Effect of high-intensity intermittent training on lactate and H+ release from human skeletal muscle

Acute antioxidant supplementation improves endurance performance in trained athletes

This study examined the acute effects of a single dose of an antioxidant (AO; Lactaway® containing pycnogenol) on time to fatigue (TTF). Nine trained cyclists [mean ± SD age 35 ± 10 yrs; body mass 71.6 ± 10.2 kg; VO2 peak 63 ± 11 ml/kg/min] performed on two separate occasions a continuous protocol of 5 min at 50% of peak power output (PPO), 8 min at 70% of PPO, and then cycled to fatigue at 95% PPO. Four hours prior to the exercise protocol, the subjects consumed the supplement or a placebo (counterbalanced, double blind protocol). Cyclists, on average, rode for 80 s more in the Lactaway trial than they did in the placebo trial. There was considerable evidence (chances ≥94.5%) for substantial positive treatment effects for TTF and the other performance-related variables (excluding [BLa] at 95% PPO). Other studies are necessary to confirm these results and identify the mechanisms underlying the observed effects.

Skeletal muscle vasodilatation during maximal exercise in health and disease

Maximal exercise vasodilatation results from the balance between vasoconstricting and vasodilating signals combined with the vascular reactivity to these signals. During maximal exercise with a small muscle mass the skeletal muscle vascular bed is fully vasodilated. During maximal whole body exercise, however, vasodilatation is restrained by the sympathetic system. This is necessary to avoid hypotension since the maximal vascular conductance of the musculature exceeds the maximal pumping capacity of the heart. Endurance training and high-intensity intermittent knee extension training increase the capacity for maximal exercise vasodilatation by 20-30%, mainly due to an enhanced vasodilatory capacity, as maximal exercise perfusion pressure changes little with training. The increase in maximal exercise vascular conductance is to a large extent explained by skeletal muscle hypertrophy and vascular remodelling. The vasodilatory capacity during maximal exercise is reduced or blunted with ageing, as well as in chronic heart failure patients and chronically hypoxic humans; reduced vasodilatory responsiveness and increased sympathetic activity (and probably, altered sympatholysis) are potential mechanisms accounting for this effect. Pharmacological counteraction of the sympathetic restraint may result in lower perfusion pressure and reduced oxygen extraction by the exercising muscles. However, at the same time fast inhibition of the chemoreflex in maximally exercising humans may result in increased vasodilatation, further confirming a restraining role of the sympathetic nervous system on exercise-induced vasodilatation. This is likely to be critical for the maintenance of blood pressure in exercising patients with a limited heart pump capacity.

Effects of physical activity and inactivity on muscle fatigue

The aim of this review was to examine the mechanisms by which physical activity and inactivity modify muscle fatigue. It is well known that acute or chronic increases in physical activity result in structural, metabolic, hormonal, neural, and molecular adaptations that increase the level of force or power that can be sustained by a muscle. These adaptations depend on the type, intensity, and volume of the exercise stimulus, but recent studies have highlighted the role of high intensity, short-duration exercise as a time-efficient method to achieve both anaerobic and aerobic/endurance type adaptations. The factors that determine the fatigue profile of a muscle during intense exercise include muscle fiber composition, neuromuscular characteristics, high energy metabolite stores, buffering capacity, ionic regulation, capillarization, and mitochondrial density. Muscle fiber-type transformation during exercise training is usually toward the intermediate type IIA at the expense of both type I and IIx myosin heavy-chain isoforms. High-intensity training results in increases of both glycolytic and oxidative enzymes, muscle capillarization, improved phosphocreatine resynthesis and regulation of K⁺, H⁺, and lactate ions. Decreases of the habitual activity level due to injury or sedentary lifestyle result in partial or even compete reversal of the adaptations due to previous training, manifested by reductions in fiber cross-sectional area, decreased oxidative capacity, and capillarization. Complete immobilization due to injury results in markedly decreased force output and fatigue resistance. Muscle unloading reduces electromyographic activity and causes muscle atrophy and significant decreases in capillarization and oxidative enzymes activity. The last part of the review discusses the beneficial effects of intermittent high-intensity exercise training in patients with different health conditions to demonstrate the powerful effect of exercise on health and well being.

Repeated-sprint ability - part II: recommendations for training

Short-duration sprints, interspersed with brief recoveries, are common during most team sports. The ability to produce the best possible average sprint performance over a series of sprints (≤10 seconds), separated by short (≤60 seconds) recovery periods has been termed repeated-sprint ability (RSA). RSA is therefore an important fitness requirement of team-sport athletes, and it is important to better understand training strategies that can improve this fitness component. Surprisingly, however, there has been little research about the best training methods to improve RSA. In the absence of strong scientific evidence, two principal training theories have emerged. One is based on the concept of training specificity and maintains that the best way to train RSA is to perform repeated sprints. The second proposes that training interventions that target the main factors limiting RSA may be a more effective approach. The aim of this review (Part II) is to critically analyse training strategies to improve both RSA and the underlying factors responsible for fatigue during repeated sprints (see Part I of the preceding companion article). This review has highlighted that there is not one type of training that can be recommended to best improve RSA and all of the factors believed to be responsible for performance decrements during repeated-sprint tasks. This is not surprising, as RSA is a complex fitness component that depends on both metabolic (e.g. oxidative capacity, phosphocreatine recovery and H+ buffering) and neural factors (e.g. muscle activation and recruitment strategies) among others. While different training strategies can be used in order to improve each of these potential limiting factors, and in turn RSA, two key recommendations emerge from this review; it is important to include (i) some training to improve single-sprint performance (e.g. 'traditional' sprint training and strength/power training); and (ii) some high-intensity (80-90% maximal oxygen consumption) interval training to best improve the ability to recover between sprints. Further research is required to establish whether it is best to develop these qualities separately, or whether they can be developed concurrently (without interference effects). While research has identified a correlation between RSA and total sprint distance during soccer, future studies need to address whether training-induced changes in RSA also produce changes in match physical performance.

Effects of acute and chronic exercise on sarcolemmal MCT1 and MCT4 contents in human skeletal muscles: current status

Two lactate/proton cotransporter isoforms (monocarboxylate transporters, MCT1 and MCT4) are present in the plasma (sarcolemmal) membranes of skeletal muscle. Both isoforms are symports and are involved in both muscle pH and lactate regulation. Accordingly, sarcolemmal MCT isoform expression may play an important role in exercise performance. Acute exercise alters human MCT content, within the first 24 h from the onset of exercise. The regulation of MCT protein expression is complex after acute exercise, since there is not a simple concordance between changes in mRNA abundance and protein levels. In general, exercise produces greater increases in MCT1 than in MCT4 content. Chronic exercise also affects MCT1 and MCT4 content, regardless of the initial fitness of subjects. On the basis of cross-sectional studies, intensity would appear to be the most important factor regulating exercise-induced changes in MCT content. Regulation of skeletal muscle MCT1 and MCT4 content by a variety of stimuli inducing an elevation of lactate level (exercise, hypoxia, nutrition, metabolic perturbations) has been demonstrated. Dissociation between the regulation of MCT content and lactate transport activity has been reported in a number of studies, and changes in MCT content are more common in response to contractile activity, whereas changes in lactate transport capacity typically occur in response to changes in metabolic pathways. Muscle MCT expression is involved in, but is not the sole determinant of, muscle H(+) and lactate anion exchange during physical activity.

Effect of expertise on postmaximal long sprint blood metabolite responses

The aim of this study was to describe and compare the blood metabolic responses obtained after a single maximal exercise in elite and less-successful athletes and to investigate whether these responses are related to sprint performance. Eleven elite (ELI) and 14 regional (REG) long sprint runners performed a 300-m running test as fast as possible. Blood samples were taken at rest and at 4 minutes after exercise for measurements of blood lactate concentration [La] and acid-base status. The blood metabolic responses of ELI subjects compared to those of REG subjects for pH (7.07 ± 0.05 vs. 7.14 ± 1.5), sodium bicarbonate concentration ([HCO(3)(-)], 8.1 ± 1.5 vs. 9.8 ± 1.8 mmol·L(-1)), hemoglobin O(2) saturation (SaO(2)) (94.7 ± 1.8 vs. 96.2 ± 1.6%) were significantly lower (p < 0.05), and [La] was significantly higher in ELI (21.1 ± 2.9 vs. 19.1 ± 1.2 mmol·L(-1), p < 0.05). The 300-m performance (in % world record) was negatively correlated with pH (r = -0.55, p < 0.01), SaO2 (r = -0.64, p < 0.001), [HCO(3)(-)] (r = -0.40, p < 0.05), and positively correlated with [La] (r = 0.44, p < 0.05). In conclusion, for the same quantity of work, the best athletes are able to strongly alter their blood acid-base balance compared to underperforming runners, with larger acidosis and lactate accumulation. To obtain the pH limits with acute maximal exercise, coaches must have their athletes perform a distance run with duration of exercise superior to 35 seconds. The blood lactate accumulation values (mmol·L(-1)·s(-1)) recorded in this study indicate that the maximal glycolysis rate obtained in the literature from short sprint distances is maintained, but not increased, until 35 seconds of exercise.

[High intensity training (HIT) for the improvement of endurance capacity of recreationally active people and in prevention & rehabilitation]

Although intensive exercise protocols are commonly used in practical training and scientific studies, there is recently a great scientific discussion about "high intensity (interval) training" (HIT). New are the large amounts of studies and the more detailed knowledge about the physiological responses and adaptations to HIT in comparison to the classic high volume, low intensity endurance training. The present article summarizes the current knowledge about HIT in endurance exercise for clinical applications. In the first part, molecular and cellular adaptations to HIT are discussed in comparison to low intensity high volume training. Furthermore, studies are summarized which compare HIT vs. HVT in the field of prevention and rehabilitation. Terminally the differences in physiological stimuli of both training interventions are considered.

Speed endurance training is a powerful stimulus for physiological adaptations and performance improvements of athletes

The present article reviews the physiological and performance effects of speed endurance training consisting of exercise bouts at near maximal intensities in already trained subjects. Despite a reduction in training volume, speed endurance training of endurance-trained athletes can maintain the oxidative capacity and improve intense short-duration/repeated high-intensity exercise performance lasting 30 s to 4 min, as it occurs in a number of sports. When combined with a basic volume of training including some aerobic high-intensity sessions, speed endurance training is also useful in enhancing performance during longer events, e.g. 40 K cycling and 10 K running. Athletes in team sports involving intense exercise actions and endurance aspects can also benefit from performing speed endurance training. These improvements don't appear to depend on changes in maximum oxygen uptake (VO2max), muscle substrate levels, glycolytic and oxidative enzymes activity, and membrane transport proteins involved in pH regulation. Instead they appear to be related to a reduced energy expenditure during submaximal exercise and a higher expression of muscle Na(+) ,K(+) pump α-subunits, which via a higher Na(+) ,K(+) pump activity during exercise may delay fatigue development during intense exercise. In conclusion, athletes from disciplines involving periods of intense exercise can benefit from the inclusion of speed endurance sessions in their training programs.

Aerobic fitness determines whole-body fat oxidation rate during exercise in the heat

The purpose of this study was to determine whole-body fat oxidation in endurance-trained (TR) and untrained (UNTR) subjects exercising at different intensities in the heat. On 3 occasions, 10 TR cyclists and 10 UNTR healthy subjects (peak oxygen uptake = 60 ± 6 vs. 44 ± 3 mL·kg-1·min-1; p < 0.05) exercised at 40%, 60%, and 80% peak oxygen uptake in a hot, dry environment (36 °C; 25% relative humidity). To complete the same amount of work in all 3 trials, exercise duration varied (107 ± 4, 63 ± 1, and 45 ± 0 min for 40%, 60%, and 80% peak oxygen uptake, respectively). Substrate oxidation was calculated using indirect calorimetry. Blood samples were collected at the end of exercise to determine plasma epinephrine ([EPI]plasma) and norepinephrine ([NEPI]plasma) concentrations. The maximal rate of fat oxidation was achieved at 60% peak oxygen uptake for the TR group (0.41 ± 0.01 g·min-1) and at 40% peak oxygen uptake for the UNTR group (0.28 ± 0.01 g·min-1). TR subjects oxidized absolutely (g·min-1) and relatively (% of total energy expenditure) more fat than UNTR subjects at 60% and 80% peak oxygen uptake (p < 0.05). At these exercise intensities, TR subjects also had higher [NEPI]plasma concentrations than UNTR subjects (p < 0.05). In the heat, whole-body peak fat oxidation occurs at higher relative exercise intensities in TR than in UNTR subjects (60% vs. 40% peak oxygen uptake). Moreover, TR subjects oxidize more fat than UNTR subjects when exercising at moderate to high intensities (>60% peak oxygen uptake).

Sodium bicarbonate ingestion and repeated swim sprint performance

The purpose of the present investigation was to observe the ergogenic potential of 0.3 g·kg-1 of sodium bicarbonate (NaHCO3) in competitive, nonelite swimmers using a repeated swim sprint design that eliminated the technical component of turning. Six male (181.2 ± 7.2 cm; 80.3 ± 11.9 kg; 50.8 ± 5.5 ml·kg-1·min-1 VO2max) and 8 female (168.8 ± 5.6 cm; 75.3 ± 10.1 kg; 38.8 ± 2.6 ml·kg-1·min-1 VO2max) swimmers completed 2 trial conditions (NaHCO3 [BICARB] and NaCl placebo [PLAC]) implemented in a randomized (counterbalanced), single blind manner, each separated by 1 week. Swimmers were paired according to ability and completed 8, 25-m front crawl maximal effort sprints each separated by 5 seconds. Blood acid-base status was assessed preingestion, pre, and postswim via capillary finger sticks, and total swim time was calculated as a performance measure. Total swim time was significantly decreased in the BICARB compared to PLAC condition (p = 0.04), with the BICARB condition resulting in a 2% decrease in total swim time compared to the PLAC condition (159.4 ± 25.4 vs. 163.2 ± 25.6 seconds; mean difference = 4.4 seconds; 95% confidence interval = 8.7-0.1). Blood analysis revealed significantly elevated blood buffering potential preswim (pH: BICARB = 7.48 ± 0.01, PLAC = 7.41 ± 0.01) along with a significant decrease in extracellular K+ (BICARB = 4.0 ± 0.1 mmol·L-1, PLAC = 4.6 ± 0.1 mmol·L-1). The findings suggest that 0.3 g·kg-1 NaHCO3 ingested 2.5 hours before exercise enhances the blood buffering potential and may positively influence swim performance.

Disparity in regional and systemic circulatory capacities: do they affect the regulation of the circulation?

In this review we integrate ideas about regional and systemic circulatory capacities and the balance between skeletal muscle blood flow and cardiac output during heavy exercise in humans. In the first part of the review we discuss issues related to the pumping capacity of the heart and the vasodilator capacity of skeletal muscle. The issue is that skeletal muscle has a vast capacity to vasodilate during exercise [approximately 300 mL (100 g)(-1) min(-1)], but the pumping capacity of the human heart is limited to 20-25 L min(-1) in untrained subjects and approximately 35 L min(-1) in elite endurance athletes. This means that when more than 7-10 kg of muscle is active during heavy exercise, perfusion of the contracting muscles must be limited or mean arterial pressure will fall. In the second part of the review we emphasize that there is an interplay between sympathetic vasoconstriction and metabolic vasodilation that limits blood flow to contracting muscles to maintain mean arterial pressure. Vasoconstriction in larger vessels continues while constriction in smaller vessels is blunted permitting total muscle blood flow to be limited but distributed more optimally. This interplay between sympathetic constriction and metabolic dilation during heavy whole-body exercise is likely responsible for the very high levels of oxygen extraction seen in contracting skeletal muscle. It also explains why infusing vasodilators in the contracting muscles does not increase oxygen uptake in the muscle. Finally, when approximately 80% of cardiac output is directed towards contracting skeletal muscle modest vasoconstriction in the active muscles can evoke marked changes in arterial pressure.

Effect of 2-wk intensified training and inactivity on muscle Na+-K+ pump expression, phospholemman (FXYD1) phosphorylation, and performance in soccer players

The present study examined muscle adaptations and alterations in performance of highly trained soccer players with intensified training or training cessation. Eighteen elite soccer players were, for a 2-wk period, assigned to either a group that performed high-intensity training with a reduction in the amount of training (HI, n = 7), or an inactivity group without training (IN, n = 11). HI improved ( P < 0.05) performance of the 4th, 6th, and 10th sprint in a repeated 20-m sprint test, and IN reduced ( P < 0.05) performance in the 5th to the 10th sprints after the 2-wk intervention period. In addition, the Yo-Yo intermittent recovery level 2 test performance of IN was lowered from 845 ± 48 to 654 ± 30 m. In HI, the protein expression of the Na+-K+ pump α2-isoform was 15% higher ( P < 0.05) after the intervention period, whereas no changes were observed in α1- and β1-isoform expression. In IN, Na+-K+ pump expression was not changed. In HI, the FXYD1ser68-to-FXYD1 ratio was 27% higher ( P < 0.01) after the intervention period, and, in IN, the AB_FXYD1ser68 signal was 18% lower ( P < 0.05) after inactivity. The change in FXYD1ser68-to-FXYD1 ratio was correlated ( r2 = 0.35; P < 0.05) with change in performance in repeated sprint test. The present data suggest that short-term intensified training, even for trained soccer players, can increase muscle Na+-K+ pump α2-isoform expression, and that cessation of training for 2 wk does not affect the expression of Na+-K+ pump isoforms. Resting phosphorylation status of the Na+-K+ pump is changed by training and inactivity and may play a role in performance during repeated, intense exercise.

Restoration of blood pH between repeated bouts of high-intensity exercise: effects of various active-recovery protocols

To determine which active-recovery protocol would reduce faster the high blood H(+) and lactate concentrations produced by repeated bouts of high-intensity exercise (HIE). On three occasions, 11 moderately trained males performed 4 bouts (1.5 min) at 163% of their respiratory compensation threshold (RCT) interspersed with active-recovery: (1) 4.5 min pedalling at 24% RCT (S(HORT)); (2) 6 min at 18% RCT (M(EDIUM)); (3) 9 min at 12% RCT (L(ONG)). The total work completed during recovery was the same in all three trials. Respiratory gases and arterialized-blood samples were obtained during exercise. At the end of exercise, L(ONG) in comparison to S(HORT) and M(EDIUM) increased plasma pH (7.32 +/- 0.02 vs. approximately 7.22 +/- 0.03; P < 0.05), while reduced lactate concentration (8.5 +/- 0.9 vs. approximately 10.9 +/- 0.8 mM; P < 0.05). Ventilatory equivalent for CO(2) was higher in L(ONG) than S(HORT) and M(EDIUM) (31.4 +/- 0.5 vs. approximately 29.6 +/- 0.5; P < 0.05). Low-intensity prolonged recovery between repeated bouts of HIE maximized H(+) and lactate removal likely by enhancing CO(2) unloading.

MCT1 genetic polymorphism influence in high intensity circuit training: a pilot study

Monocarboxylate Transporter 1 (MCT1) mediates the transport of the main fraction of lactate across the sarcolemma. A common polymorphic MCT1 variant has been identified, but its role in high intensity exercise performance has not been defined. We investigated the influence of MCT1 A1470T polymorphism (rs1049434) on lactate accumulation after high intensity circuit training. Ten men aged 20-26 performed three controlled circuit training (CWT) sessions at 60%, 70%, and 80% of the 15 repetition maximum (15RM), in non-consecutive days. CWT included three sets of a circuit of eight exercises, obtaining lactate measurements immediately after each set had been completed. Two independent variables were analysed: MTC1 genotypes according to the presence or absence of the A1470T polymorphism, and the intensity of circuit training. Genotype distributions were in Hardy-Weinberg equilibrium, being 30% wild-type, 50% heterozygotes, and 20% mutated homozygotes. Mean lactate concentration at 80% of 15RM were significantly higher than the mean lactate values at the other intensities (p<0.01). Significant differences between genetic groups were found in the lactate accumulation slope at 80% of 15RM (p=0.02) and in the maximal lactate concentration reached by all subjects in the study (L(max)) (p=0.03). The carriers of the A1470T polymorphism in the MTC1 gene seem to exhibit a worse lactate transport capability into the less active muscle cells for oxidation.

Reduced volume and increased training intensity elevate muscle Na+-K+ pump alpha2-subunit expression as well as short- and long-term work capacity in humans

The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners as a result of a reduced amount of training combined with speed endurance training. For a 6- to 9-wk period, 17 runners were assigned to either a speed endurance group with a 25% reduction in the amount of training but including speed endurance training consisting of six to twelve 30-s sprint runs 3-4 times/wk (SET group n = 12) or a control group (n = 5), which continued the endurance training ( approximately 55 km/wk). For the SET group, the expression of the muscle Na(+)-K(+) pump alpha(2)-subunit was 68% higher (P < 0.05) and the plasma K(+) level was reduced (P < 0.05) during repeated intense running after 9 wk. Performance in a 30-s sprint test and the first of the supramaximal exhaustive runs was improved (P < 0.05) by 7% and 36%, respectively, after the speed endurance training period. In the SET group, maximal O(2) uptake was unaltered, but the 3-km (3,000-m) time was reduced (P < 0.05) from 10.4 +/- 0.1 to 10.1 +/- 0.1 min and the 10-km (10,000-m) time was improved from 37.3 +/- 0.4 to 36.3 +/- 0.4 min (means +/- SE). Muscle protein expression and performance remained unaltered in the control group. The present data suggest that both short- and long-term exercise performances can be improved with a reduction in training volume if speed endurance training is performed and that the Na(+)-K(+) pump plays a role in the control of K(+) homeostasis and in the development of fatigue during repeated high-intensity exercise.

Growth hormone receptor antagonist treatment reduces exercise performance in young males

CONTEXT

The effects of GH on exercise performance remain unclear.

OBJECTIVE

The aim of the study was to examine the effects of GH receptor (GHR) antagonist treatment on exercise performance.

DESIGN

Subjects were treated with the GHR antagonist pegvisomant or placebo for 16 d. After the treatment period, they exercised to determine exercise performance and hormonal and metabolic responses.

PARTICIPANTS

Twenty healthy males participated in the study.

INTERVENTION

Subjects were treated with the GHR antagonist (n = 10; 10 mg/d) or placebo (n = 10). After the treatment period, they performed a maximal oxygen uptake (VO(2 max)) test and a prolonged exercise test, consisting of 60 min of submaximal cycling followed by exercise to fatigue at 90% of VO(2 max).

MAIN OUTCOME MEASURES

VO(2 max) was measured before and after the treatment period. Hormonal and metabolic responses and time to exhaustion during prolonged exercise were determined.

RESULTS

Resting serum IGF-I concentration decreased by 20% in the GHR antagonist-treated group (P < 0.05), whereas no change was observed in the placebo group. Conversely, resting serum GH concentration was significantly higher in the treatment group compared with the placebo group (P < 0.01). VO(2 max) did not change significantly in either group after the treatment period. Time to exhaustion at 90% of VO(2 max) was significantly shorter in the treatment group (P < 0.05). No significant differences were observed between the groups in terms of changes in serum free fatty acids, glycerol, VO(2), or relative fat oxidation.

CONCLUSION

GH might be an important determinant of exercise capacity during prolonged exercise, but GHR antagonist did not alter fat metabolism during exercise.

Effects of intermittent high-intensity exercise and carbohydrate supplementation on IGF-1 and glycogen of Wistar rats

OBJECTIVE

The aim of this study was to analyze the association between glucose infusion during intermittent physical exercise and its metabolic effects on rats.

DESIGN

Forty male rats were divided into eight groups based on training (intermittent), exercise and carbohydrate intake (glucose 20%): TEC (trained exercised with carbohydrate), TES (trained exercised without carbohydrate), TNC (trained non-exercised with carbohydrate), TNS (trained non-exercised without carbohydrate), UEC (untrained exercised with carbohydrate), UES (untrained exercised without carbohydrate), UNC (untrained non-exercised with carbohydrate) and UNS (untrained non-exercised without carbohydrate). The training and/or exercise protocol consisted of the rats running on a treadmill for 1 min above the lactate threshold, or running below the lactate threshold for 30s, intermittently for 30 min. Blood was analyzed for glycemia, lactate and IGF-1. Muscle and liver glycogen were measured (T2).

RESULTS

Glycemia was found to be different in T2 compared to T1 in the TEC, TNC, UEC and UNC groups. Lactate was higher in T2 than in T1, but remained within the lactate threshold. Glycogen showed higher concentrations in the trained groups and, whether trained or not, in the supplemented groups. IGF-1 levels were higher in exercised rats independent of supplementation or glycogen levels. Trained rats showed lower IGF-1 when exercising than did the untrained animals.

CONCLUSIONS

We conclude that intermittent exercise is beneficial in preventing a trained lactate pool, and that, in association with glucose supplementation, intermittent exercise will be efficient both in preventing a trained lactate pool and in maintaining sufficient glycemia levels. Exercise raises IGF-1 levels, whereas training inverts this relationship.

Effects of beta-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial

Background

Intermittent bouts of high-intensity exercise result in diminished stores of energy substrates, followed by an accumulation of metabolites, promoting chronic physiological adaptations. In addition, β-alanine has been accepted has an effective physiological hydrogen ion (H⁺) buffer. Concurrent high-intensity interval training (HIIT) and β-alanine supplementation may result in greater adaptations than HIIT alone. The purpose of the current study was to evaluate the effects of combining β-alanine supplementation with high-intensity interval training (HIIT) on endurance performance and aerobic metabolism in recreationally active college-aged men.

Methods

Forty-six men (Age: 22.2 ± 2.7 yrs; Ht: 178.1 ± 7.4 cm; Wt: 78.7 ± 11.9; VO₂peak: 3.3 ± 0.59 l·min^-1) were assessed for peak O₂ utilization (VO₂peak), time to fatigue (VO_2TTE), ventilatory threshold (VT), and total work done at 110% of pre-training VO₂peak (TWD). In a double-blind fashion, all subjects were randomly assigned into one either a placebo (PL – 16.5 g dextrose powder per packet; n = 18) or β-alanine (BA – 1.5 g β-alanine plus 15 g dextrose powder per packet; n = 18) group. All subjects supplemented four times per day (total of 6 g/day) for the first 21-days, followed by two times per day (3 g/day) for the subsequent 21 days, and engaged in a total of six weeks of HIIT training consisting of 5–6 bouts of a 2:1 minute cycling work to rest ratio.

Results

Significant improvements in VO₂peak, VO_2TTE, and TWD after three weeks of training were displayed (p < 0.05). Increases in VO₂peak, VO_2TTE, TWD and lean body mass were only significant for the BA group after the second three weeks of training.

Conclusion

The use of HIIT to induce significant aerobic improvements is effective and efficient. Chronic BA supplementation may further enhance HIIT, improving endurance performance and lean body mass.

Na+/H+ exchange inhibitor cariporide attenuates skeletal muscle infarction when administered before ischemia or reperfusion

Administration of Na(+)/H(+) exchange isoform-1 (NHE-1) inhibitors before ischemia has been shown to attenuate myocardial infarction in several animal models of ischemia-reperfusion injury. However, controversy still exists as to the efficacy of NHE-1 inhibitors in protection of myocardial infarction when administered at the onset of reperfusion. Furthermore, the efficacy of NHE-1 inhibition in protection of skeletal muscle from infarction (necrosis) has not been studied. This information has potential clinical applications in prevention or salvage of skeletal muscle from ischemia-reperfusion injury in elective and trauma reconstructive surgery. The objective of this research project is to test our hypothesis that the NHE-1 inhibitor cariporide is effective in protection of skeletal muscle from infarction when administered at the onset of sustained ischemia or reperfusion and to study the mechanism of action of cariporide. In our studies, we observed that intravenous administration of cariporide 10 min before ischemia (1 or 3 mg/kg) or reperfusion (3 mg/kg) significantly reduced infarction in pig latissimus dorsi muscle flaps compared with the control, when these muscle flaps were subjected to 4 h of ischemia and 48 h of reperfusion (P < 0.05; n = 5 pigs/group). Both preischemic and postischemic cariporide treatment (3 mg/kg) induced a significant decrease in muscle myeloperoxidase activity and mitochondrial-free Ca(2+) content and a significant increase in muscle ATP content within 2 h of reperfusion (P < 0.05; n = 4 pigs/group). Preischemic and postischemic cariporide treatment (3 mg/kg) also significantly inhibited muscle NHE-1 protein expression within 2 h of reperfusion after 4 h of ischemia, compared with the control (P < 0.05; n = 3 pigs/group). These observations support our hypothesis that cariporide attenuates skeletal muscle infarction when administered at the onset of ischemia or reperfusion, and the mechanism involves attenuation of neutrophil accumulation and mitochondrial-free Ca(2+) overload and preservation of ATP synthesis in the early stage of reperfusion.

Effects of high-intensity training on muscle lactate transporters and postexercise recovery of muscle lactate and hydrogen ions in women

The purpose of this study was to investigate the effects of high-intensity interval training (3 days/wk for 5 wk), provoking large changes in muscle lactate and pH, on changes in intracellular buffer capacity (betam(in vitro)), monocarboxylate transporters (MCTs), and the decrease in muscle lactate and hydrogen ions (H+) after exercise in women. Before and after training, biopsies of the vastus lateralis were obtained at rest and immediately after and 60 s after 45 s of exercise at 190% of maximal O2 uptake. Muscle samples were analyzed for ATP, phosphocreatine (PCr), lactate, and H+; MCT1 and MCT4 relative abundance and betam(in vitro) were also determined in resting muscle only. Training provoked a large decrease in postexercise muscle pH (pH 6.81). After training, there was a significant decrease in betam(in vitro) (-11%) and no significant change in relative abundance of MCT1 (96 +/- 12%) or MCT4 (120 +/- 21%). During the 60-s recovery after exercise, training was associated with no change in the decrease in muscle lactate, a significantly smaller decrease in muscle H+, and increased PCr resynthesis. These results suggest that increases in betam(in vitro) and MCT relative abundance are not linked to the degree of muscle lactate and H+ accumulation during training. Furthermore, training that is very intense may actually lead to decreases in betam(in vitro). The smaller postexercise decrease in muscle H+ after training is a further novel finding and suggests that training that results in a decrease in H+ accumulation and an increase in PCr resynthesis can actually reduce the decrease in muscle H+ during the recovery from supramaximal exercise.

Impressive anaerobic adaptations in elite karate athletes due to few intensive intermittent sessions added to regular karate training

The aim of this study was to investigate the effects of adding a high-intensity intermittent session twice a week during a 7-week karate training (KT) on markers of aerobic and anaerobic metabolisms in elite class karate athletes. Two groups were studied: a KT group (n=8, age 20.1+/-0.9 years, 70.0+/-8.8 kg) that followed traditional KT, and a group that followed combined traditional karate and a high-intensity intermittent training (HIT group, n=9, age 24.4+/-3.1 years, 67.0+/-7.8 kg). The subjects undertook a supramaximal exercise and a maximal oxygen uptake test before and after the training. Blood lactate, pH and plasma ammonia were determined at rest, immediately at the end of the supramaximal exercise and during the recovery period at 2, 4, 6, 8, 10 and 15 min. After the training period, no changes occurred in the KT group. However, in the HIT group, the time to exhaustion, MAOD and in the maximal oxygen uptake test were significantly improved by 23.6%, 10.3% and 4.6%, respectively. A clear-cut discrepancy was observed in the time course of lactate and pH in the supramaximal test after the training in the HIT group. We observed a significantly higher peak for lactate and a lower extreme value for pH with a shorter delay of appearance. At the end of the test, the lactate concentration increased significantly (+53.7%) and pH declined significantly, when compared with the values obtained after the same test before the training period. Ammonia was not influenced. The addition of high-intensity intermittent sessions twice per week during the period of KT induced beneficial physiological adaptations in athletes, allowing improvement in the duration of intense physical exercise before a state of fatigue is reached.

Regulation of pH in human skeletal muscle: adaptations to physical activity

Regulation of pH in skeletal muscle is the sum of mechanisms involved in maintaining intracellular pH within the normal range. Aspects of pH regulation in human skeletal muscle have been studied with various techniques from analysis of membrane proteins, microdialysis, and the nuclear magnetic resonance technique to exercise experiments including blood sampling and muscle biopsies. The present review characterizes the cellular buffering system as well as the most important membrane transport systems involved (Na(+)/H(+) exchange, Na-bicarbonate co-transport and lactate/H(+) co-transport) and describes the contribution of each transport system in pH regulation at rest and during muscle activity. It is reported that the mechanisms involved in pH regulation can undergo adaptational changes in association with physical activity and that these changes are of functional importance.

Effects of neuromuscular electrical stimulation of the knee extensor muscles on muscle soreness and different serum parameters in young male athletes: preliminary data

AIM

To evaluate the effects of neuromuscular electrical stimulation (NMES) on muscle soreness and on a variety of serum parameters during and after NMES of knee extensor muscles of young, well trained subjects over a study period of 96 h.

METHODS

Five male cyclists were included in this clinical observation. NMES (biphasic, asymmetric impulses) was applied through surface electrodes to both knee extensor muscles of each subject for 30 min. To determine changes in serum concentration of muscle proteins, blood samples were drawn at defined measure points before and after NMES. Muscle soreness was evaluated using a visual analogue scale at all measure points.

RESULTS

There was a maximum (p<0.05) for "muscle pain" during stimulation but no significant changes could be detected after the stimulation period. Serum creatine kinase showed a peak with a significant increase (p<0.05) 24 h after NMES. Serum lactate levels only increased slightly (p = 0.08) during NMES.

CONCLUSIONS

Although the changes of blood parameters measured in the present work correspond to those reported in the literature on eccentric strength training, no delayed onset muscle pain could be detected. Further studies should be carried out, also investigating different stimulation protocols in non-trained healthy subjects and in patients with less muscle mass.

Reduced volume but increased training intensity elevates muscle Na+-K+ pump α1-subunit and NHE1 expression as well as short-term work capacity in humans

The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners after a change from endurance to sprint training. Fifteen runners were assigned to either a sprint training (ST, n = 8) or a control (CON, n = 7) group. ST replaced their normal training by 30-s sprint runs three to four times a week, whereas CON continued the endurance training (∼45 km/wk). After the 4-wk sprint period, the expression of the muscle Na+-K+ pump α1-subunit and Na+/H+-exchanger isoform 1 was 29 and 30% higher ( P < 0.05), respectively. Furthermore, plasma K+ concentration was reduced ( P < 0.05) during repeated intense running. In ST, performance in a 30-s sprint test, Yo-Yo intermittent recovery test, and two supramaximal exhaustive runs was improved ( P < 0.05) by 7, 19, 27, and 19%, respectively, after the sprint training period, whereas pulmonary maximum oxygen uptake and 10-k time were unchanged. No changes in CON were observed. The present data suggest a role of the Na+-K+ pump in the control of K+ homeostasis and in the development of fatigue during repeated high-intensity exercise. Furthermore, performance during intense exercise can be improved and endurance performance maintained even with a reduction in training volume if the intensity of training is very high.

Extracellular pH defense against lactic acid in untrained and trained altitude residents

The assumption that buffering at altitude is deteriorated by bicarbonate (bi) reduction was investigated. Extracellular pH defense against lactic acidosis was estimated from changes (Delta) in lactic acid ([La]), [HCO3-], pH and PCO2 in plasma, which equilibrates with interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 10 untrained (UT) and 11 endurance-trained (TR) highlanders (2,600 m). During exercise the capacity of non-bicarbonate buffers (betanbi=-Delta[La]. DeltapH(-1)-Delta[HCO3-]. DeltapH(-1)) amounted to 40+/-2 (SEM) and 28+/-2 mmol l(-1) in UT and TR, respectively (P<0.01). During recovery beta (nbi) decreased to 20 (UT) and 16 (TR) mmol l(-1) (P<0.001) corresponding to values expected from hemoglobin, dissolved protein and phosphate concentrations related to extracellular fluid (ecf). This was accompanied by a larger decrease of base excess after than during exercise for a given Delta[La]. betabi amounted to 37-41 mmol l(-1) being lower than at sea level. The large exercise betanbi was mainly caused by increasing concentrations of buffers due to temporary shrinking of ecf. Tr has lower betanbi in spite of an increased Hb mass mainly because of an expanded ecf compared to UT. In highlanders betanbi is higher than in lowlanders because of larger Hb mass and reduced ecf and counteracts the decrease in [HCO3-]. The amount of bicarbonate is probably reduced by reduction of the ecf at altitude but this is compensated by lower maximal [La] and more effective hyperventilation resulting in attenuated exercise acidosis at exhaustion.

Effects of high-intensity training on MCT1, MCT4, and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis

This study investigated the effects of high-intensity training, with or without induced metabolic alkalosis, on lactate transporter (MCT1 and MCT4) and sodium bicarbonate cotransporter (NBC) content in rat skeletal muscles. Male Wistar rats performed high-intensity training on a treadmill 5 times/wk for 5 wk, receiving either sodium bicarbonate (ALK-T) or a placebo (PLA-T) prior to each training session, and were compared with a group of control rats (CON). MCT1, MCT4, and NBC content was measured by Western blotting in soleus and extensor digitorum longus (EDL) skeletal muscles. Citrate synthase (CS) and phosphofructokinase (PFK) activities and muscle buffer capacity (betam) were also evaluated. Following training, CS and PFK activities were significantly higher in the soleus only (P < 0.05), whereas betam was significantly higher in both soleus and EDL (P < 0.05). MCT1 (PLA-T: 30%; ALK-T: 23%) and NBC contents (PLA-T: 85%; ALK-T: 60%) increased significantly only in the soleus following training (P < 0.01). MCT4 content in the soleus was significantly greater in ALK-T (115%) but not PLA-T compared with CON. There was no significant change in protein content in the EDL. Finally, NBC content was related only to MCT1 content in soleus (r = 0.50, P < 0.01). In conclusion, these results suggest that MCT1, MCT4, and NBC undergo fiber-specific adaptive changes in response to high-intensity training and that induced alkalosis has a positive effect on training-induced changes in MCT4 content. The correlation between MCT1 and NBC expression suggests that lactate transport may be facilitated by NBC in oxidative skeletal muscle, which may in turn favor better muscle pH regulation.

Série de treinamento intervalado de alta intensidade como índice de determinação da tolerância à acidose na predição da performance anaeróbia de natação

O objetivo do presente estudo foi determinar a tolerância à acidose através de uma série de nados intervalados de alta intensidade e relacionar com a velocidade de limiar anaeróbio (VLan), concentração de lactato sanguíneo de pico ([Lac]pico), capacidade de trabalho anaeróbio (CTA), freqüência de braçada (fB), comprimento de braçada (CB) e índice de braçada (IB) na predição da performance de 100m de natação. Dez nadadores realizaram seis nados máximos de 100m no estilo crawl com intervalo de seis minutos. Amostras de sangue foram coletadas cinco minutos após cada nado para posterior análise de lactacidemia ([Lac]). Através da razão entre [Lac] e os respectivos tempos de execução dos seis nados, determinou-se a tolerância à acidose (TA). O número de braçadas realizadas durante os seis esforços foi anotado para determinação da fB, CB, IB. Um nado máximo de 100m foi utilizado como parâmetro de performance (P100) e amostras de sangue foram coletadas para determinação da concentração de lactato sanguíneo de pico ([Lac]pico). Três esforços progressivos de 400m foram realizados para determinação da VLan correspondente à concentração fixa de 3,5mM de lactato. Esforços máximos de 200 e 400m foram realizados para determinação da CTA por regressão linear (coeficiente linear). Os resultados apresentaram significativas correlações (p < 0,05) da TA com VLan (r = 0,77), [Lac]pico (r = 0,81), CB (r = 0,85) e IB (r = 0,84). Além disso, a P100 foi correlacionada com VLan (r = 0,88), TA (r = 0,95), [Lac]pico (r = 0,77), CB (r = 0,97) e IB (r = 0,96). Conclui-se que a TA determinada a partir de série de treinamento intervalado de alta intensidade parece ser útil para determinar a aptidão anaeróbia e predizer a performance de 100m de natação, além de ser influenciada pelo CB e IB.

Additive protective effects of the addition of lactic acid and adrenaline on excitability and force in isolated rat skeletal muscle depressed by elevated extracellular K+

During strenuous exercise, extracellular K(+) ([K(+)](o)) is increased, which potentially can reduce muscle excitability and force production. In addition, exercise leads to accumulation of lactate and H(+) and increased levels of circulating catecholamines. Individually, reduced pH and increased catecholamines have been shown to counteract the depressing effect of elevated K(+). This study examines (i) whether the effects of addition of lactic acid and adrenaline on the excitability of isolated muscles are caused by separate mechanisms and are additive and (ii) whether the effect of adding lactic acid or increasing CO(2) is related to a reduction of intra- or extracellular pH. Rat soleus muscles were incubated at a [K(+)](o) of 15 mM, which reduced tetanic force by 85%. Subsequent addition of 20 mM lactic acid or 10(-5) M adrenaline led to a small recovery of force, but when added together induced an almost complete force recovery. Compound action potentials showed that the force recovery was associated with recovery of muscle excitability. The improved excitability after addition of adrenaline was associated with increased Na(+)-K(+) pump activity resulting in hyperpolarization and an increase in the chemical Na(+) gradient. In contrast, addition of lactic acid had no effect on the membrane potential or the Na(+)-K(+) pump activity, but most likely increased excitability via a reduction in intracellular pH. It is concluded that the protective effects of acidosis and adrenaline on muscle excitability and force took place via different mechanisms and were additive. The results suggest that circulating catecholamines and development of acidosis during exercise may improve the tolerance of muscles to elevated [K(+)](o).

Extracellular bicarbonate and non-bicarbonate buffering against lactic acid during and after exercise

Defense of extracellular pH constancy against lactic acidosis can be estimated from changes (Delta) in lactic acid ([La]), [HCO(3)(-)], pH and PCO(2) in blood plasma because it is equilibrated with the interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 13 untrained (UT) and 21 endurance-trained (TR) males to find out if acute and chronic exercise influence the defense. During exercise the capacity of non-bicarbonate buffers (beta(nbi) = -Delta[La] . DeltapH(-1) - Delta[HCO(3)(-)] . DeltapH(-1)) available for the extracellular fluid (mainly hemoglobin, dissolved proteins and phosphates) amounted to 32 +/- 2(SEM) and 20 +/- 2 mmol l(-1) in UT and TR, respectively (P < 0.02). During recovery beta(nbi) decreased to 14 (UT) and 12(TR) mmol l(-1) (both P < 0.001) corresponding to values previously found at rest by in vivo CO(2) titration. Bicarbonate buffering (beta(bi)) amounted to 44-48 mmol l(-1) during and after exercise. The large exercise beta(nbi) seems to be mainly caused by an increasing concentration of all buffers due to shrinking of the extracellular volume, exchange of small amounts of HCO(3)(-) or H(+) with cells and delayed HCO(3)(-) equilibration between plasma and interstitial fluid. Increase of [HCO(3)(-)] during titration by these mechanisms augments total beta and thus the calculated beta(nbi) more than beta(bi) because it reduces DeltapH and Delta[HCO(3)(-)] at constant Delta[La]. The smaller rise in exercise beta(nbi) in TR than UT may be caused by an increased extracellular volume and an improved exchange of La(-), HCO(3)(-) and H(+) between trained muscles and blood.

Determination of the anaerobic threshold and maximal lactate steady state speed in equines using the lactate minimum speed protocol

Maximal blood lactate steady state concentration (MLSS) and anaerobic threshold (AT) have been shown to accurately predict long distance events performance and training loads, as well, in human athletes. Horse endurance races can take up to 160 km and, in practice, coaches use the 4 mM blood lactate concentration, a human based fixed concentration to establish AT, to predict training loads to horse athletes, what can lead to misleading training loads. The lactate minimum speed (LMS) protocol that consists in an initial elevation in blood lactate level by a high intensity bout of exercise and then establishes an individual equilibrium between lactate production and catabolism during progressive submaximal efforts, has been proposed as a nonfixed lactate concentration, to measure individual AT and at the same time predicts MLSS for human long distance runners and basketball players as well. The purpose of this study was to determine the reliability of the LMS protocol in endurance horse athletes. Five male horses that were engaged on endurance training, for at least 1 year of regular training and competition, were used in this study. Animals were submitted to a 500 m full gallop to determine each blood lactate time to peak (LP) after these determinations, animals were submitted to a progressive 1000 m exercise, starting at 15 km h(-1) to determine LMS, and after LMS determination animals were also submitted to two 10,000 m running, first at LMS and then 10% above LMS to test MLSS accuracy. Mean LP was 8.2+/-0.7 mM at approximately 5.8+/-6.09 min, mean LMS was 20.75+/-2.06 km h(-1) and mean heart rate at LMS was 124.8+/-4.7 BPM. Blood lactate remained at rest baseline levels during 10,000 m trial at LMS, but reached a six fold significantly raise during 10% above LMS trial after 4000 and 6000 m (p<0.05) and (p<0.01) after 8000 and 10,000 m. In conclusion, our adapted LMS protocol for horse athletes proposed here seems to be a reliable method to state endurance horse athletes LT and MLSS.

Divergent response of metabolite transport proteins in human skeletal muscle after sprint interval training and detraining

Skeletal muscle primarily relies on carbohydrate (CHO) for energy provision during high-intensity exercise. We hypothesized that sprint interval training (SIT), or repeated sessions of high-intensity exercise, would induce rapid changes in transport proteins associated with CHO metabolism, whereas changes in skeletal muscle fatty acid transporters would occur more slowly. Eight active men (22 +/- 1 yr; peak oxygen uptake = 50 +/- 2 ml.kg(-1).min(-1)) performed 4-6 x 30 s all-out cycling efforts with 4-min recovery, 3 days/wk for 6 wk. Needle muscle biopsy samples (vastus lateralis) were obtained before training (Pre), after 1 and 6 wk of SIT, and after 1 and 6 wk of detraining. Muscle oxidative capacity, as reflected by the protein content of cytochrome c oxidase subunit 4 (COX4), increased by approximately 35% after 1 wk of SIT and remained higher compared with Pre, even after 6 wk of detraining (P < 0.05). Muscle GLUT4 content increased after 1 wk of SIT and remained approximately 20% higher compared with baseline during detraining (P < 0.05). The monocarboxylate tranporter (MCT) 4 was higher after 1 and 6 wk of SIT compared with Pre, whereas MCT1 increased after 6 wk of training and remained higher after 1 wk of detraining (P < 0.05). There was no effect of training or detraining on the muscle content of fatty acid translocase (FAT/CD36) or plasma membrane associated fatty acid binding protein (FABPpm) (P > 0.05). We conclude that short-term SIT induces rapid increases in skeletal muscle oxidative capacity but has divergent effects on proteins associated with glucose, lactate, and fatty acid transport.

Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development

This study examined the effect of two different intense exercise training regimens on skeletal muscle ion transport systems, performance, and metabolic response to exercise. Thirteen subjects performed either sprint training [ST; 6-s sprints (n = 6)], or speed endurance training [SET; 30-s runs approximately 130% Vo(2 max), n = 7]. Training in the SET group provoked higher (P < 0.05) plasma K(+) levels and muscle lactate/H(+) accumulation. Only in the SET group was the amount of the Na(+)/H(+) exchanger isoform 1 (31%) and Na(+)-K(+)-ATPase isoform alpha(2) (68%) elevated (P < 0.05) after training. Both groups had higher (P < 0.05) levels of Na(+)-K(+)-ATPase beta(1)-isoform and monocarboxylate transporter 1 (MCT1), but no change in MCT4 and Na(+)-K(+)-ATPase alpha(1)-isoform. Both groups had greater (P < 0.05) accumulation of lactate during exhaustive exercise and higher (P < 0.05) rates of muscle lactate decrease after exercise. The ST group improved (P < 0.05) sprint performance, whereas the SET group elevated (P < 0.05) performance during exhaustive continuous treadmill running. Improvement in the Yo-Yo intermittent recovery test was larger (P < 0.05) in the SET than ST group (29% vs. 10%). Only the SET group had a decrease (P < 0.05) in fatigue index during a repeated sprint test. In conclusion, turnover of lactate/H(+) and K(+) in muscle during exercise does affect the adaptations of some but not all related muscle ion transport proteins with training. Adaptations with training do have an effect on the metabolic response to exercise and specific improvement in work capacity.

Causes of differences in exercise-induced changes of base excess and blood lactate

It has been concluded from comparisons of base excess (BE) and lactic acid (La) concentration changes in blood during exercise-induced acidosis that more H+ than La- leave the muscle and enter interstitial fluid and blood. To examine this, we performed incremental cycle tests in 13 untrained males and measured acid-base status and [La] in arterialized blood, plasma, and red cells until 21 min after exhaustion. The decrease of actual BE (-deltaABE) was 2.2 +/- 0.5 (SEM) mmol l(-1) larger than the increase of [La]blood at exhaustion, and the difference rose to 4.8 +/- 0.5 mmol l(-1) during the first minutes of recovery. The decrease of standard BE (SBE), a measure of mean BE of interstitial fluid (if) and blood, however, was smaller than the increase of [La] in the corresponding volume (delta[La](if+blood)) during exercise and only slightly larger during recovery. The discrepancy between -deltaABE and delta[La]blood mainly results from the Donnan effect hindering the rise of [La]erythrocyte to equal values like [La]plasma. The changing Donnan effect during acidosis causes that Cl- from the interstitial fluid enter plasma and erythrocytes in exchange for HCO3(-). A corresponding amount of La- remains outside the blood. SBE is not influenced by ion shifts among these compartments and therefore is a rather exact measure of acid movements across tissue cell membranes, but changes have been compared previously to delta[La]blood instead to delta[La](if+blood). When performing correct comparisons and considering Cl-/HCO3(-) exchange between erythrocytes and extracellular fluid, neither the use of deltaABE nor of deltaSBE provides evidence for differences in H+ and La- transport across the tissue cell membranes.

Effect of short-term sprint interval training on human skeletal muscle carbohydrate metabolism during exercise and time-trial performance

Our laboratory recently showed that six sessions of sprint interval training (SIT) over 2 wk increased muscle oxidative potential and cycle endurance capacity (Burgomaster KA, Hughes SC, Heigenhauser GJF, Bradwell SN, and Gibala MJ. J Appl Physiol 98: 1895–1900, 2005). The present study tested the hypothesis that short-term SIT would reduce skeletal muscle glycogenolysis and lactate accumulation during exercise and increase the capacity for pyruvate oxidation via pyruvate dehydrogenase (PDH). Eight men [peak oxygen uptake (V̇o2 peak) = 3.8 ± 0.2 l/min] performed six sessions of SIT (4–7 × 30-s “all-out” cycling with 4 min of recovery) over 2 wk. Before and after SIT, biopsies (vastus lateralis) were obtained at rest and after each stage of a two-stage cycling test that consisted of 10 min at ∼60% followed by 10 min at ∼90% of V̇o2 peak. Subjects also performed a 250-kJ time trial (TT) before and after SIT to assess changes in cycling performance. SIT increased muscle glycogen content by ∼50% (main effect, P = 0.04) and the maximal activity of citrate synthase (posttraining: 7.8 ± 0.4 vs. pretraining: 7.0 ± 0.4 mol·kg protein −1·h−1; P = 0.04), but the maximal activity of 3-hydroxyacyl-CoA dehydrogenase was unchanged (posttraining: 5.1 ± 0.7 vs. pretraining: 4.9 ± 0.6 mol·kg protein −1·h−1; P = 0.76). The active form of PDH was higher after training (main effect, P = 0.04), and net muscle glycogenolysis (posttraining: 100 ± 16 vs. pretraining: 139 ± 11 mmol/kg dry wt; P = 0.03) and lactate accumulation (posttraining: 55 ± 2 vs. pretraining: 63 ± 1 mmol/kg dry wt; P = 0.03) during exercise were reduced. TT performance improved by 9.6% after training (posttraining: 15.5 ± 0.5 vs. pretraining: 17.2 ± 1.0 min; P = 0.006), and a control group ( n = 8, V̇o2 peak = 3.9 ± 0.2 l/min) showed no change in performance when tested 2 wk apart without SIT (posttraining: 18.8 ± 1.2 vs. pretraining: 18.9 ± 1.2 min; P = 0.74). We conclude that short-term SIT improved cycling TT performance and resulted in a closer matching of glycogenolytic flux and pyruvate oxidation during submaximal exercise.