Influence of Fiber Type Composition and Capillary Density on Onset of Blood Lactate Accumulation

Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Skeletal muscle, haematological and splenic volume characteristics of elite breath-hold divers

Purpose

The aim of the study was to provide an evaluation of the oxygen transport, exchange and storage capacity of elite breath-hold divers (EBHD) compared with non-divers (ND).

Methods

Twenty-one healthy males’ (11 EBHD; 10 ND) resting splenic volumes were assessed by ultrasound and venous blood drawn for full blood count analysis. Percutaneous skeletal muscle biopsies were obtained from the m. vastus lateralis to measure capillarisation, and fibre type-specific localisation and distribution of myoglobin and mitochondrial content using quantitative immunofluorescence microscopy.

Results

Splenic volume was not different between groups. Reticulocytes, red blood cells and haemoglobin concentrations were higher (+ 24%, p < 0.05; + 9%, p < 0.05; + 3%, p < 0.05; respectively) and mean cell volume was lower (− 6.5%, p < 0.05) in the EBHD compared with ND. Haematocrit was not different between groups. Capillary density was greater (+ 19%; p < 0.05) in the EBHD. The diffusion distance (R₉₅) was lower in type I versus type II fibres for both groups (EBHD, p < 0.01; ND, p < 0.001), with a lower R₉₅ for type I fibres in the EBHD versus ND (− 13%, p < 0.05). Myoglobin content was higher in type I than type II fibres in EBHD (+ 27%; p < 0.01) and higher in the type I fibres of EBHD than ND (+ 27%; p < 0.05). No fibre type differences in myoglobin content were observed in ND. Mitochondrial content was higher in type I than type II fibres in EBHD (+ 35%; p < 0.05), with no fibre type differences in ND or between groups.

Conclusions

In conclusion, EBDH demonstrate enhanced oxygen storage in both blood and skeletal muscle and a more efficient oxygen exchange capacity between blood and skeletal muscle versus ND.

The Science of Cycling

The aim of this review is to provide greater insight and understanding regarding the scientific nature of cycling. Research findings are presented in a practical manner for their direct application to cycling. The two parts of this review provide information that is useful to athletes, coaches and exercise scientists in the prescription of training regimens, adoption of exercise protocols and creation of research designs. Here for the first time, we present rationale to dispute prevailing myths linked to erroneous concepts and terminology surrounding the sport of cycling. In some studies, a review of the cycling literature revealed incomplete characterisation of athletic performance, lack of appropriate controls and small subject numbers, thereby complicating the understanding of the cycling research. Moreover, a mixture of cycling testing equipment coupled with a multitude of exercise protocols stresses the reliability and validity of the findings. Our scrutiny of the literature revealed key cycling performance-determining variables and their training-induced metabolic responses. The review of training strategies provides guidelines that will assist in the design of aerobic and anaerobic training protocols. Paradoxically, while maximal oxygen uptake (V-O(2max)) is generally not considered a valid indicator of cycling performance when it is coupled with other markers of exercise performance (e.g. blood lactate, power output, metabolic thresholds and efficiency/economy), it is found to gain predictive credibility. The positive facets of lactate metabolism dispel the 'lactic acid myth'. Lactate is shown to lower hydrogen ion concentrations rather than raise them, thereby retarding acidosis. Every aspect of lactate production is shown to be advantageous to cycling performance. To minimise the effects of muscle fatigue, the efficacy of employing a combination of different high cycling cadences is evident. The subconscious fatigue avoidance mechanism 'teleoanticipation' system serves to set the tolerable upper limits of competitive effort in order to assure the athlete completion of the physical challenge. Physiological markers found to be predictive of cycling performance include: (i) power output at the lactate threshold (LT2); (ii) peak power output (W(peak)) indicating a power/weight ratio of > or =5.5 W/kg; (iii) the percentage of type I fibres in the vastus lateralis; (iv) maximal lactate steady-state, representing the highest exercise intensity at which blood lactate concentration remains stable; (v) W(peak) at LT2; and (vi) W(peak) during a maximal cycling test. Furthermore, the unique breathing pattern, characterised by a lack of tachypnoeic shift, found in professional cyclists may enhance the efficiency and metabolic cost of breathing. The training impulse is useful to characterise exercise intensity and load during training and competition. It serves to enable the cyclist or coach to evaluate the effects of training strategies and may well serve to predict the cyclist's performance. Findings indicate that peripheral adaptations in working muscles play a more important role for enhanced submaximal cycling capacity than central adaptations. Clearly, relatively brief but intense sprint training can enhance both glycolytic and oxidative enzyme activity, maximum short-term power output and V-O(2max). To that end, it is suggested to replace approximately 15% of normal training with one of the interval exercise protocols. Tapering, through reduction in duration of training sessions or the frequency of sessions per week while maintaining intensity, is extremely effective for improvement of cycling time-trial performance. Overuse and over-training disabilities common to the competitive cyclist, if untreated, can lead to delayed recovery.

Effect of training intensity on muscle lactate transporters and lactate threshold of cross-country skiers

The training intensity may affect the monocarboxylate transporters MCT1 and MCT4 in skeletal muscle. Therefore, 20 elite cross-country skiers (11 men and nine women) trained hard for 5 months at either moderate (MIG, 60-70% of VO2max) or high intensity (HIG, 80-90%). The lactate threshold, several performance parameters, and the blood lactate concentration (cLa) after exhausting treadmill running were also determined. Muscle biopsies taken from the vastus lateralis muscle before and after the training period were analysed for the two MCTs and for muscle fibre types and six enzymes. The concentration of MCT1 did not change for HIG (P=0.3) but fell for MIG (-12 +/- 3%, P=0.01); the training response differed between the two groups (P=0.05). The concentration of MCT4 did not change during the training period (P > 0.10). The concentration of the two MCTs did not differ between the two sexes (P=0.9). The running speed at the lactate threshold rose for HIG (+3.2 +/- 0.9%, P=0.003), while no change was seen for MIG (P=0.54); the training response differed between the two groups (P=0.04). The cLa after long-lasting exhausting treadmill running correlated with the concentration of MCT1 (rs=0.69, P=0.002), but not with that of MCT4 (rs=0.2, P=0.2). There were no other significant correlations between the concentrations of the two MCTs and the performance parameters, muscle fibre types, or enzymes (r < or = 0.36, P > 0.10). Thus, the training response differed between MIG and HIG both in terms of performance and of the effect on MCT1. Training at high intensity may be more effective for cross-country skiers. Finally, MCT1 may be important for releasing lactate to the blood during long-lasting exercise.

African runners exhibit greater fatigue resistance, lower lactate accumulation, and higher oxidative enzyme activity

Nine African and eight Caucasian 10-km runners resident at sea level volunteered. Maximal O2 consumption and peak treadmill velocity (PTV) were measured by using a progressive test, and fatigue resistance [time to fatigue (TTF)] was measured by using a newly developed high-intensity running test: 5 min at 72, 80, and 88% of individual PTV followed by 92% PTV to exhaustion. Skeletal muscle enzyme activities were determined in 12 runners and 12 sedentary control subjects. In a comparison of African and Caucasian runners, mean 10-km race time, maximal O2 consumption, and PTV were similar. In African runners, TTF was 21% longer (P < 0.01), plasma lactate accumulation after 5 min at 88% PTV was 38% lower (P < 0.05), and citrate synthase activity was 50% higher (27.9 +/- 7.5 vs. 18.6 +/- 2.1 micromol. g wet wt-1. min-1, P = 0.02). Africans accumulated lactate at a slower rate with increasing exercise intensity (P < 0.05). Among the entire group of runners, a higher citrate synthase activity was associated with a longer TTF (r = 0.70, P < 0.05), a lower plasma lactate accumulation (r = -0.73, P = 0.01), and a lower respiratory exchange ratio (r = -0.63, P < 0.05). We conclude that the African and Caucasian runners in the present study differed with respect to oxidative enzyme activity, rate of lactate accumulation, and their ability to sustain high-intensity endurance exercise.

The relationship between plasma lactate parameters, Wpeak and 1-h cycling performance in women

PURPOSE

The relationship between six descriptors of lactate increase, peak VO2, Wpeak, and 1-h cycling performance were compared in 24 trained, female cyclists (peak VO(2) = 48.11 +/- 6.32 mLxkg(-1)xmin(-1).

METHODS

The six descriptors of lactate increase were: 1) lactate threshold (LT; the power output at which plasma lactate concentration begins to increase above the resting level during an incremental exercise test), 2) LT(1) the power output at which plasma lactate increases by 1 mM or more), 3) LT(D) (the lactate threshold calculated by the D-max method), 4) LT(MOD) (the lactate threshold calculated by a modified D-max method), 5) L4 (the power output at which plasma lactate reaches a concentration of 4 mmolxL(-1), and 6) LT(LOG) (the power output at which plasma lactate concentration begins to increase when the log ([La(-1]) is plotted against the log (power output). Subjects first completed a peak VO(2) test on a cycle ergometer. Finger-tip capillary blood was sampled within 30 s of the end of each 3-min stage for analysis of plasma lactate. Endurance performance was assessed 7 d later using a 1-h cycle test (OHT) in which subjects were directed to achieve the highest possible average power output.

RESULTS

The mean power output (W) for the OHT (+/- SD) was 183.01 +/- 18.88, and for each lactate variable was:LT (138.54 +/- 46.61), LT(1) (179.17 +/- 27.25), LT(log) (143.97 +/- 45.74), L4 (198.09 +/- 33.84), LT(D) (178.79 +/- 24.07), LT(MOD)(212.28 +/- 31.75). Average power output during the OHT was more strongly correlated with all plasma lactate parameters (0.61<r<0.84) and W(peak) (r = 0.81) than with peak VO(2) (r = 0.55). The six lactate parameters were strongly correlated with each other (0.54<r<0.91) and of six lactate parameters, LT(D) correlated best with endurance performance (r = 0.84).

CONCLUSIONS

It was concluded that plasma lactate parameters and W(peak) provide better indices of endurance performance than peak VO(2) and that, of the six descriptors of lactate increase measured in this study, LT(D) is most strongly related to 1-h cycling performance in trained, female cyclists.

Reproducibility and validity of physiological parameters measured in cyclists riding on racing bikes placed on a stationary magnetic brake

The purpose of this study was: 1) To evaluate the reproducibility of physiological parameters measured during cycle exercise, and 2) To validate the predictive capacity of physiological parameters related to endurance performance. Therefore, physiological variables were measured twice during cycling exercise in a group of seven cyclists. Each cycle exercise session was separated by one week and included progressive submaximal cycling followed by a 5-km time trial. Two and three weeks later, endurance performance was evaluated by calculating average work output during a 50-km time trial (W50km). To simulate cycle performance, the cyclists' private racing bikes were placed on a stationary magnetic brake. No differences were observed between paired physiological observations in the test-retest (P>0.05). The coefficient of variation (CV) was calculated from the differences between test-retest parameters. CV for the maximal oxygen uptake (VO2max), average work output during the 5-km trial (W5km), the calculated work intensity which increased the blood lactate concentration to 2 and 4 mmol/l (W2mM and W4mM) and W50km were 1.9, 2.7, 6.1, 5.9 and 6.3%, respectively, while the 95% confidence interval (CI) showing the expected range for variation in a retest was calculated to be 80 ml.min(-1), 9, 16, 18 and 18 W, respectively. Simple linear regression showed significant correlations between VO2max, W5km, W2mM, W4mM and W50km (r-values: range 0.83-0.98, P<0.01).

IN CONCLUSION

1) Physiological parameters can be reproduced during an exercise test procedure in cyclists riding on racing bikes placed on a stationary magnetic brake, and 2) The validity of VO2max, W5km, W2mM, and W4mM as predictive parameters of endurance was demonstrated.

The association among fat distribution, physical fitness, and the risk factors of cardiovascular disease in obese women

The purpose of this study was to see whether fat distribution and physical fitness are independent risk factors of cardiovascular diseases in obese women. Seventy-four obese women aged 19 to 65 years participated in this study. The data were collected on plasma lipid profiles, plasma glucose and insulin during an oral glucose tolerance test, blood pressure, fat distribution determined by the waist to hip ratio (WHR), total body fat determined by the hydrostatic weighing method and a direct measurement of blood lactate threshold. Significant correlations were found between WHR and plasma cholesterol (TC), plasma LDL cholesterol (LDL-c) and LDL-c to the plasma HDL cholesterol ratio (LDL-c/HDL-c), independent of age, percent body fat, and VO2 per lean body mass at blood lactate threshold (LT). On the other hand, LT was significantly related to the area under the curve of insulin during OGTT (insulin area) and DBP, independent of age, percent body fat, and WHR. In conclusion, both fat distribution and physical fitness are considered to be independently related to some important risk factors in obese women after adjustment for percent body fat.

Effect of exercise duration on lactate kinetics after short muscular exercise

Arterial blood lactate concentrations were measured in six normal males before, during and after 3- and 6-min bicycle exercises performed at three different work rates. The lactate recovery curves were fitted to a bi-exponential time function consisting of a rapidly increasing and a slowly decreasing component, which supplied an accurate representation of the changes in lactate concentration. Variations in the parameters of this mathematical model have been studied as a function of the duration of exercise and of the work rate, showing a clear dependence on exercise duration such that increasing exercise length decreases the velocity constants of the fitted curves. In terms of the functional meaning which can be given to these constants, this result indicates that extending exercise duration from 3 to 6 min reduces the ability of the whole body to exchange and remove lactate. This effect did not qualitatively modify the one already described, which is due to increased work rates, but it shifted the ability to exchange and remove lactate towards lower values. The main conclusion of the study is that lactate kinetic data vary as a function of time during exercise. This inference must be accounted for in the interpretation of lactate data obtained during muscular exercise.

Relationship between the size of the capillary bed and oxidative capacity in various cat skeletal muscles

The size of the capillary bed, assessed by capillary density (CD), capillary per muscle fibre ratio (C/F), total capillary length, surface area and volume was related to the oxidative capacity, assessed by the volume density of mitochondria and VO2max in cat muscles with a different composition of glycolytic and oxidative fibres: predominantly glycolytic gracilis, purely oxidative soleus and gracilis transformed towards oxidative by chronic low frequency (10 Hz) electrical stimulation. Maximal blood flow and lactate output were measured in the muscles during isometric contractions. When capillary supply was estimated by C/F ratio, there was a close correlation between various parameters only in stimulated gracilis. The combined data of all muscles showed a significant correlation between the total volume of mitochondria, VO2max and total capillary surface area. Capillary volume showed a tight correlation with maximal blood flow in both control and stimulated gracilis, but not in soleus. Maximal blood flow was correlated with VO2max in oxidative muscles (stimulated gracilis and soleus) but not in control glycolytic gracilis. Moreover normal gracilis did not show any relationship between the volume density of mitochondria and the size of the capillary bed. The latter was inversely correlated with the output of lactate which was greater in muscles with a lower C/P ratio. The data on gracilis indicates that the capillary bed can adapt to the increased demand for oxygen and a greater oxidative capacity induced by long-term activity imposed on a glycolytic muscle, while it may be more important for the removal of lactate in the glycolytic muscles under their normal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Computerized detection of the lactate threshold in coronary artery disease

A computer program for identifying oxygen consumption at the lactate threshold was evaluated by expired gas analysis during treadmill exercise testing in 15 patients with prior myocardial infarction. There was a strong correlation (r = 0.85, p less than 0.001) between computer-identified oxygen consumption (14.1 +/- 4.6 ml/kg/min) and the oxygen consumption (14.6 +/- 4.8 ml/kg/min) corresponding to an increase of arterial lactate level to above the normal value at rest (1.3 mM). The computer program was superior to previously described visual methods for identifying the ventilatory threshold.

The influence of muscle metabolic characteristics on physical performance

This study describes the influence of muscle fiber type composition, enzyme activities and capillary supply on muscle strength, local muscle endurance or aerobic power and capacity. Muscle biopsies were obtained from m. vastus lateralis in thirteen physically active men. Histochemical staining procedures were applied to assess the percentage of fast twitch (FT) fibers, muscle fiber area, and capillary density. Also, the activity of citrate synthase (CS), creatine kinase (CK), hexokinase (HK), lactate dehydrogenase (LDH), and phosphofructokinase (PFK) were analysed using fluorometrical assays. Peak torque at 'low' and 'high' angular velocities was measured during leg extension. Similarly, muscle fatigue (e.g. peak torque decline) and recovery from a short-term exercise task were measured during maximal, voluntary consecutive leg extensions. Aerobic power (VO2max) and aerobic capacity (e.g. onset of blood lactate concentration; OBLA), as defined by a blood lactate concentration of 4 mol X 1(-1) were measured during cycling. Peak torque at a high angular velocity was positively correlated with % FT area (p less than 0.001). Fatigue and recovery were correlated with LDH X CS-1 (p less than 0.001). WOBLA was best correlated with PFK and PFK X CS-1 (p less than 0.001). Hence, muscle strength was partly determined by fiber type composition whereas local muscle endurance, recovery and aerobic capacity reflect mainly capillary supply and the activity of key enzymes involved in aerobic and anaerobic metabolism.

Blood lactate vs. exhaustive exercise to evaluate aerobic fitness

This study compared the predictive power of a lactate-related index determined during submaximal cycle exercise to that of an exhaustive cycle ergometer test for evaluating the endurance exercise capacity of soldiers. The subjects (n = 48 males) performed a continuous exercise test to voluntary exhaustion on the cycle ergometer. Power output (PO) increased by 50 W steps each fourth min, with determinations of heart rate (HR), RPE and blood lactate concentrations (HLa) just prior to each PO increase. The PO at a 4 mmol L(-1) HLa concentration (WOBLA) was interpolated; based on the time to exhaustion the maximal PO that could be maintained for 6 min (Wmax6) was calculated from previously documented formulae. Subjects were timed during a 3000 m cross-country run. Both the cycle test and the run were performed again 3 months later, as was an additional 3000 m run with full military equipment weighing about 21 kg. All 3000 m times were significantly correlated (p less than 0.05) with both Wmax6 and WOBLA; similar predictive power was demonstrated for both Wmax6 and WOBLA, suggesting that accuracy in evaluation would not be sacrificed by substituting the submaximal for the exhaustive exercise test. HR and RPE-related indices showed markedly lower predictive power. The results extend the previously documented relationship between HLa during treadmill ergometry and running performance to include the use of cycle ergometry for the evaluation of running performance. The results also proved applicable to running performance while load carrying.

Effects of training at and above the lactate threshold on the lactate threshold and maximal oxygen uptake

Thirty-three college women (mean age = 21.8 years) participated in a 5 d X wk-1, 12 week training program. Subjects were randomly assigned to 3 groups, above lactate threshold (greater than LT) (N = 11; trained at 69 watts above the workload associated with LT), = LT (N = 12; trained at the work load associated with LT) and control (C) (N = 10). Subjects were assessed for VO2max, VO2LT, VO2LT/VO2max, before and after training, using a discontinuous 3 min incremental (starting at 0 watts increasing 34 watts each work load) protocol on a cycle ergometer (Monark). Respiratory gas exchange measures were determined using standard open circuit spirometry while LT was determined from blood samples taken immediately following each work load from an indwelling venous catheter located in the back of a heated hand. Body composition parameters were determined before and after training via hydrostatic weighing. Training work loads were equated so that each subject expended approximately 1465 kJ per training session (Monark cycle ergometer) regardless of training intensity. Pretraining, no significant differences existed between groups for any variable. Post training the greater than LT group had significantly higher VO2max (13%), VO2LT (47%) and VO2LT/VO2max (33%) values as compared to C (p less than .05). Within group comparisons revealed that none of the groups significantly changed VO2max as a result of training, only the greater than LT group showed a significant increase in VO2LT (48%) (p less than .05), while both the = LT and greater than LT group showed significant increases in VO2LT/VO2max (= LT 16%, greater than LT 42% (p less than .05)).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships of anaerobic threshold and onset of blood lactate accumulation with endurance performance

This study was undertaken to compare the contribution of both the anaerobic threshold (AT) and onset of blood lactate accumulation (OBLA) with endurance performance in eleven non-endurance trained active male adults. AT determination was based upon both blood lactate and gas exchange criteria, while OBLA was determined as the point corresponding to a blood lactate concentration of 4 mmol X 1(-1). A dependent t-test revealed significantly higher values for OBLA related variables as compared with corresponding AT related variables, thereby validating the comparison of these two categories of variables in relation to endurance performance. Approximately 67, 60, 37, and 50% of the variance in endurance performance were accounted for by AT-VO2 (ml X kg-1 X min-1), AT-WR, OBLA-VO2 (ml X kg-1 X min-1), and OBLA-WR, respectively. When AT-HR (X2) was added to the AT-VO2 (X1) as another predictor, the contribution of these variables to endurance performance increased appreciably to 84%. The resultant multiple regression equation was Y = -4.564 X1 + 2.68 IX2 + 90.6 (SEE = 9.9 s). Consequently, it is suggested that variables related to an abrupt increase in blood lactate, together with several gas exchange responses, could explain endurance performance in a shorter distance to a greater extent than variables related to a rigid threshold of 4 mmol X 1(-1).

Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man

The relationship between muscle and blood lactate levels during progressively step-wise incrementing cycle exercise has been investigated in 10 male subjects. Steps between power outputs during exercise were 50 W and each stage, from loadless pedalling until voluntary exhaustion, lasted 4 min. Blood samples and biopsies (m. vastus lateralis) were taken for lactate determination at each power output beginning with the exercise intensity perceived by the subject as being "rather moderate". The ratio muscle:blood lactate was greater than one at all power outputs and increased most markedly at the power output closest to that eliciting 4 mmol x 1(-1) blood lactate (WOBLA). At WOBLA, blood lactate was positively correlated to muscle lactate concentrations which covaried widely among subjects (mean 8.3, range 4.5-14.4 mmol x kg-1 wet weight). Muscles fibres from the WOBLA biopsy in 6 subjects were dissected out and identified as fast twitch (FT) or slow twitch (ST). No significant difference in lactate concentration was observed between pools of FT or ST fibres.

Lactate accumulation in muscle and blood during submaximal exercise

Muscle and blood lactate concentration was studied in 10 healthy males during cycling exercise. For each subject the exercise intensity corresponding to a blood lactate concentration of 4 mmol.l-1 (OBLAw) was assessed by a step-wise increased exercise intensity protocol. In a second series of experiments the same protocol was performed but exercise was terminated at OBLAw and a muscle biopsy for subsequent analysis of lactate concentration was obtained from m. vastus lateralis. Biopsies were also taken at rest for histochemical determination of fiber type composition and capillary supply. The exercise intensity, which corresponded to OBLAw, averaged 159(117-216) W, equal to 65 (range 55-84)% of VO2max, and was found to be correlated to capillaries per fiber of the exercising muscle (r = 0.83, p less than 0.01). Muscle lactate concentration averaged 6.9 (range 2.1-12.6) mmol.kg-1 w.w. The change in blood lactate concentration (prior to and 1 min post exercise) was correlated to muscle lactate concentration (r = 0.71, p less than 0.05). It is concluded that great individual variations in the muscle/blood lactate gradient do exist during submaximal steady-state exercise, performed at a certain blood lactate level.