Effect of dietary modifications on anaerobic threshold

Multifaceted relationship between diabetes and kidney diseases: Beyond diabetes

Diabetes mellitus is one of the most common causes of chronic kidney disease. Kidney involvement in patients with diabetes has a wide spectrum of clinical presentations ranging from asymptomatic to overt proteinuria and kidney failure. The development of kidney disease in diabetes is associated with structural changes in multiple kidney compartments, such as the vascular system and glomeruli. Glomerular alterations include thickening of the glomerular basement membrane, loss of podocytes, and segmental mesangiolysis, which may lead to microaneurysms and the development of pathognomonic Kimmelstiel-Wilson nodules. Beyond lesions directly related to diabetes, awareness of the possible coexistence of nondiabetic kidney disease in patients with diabetes is increasing. These nondiabetic lesions include focal segmental glomerulosclerosis, IgA nephropathy, and other primary or secondary renal disorders. Differential diagnosis of these conditions is crucial in guiding clinical management and therapeutic approaches. However, the relationship between diabetes and the kidney is bidirectional; thus, new-onset diabetes may also occur as a complication of the treatment in patients with renal diseases. Here, we review the complex and multifaceted correlation between diabetes and kidney diseases and discuss clinical presentation and course, differential diagnosis, and therapeutic oppor-tunities offered by novel drugs.

Predicting Competition Performance in Short Trail Running Races with Lactate Thresholds

Trail running is a popular sport, yet factors related to performance are still not fully understood. Lactate thresholds have been thoroughly investigated in road running and correlate strongly with race performance, but to date few data are available about the value in trail running performance prediction. We examined 25 trail runners (age 31.2 ± 5.1 years, BMI 22.2 ± 1.82 kg/m²) with an initial graded exercise test for measurement of VO_2max (59.5 ± 5.2 ml.kg^‐1.min^{‐ 1}) and lactate thresholds (LT): LTAET (LT aerobic) 1.03 ± 0.59 mmol/l; 11.2 ± 1.1 km/h), IAT (individual lactate threshold) (2.53 ± 0.59 mmol/l; 15.4 ± 1.6 km/h) and LT4 (lactate threshold at 4 mmol/l) (16.2 ± 1.9 km/h). All runners subsequently participated in a 31.1 km XS trail race and 9 runners in a 21 km XXS trail race. Race performance times correlated negatively with the XS trail run (LTAET: r = ‐0.65, p < 0.01; LT4: r = ‐0.87, p < 0.01; IAT: r = ‐0.84, p < 0.01) and regression analysis showed that race performance could be predicted by: LT4: ‐324.15×LT4+13195.23 (R² = .753, F_1,23 = 70.02, p < 0.01). A subgroup analysis showed higher correlations with race performance for slower than faster runners. No correlations were found with the XXS race. Lactate thresholds can be of value in predicting trail race performance and help in designing training plans.

Effect of active and passive recovery on blood lactate and performance during simulated competition in high level gymnasts

The purpose of this study was to investigate the effect of two recovery strategies between men's gymnastics events on blood lactate removal (BL) and performance as rated by expert "blind" judges. Twelve male gymnasts (21.8 +/- 2.4 years) participated. The sessions were composed of routine performances in the six Olympic events, which were separated by 10 min of recovery. All gymnasts performed two recovery protocols between events on separate days: Rest protocol, 10 min rest in a sitting position; Combined protocol, 5 min rest and 5 min self-selected active recovery. Three blood samples were taken at 2, 5, and 10 min following each event. Gymnasts produced moderate values of BL following each of the six events (2.2 to 11.6 mmol.L-1). There was moderate variability in BL values between events that could not be accounted for by the athlete's event performance. Gymnasts showed higher BL concentration (p > .05) and significantly (p < .05) higher scoring performances (as rated by a panel of certified judges) when they used a combined recovery between gymnastics events rather than a passive recovery (delta BL = 40.51% vs. 28.76% of maximal BL, p < .05, and total score = 47.28 +/- 6.82 vs. 38.39 +/- 7.55, p < .05, respectively).

The influence of the site of sampling and assay medium upon the measurement and interpretation of blood lactate responses to exercise

This paper reports the findings of two investigations into methodological problems associated with the interpretation of blood lactate (BLa) in the sports sciences. In Experiment 1, brachial artery (A), antecubital venous (V) and fingertip capillary (C) blood samples were drawn simultaneously from nine subjects (mean age 21.1 +/- 1.3 years) during an incremental treadmill protocol and immediately assayed for BLa concentration. Experiment 2 investigated the extent of lactate concentration differences in whole blood (WB), lysed blood (LB) and plasma (P) measured using a YSI 23 AM analyser. In Experiment 1, a comparison of the mean BLa concentrations obtained from the three sites revealed no significant differences (P greater than 0.05). Correlations between BLa samples from different sites were very high, with r values ranging from 0.858 to 0.983. In Experiment 2, the mean lactate concentrations were: WB, 4.7 +/- 2.7 mM; LB, 5.0 +/- 3.0 mM; P, 7.0 +/- 3.8 mM. Plasma (P) values were significantly higher than WB and LB. Values from all sites were highly correlated with coefficients ranging from 0.963 to 0.987.

IN CONCLUSION

(1) Significant arterial and venous BLa concentration differences do not exist during incremental treadmill exercise. (2) As capillary BLa concentrations reflect arterial values, their use in laboratory and field settings is recommended. (3) Lactate concentration differences in whole blood, lysed blood and plasma will influence the assessment of performance at fixed lactate reference values. (4) If the inter-laboratory test procedures are to be standardized and results compared, precise reporting of lactate sampling and assay techniques is critical.

The effect of ammonium chloride and sodium bicarbonate ingestion on the physical working capacity at the fatigue threshold

The purpose of this investigation was to examine the effect of ammonium chloride (NH4Cl) and sodium bicarbonate (NaHCO3) ingestion on the physical working capacity at the fatigue threshold (PWCFT). Eighteen adult males (mean age, SD = 23, 2 years) volunteered for two experiments (experiment 1, n = 9; experiment 2, n = 9). In both experiments, the subjects orally ingested 0.3 g.kg-1 body weight of NH4Cl and NaHCO3 over a 3-h period in random order on days separated by 72 h or more. In experiment 1, following ingestion of the substance, the subjects performed a discontinuous incremental cycle ergometer test to the onset of PWCFT which was estimated from integrated electromyography voltages at the vastus lateralis muscle. In experiment 2, the subjects performed a continuous PWCFT test. The results of these experiments indicated that NH4Cl and NaHCO3 ingestion had no significant (P greater than 0.05) effect on PWCFT (experiment 1: NH4Cl = 257, SD 26 W; NaHCO3 = 256, SD 22 W; t = 0.06; r = 0.866; experiment 2: NH4Cl = 231, 14 W; NaHCO3 = 216, 16 W; t = 1.78; r = 0.857).

The effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold

The purpose of this investigation was to determine the effect of glycogen depletion and supercompensation on the physical working capacity at the fatigue threshold (PWCFT). Ten adult males (mean age 23 years, SD 3) volunteered as subjects for this study. During the first laboratory visit the subjects performed a maximal bicycle ergometer test for the determination of maximum oxygen consumption (VO2max). Between 48 and 72 h later, the subjects pedaled to exhaustion at a power output which corresponded to a mean of 76% of VO2max (range, 72-80%) for the purpose of glycogen depletion. For the next 3 days, the subjects were fed a 10.5 MJ.day-1 low carbohydrate diet which consisted of 7.5% carbohydrates, 22.0% protein and 70.5% fat. The subjects then performed an incremental cycle ergometer test to the onset of fatigue or PWCFT, which was estimated from integrated electromyographic voltages of the vastus lateralis muscle. For the next 3 days the subjects were fed a 10.5 MJ high carbohydrate diet which consisted of 72.2% carbohydrates, 12.4% protein and 15.4% fats for the purpose of glycogen supercompensation. The subjects then performed a second PWCFT test. A paired t-test indicated that there was no significant (p greater than 0.05) difference between the means of the PWCFT values (depletion 246 W, SD 30; supercompensation 265 W, SD 28) and they were highly correlated at r = 0.884. The results of this investigation suggested that the methods commonly used to affect glycogen depletion or supercompensation had no effect on PWCFT.

Post-exercise ketosis and the glycogen content of liver and muscle in rats on a high carbohydrate diet

Post-exercise ketosis is known to be suppressed by physical training and by a high carbohydrate diet. As a result it has often been presumed, but not proven, that the development of post-exercise ketosis is closely related to the glycogen content of the liver. We therefore studied the effect of 1 h of treadmill running on the blood 3-hydroxybutyrate and liver and muscle glycogen concentrations of carbohydrate-loaded trained (n = 72) and untrained rats (n = 72). Resting liver and muscle glycogen levels were 25%-30% higher in the trained than in the untrained animals. The resting 3-hydroxybutyrate concentrations of both groups of rats were very low: less than 0.08 mmol.l-1. Exercise did not significantly influence the blood 3-hydroxybutyrate concentrations of trained rats, but caused a marked post-exercise ketosis (1.40 +/- 0.40 mmol.l-1 h after exercise) in the untrained animals, the time-course of which was the approximate inverse of the changes in liver glycogen concentration. Interpreting the results in the light of similar data obtained after a normal and low carbohydrate diet it has been concluded that trained animals probably owe their relative resistance to post-exercise ketosis to their higher liver glycogen concentrations as well as to greater peripheral stores of mobilizable carbohydrate.

Dietary regimen and performance of high intensity ergometer exercise

The influence of preceding diet (mixed, MD; carbohydrate CD; protein PD) on performance during high intensity endurance cycling was examined in six middle distance runners. Subjects undertook cycle ergometer exercise at a workload equivalent to 80% VO2 max until exhaustion following each of the three dietary regimens. Dietary analyses were performed using a computerised evaluation technique and cardiorespiratory, blood glucose and lactate responses to exercise were measured along with exercise time to exhaustion. Significant differences in carbohydrate and protein intakes were noted between respective diets as well as significantly higher total energy intake in MD (P less than 0.05). A significant relationship was observed between carbohydrate intake and exercise time to exhaustion (r = 0.59, P less than 0.05). No significant differences were noted in cardiorespiratory measures or blood glucose response after exhaustive exercise between the three dietary regimens but peak blood lactate concentration was lower following PD (P less than 0.05). Total time to exhaustion was significantly higher on CD (1070.0 +/- 106.7 s) than on PD (642.5 +/- 84.3 s, P less than 0.01). Performance time on MD (895.7 +/- 84.3 s) did not differ significantly for performance time on either CD or PD. It was concluded that dietary manipulation significantly improves exercise time to exhaustion during short term, high intensity cycling.

Lactate threshold and onset of blood lactate accumulation during incremental exercise after dietary modifications

This study was designed to clarify the effects of dietary modifications on the lactate threshold (LT) and on the onset of blood lactate accumulation (OBLA) during progressive incremental exercise. Six healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions: a 48-h period of mixed dieting (53% carbohydrates, 30% lipids, 17% proteins) preceding the first exercise test, immediately followed by a 48-h period of either a carbohydrate-rich (68% CHO, 23% lipids, 9% proteins) or a fat-rich (19% CHO, 57% lipids, 26% proteins) iso-caloric diet leading to the second exercise and separated from the third test by a 12-days period. Exercise tests were conducted on an electrically-braked ergocycle, and consisted of a progressive incremental maximal exercise. Respiratory parameters were continuously monitored by an automated open circuit sampling system. Exercise blood lactate (LA), free fatty acids (FFA), glucose levels and acid-base balance were determined from venous blood samples obtained through an indwelling brachial catheter. Peak lactate values, workload and performance time were not significantly altered by imposed diets. Furthermore, dietary modifications had no significant effect on LT, OBLA fixed at 4 mmol and ventilatory threshold. Increased pH and FFA mobilization were observed with fat-rich diet, while CHO-rich diet markedly increased the respiratory exchange ratio (R). It is concluded that LT and OBLA are not significantly altered by fat or CHO enrichment of diets.

Blood lactate parameters related to aerobic capacity and endurance performance

The relationships among four descriptors of lactate increase: lactate threshold (LT) (the VO2 at which blood lactate concentration begins to increase above the resting level during an incremental exercise test), LT1 (the VO2 at which blood lactate increases 1 mM above the resting level), LT2 (the VO2 at which blood lactate concentration reaches a fixed value of 2 mM), onset of blood lactate accumulation (OBLA; the VO2 at which blood lactate reaches a concentration of 4 mM), were compared with aerobic capacity (VO2max) and 12 min running performance in 19 untrained female students. The VO2 (+/- SD) of LT, LT1, LT2, OBLA, and VO2max were 14.5 +/- 3.7 ml X kg-1 X min-1, 22.5 +/- 4.3 ml X kg-1 X min-1, 22.2 +/- 4.5 ml X kg-1 X min-1, 30.3 +/- 5.2 ml X kg-1 X min-1 and 36.0 +/- 5.1 ml X kg-1 X min-1, respectively. The mean (+/- SD) distance covered in the 12 min running was 2356 +/- 160 m. The results were as follows: 1) the lactate parameters (i.e. LT, LT1, LT2, and OBLA) were highly correlated with each other. 2) all the lactate parameters were related to VO2max and endurance running performance with a high correlation coefficient. Of the four descriptors of lactate change with exercise, LT correlated best with VO2max and endurance running performance compared to LT1, LT2 and OBLA. It is concluded that lactate threshold is the best index for aerobic capacity and endurance running performance.