Search

A non‐exercise method equation using seismocardiography for estimating V̇O2peak (SCG V̇O2peak) has previously been validated in healthy subjects. However, the performance of the SCG V̇O2peak within a trained population is unknown, and the ability of the model to detect changes over time is not well elucidated. Forty‐seven sub‐elite football players were tested at the start of pre‐season (SPS) and 36 players completed a test after eight weeks at the end of the pre‐season (EPS). Testing included an SCG V̇O2peak estimation at rest and a graded cardiopulmonary exercise test (CPET) on a treadmill for determination of V̇O2peak. Agreement between SCG V̇O2peak and CPET V̇O2peak showed a large underestimation at SPS (bias ± 95% CI: −9.9 ± 1.8, 95% Limits of Agreement: 2.2 to −22.0 mL·min−1 kg−1). At EPS no interaction (p = 0.3590) but a main effect of time (p < 0.0001) and methods (p < 0.0001) was observed between SCG and CPET V̇O2peak. No correlation in V̇O2peak changes was observed between SCG and CPET (r = −20.0, p = 0.2484) but a fair agreement in classifying the correct directional change in V̇O2peak with the SCG method was found (Cohen's κ coefficient = 0.28 ± 0.25). Overall, the SCG V̇O2peak method lacks accuracy and despite being able to estimate group changes, it was incapable of detecting individual changes in V̇O2peak following a pre‐season period in sub‐elite football players. The SCG algorithm needs to be further adjusted and the accuracy and precision improved for the method to be applicable for use within a trained population. Highlights: This is the first time a non‐exercise method using seismocardiography for the estimation of V̇O2peak has been validated in sub‐elite football players.The seismocardiography V̇O2peak method lacks accuracy within a trained population as it underestimates V̇O2peak compared to the gold standard measurement in sub‐elite football players.The seismocardiography V̇O2peak method can estimate the group changes in V̇O2peak following the pre‐season training period in sub‐elite football players. However, it is incapable of detecting individual changes.Adjustment of the seismocardiography V̇O2peak algorithm is needed and the accuracy and precision improved for the method to be applicable for use within a trained population. [ABSTRACT FROM AUTHOR]

Introduction: Liver fat (LF) and visceral adipose tissue (VAT) content decreases with training, however, this has mainly been investigated in sedentary obese or healthy participants. The aim of this study was to investigate the effects of repeated prolonged exercise on LF and VAT content in well‐trained older men and to compare baseline LF and VAT content to recreationally active older men. Method: A group of five well‐trained older men were tested before and after cycling a total distance of 2558 km in 16 consecutive days. VAT content and body composition was measured using DXA before a bicycle ergometer test was performed to determine maximal fat oxidation (MFO), maximal oxygen consumption (VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$), and the relative intensity at which MFO occurred (Fatmax). LF content was measured on a separate day using MRI. For comparison of baseline values, a control group of eight healthy age‐ and BMI‐matched recreationally active men were recruited. Results: The well‐trained older men had lower VAT (p = 0.02), and a tendency toward lower LF content (p = 0.06) compared with the control group. The intervention resulted in decreased LF content (p = 0.02), but VAT, fat mass, and lean mass remained unchanged. VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$, MFO, and Fatmax were not affected by the intervention. Conclusion: The study found that repeated prolonged exercise reduced LF content, but VAT and VO2max$$ {\mathrm{VO}}_{2_{\mathrm{max}}} $$ remained unchanged. Aerobic capacity was aligned with lower LF and VAT in older active men. [ABSTRACT FROM AUTHOR]

Purpose: In Football, the high‐intensity running bouts during matches are considered decisive. Interestingly, recent studies showed that peak fat oxidation rates (PFO) are higher in football players than other athletes. This study aimed to investigate whether PFO increases following a pre‐season. Secondarily, and due to COVID‐19, we investigated whether PFO is related to the physical performance in a subgroup of semi‐professional male football players. Methods: Before and after 8 weeks of pre‐season training, 42 sub‐elite male football players (18 semi‐professionals and 24 non‐professionals) had a dual‐energy x‐ray absorptiometry scan and performed a graded exercise test on a treadmill for the determination of PFO, the exercise intensity eliciting PFO (Fatmax) and peak oxygen uptake (V̇O2peak). Additionally, the semi‐professional players performed a Yo‐Yo Intermittent Recovery Test level 2 (YYIR2) before and after pre‐season training to determine football‐specific running performance. Results: PFO increased by 11 ± 10% (mean ± 95% CI), p = 0.031, and V̇O2peak increased by 5 ± 1%, p < 0.001, whereas Fatmax was unchanged (+12 ± 9%, p = 0.057), following pre‐season training. PFO increments were not associated with increments in V̇O2peak (Pearson's r2 = 0.00, p = 0.948) or fat‐free mass (FFM) (r2 = 0.00, p = 0.969). Concomitantly, YYIR2 performance increased in the semi‐professional players by 39 ± 17%, p < 0.001, which was associated with changes in V̇O2peak (r2 = 0.35, p = 0.034) but not PFO (r2 = 0.13, p = 0.244). Conclusions: PFO, V̇O2peak, and FFM increased following pre‐season training in sub‐elite football players. However, in a subgroup of semi‐professional players, increments in PFO were not associated with improvements in YYIR2 performance nor with increments in V̇O2peak and FFM. [ABSTRACT FROM AUTHOR]

Introduction: Decreased fasting and oral glucose-stimulated incretin hormone concentrations following moderate-intensity continuous endurance training interventions have been reported in glucose-tolerant people, however results are conflicting. The effect of more time-efficient, very low-volume, high-intensity interval training (HIT) on circulating incretin hormone levels has never been studied. Materials and methods: Ten sedentary and overweight-to-obese participants (4 women and 6 men; age 43 ± 6 years (mean ± SD); BMI 30.2 ± 3.2 kg∙m−2; HbA1c 35 ± 5.1 mmol∙mol−1 (5.3 ± 0.3%); VO2max 30 ± 5 ml∙min−1∙kg−1) from the Copenhagen cohort of the METAPREDICT trial underwent 6 weeks of supervised low-volume HIT (3 sessions per week: 7 × 1 min at ∼100% VO2max separated by 1 min of active recovery). We measured glucose, insulin, C-peptide, glucagon, GLP-1 and GIP concentrations during a frequently sampled 75 g oral glucose tolerance test as well as VO2max and body composition before and after the intervention. Results: Training compliance was 100%. Relative VO2max improved after the intervention (median 2.69 ml∙min−1∙kg−1, IQR [0.43; 3.14], p = 0.037) while there were no significant effects on body weight and composition. No significant effects on oral glucose-stimulated glucose and hormone responses or estimates of insulin sensitivity and β-cell function were observed. Conclusion: Low-volume HIT improved aerobic fitness, but neither affected glucose tolerance nor oral glucose-stimulated incretin hormone responses in sedentary and overweight-to-obese people. Highlights Ten sedentary, overweight-to-obese, glucose-tolerant participants underwent 6 weeks of supervised, very low-volume HIT. Aerobic fitness improved. Fasting and oral glucose-stimulated incretin hormone concentrations were not affected. [ABSTRACT FROM AUTHOR]

Statins are prescribed for the treatment of elevated cholesterol, but they may negatively affect metabolism, muscle performance, and the response to training. Coenzyme Q10 (CoQ10) supplementation may alleviate these effects. Combined simvastatin and CoQ10 treatment during physical training has never been tested. We studied the response to 8 weeks training (maximal oxygen uptake (V̇O2max${\dot{V}_{{{\rm{O}}_{\rm{2}}}{\rm{max}}}}$), fat oxidation (MFO), the workload at which MFO occurred, and muscle strength) in statin naive dyslipidaemic patients who received simvastatin (40 mg/day) with (S + Q, n = 9) or without (S + Pl, n = 10) CoQ10 supplementation (2 × 200 mg/day) or placebo (Pl + Pl, n = 7) in a randomized, double‐blind placebo‐controlled study. V̇O2max${\dot{V}_{{{\rm{O}}_{\rm{2}}}{\rm{max}}}}$ and maximal workload increased with training (main effect of time, P < 0.05). MFO increased from 0.29 ± 0.10, 0.26 ± 0.10, and 0.38 ± 0.09 to 0.42 ± 0.09, 0.38 ± 0.10 and 0.48 ± 0.16 g/min in S + Q, S + Pl, and Pl + Pl, respectively (main effect of time, P = 0.0013). The workload at MFO increased from 75 ± 25, 56 ± 23, and 72 ± 17 to 106 ± 25, 84 ± 13 and 102 ± 31 W in S + Q, S + Pl, and Pl + Pl, respectively (main effect of time, P < 0.0001). Maximal voluntary contraction and rate of force development were unchanged. Exercise improved aerobic physical capacity and simvastatin with or without CoQ10 supplementation did not inhibit this adaptation. The similar increases in MFO and in the workload at which MFO occurred in response to training shows that the ability to adapt substrate selection and oxidation rates is preserved with simvastatin treatment, despite the potential negative impact of simvastatin at the mitochondrial level. CoQ10 supplementation does not augment this adaptation. Key points: Simvastatins are prescribed for treatment of elevated cholesterol, but they may negatively affect metabolism, muscle performance and the response to training.Coenzyme Q10 (CoQ10) supplementation may alleviate some of these effects.We found that simvastatin treatment does not negatively affect training‐induced adaptations of substrate oxidation during exercise.Likewise, maximal oxygen uptake increases with physical training also in patients in treatment with simvastatin.CoQ10 supplementation in simvastatin‐treated patients presents no advantage in the adaptations to physical trainingSimvastatin treatment decreases plasma concentrations of total CoQ10, but this can be alleviated by simultaneous supplementation with CoQ10 [ABSTRACT FROM AUTHOR]

Purpose: To examine efficacy of 12 months Football Fitness offered twice per week on bone mineral density (BMD), bone turnover markers (BTM), postural balance, muscle strength, and body composition in women treated for early‐stage breast cancer (BC). Methods: Women treated for early‐stage BC were randomized to Football Fitness (FFG, n = 46) or control (CON, n = 22) in a 2:1 ratio for 12 months, with assessments performed at baseline, 6 months and 12 months. Outcomes were total body‐, lumbar spine‐ and proximal femur BMD, total body lean and fat mass, leg muscle strength, postural balance, and plasma amino‐terminal propeptide of type 1 procollagen (P1NP), osteocalcin, and C‐terminal telopeptide of type 1 collagen (CTX). Intention‐to‐treat (ITT) analyses and per‐protocol analyses (≥50% attendance in FFG) were performed using linear mixed models. Results: Participants in FFG completing the 12‐month intervention (n = 33) attended 0.8 (SD = 0.4) sessions per week. Intention to treat analysis of mean changes over 12 months showed significant differences (p<.05) in L1–L4 BMD (0.029 g/cm2, 95%CI: 0.001 to 0.057), leg press strength (7.2 kg, 95%CI: 0.1 to 14.3), and postural balance (−4.3 n need of support, 95%CI: −8.0 to −0.7) favoring FFG compared to CON. In the per‐protocol analyses, L1–L4 and trochanter major BMD were improved (p =.012 and.030, respectively) in FFG compared with CON. No differences were observed between groups in BTMs in the ITT or per protocol analyses. Conclusion: One year of Football Fitness training may improve L1–L4 BMD, leg muscle strength, and postural balance in women treated for early‐stage breast cancer. [ABSTRACT FROM AUTHOR]

Purpose: We tested the hypothesis that participation in small‐sided team handball training could provide beneficial effects on cardiovascular and metabolic parameters in overweight premenopausal women with special focus on the importance of prior team handball experience. Methods: A 16‐week RCT training intervention was conducted in overweight premenopausal women randomized into three groups: a team handball training group without prior experience (UN; n = 13), a team handball group with prior experience (EXP; n = 10), and an inactive control group (CON; n = 9). Both UN and EXP completed 1.6 ± 0.3 training sessions per week with average heart rates of 84 ± 5 and 85 ± 9% of maximal heart rate, respectively. Cardiovascular and metabolic parameters were assessed before and after the intervention. Results: Compared to CON, UN had significant increases in VO2max (7 ± 4%) and intermittent endurance performance (26 ± 14%) as well as reduced total fat mass (4 ± 6%), total fat percentage (4 ± 5%), and android fat mass (7 ± 12%), respectively (all P <.05). Compared to UN and CON, EXP displayed increased left ventricular mass and left ventricular mass index (both P <.05) after the training period. There were no significant changes between any of the groups in muscle mass, blood lipids, resting heart rate, and blood pressure (all P >.05). Conclusion: Small‐sided team handball training in overweight premenopausal women resulted in improvement of VO2max and body composition for participants with minimal team handball experience, indicating that prior team handball experience is not a prerequisite for improving physiological parameters of importance for health. Furthermore, EXP displayed cardiac adaptations, including increased left ventricular mass and left ventricular mass index. [ABSTRACT FROM AUTHOR]

Introduction: High intensity interval training (HIIT) has shown to be as effective as moderate intensity endurance training to improve metabolic health. However, the current knowledge on the effect of HIIT in older individuals is limited and it is uncertain whether the adaptations are sex specific. The aim was to investigate effects of HIIT on mitochondrial respiratory capacity and mitochondrial content in older females and males. Methods: Twenty-two older sedentary males (n = 11) and females (n = 11) completed 6 weeks of supervised HIIT 3 days per week. The training consisted of 5 × 1 min cycling (124 ± 3% of max power output at session 2–6 and 135 ± 3% of max power output at session 7–20) interspersed by 1½ min recovery. Before the intervention and 72 h after last training session a muscle biopsy was obtained and mitochondrial respiratory capacity, citrate synthase activity and proteins involved in mitochondria metabolism were assessed. Furthermore, body composition and ⩒O2max were measured. Results: ⩒O2max increased and body fat percentage decreased after HIIT in both sexes (p < 0.05). In addition, CS activity and protein content of MnSOD and complex I-V increased in both sexes. Coupled and uncoupled mitochondrial respiratory capacity increased only in males. Mitochondrial respiratory capacity normalised to CS activity (intrinsic mitochondrial respiratory capacity) did not change following HIIT. Conclusion: HIIT induces favourable adaptions in skeletal muscle in older subjects by increasing mitochondrial content, which may help to maintain muscle oxidative capacity and slow down the process of sarcopenia associated with ageing. [ABSTRACT FROM AUTHOR]

Peak fat oxidation rate (PFO) and the intensity that elicits PFO (Fatmax) are commonly determined by a validated graded exercise test (GE) on a cycling ergometer with indirect calorimetry. However, for upper body exercise fat oxidation rates are not well elucidated and no protocol has been validated. Thus, our aim was to test validity and inter‐method reliability for determination of PFO and Fatmax in trained men using a GE protocol applying double poling on a ski‐ergometer. PFO and Fatmax were assessed during two identical GE tests (GE1 and GE2) and validated against separated short continuous exercise bouts (SCE) at 35%, 50%, and 65% of V̇O2peak on the ski‐ergometer in 10 endurance‐trained men (V̇O2peak: 65.1 ± 1.0 mL·min−1·kg−1, mean ± SEM). Between GE tests no differences were found in PFO (GE1: 0.42 ± 0.03; GE2: 0.45 ± 0.03 g·min−1, P = .256) or Fatmax (GE1: 41 ± 2%; GE2: 43 ± 3% of V̇O2peak, P = .457) and the intra‐individual coefficient of variation (CV) was 8 ± 2% and 11 ± 2% for PFO and Fatmax, respectively. Between GE and SCE tests, PFO (GEavg: 0.44 ± 0.03; SCE; 0.47 ± 0.06 g·min−1, P = .510) was not different, whereas a difference in Fatmax (GEavg: 42 ± 2%; SCE: 52 ± 4% of V̇O2peak, P = .030) was observed with a CV of 17 ± 4% and 15 ± 4% for PFO and Fatmax, respectively. In conclusion, GE has a high day‐to‐day reliability in determination of PFO and Fatmax in trained men, whereas it is unclear if PFO and Fatmax determined by GE reflect continuous exercise in general. [ABSTRACT FROM AUTHOR]

Background: No former studies have examined how blood donation influences physical performance in women, who due to menstruation may have a slower recovery of performance. Therefore, the aim of this study was to clarify how VO2peak , time trial (TT) performance, and hematologic variables are affected in 18 iron-sufficient (plasma ferritin [P-ferritin] > 30 µg/L) women after a standard 450-mL blood donation.Study Design and Methods: VO2peak , TT performance, and blood variables were measured at baseline and 3, 7, 14, 21, and 28 days after blood donation in 18 iron-sufficient women. Anthropometrics were measured at baseline and Day 28.Results: VO2peak was reduced by 7.5 ± 1.1% from 2973 ± 87 mL/min at baseline to 2765 ± 73 mL/min 3 days after blood donation and remained below baseline until 28 days. The TT performance was reduced by 5.2 ± 1.0% from baseline (868 ± 31 sec) to Day 3 (915 ± 29 sec), but was not different from baseline 14 days after blood donation. Blood hemoglobin (B-Hb) concentration declined by 7.6 ± 2.1% from 8.4 ± 0.1 to 7.8 ± 0.1 mmol/L at baseline and on Day 3, respectively. P-ferritin at baseline was 58 ± 7 µg/L and it decreased (55 ± 3%) to a nadir of 24 ± 3 µg/L 28 days after blood donation and remained lower at 36 ± 4 µg/L after 90 days.Conclusion: VO2peak and B-Hb were only recovered 28 days after a blood donation whereas TT performance was back to baseline 14 days after blood donation. [ABSTRACT FROM AUTHOR]

Key points Hepatic insulin resistance in patients with obesity or type 2 diabetes has been suggested to result from hepatic mitochondrial dysfunction., High-resolution respirometry (HRR) can be used to assess oxidative phosphorylation by measuring the mitochondrial oxygen consumption rate in the individual complexes of the mitochondria., By using HRR, the present study demonstrates no difference in hepatic mitochondrial oxidative phosphorylation among subjects with obesity with or without type 2 diabetes and non-obese controls., Furthermore, the amount of mitochondria, assessed by the citrate synthase activity, is not different between the three groups., Together the present findings indicate that hepatic mitochondrial oxidative phosphorylation capacity is not impaired in patients with obesity or type 2 diabetes., Abstract Obese patients with type 2 diabetes (T2DM) and without type 2 diabetes (OB) are characterized by high hepatic lipid content and hepatic insulin resistance. This may be linked to impaired hepatic mitochondrial oxidative phosphorylation (OXPHOS) capacity. The aim of the present study was to investigate and compare hepatic mitochondrial OXPHOS capacity in T2DM, OB and non-obese controls (CON). Seventeen obese patients (nine OB and eight T2DM) and six CON patients had perioperative liver biopsies taken. Samples were divided into three parts to measure (1) complex I, II and IV linked respiration, (2) citrate synthase (CS) activity and (3) lipid droplet (LD) size and area (% of total tissue area filled by LDs). State 3 respiration of complex I, II and IV and the CS activity did not differ in OB, T2DM and CON. LD size was significantly higher in T2DM compared with CON, and LD area tended ( P = 0.10) to be higher in T2DM and OB compared with CON. The present findings indicate that hepatic OXPHOS capacity is not different in patients with markedly different weight and glycaemic control. Furthermore, the results do not support impaired hepatic mitochondrial respiratory capacity playing a major role in the development of obesity-induced type 2 diabetes. [ABSTRACT FROM AUTHOR]

Key points Currently, it is not known whether impaired mitochondrial function contributes to human ageing or whether potential impairments in mitochondrial function with age are secondary to physical inactivity., The present study investigated mitochondrial respiratory function and reactive oxygen species emission at a predefined membrane potential in young and older men subjected to 2 weeks of one-leg immobilization followed by 6 weeks of aerobic cycle training., Immobilization increased reactive oxygen species emission and decreased ATP generating respiration. Subsequent aerobic training reversed these effects., By contrast, age had no effect on the measured variables., The results of the present study support the notion that increased mitochondrial reactive oxygen species production mediates the detrimental effects seen after physical inactivity and that ageing per se does not cause mitochondrial dysfunction., Abstract Mitochondrial dysfunction, defined as increased oxidative stress and lower capacity for energy production, may be seen with ageing and may cause frailty, or it could be that it is secondary to physical inactivity. We studied the effect of 2 weeks of one-leg immobilization followed by 6 weeks of supervised cycle training on mitochondrial function in 17 young (mean ± SEM: 23 ± 1 years) and 15 older (68 ± 1 years) healthy men. Submaximal H2O2 emission and respiration were measured simultaneously at a predefined membrane potential in isolated mitochondria from skeletal muscle using two protocols: pyruvate + malate (PM) and succinate + rotenone (SR). This allowed measurement of leak and ATP generating respiration from which the coupling efficiency can be calculated. The protein content of the anti-oxidants manganese superoxide dismuthase (MnSOD), CuZn superoxide dismuthase, catalase and gluthathione peroxidase 1 was measured by western blotting. Immobilization decreased ATP generating respiration using PM and increased H2O2 emission using both PM and SR similarly in young and older men. Both were restored to baseline after the training period. Furthermore, MnSOD and catalase content increased with endurance training. The young men had a higher leak respiration at inclusion using PM and a higher membrane potential in State 3 using both substrate combinations. Collectively, the findings of the present study support the notion that increased mitochondrial reactive oxygen species mediates the detrimental effects seen after physical inactivity. Age, on the other hand, was not associated with impairments in anti-oxidant protein levels, mitochondrial respiration or H2O2 emission using either protocol. [ABSTRACT FROM AUTHOR]

Key points Roux-en-Y gastric bypass surgery leads to remission of type 2 diabetes in the majority of patients suffering from the disease., The gut hormone glucagon-like peptide-1 is believed to be of major importance for the remission process., The present project demonstrates a marked difference in the chance of remission of type 2 diabetes in patients with low or high preoperative β-cell function in spite of a similar post-surgery increase in postprandial glucagon-like peptide-1 release., Furthermore, post-surgery intravenous glucose administration, which does not stimulate release of glucagon-like peptide-1, leads to increased insulin secretion in the patients with the best preoperative β-cell function., Together the present findings indicate that patients with type 2 diabetes with high preoperative β-cell function experience a glucagon-like peptide-1-independent increase in β-cell function after gastric bypass surgery., Abstract The majority of the patients with type 2 diabetes (T2DM) show remission after Roux-en-Y gastric bypass (RYGB). This is the result of increased postoperative insulin sensitivity and β-cell secretion. The aim of the present study was to elucidate the importance of the preoperative β-cell function in T2DM for the chance of remission after RYGB. Fifteen patients with and 18 without T2DM had 25 g oral (OGTT) and intravenous (IVGTT) glucose tolerance tests performed at inclusion, after a diet-induced weight loss, and 4 and 18 months after RYGB. Postoperative first phase insulin secretion rate (ISR) during the IVGTT and β-cell glucose sensitivity during the OGTT increased in T2DM. Postoperative insulin sensitivity and the disposition index (DI) markedly increased in both groups. By stratifying the T2DM into two groups according to highest (T2DMhigh) and lowest (T2DMlow) baseline DI, a restoration of first phase ISR and β-cell glucose sensitivity were seen only in T2DMhigh. Remission of type 2 diabetes was 71 and 38% in T2DMhigh and T2DMlow, respectively. Postoperative postprandial GLP-1 concentrations increased markedly, but did not differ between the groups. Our findings emphasize the importance of the preoperative of β-cell function for remission of diabetes after RYGB. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Physiology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Key points Several biochemical measures of mitochondrial components are used as biomarkers of mitochondrial content and muscle oxidative capacity. However, no studies have validated these surrogates against a morphological measure of mitochondrial content in human subjects., The most commonly used markers (citrate synthase activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I-V protein, and complex I-IV activity) were correlated with a measure of mitochondrial content (transmission electron microscopy) and muscle oxidative capacity (respiration in permeabilized fibres)., Cardiolipin content followed by citrate synthase activity and complex I activity were the biomarkers showing the strongest association with mitochondrial content., mtDNA was found to be a poor biomarker of mitochondrial content., Complex IV activity was closely associated with mitochondrial oxidative phosphorylation capacity., Abstract Skeletal muscle mitochondrial content varies extensively between human subjects. Biochemical measures of mitochondrial proteins, enzyme activities and lipids are often used as markers of mitochondrial content and muscle oxidative capacity (OXPHOS). The purpose of this study was to determine how closely associated these commonly used biochemical measures are to muscle mitochondrial content and OXPHOS. Sixteen young healthy male subjects were recruited for this study. Subjects completed a graded exercise test to determine maximal oxygen uptake () and muscle biopsies were obtained from the vastus lateralis. Mitochondrial content was determined using transmission electron microscopy imaging and OXPHOS was determined as the maximal coupled respiration in permeabilized fibres. Biomarkers of interest were citrate synthase (CS) activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I-V protein content, and complex I-IV activity. Spearman correlation coefficient tests and Lin's concordance tests were applied to assess the absolute and relative association between the markers and mitochondrial content or OXPHOS. Subjects had a large range of (range 29.9-71.6 ml min−1 kg−1) and mitochondrial content (4-15% of cell volume). Cardiolipin content showed the strongest association with mitochondrial content followed by CS and complex I activities. mtDNA was not related to mitochondrial content. Complex IV activity showed the strongest association with muscle oxidative capacity followed by complex II activity. We conclude that cardiolipin content, and CS and complex I activities are the biomarkers that exhibit the strongest association with mitochondrial content, while complex IV activity is strongly associated with OXPHOS capacity in human skeletal muscle. [ABSTRACT FROM AUTHOR]

In rat skeletal muscle prolonged exercise affects the content and composition of ceramides, but in human skeletal muscle no data are available on this compound. Our aim was to examine the content of ceramide- and sphingomyelin fatty acids and neutral, Mg2+-dependent sphingomyelinase activity in skeletal muscle in untrained and trained subjects before and after prolonged exercise. Healthy male subjects were recruited into an untrained (n = 8, VO2,max 3.8 ± 0.2 1 min1) and a trained (n = 8, VO2,max 5.1 ± 0.1 1 min1) group. Before and after a 3-h exercise bout (58 ± 1% VO2,max) a muscle biopsy was excised from the vastus lateralis. Ceramide and sphingomyelin were isolated using thin-layer chromatography. The content of individual ceramide fatty acids and sphingomyelin fatty acids was measured by means of gas-liquid chromatography. The activity of neutral, Mg2+-dependent sphingomyelinase was measured using N-[14CH3]-sphingomyelin as a substrate. Prior to exercise, the muscle total ceramide fatty acid content in both groups was similar (201 ± 18 and 197 ± 9 nmol g-1 in the untrained and trained group, respectively) and after exercise a 25% increase in the content was observed in each group. At rest, the muscle total sphingomyelin fatty acid content was higher in untrained than in trained subjects (456 ± 10, 407 ± 7 nmol g-1, respectively; P < 0.05). After exercise a 20% increase (P < 0.05) in total sphingomyelin was observed only in the trained subjects. The muscle neutral, Mg2+-dependent sphingomyelinase activity was similar in the two groups at rest and a similar reduction was observed after exercise in both groups (untrained from 2.19 ± 0.08 to 1.78 ± 0.08 and trained from 2.31 ± 0.12 to 1.80 ± 0.09 nmol (mg protein)-1 h-1; P... [ABSTRACT FROM AUTHOR]

Aim: To examine the effect of high‐intensity interval training (HIIT) on glucose clearance rates in skeletal muscle and explore the mechanism within the muscle. Methods: Ten males with type 2 diabetes mellitus (T2DM) and ten matched healthy subjects performed 2 weeks of one‐legged HIIT (total of eight sessions, each comprised of 10 × 1 minute ergometer bicycle exercise at >80% of maximal heart rate, interspersed with one min of rest). Insulin sensitivity was assessed by an isoglycaemic, hyperinsulinaemic clamp combined with arteriovenous leg balance technique of the trained (T) and the untrained (UT) leg and muscle biopsies of both legs. Results: Insulin‐stimulated glucose clearance in T legs was ~30% higher compared with UT legs in both groups due to increased blood flow in T vs UT legs and maintained glucose extraction. With each training session, muscle glycogen content decreased only in the training leg, and after the training, glycogen synthase and citrate synthase activities were higher in T vs UT legs. No major changes occurred in the expression of proteins in the insulin signalling cascade. Mitochondrial respiratory capacity was similar in T2DM and healthy subjects, and unchanged by HIIT. Conclusion: HIIT improves skeletal muscle insulin sensitivity. With HIIT, the skeletal muscle of patients with T2DM becomes just as insulin sensitive as untrained muscle in healthy subjects. The mechanism includes oscillations in muscle glycogen stores and a maintained ability to extract glucose from the blood in the face of increased blood flow in the trained leg. [ABSTRACT FROM AUTHOR]

Aim & Methods: Extreme endurance exercise provides a valuable research model for understanding the adaptive metabolic response of older and younger individuals to intense physical activity. Here, we compare a wide range of metabolic and physiologic parameters in two cohorts of seven trained men, age 30 ± 5 years or age 65 ± 6 years, before and after the participants travelled ≈3000 km by bicycle over 15 days., Results: Over the 15-day exercise intervention, participants lost 2-3 kg fat mass with no significant change in body weight. V̇O 2 max did not change in younger cyclists, but decreased (p = 0.06) in the older cohort. The resting plasma FFA concentration decreased markedly in both groups, and plasma glucose increased in the younger group. In the older cohort, plasma LDL-cholesterol and plasma triglyceride decreased. In skeletal muscle, fat transporters CD36 and FABPm remained unchanged. The glucose handling proteins GLUT4 and SNAP23 increased in both groups. Mitochondrial ROS production decreased in both groups, and ADP sensitivity increased in skeletal muscle in the older but not in the younger cohort., Conclusion: In summary, these data suggest that older but not younger individuals experience a negative adaptive response affecting cardiovascular function in response to extreme endurance exercise, while a positive response to the same exercise intervention is observed in peripheral tissues in younger and older men. The results also suggest that the adaptive thresholds differ in younger and old men, and this difference primarily affects central cardiovascular functions in older men after extreme endurance exercise., (© 2022 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.)