β-Alanine supplementation reduces acidosis but not oxygen uptake response during high-intensity cycling exercise

The oral ingestion of β-alanine, the rate-limiting precursor in carnosine synthesis, has been shown to elevate the muscle carnosine content. Carnosine is thought to act as a physiologically relevant pH buffer during exercise but direct evidence is lacking. Acidosis has been hypothesised to influence oxygen uptake kinetics during high-intensity exercise. The present study aimed to investigate whether oral β-alanine supplementation could reduce acidosis during high-intensity cycling and thereby affect oxygen uptake kinetics. 14 male physical education students participated in this placebo-controlled, double-blind study. Subjects were supplemented orally for 4 weeks with 4.8 g/day placebo or β-alanine. Before and after supplementation, subjects performed a 6-min cycling exercise bout at an intensity of 50% of the difference between ventilatory threshold (VT) and [(V)dot]textO_2textpeak dot{V}{text{O}}_{2{text{peak}}} . Capillary blood samples were taken for determination of pH, lactate, bicarbonate and base excess, and pulmonary oxygen uptake kinetics were determined with a bi-exponential model fitted to the averaged breath-by-breath data of three repetitions. Exercise-induced acidosis was significantly reduced following β-alanine supplementation compared to placebo, without affecting blood lactate and bicarbonate concentrations. The time delay of the fast component (Td₁) of the oxygen uptake kinetics was significantly reduced following β-alanine supplementation compared to placebo, although this did not reduce oxygen deficit. The parameters of the slow component did not differ between groups. These results indicate that chronic β-alanine supplementation, which presumably increased muscle carnosine content, can attenuate the fall in blood pH during high-intensity exercise. This may contribute to the ergogenic effect of the supplement found in some exercise modes.     

Metabolic implications of resistive force selection for oxidative stress and markers of muscle damage during 30 s of high-intensity exercise

The purpose of this study was to compare power outputs, and blood concentrations of lipid hydroperoxides (LH), malondialdehyde (MDA), creatine kinase (CK), myoglobin (Mb) and lactate ([La^–]_B) following 30 s of maximal cycle ergometry when resistive forces were derived from total-body mass (TBM) or fat-free mass (FFM). Alpha-tocopherol (AT), retinol (R) and uric acid (UA) concentrations were also measured to qualify the activity of antioxidants. Cardiac troponin levels were determined to exclude myocardial damage and to verify that any CK was predominantly derived from skeletal muscle. Differences (P<0.05) in peak power output, pedal velocity and resistive forces were observed when the TBM and FFM protocols were compared [953 (114) W vs 1,020 (134) W; 134 (8) rpm vs 141 (7) rpm; 6 (1) kg vs 5 (1) kg respectively). LH and MDA concentrations increased immediately post-exercise during the TBM protocol only (P<0.05) and were greater when compared to FFM (P<0.05). LH and MDA values decreased 24 h post-exercise. Increases in CK concentrations were recorded immediately post-exercise for both the TBM and FFM protocols with greater concentrations recorded for TBM (P<0.05). Decreases were observed 24 h post-exercise. Mb concentrations were greater immediately post-exercise for the TBM protocol and were greater than those recorded for FFM (P<0.05). Values decreased 24 h later (P<0.05). AT and UA concentrations decreased immediately post-exercise for both protocols (P<0.05) and increased 24 h later (P<0.05). There were no changes observed in R concentrations at any of the blood sampling stages. [La^–]_B increased (P<0.05) immediately post-exercise for both protocols, and decreased 24 h later (P<0.05). The results of the study suggest that greater power outputs are obtainable with significantly less oxidative stress and muscle disruption when resistive forces reflect FFM mass as opposed to TBM.     

The influence of loading intensity on muscle–tendon unit behavior during maximal knee extensor stretch shortening cycle exercise

Tendon stiffness increases as the magnitude and rate of loading increases, according to its viscoelastic properties. Thus, under some loading conditions tendons should become exceptionally stiff and act almost as rigid force transducers. Nonetheless, observations of tendon behavior during multi-joint sprinting and jumping tasks have shown that tendon strain increases whilst muscle strain decreases as the loading intensity increases. The purpose of the current study was to examine the influence of external loading intensity on muscle–tendon unit (MTU) behavior during a high-speed single-joint, stretch-shortening cycle (SSC) knee extension task. Eighteen men (n = 9) and women (n = 9) performed single-leg, maximum intensity SSC knee extensions at loads of 20, 60 and 90?% of their one repetition maximum. Vastus lateralis fascicle length (L _f) and velocity (v _f) as well as MTU (L _MTU) and tendinous tissue (L _t) length were measured using high-speed ultrasonography (96 Hz). Patellar tendon force (F _t) and rate of force development (RFD_t) were estimated using inverse dynamics. Results showed that as loading intensity increased, concentric joint velocity and shortening v _f decreased whilst F _t and RFD_t increased, but no significant differences were observed in eccentric joint velocity or peak L _MTU or L _f. In addition, the tendon lengthened significantly less at the end of the eccentric phase at heavier loads. This is the first observation that tendon strain decreases significantly during a SSC movement as loading intensity increases in vivo, resulting in a shift in the tendon acting as a power amplifier at light loads to a more rigid force transducer at heavy loads.     

Influence of priming exercise on muscle deoxy[Hb?+?Mb] during ramp cycle exercise

The aim of the present study was to gain better insight into the mechanisms underpinning the sigmoid pattern of deoxy[Hb + Mb] during incremental exercise by assessing the changes in the profile following prior high-intensity exercise. Ten physically active students performed two incremental ramp (25 W min⁻¹) exercises (AL and LL, respectively) preceded on one occasion by incremental arm (10 W min⁻¹) and on another occasion by incremental leg exercise (25 W min⁻¹), which served as the reference test (RT). Deoxy[Hb + Mb] was measured by means of near-infrared spectroscopy and surface EMG was recorded at the Vastus Lateralis throughout the exercises. Deoxy[Hb + Mb], integrated EMG and Median Power Frequency (MdPF) were expressed as a function of work rate (W) and compared between the exercises. During RT and AL deoxy[Hb + Mb] followed a sigmoid increase as a function of work rate. However, during LL deoxy[Hb + Mb] increased immediately from the onset of the ramp exercise and thus no longer followed a sigmoid pattern. This different pattern in deoxy[Hb + Mb] was accompanied by a steeper slope of the iEMG/W-relationship below the GET (LL: 0.89 ± 0.11% W⁻¹; RT: 0.74 ± 0.08% W⁻¹; AL: 0.72 ± 0.10% W⁻¹) and a more pronounced decrease in MdPF in LL (17.2 ± 4.5%) compared to RT (5.0 ± 2.1%) and AL (3.9 ± 3.2%). It was observed that the sigmoid pattern of deoxy[Hb + Mb] was disturbed when the ramp exercise was preceded by priming leg exercise. Since the differences in deoxy[Hb + Mb] were accompanied by differences in EMG it can be suggested that muscle fibre recruitment is an important underlying mechanism for the pattern of deoxy[Hb + Mb] during ramp exercise.     

Are the effects of training on fat metabolism involved in the improvement of performance during high-intensity exercise?

The objective of the present study was to relate changes in certain muscle characteristics and indicators of metabolism in response to endurance training to the concomitant changes in time to exhaustion (T_lim) at a work rate corresponding to maximal oxygen uptake Eight healthy sedentary subjects pedalled on a cycle ergometer 2 h a day, 6 days a week, for 4 weeks. Training caused increases in O_2peak (by 8%), T_lim (from 299±23 s before to 486±63 s after training), citrate synthase and 3-hydroxyl-acyl-CoA dehydrogenase (HAD) activities (by 54% and 16%, respectively) and capillary density (by 31%). Decreases in activity of lactate dehydrogenase (LDH) and muscle type of LDH (by 24% and 28%, respectively) and the phosphofructokinase/citrate synthase ratio (by 37%) were also observed. Respiratory exchange ratio (RER) tended to be lower (P<0.1) at all relative work rates after training while the corresponding ventilation rates ( E) were unchanged. At the same absolute work rate, RER and E were lower after training (P<0.05). The improvement of T_lim with training was related to the increases in HAD activity (r=0.91, P=0.0043), and to the decreases in RER calculated for Pa_peak (r=0.71, P=0.0496). The present results suggest that the training-induced adaptations in fat metabolism might influence T_lim at a work rate corresponding to O_2peak and stimulate the still debated and incompletely understood role of fat metabolism during short high-intensity exercise     

Resistance exercise, but not endurance exercise, induces IKKβ phosphorylation in human skeletal muscle of training-accustomed individuals

The mammalian target of rapamycin complex 1 (mTORC1) is considered an important role in the muscular adaptations to exercise. It has been proposed that exercise-induced signaling to mTORC1 do not require classic growth factor PI3K/Akt signaling. Activation of IKKβ and the mitogen-activated protein kinases (MAPKs) Erk1/2 and p38 has been suggested to link inflammation and cellular stress to activation of mTORC1 through the tuberous sclerosis 1 (TSC1)/tuberous sclerosis 2 (TSC2) complex. Consequently, activation of these proteins constitutes potential alternative mechanisms of mTORC1 activation following exercise. Previously, we demonstrated that mTOR is preferentially activated in response to resistance exercise compared to endurance exercise in trained individuals without concomitant activation of Akt. In the present study, we extended this investigation by examining IκB kinase complex (IKK), TSC1, MAPK, and upstream Akt activators, along with gene expression of selected cytokines, in skeletal muscles from these subjects. Biopsies were sampled prior to, immediately after, and in the recovery period following resistance exercise, endurance exercise, and control interventions. The major finding was that IKKβ phosphorylation increased exclusively after resistance exercise. No changes in TSC1, Erk1/2, insulin receptor, or insulin receptor substrate 1 phosphorylation were observed in any of the groups, while p38 phosphorylation was higher in the resistance exercise group compared to both other groups immediately after the intervention. Resistance and endurance exercise increased IL6, IL8, and TNFα gene expression immediately after exercise. The non-exercise control group demonstrated that cytokine gene expression is also sensitive to repeated biopsy sampling, whereas no effect of repeated biopsy sampling on protein expression and phosphorylation was observed. In conclusion, resistance exercise, but not endurance exercise, increases IKKβ phosphorylation in trained human subjects, which support the idea that IKKβ can influence the activation of mTORC1 in human skeletal muscle.     

The effect of β-alanine and NaHCO3 co-ingestion on buffering capacity and exercise performance with high-intensity exercise in healthy males

Introduction

β-alanine (BAl) and NaHCO₃ (SB) ingestion may provide performance benefits by enhancing concentrations of their respective physiochemical buffer counterparts, muscle carnosine and blood bicarbonate, counteracting acidosis during intense exercise. This study examined the effect of BAl and SB co-supplementation as an ergogenic strategy during high-intensity exercise.

Methods

Eight healthy males ingested either BAl (4.8 g day^?1 for 4 weeks, increased to 6.4 g day^?1 for 2 weeks) or placebo (Pl) (CaCO₃) for 6 weeks, in a crossover design (6-week washout between supplements). After each chronic supplementation period participants performed two trials, each consisting of two intense exercise tests performed over consecutive days. Trials were separated by 1 week and consisted of a repeated sprint ability (RSA) test and cycling capacity test at 110 % Wmax (CCT_110 %). Placebo (Pl) or SB (300 mg kgbw^?1) was ingested prior to exercise in a crossover design to creating four supplement conditions (BAl-Pl, BAl-SB, Pl–Pl, Pl-SB).

Results

Carnosine increased in the gastrocnemius (n = 5) (p = 0.03) and soleus (n = 5) (p = 0.02) following BAl supplementation, and Pl-SB and BAl-SB ingestion elevated blood HCO₃ ^? concentrations (p < 0.01). Although buffering capacity was elevated following both BAl and SB ingestion, performance improvement was only observed with BAl-Pl and BAl-SB increasing time to exhaustion of the CCT_110 % test 14 and 16 %, respectively, compared to Pl–Pl (p < 0.01).

Conclusion

Supplementation of BAl and SB elevated buffering potential by increasing muscle carnosine and blood bicarbonate levels, respectively. BAl ingestion improved performance during the CCT_110 %, with no aggregating effect of SB supplementation (p > 0.05). Performance was not different between treatments during the RSA test.     

Indices of electromyographic activity and the “slow” component of oxygen uptake kinetics during high-intensity knee-extension exercise in humans

The control of pulmonary oxygen uptake kinetics above the lactate threshold (LT) is complex and controversial. Above LT, for square-wave exercise is greater than predicted from the sub-LT –WR relationship, reflecting the contribution of an additional “slow” component Investigators have argued for a contribution to this slow component from the recruitment of fast-twitch muscle fibres, which are less aerobically efficient than slow-twitch fibres. Six healthy subjects performed a rapid-incremental bilateral knee-extension exercise test to the limit of tolerance for the estimation of ventilatory threshold (VT), and the difference between and at VT (Δ). Subjects then completed three repetitions of square-wave exercise at 30% of VT for 10 min (moderate intensity), and at VT + 25%Δ (heavy intensity) for 20 min. Pulmonary gas exchange was measured breath-by-breath. Surface EMG was recorded from m. rectus femoris; integrated EMG (IEMG) and mean power frequency (MPF) were derived for successive contractions. In comparison to moderate-intensity exercise, the phase 2 kinetics in heavy exercise were marginally slower than for moderate-intensity exercise (time constant (± SD) 25 ± 9 and 22 ± 10 s, respectively; NS), with a discernible ( difference between minutes 6 and 3 of exercise: 74 ± 21 and 0 ± 20 ml min⁻¹, respectively). However, there was no significant change in IEMG or MPF, either in the moderate domain or in the heavy domain over the period when the slow component was manifest. These observations argue against an appreciable preferential recruitment of fast-twitch units with high force-generating characteristics and fast sarcolemmal conduction velocities in concert with the development of the slow component during heavy-intensity knee-extensor exercise. The underlying mechanism(s) remains to be resolved.     

Glutathione S-Transferase Ω 1 variation does not influence age at onset of Huntington's disease

Background

Huntington's disease (HD) is a fully penetrant, autosomal dominantly inherited disorder associated with abnormal expansions of a stretch of perfect CAG repeats in the 5' part of the IT15 gene. The number of repeat units is highly predictive for the age at onset (AO) of the disorder. But AO is only modestly correlated with repeat length when intermediate HD expansions are considered. Circumstantial evidence suggests that additional features of the HD course are based on genetic traits. Therefore, it may be possible to investigate the genetic background of HD, i.e. to map the loci underlying the development and progression of the disease. Recently an association of Glutathione S-Transferase Ω 1 (GSTO1) and possibly of GSTO2 with AO was demonstrated for, both, Alzheimer's (AD) and Parkinson's disease (PD).

Methods

We have genotyped the polymorphisms rs4925 GSTO1 and rs2297235 GSTO2 in 232 patients with HD and 228 controls.

Results

After genotyping GSTO1 and GSTO2 polymorphisms, firstly there was no statistically significant difference in AO for HD patients, as well as secondly for HD patients vs. controls concerning, both, genotype and allele frequencies, respectively.

Conclusion

The GSTO1 and GSTO2 genes flanked by the investigated polymorphisms are not comprised in a primary candidate region influencing AO in HD.     

70 μM caffeine treatment enhances in vitro force and power output during cyclic activities in mouse extensor digitorum longus muscle

Caffeine ingestion by human athletes has been found to improve endurance performance primarily acting via the central nervous system as an adenosine receptor antagonist. However, a few studies have implied that the resultant micromolar levels of caffeine in blood plasma (70 M maximum for humans) may directly affect skeletal muscle causing enhanced force production. In the present study, the effects of 70 M caffeine on force and power output in isolated mouse extensor digitorum longus muscle were investigated in vitro at 35°C. Muscle preparations were subjected to cyclical sinusoidal length changes with electrical stimulation conditions optimised to produce maximal work. 70 M caffeine caused a small but significant increase (2–3%) in peak force and net work produced during work loops (where net work represents the work input required to lengthen the muscle subtracted from the work produced during shortening). However, these micromolar caffeine levels did not affect the overall pattern of fatigue or the pattern of recovery from fatigue. Our results suggest that the plasma concentrations found when caffeine is used to enhance athletic performance in human athletes might directly enhance force and power during brief but not prolonged activities. These findings potentially confirm previous in vivo studies, using humans, which implied caffeine ingestion may cause acute improvements in muscle force and power output but would not enhance endurance.     

Pattern of deoxy[Hb + Mb] during ramp cycle exercise: influence of aerobic fitness status

During ramp exercise the deoxy[Hb + Mb] pattern follows a sigmoid model [f(x) = f ₀ + A/(1 + exp^{−(−c  + dx)})], indicating a non-linear muscle blood flow -relationship. We hypothesised that in trained cyclists the sigmoid would display a rightward shift, due to an increased oxidative capacity and/or higher percentage of slow-twitch fibres. A total of 10 cyclists and 11 physically active students (PA students) performed a relative ramp exercise (±12 min) and a ramp25-exercise (25 W min⁻¹). Deoxy[Hb + Mb] was measured at the M. Vastus Lateralis by NIRS, normalized to the total amplitude of the response and expressed as a function of absolute and relative (%peakP) work rate. The work rate corresponding to c/d (i.e.50% of the amplitude of the deoxy[Hb + Mb] response) was the only parameter of the sigmoid that differed significantly between cyclists (57.9 ± 4.4% and 60.1 ± 4.1%peakP in the relative and ramp25, respectively) and PAstudents (49.6 ± 4.2% and 48.2 ± 5.1%peakP, respectively), indicating a rightward shift of the sigmoid in the cyclists. These results suggest a change in the time course of C_(a–v)O₂ as a function of aerobic fitness status.     

Cytosolic pH buffering during exercise and recovery in skeletal muscle of patients with McArdle’s disease

Cellular pH control is important in muscle physiology, and for interpretation of ³¹P magnetic resonance spectroscopy (MRS) data. Cellular acidification in exercise results from coupled glycolytic ATP production mitigated by cytosolic buffering, ‘consumption’ of H⁺ by phosphocreatine (PCr) breakdown, and membrane transport processes. Ex vivo methods for cytosolic buffer capacity are vulnerable to artefact, and MRS methods often require assumptions. ³¹P MRS of early exercise, when pH increases unopposed by glycolysis, is conceptually simple, but limited in normal muscle by time resolution and signal-to-noise. A therapeutic trial (Martinuzzi A et al. Musc Nerve 37: 350–357, 2007) in McArdle’s disease (glycogen phosphorylase deficiency), where pH does not decrease with exercise, offered the opportunity to test ³¹P MRS data obtained throughout incremental plantar flexion exercise and recovery in ten McArdle’s patients against the simple model of cellular pH control. Changes in pH, [Pi] and [PCr] throughout exercise and recovery were quantitatively consistent with mean ± SEM buffer capacity of 10 ± 1 mM/(pH unit), which was not significantly different from the control subjects under the initial-exercise conditions where the comparison could be made. The simple model of cellular acid–base balance therefore gives an adequate account of cellular pH changes during both exercise and recovery in McArdle’s disease.     

Remodelling of human atrial K<Superscript>+</Superscript> currents but not ion channel expression by chronic β-blockade

Chronic β-adrenoceptor antagonist (β-blocker) treatment in patients is associated with a potentially anti-arrhythmic prolongation of the atrial action potential duration (APD), which may involve remodelling of repolarising K⁺ currents. The aim of this study was to investigate the effects of chronic β-blockade on transient outward, sustained and inward rectifier K⁺ currents (I_TO, I_KSUS and I_K1) in human atrial myocytes and on the expression of underlying ion channel subunits. Ion currents were recorded from human right atrial isolated myocytes using the whole-cell-patch clamp technique. Tissue mRNA and protein levels were measured using real time RT-PCR and Western blotting. Chronic β-blockade was associated with a 41% reduction in I_TO density: 9.3 ± 0.8 (30 myocytes, 15 patients) vs 15.7 ± 1.1 pA/pF (32, 14), p < 0.05; without affecting its voltage-, time- or rate dependence. I_K1 was reduced by 34% at −120 mV (p < 0.05). Neither I_KSUS, nor its increase by acute β-stimulation with isoprenaline, was affected by chronic β-blockade. Mathematical modelling suggested that the combination of I_TO- and I_K1-decrease could result in a 28% increase in APD₉₀. Chronic β-blockade did not alter mRNA or protein expression of the I_TO pore-forming subunit, Kv4.3, or mRNA expression of the accessory subunits KChIP2, KChAP, Kvβ1, Kvβ2 or frequenin. There was no reduction in mRNA expression of Kir2.1 or TWIK to account for the reduction in I_K1. A reduction in atrial I_TO and I_K1 associated with chronic β-blocker treatment in patients may contribute to the associated action potential prolongation, and this cannot be explained by a reduction in expression of associated ion channel subunits.     

Dichloroacetate does not speed phase-II pulmonary V̇O2 kinetics following the onset of heavy intensity cycle exercise

We hypothesised that pharmacological activation of the pyruvate dehydrogenase enzyme complex (PDC) by dichloroacetate (DCA) would speed phase-II pulmonary O₂ uptake (O₂) kinetics following the onset of high-intensity, sub-maximal exercise. Eight healthy males (aged 19–33 years) completed two square-wave transitions of 6 min duration from unloaded cycling to a work-rate equivalent to ~80% of peak O₂ either with or without prior i.v. infusion of DCA (50 mg kg^–1 body mass in 50 ml saline). Pulmonary O₂ was measured breath-by-breath throughout all tests, and O₂ kinetics were determined using non-linear regression techniques from the averaged individual response to each of the conditions. Infusion of DCA resulted in significantly lower blood [lactate] during the baseline cycling period (means±SEM: control 0.9±0.1, DCA 0.5±0.1 mM; P<0.01) consistent with successful activation of PDC. However, DCA had no discernible effect on the rate at which O₂ increased towards the initially anticipated steady state following the onset of exercise as reflected in the time constant of the fundamental O₂ response (control 26.7±4.1, DCA 27.7±2.8 s). These results indicate that the principal limitation to oxidative metabolism following the onset of high-intensity, sub-maximal cycle exercise lies downstream from PDC and/or that muscle O₂ consumption is primarily under feedback control via the concentration of one or more of the reactants associated with ATP hydrolysis.