Protocols for High-Resolution FluoRespirometry of intact cells, permeabilized cells, permeabilized muscle fibers, isolated mitochondria, and tissue homogenates offer sensitive diagnostic tests of ...integrated mitochondrial function using standard cell culture techniques, small needle biopsies of muscle, and mitochondrial preparation methods. Multiple substrate-uncoupler-inhibitor titration (SUIT) protocols for analysis of oxidative phosphorylation (OXPHOS) improve our understanding of mitochondrial respiratory control and the pathophysiology of mitochondrial diseases. Respiratory states are defined in functional terms to account for the network of metabolic interactions in complex SUIT protocols with stepwise modulation of coupling control and electron transfer pathway states. A regulated degree of intrinsic uncoupling is a hallmark of oxidative phosphorylation, whereas pathological and toxicological dyscoupling is evaluated as a mitochondrial defect. The noncoupled state of maximum respiration is experimentally induced by titration of established uncouplers (CCCP, FCCP, DNP) to collapse the protonmotive force across the mitochondrial inner membrane and measure the electron transfer (ET) capacity (open-circuit operation of respiration). Intrinsic uncoupling and dyscoupling are evaluated as the flux control ratio between non-phosphorylating LEAK respiration (electron flow coupled to proton pumping to compensate for proton leaks) and ET capacity. If OXPHOS capacity (maximally ADP-stimulated O
flux) is less than ET capacity, the phosphorylation pathway contributes to flux control. Physiological substrate combinations supporting the NADH and succinate pathway are required to reconstitute tricarboxylic acid cycle function. This supports maximum ET and OXPHOS capacities, due to the additive effect of multiple electron supply pathways converging at the Q-junction. ET pathways with electron entry separately through NADH (pyruvate and malate or glutamate and malate) or succinate (succinate and rotenone) restrict ET capacity and artificially enhance flux control upstream of the Q-cycle, providing diagnostic information on specific ET-pathway branches. O
concentration is maintained above air saturation in protocols with permeabilized muscle fibers to avoid experimental O
limitation of respiration. Standardized two-point calibration of the polarographic oxygen sensor (static sensor calibration), calibration of the sensor response time (dynamic sensor calibration), and evaluation of instrumental background O
flux (systemic flux compensation) provide the unique experimental basis for high accuracy of quantitative results and quality control in High-Resolution FluoRespirometry.
Abstract
Multipartite patella is an anatomical variant classified by the fragmentation of the main patellar body. The cause of this variant is due to failure in fusion of the patellar ossification ...centers. It is commonly misdiagnosed as a fracture of the patella in clinical practice, leading to unnecessary treatment measures. The aim of this review is to provide an overview of the development and classification of this variation, diagnostic imaging techniques, and assess the optimal management technique for the symptomatic patient. Multiple radiographic methods are used to identify this variant, with recent studies highlighting high sensitivity rates for nonradiative methods (ultrasound). In terms of symptomatic management, accessory fragment excision and vastus lateralis release provide the greatest alleviation of symptoms, with screw fixation being less favorable.
The effects of low-load resistance training with blood flow restriction (BFR) on hypertrophy of type I/II myofibers remains unclear, especially in females. The purpose of the present study is to ...examine changes in type I/II myofiber cross-sectional area (fCSA) and muscle CSA (mCSA) of the vastus lateralis (VL) from before (Pre) to after (Post) 6 wk of high-load resistance training (HL;
= 15, 8 females) and low-load resistance training with BFR (
= 16, 8 females). Mixed-effects models were used to analyze fCSA with group (HL, BFR), sex (M, F), fiber type (I, II), and time (Pre, Post) included as factors. mCSA increased from pre- to posttraining (
< 0.001,
= 0.91) and was greater in males compared with females (
< 0.001,
= 2.26). Type II fCSA increased pre- to post-HL (
< 0.05,
= 0.46) and was greater in males compared with females (
< 0.05,
= 0.78). There were no significant increases in fCSA pre- to post-BFR for either fiber type or sex. Cohen's
, however, revealed moderate effect sizes in type I and II fCSA for males (
= 0.59 and 0.67), although this did not hold true for females (
= 0.29 and 0.34). Conversely, the increase in type II fCSA was greater for females than for males after HL. In conclusion, low-load resistance training with BFR may not promote myofiber hypertrophy to the level of HL resistance training, and similar responses were generally observed for males and females. In contrast, comparable effect sizes for mCSA and 1-repetition maximum (1RM) between groups suggest that BFR could play a role in a resistance training program.
This is the first study, to our knowledge, to examine myofiber hypertrophy from low-load resistance training with blood flow restriction (BFR) in females. Although this type of training did not result in myofiber hypertrophy, there were comparable increases in muscle cross-sectional area compared with high-load resistance training. These findings possibly highlight that males and females respond in a similar manner to high-load resistance training and low-load resistance training with BFR.
Ultrasound-derived echo intensity (EI) has been used as a physiological marker for changes in skeletal muscle "quality" with physical training, disuse, aging, and neuromuscular disorders. However, ...the methodological and physiological factors influencing EI and its longitudinal change are still unclear. Here, we performed two separate experiments to investigate the effects of muscle temperature and fascicle angle, which are known to influence muscle tissue and sound wave properties and therefore affect EI.
In experiment 1 ( n = 16, 28.0 ± 6.6 yr), vastus lateralis (VL) ultrasonographic images were acquired and intramuscular temperature continuously recorded for 15 min after 20 min of heating to 40.4°C ± 0.7°C using a microwave device. In experiment 2 ( n = 17, 30.2 ± 9.8 yr), VL sonographic images were obtained with the knee both fully extended (0°) and flexed to 90° and EI and fascicle angle measured post hoc . Fascicle movement was tracked during the passive knee flexion to ensure that sonographic images were obtained at the same muscle region. Knee flexion reduced muscle thickness, and we therefore reran analyses calculating EI using identical dimensions to minimize this effect.
EI decreased only immediately after the passive heating, and although a moderate, negative correlation was observed between EI and temperature ( rrm = -0.36), the effect of muscle temperature was small ( β = 0.97 (-1.89 to -0.06) per degree Celsius, P = 0.051). Nonetheless, EI increased as fascicle angle decreased, and a large, negative correlation ( rrm = -0.85) was observed; the effect of fascicle angle on EI was large ( β = 3.0 (-3.8 to -2.2) per degree, P < 0.01), and this was maintained when analyses were performed at a constant depth of the region of interest ( β = 3.5 (-4.4 to -2.7) per degree, P < 0.01).
These findings support the hypothesis that fascicle angle meaningfully affects VL EI but provides weak evidence of a temperature effect in vivo . Thus, acute fascicle angle alterations should be accounted for in studies using EI measurements, and longer-term studies should consider whether changes in EI might be partly explained by a change in fascicle angle.
Direct determination of muscle fiber composition is invasive and expensive, with indirect methods also requiring specialist resources and expertise. Performing resistance exercises at 80% 1RM is ...suggested as a means of indirectly estimating muscle fiber composition, though this hypothesis has never been validated against a direct method. The aim of the study was to investigate the relationship between the number of completed repetitions at 80% 1RM of back squat exercise and muscle fiber composition. Thirty recreationally active participants’ (10 females, 20 males) 1RM back squat load was determined, before the number of consecutive repetitions at 80% 1RM was recorded. The relationship between the number of repetitions and the percentage of fast-twitch fibers from vastus lateralis was investigated. The number of completed repetitions ranged from 5 to 15 and was independent of sex, age, 1RM, training frequency, training type, training experience, BMI or muscle fiber cross-sectional area. The percentage of fast-twitch muscle fibers was inversely correlated with the number of repetitions completed (r = –0.38,
P
= 0.039). Participants achieving 5 to 8 repetitions (
n
= 10) had significantly more fast-twitch muscle fibers (57.5 ± 9.5 vs 44.4 ± 11.9%,
P
= 0.013) than those achieving 11–15 repetitions (
n
= 11). The remaining participants achieved 9 or 10 repetitions (
n
= 9) and on average had equal proportion of fast- and slow-twitch muscle fibers. In conclusion, the number of completed repetitions at 80% of 1RM is moderately correlated with muscle fiber composition.
The firing properties of the motor units are usually affected by the motor task. However, it has not been clarified whether the firing properties of the motor units of a specific muscle are different ...between postural and voluntary tasks. Therefore, this study investigated whether the recruitment and rate coding of the motor units differ between these two motor tasks. Thirteen healthy volunteers performed trapezoidal muscle contraction with a target value of 15% maximum electromyography (EMG) activity by voluntary left knee extension in the sitting position (voluntary task) and postural maintenance in the semi-squatting position (postural task) with a knee flexion angle of 30°. We obtained four channels of surface EMG activity during each task from left vastus lateralis muscle. We extracted the firing properties of individual motor units using the EMG decomposition algorithm. The recruitment threshold and motor unit action potential amplitude were significantly lower in the postural task than in the voluntary task, and conversely, the mean firing rate was significantly higher. These results were explained by the preferential recruitment of motor units with higher recruitment threshold and amplitude in the voluntary task, while motor units with lower recruitment threshold and higher firing rate were preferentially recruited in the postural task. Preferential activation of fatigue-resistant motor units in the postural task is a reasonable strategy as it allows for sustained postural maintenance. We provide the first evidence that motor unit firing properties are clearly different between postural and voluntary tasks, even at the same muscle activity level.
The current randomized controlled study investigated whether or not the inclusion of the eccentric phase in resistance training favors the contralateral strength gains after different unilateral ...protocols, and whether such gains are retained after detraining. Sixty healthy women were randomly assigned to a unilateral concentric-only (CONC), eccentric-only (ECC), concentric-eccentric (TRAD) volume-equated knee extension training or control group (CON). The participants trained 2 days/week for 8 weeks and then did not train for further 8 weeks. Knee extensors isokinetic concentric, eccentric, and isometric peak torque and
muscle thickness were assessed in the contralateral limb at baseline, post-training, and post-detraining. At post-training, concentric peak torque increased in CONC +9.2%, 95%CI (+6.2/+12.3),
< 0.001, ES: 0.70, 95%CI (0.01/1.39), ECC +11.0% (+7.7/+14.2),
< 0.001: ES: 0.66(0.09/1.23) and TRAD +8.5%(+5.7/+11.6),
< 0.001, ES: 0.50(0.02/0.98). Eccentric peak torque increased in ECC in ECC +15.0%(+11.4/+20.7),
< 0.001, ES: 0.91(0.14/1.63) and TRAD +5.5%(+0.3/10.7),
= 0.013, ES: 0.50(0.05/0.95). Isometric peak torque increased in ECC +11.3(+5.8/16.8),
< 0.001, ES: 0.52(0.10/0.94) and TRAD +8.6%(+3.4/+13.7),
< 0.001, ES: 0.55(0.14/0.96). No change in eccentric and isometric peak torque occurred in CONC (
> 0.05). Muscle thickness did not change in any group (
> 0.05). At post-detraining, all groups preserved the contralateral strength gains observed at post-training (
< 0.05). The findings showed that ECC and TRAD increased contralateral knee extensors strength in concentric, eccentric, and isometric modality, while CONC only increased concentric strength. The eccentric phase appears to amplify the cross-education effect, permitting a transfer in strength gaining toward multiple testing modalities. Both eccentric-based and traditional eccentric-concentric resistance protocols are recommended to increase the contralateral retention in strength gains after a detraining period.
Aim
To investigate the relationships between motor unit action potential amplitudes (MUAPAMP), muscle cross‐sectional area (mCSA) and composition (mEI), per cent myosin heavy chain (%MHC) areas and ...sex in the vastus lateralis (VL).
Methods
Ten males and 10 females performed a submaximal isometric trapezoid muscle action that included a linearly increasing, steady torque at 40% maximal voluntary contraction, and linearly decreasing segments. Surface electromyographic decomposition techniques were utilized to determine MUAPAMPS in relation to recruitment thresholds (RT). Ultrasound images were taken to quantify muscle mCSA and mEI. Muscle biopsies were collected to calculate %MHC areas. Y‐intercepts and slopes were calculated for the MUAPAMP vs RT relationships for each subject. Independent‐samples t tests and ANOVA models examined sex‐related differences in mCSA, mEI, slopes and y‐intercepts for the MUAPAMP vs RT relationships and %MHC areas. Correlations were performed among type IIA and total type II %MHC area, mCSA and the slopes and y‐intercepts for the MUAPAMP vs RT relationships.
Results
Males exhibited greater slopes for the MUAPAMP vs RT relationships (P = .003), mCSA (P < .001) and type IIA %MHC (P = .011), whereas females had greater type I %MHC area (P = .010) and mEI (P = .024). The mCSA, type IIA and total II %MHC area variables were correlated (P < .001‐.015, r = .596‐.836) with the slopes from the MUAPAMP vs RT relationships.
Conclusion
Sex‐related differences in mCSA and MUAPAMPS of the higher‐threshold MUs were likely the result of larger muscle fibres expressing type II characteristics for males.
To describe the possible effects of chronic specific exercise training, the present study compared the anthropometric variables, muscle–tendon unit (MTU) architecture, passive stiffness, and force ...production capacity between a group of competitive cyclists and runners. Twenty-seven competitive male cyclists (n = 16) and runners (n = 11) participated. B-mode ultrasound evaluation of the vastus lateralis muscle and patellar tendon as well as passive stiffness of the knee extensors MTU were assessed. The athletes then performed a test of knee extensor maximal voluntary isometric contractions. Cyclists displayed greater thigh girths, vastus lateralis pennation angle and muscle thickness, patellar tendon cross-sectional area, and MTU passive stiffness than runners (
P
< .05). Knee extensor force production capacity also differed significantly, with cyclists showing greater values compared with runners (
P
< .05). Overall, the direct comparison of these 2 populations revealed specific differences in the MTU, conceivably related to the chronic requirements imposed through the training for the different disciplines.
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