Hormonal responses to consecutive days of heavy-resistance exercise with or without nutritional supplementation

Nineresistance-trained men consumed either a protein-carbohydratesupplement or placebo for 1 wk in a crossover design separated by 7 days. The last 3 days of each treatment, subjects performed resistanceexercise. The supplement was consumed 2 h before and immediately afterthe workout, and blood was obtained before and after exercise (0, 15, 30, 45, and 60 min postexercise). Lactate, growth hormone, andtestosterone were significantly (P  0.05) elevated immediately postexercise. The lactate response wassignificantly lower during supplementation on days2 and 3. Growthhormone and prolactin responses on day1 were significantly higher during supplementation.After exercise, testosterone declined below resting values duringsupplementation. Cortisol decreased immediately postexercise onday 1; the response was diminished ondays 2 and 3. Glucose and insulin weresignificantly elevated by 30 min during supplementation and remainedstable during placebo. Insulin-like growth factor-I was higher duringsupplementatiom on days 2 and 3. These data indicate thatprotein-carbohydrate supplementation before and after training canalter the metabolic and hormonal responses to consecutive days ofheavy-resistance exercise.

     

Lymphocyte enzymatic antioxidant responses to oxidative stress following high-intensity interval exercise

The purposes of this study were to 1) examine the immune and oxidative stress responses following high-intensity interval training (HIIT); 2) determine changes in antioxidant enzyme gene expression and enzyme activity in lymphocytes following HIIT; and 3) assess pre-HIIT, 3-h post-HIIT, and 24-h post-HIIT lymphocyte cell viability following hydrogen peroxide exposure in vitro. Eight recreationally active males completed three identical HIIT protocols. Blood samples were obtained at preexercise, immediately postexercise, 3 h postexercise, and 24 h postexercise. Total number of circulating leukocytes, lymphocytes, and neutrophils, as well as lymphocyte antioxidant enzyme activities, gene expression, cell viability (CV), and plasma thiobarbituric acid-reactive substance (TBARS) levels, were measured. Analytes were compared using a three (day) × four (time) ANOVA with repeated measures on both day and time. The a priori significance level for all analyses was P < 0.05. Significant increases in superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities were observed in lymphocytes following HIIT. No significant increases in lymphocyte SOD, CAT, or GPX gene expression were found. A significant increase in TBARS was found immediately post-HIIT on days 1 and 2. Lymphocyte CV in vitro significantly increased on days 2 and 3 compared with day 1. Additionally, there was a significant decrease in CV at 3 h compared with pre- and 24 h postexercise. These findings indicate lymphocytes respond to oxidative stress by increasing antioxidant enzyme activity. Additionally, HIIT causes oxidative stress but did not induce a significant postexercise lymphocytopenia. Analyses in vitro suggest that lymphocytes may become more resistant to subsequent episodes of oxidative stress. Furthermore, the analysis in vitro confirms that lymphocytes are more vulnerable to cytotoxic molecules during recovery from exercise.     

Effects of L-tyrosine and carbohydrate ingestion on endurance exercise performance.

To test the effects of tyrosine ingestion with or without carbohydrate supplementation on endurance performance, nine competitive cyclists cycled at 70% peak oxygen uptake for 90 min under four different feeding conditions followed immediately by a time trial. At 30-min intervals, beginning 60 min before exercise, each subject consumed either 5 ml/kg body wt of water sweetened with aspartame [placebo (Pla)], polydextrose (70 g/l) (CHO), L-tyrosine (25 mg/kg body wt) (Tyr), or polydextrose (70 g/l) and L-tyrosine (25 mg/kg body wt) (CHO+Tyr). The experimental trials were given in random order and were carried out by using a counterbalanced double-blind design. No differences were found between treatments for oxygen uptake, heart rate, or rating of perceived exertion at any time during the 90-min ride. Plasma tyrosine rose significantly from 60 min before exercise to test termination (TT) in Tyr (means +/- SE) (480 +/- 26 micromol) and CHO+Tyr (463 +/- 34 micromol) and was significantly higher in these groups from 30 min before exercise to TT vs. CHO (90 +/- 3 micromol) and Pla (111 +/- 7 micromol) (P < 0.05). Plasma free tryptophan was higher after 90 min of exercise, 15 min into the endurance time trial, and at TT in Tyr (10.1 +/- 0.9, 10.4 +/- 0.8, and 12.0 +/- 0.9 micromol, respectively) and Pla (9.7 +/- 0.5, 10.0 +/- 0.3, and 11.7 +/- 0.5 micromol, respectively) vs. CHO (7.8 +/- 0.5, 8.6 +/- 0.5, and 9.3 +/- 0.6 micromol, respectively) and CHO+Tyr (7.8 +/- 0.5, 8.5 +/- 0.5, 9.4 +/- 0.5 micromol, respectively) (P < 0.05). The plasma tyrosine-to-free tryptophan ratio was significantly higher in Tyr and CHO+Tyr vs. CHO and Pla from 30 min before exercise to TT (P < 0.05). CHO (27.1 +/- 0.9 min) and CHO+Tyr (26.1 +/- 1.1 min) treatments resulted in a reduced time to complete the endurance time trial compared with Pla (34.4 +/- 2.9 min) and Tyr (32.6 +/- 3.0 min) (P < 0.05). These findings demonstrate that tyrosine ingestion did not enhance performance during a cycling time trial after 90 min of steady-state exercise.     

Effects of liquid carbohydrate ingestion on markers of anabolism following high-intensity resistance exercise

We examined the effects of liquid carbohydrate (CHO) supplementation on markers of anabolism following high-intensity resistance exercise. Nine resistance-trained men consumed either CHO or placebo (PLC) 10 minutes before and immediately following 2 resistance exercise sessions. Cortisol (CORT), insulin (INS), ammonia (AMM), and glucose (GLU) were measured before, immediately after, and 1.5 and 4 hours after exercise. Urinary nitrogen (NH(+3)) was measured 24 hours before and after exercise. There was a significant difference in INS levels immediately after exercise and 1.5 hours after exercise. No significant differences were observed for CORT, AMM, GLU, or NH(+3)between treatments. Significant within-group differences were found for the PLC group: CORT before compared with immediately after exercise; INS before compared with immediately after exercise and before compared with 1.5 hours after exercise; and AMM before compared with immediately after exercise and before compared with 1.5 hours after exercise. Significant within-group differences were found for the CHO group: CORT immediately after compared with 1.5 hours after exercise and immediately after compared with 4 hours after exercise; INS before compared with 1.5 hours after exercise; and AMM before compared with immediately after exercise. Liquid CHO ingestion leads to a more favorable anabolic environment immediately following a resistance exercise bout; however, our indirect measures of protein degradation were not altered by CHO ingestion.     

Metabolic response to carbohydrate ingestion during exercise in males and females

The present study investigated potential sex-related differences in the metabolic response to carbohydrate (CHO) ingestion during exercise. Moderately endurance-trained men and women (n = 8 for each sex) performed 2 h of cycling at approximately 67% Vo(2 max) with water (WAT) or CHO ingestion (1.5 g of glucose/min). Substrate oxidation and kinetics were quantified during exercise using indirect calorimetry and stable isotope techniques ([(13)C]glucose ingestion, [6,6-(2)H(2)]glucose, and [(2)H(5)]glycerol infusion). In both sexes, CHO ingestion significantly increased the rates of appearance (R(a)) and disappearance (R(d)) of glucose during exercise compared with WAT ingestion [males: WAT, approximately 28-29 micromol x kg lean body mass (LBM)(-1) x min(-1); CHO, approximately 53 micromol x kg LBM(-1) x min(-1); females: WAT, approximately 28-29 micromol x kg LBM(-1) x min(-1); CHO, approximately 61 micromol x kg LBM(-1) x min(-1); main effect of trial, P < 0.05]. The contribution of plasma glucose oxidation to the energy yield was significantly increased with CHO ingestion in both sexes (from approximately 10% to approximately 20% of energy expenditure; main effect of trial, P < 0.05). Liver-derived glucose oxidation was reduced, although the rate of muscle glycogen oxidation was unaffected with CHO ingestion (males: WAT, 108 +/- 12 micromol x kg LBM(-1) x min(-1); CHO, 108 +/- 11 micromol x kg LBM(-1) x min(-1); females: WAT, 89 +/- 10 micromol x kg LBM(-1) x min(-1); CHO, 93 +/- 11 micromol x kg LBM(-1) x min(-1)). CHO ingestion reduced fat oxidation and lipolytic rate (R(a) glycerol) to a similar extent in both sexes. Finally, ingested CHO was oxidized at similar rates in men and women during exercise (peak rates of 0.70 +/- 0.08 and 0.65 +/- 0.06 g/min, respectively). The present investigation suggests that the metabolic response to CHO ingestion during exercise is largely similar in men and women.     

Effect of carbohydrate ingestion on ammonia metabolism during exercise in humans.

The present study was undertaken to examine the effect of carbohydrate ingestion on plasma and muscle ammonia (NH(3) denotes ammonia and ammonium) accumulation during prolonged exercise. Eleven trained men exercised for 2 h at 65% peak pulmonary oxygen consumption while ingesting either 250 ml of an 8% carbohydrate-electrolyte solution every 15 min (CHO) or an equal volume of a sweet placebo. Blood glucose and plasma insulin levels during exercise were higher in CHO, but plasma hypoxanthine was lower after 120 min (1.7 +/- 0.3 vs. 2.6 +/- 0.1 micromol/l; P < 0. 05). Plasma NH(3) levels were similar at rest and after 30 min of exercise in both trials but were lower after 60, 90, and 120 min of exercise in CHO (62 +/- 9 vs. 76 +/- 9 micromol/l; P < 0.05). Muscle NH(3) levels were similar at rest and after 30 min of exercise but were lower after 120 min of exercise in CHO (1.51 +/- 0.21 vs. 2.07 +/- 0.23 mmol/kg dry muscle; P < 0.05; n = 5). These data are best explained by carbohydrate ingestion reducing muscle NH(3) production from amino acid degradation, although a small reduction in net AMP catabolism within the contracting muscle may also make a minor contribution to the lower tissue NH(3) levels.     

Failure to expand influenza and tetanus toxoid memory T cells in vitro correlates with disease course in SIV infected rhesus macaques

Marked decreases in influenza (flu) and tetanus toxoid (T.T.) antigen specific CD8(+) and CD4(+) T cell memory responses were noted shortly after SIV infection in monkeys that go on to develop clinical disease within 18 months (normal progressor, NP) following SIV infection but not in monkeys that remain asymptomatic >3 years post SIV infection (long-term nonprogressor, LTNP). While PBMCs from NP and LTNP monkeys demonstrate both low and high avidity flu and T.T. specific CD8(+) and CD4(+)T cell immune responses prior to SIV infection, the PBMCs from NP but not LTNP fail to generate high avidity T cell responses post SIV infection. This failure to generate high avidity T cell responses in vitro correlated with increased apoptotic cell death in PBMC cultures from NP animals. Since high avidity antigen specific CTLs have been shown to be most efficient in eliminating viral infections, the present finding has important implications for the evaluation of the level of immune reconstitution following various modalities of therapy in HIV-1 infected patients.     

Effect of resistance exercise and carbohydrate ingestion on oxidative stress

Some research studies have produced data indicating that resistance exercise induces oxidative stress, despite minimal increases in VO₂. These studies have primarily relied on oxidative stress markers with low sensitivity and debatable reliability. However, F₂-isoprostanes as measured by gas chromatography mass spectrometry are considered to be a reliable and precise indicator of oxidative stress. Carbohydrate ingestion during exercise is associated with reduced levels of stress hormones, which may influence oxidative stress and plasma antioxidant potential. Therefore, the purpose of this study was to investigate the influence of carbohydrate ingestion during resistance training on F₂-isoprostanes and plasma antioxidant potential. Thirty strength-trained subjects were randomized to carbohydrate (CHO) or placebo (PLA) groups that lifted weights for 2 h. Subjects received 10 ml kg^- 1 h^- 1 CHO (6%) or PLA beverages during the exercise. Blood and vastus lateralis muscle biopsy samples were collected before and after exercise and analyzed for cortisol as a marker of general stress, F₂-isoprostanes as a measure of oxidative stress, and ferric reducing ability of plasma (FRAP) as a measure of antioxidant potential, and for muscle glycogen, respectively. Decreases in muscle glycogen content did not differ between CHO and PLA. Cortisol and FRAP increased significantly in CHO and PLA (P = 0.008 and 0.044, respectively), but the pattern of change was not different between groups. F₂-isoprostanes were unaffected by exercise. These results indicate that exhaustive resistance exercise and carbohydrate ingestion have no effect on oxidative stress or plasma antioxidant potential in trained subjects.     

Acute and habitual caffeine ingestion and metabolic responses to steady-state exercise.

This study compared the exercise catecholamine and metabolic responses to a caffeine challenge in trained subjects before and after a 6-wk period of increased caffeine ingestion. Trained subjects (n = 6) were challenged with 500 mg of caffeine followed by prolonged exercise before and after 6 wk of increased caffeine ingestion (500 mg ingested before each daily run). A control group (n = 6) of trained subjects followed the same protocol except for caffeine ingestion. Acute caffeine ingestion resulted in increased plasma epinephrine and decreased respiratory exchange ratio (RER) during exercise. After 6 wk of caffeine supplementation, the epinephrine response to exercise or caffeine plus exercise was decreased, although the latter still resulted in a lower RER value compared with exercise without caffeine ingestion. Activity of key metabolic enzymes (hexokinase, citrate synthase, phosphorylase, and 3-hydroxyacyl-coenzyme A dehydrogenase) from biopsies of the gastrocnemius showed no response to 6 wk of this increased adrenergic receptor stimulation and, on the basis of the lower RER, enhanced fat metabolism. This study suggests that caffeine ingestion by trained subjects causes increases in plasma epinephrine and reduces the RER during exercise. However, habitual stimulation results in a general dampening of the epinephrine response to caffeine or exercise. There was no indication that increased adrenergic stimulation and fat oxidation caused any adaptation in the activity of metabolic enzymes.     

Effect of carbohydrate ingestion on glucose kinetics during exercise in the heat.

Six endurance-trained men [peak oxygen uptake (V(O(2))) = 4.58 +/- 0.50 (SE) l/min] completed 60 min of exercise at a workload requiring 68 +/- 2% peak V(O(2)) in an environmental chamber maintained at 35 degrees C (<50% relative humidity) on two occasions, separated by at least 1 wk. Subjects ingested either a 6% glucose solution containing 1 microCi [3-(3)H]glucose/g glucose (CHO trial) or a sweet placebo (Con trial) during the trials. Rates of hepatic glucose production [HGP = glucose rate of appearance (R(a)) in Con trial] and glucose disappearance (R(d)), were measured using a primed, continuous infusion of [6,6-(2)H]glucose, corrected for gut-derived glucose (gut R(a)) in the CHO trial. No differences in heart rate, V(O(2)), respiratory exchange ratio, or rectal temperature were observed between trials. Plasma glucose concentrations were similar at rest but increased (P < 0.05) to a greater extent in the CHO trial compared with the Con trial. This was due to the absorption of ingested glucose in the CHO trial, because gut R(a) after 30 and 50 min (16 +/- 5 micromol. kg(-1). min(-1)) was higher (P < 0.05) compared with rest, whereas HGP during exercise was not different between trials. Glucose R(d) was higher (P < 0.05) in the CHO trial after 30 and 50 min (48.0 +/- 6.3 vs 34.6 +/- 3.8 micromol. kg(-1). min(-1), CHO vs. Con, respectively). These results indicate that ingestion of carbohydrate, at a rate of approximately 1.0 g/min, increases glucose R(d) but does not blunt the rise in HGP during exercise in the heat.     

Antibodies to acetylcholine receptor and tetanus toxoid: in vitro synthesis by thymic lymphocytes

Thymic lymphocytes (TL) of patients with myasthenia gravis (MG) have been reported to synthesize antibodies to acetylcholine receptors (anti-AChR). Incubation of TL with pokeweed mitogen (PWM), a polyclonal T cell- and monocyte-dependent activator of B cell differentiation, was reported to inhibit TL in vitro synthesis of anti-AChR. We studied the TL of 16 patients with MG without thymoma. TL of 10 of 16 patients synthesized anti-AChR in vitro without stimulation. In the presence of PWM, the amount of anti-AChR synthesized by the TL of these 10 patients increased in five, decreased in three, and was unaffected in two. There was a correlation between serum anti-AChR titer and PWM-stimulated synthesis (r = 0.87), but not with unstimulated synthesis (r = 0.33) of anti-AChR by TL. There was no correlation between the amount of synthesized anti-AChR and the amount of secreted IgG or with the percentage of B cells (surface Ig+) in the TL suspensions. TL of three age-matched cardiac surgery controls failed to synthesize detectable anti-AChR, although two of three synthesized IgG. Four patients with MG were booster immunized with tetanus toxoid (TT) 3 to 4 wk prior to thymectomy. TL of three synthesized anti-TT in vitro, whereas TL of three nonboosted MG patients failed to synthesize anti-TT. Thus, we have shown that TL of some patients with MG are capable of anti-AChR synthesis, with evidence of heterogeneity of the in vitro response, and the B cell repertoire in the thymus may, in part, reflect recent systemic immune events of the host.     

Lymphocyte subset responses to repeated submaximal exercise in men

The effects of repeated bouts of submaximal cycle ergometry exercise on changes in the percentage of peripheral blood T-lymphocytes, the T-helper/inducer and T-cytotoxic/suppressor subsets, and natural killer (NK) cells were studied in 18 healthy young men who had no history of regular exercise training. Subjects were matched on the basis of maximal O2 uptake and assigned randomly to exercise or control groups, with controls resting quietly during the exercise sessions. The percentage of peripheral blood mononuclear leukocytes that reacted with monoclonal antibodies specific for T-lymphocytes (CD3+ cells), the helper/inducer subset (CD4+ cells) and cytotoxic/suppressor subset (CD8+ cells) of T-lymphocytes, and cells with NK activity (Leu7+ cells) were enumerated by fluorescence-activated flow cytometry for samples obtained immediately before and after exercise on days 1, 3, and 5 of a 5-day exercise regimen. The results of this study were mixed with decreases in the percentage of T-lymphocytes before vs. after exercise on days 1 and 3 (P less than 0.001), a decrease in the percentage of T-helper/inducer cells before vs. after exercise on day 3 (P less than 0.05), no effect of exercise on the percentage of T-cytotoxic/suppressor cells, and a marked increase in the percentage of NK cells after exercise on days 1 (P less than 0.05) and 3 (P less than 0.01). The total number of recovered NK cells in the mononuclear leukocyte fraction of blood also increased significantly after exercise on days 1 (P less than 0.05) and 3 (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of carbohydrate ingestion before and during exercise on glucose kinetics and performance.

We investigated the effect of carbohydrate (CHO) ingestion before and during exercise and in combination on glucose kinetics, metabolism and performance in seven trained men, who cycled for 120 min (SS) at approximately 63% of peak power output, followed by a 7 kJ/kg body wt time trial (TT). On four separate occasions, subjects received either a placebo beverage before and during SS (PP); placebo 30 min before and 2 g/kg body wt of CHO in a 6.4% CHO solution throughout SS (PC); 2 g/kg body wt of CHO in a 25.7% CHO beverage 30 min before and placebo throughout SS (CP); or 2 g/kg body wt of CHO in a 25.7% CHO beverage 30 min before and 2 g/kg of CHO in a 6.4% CHO solution throughout SS (CC). Ingestion of CC and CP markedly (>8 mM) increased plasma glucose concentration ([glucose]) compared with PP and PC (5 mM). However, plasma [glucose] fell rapidly at the onset of SS so that after 80 min it was similar (6 mM) between all treatments. After this time, plasma [glucose] declined in both PP and CP (P < 0.05) but was well maintained in both CC and PC. Ingestion of CC and CP increased rates of glucose appearance (R(a)) and disappearance (R(d)) compared with PP and PC at the onset of, and early during, SS (P < 0.05). However, late in SS, both glucose R(a) and R(d) were higher in CC and PC compared with other trials (P < 0.05). Although calculated rates of glucose oxidation were different when comparing the four trials (P < 0.05), total CHO oxidation and total fat oxidation were similar. Despite this, TT was improved in CC and PC compared with PP (P < 0.05). We conclude that 1) preexercise ingestion of CHO improves performance only when CHO ingestion is maintained throughout exercise, and 2) ingestion of CHO during 120 min of cycling improves subsequent TT performance.     

The effect of carbohydrate ingestion on plasma interleukin-6, hepcidin and iron concentrations following prolonged exercise

The aim of our study was twofold, firstly to examine the relationship between plasma concentrations of IL-6, hepcidin and iron following prolonged exercise and secondly, to assess the effect of carbohydrate ingestion on circulating hepcidin concentration post-exercise. The study was a randomised double-blind cross-over design, with participants consuming either a carbohydrate (CHO) or an isovolumetric placebo drink throughout the trial. Nine healthy, trained males completed a treadmill run at 60% vVO(2max) for 120 min followed by a 5 km time trial. Plasma concentrations of both IL-6 and hepcidin significantly increased post-exercise following both trials (p<.05) and returned to baseline by 24 h post (p>.05). A positive correlation between hepcidin and IL-6 was demonstrated immediately following exercise during PLA while there was a trend for a moderate correlation during CHO (PLA trial rho=0.81, p<0.001; CHO trial rho=0.36, p=0.07). Plasma iron was unaffected immediately post-exercise but significantly reduced by 24 h post-exercise compared to baseline. CHO ingestion significantly reduced post-exercise IL-6 (p<.05) but this had no effect on plasma hepcidin or iron concentration. Our data demonstrate CHO supplementation does not alter the rapid hepcidin response associated with exercise and does not prevent a subsequent fall in plasma iron concentration. This finding adds further support to the theory that an exercise-induced, up-regulation of hepcidin activity is a mechanism causing iron deficiency in endurance athletes.     

Water and carbohydrate ingestion during prolonged exercise increase maximal neuromuscular power.

This study investigated the individual and combined effects of water and carbohydrate ingestion during prolonged cycling on maximal neuromuscular power (P(max)), thermoregulation, cardiovascular function, and metabolism. Eight endurance-trained cyclists exercised for 122 min at 62% maximal oxygen uptake in a 35 degrees C environment (50% relative humidity, 2 m/s fan speed). P(max) was measured in triplicate during 6-min periods beginning at 26, 56, 86, and 116 min. On four different occasions, immediately before and during exercise, subjects ingested 1) 3.28 +/- 0.21 liters of water with no carbohydrate (W); 2) 3.39 +/- 0.23 liters of a solution containing 204 +/- 14 g of carbohydrate (W+C); 3) 204 +/- 14 g of carbohydrate in only 0.49 +/- 0.03 liter of solution (C); and 4) 0. 37 +/- 0.02 liter of water with no carbohydrate (placebo; Pl). These treatments were randomized, disguised, and presented double blind. At 26 min of exercise, P(max) was similar in all trials. From 26 to 116 min, P(max) declined 15.2 +/- 3.3 and 14.5 +/- 2.1% during C and Pl, respectively; 10.4 +/- 1.9% during W (W > C, W > Pl; P < 0.05); and 7.4 +/- 2.2% during W+C (W+C > W, W+C > C, and W+C > Pl; P < 0. 05). As an interesting secondary findings, we also observed that carbohydrate ingestion increased heat production, final core temperature, and whole body sweating rate. We conclude that, during prolonged moderate-intensity exercise in a warm environment, ingestion of W attenuates the decline in P(max). Furthermore, ingestion of W+C attenuates the decline in maximal power more than does W alone, and ingestion of C alone does not attenuate the decline in P(max) compared with Pl.     

Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery

This study investigated the responses in substrate- and energy-based properties to repetitive days of prolonged submaximal exercise and recovery. Twelve untrained volunteers (Vo(2)(peak) = 44.8 +/- 2.0 ml.kg(-1).min(-1), mean +/- SE) cycled ( approximately 60 Vo(2)(peak)) on three consecutive days followed by 3 days of recovery. Tissue samples were extracted from the vastus lateralis both pre- and postexercise on day 1 (E1), day 3 (E3), and during recovery (R1, R2, R3) and were analyzed for changes in metabolism, substrate, and enzymatic and transporter responses. For the metabolic properties (mmol/kg(-1) dry wt), exercise on E1 resulted in reductions (P < 0.05) in phosphocreatine (PCr; 80 +/- 1.9 vs. 41.2 +/- 3.0) and increases (P < 0.05) in inosine monophosphate (IMP; 0.13 +/- 0.01 vs. 0.61 +/- 0.2) and lactate (3.1 +/- 0.4 vs. 19.2 +/- 4.3). At E3, both IMP and lactate were lower (P < 0.05) during exercise. For the transporters, the experimental protocol resulted in a decrease (P < 0.05) in glucose transporter-1 (GLUT1; 29% by R1), an increase in GLUT4 (29% by E3), and increases (P < 0.05) for both monocarboxylate transporters (MCT) (for MCT1, 23% by R2 and for MCT4, 18% by R1). Of the mitochondrial and cytosolic enzyme activities examined, cytochrome c oxidase (COX), and hexokinase were both reduced (P < 0.05) by exercise at E1 and in the case of hexokinase and phosphorylase by exercise on E3. With the exception at COX, which was lower (P < 0.05) at R1, no differences in enzyme activities existed at rest between E, E3, and recovery days. Results suggest that the glucose and lactate transporters are among the earliest adaptive responses of substrate and metabolic properties studied to the sudden onset of regular low-intensity exercise.