Metabolic and hormonal response to short term fasting after endurance training in the rat

The metabolic and hormonal response to short term fasting was studied after endurance exercise training. Rats were kept running on a motor driven rodent treadmill 5 days/wk for periods up to 1 h/day for 6 wk. Trained and untrained rats were then fasted for 24 h and 48 h. Liver and muscle glycogen, blood glucose, lactate, beta OH butyrate, glycerol, plasma insulin, testosterone and corticosterone were measured in fed and fasted trained and untrained rats. 48 h fasted trained rats show a lower level of blood lactate (1.08 +/- 0.05 vs 1.33 +/- 0.08 mmol/l-1 of blood glycerol (1 +/- 0.11 vs 0.84 +/- 0.08 mmol/l-1), and of muscle glycogen. There is a significant increase in plasma corticosterone in 48 h fasted trained rats from fed values. Plasma testosterone decreases during fasting, the values are higher in trained rats. Plasma insulin decreases during fasting without any difference between the two groups. These results show higher lipolysis, and decreased glycogenolysis in trained animals during 48 h fasting. The difference between the groups in steroid hormone response could reduce neoglucogenesis and muscle proteolysis in trained animals.     

Adaptive response of hypertrophied skeletal muscle to endurance training

The response of hypertrophied soleus and plantaris muscle of rats to endurance training was studied. Hypertrophy was produced by bilateral extirpation of the gastrocnemius muscle. A 13-wk training program of treadmill running initiated 30 days after removal of the gastrocnemius muscle accentuated (P less than 0.01) the hypertrophy. Succinate dehydrogenase activities of the enlarged muscles of sedentary rats were similar to those of normal animals, as were the increases associated with training. Phosphorylase and hexokinase activities were unaltered as a result of the experimental perturbations. Rates of glycogen depletion during exercise were lower (P less than 0.01) in the liver and soleus and plantaris muscles of endurance-trained animals. No difference existed in the rate of glycogen depletion of normal and hypertrophied muscle within the sedentary or trained groups. These data demonstrate that extensively hypertrophied muscle responds to training and exercise in a manner similar to that of normal muscle.     

Impact of training intensity distribution on performance in endurance athletes

The purpose of this study was to compare the effect of 2 training programs differing in the relative contribution of training volume, clearly below vs. within the lactate threshold/maximal lactate steady state region on performance in endurance runners. Twelve subelite endurance runners (who are specialists in track events, mostly the 5,000-m race usually held during spring-summer months and who also participate in cross-country races [9-12 km] during fall and winter months) were randomly assigned to a training program emphasizing low-intensity (subthreshold) (Z1) or moderately high-intensity (between thresholds) (Z2) training intensities. At the start of the study, the subjects performed a maximal exercise test to determine ventilatory (VT) and respiratory compensation thresholds (RCT), which allowed training to be controlled based on heart rate during each training session over a 5-month training period. Subjects performed a simulated 10.4-km cross-country race before and after the training period. Training was quantified based on the cumulative time spent in 3 intensity zones: zone 1 (low intensity; RCT). The contribution of total training time spent in zones 1 and 2 was controlled to have relatively more low-intensity training in Z1 (80.5 +/- 1.8% and 11.8 +/- 2.0%, respectively) than in Z2 (66.8 +/- 1.1% and 24.7 +/- 1.5%, respectively), whereas the contribution of high-intensity (zone 3) training was similar (8.3 +/- 0.7% [Z1] and 8.5 +/- 1.0% [Z2]). The magnitude of the improvement in running performance was significantly greater (p = 0.03) in Z1 (-157 +/- 13 seconds) than in Z2 (-121.5 +/- 7.1 seconds). These results provide experimental evidence supporting the value of a relatively large percentage of low-intensity training over a long period ( approximately 5 months), provided that the contribution of high-intensity training remains sufficient.     

Respiratory sinus arrhythmia alteration following training in endurance athletes.

Significant increases in maximum oxygen consumption (VO2max) were noted in nine young track athletes following an 8-week high-intensity running period (P less than 0.05). VO2max was measured, prior to and following the training program, using an on-line, open-circuit spirometry system. Parasympathetic activity was assessed using heart period variation (R-R interval in milliseconds) during carefully controlled breathing activity (R sinus arrhythmia). Following the training program, a 7.3% increase in aerobic capacity was associated with a 23.1% augmentation of efferent parasympathetic activity (P less than 0.01). These data suggest that enhanced aerobic capacity increases efferent parasympathetic tone.     

Mediation of reduced ventilatory response to exercise after endurance training

To investigate the mechanism by which ventilatory (VE) demand is modulated by endurance training, 10 normal subjects performed cycle ergometer exercise of 15 min duration at each of four constant work rates. These work rates represented 90% of the anaerobic threshold (AT) work rate and 25, 50, and 75% of the difference between maximum O2 consumption and AT work rates for that subject (as determined from previous incremental exercise tests). Subjects then underwent 8 wk of strenuous cycle ergometer exercise for 45 min/day. They then repeated the four constant work rate tests at work rates identical to those used before training. During tests before and after training, VE and gas exchange were measured breath by breath and rectal temperature (Tre) was measured continuously. A venous blood sample was drawn at the end of each test and assayed for lactate (La), epinephrine (EPI), and norepinephrine (NE). We found that the VE for below AT work was reduced minimally by training (averaging 3 l/min). For the above AT tests, however, training reduced VE markedly, by an average of 7, 23, and 37 l/min for progressively higher work rates. End-exercise La, NE, EPI, and Tre were all lower for identical work rates after training. Importantly, the magnitude of the reduction in VE was well correlated with the reduction in end-exercise La (r = 0.69) with an average decrease of 5.8 l/min of VE per milliequivalent per liter decrease in La. Correlations of VE with NE, EPI, and Tre were much less strong (r = 0.49, 0.43, and 0.15, respectively).     

Atrial natriuretic peptide response to endurance physical training in the rat

The effect of an endurance physical training programme on the plasma and atrial natriuretic peptides (ANP) and on renal glomerular ANP receptors was evaluated in male normotensive Wistar rats. Maximal O2 uptake was significantly greater in the endurance trained (117.1 ml O2.kg-1.min-1, SEM 6.18 versus the control rats 84.2 ml O2.kg-1.min-1, SEM 4.88, P less than 0.01. In addition, various muscle oxidative enzymes were also significantly higher in endurance trained animals. An increase in resting plasma [ANP] was observed after 11 weeks of physical training (40.02 pg.ml-1, SEM 7.07 vs 22.8 pg.ml-1, SEM 3.83, P less than 0.05). Glomerular ANP receptor density was lower in trained rats (272 fmol.mg-1 protein, SEM 3.1 vs 380 fmol.mg-1 protein, SEM 6.1, P less than 0.05), whereas atrial tissue [ANP] was not significantly different between controls and trained animals. However, in trained rats, circulating [ANP] was closely correlated with left atrial [ANP] (r = -0.92, P less than 0.05). Resting systolic blood pressure had not changed at the end of this physical training programme. It is considered that under physiological conditions ANP may be involved in long-term extracellular fluid volume homeostasis through the regulation of renal glomerular ANP receptors, and that the left atrium might play a significant role in this long term fluid volume control.     

Muscle enzyme adaptations to added load during training and nontraining hours in rats

The effects of added load (20% of body mass) on the selected enzyme activities of red and white quadriceps femoris (QF), soleus, and gastrocnemius muscles of rats were studied. The rats were divided into sedentary control (SC), sedentary control with added load (SC+AL), endurance training (ET), and endurance training with added load (ET+AL) groups (n = 10 rats/group). After 6 wk, the SC+AL group had 57% higher (P less than 0.001) beta-glucuronidase (beta-GU) activity and 24% lower (P less than 0.05) citrate synthase activity in white QF than SC. Citrate synthase activity was also decreased in red QF (P less than 0.05) after the added load was used during nontraining hours. The training with added load induced similar but more pronounced changes than normal endurance training, especially in white QF. The ET+AL group demonstrated higher citrate synthase activity in white QF (P less than 0.001) and gastrocnemius (P less than 0.01) and higher malate dehydrogenase activity (P less than 0.05) and beta-GU activity (P less than 0.001) in white QF than the ET group. ET+AL rats also had higher phosphofructokinase (P less than 0.01) and lower creatine kinase (P less than 0.001) activity in white QF than ET rats. In conclusion, the added load without training had minor adaptive influences on muscles. The added load during training hours seemed to be an effective means of influencing the activation and adaptation in muscles that contain fast glycolytic fibers.     

Changes in protein synthesis in rats in response to endurance training

Experiments were conducted to investigate the influence of endurance exercise training on protein synthesis in skeletal muscle, heart, and liver. Training decreased incorporation of [¹⁴C]-leucine into proteins of the stromal fraction of muscle but there was no change in amino acid incorporation into proteins of the sarcoplasmic and myofibrillar fractions. Incorporation of [¹⁴C]-leucine into the protein of heart, liver, and plasma was depressed in trained rats compared to untrained rats. The specific radioactivity of [¹⁴C]-leucine was similar in tissues of trained and untrained rats and thus the depressed amino acid incorporation represents a decrease in the rate of protein synthesis. These observations demonstrate that the adaptation of muscle protein metabolism to endurance training is quite different than the alterations during work-induced hypertrophy of muscle. The difference in adaptation probably relates to the functional differences between the types of exercise. However depression of protein synthesis in trained rats is a general effect in several tissues and not an effect localized in muscle tissue.     

Adaptation of protein metabolism to endurance training. Increased amino acid oxidation in response to training.

This study was conducted to investigate alterations in excretion of urea and total nitrogen after6-8 weeks of daily exercise and to establish if the capacity for amino acid oxidation in muscle is influenced by endurance training. Urea nitrogen excretion was increased in trained compared with untrained rats and nitrogen balance was less positive in trained than in untrained rats. Increased [14C]leucine oxidation with training was observed both in vivo and in vitro. The results of this study demonstrate that amino acid catabolism is increased during exercise training and that the muscle enzymes involved in leucine oxidation adapt to endurance training in a manner similar to the enzymes of carbohydrate and fat catabolism.     

Metabolic response of Acylation Stimulating Protein to an oral fat load

Acylation Stimulating Protein (ASP) is a small (mol wt 14,000), basic (pI 9.0) protein present in human plasma. When examined in vitro with normal human cultured skin fibroblasts and adipocytes, ASP appears to be the most potent stimulant of triglyceride synthesis yet described. In this study, a competitive ELISA assay for ASP has been developed using immunospecific polyclonal antibodies, and ASP levels have been measured in seven normal subjects. Following an oral fat load, a sustained significant increase in ASP occurs, whereas after an oral glucose load, ASP levels do not change significantly. These responses are entirely opposite to those of insulin, which rises sharply but transiently after an oral glucose load but is unchanged after an oral fat load. Both the fasting and peak ASP levels were significantly related to the postprandial lipemia. These data provide the first in vivo evidence that Acylation Stimulating Protein may play an important physiological role in the normal response to an oral fat load.     

Erythropoietic adaptations to endurance training

Erythropoietic adaptations involving the oxygen dissociation curve (ODC) and erythropoietin production have been implicated in the etiology of reduced blood haemoglobin concentrations in sportspersons (known as sports anaemia). A significant increase in the half-saturation pressure indicating a right-shift in the ODC was measured in 34 male [25.8-27.4 mmHg (3.44-3.65 kPa)] and 16 female (25.8-27.7 mmHg (3.44-3.69 kPa)] trained distance runners (P less than 0.01 for both genders) after completing a standard 42-km marathon. Erythrocyte 2,3-diphosphoglycerate concentrations measured concurrently were unaltered by exercise, although consistently higher in the female compared to the male athletes (P less than 0.05). The serum erythropoietin (EPO) concentrations of 15 male triathletes (26.3 U.ml-1) were significantly lower than those of 45 male distance runners (31.6 U.ml-1; P less than 0.05). However, the mean serum EPO concentrations of male and female athletes engaged in a variety of sports were not different from those of sedentary control subjects of both sexes (26.5-35.3 U.ml-1). Furthermore, the serum EPO concentrations were unaltered after prolonged strenuous exercise in 20 male marathon runners. These data suggest that the haematological status of these endurance athletes is in fact normal and that the observed shift in the ODC, while providing a physiological advantage during exercise, has no measurable effect on the erythropoietic drive.     

Living high-training low increases hypoxic ventilatory response of well-trained endurance athletes.

This study determined whether "living high-training low" (LHTL)-simulated altitude exposure increased the hypoxic ventilatory response (HVR) in well-trained endurance athletes. Thirty-three cyclists/triathletes were divided into three groups: 20 consecutive nights of hypoxic exposure (LHTLc, n = 12), 20 nights of intermittent hypoxic exposure (four 5-night blocks of hypoxia, each interspersed with 2 nights of normoxia, LHTLi, n = 10), or control (Con, n = 11). LHTLc and LHTLi slept 8-10 h/day overnight in normobaric hypoxia (approximately 2,650 m); Con slept under ambient conditions (600 m). Resting, isocapnic HVR (DeltaVE/DeltaSp(O(2)), where VE is minute ventilation and Sp(O(2)) is blood O(2) saturation) was measured in normoxia before hypoxia (Pre), after 1, 3, 10, and 15 nights of exposure (N1, N3, N10, and N15, respectively), and 2 nights after the exposure night 20 (Post). Before each HVR test, end-tidal PCO(2) (PET(CO(2))) and VE were measured during room air breathing at rest. HVR (l. min(-1). %(-1)) was higher (P < 0.05) in LHTLc than in Con at N1 (0.56 +/- 0.32 vs. 0.28 +/- 0.16), N3 (0.69 +/- 0.30 vs. 0.36 +/- 0.24), N10 (0.79 +/- 0.36 vs. 0.34 +/- 0.14), N15 (1.00 +/- 0.38 vs. 0.36 +/- 0.23), and Post (0.79 +/- 0.37 vs. 0.36 +/- 0.26). HVR at N15 was higher (P < 0.05) in LHTLi (0.67 +/- 0.33) than in Con and in LHTLc than in LHTLi. PET(CO(2)) was depressed in LHTLc and LHTLi compared with Con at all points after hypoxia (P < 0.05). No significant differences were observed for VE at any point. We conclude that LHTL increases HVR in endurance athletes in a time-dependent manner and decreases PET(CO(2)) in normoxia, without change in VE. Thus endurance athletes sleeping in mild hypoxia may experience changes to the respiratory control system.     

Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

While production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 ± 1 y, BMI 25 ± 3 kg/m(2)) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (α-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (Vo(2max)) and maximal power output (P(max)) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P < 0.05) and α-tocopherol (P < 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P < 0.05) and the PL (18.9%, P < 0.05) group in response to training. Vo(2max) and P(max) also increased similarly in both groups (time effect, P < 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P ≤ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.     

Concurrent endurance and explosive type strength training increases activation and fast force production of leg extensor muscles in endurance athletes

The purpose of this experiment was to examine the effects of concurrent endurance and explosive strength training on electromyography (EMG) and force production of leg extensors, sport-specific rapid force production, aerobic capacity, and work economy in cross-country skiers. Nineteen male cross-country skiers were assigned to an experimental group (E, n = 8) or a control group (C, n = 11). The E group trained for 8 weeks with the same total training volume as C, but 27% of endurance training in E was replaced by explosive strength training. The skiers were measured at pre- and post training for concentric and isometric force-time parameters of leg extensors and EMG activity from the vastus lateralis (VL) and medialis (VM) muscles. Sport-specific rapid force production was measured by performing a 30-m double poling test with the maximal velocity (V(30DP)) and sport-specific endurance economy by constant velocity 2-km double poling test (CVDP) and performance (V(2K)) by 2-km maximal double poling test with roller skis on an indoor track. Maximal oxygen uptake (Vo(2)max) was determined during the maximal treadmill walking test with the poles. The early absolute forces (0-100 ms) in the force-time curve in isometric action increased in E by 18 +/- 22% (p < 0.05), with concomitant increases in the average integrated EMG (IEMG) (0-100 ms) of VL by 21 +/- 21% (p < 0.05). These individual changes in the average IEMG of VL correlated with the changes in early force (r = 0.86, p < 0.01) in E. V(30DP) increased in E (1.4 +/- 1.6%) (p < 0.05) but not in C. The V(2K) increased in C by 2.9 +/- 2.8% (p < 0.01) but not significantly in E (5.5 +/- 5.8%, p < 0.1). However, the steady-state oxygen consumption in CVDP decreased in E by 7 +/- 6% (p < 0.05). No significant changes occurred in Vo(2)max either in E or in C. The present concurrent explosive strength and endurance training in endurance athletes produced improvements in explosive force associated with increased rapid activation of trained leg muscles. The training also led to more economical sport-specific performance. The improvements in neuromuscular characteristics and economy were obtained without a decrease in maximal aerobic capacity, although endurance training was reduced by about 20%.     

Potential for strength and endurance training to amplify endurance performance

The impact of adding heavy-resistance training to increase leg-muscle strength was studied in eight cycling- and running-trained subjects who were already at a steady-state level of performance. Strength training was performed 3 days/wk for 10 wk, whereas endurance training remained constant during this phase. After 10 wk, leg strength was increased by an average of 30%, but thigh girth and biopsied vastus lateralis muscle fiber areas (fast and slow twitch) and citrate synthase activities were unchanged. Maximal O2 uptake (VO2max) was also unchanged by heavy-resistance training during cycling (55 ml.kg-1.min-1) and treadmill running (60 ml.kg-1.min-1); however, short-term endurance (4-8 min) was increased by 11 and 13% (P less than 0.05) during cycling and running, respectively. Long-term cycling to exhaustion at 80% VO2max increased from 71 to 85 min (P less than 0.05) after the addition of strength training, whereas long-term running (10 km times) results were inconclusive. These data do not demonstrate any negative performance effects of adding heavy-resistance training to ongoing endurance-training regimens. They indicate that certain types of endurance performance, particularly those requiring fast-twitch fiber recruitment, can be improved by strength-training supplementation.     

Plasticity of response to equal quantities of endurance training separated by non-training in humans

1. 1. The pattern of elevation of several serum biochemical indices (BI) of training stress (creatine kinase, CK; lactate dehydrogenase, LDH; aspartate aminotransferase, AST, Ca²⁺; urate, UR; urea, U; total protein, Prot; cholesterol, C) were measured serially through two extended periods of training, including taper (50 days each) separated by a period of complete non-training (90 days) in two male subjects.

2. 2. The patterns of variation in BI were compared with similar variation in elements of a two compartment model predicting performance from training.

3. 3. These elements arbitrarily described as Fitness [g(t)] and Fatigue [h(t)] were estimated daily from a daily training impulse [w(t)] defined from the duration time and heart rate elevation of an individual in a training session.

4. 4. g(t) and h(t) were used to predict performance [p(t)] which might be expected from the training undertaken. So that: p(t) = k₁g(t) — k₂h(t) where k₁ and k₂ are arbitrary constants.

5. 5. Performance p(t) when iteratively modelled against a Criterion running Performance, Cp(t) measured serially throughout training, over a standard distance, then defines the pattern of variation in the elements g(t) and h(t) (Morton et al., 1990).

6. 6. Hard training for 28 days and a succeeding 22 days of taper in each training period produced a rise and fall in elevated serum enzyme activity, ESEA, (CK, LDH and AST) which mirrored the time-course pattern of h(t), the fatigue element of the dose/response model of training, with a slight phase delay.

7. 7. Thus ESEA was already declining during hard training.

8. 8. During the taper period ESEA declined rapidly to base line. This response was remarkably symmetrical in each, separate training period.

9. 9. The Criterion running performance (CP) declined during hard training and rebounded throughout the taper period reaching an asymptote before beginning to decline again as training fitness [g(t)] was lost, although the fatigue [h(t)] state was now minimal.

10. 10. Serum Prot, U, Ur respectively were also elevated throughout hard training, first following the hypothesized h(t) curve but showing a biphasic response, declining during the latter phase of hard training, and rising again during taper.

11. 11. The symmetry of response of these indices in each period was less evident than the ESEA response. None of the BI patterns measured was in phase with g(t), all, seemingly, reflected the catabolic rather than the anabolic process of hard training.