Lactate threshold determination: a Monte Carlo comparison of two interpolation methods.

A heuristic model of the relation between blood lactate (L) and VO2 during exercise was used to assess the comparative merits of two methods of reference threshold determination: the habitual linear interpolation method (LT), and a new method using inverse parabolic (second degree) interpolation (PT); the new method capitalizes on the demonstrated curvilinear relation between blood lactate and O2 uptake. Both types of interpolated thresholds were computed, and their error evaluated against the "true" 4-mmol lactate threshold. A combined parametric and Monte Carlo investigation showed that parabolic thresholds are generally superior, being less biased and more precise than their linear counterpart.

Influence of moderate cold exposure on blood lactate during incremental exercise.

This study examined the effect of exposure of the whole body to moderate cold on blood lactate produced during incremental exercise. Nine subjects were tested in a climatic chamber, the room temperature being controlled either at 30 degrees C or at 10 degrees C. The protocol consisted of exercise increasing in intensity in 35 W increments every 3 min until exhaustion. Oxygen consumption (VO2) was measured during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for the measurement of blood glucose, free fatty acid (FFA), noradrenaline (NA) and adrenaline (A) concentrations and, during the last 15 s of each exercise intensity, for the determination of blood lactate concentration [la-]b. The VO2 was identical under both environments. At 10 degrees C, as compared to 30 degrees C, the lactate anaerobic threshold (Than,la-) occurred at an exercise intensity 15 W higher and [la-]b was lower for submaximal intensities above the Than,la-. Regardless of ambient temperature, glycaemia, A and NA concentrations were higher at exhaustion while FFA was unchanged. At exhaustion the NA concentration was greater at 10 degrees C [15.60 (SEM 3.15) nmol.l-1] than at 30 degrees C [8.64 (SEM 2.37) nmol.l-1]. We concluded that exposure to moderate cold influences the blood lactate produced during incremental exercise. These results suggested that vasoconstriction was partly responsible for the lower [la-]b observed for submaximal high intensities during severe cold exposure.

Hormonal and metabolic changes during a strenuous tennis match. Effect of ageing.

The effect of a strenuous tennis match was studied in 9 young (21.2 +/- 1.9 yr) and 10 veteran women players (46.5 +/- 1.3 yr) of equivalent skill. Each match was carried out during the summer (ambient temperature 27 +/- 1 degree C), as an official competition, under conditions as similar as possible. Heart rate (HR) was monitored throughout the match, weight loss was evaluated and pre- and post-match values of haematocrit, plasma lactate, free fatty acid (FFA), glycemia, ionogram, norepinephrine (NOR), epinephrine, arginine vasopressin (AV) concentrations and plasma renin activity (PRA) were measured. Plasma volume was calculated. While mean HR remained steady in young players, it increased progressively in veteran players as the match went on and reached a very high level towards the end of the match. When post-match values were compared to pre-match values, the mean results were: no substantial changes in plasma lactate and electrolyte concentrations, a large increase in FFA, no increase in epinephrine, a moderate rise in NOR and a large increase in PRA and AV. Despite a similar weight loss, a large drop in plasma volume occurred only in veteran players, who also showed FFA and AV values greater than in young players. During these strenuous matches the large response of hormones which control body fluid probably contributed to the limiting of changes in water and electrolyte balances. However, under similar conditions marked differences occurred as a function of ageing concerning the control of plasma volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of age on heart rate response during a strenuous match of tennis.

Ten young women tennis players (YP: 15-30 years) and 10 veteran women tennis players (VP: 40-51 years) of equivalent skill took part in this study. In the laboratory, maximal heart rate (maxHR), VO2max and blood lactate concentration (LA) at exhaustion were measured. On the field, each match was carried out as an official competition. However, in order to obtain a strenuous match, some experimental conditions were imposed (duration, hydration, skill of opponent, etc.). Heart rate (HR) was recorded throughout the match and LA was measured at rest before the match and immediately at the end of the match. While mean heart rate intensity remained relatively steady in YP it tended to increase as the game went on in VP. Due to the lower maxHR and VO2max, VP play at a higher percentage of maxHR and thus probably at a greater relative exercise intensity than YP. For the last part of the match, in some VP, who stopped playing due to exhaustion, HR intensity reached a considerable high level. No significant increase in LA was found at the end of the match in either group. If individual values were considered, no large increase in LA was found in the exhausted women. Obviously fatigue did not result from a muscle lactate accumulation. On the other hand, this moderate LA suggests that the oxygen transport was not a limiting factor of activity, although maxHR, thus probably a maximum cardiac output, was reached. Among the possible factors responsible for the exhaustion a decrease in kinetics of heart rate recovery may be considered in veteran tennis players.

Physiological adjustments of facial cooling during exercise.

Physiological and metabolic output responses to facial cooling during a graded maximal exercise and a prolonged submaximal exercise lasting 30 min at 65% VO2 max were investigated in five male subjects. Pedalling on a cycle ergometer was performed both with and without facial cooling (10 degrees C, 4.6 M.S-1). Facial cooling at the end of greated maximal exercise apparently had no effect on plasma lactate (LA), maximal oxygen consumption (VO2 max), maximal heart rate (HR max), rectal temperature (Tre), work load, lactate threshold (LT), ventilatory threshold (VT) and onset of blood lactate accumulation (OBLA). However, the response to facial cooling after prolonged submaximal exercise is significantly different for heart rate and work load. The results suggest that facial wind stimulation during maximal exercise does not produce a stress high enough to alter the metabolic and physiological responses.

Hematological variations at rest and during maximal and submaximal exercise in a cold (0 degree C) environment.

The affect of negative thermal stress on hematological variables at rest, and during submaximal (sub ex) and maximal exercise (max ex) were observed for young males who volunteered in two experimental sessions, performed in cold (0 degree C) and in normal room temperature (20 degrees C). At rest, hematological variables such as RBC and derivates Hb and Hct were significantly increased (P less than 0.05) during cold stress exposure, while plasma volume decreased. The findings of this study suggest that the major factor inducing hypovolemia during low thermal stress can be imputed to local plasma water-shift mechanisms and especially to a transient shift of plasma water from intra- to extravascular compartments. Rest values for WBC and platelets (Pla) were also slightly increased during cold stress exposure. However this increase can partly be related to hemoconcentration but also to the cold induced hyperventilation activating the lung circulation. Maximal exhaustive exercise induced, in both experimental temperatures, significant (P less than 0.05) increments of RBC, Hb, Hct, and WBC while plasma volume decreased. However, Pla increase was less marked. On the other hand, cold stress raised slightly the observed variations of the different hematological variables. Submaximal exercise induced a similar, though non-significant, pattern for the different hematological variables in both experimental conditions. Observed plasma volume (delta PV%) reduction appears during exercise. However cold stress induced resting plasma volume variations that are transferred at every exercise level. Neither exercise nor cold inducement significantly modified the hematological indices (MCH, MCV, MCHC). In conclusion hematological variables are affected by cold stress exposure, even when subjects perform a physical activity.

Metabolic and hormonal responses during exercise at 20 degrees, 0 degrees and -20 degrees C.

This study was designed to clarify the effects of cold air exposure on metabolic and hormonal responses during progressive incremental exercise. Eight healthy males volunteered for the study. Informed consent was obtained from every participant. The following protocol was administered to each subject on three occasions in a climatic chamber in which the temperature was 20 degrees, 0 degree or -20 degrees C with relative humidity at 60% +/- 1%. 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, bicarbonate concentration (HCO-3), acid-base balance, plasma epinephrine (E) and norepinephrine (NE) were determined from venous blood samples obtained through an indwelling brachial catheter. Maximal oxygen uptake was significantly different between conditions: 72.0 +/- 5.4 ml kg-1 min-1 at 20 degrees C; 68.9 +/- 5.1 ml kg-1 min-1 at 0 degree C and 68.5 +/- 4.6 ml kg-1 min-1 at -20 degrees C. Workload, time to exhaustion, glucose levels and rectal temperature decreased significantly at -20 degrees C. Catecholamines and lactate values were not significantly altered by thermal conditions after maximal exercise but the catecholamines were decreased during rest. Bicarbonate, respiratory quotient, lactate and ventilatory thresholds increased significantly at -20 degrees C. The data support the contention that metabolic and hormonal responses following progressive incremental exercise are altered by cold exposure and they indicate a marked decrease in maximal oxygen uptake, time to exhaustion and workload.

Effects of selective cooling of the facial area on physiological and metabolic output during graded maximal or prolonged submaximal exercise.

Physiological and metabolic output responses to facial cooling during a graded maximal exercise and a prolonged submaximal exercise lasting 30 min at 65% VO2 max were investigated in five male subjects. Pedalling on a cycle ergometer was performed both with and without facial cooling (10 degrees C, 4.6 m s-1). Facial cooling at the end of graded maximal exercise apparently had no effect on plasma lactate (LA), maximal oxygen consumption (VO2 max), maximal heart rate (HR max), rectal temperature (Tre), work-load, lactate threshold (LT), ventilatory threshold (VT) and onset of blood lactate accumulation (OBLA). However, the response to facial cooling after prolonged submaximal exercise is significantly different for heart rate and work-load. The results suggest that facial wind stimulation during maximal exercise does not produce a stress high enough to alter the metabolic and physiological responses.

Face cooling-induced reduction of plasma prolactin response to exercise as part of an integrated response to thermal stress.

This study was designed to verify if the decrease in blood prolactin (PRL) induced by selective face cooling during exercise could be part of a response to specific body thermal stress. Five healthy trained male cyclists presenting a significant plasma PRL elevation to exercise were, on three occasions and at weekly interval, submitted to a submaximal exercise (approx. 65% VO2max) on ergocycle with and without selective face cooling. In absence of face cooling a first trial served to establish reference values for workload, heart rate and plasma PRL levels, the latter increasing markedly (450% of resting values) in these conditions. On a second trial but with workload maintained at reference values (222 +/- 9 W), a significant bradycardia was observed with face cooling; furthermore, plasma PRL response to exercise was significantly reduced (to 31% of original response). On a third trial with face cooling, workload had to be significantly augmented (242 +/- 10 W) to maintain heart rate at reference level (78% HRmax); in addition, plasma PRL response to exercise was almost unchanged compared to the reference-value level. The absence of a significant face cooling-induced decrease in sympathetic tonus, as evaluated through peripheral plasma catecholamines response, does not indicate a role for the autonomic nervous system in the face cooling-induced reduction of both heart rate and PRL responses during exercise. Assay of circulating peripheral beta-endorphins could indicate that the face cooling-induced PRL blunted response does not necessarily involve an opioid mediation.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of cold exposure on blood lactate response during incremental exercise.

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)

[Hematological variations with submaximal long-term physical exercise]. / Variations hematologiques à l'exercice physique sous maximal de longue durée.

The purpose of this study was to determine the effects of cold stress on routine hematologic parameters when subjects are submitted on long-lasting exercise. Eight male subjects, aged 22.7 +/- 1.3 years with a peak oxygen consumption of 54.3 +/- 5.2 mL/kg/min performed, respectively at 20 degrees C and 0 degrees C, a two-hour submaximal cyclergometry at an intensity of 40% of that performed during a previous exhaustive test. A 21-gauge catheter was inserted into an ante cubital vein for collection of the blood samples. Platelets and WBC count was significantly (p less than 0.05) increased during exercise in both 20 degrees C and 0 degrees C environmental temperatures. A slight but not statistically significant increase of RBC, Hb and Hct and a plasma concentration during cold exposure was observed. Indices are unchanged in both experiments. The findings of this study suggest that physical exercise is a major factor inducing hypervolemia and that low thermal environment does not appear to be an effective factor influencing hematologic variables during exercise.

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.

Metabolic and hormonal responses to long-distance swimming in cold water.

The acute effects of long-distance swimming in cold water on selected hormonal and metabolic variables were evaluated on 22 long-distance swimmers (16 males and 6 females) during a 32-km swimming competition (La Traversée Internationale du Lac St-Jean). The water temperature was 18.5 degrees C and the mean performance times were 8 h and 32 min for men (M) and 9 h and 1 min for women (F). The blood samples were withdrawn in the fasting state during the week preceding the event and within 30 min after completion of the race. A positive correlation was obtained, for both groups, between percent body fat and rectal temperature measured at the end of the competition. After the competition, an increase in plasma epinephrine, norepinephrine, cortisol, thyroxine, free fatty acids, lactate, a decrease in glucose and insulin and no change in growth hormone, triiodothyronine, triglycerides, and cholesterol concentrations were observed in both groups. The increase in plasma thyroxine was more pronounced in the slower swimmers while the change in blood cortisol concentrations was higher in the subjects having the most acute decrease in body temperature. Male and female swimmers have a similar metabolic and hormonal response to a long-distance swimming competition in cold water.

[Hormonal responses to repeated lactic acid anaerobic exercise in male subjects]. / Réponses hormonales à une répétition d'exercices anaérobies lactacides chez des sujects masculins.

The hormonal response to repeated lactic acid anaerobic exercise was investigated in 6 young male adults. The exercise protocol consisted of 3 one-minute bouts of voluntary maximal effort, each bout being separated from the subsequent one by a two-minute rest period. Venous blood samples were obtained at rest and at the end of each of the 3 work bouts, as well as following 15 minutes of recovery. A marked increase in plasma catecholamine concentrations was observed in response to the repeated exercise bouts, the rise being more important for the adrenaline (x 22) than the noradrenaline (x 10) concentrations. A progressive increase in plasma somatotropin hormone was observed between the first and the last venous sampling. Moreover, a delayed rise in plasma cortisol, insulin, prolactin, and androstenedione was also observed. Hormonal concentrations of LH, FSH, DHEA-SO4, testosterone, SHBG and testosterone/SHBG ratio were not modified in response to the type of exercise.