European journal of applied physiology, Jan 13, 2018
Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it ... more Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it may improve endurance exercise performance. This study investigated some of the physiological mechanisms by which acute acetaminophen ingestion might blunt muscle fatigue development. Thirteen active males completed 60 × 3 s maximum voluntary contractions (MVC) of the knee extensors with each contraction separated by a 2 s passive recovery period. This protocol was completed 60 min after ingesting 1 g of maltodextrin (placebo) or 1 g of acetaminophen on two separate visits. Peripheral nerve stimulation was administered every 6th contraction for assessment of neuromuscular fatigue development, with the critical torque (CT), which reflects the maximal sustainable rate of oxidative metabolism, taken as the mean torque over the last 12 contractions. Surface electromyography was recorded continuously as a measure of muscle activation. Mean torque (61 ± 11 vs. 58 ± 14% pre-exercise MVC) and CT...
The aim of this study was to determine whether low-frequency whole-body vibration (WBV) modulates... more The aim of this study was to determine whether low-frequency whole-body vibration (WBV) modulates the excitability of the corticospinal and intracortical pathways related to tibialis anterior (TA) muscle activity, thus contributing to the observed changes in neuromuscular function during and after WBV exercise. Motor-evoked potentials (MEPs) elicited in response to transcranial magnetic stimulation (TMS) of the leg area of the motor cortex were recorded in TA and soleus (SOL) muscles of seven healthy male subjects whilst performing 330 s continuous static squat exercise. Each subject completed two conditions: control (no WBV) and WBV (30 Hz, 1.5 mm vibration applied from 111 to 220 s). Five single suprathreshold and five paired TMS were delivered during each squat period lasting 110 s (pre-, during and post-WBV). Two interstimulus intervals (ISIs) between the conditioning and the testing stimuli were employed in order to study the effects of WBV on short-interval intracortical inhibition (SICI, ISI = 3 ms) and intracortical facilitation (ICF, ISI = 13 ms). During vibration relative to squat exercise alone, single-pulse TMS provoked significantly higher TA MEP amplitude (56 ± 14%, P = 0.003) and total area (71 ± 19%, P = 0.04), and paired TMS with ISI = 13 ms provoked smaller MEP amplitude (−21 ± 4%, P = 0.01) but not in SOL. Paired-pulse TMS with ISI = 3 ms elicited significantly lower MEP amplitude (TA, −19 ± 4%, P = 0.009; and SOL, −13 ± 4%, P = 0.03) and total area (SOL, −17 ± 6%, P = 0.02) during vibration relative to squat exercise alone in both muscles. Tibialis anterior MEP facilitation in response to single-pulse TMS suggests that WBV increased corticospinal pathway excitability. Increased TA and SOL SICI and decreased TA ICF in response to paired-pulse TMS during WBV indicate vibration-induced alteration of the intracortical processes as well.
Design: 8 male, active subjects (age: 33.6 ± 2.0 yrs; VO2max: 3.6 ± 0.2 l.min -1 ) completed two ... more Design: 8 male, active subjects (age: 33.6 ± 2.0 yrs; VO2max: 3.6 ± 0.2 l.min -1 ) completed two trials separated by at least 14 d. Subjects cycled for 3 min at 95% VO2max with prior infusion (2ml.kg -1 bm) of either saline (CON) or DCA (25mg.ml -1 ) , see for detailed protocol. Kinetic analysis: Breath-by-breath VO2 & Near Infrared Spectroscopy (%Hb, NIRS) data (where %Hb = Hb(t) / (Hb(max) -Hb(min)) were fitted to a monoexponential model with a delay relative to the start of exercise of the form:
After exhaustive exercise, intravenous or oral glutamine promoted skeletal muscle glycogen storag... more After exhaustive exercise, intravenous or oral glutamine promoted skeletal muscle glycogen storage. However, when glutamine was ingested with glucose polymer, whole-body carbohydrate storage was elevated, the most likely site being liver and not muscle, possibly due to increased glucosamine formation. The rate of tricarboxylic acid (TCA) cycle flux and hence oxidative metabolism may be limited by the availability of TCA intermediates. There is some evidence that intramuscular glutamate normally provides alpha-ketoglutarate to the mitochondrion. We hypothesized that glutamine might be a more efficient anaplerotic precursor than endogenous glutamate alone. Indeed, a greater expansion of the sum of muscle citrate, malate, fumarate and succinate concentrations was observed at the start of exercise (70% VO2(max)) after oral glutamine than when placebo or ornithine alpha-ketoglutarate was given. However, neither endurance time nor the extent of phosphocreatine depletion or lactate accumul...
Journal of applied physiology (Bethesda, Md. : 1985), 2000
Seven untrained male subjects participated in a double-blind, crossover study conducted to determ... more Seven untrained male subjects participated in a double-blind, crossover study conducted to determine the efficacy of different carbohydrate drinks in promoting carbohydrate storage in the whole body and skeletal muscle during recovery from exhaustive exercise. The postabsorptive subjects first completed an exercise protocol designed to deplete muscle fibers of glycogen, then consumed 330 ml of one of three carbohydrate drinks (18.5% glucose polymer, 18.5% sucrose, or 12% sucrose; wt/vol) and also received a primed constant infusion of [1-(13)C]glucose for 2 h. Nonoxidative glucose disposal (3.51 +/- 0.28, 18.5% glucose polymer; 2.96 +/- 0.32, 18.5% sucrose; 2.97 +/- 0.16, 12% sucrose; all mmol. kg(-1). h(-1)) and storage of muscle glycogen (5.31 +/- 1.11, 18.5% glucose polymer; 4.07 +/- 1.05, 18.5% sucrose; 3.45 +/- 0.85, 12% sucrose; all mmol. kg wet wt(-1). h(-1); P < 0.05) were greater after consumption of the glucose polymer drink than after either sucrose drink. The results ...
Journal of applied physiology (Bethesda, Md. : 1985), 1999
The purpose of this study was to determine the efficacy of glutamine in promoting whole body carb... more The purpose of this study was to determine the efficacy of glutamine in promoting whole body carbohydrate storage and muscle glycogen resynthesis during recovery from exhaustive exercise. Postabsorptive subjects completed a glycogen-depleting exercise protocol, then consumed 330 ml of one of three drinks, 18.5% (wt/vol) glucose polymer solution, 8 g glutamine in 330 ml glucose polymer solution, or 8 g glutamine in 330 ml placebo, and also received a primed constant infusion of [1-13C]glucose for 2 h. Plasma glutamine concentration was increased after consumption of the glutamine drinks (0.7-1.1 mM, P < 0.05). In the second hour of recovery, whole body nonoxidative glucose disposal was increased by 25% after consumption of glutamine in addition to the glucose polymer (4.48 +/- 0.61 vs. 3.59 +/- 0.18 mmol/kg, P < 0.05). Oral glutamine alone promoted storage of muscle glycogen to an extent similar to oral glucose polymer. Ingestion of glutamine and glucose polymer together promot...
Journal of applied physiology (Bethesda, Md. : 1985), 1998
The aim of this study was to investigate dietary protein-induced changes in whole body leucine tu... more The aim of this study was to investigate dietary protein-induced changes in whole body leucine turnover and oxidation and in skeletal muscle branched chain 2-oxo acid dehydrogenase (BCOADH) activity, at rest and during exercise. Postabsorptive subjects received a primed constant infusion of L-[1-13C,15N]leucine for 6 h, after previous consumption of a high- (HP; 1.8 g . kg-1 . day-1, n = 8) or a low-protein diet (LP; 0.7 g . kg-1 . day-1, n = 8) for 7 days. The subjects were studied at rest for 2 h, during 2-h exercise at 60% maximum oxygen consumption, then again for 2 h at rest. Exercise induced a doubling of both leucine oxidation from 20 micromol . kg-1 . h-1 and BCOADH percent activation from 7% in all subjects. Leucine oxidation was greater before (+46%) and during (+40%, P < 0.05) the first hour of exercise in subjects consuming the HP rather than the LP diet, but there was no additional change in muscle BCOADH activity. The results suggest that leucine oxidation was incre...
FIG. 2. Theoretical considerations for calculating FI nmsk illustrated on exemplary data. A: effe... more FIG. 2. Theoretical considerations for calculating FI nmsk illustrated on exemplary data. A: effect of segment location: ( ) concentric; ( ) eccentric; ( ) centered to peak knee extension; ( ) 50Hz notch filter. B: effect of k: ( ) k=2; ( ) k=3; ( ) k=4; ( ) k=5. (from1 st and 4 th set). C, D: relative changes of FInsm5 and Fmed during the 1 st ( ), 2 nd ( ), 3 rd ( ) and 4 th ( ) set of the exercise protocol.
Respiratory physiology & neurobiology, Jan 29, 2008
To investigate whether 10 breaths against a vibration stimulus elicits increments of spontaneous ... more To investigate whether 10 breaths against a vibration stimulus elicits increments of spontaneous and maximal inspiratory mouth pressure (maxMP) and tidal mean inspiratory flow (iV(T)/T(I)) upon stimulus removal. Twelve healthy subjects (8 female, 4 male; 22-50 years old), recruited from the University student body, completed 3 maximal inspirations before (pre) and after (post) 10 inspirations against resistive loading with a vibration-type stimulus (VIB; youbreathe, Exoscience Ltd., London, UK), pressure-matched resistive loading (RES) or resting breathing (CON; no load). The trials were presented in a random order. maxMP and involuntary tidal breathing were compared pre and post conditioning. Inspiratory neural drive increased only after VIB as evidenced by increased tidal and maxMP and mean inspiratory flow (iV(T)/T(I); p < 0.05). There was no effect of either resistance or control breathing on maximal maxMP or tidal responses. Ten conditioning breaths of VIB lead to increased ...
1. The aim of this study was to determine the effect of glucose supplementation on leucine turnov... more 1. The aim of this study was to determine the effect of glucose supplementation on leucine turnover during and after exercise and whether variation in the previous dietary protein content modulated this effect. 2. Postabsorptive subjects received a primed constant [1-13 C, 15 N]leucine infusion for 6 h, after previous consumption of a high (1·8 g kg¢ day¢, HP, n = 16) or low (0·7 g kg¢ day¢, LP, n = 16) protein diet for 7 days. The subjects were studied at rest; during 2 h of exercise, during which half of the subjects from each dietary protocol received 0·75 g kg¢ h¢ glucose (HP + G, LP + G) and the other half received water (HP + W, LP + W); then again for 2 h of rest. 3. Glucose supplementation suppressed leucine oxidation (P < 0·01) by 20% in subjects consuming the high protein diet (58·2 ± 2·8 ìmol kg¢ h¢, HP + G; 72·4 ± 3·9 ìmol kg¢ h¢, HP + W) but not the low protein diet (51·1 ± 5·9 ìmol kg¢ h¢, LP + G; 51·7 ± 5·5 ìmol kg¢ h¢, LP + W), with no difference in skeletal muscle branched-chain 2-oxo acid dehydrogenase (BCOADH) activity between groups. Glucose supplementation did not alter the rate of whole-body protein synthesis or breakdown. 4. The sparing effect of glucose on leucine oxidation appears only to occur if previous protein intake was high. It was not mediated by a suppression of BCOADH fractional activity but may be due to reduced substrate availability. 0584
The tricarboxylic acid cycle is essential for oxidative energy production. The expansion (anapler... more The tricarboxylic acid cycle is essential for oxidative energy production. The expansion (anaplerosis) of the intermediates of the TCA cycle (TCAI) is achieved via number of pathways and is known to be influenced by metabolic status and nutritional and pharmacological interventions. Contraction is associated with anaplerosis in skeletal muscle and some authors have suggested that the rate of anaplerosis can limit oxidative energy delivery. However, the results of more recent studies are consistent with the idea that expansion of the muscle TCAI pool is principally a reflection of muscle pyruvate availability, and is of little functional importance to TCA cycle flux, thereby signifying any intervention aimed at increasing TCAI expansion will be of little practical value.
COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxida... more COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxidative metabolism to exercise. We hypothesised that prior glutamine supplementation would enhance V(O2) peak, V(O2) at lactate threshold and speed pulmonary oxygen uptake kinetics in COPD. 13 patients (9 males, age 66±5 years, mean±SD) with severe COPD (mean FEV(1) 0.88±0.23l, 33±7% predicted) performed on separate days ramp cycle-ergometry (5-10 W min(-1)) to volitional exhaustion and subsequently square-wave transitions to 80% estimated lactate threshold (LT) following consumption of either placebo (CON) or 0.125 g kg bm(-1) of glutamine (GLN) in 5 ml kg bm(-1) placebo. Oral glutamine had no effect on peak or V(O2) at LT, {V(O2) peak: CON=0.70±0.1 l min(-1) vs. GLN=0.73±0.2 l min(-1); LT: CON=0.57±0.1 l min(-1) vs. GLN=0.54±0.1 lmin(-1)} or V(O2) kinetics {tau: CON=68±22 s vs. GLN=68±16 s}. Ingestion of glutamine before exercise did not improve indices of oxidative metabolism in this patient group.
A sharp intake of breath followed by a strong vocalisation is widely observed in response to acut... more A sharp intake of breath followed by a strong vocalisation is widely observed in response to acute pain although its function and mechanism is poorly understood. This study investigated the effect of percutaneous (overlying the tibial bone) electrical stimulation delivered early (20-30% of inspiratory time) during inspiration (INSP) or expiration (EXP) (20-30% of expiratory time) at sensory intensities at (100%), above (125%) and below (50% and 75%) the pre-determined pain threshold (PT), upon within-a-breath respiratory parameters (via pneumotachography).
The extent to which physical activity influences protein requirements is a difficult question to ... more The extent to which physical activity influences protein requirements is a difficult question to answer on two counts. First, physical activity results in a complex and presently poorly understood set of physiological and metabolic responses which are variable according to the intensity, duration and qualitative nature of work performed . Second, protein requirements for the normal individual are difficult to define and subject to controversy ). It will not be surprising to find, therefore, that there is no consensus as to whether protein requirements are influenced by physical activity. Our objective here is to present an overview of the metabolic impact of exercise on amino acid and N metabolism and the consequences of that impact on dietary protein needs from the perspective of our own view of the metabolic basis of protein requirements.
Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spi... more Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spinal and supraspinal neurophysiological mechanism termed the tonic vibration reflex (TVR). However, TVR has not been experimentally demonstrated during low-frequency WBV, therefore this investigation aimed to determine the expression of TVR during WBV. Whilst seated, eight healthy males were exposed to either vertical WBV applied to the leg via the plantar-surface of the foot, or Achilles tendon vibration (ATV) at 25Hz and 50Hzfor 70s. Ankle plantarflexion force, tri-axial accelerations at the shank and vibration source, and surface EMG activity of m. soleus (SOL) and m. tibialis anterior (TA) were recorded from the unloaded and passively loaded leg to simulate body mass supported during standing. Plantar flexion force was similarly augmented by WBV and ATV and increased over time in a load-and frequency dependent fashion. SOL and TA EMG amplitudes increased over time in all conditions independently of vibration mode. 50Hz WBV and ATV resulted in greater muscle activation than 25Hz in SOL when the shank was loaded and in TA when the shank was unloaded despite the greater transmission of vertical acceleration from source to shank with 25Hz and WBV, especially during loading. Low-amplitude WBV of the unloaded and passively loaded leg produced slow tonic muscle contraction and plantar-flexion force increase of similar magnitudes to those induced by Achilles tendon vibration at the same frequencies. This study provides the first experimental evidence supporting the TVR as a plausible mechanism underlying the neuromuscular response to whole-body vibration.
We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary a... more We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary activation are implicated in hypohydration-induced reductions in muscle isometric and isokinetic (90u.s 21 ) strength. Nine male athletes completed two trials (hypohydrated, euhydrated) comprising 90 min cycling at 40uC, with body weight losses replaced in euhydrated trial. Peripheral nerve and transcranial magnetic stimulations were applied during voluntary contractions pre-and 40 min postexercise to quantify voluntary activation and peripheral (M-wave) and corticospinal (motor evoked potential) evoked responses in m. vastus medialis. Both maximum isometric (215.363.1 vs 25.463.5%) and isokinetic eccentric (224.864.6 vs 27.367.2%) torque decreased to a greater extent in hypohydrated than euhydrated trials (p,0.05). Half relaxation time of the twitch evoked by peripheral nerve stimulation during maximal contractions increased after exercise in the hypohydrated (21.869.3%) but stayed constant in the euhydrated (1.6610.7%; p = 0.017) condition. M-wave amplitude during maximum voluntary contraction increased after exercise in the heat in hypohydrated (10.7618.0%) but decreased in euhydrated condition (217.4616.9%; p = 0.067). Neither peripheral nor cortical voluntary activation were significantly different between conditions. Motor evoked potential amplitude increased similarly in both conditions (hypohydrated: 25.7628.5%; euhydrated: 52.9633.5%) and was accompanied by lengthening of the cortical silent period in euhydrated but not hypohydrated condition (p = 0.019). Different neural strategies seem to be adopted to regulate neural drive in the two conditions, with increases in inhibitory input of either intracortical or corticospinal origin during the euhydrated trial. Such changes were absent in the hypohydrated condition, yet voluntary activation was similar to the euhydrated condition, perhaps due to smaller increases in excitatory drive rather than increased inhibition. Despite this maximal isometric and eccentric strength were impaired in the hypohydrated condition. The increase in peripheral muscle excitability evident in the hypohydrated condition was not sufficient to preserve performance in the face of reduced muscle contractility or impaired excitation-contraction coupling.
Purpose: Montmorency cherries contain high levels of polyphenolic compounds including flavonoids ... more Purpose: Montmorency cherries contain high levels of polyphenolic compounds including flavonoids and anthocyanins possessing antioxidant and anti-inflammatory effects. We investigated whether the effects of intensive unilateral leg exercise on oxidative damage and muscle function were attenuated by consumption of a Montmorency cherry juice concentrate using a crossover experimental design. Methods: Ten well-trained male overnight-fasted athletes completed two trials of 10 sets of 10 single-leg knee extensions at 80% one-repetition maximum. Trials were separated by 2 wk, and alternate legs were used in each trial. Participants consumed each supplement (CherryActive (CA) or isoenergetic fruit concentrate (FC)) for 7 d before and 48 h after exercise. Knee extension maximum voluntary contractions (MVC) were performed before, immediately after, and 24 and 48 h after the damaging exercise. Venous blood samples were collected at each time point, and serum was analyzed for creatine kinase (CK) activity, nitrotyrosine, high-sensitivity C-reactive protein, total antioxidant capacity, and protein carbonyls (PC). Two-way repeated-measures ANOVA were used for statistical analysis of the data. Results: MVC force recovery was significantly faster (24 h: CA 90.9% T 4.2% of initial MVC vs FC 84.9% T 3.4% of initial MVC; 48 h: CA 92.9% T 3.3% of initial MVC vs FC 88.5% T 2.9% of initial MVC (mean T SEM); P G 0.05) after CA than FC consumption. Only serum CK and PC increased significantly from baseline, peaking 24 h after exercise (P G 0.001). The exercise-induced increase in CK activity was not different between trials. However, both the percentage (24 h after: CA 23.8% T 2.9% vs FC 82.7% T 11.7%; P = 0.013) and absolute (24 h after: CA 0.31 T 0.03 nmolImg j1 protein vs FC 0.60 T 0.08 nmolImg j1 protein; P = 0.079) increase in PC was lower in CA than FC trials. Conclusions: Montmorency cherry juice consumption improved the recovery of isometric muscle strength after intensive exercise perhaps owing to the attenuation of the oxidative damage induced by the damaging exercise. FIGURE 2-MVC force normalized to preexercise values. There was a main effect of time (P G 0.001) and a significant interaction effect (P = 0.04) with enhanced MVC force recovery in the CA trial.
Purpose: The aim of the present study was to test the applicability and sensitivity of new electr... more Purpose: The aim of the present study was to test the applicability and sensitivity of new electromyography (EMG) spectral indices in assessing peripheral muscle fatigue during dynamic knee-extension exercise. Methods: Seven subjects completed 10 sets of 15 repetitions of right knee-extension exercise lifting 50% of their one-repetition maximum. Torque (T), knee-joint angle, and the interference EMG of rectus femoris muscle were recorded simultaneously. Maximal voluntary isometric contraction (MVC) was tested before and after exercise. Median spectral frequency (F med ) and new spectral indices of muscle fatigue (FI nsmk ) were calculated for each repetition. Results: The rate and range of FI nsmk -and F med -relative changes against the first repetition of the corresponding set increased gradually across successive repetitions within the set, reflecting accumulation of peripheral muscle fatigue. The maximal change of FI nsmk observed in the present experiment was approximately eightfold, whereas that of F med was only 32%. Significant between-subject variability in the range of FI nsmk changes (P G 0.0001) was found, so a hierarchical cluster analysis of muscle fatigue indices was conducted. Three distinct subgroups of subjects were identified: high (N = 1, FI nsmk change 9 400%), medium (N = 4, 200% G FI nsmk change G 400%), and low (N = 2, FI nsmk change G 200%) muscle fatigability. The changes in muscle performance during (last vs first repetition peak T, P = 0.03) and after (post-vs preexercise MVC, P = 0.012) exercise were significantly different between clusters (one-way ANOVA). The rate of fatigue development was also significantly different between clusters (linear regression analysis of F med and FI nsmk changes). Conclusions: The new spectral indices are a valid and reliable tool for assessment of muscle fatigability irrespective of EMG signal variability caused by dynamic muscle contractions, and these indices are more sensitive than those traditionally used.
European journal of applied physiology, Jan 13, 2018
Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it ... more Acetaminophen is a commonly used medicine for pain relief and emerging evidence suggests that it may improve endurance exercise performance. This study investigated some of the physiological mechanisms by which acute acetaminophen ingestion might blunt muscle fatigue development. Thirteen active males completed 60 × 3 s maximum voluntary contractions (MVC) of the knee extensors with each contraction separated by a 2 s passive recovery period. This protocol was completed 60 min after ingesting 1 g of maltodextrin (placebo) or 1 g of acetaminophen on two separate visits. Peripheral nerve stimulation was administered every 6th contraction for assessment of neuromuscular fatigue development, with the critical torque (CT), which reflects the maximal sustainable rate of oxidative metabolism, taken as the mean torque over the last 12 contractions. Surface electromyography was recorded continuously as a measure of muscle activation. Mean torque (61 ± 11 vs. 58 ± 14% pre-exercise MVC) and CT...
The aim of this study was to determine whether low-frequency whole-body vibration (WBV) modulates... more The aim of this study was to determine whether low-frequency whole-body vibration (WBV) modulates the excitability of the corticospinal and intracortical pathways related to tibialis anterior (TA) muscle activity, thus contributing to the observed changes in neuromuscular function during and after WBV exercise. Motor-evoked potentials (MEPs) elicited in response to transcranial magnetic stimulation (TMS) of the leg area of the motor cortex were recorded in TA and soleus (SOL) muscles of seven healthy male subjects whilst performing 330 s continuous static squat exercise. Each subject completed two conditions: control (no WBV) and WBV (30 Hz, 1.5 mm vibration applied from 111 to 220 s). Five single suprathreshold and five paired TMS were delivered during each squat period lasting 110 s (pre-, during and post-WBV). Two interstimulus intervals (ISIs) between the conditioning and the testing stimuli were employed in order to study the effects of WBV on short-interval intracortical inhibition (SICI, ISI = 3 ms) and intracortical facilitation (ICF, ISI = 13 ms). During vibration relative to squat exercise alone, single-pulse TMS provoked significantly higher TA MEP amplitude (56 ± 14%, P = 0.003) and total area (71 ± 19%, P = 0.04), and paired TMS with ISI = 13 ms provoked smaller MEP amplitude (−21 ± 4%, P = 0.01) but not in SOL. Paired-pulse TMS with ISI = 3 ms elicited significantly lower MEP amplitude (TA, −19 ± 4%, P = 0.009; and SOL, −13 ± 4%, P = 0.03) and total area (SOL, −17 ± 6%, P = 0.02) during vibration relative to squat exercise alone in both muscles. Tibialis anterior MEP facilitation in response to single-pulse TMS suggests that WBV increased corticospinal pathway excitability. Increased TA and SOL SICI and decreased TA ICF in response to paired-pulse TMS during WBV indicate vibration-induced alteration of the intracortical processes as well.
Design: 8 male, active subjects (age: 33.6 ± 2.0 yrs; VO2max: 3.6 ± 0.2 l.min -1 ) completed two ... more Design: 8 male, active subjects (age: 33.6 ± 2.0 yrs; VO2max: 3.6 ± 0.2 l.min -1 ) completed two trials separated by at least 14 d. Subjects cycled for 3 min at 95% VO2max with prior infusion (2ml.kg -1 bm) of either saline (CON) or DCA (25mg.ml -1 ) , see for detailed protocol. Kinetic analysis: Breath-by-breath VO2 & Near Infrared Spectroscopy (%Hb, NIRS) data (where %Hb = Hb(t) / (Hb(max) -Hb(min)) were fitted to a monoexponential model with a delay relative to the start of exercise of the form:
After exhaustive exercise, intravenous or oral glutamine promoted skeletal muscle glycogen storag... more After exhaustive exercise, intravenous or oral glutamine promoted skeletal muscle glycogen storage. However, when glutamine was ingested with glucose polymer, whole-body carbohydrate storage was elevated, the most likely site being liver and not muscle, possibly due to increased glucosamine formation. The rate of tricarboxylic acid (TCA) cycle flux and hence oxidative metabolism may be limited by the availability of TCA intermediates. There is some evidence that intramuscular glutamate normally provides alpha-ketoglutarate to the mitochondrion. We hypothesized that glutamine might be a more efficient anaplerotic precursor than endogenous glutamate alone. Indeed, a greater expansion of the sum of muscle citrate, malate, fumarate and succinate concentrations was observed at the start of exercise (70% VO2(max)) after oral glutamine than when placebo or ornithine alpha-ketoglutarate was given. However, neither endurance time nor the extent of phosphocreatine depletion or lactate accumul...
Journal of applied physiology (Bethesda, Md. : 1985), 2000
Seven untrained male subjects participated in a double-blind, crossover study conducted to determ... more Seven untrained male subjects participated in a double-blind, crossover study conducted to determine the efficacy of different carbohydrate drinks in promoting carbohydrate storage in the whole body and skeletal muscle during recovery from exhaustive exercise. The postabsorptive subjects first completed an exercise protocol designed to deplete muscle fibers of glycogen, then consumed 330 ml of one of three carbohydrate drinks (18.5% glucose polymer, 18.5% sucrose, or 12% sucrose; wt/vol) and also received a primed constant infusion of [1-(13)C]glucose for 2 h. Nonoxidative glucose disposal (3.51 +/- 0.28, 18.5% glucose polymer; 2.96 +/- 0.32, 18.5% sucrose; 2.97 +/- 0.16, 12% sucrose; all mmol. kg(-1). h(-1)) and storage of muscle glycogen (5.31 +/- 1.11, 18.5% glucose polymer; 4.07 +/- 1.05, 18.5% sucrose; 3.45 +/- 0.85, 12% sucrose; all mmol. kg wet wt(-1). h(-1); P < 0.05) were greater after consumption of the glucose polymer drink than after either sucrose drink. The results ...
Journal of applied physiology (Bethesda, Md. : 1985), 1999
The purpose of this study was to determine the efficacy of glutamine in promoting whole body carb... more The purpose of this study was to determine the efficacy of glutamine in promoting whole body carbohydrate storage and muscle glycogen resynthesis during recovery from exhaustive exercise. Postabsorptive subjects completed a glycogen-depleting exercise protocol, then consumed 330 ml of one of three drinks, 18.5% (wt/vol) glucose polymer solution, 8 g glutamine in 330 ml glucose polymer solution, or 8 g glutamine in 330 ml placebo, and also received a primed constant infusion of [1-13C]glucose for 2 h. Plasma glutamine concentration was increased after consumption of the glutamine drinks (0.7-1.1 mM, P < 0.05). In the second hour of recovery, whole body nonoxidative glucose disposal was increased by 25% after consumption of glutamine in addition to the glucose polymer (4.48 +/- 0.61 vs. 3.59 +/- 0.18 mmol/kg, P < 0.05). Oral glutamine alone promoted storage of muscle glycogen to an extent similar to oral glucose polymer. Ingestion of glutamine and glucose polymer together promot...
Journal of applied physiology (Bethesda, Md. : 1985), 1998
The aim of this study was to investigate dietary protein-induced changes in whole body leucine tu... more The aim of this study was to investigate dietary protein-induced changes in whole body leucine turnover and oxidation and in skeletal muscle branched chain 2-oxo acid dehydrogenase (BCOADH) activity, at rest and during exercise. Postabsorptive subjects received a primed constant infusion of L-[1-13C,15N]leucine for 6 h, after previous consumption of a high- (HP; 1.8 g . kg-1 . day-1, n = 8) or a low-protein diet (LP; 0.7 g . kg-1 . day-1, n = 8) for 7 days. The subjects were studied at rest for 2 h, during 2-h exercise at 60% maximum oxygen consumption, then again for 2 h at rest. Exercise induced a doubling of both leucine oxidation from 20 micromol . kg-1 . h-1 and BCOADH percent activation from 7% in all subjects. Leucine oxidation was greater before (+46%) and during (+40%, P < 0.05) the first hour of exercise in subjects consuming the HP rather than the LP diet, but there was no additional change in muscle BCOADH activity. The results suggest that leucine oxidation was incre...
FIG. 2. Theoretical considerations for calculating FI nmsk illustrated on exemplary data. A: effe... more FIG. 2. Theoretical considerations for calculating FI nmsk illustrated on exemplary data. A: effect of segment location: ( ) concentric; ( ) eccentric; ( ) centered to peak knee extension; ( ) 50Hz notch filter. B: effect of k: ( ) k=2; ( ) k=3; ( ) k=4; ( ) k=5. (from1 st and 4 th set). C, D: relative changes of FInsm5 and Fmed during the 1 st ( ), 2 nd ( ), 3 rd ( ) and 4 th ( ) set of the exercise protocol.
Respiratory physiology & neurobiology, Jan 29, 2008
To investigate whether 10 breaths against a vibration stimulus elicits increments of spontaneous ... more To investigate whether 10 breaths against a vibration stimulus elicits increments of spontaneous and maximal inspiratory mouth pressure (maxMP) and tidal mean inspiratory flow (iV(T)/T(I)) upon stimulus removal. Twelve healthy subjects (8 female, 4 male; 22-50 years old), recruited from the University student body, completed 3 maximal inspirations before (pre) and after (post) 10 inspirations against resistive loading with a vibration-type stimulus (VIB; youbreathe, Exoscience Ltd., London, UK), pressure-matched resistive loading (RES) or resting breathing (CON; no load). The trials were presented in a random order. maxMP and involuntary tidal breathing were compared pre and post conditioning. Inspiratory neural drive increased only after VIB as evidenced by increased tidal and maxMP and mean inspiratory flow (iV(T)/T(I); p < 0.05). There was no effect of either resistance or control breathing on maximal maxMP or tidal responses. Ten conditioning breaths of VIB lead to increased ...
1. The aim of this study was to determine the effect of glucose supplementation on leucine turnov... more 1. The aim of this study was to determine the effect of glucose supplementation on leucine turnover during and after exercise and whether variation in the previous dietary protein content modulated this effect. 2. Postabsorptive subjects received a primed constant [1-13 C, 15 N]leucine infusion for 6 h, after previous consumption of a high (1·8 g kg¢ day¢, HP, n = 16) or low (0·7 g kg¢ day¢, LP, n = 16) protein diet for 7 days. The subjects were studied at rest; during 2 h of exercise, during which half of the subjects from each dietary protocol received 0·75 g kg¢ h¢ glucose (HP + G, LP + G) and the other half received water (HP + W, LP + W); then again for 2 h of rest. 3. Glucose supplementation suppressed leucine oxidation (P < 0·01) by 20% in subjects consuming the high protein diet (58·2 ± 2·8 ìmol kg¢ h¢, HP + G; 72·4 ± 3·9 ìmol kg¢ h¢, HP + W) but not the low protein diet (51·1 ± 5·9 ìmol kg¢ h¢, LP + G; 51·7 ± 5·5 ìmol kg¢ h¢, LP + W), with no difference in skeletal muscle branched-chain 2-oxo acid dehydrogenase (BCOADH) activity between groups. Glucose supplementation did not alter the rate of whole-body protein synthesis or breakdown. 4. The sparing effect of glucose on leucine oxidation appears only to occur if previous protein intake was high. It was not mediated by a suppression of BCOADH fractional activity but may be due to reduced substrate availability. 0584
The tricarboxylic acid cycle is essential for oxidative energy production. The expansion (anapler... more The tricarboxylic acid cycle is essential for oxidative energy production. The expansion (anaplerosis) of the intermediates of the TCA cycle (TCAI) is achieved via number of pathways and is known to be influenced by metabolic status and nutritional and pharmacological interventions. Contraction is associated with anaplerosis in skeletal muscle and some authors have suggested that the rate of anaplerosis can limit oxidative energy delivery. However, the results of more recent studies are consistent with the idea that expansion of the muscle TCAI pool is principally a reflection of muscle pyruvate availability, and is of little functional importance to TCA cycle flux, thereby signifying any intervention aimed at increasing TCAI expansion will be of little practical value.
COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxida... more COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxidative metabolism to exercise. We hypothesised that prior glutamine supplementation would enhance V(O2) peak, V(O2) at lactate threshold and speed pulmonary oxygen uptake kinetics in COPD. 13 patients (9 males, age 66±5 years, mean±SD) with severe COPD (mean FEV(1) 0.88±0.23l, 33±7% predicted) performed on separate days ramp cycle-ergometry (5-10 W min(-1)) to volitional exhaustion and subsequently square-wave transitions to 80% estimated lactate threshold (LT) following consumption of either placebo (CON) or 0.125 g kg bm(-1) of glutamine (GLN) in 5 ml kg bm(-1) placebo. Oral glutamine had no effect on peak or V(O2) at LT, {V(O2) peak: CON=0.70±0.1 l min(-1) vs. GLN=0.73±0.2 l min(-1); LT: CON=0.57±0.1 l min(-1) vs. GLN=0.54±0.1 lmin(-1)} or V(O2) kinetics {tau: CON=68±22 s vs. GLN=68±16 s}. Ingestion of glutamine before exercise did not improve indices of oxidative metabolism in this patient group.
A sharp intake of breath followed by a strong vocalisation is widely observed in response to acut... more A sharp intake of breath followed by a strong vocalisation is widely observed in response to acute pain although its function and mechanism is poorly understood. This study investigated the effect of percutaneous (overlying the tibial bone) electrical stimulation delivered early (20-30% of inspiratory time) during inspiration (INSP) or expiration (EXP) (20-30% of expiratory time) at sensory intensities at (100%), above (125%) and below (50% and 75%) the pre-determined pain threshold (PT), upon within-a-breath respiratory parameters (via pneumotachography).
The extent to which physical activity influences protein requirements is a difficult question to ... more The extent to which physical activity influences protein requirements is a difficult question to answer on two counts. First, physical activity results in a complex and presently poorly understood set of physiological and metabolic responses which are variable according to the intensity, duration and qualitative nature of work performed . Second, protein requirements for the normal individual are difficult to define and subject to controversy ). It will not be surprising to find, therefore, that there is no consensus as to whether protein requirements are influenced by physical activity. Our objective here is to present an overview of the metabolic impact of exercise on amino acid and N metabolism and the consequences of that impact on dietary protein needs from the perspective of our own view of the metabolic basis of protein requirements.
Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spi... more Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spinal and supraspinal neurophysiological mechanism termed the tonic vibration reflex (TVR). However, TVR has not been experimentally demonstrated during low-frequency WBV, therefore this investigation aimed to determine the expression of TVR during WBV. Whilst seated, eight healthy males were exposed to either vertical WBV applied to the leg via the plantar-surface of the foot, or Achilles tendon vibration (ATV) at 25Hz and 50Hzfor 70s. Ankle plantarflexion force, tri-axial accelerations at the shank and vibration source, and surface EMG activity of m. soleus (SOL) and m. tibialis anterior (TA) were recorded from the unloaded and passively loaded leg to simulate body mass supported during standing. Plantar flexion force was similarly augmented by WBV and ATV and increased over time in a load-and frequency dependent fashion. SOL and TA EMG amplitudes increased over time in all conditions independently of vibration mode. 50Hz WBV and ATV resulted in greater muscle activation than 25Hz in SOL when the shank was loaded and in TA when the shank was unloaded despite the greater transmission of vertical acceleration from source to shank with 25Hz and WBV, especially during loading. Low-amplitude WBV of the unloaded and passively loaded leg produced slow tonic muscle contraction and plantar-flexion force increase of similar magnitudes to those induced by Achilles tendon vibration at the same frequencies. This study provides the first experimental evidence supporting the TVR as a plausible mechanism underlying the neuromuscular response to whole-body vibration.
We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary a... more We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary activation are implicated in hypohydration-induced reductions in muscle isometric and isokinetic (90u.s 21 ) strength. Nine male athletes completed two trials (hypohydrated, euhydrated) comprising 90 min cycling at 40uC, with body weight losses replaced in euhydrated trial. Peripheral nerve and transcranial magnetic stimulations were applied during voluntary contractions pre-and 40 min postexercise to quantify voluntary activation and peripheral (M-wave) and corticospinal (motor evoked potential) evoked responses in m. vastus medialis. Both maximum isometric (215.363.1 vs 25.463.5%) and isokinetic eccentric (224.864.6 vs 27.367.2%) torque decreased to a greater extent in hypohydrated than euhydrated trials (p,0.05). Half relaxation time of the twitch evoked by peripheral nerve stimulation during maximal contractions increased after exercise in the hypohydrated (21.869.3%) but stayed constant in the euhydrated (1.6610.7%; p = 0.017) condition. M-wave amplitude during maximum voluntary contraction increased after exercise in the heat in hypohydrated (10.7618.0%) but decreased in euhydrated condition (217.4616.9%; p = 0.067). Neither peripheral nor cortical voluntary activation were significantly different between conditions. Motor evoked potential amplitude increased similarly in both conditions (hypohydrated: 25.7628.5%; euhydrated: 52.9633.5%) and was accompanied by lengthening of the cortical silent period in euhydrated but not hypohydrated condition (p = 0.019). Different neural strategies seem to be adopted to regulate neural drive in the two conditions, with increases in inhibitory input of either intracortical or corticospinal origin during the euhydrated trial. Such changes were absent in the hypohydrated condition, yet voluntary activation was similar to the euhydrated condition, perhaps due to smaller increases in excitatory drive rather than increased inhibition. Despite this maximal isometric and eccentric strength were impaired in the hypohydrated condition. The increase in peripheral muscle excitability evident in the hypohydrated condition was not sufficient to preserve performance in the face of reduced muscle contractility or impaired excitation-contraction coupling.
Purpose: Montmorency cherries contain high levels of polyphenolic compounds including flavonoids ... more Purpose: Montmorency cherries contain high levels of polyphenolic compounds including flavonoids and anthocyanins possessing antioxidant and anti-inflammatory effects. We investigated whether the effects of intensive unilateral leg exercise on oxidative damage and muscle function were attenuated by consumption of a Montmorency cherry juice concentrate using a crossover experimental design. Methods: Ten well-trained male overnight-fasted athletes completed two trials of 10 sets of 10 single-leg knee extensions at 80% one-repetition maximum. Trials were separated by 2 wk, and alternate legs were used in each trial. Participants consumed each supplement (CherryActive (CA) or isoenergetic fruit concentrate (FC)) for 7 d before and 48 h after exercise. Knee extension maximum voluntary contractions (MVC) were performed before, immediately after, and 24 and 48 h after the damaging exercise. Venous blood samples were collected at each time point, and serum was analyzed for creatine kinase (CK) activity, nitrotyrosine, high-sensitivity C-reactive protein, total antioxidant capacity, and protein carbonyls (PC). Two-way repeated-measures ANOVA were used for statistical analysis of the data. Results: MVC force recovery was significantly faster (24 h: CA 90.9% T 4.2% of initial MVC vs FC 84.9% T 3.4% of initial MVC; 48 h: CA 92.9% T 3.3% of initial MVC vs FC 88.5% T 2.9% of initial MVC (mean T SEM); P G 0.05) after CA than FC consumption. Only serum CK and PC increased significantly from baseline, peaking 24 h after exercise (P G 0.001). The exercise-induced increase in CK activity was not different between trials. However, both the percentage (24 h after: CA 23.8% T 2.9% vs FC 82.7% T 11.7%; P = 0.013) and absolute (24 h after: CA 0.31 T 0.03 nmolImg j1 protein vs FC 0.60 T 0.08 nmolImg j1 protein; P = 0.079) increase in PC was lower in CA than FC trials. Conclusions: Montmorency cherry juice consumption improved the recovery of isometric muscle strength after intensive exercise perhaps owing to the attenuation of the oxidative damage induced by the damaging exercise. FIGURE 2-MVC force normalized to preexercise values. There was a main effect of time (P G 0.001) and a significant interaction effect (P = 0.04) with enhanced MVC force recovery in the CA trial.
Purpose: The aim of the present study was to test the applicability and sensitivity of new electr... more Purpose: The aim of the present study was to test the applicability and sensitivity of new electromyography (EMG) spectral indices in assessing peripheral muscle fatigue during dynamic knee-extension exercise. Methods: Seven subjects completed 10 sets of 15 repetitions of right knee-extension exercise lifting 50% of their one-repetition maximum. Torque (T), knee-joint angle, and the interference EMG of rectus femoris muscle were recorded simultaneously. Maximal voluntary isometric contraction (MVC) was tested before and after exercise. Median spectral frequency (F med ) and new spectral indices of muscle fatigue (FI nsmk ) were calculated for each repetition. Results: The rate and range of FI nsmk -and F med -relative changes against the first repetition of the corresponding set increased gradually across successive repetitions within the set, reflecting accumulation of peripheral muscle fatigue. The maximal change of FI nsmk observed in the present experiment was approximately eightfold, whereas that of F med was only 32%. Significant between-subject variability in the range of FI nsmk changes (P G 0.0001) was found, so a hierarchical cluster analysis of muscle fatigue indices was conducted. Three distinct subgroups of subjects were identified: high (N = 1, FI nsmk change 9 400%), medium (N = 4, 200% G FI nsmk change G 400%), and low (N = 2, FI nsmk change G 200%) muscle fatigability. The changes in muscle performance during (last vs first repetition peak T, P = 0.03) and after (post-vs preexercise MVC, P = 0.012) exercise were significantly different between clusters (one-way ANOVA). The rate of fatigue development was also significantly different between clusters (linear regression analysis of F med and FI nsmk changes). Conclusions: The new spectral indices are a valid and reliable tool for assessment of muscle fatigability irrespective of EMG signal variability caused by dynamic muscle contractions, and these indices are more sensitive than those traditionally used.
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