A noninvasive test for estimating myosin heavy chain of the vastus lateralis in females with mechanomyography.

This study examined relationships between percent myosin heavy chain (%MHC) expression and mechanomyographic amplitude (MMGRMS). Fifteen females (age ± SD=21.3 ± 5.3 yrs) completed isometric trapezoidal contractions at 30% and 70% maximal voluntary contraction (MVC). MMG was recorded from the vastus lateralis (VL). Participants gave a muscle biopsy of the VL post-testing. MMGRMS-torque relationships during the linearly varying segments were log-transformed and linear regressions were applied to calculate b terms (slopes). For the steady torque segment, MMGRMS was averaged. Correlations were performed for type I%MHC with the MMG variables. Multiple regression was utilized to examine prediction equations for type I%MHC. Type I%MHC was significantly correlated with the b terms during the increasing segment of the 70% MVC (p = 0.003; r = -0.718), and MMGRMS during steady torque at 30% (p = 0.008; r = -0.652) and 70% MVC (p = 0.040; r = -0.535). Type I%MHC reduced the linearity of the MMGRMS-torque relationship during the high-intensity linearly increasing segment, and MMGRMS at a low- and high-intensity steady torque. A combination of MMG variables estimated type I%MHC expression with 81.2% accuracy. MMG recorded during a low- and high-intensity isometric trapezoidal contraction may offer a simple, noninvasive test for estimating type I%MHC expression of the VL in sedentary females.

Similar Responses in the Akt/Protein Kinase B Signaling Pathway Following Different Lower-Body Exercise Volumes in Recreationally Active Men.

ABSTRACT: Pearson, JR, Moodie, N, Stout, KW, Hawkins, WC, Matuszek, M, Graham, ZA, Siedlik, JA, Vardiman, JP, and Gallagher, PM. Similar responses in the Akt/protein kinase B (PKB) signaling pathway after different lower-body exercise volumes in recreationally active men. J Strength Cond Res 37(5): 1034-1041, 2023-This project examined the differences between a single set (SS) compared to multiple sets (MS) of resistance exercise on the Akt/protein kinase B (PKB) signaling pathway, the expression of insulin-like growth factor-1 ( IGF-1 ), and the receptor for IGF -1 ( IGF-1R ) to better understand the types of resistance training protocols that are most beneficial in stimulating the muscle hypertrophic response. Sixteen healthy men were randomly selected into 2 groups of 8. Subjects in each group received 3 biopsies: (a) before exercise, (b) 15 minutes postexercise, and (c) 180 minutes postexercise. Subjects in the SS group performed 1 set of leg press to failure at 80% of their predetermined 1 repetition maximum (1RM). Subjects in the MS group performed 2 sets of 10 repetitions and 1 set to failure at 80% of their predetermined 1RM, with 3 minutes of rest between each set. Our results indicated no group × time interactions in the concentration of Akt signaling proteins. Furthermore, there were no group × time interactions in IGF-1 or IGF-1R expression. However, phosphorylated 4E-binding protein 1 levels increased 150% from pre to 180 minutes post ( p = 0.005). In addition, there was a significantly greater increase in IGF-1R expression in the SS group compared with the MS group (7.99 ± 10.07 vs. 4.41 ± 6.28; p = 0.026). Collectively, we found that a SS of resistance training evokes a similar acute Akt/PKB pathway response as MS in recreationally active men.

Notch, Numb and Numb-like responses to exercise-induced muscle damage in human skeletal muscle.

NEW FINDINGS: What is the central question of this study? Do Notch, Numb and Numb-like expression change in human skeletal muscle after exercise-induced muscle damage? What are the main finding and its importance? Notch gene expression trends toward an increase in response to an acute bout of exercise-induced muscle damage, while Numb and Numb-like expression does not change. These results suggest that human skeletal muscle response to exercise-induced muscle damage is dynamic and may differ from Drosophila and rodent models. Furthermore, the timing of muscle biopsies, training status and muscle damage protocols should be considered. ABSTRACT: This investigation examined changes in the gene and protein expression of Notch, Numb and Numb-like (Numbl) in human skeletal muscle after an acute bout of eccentric exercise-induced muscle damage. Twelve recreationally active male subjects participated in this study. These individuals completed seven sets of 10 repetitions of eccentric leg extension at 120% of one-repetition max with 2 min of rest period between sets. Four muscle biopsies of the vastus lateralis were collected: before exercise (Pre), and 3 h, 2 days and 5 days post-muscle damage. Biopsy samples were used to probe Notch, Numb and Numbl utilizing western blot and RT-qPCR techniques. The results were analysed using a one-way repeated-measures ANOVA. Notch1 mRNA expression trended toward a significant increase from Pre to 2 days post-muscle damage from baseline measures (P = 0.087), while Numb (P = 0.804) and Numbl (P = 0.480) expression was unaltered post-muscle damage. There were no significant differences in protein expression post-muscle damage for any of the proteins. These results suggest that exercise-induced muscle damage, via eccentric exercise, slightly elevates Notch1 mRNA expression.

Effect of Three Different Maximal Concentric Velocity Squat Protocols on MAPK Phosphorylation and Endocrine Responses.

Kudrna, RA, Fry, AC, Nicoll, JX, Gallagher, PM, and Prewitt, MR. Effect of three different maximal concentric velocity squat protocols on MAPK phosphorylation and endocrine responses. J Strength Cond Res 33(6): 1693-1703, 2019-The purpose of this study was to determine the effect of 3 different back squat protocols on intracellular signaling, endocrine responses, and power fatigue. Nine recreationally trained men (X ± SD; age: 21.4 ± 0.6 years; height: 177.8 ± 5.1 cm; body mass: 78.7 ± 9.7 kg), completed 3 maximal concentric velocity squat protocols in a randomized order. Testing protocols consisted of 5 sets of 10 repetitions at 30% of 1 repetition maximum (1RM); 5 sets of 5 repetitions at 70% of 1RM; and 5 sets of 3 repetitions at 90% of 1RM. Average system power for each set was obtained using a tethered external dynamometer. Pre-exercise and postexercise blood draws were analyzed for lactate, testosterone, human growth hormone (hGH), and cortisol. Muscle biopsies assessed pre-exercise and postexercise extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 phosphorylation using western blotting. Cortisol, hGH, and lactate increased after exercise (p ≤ 0.05), but did not differ between protocols (p > 0.05). Testosterone was unaltered (p > 0.05). Average power was lower for the 90% protocol than for the 30% protocol across all sets (p < 0.01). Average power was lower after the fourth and fifth set compared with the first and second set in the 90% protocol only (p ≤ 0.05). The ratio of phosphorylated-to-total ERK1/2 was higher postexercise after 90% protocol only (p ≤ 0.05). The ratio of phosphorylated-to-total p38 was unaltered after exercise (p > 0.05). Resistance load seems to affect power fatigue across the 5 sets of resistance exercise. This study found modest changes in ERK1/2 and no changes in p38 phosphorylation after maximal concentric velocity squats. Exercise volume, modality, and training status of subjects may account for these findings.

Targeting protein homeostasis in sporadic inclusion body myositis.

Sporadic inclusion body myositis (sIBM) is the commonest severe myopathy in patients more than 50 years of age. Previous therapeutic trials have targeted the inflammatory features of sIBM but all have failed. Because protein dyshomeostasis may also play a role in sIBM, we tested the effects of targeting this feature of the disease. Using rat myoblast cultures, we found that up-regulation of the heat shock response with arimoclomol reduced key pathological markers of sIBM in vitro. Furthermore, in mutant valosin-containing protein (VCP) mice, which develop an inclusion body myopathy, treatment with arimoclomol ameliorated disease pathology and improved muscle function. We therefore evaluated arimoclomol in an investigator-led, randomized, double-blind, placebo-controlled, proof-of-concept trial in sIBM patients and showed that arimoclomol was safe and well tolerated. Although arimoclomol improved some IBM-like pathology in the mutant VCP mouse, we did not see statistically significant evidence of efficacy in the proof-of-concept patient trial.

Short-Wave Diathermy Pretreatment and Inflammatory Myokine Response After High-Intensity Eccentric Exercise.

CONTEXT: Various modalities have been used to pretreat skeletal muscle to attenuate inflammation. OBJECTIVE: To determine the effects of short-wave diathermy (SWD) preheating treatment on inflammation and stress markers after eccentric exercise. DESIGN: Controlled laboratory study. SETTING: University laboratory setting. PATIENTS OR OTHER PARTICIPANTS: Fifteen male (age = 22 ± 4.9 years, height = 179.75 ± 9.56 cm, mass = 82.22 ± 12.67 kg) college-aged students. INTERVENTION(S): Seven participants were selected randomly to receive 40 minutes of SWD heat treatment (HT), and 8 participants served as the control (CON) group and rested without SWD. Both groups completed 7 sets of 10 repetitions of a high-intensity eccentric exercise protocol (EEP) at 120% of the 1-repetition maximum (1-RM) leg extension. MAIN OUTCOME MEASURE(S): We biopsied muscles on days 1, 3 (24 hours post-EEP), and 4 (48 hours post-EEP) and collected blood samples on days 1, 2 (4 hours post-EEP), 3, and 4. We determined 1-RM on day 2 (24 hours post-SWD) and measured 1-RM on days 3 and 4. We analyzed the muscle samples for interleukin 6 (IL-6), tumor necrosis factor α, and heat shock protein 70 and the blood for serum creatine kinase. RESULTS: We found a group × time interaction for intramuscular IL-6 levels after SWD (F2,26 = 7.13, P = .003). The IL-6 decreased in HT (F1,6 = 17.8, P = .006), whereas CON showed no change (P > .05). We found a group × time interaction for tumor necrosis factor α levels (F2,26 = 3.71, P = .04), which increased in CON (F2,14 = 7.16, P = .007), but saw no changes for HT (P > .05). No group × time interactions were noted for 1-RM, heat shock protein 70, or creatine kinase (P > .05). CONCLUSIONS: The SWD preheating treatment provided a treatment effect for intramuscular inflammatory myokines induced through high-intensity eccentric exercise but did not affect other factors associated with intense exercise and inflammation.

Acute heat stress prior to downhill running may enhance skeletal muscle remodeling.

Heat shock proteins (HSPs) are chaperones that are known to have important roles in facilitating protein synthesis, protein assembly and cellular protection. While HSPs are known to be induced by damaging exercise, little is known about how HSPs actually mediate skeletal muscle adaption to exercise. The purpose of this study was to determine the effects of a heat shock pretreatment and the ensuing increase in HSP expression on early remodeling and signaling (2 and 48 h) events of the soleus (Sol) muscle following a bout of downhill running. Male Wistar rats (10 weeks old) were randomly assigned to control, eccentric exercise (EE; downhill running) or heat shock + eccentric exercise (HS; 41°C for 20 min, 48 h prior to exercise) groups. Markers of muscle damage, muscle regeneration and intracellular signaling were assessed. The phosphorylation (p) of HSP25, Akt, p70s6k, ERK1/2 and JNK proteins was also performed. As expected, following exercise the EE group had increased creatine kinase (CK; 2 h) and mononuclear cell infiltration (48 h) compared to controls. The EE group had an increase in p-HSP25, but there was no change in HSP72 expression, total protein concentration, or neonatal MHC content. Additionally, the EE group had increased p-p70s6k, p-ERK1/2, and p-JNK (2 h) compared to controls; however no changes in p-Akt were seen. In contrast, the HS group had reduced CK (2 h) and mononuclear cell infiltration (48 h) compared to EE. Moreover, the HS group had increased HSP72 content (2 and 48 h), total protein concentration (48 h), neonatal MHC content (2 and 48 h), p-HSP25 and p-p70s6k (2 h). Lastly, the HS group had reduced p-Akt (48 h) and p-ERK1/2 (2 h). These data suggest that heat shock pretreatment and/or the ensuing HSP72 response may protect against muscle damage, and enhance increases in total protein and neonatal MHC content following exercise. These changes appear to be independent of Akt and MAPK signaling pathways.

Forskolin attenuates the action of insulin on the Akt-mTOR pathway in human skeletal muscle.

Forskolin (FSK) is capable of both stimulating and inhibiting the intracellular signaling pathways of protein synthesis tissues other than skeletal muscle. The purpose of this investigation was to determine if FSK administration affects various elements of the protein kinase B (Akt)-mammalian target of rapamycin (mTOR) pathway in human skeletal muscle. Ten (n = 10) healthy, young (21.6 +/- 1.3 years), nonobese (body mass index = 25.5 +/- 3.5 kg.m-2), recreationally active males were selected for participation. Following an 8 h fast, 2 muscle biopsies of the vastus lateralis were performed. The samples were sectioned and exposed to 4 in vitro treatment conditions: basal, FSK, insulin (INS), and FSK+INS. The samples were then analyzed for total and phosphorylated levels of Akt, mTOR, S6 kinase (S6K1), and 4E binding protein (4EBP1). Akt phosphorylation was significantly greater in the INS-treated samples compared with the basal and FSK conditions (p = 0.007). Furthermore, the ratio of phosphorylated Akt to total Akt (P/T) was higher in the INS samples compared with the basal and FSK samples (p = 0.001). There were no differences in mTOR phosphorylation among the 4 groups; however, total mTOR was significantly greater in the FSK+INS group (p = 0.006). There were also no differences in phosphorylated or total levels of S6K1 among the 4 groups. However, 4EBP1 phosphorylation was significantly greater in the INS-treated samples compared with the basal (p = 0.003) and FSK (p = 0.004) treatments. There were no differences in the ratio of phosphorylated 4EBP1 to total 4EBP1 (P/T) among the 4 groups. These results indicate that FSK does not activate the Akt-mTOR pathway in human skeletal muscle; however, these results suggest that FSK may inhibit the actions of INS on this pathway.

Exercise in space: human skeletal muscle after 6 months aboard the International Space Station.

The aim of this investigation was to document the exercise program used by crewmembers (n = 9; 45 +/- 2 yr) while aboard the International Space Station (ISS) for 6 mo and examine its effectiveness for preserving calf muscle characteristics. Before and after spaceflight, we assessed calf muscle volume (MRI), static and dynamic calf muscle performance, and muscle fiber types (gastrocnemius and soleus). While on the ISS, crewmembers had access to a running treadmill, cycle ergometer, and resistance exercise device. The exercise regimen varied among the crewmembers with aerobic exercise performed approximately 5 h/wk at a moderate intensity and resistance exercise performed 3-6 days/wk incorporating multiple lower leg exercises. Calf muscle volume decreased (P < 0.05) 13 +/- 2% with greater (P < 0.05) atrophy of the soleus (-15 +/- 2%) compared with the gastrocnemius (-10 +/- 2%). Peak power was 32% lower (P < 0.05) after spaceflight. Force-velocity characteristics were reduced (P < 0.05) -20 to -29% across the velocity spectrum. There was a 12-17% shift in myosin heavy chain (MHC) phenotype of the gastrocnemius and soleus with a decrease (P < 0.05) in MHC I fibers and a redistribution among the faster phenotypes. These data show a reduction in calf muscle mass and performance along with a slow-to-fast fiber type transition in the gastrocnemius and soleus muscles, which are all qualities associated with unloading in humans. Future long-duration space missions should modify the current ISS exercise prescription and/or hardware to better preserve human skeletal muscle mass and function, thereby reducing the risk imposed to crewmembers.

Technique for quantitative RT-PCR analysis directly from single muscle fibers.

The use of single-cell quantitative RT-PCR has greatly aided the study of gene expression in fields such as muscle physiology. For this study, we hypothesized that single muscle fibers from a biopsy can be placed directly into the reverse transcription buffer and that gene expression data can be obtained without having to first extract the RNA. To test this hypothesis, biopsies were taken from the vastus lateralis of five male subjects. Single muscle fibers were isolated and underwent RNA isolation (technique 1) or placed directly into reverse transcription buffer (technique 2). After cDNA conversion, individual fiber cDNA was pooled and quantitative PCR was performed using primer-probes for beta(2)-microglobulin, glyceraldehyde-3-phosphate dehydrogenase, insulin-like growth factor I receptor, and glucose transporter subtype 4. The no RNA extraction method provided similar quantitative PCR data as that of the RNA extraction method. A third technique was also tested in which we used one-quarter of an individual fiber's cDNA for PCR (not pooled) and the average coefficient of variation between fibers was <8% (cycle threshold value) for all genes studied. The no RNA extraction technique was tested on isolated muscle fibers using a gene known to increase after exercise (pyruvate dehydrogenase kinase 4). We observed a 13.9-fold change in expression after resistance exercise, which is consistent with what has been previously observed. These results demonstrate a successful method for gene expression analysis directly from single muscle fibers.

Diathermy treatment increases heat shock protein expression in female, but not male skeletal muscle.

Heat shock treatments have been used to appreciably increase heat shock protein 70 (Hsp70) content and the phosphorylation of heat shock protein 27 (Hsp27p). The purpose of this investigation was to determine whether diathermy can increase Hsp70 and Hsp27p content in skeletal muscle. Fourteen subjects (7 males and 7 females, 18-35 years) received a muscle biopsy from the v. lateralis and then underwent 20 min of diathermy followed by 20 min of hot pack heating on the contralateral leg. Twenty-four hours following treatment, a second muscle biopsy was performed on the treated leg. All samples were analyzed for Hsp70 and Hsp27p content using western immunoblotting. Images of the blots were obtained and analyzed via densitometry. A paired t-test was used to examine differences in heat shock protein content between the treated and untreated legs. Twenty-four hours following the heat treatment, female subjects significantly (P < 0.05) increased Hsp70 (+58%) and Hsp27p (+100%) content compared to the untreated leg. Male subjects had non-significant increases in Hsp70 (+35%) and Hsp27p (+32%) skeletal muscle content. These results implicate that diathermy can be an effective means to induce Hsp70 and Hsp27p in human skeletal muscle.

Influence of muscle glycogen availability on ERK1/2 and Akt signaling after resistance exercise in human skeletal muscle.

Two pathways that have been implicated for cellular growth and development in response to muscle contraction are the extracellular signal-regulated kinase (ERK1/2) and Akt signaling pathways. Although these pathways are readily stimulated after exercise, little is known about how nutritional status may affect stimulation of these pathways in response to resistance exercise in human skeletal muscle. To investigate this, experienced cyclists performed 30 repetitions of knee extension exercise at 70% of one repetition maximum after a low (2%) or high (77%) carbohydrate (LCHO or HCHO) diet, which resulted in low or high (approximately 174 or approximately 591 mmol/kg dry wt) preexercise muscle glycogen content. Muscle biopsies were taken from the vastus lateralis before, approximately 20 s after, and 10 min after exercise. ERK1/2 and p90 ribosomal S6 kinase phosphorylation increased (P < or = 0.05) 10 min after exercise, regardless of muscle glycogen availability. Akt phosphorylation was elevated (P < 0.05) 10 min after exercise in the HCHO trial but was unaffected after exercise in the LCHO trial. Mammalian target of rapamycin phosphorylation was similar to that of Akt during each trial; however, change or lack of change was not significant. In conclusion, the ERK1/2 pathway appears to be unaffected by muscle glycogen content. However, muscle glycogen availability appears to contribute to regulation of the Akt pathway, which may influence cellular growth and adaptation in response to resistance exercise in a low-glycogen state.

Skeletal muscle characteristics of people with multiple sclerosis.

OBJECTIVE: To compare the single-fiber characteristics and muscle weakness of persons with multiple sclerosis (MS) with that of healthy persons without MS. DESIGN: Descriptive. SETTING: A university-based exercise physiology laboratory. PARTICIPANTS: Fourteen subjects (7 controls, 7 people with relapsing-remitting MS; Expanded Disability Status Scale median score, 6.0; range, 2.5-6.5). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Singe muscle fiber myosin heavy chain (MHC) distribution, myosin adenosine triphosphatase fiber type, and single muscle fiber cross-sectional area (CSA). RESULTS: The distribution of MHC I, MHC IIa, MHC IIx, and total hybrid fibers (I/IIa+I/IIa/IIx+IIa/IIx) did not differ between the 2 groups. However, the distribution of MHC I/IIa/IIx fibers was greater ( P <.040) in the MS group (MS: 6% vs controls: 2%). MS subjects also had a greater proportion ( P <.002) of MHC IIx-dominant IIa/IIx fibers (MS: 46% vs controls: 13%). Single-fiber CSA and fiber type, for all fiber types, did not differ between groups. CONCLUSIONS: These data suggest that, in general, moderately impaired MS subjects with documented muscle weakness have similar MHC and fiber-type characteristics as age-matched sedentary controls. The data indicate that the quality of skeletal muscle, with regard to MHC distribution, is unaffected by MS.

Single muscle fibre contractile properties in young and old men and women.

The purpose of this study was to determine whether there was an age-related decline in the isometric and isotonic contractile function of permeabilized slow (MHC I) and fast (MHC IIa) single muscle fibres. Vastus lateralis muscle fibres from six young men (YM; 25 +/- 1 years), six young women (YW; 25 +/- 1 years), six old men (OM; 80 +/- 4 years) and six old women (OW; 78 +/- 2 years) were studied at 15 degrees C for in vitro force-velocity properties, peak force and contractile velocity. Peak power was 23-28 % lower (P < 0.05) in MHC I fibres of YW compared to the other three groups. MHC IIa peak power was 25-40 % lower (P < 0.05) in OW compared to the other three groups. No difference was found in MHC I and IIa normalized peak power among any of the groups. Peak force was lower (P < 0.05) in the YW (MHC I fibres) and OW (MHC IIa fibres) compared to the other groups. Differences in peak force with ageing were negated when normalized to cell size. No age-related differences were observed in single fibre contractile velocity of MHC I and IIa fibres. These data show that YW (MHC I) and OW (MHC IIa) have lower single fibre absolute peak power and peak force compared to men; however, these differences are negated when normalized to cell size. General muscle protein concentrations (i.e. total, sarcoplasmic and myofibrillar) from the same biopsies were lower (4-9 %, P < 0.05) in the OM and OW. However, myosin and actin concentrations were not different (P > 0.05) among the four groups. These data suggest that differences in whole muscle strength and function that are often observed with ageing appear to be regulated by quantitative rather than qualitative parameters of single muscle fibre contractile function.