride using respiratory measurements. Biomechanical simulations with equations for calculating metabolic rate can estimate the time profile of metabolic rate within the stride cycle. A variety of methods and metabolic equations have been proposed, including metabolic time profile estimations based on joint parameters. It is unclear whether differences in estimations are due to differences in experimental data or due to methodological differences. This study aimed to compare two methods for estimating the time profile of metabolic rate, within a single dataset. Knowledge about the consistency of different methods could be useful for applications such as detecting which part of the gait cycle causes increased metabolic cost in patients. Here we compare estimations of metabolic rate time profiles using a musculoskeletal and a joint-space method. The musculoskeletal method was driven by kinematics and electromyography data and used muscle metabolic rate equations, whereas the joint-space method used metabolic rate equations based on joint parameters. Both estimations of changes in stride average metabolic rate correlated significantly with large changes in indirect calorimetry from walking on different grades showing that both methods accurately track changes. However, estimations of changes in stride average metabolic rate did not correlate significantly with more subtle changes in indirect calorimetry due to walking with different shoe inclinations, and both the musculoskeletal and joint-space time profile estimations did not correlate significantly with each other except in the most downward shoe inclination. Estimations of the relative cost of stance and swing matched well with previous simulations with similar methods and estimations from experimental perturbations. Rich experimental datasets could further advance time profile estimations. This knowledge could be useful to develop therapies and assistive devices that target the least metabolically economic part of the gait cycle.

Putting the muscle back in microcirculation: From firefighters to near-infrared spectroscopy.

Putting the muscle back in microcirculation: From firefighters to near-infrared spectroscopy.

NIRS‐derived Microvascular Oxygen Saturation Kinetics Related to Skeletal Muscle Metabolic Rate

IntroductionSkeletal muscle tissue oxygen hemoglobin/myoglobin saturation (STO2) measured during post occlusive reactive hyperemia (PORH) provides a kinetic parameter (STO2 upslope (%/time)) that has increasingly been used as a measure of microvascular responsiveness. The magnitude of the oxygen saturation prior to cuff release (STO2 min) often correlates to STO2 upslope but the physiological variable associated with variability in STO2 min is most likely muscle metabolic rate (MR). This physiologic variable likely influences the rate of reperfusion after cuff release. The purpose of this study, therefore, was to isolate variables contributing to differences in STO2 upslope through their influence on STO2 min. Our hypothesis was that MR would significantly affect STO2 upslope.MethodsThe anterior antebrachium of twenty‐two (11 male, 11 female), 18–26 years, normoglycemic subjects was monitored continuously by near infrared spectroscopy during three upper limb PORH tests. Tissue oxygenation variables were determined prior to, during the cuff and for 2.5 min. post‐cuff release. MR was calculated in ml O2/100 g lean tissue/min and used both corrected and uncorrected for ATT (MRC). Body fat and abdominal adiposity (%) were quantified by dual energy‐ray absorptiometry. Forearm adipose tissue thickness (ATT) (3.32 + 1.43 mm, range 2.8–6.7 mm) was measured by ultrasound.ResultsSTO2 min and STO2 upslope were significantly negatively correlated (r=−0.47, P= 0.03) and both were significantly negatively correlated with MR (r = −0.75, P = &lt;0.001 and r = −0.52, P = 0.01, respectively). In a multiple, forward step‐wise regression analysis with a dependent variable of STO2 upslope and independent variables of ATT, MR or MRC, STO2min, and total body fat, only ATT entered the equation (R squared 0.334, P= 0.006); no other variable statistically added any independent predictive power to the regression equation.ConclusionsTo our knowledge, this is the first study to assess the effects of MR on NIRS STO2 upslope. In contrast to our hypothesis, MR did not affect STO2 upslope but ATT did. This finding suggests that ATT must be taken into account when assuming differences in STO2 upslope reflect differences in microvascular reactivity even in largely lean subjects.Support or Funding InformationAmerican Heart Association, Grant/Award Number: 0151183ZWheaton College Alumni Summer Research Support

Relationship between muscle metabolic rate and muscle torque complexity during fatiguing intermittent isometric contractions in humans.

To test the hypothesis that a system’s metabolic rate and the complexity of fluctuations in the output of that system are related, thirteen healthy participants performed intermittent isometric knee extensor contractions at intensities where a rise in metabolic rate would (40% maximal voluntary contraction, MVC) and would not (20% MVC) be expected. The contractions had a 60% duty factor (6 sec contraction, 4 sec rest) and were performed until task failure or for 30 min, whichever occurred sooner. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Muscle metabolic rate was determined using near‐infrared spectroscopy. At 40% MVC, task failure occurred after (mean ± SD) 11.5 ± 5.2 min, whereas all participants completed 30 min of contractions at 20% MVC. Muscle metabolic rate increased significantly after 2 min at 40% MVC (2.70 ± 1.48 to 4.04 ± 1.23 %·s‐1, P < 0.001), but not at 20% MVC. Similarly, complexity decreased significantly at 40% MVC (ApEn, 0.53 ± 0.19 to 0.15 ± 0.09; DFA α, 1.37 ± 0.08 to 1.60 ± 0.09; both P < 0.001), but not at 20% MVC. The rates of change of torque complexity and muscle metabolic rate at 40% MVC were significantly correlated (ApEn, ρ = −0.63, P = 0.022; DFA, ρ = 0.58, P = 0.037). This study demonstrated that an inverse relationship exists between muscle torque complexity and metabolic rate during high‐intensity contractions.

The Super Relaxed State of Myosin in Human Muscle

The Super Relaxed State of myosin (SRX) plays a role in maintaining the low resting metabolic rate of skeletal muscle. Pharmaceuticals that destabilize this state could increase resting muscle and whole body metabolic rate by as much as 1000 Calories/day, providing an effective treatment for obesity and type 2 diabetes. Our previous work on this state in skeletal muscle has all been in animal models. Here we extend this approach to human muscle. Biopsies from the quadriceps lateralis of both lean and obese subjects were used. Measurements of single turnovers showed an SRX with a population of 0.27 ± 0.02 and a lifetime of 150 ± 8 sec in lean subjects and a population of 0.28 ± 0.02 and a lifetime of 158 ± 10 sec in obese subjects. Piperine is a small molecule that has been shown to destabilize the SRX in rabbit fast twitch fibers, with no effect on slow twitch fibers. In human muscle, addition 100μM piperine reduced the population of the SRX by 34% in lean subjects and 25% in obese subjects, with little change in the lifetimes. The human quadriceps lateralis contains ∼50% fast twitch and ∼50% slow twitch fibers. Data obtained with piperine showed two responses with ∼50% of fibers showing a strong inhibition of the SRX and the remaining fibers showing very little, in both lean and obese subjects. Presumably the fibers showing strong inhibition are fast twitch, but this remains to be proven. We conclude that in human muscle the SRX and its response to piperine are similar to those seen previously in rabbit muscle, with little difference between lean and obese subjects. This shows that analogs of piperine that have higher affinity would provide effective treatment for metabolic diseases.

Estimation of pork quality in live pigs using biopsied muscle fibre number composition

Here, we newly provided the parameters for estimating meat quality in live pigs using the muscle biopsy. The biopsied longissimus thoracis muscle was used to identify the muscle fibre characteristics (MFCs). Of the various MFCs in biopsied muscle, muscle fibre number (MFN) composition showed the greatest correlation with the MFCs in postmortem muscle (P<0.001). Moreover, the pigs cluster groups, based on the biopsied MFN composition, demonstrated statistically significant differences in meat quality traits such as muscle pH, drip loss, and meat colour (P<0.05). Therefore, we conclude that the MFN parameters in live pigs are closely related to the postmortem muscle metabolic rate and ultimately with the quality of meat. We suggest that the higher type I and lower type IIB MFN in biopsied muscle will result in better pork quality.

Industrial Applications of Selected JFS Articles

Industrial Applications of Selected <i>JFS</i> Articles

Muscle-tendon mechanics explain unexpected effects of exoskeleton assistance on metabolic rate during walking.

The goal of this study was to gain insight into how ankle exoskeletons affect the behavior of the plantarflexor muscles during walking. Using data from previous experiments, we performed electromyography-driven simulations of musculoskeletal dynamics to explore how changes in exoskeleton assistance affected plantarflexor muscle-tendon mechanics, particularly for the soleus. We used a model of muscle energy consumption to estimate individual muscle metabolic rate. As average exoskeleton torque was increased, while no net exoskeleton work was provided, a reduction in tendon recoil led to an increase in positive mechanical work performed by the soleus muscle fibers. As net exoskeleton work was increased, both soleus muscle fiber force and positive mechanical work decreased. Trends in the sum of the metabolic rates of the simulated muscles correlated well with trends in experimentally observed whole-body metabolic rate (R2=0.9), providing confidence in our model estimates. Our simulation results suggest that different exoskeleton behaviors can alter the functioning of the muscles and tendons acting at the assisted joint. Furthermore, our results support the idea that the series tendon helps reduce positive work done by the muscle fibers by storing and returning energy elastically. We expect the results from this study to promote the use of electromyography-driven simulations to gain insight into the operation of muscle-tendon units and to guide the design and control of assistive devices.

Flipper stroke rate and venous oxygen levels in free-ranging California sea lions.

The depletion rate of the blood oxygen store, development of hypoxemia and dive capacity are dependent on the distribution and rate of blood oxygen delivery to tissues while diving. Although blood oxygen extraction by working muscle would increase the blood oxygen depletion rate in a swimming animal, there is little information on the relationship between muscle workload and blood oxygen depletion during dives. Therefore, we examined flipper stroke rate, a proxy of muscle workload, and posterior vena cava oxygen profiles in four adult female California sea lions (Zalophus californianus) during foraging trips at sea. Flipper stroke rate analysis revealed that sea lions minimized muscle metabolism with a stroke-glide strategy when diving, and exhibited prolonged glides during the descent of deeper dives (>100 m). During the descent phase of these deep dives, 55±21% of descent was spent gliding, with the longest glides lasting over 160 s and covering a vertical distance of 340 m. Animals also consistently glided to the surface from 15 to 25 m depth during these deeper dives. Venous hemoglobin saturation (SO2 ) profiles were highly variable throughout dives, with values occasionally increasing during shallow dives. The relationship between SO2 and flipper stroke rate was weak during deeper dives, while this relationship was stronger during shallow dives. We conclude that (1) the depletion of oxygen in the posterior vena cava in deep-diving sea lions is not dependent on stroke effort, and (2) stroke-glide patterns during dives contribute to a reduction of muscle metabolic rate.

Body composition and basal metabolic rate in systemic lupus erythematosus patients

Aim of the workDescriptions of the body composition parameters and metabolism in systemic lupus erythematosus (SLE) patients are limited. The aim of the present work was to assess the body composition factors and basal metabolic rate (BMR) in Iranian SLE patients and to study its relation to disease activity. Patients and methodsSeventy-four female SLE patients and 76 matched controls were included in the present study. The body mass index (BMI), body fat (BF), visceral fat (VF), body muscle (BM) and basal metabolic rate (BMR) were measured using BIA (bioelectrical impedance analysis). The international physical activity questionnaire (IPAQ) was used to assess physical activity. SLE disease activity index (SLEDAI) was assessed for all the patients. ResultsThe mean age of the patients was 38.5±10.1years with a median disease duration of 7.5years. The median SLEDAI was 4. Body composition factors (BMI, BF, VF, and BM) were not significantly different between the patients and their controls. The BMR in SLE patients was significantly lower (1328.4±154.6kcal/day) than the controls (1400.4±200.4kcal/day) (p=0.01). No differences have been found in body composition parameters and BMR between the SLE patients with high and low SLEDAI or daily corticosteroid dose. There was no significant correlation between the SLEDAI and any of the studied parameters except for a negative association with age (r=−0.3, p=0.03). ConclusionSLE women have a significantly lower BMR compared to their controls. No significant differences have been observed regarding BMI, BF, BM and VF between the groups.