A noninvasive,log-transform method for fiber type discrimination using mechanomyography

This study examined the log-transformed mechanomyographic (MMG_RMS) and electromyographic (EMG_RMS) amplitude vs. force relationships for aerobically-trained (AT), resistance-trained (RT), and sedentary (SED) individuals. Subjects performed isometric ramp contractions from 5% to 90% maximal voluntary contraction. Muscle biopsies were collected and thigh skinfolds, MMG and EMG were recorded from the vastus lateralis muscle. Linear regression models were fit to the log-transformed EMG_RMS and MMG_RMS vs. force relationships. The slope (b coefficient) and the antilog of the y-intercept (a coefficient) were calculated. The AT group had the highest percentage of type I fiber area, the RT group had the highest percentage of type IIa fiber area, and the SED group had the highest percentage of type IIx fiber area. The a coefficients were higher for the AT group than the RT and SED groups in both the MMG_RMS and EMG_RMS vs. force relationships, whereas the b coefficients were lower for the AT group than the RT and SED groups only in the MMG_RMS vs. force relationship. The group differences among the a coefficients may have reflected subcutaneous fat acting as a filter thereby reducing EMG_RMS and MMG_RMS. The lower b coefficients for the AT group in the MMG_RMS patterns may have reflected fiber area-related differences in motor unit activation strategies.     

The influence of myosin heavy chain isoform content on mechanical behavior of the vastus lateralis in vivo

This study examined correlations between type I percent myosin heavy chain isoform content (%MHC) and mechanomyographic amplitude (MMG_RMS) during isometric muscle actions. Fifteen (age = 21.63 ± 2.39) participants performed 40% and 70% maximal voluntary contractions (MVC) of the leg extensors that included increasing, steady force, and decreasing segments. Muscle biopsies were collected and MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMG_RMS–force relationships (increasing and decreasing segments) and MMG_RMS was selected at the targeted force level during the steady force segment. Correlations were calculated among type I%MHC and the b (slopes) terms from the MMG_RMS–force relationships and MMG_RMS at the targeted force. For the 40% MVC, correlations were significant (P < 0.02) between type I%MHC and the b terms from the increasing (r = −0.804) and decreasing (r = −0.568) segments, and MMG_RMS from the steady force segment (r = −0.606). Type I%MHC was only correlated with MMG_RMS during the steady force segment (P = 0.044, r = −0.525) during the 70% MVC. Higher type I%MHC reduced acceleration in MMG_RMS (b terms) during the 40% MVC and the amplitude during the steady force segments. The surface MMG signal recorded during a moderate intensity contraction provided insight on the contractile properties of the VL in vivo.     

Relationships between skinfold thickness and electromyographic and mechanomyographic amplitude recorded during voluntary and non-voluntary muscle actions

IntroductionThe purpose of this study was to examine possible correlations between skinfold thicknesses and the a terms from the log-transformed electromyographic (EMG_RMS) and mechanomyographic amplitude (MMG_RMS)-force relationships, EMG M-Waves, and MMG gross lateral movements (GLM).MethodsForty healthy subjects performed a 6-s isometric ramp contraction from 5% to 85% of their maximal voluntary contraction with EMG and MMG sensors placed on the vastus lateralis (VL) and rectus femoris (RF). A single electrical stimulus was applied to the femoral nerve to record the EMG M-waves and MMG GLMs. Skinfold thickness was assessed at the site of each electrode. Pearson’s product correlation coefficients were calculated comparing skinfold thicknesses with the a terms from the log-transformed EMG_RMS-and MMG_RMS-force relationships, EMG M-waves, and MMG GLMs.ResultsThere were no significant cor1relations (p > 0.05) between the a terms and skinfold thicknesses for the RF and VL from the EMG_RMS and MMG_RMS-force relationships. However, there were significant correlations (p < 0.05) between skinfold thicknesses and the EMG M-waves and MMG GLMs for the RF (r = −0.521, −0.376) and VL (r = −0.479, −0.484).DiscussionRelationships were only present between skinfold thickness and the amplitudes of the EMG and MMG signals during the non-voluntary muscle actions.     

Electromyographic,but not mechanomyographic amplitude–force relationships,distinguished differences in voluntary activation capabilities between individuals

The purpose of the present study was to examine the influence of activation capabilities on the electromyography (EMG_RMS) and mechanomyography amplitude (MMG_RMS)–force relationships of the vastus lateralis (VL) and rectus femoris (RF). Thirteen men (mean ± SD; age = 22 ± 3 year) performed nine submaximal contractions (10–90% maximal voluntary contraction [MVC]) with the interpolated twitch technique performed during a separate contraction at 90% MVC to calculate percent voluntary activation (%VA). Nine participants with >90% VA were categorized into the high-activated group with the remaining categorized into the moderate-activated group. Slopes (b terms) were calculated from the log-transformed EMG_RMS and MMG_RMS–force relationships. The b terms (collapsed across the VL and RF) for the EMG_RMS–force relationships were greater for the high- (1.29 ± 0.31) than the moderate-activated (1.10 ± 0.20) group. In contrast, there were no differences in the b terms for the MMG_RMS–force relationships between the high- and moderate-activated groups. For the EMG_RMS and MMG_RMS–force relationships, the b terms were greater for the RF (1.38 ± 0.30, 0.81 ± 0.20) than the VL (1.08 ± 0.19, 0.60 ± 0.13) collapsed across groups. The b terms from the EMG_RMS–force relationships, but not the MMG_RMS–force relationships, reflected differences in %VA.     

Mechanomyography is more sensitive than EMG in detecting age-related sarcopenia

The aim of this work was to investigate the effects of age-related sarcopenia on the time and frequency domain properties of lower extremity muscles’ electromyographic and mechanomyographic activities. Healthy elderly (n=10, 64.5±4.5 yr) and young (n=10, 22.6±2.8 yr) were recruited as participants. Participants’ lean thigh volumes (LTV) and 1 RM (one repetition maximum) leg strength of quadriceps and maximum speed knee extension with different load levels (45%, 60% and 75% 1 RM) were recorded. The root mean square (RMS) and the mean frequency (MF) of the surface electromyography (EMG_RMS, EMG_MF) and mechanomyography (MMG_RMS, MMG_MF) signals were collected at vastus lateralis during concentric contraction with different intensity levels. Compared to the young, the elderly had significantly less LTV, absolute and relative maximal force, as well as absolute and relative maximal power (p<.05). EMG_MF of the elderly and the young increased monotonically from 45% to 75% 1 RM testing conditions. While the MMG_RMS of the young increased with testing intensities, the MMG_RMS of the elderly increased only from 45% to 60% but leveled off from 60% to 75% 1 RM testing conditions. The results indicate the declines of muscle mass, force and power production capacity with aging. The observations could be explained by neuromuscular performance and change of MU activation patterns may result from age-related sarcopenia. Aging affected muscle power more than muscle strength, which could be due to fast fiber reduction. This is supported by our observations that the MMG_RMS differences between the young and the elderly across all three intensity level where EMG_RMS was only different at the greatest intensity. We suggest that MMG could be used as an important measurement in studying muscle contraction in age-related sarcopenia.     

Influence of energy and nutrient supply pre and post partum on performance of multiparous Simmental,Brown Swiss and Holstein cows in early lactation

A study was conducted to evaluate the effects of pre partum (PRE) and post partum (POST) dietary energy and nutrient supply (E) and their interactions on feed intake, performance and energy status in dairy cows of three breeds. In this experiment, the effects of three energy and nutrient supply levels (low (L), medium (M), high (H)), both pre-calving and post-calving, were investigated, using a 3×3 factorial arrangement of treatments. In both phases (84 days pre- and 105 days post-calving) E levels applied to a total of 81 multiparous cows of breeds Simmental (SI), Brown Swiss (BS) and Holstein–Friesian (HF; n=27 for each breed), were 75%, 100% and 125% of recommendations of the German Society of Nutrition Physiology (GfE). Dry matter intake (DMI) was restricted, if energy intake exceeded target values. Pre partum DMI and energy intake were different as designed, liveweight and body condition score (BCS) of SI cows were higher, but EB was lower, compared to BS and HF cows. Milk yield and composition were influenced by all three main experimental factors (E_PRE, E_POST, breed). Energy-corrected milk yield was 25.6, 28.6 and 30.1 kg/day for L_PRE, M_PRE and H_PRE as well as 21.5, 30.1 and 32.6 kg/day for L_POST, M_POST and H_POST, respectively. Numerically, only for milk protein content the interactions E_PRE×E_POST and E_PRE×breed reached significance. Impact of energy supply pre-calving was more pronounced when cows had lower energy supply post-calving and vice versa. On the other hand, milk yield response of cows to energy supply above requirements was greater for cows that were fed on a low energy level pre partum. Impact of energy level pre partum was higher for HF cows, showing that their milk production relies to a greater extent on mobilization of body reserves. Increasing energy supply pre partum led to a more negative energy balance post partum, mainly by increasing milk yield and content, whereas feed intake was slightly reduced. Increasing energy supply post partum enhanced milk yield as well as milk protein and lactose content. Calculated energy balance corresponded well with liveweight and BCS change. Response of milk yield to increasing energy supply followed the principle of diminishing returns, since energy was increasingly partitioned to body retention. Increasing energy supply pre partum enhances milk yield and content post partum, but exacerbates negative energy balance and its consequences.     

Method of analysis influences interpretations of sex-related differences in firing rates during prolonged submaximal isometric contractions

Objective:This study examined motor unit (MU) firing rates during a prolonged isometric contraction of the vastus lateralis (VL) for females and males.Methods:Surface electromyographic (sEMG) signals were recorded from the VL for eleven females and twelve males during a 45-second isometric trapezoid muscle actions at 40% of maximal voluntary contraction (MVC). For each MU, mean firing rate (MFR) was calculated for the initial and final 10-second epochs of the steady torque segment and regressed against recruitment threshold (RT, expressed as %MVC), as well as time at recruitment (T_REC, seconds). MFR was also averaged for each subject.Results:Significant differences existed across epochs for the y-intercepts (P=0.009) of the MFR vs. T_REC relationship, as well as the grouped MFR analysis (P<0.001); no differences were observed between epochs for the MFR vs. RT relationship. Significant differences existed between sexes for the grouped MFR analysis (P=0.049), but no differences were observed for the MFR vs. T_REC or MFR vs. RT relationships.Conclusion:Analysis method may impact interpretation of firing rate behavior; increases in MU firing rates across a prolonged isometric contraction were observed in the MFR vs. T_REC relationship and the grouped MFR analysis.     

Geographic Variation in Maternal Smoking during Pregnancy in the Missouri Adolescent Female Twin Study (MOAFTS)

ObjectiveDespite well-known adverse health effects of maternal smoking during pregnancy (MSP), it is still unclear if MSP varies geographically and if neighborhood socioeconomic deprivation (SED) plays an important role in MSP. This study aims to investigate small-area geographic variation in MSP and examine the association of SED with MSP.MethodsThe Missouri Adolescent Female Twin Study (MOAFTS) is a cohort study of female like-sex twins born in Missouri to Missouri-resident parents during 1975–1985. Biological mothers completed a baseline interview in 1995–1998 and reported MSP with the twins. Residential address of the mother at birth was geocoded. We developed a census tract-level SED index using a common factor approach based on 21 area-level socioeconomic variables from the 1980 Census data. Multilevel logistic regressions estimated geographic heterogeneity (random effect) in MSP and the odds ratios (ORs, fixed effects) of neighborhood SED associated with MSP.ResultsOf 1658 MOAFTS mothers, 35.2% reported any MSP and 21.9% reported MSP beyond the first trimester. Neighborhood SED was associated with any MSP (the highest vs. the lowest quartile: OR = 1.90, 95% confidence interval [CI] = 1.40–2.57, P_trend<0.001) and MSP beyond the first trimester (OR = 1.98, 95% CI = 1.38–2.85, P_trend = 0.002) in unadjusted analyses. After adjusting for individual covariates (demographics, socioeconomic conditions, alcohol use, and parents’ cohabitation), neighborhood SED was not associated with MSP, but geographic variation still persisted in MSP (variance = 0.41, P = 0.003) and in MSP beyond the first trimester (variance = 0.82, P<0.001).ConclusionsNeighborhood SED was associated with MSP in unadjusted analyses but this association could be explained by individual socioeconomic conditions. Nonetheless, significant geographic variation in MSP persisted and was not accounted for by differences in neighborhood SED. To develop effective interventions to reduce MSP, further studies are necessary to explore underlying reasons for its geographic variation.     

Effect of the contraction of medial rotators of the tibia on the electromyographic activity of vastus medialis and vastus lateralis

PurposeThis study attempted to assess if the resisted contraction of medial rotators of the tibia increases the ratio between the activity of vastus medialis (VM) and vastus lateralis (VL) during maximal isometric contractions (MIC) of the quadriceps femoral (QF) muscle at 90° of knee flexion.MethodsAbout 24 female subjects participated in this study, performing four series MIC of the QF. In the first series subjects performed only MIC of the QF muscle, whereas in the other three there was MIC of the QF with resisted contraction of medial rotators of the tibia, with the tibia positioned in medial, neutral and lateral rotation. During each contraction, VM and VL electromyographic signal (EMGs) and QF force were collected, being the EMGs root mean square (RMS) used to access the activity level of these muscles.ResultsThe use of the General Linear Model (GLM) test showed that for α = 0.05 there was a significant increase in the VM:VL ratio when the resisted contraction of medial rotators of the tibia was performed with the tibia in medial (p = <0.0001), neutral (p = <0.0001) and lateral rotation (p = 0.001). The same test showed that during MIC of the QF associated to resisted contraction of medial rotators of the tibia there were no significant differences in the VM:VL ratio between the three tibial rotation positions adopted (p = 0.866 [medial–neutral]; p = 0.106 [medial–lateral]; p = 0.068 [neutral–lateral]).ConclusionsThe resisted contraction of medial rotators of the tibia increases the VM:VL ratio during MIC of the QF and the tibial rotation position does not influence the VM:VL ratio during MIC associated to resisted contraction of medial rotators of the tibia.     

Task-specific performance fatigability and the bilateral deficit during isokinetic leg extensions

Objectives:The purpose of the present study was to compare the fatigue-induced changes in performance fatigability, bilateral deficit, and patterns of responses for the electromyographic (EMG) and mechanomyographic (MMG) amplitude (AMP) and mean power frequency (MPF), during unilateral and bilateral maximal, fatiguing leg extensions.Methods:Nine men (Mean±SD; age =21.9±2.4 yrs; height =181.8±11.9 cm; body mass =85.8±6.2 kg) volunteered to perform 50 consecutive maximal, bilateral (BL), unilateral dominant (DL), and unilateral non-dominant (NL) isokinetic leg extensions at 180°·s^-1, on 3 separate days. Electromyographic and MMG signals from both vastus lateralis (VL) muscles were recorded. Repeated measures ANOVAs were utilized to examine mean differences in normalized force, EMG AMP, EMG MPF, MMG AMP, MMG MPF and the bilateral deficit.Results:The results demonstrated a Condition × Repetition interaction for normalized force (p=0.004, η²_p=0.222) and EMG MPF (p=0.034, η²_p=0.214) and main effects for Repetition for EMG AMP (p=0.019, η²_p=0.231), MMG AMP (p<0.001, η²_p=0.8550), MMG MPF (p=0.009, η²_p=0.252), and the bilateral deficit (p<0.001, η²_p=0.366).Conclusions:The findings demonstrated less performance fatigability during the BL than the unilateral tasks, likely due to a reduced relative intensity via interhemispheric inhibition that attenuated the development of excitation-contraction coupling failure during the BL task.     

Rectus abdominis activity,but not femoris,is similar in different core training exercises: A statistical parametric mapping analysis

Rectus abdominis (RA) and rectus femoris (RF) differently activate in hip and trunk flexion movements. Previous studies using surface electromyography (sEMG) showed heterogenous results in mean and maximum activity of Upper (URA), Middle (MRA), and Lower (LRA) RA. Statistical Parametric Mapping (SPM) and Time-Varying Multi-muscle Co-activation function (TMCf) are emerging methods for whole-time-course continuous comparisons of muscle activity and co-activation. The aim was to analyse RA and RF activity in three core training exercises with continuous approach. Eight subjects performed Curl-up, Sit-up 45° and Sit-up 90° (where 45° is half and 90° is complete trunk flexion). sEMG from URA, MRA, LRA and RF were normalized to the maximum voluntary contraction root-mean-square (RMS_MVC), and compared among muscles/exercises with SPM and TMCf. Angular displacement was assessed using stereophotogrammetry. Curl-up, Sit-up 45° and Sit-up 90° did not differently activate URA, MRA or LRA, and in their common range of motion (ROM) RA activity was similar among the three exercises. Conversely, Sit-up exercises elicited higher RF activity than Curl-up (on average 45% vs. 25% RMS_MVC) mainly due to the wider ROM. RA-RF co-activation pattern was different in concentric and eccentric phases between Sit-up exercises and Curl-up, leading to significantly higher co-activation in Sit-up exercises.     

Effects of vitamin C,vitamin E,zinc gluconate,and selenomethionine supplementation on muscle function and oxidative stress biomarkers in patients with facioscapulohumeral dystrophy: A double-blind randomized controlled clinical trial

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disease characterized by progressive weakness and atrophy of specific skeletal muscles. As growing evidence suggests that oxidative stress may contribute to FSHD pathology, antioxidants that might modulate or delay oxidative insults could help in maintaining FSHD muscle function. Our primary objective was to test whether oral administration of vitamin C, vitamin E, zinc gluconate, and selenomethionine could improve the physical performance of patients with FSHD. Adult patients with FSHD (n=53) were enrolled at Montpellier University Hospital (France) in a randomized, double-blind, placebo-controlled pilot clinical trial. Patients were randomly assigned to receive 500 mg vitamin C, 400 mg vitamin E, 25 mg zinc gluconate and 200 μg selenomethionine (n=26), or matching placebo (n=27) once a day for 17 weeks. Primary outcomes were changes in the two-minute walking test (2-MWT), maximal voluntary contraction, and endurance limit time of the dominant and nondominant quadriceps (MVC_QD, MVC_QND, T_limQD, and T_limQND, respectively) after 17 weeks of treatment. Secondary outcomes were changes in the antioxidant status and oxidative stress markers. Although 2-MWT, MVC_Q, and T_limQ were all significantly improved in the supplemented group at the end of the treatment compared to baseline, only MVC_Q and T_limQ variations were significantly different between groups (MVC_QD: P=0.011; MVC_QND: P=0.004; T_limQD: P=0.028; T_limQND: P=0.011). Similarly, the vitamin C (P<0.001), vitamin E as α-tocopherol (P<0.001), vitamin C/vitamin E ratio (P=0.017), vitamin E γ/α ratio (P=0.022) and lipid peroxides (P<0.001) variations were significantly different between groups. In conclusion, vitamin E, vitamin C, zinc, and selenium supplementation has no significant effect on the 2-MWT, but improves MVC_Q and T_limQ of both quadriceps by enhancing the antioxidant defenses and reducing oxidative stress. This trial was registered at clinicaltrials.gov (number: NCT01596803).     

Endurance and strength training effects on physiological and muscular parameters during prolonged cycling

PurposeThis study investigated the effects of a combined endurance and strength training on the physiological and neuromuscular parameters during a 2-h cycling test.MethodsFourteen triathletes were assigned to an endurance-strength training group and an endurance-only training group. They performed three experimental trials before and after training: an incremental cycling test to exhaustion, a maximal concentric lower-limbs strength measurement and a 2-h cycling exercise. Physiological parameters, free cycling chosen cadence and the EMG of Vastus Lateralis (VL) and Rectus Femoris (RF) were analysed during the 2-h cycling task before and after a strength training programme of 5 weeks (three times per week).ResultsThe results showed that the maximum strength and the isometric maximal voluntary contraction (isoMVC) after training were significantly higher (P < 0.01) and lower (P < 0.01) than those before training, respectively, in endurance-strength training group and endurance-only group. The physiological variables measured during the cycling tests and the progressive increase (P < 0.01) in EMGi_(VL) and EMGi_(RF) throughout the 2-h cycling test did not differ between the two groups before and after training, except for the variation of EMGi_(VL) over the cycle time which was stabilized during the second hour of the 2-h cycling test due to training in endurance-strength training group. The decrease in free cycling chosen cadence observed in pre-training (P < 0.01) was also replaced by a steady free cycling chosen cadence for the endurance-strength training group during the second hour of exercise.ConclusionThis study confirmed the decrease in the free cycling chosen cadence with exercise duration and demonstrated that a specific combined endurance and strength training can prevent this decrease during a 2-h constant cycling exercise.     

Association of Ficolin-2 Serum Levels and FCN2 Genetic Variants with Indian Visceral Leishmaniasis

BackgroundVisceral leishmaniasis (VL), one of the neglected tropical diseases, is endemic in the Indian subcontinent. Ficolins are circulating serum proteins of the lectin complement system and involved in innate immunity.MethodsWe have estimated ficolin-2 serum levels and analyzed the functional variants of the encoding gene FCN2 in 218 cases of VL and in 225 controls from an endemic region of India.ResultsElevated levels of serum ficolin-2 were observed in VL cases compared to the controls (adjusted P<0.0001). The genetic analysis revealed that the FCN2 structural variant +6359 C>T (p.T236M) was associated with VL (OR=2.2, 95% CI=1.23-7.25, P=0.008) and with high ficolin-2 serum levels. We also found that the FCN2*AAAC haplotype occurred more frequently among healthy controls when compared to cases (OR=0.59, 95%CI=0.37-0.94, P=0.023).ConclusionsOur findings indicate that the FCN2 variant +6359C>T is associated with the occurrence of VL and that ficolin-2 serum levels are elevated in Leishmania infections.     

Efficacy of liposome-encapsulated mepivacaine for infiltrative anesthesia in volunteers

This blinded crossover study evaluated the efficacy and pain sensitivity evoked by a previously reported liposome-encapsulated mepivacaine formulation (). Thirty healthy volunteers received an intraoral injection (1.8?mL), at four different sessions, of the following formulations: 2% mepivacaine with 1:100,000 epinephrine (MVC_2%EPI), 3% mepivacaine (MVC_3%), and 2 and 3% liposome-encapsulated mepivacaine (MVC_2%LUV and MVC_3%LUV). Latency period and duration of anesthesia were assessed by an electrical pulp tester and injection discomfort by a visual analog scale (VAS). Data were analyzed with Tukey-Kramer and Friedman tests (P?<?0.05). No significant difference was found regarding latency period (in minutes) among the formulations (P?>?0.05). The duration of anesthesia after the injection of MVC_3%LUV was higher than the one obtained after the infiltration of MVC_2%LUV and of MVC_3% (P?<?0.05). However, the duration of anesthesia obtained with MVC_3% did not differ from the one obtained with MVC_2%LUV (P?>?0.05). MVC_3%LUV showed lower VAS median values than MVC_2%EPI (P?<?0.05), and there were no significant differences among the others formulations. Liposome-encapsulated 3% mepivacaine showed longer duration of anesthesia, in comparison to the commercial formulation of MVC_3%. MVC_2%LUV was able to produce a similar duration of anesthesia as the 3% commercial formulation, despite the 50% decrease in the anesthetic concentration. Thus, the encapsulation of mepivacaine increased the duration of anesthesia and reduced the injection discomfort caused by vasoconstrictor-associated formulations in healthy volunteers.     

Light-illumination effects on the cellular concentration of photolyase molecules in yeast

Summary The effects of light-illumination in the absence or presence of cycloheximide (CHX) on the number of photoreactivating enzyme molecules per haploid cell ofSaccharomyces cerevisiae (N _PRE) were investigated.N _PRE increased, when the cells were held in buffer in light in the absence of CHX for 24 or 48 h before UV-irradiation (buffer-holding). The increase ofN _PRE was clearly observed in cells, whoseN _PRE before bufferholding was small, that is, in stationary growth phase cells grown at 37° C and in logarithmic growing cells incubated at 30° C. In the case of buffer-holding in light in the presence of CHX or in the dark in the absence or presence of CHX, the increase ofN _PRE was small or not observed.     

Cross-Talk in Mechanomyographic Signals from the Forearm Muscles during Sub-Maximal to Maximal Isometric Grip Force

Purpose

This study aimed: i) to examine the relationship between the magnitude of cross-talk in mechanomyographic (MMG) signals generated by the extensor digitorum (ED), extensor carpi ulnaris (ECU), and flexor carpi ulnaris (FCU) muscles with the sub-maximal to maximal isometric grip force, and with the anthropometric parameters of the forearm, and ii) to quantify the distribution of the cross-talk in the MMG signal to determine if it appears due to the signal component of intramuscular pressure waves produced by the muscle fibers geometrical changes or due to the limb tremor.

Methods

Twenty, right-handed healthy men (mean ± SD: age  = 26.7±3.83 y; height  = 174.47±6.3 cm; mass  = 72.79±14.36 kg) performed isometric muscle actions in 20% increment from 20% to 100% of the maximum voluntary isometric contraction (MVIC). During each muscle action, MMG signals generated by each muscle were detected using three separate accelerometers. The peak cross-correlations were used to quantify the cross-talk between two muscles.

Results

The magnitude of cross-talk in the MMG signals among the muscle groups ranged from, R²_{x, y} = 2.45–62.28%. Linear regression analysis showed that the magnitude of cross-talk increased linearly (r² = 0.857–0.90) with the levels of grip force for all the muscle groups. The amount of cross-talk showed weak positive and negative correlations (r² = 0.016–0.216) with the circumference and length of the forearm respectively, between the muscles at 100% MVIC. The cross-talk values significantly differed among the MMG signals due to: limb tremor (MMG_TF), slow firing motor unit fibers (MMG_SF) and fast firing motor unit fibers (MMG_FF) between the muscles at 100% MVIC (p<0.05, η ² = 0.47–0.80).

Significance

The results of this study may be used to improve our understanding of the mechanics of the forearm muscles during different levels of the grip force.     

The photochemical activities and electron carriers of developing barley leaves

The development of photochemical activities in isolated barley plastids during illumination of dark-grown plants has been studied and compared with the behaviour of plastocyanin, cytochromes f, b-559_LP, b-563 and b-559_HP and pigments P546 (C550) and P700. Electron-transport activity dependent on Photosystem 1 and cyclic photophosphorylation dependent on N-methylphenazonium methosulphate (phenazine methosulphate) were very active relative to the chlorophyll content after only a few minutes of illumination of etiolated leaves, and then rapidly declined during the first few hours of greening. By contrast, Photosystem 2 activity (measured with ferricyanide as electron acceptor) and non-cyclic photophosphorylation were not detectable during the first 2½h of greening, but then increased in total amount in parallel with chlorophyll. The behaviour of the electron carriers suggested their association with either Photosystem 1 or 2 respectively. In the first group were plastocyanin, cytochrome f and cytochrome b-563, whose concentrations in the leaf did not change during greening, and cytochrome b-559_LP whose concentration fell to one-half its original value, and in the second group were cytochrome b-559_HP and pigment P546, the concentrations of which closely followed the activities of Photosystem 2. Pigment P700 could not be detected during the first hour, during which time some other form of chlorophyll may take its place in the reaction centre of Photosystem 1. The plastids started to develop grana at about the time that Photosystem 2 activity became detectable.     

Resistance Training Preserves Fat‐free Mass Without Impacting Changes in Protein Metabolism After Weight Loss in Older Women

This study assessed the effects of resistance training (RT) on energy restriction–induced changes in body composition, protein metabolism, and the fractional synthesis rate of mixed muscle proteins (FSRm) in postmenopausal, overweight women. Sixteen women (age 68 ± 1 years, BMI 29 ± 1 kg/m², mean ± s.e.m.) completed a 16‐week controlled diet study. Each woman consumed 1.0 g protein/kg/day. At baseline (weeks B1–B3) and poststudy (weeks RT12–RT13), energy intake matched each subject's need and during weeks RT1–RT11 was hypoenergetic by 2,092 kJ/day (500 kcal/day). From weeks RT1 to RT13, eight women performed RT 3 day/week (RT group) and eight women remained sedentary (SED group). RT did not influence the energy restriction–induced decrease in body mass (SED ?5.8 ± 0.6 kg; RT ?5.0 ± 0.2 kg) and fat mass (SED ?4.1 ± 0.9 kg; RT ?4.7 ± 0.5 kg). Fat free mass (FFM) and total body water decreased in SED (?1.6 ± 0.4 and ?2.1 ± 0.5 kg) and were unchanged in RT (?0.3 ± 0.4 and ?0.4 ± 0.7 kg) (group‐by‐time, P ≤ 0.05 and P = 0.07, respectively). Protein–mineral mass did not change in either group (SED 0.4 ± 0.2 kg; RT 0.1 ± 0.4 kg). Nitrogen balance, positive at baseline (2.2 ± 0.3 g N/day), was unchanged poststudy. After body mass loss, postabsorptive (PA) and postprandial (PP) leucine turnover, synthesis, and breakdown decreased. Leucine oxidation and balance were not changed. PA and total (PA + PP) FSRm in the vastus lateralis were higher after weight loss. RT did not influence these protein metabolism responses. In summary, RT helps older women preserve FFM during body mass loss. The comparable whole‐body nitrogen retentions, leucine kinetics, and FSRm between groups are consistent with the lack of differential protein–mineral mass change.