Joanna L. Bowtell

Montmorency Cherry Juice Reduces Muscle Damage Caused by Intensive Strength Exercise

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% ± 4.2% of initial MVC vs FC 84.9% ± 3.4% of initial MVC; 48 h: CA 92.9% ± 3.3% of initial MVC vs FC 88.5% ± 2.9% of initial MVC (mean ± SEM); P < 0.05) after CA than FC consumption. Only serum CK and PC increased significantly from baseline, peaking 24 h after exercise (P < 0.001). The exercise-induced increase in CK activity was not different between trials. However, both the percentage (24 h after: CA 23.8% ± 2.9% vs FC 82.7% ± 11.7%; P = 0.013) and absolute (24 h after: CA 0.31 ± 0.03 nmol·mg(-1) protein vs FC 0.60 ± 0.08 nmol·mg(-1) 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.

Effects of low‐frequency whole‐body vibration on motor‐evoked potentials in healthy men

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.

Repeated sprint training in normobaric hypoxia

Repeated sprint ability (RSA) is a critical success factor for intermittent sport performance. Repeated sprint training has been shown to improve RSA, we hypothesised that hypoxia would augment these training adaptations. Thirty male well-trained academy rugby union and rugby league players (18.4±1.5 years, 1.83±0.07 m, 88.1±8.9 kg) participated in this single-blind repeated sprint training study. Participants completed 12 sessions of repeated sprint training (10×6 s, 30 s recovery) over 4 weeks in either hypoxia (13% FiO2) or normoxia (21% FiO2). Pretraining and post-training, participants completed sports specific endurance and sprint field tests and a 10×6 s RSA test on a non-motorised treadmill while measuring speed, heart rate, capillary blood lactate, muscle and cerebral deoxygenation and respiratory measures. Yo-Yo Intermittent Recovery Level 1 test performance improved after RS training in both groups, but gains were significantly greater in the hypoxic (33±12%) than the normoxic group (14±10%, p<0.05). During the 10×6 s RS test there was a tendency for greater increases in oxygen consumption in the hypoxic group (hypoxic 6.9±9%, normoxic (−0.3±8.8%, p=0.06) and reductions in cerebral deoxygenation (% changes for both groups, p=0.09) after hypoxic than normoxic training. Twelve RS training sessions in hypoxia resulted in twofold greater improvements in capacity to perform repeated aerobic high intensity workout than an equivalent normoxic training. Performance gains are evident in the short term (4 weeks), a period similar to a preseason training block.

Acute physiological and performance responses to repeated sprints in varying degrees of hypoxia

OBJECTIVES Our aim was to determine the effects of different inspired oxygen fractions on repeated sprint performance and cardiorespiratory and neuromuscular responses, to construct a hypoxic dose response. DESIGN Nine male well-trained multi-sport athletes completed 10×6s all-out running sprints with 30s recovery in 5 conditions with different inspired oxygen fraction (FIO2: 12%, 13%, 14%, 15%, 21%). METHODS Peak running speed was measured in each sprint and electromyography data were recorded from m. vastus lateralis in parallel with heart rate and blood oxygen saturation. Cardiorespiratory response was assessed via breath by breath expired air analysis and muscle oxygenation status was evaluated via near infrared spectroscopy. RESULTS In parallel with the higher heart rate, minute ventilation, blood lactate concentration, and muscle deoxygenation; lower blood oxygen saturation, pulmonary oxygen uptake and integrated EMG (all p<0.05) were registered in all hypoxic conditions, with the greatest changes from baseline observed during the 13% trial. However, fatigue index and speed decrement were significantly greater only during the 12% vs 21% trial (p<0.05). CONCLUSIONS Physiological responses associated with performing 10×6s sprints interspersed with 30s passive recovery was incrementally greater as FIO2 decreased to 13%, yet fatigue development was significantly exacerbated relative to normoxia (FIO2: 21%) only at the 12% FIO2.

Tricarboxylic acid cycle intermediate pool size: functional importance for oxidative metabolism in exercising human skeletal muscle.

The tricarboxylic acid (TCA) cycle is the major final common pathway for oxidation of carbohydrates, lipids and some amino acids, which produces reducing equivalents in the form of nicotinamide adenine dinucleotide and flavin adenine dinucleotide that result in production of large amounts of adenosine triphosphate (ATP) via oxidative phosphorylation. Although regulated primarily by the products of ATP hydrolysis, in particular adenosine diphosphate, the rate of delivery of reducing equivalents to the electron transport chain is also a potential regulatory step of oxidative phosphorylation. The TCA cycle is responsible for the generation of ≈67% of all reducing equivalents per molecule of glucose, hence factors that influence TCA cycle flux will be of critical importance for oxidative phosphorylation. TCA cycle flux is dependent upon the supply of acetyl units, activation of the three non-equilibrium reactions within the TCA cycle, and it has been suggested that an increase in the total concentration of the TCA cycle intermediates (TCAi) is also necessary to augment and maintain TCA cycle flux during exercise.This article reviews the evidence of the functional importance of the TCAi pool size for oxidative metabolism in exercising human skeletal muscle. In parallel with increased oxidative metabolism and TCA cycle flux during exercise, there is an exercise intensity-dependent 4- to 5-fold increase in the concentration of the TCAi. TCAi concentration reaches a peak after 10–15 minutes of exercise, and thereafter tends to decline. This seems to support the suggestion that the concentration of TCAi may be of functional importance for oxidative phosphorylation. However, researchers have been able to induce dissociations between TCAi pool size and oxidative energy provision using a variety of nutritional, pharmacological and exercise interventions.Brief periods of endurance training (5 days or 7 weeks) have been found to result in reduced TCAi pool expansion at the start of exercise (same absolute work intensity) in parallel with either equivalent or increased oxidative energy provision. Cycloserine inhibits alanine aminotransferase, which catalyses the predominant anaplerotic reaction in exercising human muscle. When infused into contracting rat hindlimb muscle, TCAi pool expansion was reduced by 25% with no significant change in oxidative energy provision or power output. Glutamine supplementation has been shown to enhance TCAi pool expansion at the start of exercise with no increase in oxidative energy provision. In summary, there is a consistent dissociation between the extent of TCAi pool expansion at the onset of exercise and oxidative energy provision.At the other end of the spectrum, the parallel loss of TCAi, glycogen and adenine nucleotides and accumulation of inosine monophosphate during prolonged exercise has led to the suggestion that there is a link between muscle glycogen depletion, reduced TCA cycle flux and the development of fatigue. However, analysis of serial biopsies during prolonged exercise demonstrated dissociation between muscle TCAi content and both muscle glycogen content and muscle oxygen uptake. In addition, the delay in fatigue development achieved through increased carbohydrate availability does not attenuate TCAi reduction during prolonged exercise. Therefore, TCAi concentration in whole muscle homogenate does not seem to be of functional importance. However, TCAi content can currently only be measured in whole muscle homogenate rather than the mitochondrial subfraction where TCA cycle reactions occur. In addition, anaplerotic flux rather than TCAi content per se is likely to be of greater importance in determining TCA cycle flux, since TCAi content is probably merely reflective of anaplerotic substrate concentration. Methodological advances are required to allow researchers to address the questions of whether oxidative phosphorylation is limited by mitochondrial TCAi content and/or anaplerotic flux.

Interaction between Glutamine Availability and Metabolism of Glycogen, Tricarboxylic Acid Cycle Intermediates and Glutathione

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 accumulation during the exercise was altered, suggesting either that TCA intermediates were not limiting for energy production or that the severity of exercise was insufficient for the limitation to be operational. We have also shown that in the perfused working rat heart, there is a substantial fall in intramuscular glutamine and alpha-ketoglutarate, especially after ischemia. Glutamine (but not glutamate, alpha-ketoglutarate or aspartate) was able to rescue the performance of the postischemic heart. This ability appears to be connected to the ability to sustain intracardiac ATP, phosphocreatine and glutathione.

Experimental Evidence of the Tonic Vibration Reflex during Whole-Body Vibration of the Loaded and Unloaded Leg

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 plantar-flexion 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.

Effect of oral glucose on leucine turnover in human subjects at rest and during exercise at two levels of dietary protein

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 [1‐13C, 15N]leucine infusion for 6 h, after previous consumption of a high (1.8 g kg−1 day−1, HP, n= 16) or low (0.7 g kg−1 day−1, 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−1 h−1 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 μmol kg−1 h−1, HP + G; 72.4 ± 3.9 μmol kg−1 h−1, HP + W) but not the low protein diet (51.1 ± 5.9 μmol kg−1 h−1, LP + G; 51.7 ± 5.5 μmol kg−1 h−1, 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.

Glutamine: An anaplerotic precursor

There is an up to four-fold increase in the concentration of the tricarboxylic acid (TCA) cycle intermediates at the start of exercise. The rate of TCA cycle flux and, hence, oxidative metabolism may be limited by the concentration of the intermediates in the cycle. The dramatic decline in intramuscular glutamate at the start of exercise, in tandem with increased intramuscular alanine, suggests that glutamate is an important anaplerotic precursor. We hypothesized that oral glutamine might enhance the exercise-induced TCA cycle intermediate pool expansion. Indeed, a greater increase in the sum of muscle citrate, malate, fumarate, and succinate concentrations (approximately 85% total TCA intermediate pool) occurred at the start of exercise after ingestion of glutamine rather than of placebo or ornithine alpha-ketoglutarate. However, neither endurance capacity nor the degree of phosphocreatine depletion or lactate accumulation was altered. This suggests that TCA cycle intermediates do not limit flux through the cycle or that more intense exercise is required to show the limitation.

ACUTE EFFECTS OF FLEXI-BAR VS. SHAM-BAR EXERCISE ON MUSCLE ELECTROMYOGRAPHY ACTIVITY AND PERFORMANCE

Mileva, KN, Kadr, M, Amin, N, and Bowtell, JL. Acute effects of flexi-bar vs. sham-bar exercise on muscle electromyography activity and performance. J Strength Cond Res 24(3): 737-748, 2010-This study was conducted to investigate whether the low-frequency (5-Hz) oscillatory vibration-like stimulus, purported to be delivered by exercising with Flexi-bar, acutely affects muscle activation and maximal voluntary contraction (MVC) force. Nine healthy men participated in 2 trials, separated by at least 1 week, during which 4 × 30-second sets of exercise were performed with either the Flexi bar or a Sham bar. Maximal voluntary contraction force for elbow flexion, elbow extension, and knee extension were measured before and after the exercise. Root-mean-square amplitude and median frequency of electromyography (EMG) signal were calculated for the first and last 10 seconds of each exercise set and during the MVCs from biceps brachii (BB), triceps brachii (TB), rectus femoris (RF), and vastus lateralis (VL) for each trial. Electromyography amplitude was significantly higher for all studied muscles during Flexi-bar than Sham-bar exercise (32-203%, p < 0.05). Median frequency of EMG power spectrum was significantly lower in arm (TB: −40 ± 13%, p < 0.0001; BB: −32 ± 25%, p = 0.015) but not in leg (RF: −12 ± 18%; VL: +6 ± 32%; p > 0.05) muscles during Flexi-bar compared with Sham-bar exercise. Knee extension MVC force significantly decreased after Flexi-bar exercise (−3 ± 7%, p = 0.048) in parallel with reduced RF EMG amplitude (−8 ± 5%, p = 0.04), but there were no acute residual effects on elbow flexion/extension MVC or arm and VL EMG muscle activity. Using Flexi bar during exercise provoked acute alterations in arm- and leg-muscle EMG parameters and maximum force-generating capacity, indicating greater fatigue development than when exercising with the Sham bar. The results of this study indicate that Flexi bar may therefore be used to impose a stronger training stimulus on the muscle during submaximal exercise.