Hyperammonaemia in relation to high-intensity exercise duration in man

Analysis and study on biomarkers of local muscle fatigue caused by repetitive lifting task

BACKGROUND

Work-related musculoskeletal disorders (WMSDs) show a rapid growth trend. It has brought a huge economic burden to the society and become a serious occupational health problem that needs to be solved urgently. This study aimed to analyze the local muscle response under continuous ergonomic load, screen sensitive fatigue-related biomarkers and provide data support for the early prevention of local muscle damage and the exploration of early warning indicators.

METHODS

Thirteen male college student volunteers were recruited to perform simulated repetitive manual lifting tasks in the laboratory. The lifting task was designed for 4 periods which lasted for 12 min in each, and then paused for 3 min for sampling. Local muscle fatigue is assesed by the Rating of perceived exertion (RPE) and the Joint analysis of sEMG spectrum and amplitude (JASA). Elbow venous blood was collected and 14 kinds of biomarkers were analyzed, which included Metabolic markers Ammonia (AMM), Lactic acid (LAC), Creatine kinase (CK), Lactate dehydrogenase (LDH), Cartilage oligomeric matrix protein (COMP), C-telopeptide of collagen I and II (CTX-I, CTX-II) and Calcium ion (Ca2+); Oxidative stress marker Glutathione (GSH); Inflammatory markers C-reaction protein (CRP), Prostaglandin E2 (PG-E2), Interleukin-6 (IL-6) and Tumor necrosis factor α (TNF-α); Pain marker Neuropeptide Y (NPY). Repeated measures analysis of variance (Repeated ANOVA), linear regression analysis, t-test and spearman correlation analysis were used to analyze the data.

RESULTS

Both subjective and objective fatigue appeared at the same period. Serum AMM, LAC, CK, LDH, COMP, CTX-II, Ca2+ and NPY after fatigue were significantly higher than those before fatigue (p < 0.05). There was a certain degree of correlation between the markers with statistical differences before and after fatigue.

CONCLUSIONS

Metabolic markers (serum AMM, LAC, CK, LDH, COMP, CTX-II, Ca2+) and pain markers (serum NPY) can reflect local muscle fatigue to a certain extent in repetitive manual lifting tasks. It is necessary to further expand the research on fatigue-related biomarkers in different types of subjects and jobs in the future.

Effect of rest duration between sets on fatigue and recovery after short intense plyometric exercise

Plyometric training is characterized by high-intensity exercise which is performed in short term efforts divided into sets. The purpose of the present study was twofold: first, to investigate the effects of three distinct plyometric exercise protocols, each with varying work-to-rest ratios, on muscle fatigue and recovery using an incline-plane training machine; and second, to assess the relationship between changes in lower limb muscle strength and power and the biochemical response to the three exercise variants employed. Forty-five adult males were randomly divided into 3 groups (n = 15) performing an exercise of 60 rebounds on an incline-plane training machine. The G0 group performed continuous exercise, while the G45 and G90 groups completed 4 sets of 15 repetitions, each set lasting 45 s with 45 s rest in G45 (work-to-rest ratio of 1:1) and 90 s rest in G90 (1:2 ratio). Changes in muscle torques of knee extensors and flexors, as well as blood lactate (LA) and ammonia levels, were assessed before and every 5 min for 30 min after completing the workout. The results showed significantly higher (p < 0.001) average power across all jumps generated during intermittent compared to continuous exercise. The greatest decrease in knee extensor strength immediately post-exercise was recorded in group G0 and the least in G90. The post-exercise time course of LA changes followed a similar pattern in all groups, while the longer the interval between sets, the faster LA returned to baseline. Intermittent exercise had a more favourable effect on muscle energy metabolism and recovery than continuous exercise, and the work-to-rest ratio of 1:2 in plyometric exercises was sufficient rest time to allow the continuation of exercise in subsequent sets at similar intensity.

How training loads in the preparation and competitive period affect the biochemical indicators of training stress in youth soccer players?

Background

Physical fitness optimization and injury risk-reducing require extensive monitoring of training loads and athletes' fatigue status. This study aimed to investigate the effect of a 6-month training program on the training-related stress indicators (creatine kinase - CK; cortisol - COR; serotonin - SER; brain-derived neurotrophic factor - BDNF) in youth soccer players.

Methods

Eighteen players (17.8 ± 0.9 years old, body height 181.6 ± 6.9 cm, training experience 9.7 ± 1.7 years) were blood-tested four times: at the start of the preparation period (T0), immediately following the preparation period (T1), mid-competitive period (T2), and at the end of the competitive period (T3). CK activity as well as concentrations of serum COR, SER and BDNF were determined. Training loads were recorded using a session rating of perceived exertion (sRPE).

Results

Statistical analyzes revealed significant effects for all biochemical parameters in relation to their time measurements (T0, T1, T2, T3). The statistical analyzes of sRPE and differences of biochemical parameters in their subsequent measurements (T0-T1, T1-T2, T2-T3) also demonstrated significant effects observed for all variables: sRPE (H^KW = 13.189 (df = 2); p = 0.00), COR (H^KW = 9.261 (df = 2); p = 0.01), CK (H^KW = 12.492 (df = 2); p = 0.00), SER (H^KW = 7.781 (df = 2); p = 0.02) and BDNF (H^KW = 15.160 (df = 2); p < 0.001).

Discussion

In conclusion, it should be stated that the most demanding training loads applied in the preparation period (highest sRPE values) resulted in a significant increase in all analyzed biochemical training stress indicators. The reduction in the training loads during a competitive period and the addition of recovery training sessions resulted in a systematic decrease in the values of the measured biochemical indicators. The results of the study showed that both subjective and objective markers, including training loads, are useful in monitoring training stress in youth soccer players.

Mechanism of the Effect of High-Intensity Training on Urinary Metabolism in Female Water Polo Players Based on UHPLC-MS Non-Targeted Metabolomics Technique

OBJECTIVE

To study the changes in urine metabolism in female water polo players before and after high-intensity training by using ultra-high performance liquid chromatography-mass spectrometry, and to explore the biometabolic characteristics of urine after training and competition.

METHODS

Twelve young female water polo players (except goalkeepers) from Shanxi Province were selected. A 4-week formal training was started after 1 week of acclimatization according to experimental requirements. Urine samples (5 mL) were collected before formal training, early morning after 4 weeks of training, and immediately after 4 weeks of training matches, and labeled as T1, T2, and T3, respectively. The samples were tested by LC-MS after pre-treatment. XCMS, SIMCA-P 14.1, and SPSS16.0 were used to process the data and identify differential metabolites.

RESULTS

On comparing the immediate post-competition period with the pre-training period (T3 vs. T1), 24 differential metabolites involved in 16 metabolic pathways were identified, among which niacin and niacinamide metabolism and purine metabolism were potential post-competition urinary metabolic pathways in the untrained state of the athletes. On comparing the immediate post-competition period with the post-training period (T3 vs. T2), 10 metabolites involved in three metabolic pathways were identified, among which niacin and niacinamide metabolism was a potential target urinary metabolic pathway for the athletes after training. Niacinamide, 1-methylnicotinamide, 2-pyridone, L-Gln, AMP, and Hx were involved in two metabolic pathways before and after the training.

CONCLUSION

Differential changes in urine after water polo games are due to changes in the metabolic pathways of niacin and niacinamide.

The Efficacy of Pilates on Urinary Incontinence in Korean Women: A Metabolomics Approach

Pilates has been known as exercise intervention that improves the function of pelvic floor muscle (PFM) associated with impacting urinary incontinence (UI). This study investigated the effect of Pilates on UI in Korean women by determining the change in functional movement of PFM (FMP) and metabolic profiles. UI group with Pilates (UIP, n = 13) participated in 8-weeks Oov Pilates program, and 8 subjects were assigned to Control and UI group with no Pilates (UINP), respectively. Before and after 8 weeks, plasma samples were collected from all participants, and ultrasonography was used to measure the functional change of PFM for calculating FMP ratio. Plasma samples were analyzed by mass spectrometry to identify the change of metabolic features. After 8-weeks intervention, FMP ratio was remarkably decreased in UIP (48.1% ↓, p < 0.001), but not in Control and UINP (p > 0.05). In metabolic features, L-Glutamine (m/z: 147.07 [M + H]⁺), L-Cystathionine (m/z: 240.09 [M + NH₄]⁺), L-Arginine (m/z: 197.1 [M + Na]⁺), and L-1-Pyrroline-3-hydroxy-5-carboxylate (m/z: 147.07 [M + NH₄]⁺) were significantly elevated solely in UIP (p < 0.001). Our study elucidated that Pilates can ameliorate the FMP and enhance the specific metabolic characteristics, which was potentially associated with invigorated PFM contractility to effectively control the bladder base and continence.

Glutamine as an Anti-Fatigue Amino Acid in Sports Nutrition

Glutamine is a conditionally essential amino acid widely used in sports nutrition, especially because of its immunomodulatory role. Notwithstanding, glutamine plays several other biological functions, such as cell proliferation, energy production, glycogenesis, ammonia buffering, maintenance of the acid-base balance, among others. Thus, this amino acid began to be investigated in sports nutrition beyond its effect on the immune system, attributing to glutamine various properties, such as an anti-fatigue role. Considering that the ergogenic potential of this amino acid is still not completely known, this review aimed to address the main properties by which glutamine could delay fatigue, as well as the effects of glutamine supplementation, alone or associated with other nutrients, on fatigue markers and performance in the context of physical exercise. PubMed database was selected to examine the literature, using the keywords combination “glutamine” and “fatigue”. Fifty-five studies met the inclusion criteria and were evaluated in this integrative literature review. Most of the studies evaluated observed that glutamine supplementation improved some fatigue markers, such as increased glycogen synthesis and reduced ammonia accumulation, but this intervention did not increase physical performance. Thus, despite improving some fatigue parameters, glutamine supplementation seems to have limited effects on performance.

Changes in acid-base and ion balance during exercise in normoxia and normobaric hypoxia

Purpose

Both exercise and hypoxia cause complex changes in acid–base homeostasis. The aim of the present study was to investigate whether during intense physical exercise in normoxia and hypoxia, the modified physicochemical approach offers a better understanding of the changes in acid–base homeostasis than the traditional Henderson–Hasselbalch approach.

Methods

In this prospective, randomized, crossover trial, 19 healthy males completed an exercise test until voluntary fatigue on a bicycle ergometer on two different study days, once during normoxia and once during normobaric hypoxia (12% oxygen, equivalent to an altitude of 4500 m). Arterial blood gases were sampled during and after the exercise test and analysed according to the modified physicochemical and Henderson–Hasselbalch approach, respectively.

Results

Peak power output decreased from 287 ± 9 Watts in normoxia to 213 ± 6 Watts in hypoxia (−26%, P < 0.001). Exercise decreased arterial pH to 7.21 ± 0.01 and 7.27 ± 0.02 (P < 0.001) during normoxia and hypoxia, respectively, and increased plasma lactate to 16.8 ± 0.8 and 17.5 ± 0.9 mmol/l (P < 0.001). While the Henderson–Hasselbalch approach identified lactate as main factor responsible for the non-respiratory acidosis, the modified physicochemical approach additionally identified strong ions (i.e. plasma electrolytes, organic acid ions) and non-volatile weak acids (i.e. albumin, phosphate ion species) as important contributors.

Conclusions

The Henderson–Hasselbalch approach might serve as basis for screening acid–base disturbances, but the modified physicochemical approach offers more detailed insights into the complex changes in acid–base status during exercise in normoxia and hypoxia, respectively.

Electronic supplementary material

The online version of this article (doi:10.1007/s00421-017-3712-z) contains supplementary material, which is available to authorized users.

Blood ammonia and lactate as markers of muscle metabolites during leg press exercise

To examine whether blood lactate and ammonia concentrations can be used to estimate the functional state of the muscle contractile machinery with regard to muscle lactate and adenosine triphosphate (ATP) levels during leg press exercise. Thirteen men (age, 34 ± 5 years; 1 repetition maximum leg press strength 199 ± 33 kg) performed either 5 sets of 10 repetitions to failure (5×10RF), or 10 sets of 5 repetitions not to failure (10×5RNF) with the same initial load (10RM) and interset rests (2 minutes) on 2 separate sessions in random order. Capillary blood samples were obtained before and during exercise and recovery. Six subjects underwent vastus lateralis muscle biopsies at rest, before the first set and after the final exercise set. The 5×10RF resulted in a significant and marked decrease in power output (37%), muscle ATP content (24%), and high levels of muscle lactate (25.0 ± 8.1 mmol·kg wet weight), blood lactate (10.3 ± 2.6 mmol·L), and blood ammonia (91.6 ± 40.5 μmol·L). During 10×5RNF no or minimal changes were observed. Significant correlations were found between: (a) blood ammonia and muscle ATP (r = -0.75), (b) changes in peak power output and blood ammonia (r = -0.87) and blood lactate (r = -0.84), and (c) blood and muscle lactate (r = 0.90). Blood lactate and ammonia concentrations can be used as extracellular markers for muscle lactate and ATP contents, respectively. The decline in mechanical power output can be used to indirectly estimate blood ammonia and lactate during leg press exercise.

Velocity loss as an indicator of neuromuscular fatigue during resistance training

PURPOSE

This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REP) differing in the number of repetitions (R) performed in each set (S) with respect to the maximum predicted number (P).

METHODS

Over 21 exercise sessions separated by 48-72 h, 18 strength-trained males (10 in bench press (BP) and 8 in squat (SQ)) performed 1) a progressive test for one-repetition maximum (1RM) and load-velocity profile determination, 2) tests of maximal number of repetitions to failure (12RM, 10RM, 8RM, 6RM, and 4RM), and 3) 15 REP (S × R[P]: 3 × 6[12], 3 × 8[12], 3 × 10[12], 3 × 12[12], 3 × 6[10], 3 × 8[10], 3 × 10[10], 3 × 4[8], 3 × 6[8], 3 × 8[8], 3 × 3[6], 3 × 4[6], 3 × 6[6], 3 × 2[4], 3 × 4[4]), with 5-min interset rests. Kinematic data were registered by a linear velocity transducer. Blood lactate and ammonia were measured before and after exercise.

RESULTS

Mean repetition velocity loss after three sets, loss of velocity pre-post exercise against the 1-m·s load, and countermovement jump height loss (SQ group) were significant for all REP and were highly correlated to each other (r = 0.91-0.97). Velocity loss was significantly greater for BP compared with SQ and strongly correlated to peak postexercise lactate (r = 0.93-0.97) for both SQ and BP. Unlike lactate, ammonia showed a curvilinear response to loss of velocity, only increasing above resting levels when R was at least two repetitions higher than 50% of P.

CONCLUSIONS

Velocity loss and metabolic stress clearly differs when manipulating the number of repetitions actually performed in each training set. The high correlations found between mechanical (velocity and countermovement jump height losses) and metabolic (lactate, ammonia) measures of fatigue support the validity of using velocity loss to objectively quantify neuromuscular fatigue during resistance training.

Amino acid profile during exercise and training in Standardbreds

The objective of this study is to assess the influence of acute exercise, training and intensified training on the plasma amino acid profile. In a 32-week longitudinal study using 10 Standardbred horses, training was divided into four phases, including a phase of intensified training for five horses. At the end of each phase, a standardized exercise test, SET, was performed. Plasma amino acid concentrations before and after each SET were measured. Training significantly reduced mean plasma aspartic acid concentration, whereas exercise significantly increased the plasma concentrations of alanine, taurine, methionine, leucine, tyrosine and phenylalanine and reduced the plasma concentrations of glycine, ornithine, glutamine, citrulline and serine. Normally and intensified trained horses differed not significantly. It is concluded that amino acids should not be regarded as limiting training performance in Standardbreds except for aspartic acid which is the most likely candidate for supplementation.

Vertical jump performance and blood ammonia and lactate levels during typical training sessions in elite 400-m runners

This study described the effects of 6 typical high-intensity intermittent running training sessions of varying distances (60-300 m) and intensities (80-105% of the individual best 400-m record time) on blood ammonia and lactate concentration changes and on vertical jumping height, in twelve 400-m elite male runners. At the end of the training sessions, similar patterns of extremely high blood lactate (14-23 mmol.L) and ammonia levels (50-100 mumol.L) were observed. Vertical jumping performance was maintained during the initial exercise bouts up to a break zone of further increase in the number of exercise bouts, which was associated, especially in subjects with the highest initial vertical jump, with a pronounced decrease (6-28%) in vertical jumping performance, as well as with blood lactate concentrations exceeding 8-12 mmol.L, and blood ammonia levels increasing abruptly from rest values. This break zone may be related to signs of energetic deficiency of the muscle contractile machinery associated with the ability to regenerate adenosine triphosphate at high rates. It is suggested that replacing some of these extremely demanding training sessions with other intermittent training sessions that preserve muscle generating capacity should allow elite athletes to practice more frequently at competitive intensity with lower fatigue.

Dosing and efficacy of glutamine supplementation in human exercise and sport training

Some athletes can have high intakes of l-glutamine because of their high energy and protein intakes and also because they consume protein supplements, protein hydrolysates, and free amino acids. Prolonged exercise and periods of heavy training are associated with a decrease in the plasma glutamine concentration and this has been suggested to be a potential cause of the exercise-induced immune impairment and increased susceptibility to infection in athletes. However, several recent glutamine feeding intervention studies indicate that although the plasma glutamine concentration can be kept constant during and after prolonged strenuous exercise, the glutamine supplementation does not prevent the postexercise changes in several aspects of immune function. Although glutamine is essential for lymphocyte proliferation, the plasma glutamine concentration does not fall sufficiently low after exercise to compromise the rate of proliferation. Acute intakes of glutamine of approximately 20-30 g seem to be without ill effect in healthy adult humans and no harm was reported in 1 study in which athletes consumed 28 g glutamine every day for 14 d. Doses of up to 0.65 g/kg body mass of glutamine (in solution or as a suspension) have been reported to be tolerated by patients and did not result in abnormal plasma ammonia levels. However, the suggested reasons for taking glutamine supplements (support for immune system, increased glycogen synthesis, anticatabolic effect) have received little support from well-controlled scientific studies in healthy, well-nourished humans.

Plasma Glutamine Changes After High-Intensity Exercise in Elite Male Swimmers

The aim of this study was to establish the pattern and time course of plasma glutamine recovery after acute, high-intensity exercise in well-trained swimmers. In Study 1, elite male swimmers (n=8) performed 15 x 100 m swimming intervals (ITS) at 70% and 95% of maximal 100m freestyle time. Resting plasma glutaminle levels were determined on a nonexercise control day (0% ITS). Venous blood samples were obtained prior to, immediately afte;, and 30, 60, 120, and 150 mini postexercise. In Study 2, the 95% ITS was repeated in elite male swuimmers (n=8), while control subjects (n=8) did not exercise, to test for any diurnal variation in plasma glutamine levels. Venous blood samples were obtained prior to and 2, 4, 6, and 8 h postexercise. In Study 1, no change was observed in plasma glutamine following the 0% (control) and 70% ITS, but following the 95% ITS glutamine decreased significantly (p < 0.01) over the recovery period. In Study 2, plasma glutamine again decreased over the recovery period in the swimmers, but no changes were observed in the controls. It was concluded that intensive swim traininlg results in postexercise decreases in plasma glutamine levels. Because glutamine has been suggested as a marker of overtraining, a need to measure glutaminle at standard times within training programs is indicated.

Plasma glutamine responses to high-intensity exercise before and after endurance training

Glutamine responses to strenuous interval exercise were examined before and after 6 weeks of endurance training. Glutamine measures were obtained before and after the interval exercise sessions and training in untrained males assigned to training (T; n = 10) or control (C; n = 10) groups. Before training, C and T group glutamine progressively decreased (p < 0.05) by 18% and 16%, respectively, by 150-min postinterval exercise. Over the training period C group glutamine did not change, while T group values increased (p < 0.05) by 14%. After training, glutamine again decreased (p < 0.05) by similar percentages (C = 16% and T = 15%) by 150-min postinterval exercise, but the T group recorded higher (p < 0.05) resting and postexercise glutamine concentrations than the C group. Training induced increases in glutamine may prevent the decline in glutamine levels following strenuous exercise falling below a threshold where immune function might be acutely compromised.

Exercise-induced immunodepression- plasma glutamine is not the link

The amino acid glutamine is known to be important for the function of some immune cells in vitro. It has been proposed that the decrease in plasma glutamine concentration in relation to catabolic conditions, including prolonged, exhaustive exercise, results in a lack of glutamine for these cells and may be responsible for the transient immunodepression commonly observed after acute, exhaustive exercise. It has been unclear, however, whether the magnitude of the observed decrease in plasma glutamine concentration would be great enough to compromise the function of immune cells. In fact, intracellular glutamine concentration may not be compromised when plasma levels are decreased postexercise. In addition, a number of recent intervention studies with glutamine feeding demonstrate that, although the plasma concentration of glutamine is kept constant during and after acute, strenuous exercise, glutamine supplementation does not abolish the postexercise decrease in in vitro cellular immunity, including low lymphocyte number, impaired lymphocyte proliferation, impaired natural killer and lymphokine-activated killer cell activity, as well as low production rate and concentration of salivary IgA. It is concluded that, although the glutamine hypothesis may explain immunodepression related to other stressful conditions such as trauma and burn, plasma glutamine concentration is not likely to play a mechanistic role in exercise-induced immunodepression.

Glutamine, exercise and immune function. Links and possible mechanisms

Glutamine is the most abundant free amino acid in human muscle and plasma and is utilised at high rates by rapidly dividing cells, including leucocytes, to provide energy and optimal conditions for nucleotide biosynthesis. As such, it is considered to be essential for proper immune function. During various catabolic states including surgical trauma, infection, starvation and prolonged exercise, glutamine homeostasis is placed under stress. Falls in the plasma glutamine level (normal range 500 to 750 mumol/L after an overnight fast) have been reported following endurance events and prolonged exercise. These levels remain unchanged or temporarily elevated after short term, high intensity exercise. Plasma glutamine has also been reported to fall in patients with untreated diabetes mellitus, in diet-induced metabolic acidosis and in the recovery period following high intensity intermittent exercise. Common factors among all these stress states are rises in the plasma concentrations of cortisol and glucagon and an increased tissue requirement for glutamine for gluconeogenesis. It is suggested that increased gluconeogenesis and associated increases in hepatic, gut and renal glutamine uptake account for the depletion of plasma glutamine in catabolic stress states, including prolonged exercise. The short term effects of exercise on the plasma glutamine level may be cumulative, since heavy training has been shown to result in low plasma glutamine levels (< 500 mumol/L) requiring long periods of recovery. Furthermore, athletes experiencing discomfort from the overtraining syndrome exhibit lower resting levels of plasma glutamine than active healthy controls. Therefore, physical activity directly affects the availability of glutamine to the leucocytes and thus may influence immune function. The utility of plasma glutamine level as a marker of overtraining has recently been highlighted, but a consensus has not yet been reached concerning the best method of determining the level. Since injury, infection, nutritional status and acute exercise can all influence plasma glutamine level, these factors must be controlled and/or taken into consideration if plasma glutamine is to prove a useful marker of impending overtraining.

The influence of exercise-induced plasma volume changes on the interpretation of biochemical parameters used for monitoring exercise, training and sport

A number of studies have demonstrated considerable plasma volume changes during and after exposure to different environmental and physiological conditions. These changes are thought to result from transient fluid shifts into (haemodilution) and out of (haemoconcentration) the intravascular space. If the levels of plasma constituents are to be routinely measured for research purposes or used as indicators of training adaptation or the health of an athlete, then it is important to consider the dynamic nature of plasma volume. Controversy still exists over the relevance of plasma volume interactions with plasma constituent levels, and while some investigators have taken plasma volume shifts into account, others have chosen to ignore these changes. Bouts of acute exercise have been shown to produce a transient haemoconcentration immediately after long distance running, bicycle ergometry and both maximal and submaximal swimming exercise. While these changes are transient, lasting only a few hours, other studies have reported a longer term haemodilution following acute exercise. In addition, endurance training has been shown to cause long term expansion of the plasma volume. It would, therefore, seem important to consider the influence of plasma volume changes on plasma solutes routinely measured for research, and as markers of training adaptation, prior to arriving at conclusions and recommendations based purely on their measured plasma level. To further confound this issue, plasma volume changes are known to be associated with heat acclimatisation, hydration state, physical training and postural changes, all of which may differ from one experiment or exercise bout to the next, and should thus be taken into account.

ATP loss with exercise in muscle fibres of the gluteus medius of the thoroughbred horse

Muscle ATP loss with exercise has implications both to the causes of fatigue and muscle damage. To study this at the single muscle fibre level, five trained thoroughbred horses performed consecutive 90 second gallops on an inclined treadmill followed by a final gallop to fatigue. Biopsies of the m. gluteus medius were taken at rest, post-exercise and during 24 hour recovery. Blood lactate was 20.0 mmol litre-1 or more, and plasma NH3 300-800 mumol litre-1, following the final gallop. Minimal changes occurred in the plasma markers, CK and AST. ATP loss with exercise was 32.2 (SD 12.2) per cent. Following exercise single fibre ATP contents showed a much broader distribution than at rest, with contents in some close to zero. Following five and 24 hour recovery, however, frequency distribution curves were close to those seen at rest. There was no difference in the ATP contents of types I, IIa and IIb at rest of with exercise or recovery. The results pointed to marked heterogeneity between individual fibres in their biochemical response with exercise, independent of fibre type.

Relationship between lactate and ammonia thresholds in heart transplant patients

The purpose of this investigation was to study the relationship between both blood ammonia thresholds (AmT) and lactate thresholds (LT) during dynamic exercise in cardiac transplant patients (CTPs). Eleven male patients who had undergone orthotopic cardiac transplantation (age: 54 +/- 11 years, mean +/- SD; height: 165.1 +/- 6.6 cm; body mass: 78.3 +/- 16.1 kg) participated in this study. Each of them performed a bicycle ergometer test (ramp protocol) until volitional fatigue. During each test, gas exchange parameters and ECG responses were determined continuously. In addition, blood lactate and ammonia concentrations were measured every 2 min for determination of both LT and AmT, respectively. Peak values of oxygen uptake (Vo2), respiratory exchange ratio, ventilation, and heart rate averaged 15.9 +/- 3.03 mL.Kg-1.min-1, 1.02 +/- 0.06, 46.69 +/- 5.69 L.min-1, and 124 +/- 16 beats per minute, respectively. However, blood concentrations of lactate and ammonia at peak exercise were 3.7 +/- 0.4 mmol.L-1 and 85.6 +/- 31.7 micrograms.dL-1, respectively. LT and AmT were detected in 8 (72.7% of total) and 9 (81.8% of total) of 11 subjects, respectively. No significant differences were found between mean values of LT and AmT, when both were expressed either as Vo2 (10.01 +/- 1.19 vs 10.5 +/- 2.38 mL.kg-1.min-1, respectively) or as percent Vo2 peak (64.62 +/- 11.362 vs 66.48 +/- 9.19%, respectively). In addition, LT and AmT were significantly correlated (p < 0.05) when both were expressed either as Vo2 (mL.kg-1.min-1) or as percent Vo2 peak (r = 0.70 and r = 0.68, respectively). Our findings suggest that in CTPs, both LT and AmT occur at similar workloads, probably as a result of skeletal muscle alterations associated with chronic deconditioning and immunosuppressive therapy.

Accumulation of uric acid in plasma after repeated bouts of exercise in the horse

Plasma concentration of uric acid, total peroxyl radical-trapping antioxidative parameter (TRAP), blood lactate concentration and plasma activity of xanthine oxidase (XO) were measured in six Standardbreed trotters after six bouts of exercise with increasing intensity on two separate days three days apart. Blood samples were taken immediately, 5, 10, 15, 30 and 60 min after each heat and 2, 4, and 6 hr after the last heat. Exercise caused an increase in TRAP and in the concentrations of lactate and uric acid. Plasma uric acid concentration increased exponentially with respect to time after the last heat performed maximal speed, indicating a rapid increase in the rate of purine degradation. Plasma XO activity increased during exercise, but the intensity of exercise had only a minor effect on the level of XO activity. In conclusion, these data suggest that a threshold for the plasma accumulation of uric acid in terms of the intensity of exercise may exist and that XO may play a role in the formation of uric acid in horse plasma. Intense exercise causes an increase in the plasma antioxidant capacity that in the horse is mainly caused by the increase in the plasma uric acid concentration.