Blood metabolites during prolonged exercise in swimming and leg cycling

Summary This study was designed to compare the influence of two modes of exercise (swimming and leg cycling) on the blood concentrations of metabolic substrates and metabolites during a 45-min exercise period. Eight college students (mean age=21.6±1.2 year) exercised at 70% of O₂ max, in water using the front crawl on one occasion, and on a cycle ergometer using the legs on another. Blood samples were drawn at 0,15, 30, and 45 min and analyzed for free fatty acids, glycerol, glucose, pyruvate, and lactate concentrations. Mean oxygen uptakes (2.23 vs 2.12 l·min^–1) and heart rates (152 vs 150 b·min^–1) for cycling and swimming respectively were not significantly different. Lactate and pyruvate were significantly (p<0.01) higher during swimming as compared to cycling. Free fatty acids, glycerol, and glucose were not significantly different between the two modes of exercise (p>0.05). Assuming venous blood concentrations provide some indication of metabolic events, these data are compatible with a tendency to a higher relative carbohydrate oxidation rate during swimming as compared to cycling during prolonged exercise at the same relative work intensities.Supported by grand from C.A.F.I.R., Université de Montréal     

Metabolic and hormonal responses to prolonged physical exercise in dogs after a single fat-enriched meal

Summary Metabolic and hormonal responses to prolonged treadmill exercise in dogs fed a fat-enriched meal 4 h prior to the exercise were compared to those measured 4 h after a mixed meal or in the postabsorptive state.Ingestion of the fat-enriched meal caused significant elevations in the resting values of plasma triglyceride (TG), free fatty acid (FFA), and glycerol concentrations. A reduction of the plasma TG concentration (from 1.6±0.2 to 1.1±0.10 mmol·l^–1,P<0.005) occurred only in dogs exercising after the fat-enriched meal. No significant changes in this variable were noted in dogs fed a mixed meal, whilst in the postabsorptive state exercise caused an increase in the plasma TG level (from 0.42±0.03 to 0.99±0.11 mmol·l^–1,P<0.01). The exercise-induced elevations in plasma FFA and glycerol concentrations were the highest in the dogs given the fat-enriched meal. Plasma glycerol during exercise correlated with the initial values of circulating TG (r=0.73). The plasma FFA-glycerol ratio, at the end of exercise was lowest in the dogs taking the fat-enriched meal (1.39±0.19), suggesting an increased utilization of FFA in comparison with that in the postabsorptive state (3.27±0.37) or after a mixed meal (2.88±0.55). Basal serum insulin (IRI) concentrations were similarly enhanced in dogs fed fat-enriched and mixed meals, and they were reduced to control values within 60 min of exercise. Plasma adrenaline and noradrenaline concentrations correlated with time of exercise (r=0.84 andr=0.96, respectively) and were unaffected by the nutritional modifications.It is concluded that ingestion of a single fat-enriched meal considerably modifies the exercise-induced changes in lipid metabolism. The pattern of changes in plasma TG, FFA, and glycerol concentrations indicates an enhanced hydrolysis of plasma chylomicron-TG, suggesting that this lipid source may contribute markedly to exercise metabolism.This work was supported by the Polish Academy of Sciences within the Project 10.4     

Effects of a rapid change in muscle glycogen availability on metabolic and hormonal responses during exercise

Summary To evaluate the metabolic and hormonal adaptations following a rapid change in muscle glycogen availability, 14 subjects had their muscle glycogen content increased in one leg (IG) and decreased in the other (DG). In group A (n=7), subjects exercised on a bicycle ergometer at 70% maximal oxygen uptake for 20 min using the DG leg. Without resting these same subjects exercised another 20 min using the IG leg. Subjects in group B (n=7) followed the same single-leg exercise protocol but in the reverse order. In order to get some information on the time sequence of these possible adaptations, blood samples were collected at rest and at the beginning and the end of each exercise period (min 5, 20, 25, and 40). Results indicated that 5 min after the switch from the DG leg to the IG leg. transient increases in plasma free fatty acids (1.20 to 1.39 meq·l^–1) and serum insulin (10.1 to 12 mU·l^–1) concentrations occured. Between minute 25 and 40 of exercise, the DG to IG switch was accompanied by a decrease in free fatty acids and glycerol concentrations as well as an increase in lactate levels. An opposite response was observed in the IG to DG condition during the same time span. Plasma norepinephrine, epinephrine, glucagon, and serum cortisol concentrations were not significantly affected by the leg change. These results suggest a rapid preferential use of muscle glycogen when available and a time lag in the response of the extramuscular substrate mobilization factors.     

Skeletal muscle metabolism and ultrastructure in relation to age in sedentary men

In order to find out if there are age-related changes in human skeletal muscle metabolism or ultrastructure, biopsy material from 56 sedentary men aged 22–65 years was studied by means of enzyme activity determinations, histochemistry and quantitative electron microscopy. For comparison, a younger (16–18 years) and an older (66–76 years) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibres with age. Mitochondrial volume fraction decreased with age, primarily due to diminished mean mitochondrial volume. In spite of this, no overall decrease in the activities of five enzymes, representative of the major pathways in energy metabolism, was observed. Thus, increased amounts of enzymes per unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fibre type distribution and oxidative enzymes, as well as between different enzymes. It was concluded, that the decrease in maximal oxygen uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.     

Dynamics of metabolic responses to prolonged elevation of circulating adrenaline in resting and exercising rats

The purpose of this study was to follow the time course of metabolic responses to hyperadrenalinemia sustained up to 3 days. Hyperadrenalinemia was produced in rats by s.c. implantation of tablets releasing adrenaline (A) at a constant rate (1.6 g x min^–1). After 6, 12, 24 and 72 h of hyperadrenalinemia and 3 days after the tablet removal rats were sacrificed and liver, 3 types of muscles and blood samples were taken. Each time 14 rats were used: 7 of them were sedentary and 7 performed treadmill endurance exercise before decapitation. Sham operated animals served as controls. In preliminary experiments working ability was examined in 10 hyperadrenalinemic and 10 control rats. Duration of exercise until exhaustion was reduced in hyperadrenalinemic rats on the average by 40%. In sedentary rats, hyperglycemia, marked depletion of liver glycogen (by approx. 80%) and muscle glycogen (by 60–80%) as well as an elevation (2–4 times) of muscle lactate (LA) were found only during the first day after A-tablet implantation. At the end of the experiment these values approached the control ones. Muscle contents of ATP and creatine phosphate (CrP) were decreased by approx. 20% and 30–60%, respectively. Plasma FFA were markedly enhanced, varying in the time-course of the experiment from 0.8 to 1.4 mmol×1^–1. Post-exercise values for blood glucose, liver and muscle glycogen were always lower in hyperadrenalinemic rats than in controls sacrificed after timematched exercise (30 min). Circulating FFA decreased during excercise at all time points following A-tablet implantation, but they were still above the post-exercise levels in sham-operated rats. The response of muscle adenine nucleotides to exercise was not uniform, and changes in their values in the time-course of hyperadrenalinemia paralelled those in circulating FFA.It is concluded that during sustained hyperadrenalinemia some metabolic effects of adrenaline in sedentary animals are only transient, but impaired exercise tolerance persists for the whole time, being caused, at least in part, by early exhaustion of liver and muscle glycogen.This work was supported by the Polish Programme for Basic Research 06.-02.III.     

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 × I^-1 blood lactate (W_OBLA). At W_OBLA. blood lactate was positively correlated to muscle lactate concentrations which covaried widely among subjects (mean 8.3. range 4.5–14.4 mmol × kg^-l wet weight). Muscle fibres from the W_OBLA 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.     

Regional differences in the lipolytic response of the subcutaneous fat depots to prolonged exercise and severe energy deficiency

Summary After five days of almost continuous strenuous combat exercise and energy deficiency, 12 well-trained young men had a mean body fat loss of 2.7 kg and the average fat cell size was reduced from 0.34 g to 0.24 g. No significant changes were found in the total number of fat cells. For the group as a whole, the decrease in fat cell size was most pronounced in the gluteal subcutaneous region, followed by the abdominal region. No significant decrease in fat cell size was encountered in tissue samples from the femoral site. Before the course, and on the last day, the subjects accomplished a short-term bicycle exercise at 50% of the individual's . On day 5, positive correlations were found between the fat cell weights estimated in the gluteal tissue samples and the pre-exercise free fatty acid (FFA) levels (r=0.87, p<0.01), and also with the plasma free glycerol obtained five minutes after the bicycle exercise (r=0.93, p<0.001). These correlations were not apparent in the control experiment performed before the course. Further, no such relationship was found between the plasma metabolites and the fat cell size of the other body sites investigated. This finding may indicate that gluteal fat deposits are more important for energy provision than abdominal and, especially, femoral deposits.     

Metabolic and temperature responses to physical exercise in thyroidectomized dogs

Summary The purpose of the present work was to further elucidate the role of thyroid hormones in the control of body temperature and metabolism during physical exercise. Changes in rectal temperature (T _re), some parameters of exercise-metabolism and in the plasma noradrenaline (NA) levels were examined in eight dogs performing submaximal treadmill exercise to exhaustion before and after thyroidectomy (THY). The metabolic responses to adrenaline (A) infusion were also compared in intact and THY dogs. During the exercise performed by THY dogs T _re increases were markedly attenuated, plasma FFA level increases were reduced and the pattern of plasma NA changes was modified in comparison with control runs. The reduced exercise-induced FFA mobilization in THY dogs might be attributed to a lower activation of the adrenergic system in the later stage of exercise and to the weaker lipolytic action of catecholamines. The attenuated T _re increases during exercise performed by THY dogs and the exercise-hyperthermia described previously in dogs treated with thyroid hormones suggest that an optimum level of thyroid hormones is necessary to induce typical changes in body temperature during physical exercise.     

Impact of twelve-day combined exposure to hypobaric hypoxia and physical exercise on structural and metabolic characteristics of skeletal muscle in rats

This study, in which rats were exposed on 12 successive days to hypoxia in combination with exercise on a treadmill, showed that a reduction in partial oxygen pressure leads to a decrease in the magnitude of the structural component of vascular resistance rather than to improvement in the system of oxygen utilization, and that such combined exposure may cause alterations in protein synthesis and result in early stimulation of capillary growth in muscles, as well as elicit differential changes of enzyme activity in different types of muscle fibers. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 6, pp. 602–605, June, 1995 Presented by A. I. Grigor'ev, Member of the Russian Academy of Medical Sciences     

Activation and inhibition of muscle and cutaneous postganglionic neurones to hindlimb during hypothalamically induced vasoconstriction and atropine-sensitive vasodilation

Summary Subcutaneous adipose tissue blood flow (ATBF) was examined in 8 subjects during 6 h exercise on a bicycle ergometer. The initial work load was 118 W corresponding to about 50% of maximal work capacity. The oxygen uptake increased from 0.26 l ·min^–1 at rest to about 1.6l·min^–1 during work. In 7 subjects ATBF increased, in 1 it remained constant. After 3 h exercise ATBF at an average reached values 3–4 times the control value. This increase was maintained for the remaining work periods. The increase was significant at the 5% level. Plasma free fatty acids increased 7-, plasma glycerol 10-fold during work.