Biomedical subjects

A X Bigard

Publications and source records attributed to A X Bigard.

At least 19 recordsLinked to original sources

PubMed2001

Effects of resistance training in humans on neck muscle performance, and electromyogram power spectrum changes.

The purpose of this study was to quantify the neuromuscular cervical adaptations to an 8 week strength training programme. Seven healthy men, with no pathological conditions of the neck, performed a lateral flexion isometric resistance-training programme three times a week. The training sessions consisted of one set of ten contractions, each of 6 s duration, at 60% of the predetermined maximal voluntary isometric torque (MVTim) (warm-up) and two sets of eight contractions, each of 6 s duration, at 80% MVTim. The training effects were evaluated in three ways: muscle size, strength and fatigability. The cross-sectional areas (CSA) of the trapezius (TRP) and sternocleidomastoideus (SCM) muscles were determined using a computerised tomographic scanner. Results showed an increase in the CSA of TRP and SCM muscles after training, 8.8% at C5 level and 6.4% at C7 level for SCM muscle and 12.2% at C7 level for TRP muscle. Strength increased significantly under both isometric and isokinetic conditions (35% and 20%, respectively). Muscle fatigability in lateral flexion was quantified during a sustained isometric contraction at 50% of MVTim. The shift of the mean power frequency of the electromyogram power spectrum density function of SCM muscle toward lower frequencies was less after training (14.6% compared to 6.8%). These results indicate the beneficial effect of a strength-training programme which increases neck muscle size and strength during lateral flexion, and decreases the fatigability of the superficial muscles of the neck.

Adult↗

PubMed2001

Diet restriction plays an important role in the alterations of heart mitochondrial function following exposure of young rats to chronic hypoxia.

Male Wistar rats aged 4 weeks, were subjected to hypobaric hypoxia (barometric pressure 505 hPa, PI,O2 106 hPa) or to diet restriction (reproducing the effect of hypoxia-induced anorexia) for 4 weeks. Each group (control, hypoxic, pair-fed, n = 16), was divided into two sub-groups housed individually in either normal cages or cages with running wheels allowing evaluation of voluntary activity (n = 8 each). The skinned-fibre technique was used to evaluate the functional properties of myofibrillar mitochondria from right and left ventricles in situ. The oxidative fibres from the soleus and diaphragm muscles were also investigated for comparison. Analysis of variance did not detect any significant effect of voluntary running activity. With calorie restriction, the maximal respiratory rate (Vmax) in the presence of 1 mM adenosine 5'-diphosphate (ADP) in myocardial fibres fell significantly (by about 25%) but was unchanged in skeletal myocytes. Following hypoxia, Vmax in myocardial fibres increased by 25% compared with the calorie restricted group and in soleus and diaphragm muscle fibres by about 30% compared with control. In myocardial fibres of control rats, creatine (20 mM) increased the sub-maximal respiratory rate by 80% in the presence of 0.1 mM ADP. Under calorie restriction or hypoxia the stimulatory effect was significantly reduced to 34-56%. This alteration was due to a decrease in the apparent Michaelis-Menten constant (Km) of mitochondrial respiration for ADP evaluated in the absence of creatine, while the Km in presence of creatine 20 mM was unchanged. In conclusion, reduced food intake decreased the oxidative capacity (Vmax) and the apparent Km for ADP of mitochondria in both left and right ventricles. Chronic hypoxia per se was responsible for an increase in the oxidative capacity of all oxidative muscles but did not exert significant effects on the control of respiration by ADP and creatine in myocardium.

Adenosine Diphosphate↗

PubMed2001

Response of mitochondrial function to hypothyroidism in normal and regenerated rat skeletal muscle.

Although thyroid hormones induce a well known decrease in muscle oxidative capacity, nothing is known concerning their effects on mitochondrial function and regulation in situ. Similarly, the influence of regeneration process is not completely understood. We investigated the effects of hypothyroidism on mitochondrial function in fast gastrocnemius (GS) and slow soleus (SOL) muscles either intact or having undergone a cycle of degeneration/regeneration (Rg SOL) following a local injection of myotoxin. Thyroid hormone deficiency was induced by thyroidectomy and propylthiouracyl via drinking water. Respiration was measured in muscle fibres permeabilised by saponin in order to assess the oxidative capacity of the muscles and the regulation of mitochondria in situ. Oxidative capacities were 8.9 in SOL, 8.5 in Rg SOL and 5.9 micromol O2/min/g dry weight in GS and decreased by 52, 42 and 39% respectively (P < 0.001) in hypothyroid rats. Moreover, the Km of mitochondrial respiration for the phosphate acceptor ADP exhibited a two-fold decrease in Rg SOL and intact SOL by hypothyroidism (P < 0.01), while mitochondrial creatine kinase activity and sensitivity of mitochondrial respiration to creatine were not altered. The results of this study demonstrate that hypothyroidism markedly altered the sensitivity of mitochondrial respiration to ADP but not to creatine in SOL muscles, suggesting that mitochondrial regulation could be partially controlled by thyroid hormones. On the other hand, mitochondrial function completely recovered following regeneration/degeneration, suggesting that thyroid hormones are not involved in the regeneration process per se.

Animals↗

PubMed2000

Lack of coordinated changes in metabolic enzymes and myosin heavy chain isoforms in regenerated muscles of trained rats.

We investigated training-induced changes in biochemical properties and myosin heavy chain (MHC) composition of regenerated (cardiotoxin-injected) plantaris muscles (PLA) in rats either maintained sedentary (S, n = 9) or endurance trained on a treadmill over a 8-week period (T, n = 7). Both endurance training and regeneration altered the pattern of fast MHC expression. An analysis of the two-way interaction between training and regeneration showed that the relative content of type IIa MHC was affected (P < 0.05). The 140% increase in type IIa MHC observed in regenerated PLA from T rats compared with nontreated muscle of S rats, exceeded the 102% increase resulting from the combination of regeneration alone (26%) and training alone (61%). A similar interaction between training and regeneration was shown for the percentage of fibres expressing either type IIa or type lIb MHC (P < 0.05). In contrast, a significant increase in the citrate synthase (CS) activity was shown in PLA as a result of endurance training, without specific effect of regeneration. Furthermore, training-induced changes in CK and LDH isoenzyme distribution occurred to a similar extent in regenerated and non-treated PLA muscles, and thus did not follow the changes in MHC isoforms. An increase in the mitochondrial CK isozyme activity (mi-CK) was shown in both non-treated and previously degenerated PLA muscles (123 and 117%, P < 0.01, respectively), without specific effect of regeneration. The ratio of mi-CK to CS activity, an estimate of the mitochondrial specific activity of mi-CK was significantly increased by training (P < 0.02) and decreased by regeneration (P < 0.05). Taken together, these data suggest that while training and regeneration have cumulative effects on the pattern of fast MHC expression, the training-induced changes in the energy metabolism shown in mature non-treated myofibres are similar to those observed in regenerated fibres.

Animals↗

PubMed2000

Myosin heavy chain composition of skeletal muscles in young rats growing under hypobaric hypoxia conditions.

This study investigated the effects of voluntary wheel running on the myosin heavy chain (MHC) composition of the soleus (Sol) and plantaris muscles (Pla) in rats developing under hypobaric choronic hypoxia (CH) conditions during 4 wk in comparison with those of control rats maintained under local barometric pressure conditions (C) or rats pair-fed an equivalent quantity of food to that consumed by CH animals (PF). Compared with C animals, sedentary rats subjected to CH conditions showed a significant decrease in type I MHC in Sol (-12%, P < 0.01). Although strongly decreased under hypoxia, spontaneous running activity increased the expression of type I MHC (P < 0.01) so that no difference in the MHC profile of Sol was shown between CH active and C active rats. The MHC distribution in Sol of PF rats was not significantly different from that found in C animals. CH resulted in a significant decrease in type I (P < 0.01) and type IIA (P < 0.005) MHC, concomitant with an increase in type IIB MHC in Pla (P < 0.001), compared with C and PF animals. In contrast to results in Sol muscle, this slow-to-fast shift in the MHC profile was unaffected by spontaneous running activity. These results suggest that running exercise suppresses the hypoxia-induced slow-to-fast transition in the MHC expression in Sol muscles only. The hypoxia-induced decrease in food intake has no major influence on MHC expression in developing rats.

Analysis of Variance↗

PubMed1999

Effects of hindlimb suspension and androgen treatment on testosterone receptors in rat skeletal muscles.

This study tested the specific and combined effects of testosterone treatment and hindlimb suspension (HS) on the properties of steroid receptors in skeletal muscle. Male rats were either administered weekly high doses of testosterone heptylate (10 mg x kg(-1)) or olive oil placebo, and were either tail-suspended or acted as controls. After 3 weeks of treatment, three muscles were excised from each animal, soleus (SOL), extensor digitorum longus (EDL), and plantaris. The results showed that the testosterone treatment was unable to minimise the HS-induced atrophy of skeletal muscle. As expected, HS altered the fibre-type composition of SOL muscles (-33% of type I, +188% and +161% of type IIa and intermediate fibres respectively, P < 0.01). No overall effect of treatment was detected on the fibre-type composition of either slow or fast-twitch muscles. Binding capacity determined by a radiocompetition technique was increased by HS, especially in SOL and EDL muscles (P < 0.01), while HS or steroid treatment decreased the affinity of the steroid receptors. The combination of HS and testosterone administration resulted in a decrease in binding capacity and affinity of steroid receptors in skeletal muscles. Steroid receptors in fast-twitch muscles exhibited a higher affinity than those in slow-twitch muscles, and it is suggested that it is likely that testosterone treatment is more effective in fast-twitch than in slow-twitch muscles. It was concluded that the lack of preventive effect of testosterone treatment on HS-induced SOL muscle atrophy could be explained by both a decrease in steroid sensitivity and the removal of mechanical factors.

Adipose Tissue↗

PubMed1999

Changes in myosin heavy chain profile of mature regenerated muscle with endurance training in rat.

The objective of the present study was to examine the response of fast-twitch muscle to endurance training long after the muscle had regenerated from toxin injury. Seventeen male Wistar rats were randomly assigned to a sedentary (S, n = 10) or a trained group (T, n = 7). Endurance training by treadmill running (5 days week(-1), 30 m min(-1), 7% grade, 2 h day(-1) for 5 weeks) was initiated 5 weeks after myofibre degeneration was induced in the right extensor digitorum longus muscle (EDL) by two injections of 0.2 mL of the unfractionated venom from Naja nigricollis snake. Gel electrophoresis analyses showed that training alone resulted in a 140% increase in type IIX myosin heavy chain (MHC) (P < 0.01) and a slight decrease in type IIB MHC (-14% P < 0.05). Regeneration alone induced an increase in both type IIA and IIX MHC expression (103%, P < 0.05, and 131%, P < 0.01, respectively), and a concomitant decrease in the percentage of type IIB MHC (P < 0.05). The shift from type IIB toward type IIA MHC composition observed in regenerated muscles of T rats resulted not only from an additive, but from a cumulative effect of training and regeneration. Immunohistochemical analysis of MHC content in individual fibres showed similar changes. These data suggest that the impact of endurance training on fast-type MHCs was more marked in mature regenerated muscles than in regenerating ones, and provide evidence of the heightened plasticity of fully regenerated muscles to repeated exercise.

Animals↗

PubMed1998

Muscle unloading induces slow to fast transitions in myofibrillar but not mitochondrial properties. Relevance to skeletal muscle abnormalities in heart failure.

Muscle deconditioning is a common observation in patients with congestive heart failure (CHF), chronic obstructive pulmonary disease, neuromuscular diseases or prolonged bed rest. To gain further insight into metabolic and mechanical properties of deconditioned slow-twitch (soleus) or fast-twitch (EDL) skeletal muscles, we induced experimental muscle deconditioning by hindlimb suspension (HS) in rats for 3 weeks. Cardiac muscle was also studied. Besides profound muscle atrophy, increased proportion of fast type II fibers as well as fast myosin isoenzymes, we found decreased calcium sensitivity of Triton X-100 skinned fiber bundles of soleus muscle directed towards the fast muscle phenotype. Glycolytic enzymes such as hexokinase and pyruvate kinase were increased, and the LDH isoenzyme pattern was clearly shifted from an oxidative to an anaerobic profile. Creatine kinase (CK) and myokinase activities were increased in HS soleus towards EDL values. Moreover, the M-CK mRNA level was greatly increased in soleus, with no change in EDL. However, oxygen consumption rate assessed in situ in saponin skinned fibers (12.5 +/- 0.8 in C and 15.1 +/- 0.9 micromol O2/min/g dw in HS soleus compared to 7.3 +/- 1.3 micromol O2/min/g dw in control EDL), as well as mitochondrial CK (mi-CK) and citrate synthase activities, were preserved in HS soleus. Following deconditioning no change in Km for ADP of mitochondrial respiration, either in the absence (511 +/- 92 in C and 511 +/- 111 microM in HS soleus compared to 9 +/- 4 microM in control EDL) or presence of creatine (88 +/- 10 in C and 95 +/- 16 microM in HS soleus compared to 32 +/- 9 microM in control EDL), was found. The results show that muscle deconditioning induces a biochemical and functional slow to fast phenotype transition in myofibrillar and cytosolic compartments of postural muscle, but not in the mitochondrial compartment, suggesting that these compartments are differently regulated under conditions of decreased activity.

Animals↗

PubMed1998

Nutrient intake of elite sailors during a solitary long-distance offshore race.

The purpose of the present study was to determine the nutritional intake of 11 skippers during the four stages of a solitary long-distance offshore race. Body weight significantly decreased during the race (-1.31 +/- 0.32 kg, range 3.5 to 0.1 kg, p <.01). Total daily energy intake was 18.53 +/- 0.71 MJ x day-1 during the race, and it correlated negatively with the rate duration of each leg. Energy intake during the race was 19% greater than that determined for a subgroup of 5 sailors during a control period 2 months after the race. Nutrient intake expressed as percentage calories of total energy was estimated at 50%, 35%, and 15% for carbohydrate, fat, and protein, respectively. Voluntary fluid intake decreased with increasing race duration (p<.001). Despite high energy intakes, sailors lost body weight during the solitary offshore race. It was not possible to conclude that this change in body weight was related to fluid loss and/or a discrepancy between energy intake and energy expenditure.

Adult↗

PubMed1998

Evaluation of abdominal fat distribution in noninsulin-dependent diabetes mellitus: relationship to insulin resistance.

Accumulation of visceral adipose tissue is associated with metabolic complications such as noninsulin-dependent diabetes mellitus. The aim of this study was to evaluate the effect of abdominal adipose tissue on insulin sensitivity in subjects with noninsulin-dependent diabetes mellitus (NIDDM). Areas of abdominal fat were calculated from axial magnetic resonance images obtained at the level of the umbilicus in 21 men with NIDDM [age, 45.6 +/- 8.3 (+/-SD) yr; body mass index, 29.3 +/- 4.5 kg/m(-2); total body fat (skinfold thickness), 26.8 +/- 5.4%; waist to hip ratio, 0.97 +/- 0.07; duration of diabetes, 59 +/- 47 months; hemoglobin A1c, 8.1 +/- 1.5%]. Insulin sensitivity was evaluated by an insulin tolerance test. The areas of deep abdominal fat and sc abdominal fat were, respectively, 135.3 +/- 55.1 and 211.8 +/- 99.1 cm2. The blood glucose disappearance rate was 2.11 +/- 0.87%/min and was negatively related to deep abdominal fat (r = 0.72; P = 0.0025). In contrast, areas of sc abdominal fat, total body fat, body mass index, and waist to hip ratio were not related to the blood glucose disappearance rate. Plasma triglyceride concentrations averaged 1.8 +/- 0.8 mmol/L and were positively related to deep abdominal fat (r = 0.69; P = 0.0018). We conclude that insulin sensitivity is strongly related to visceral adipose tissue accumulation in NIDDM.

Abdomen↗

PubMed1998

Alterations in muscular performance and orthostatic tolerance during Ramadan.

BACKGROUND: During Ramadan, physiological changes are expected to result from both long-term dietary restriction and partial sleep loss. HYPOTHESIS: We speculated that Ramadan fasting has deleterious effects on muscle performances and on orthostatic tolerance. METHODS: There were 11 senior fighter pilots tested on three occasions during the first week of Ramadan (Beg-R), during the fourth week (End-R) and during a control period, 2 mo after Ramadan (C). Each test session consisted of an assessment of the strength and endurance performances of the knee extensors and elbow flexors and of an analysis of the HR and BP responses to the orthostatic stress imposed by a 80 degrees head-up tilt. RESULTS: Body weight decreased by 2.7% at End-R in comparison with C period (p < 0.01). Maximum isometric strength (MVC) of elbow flexor muscles decreased immediately (by 10-12%; p < 0.05). Muscular endurance at both 35 and 70% MVC were lower at End-R in comparison with C period (-28%, -22%, respectively; p < 0.05). The head-up tilt test at End-R was accompanied by a higher increase in heart response than during orthostasis during C and Beg-R periods, and by a decrease in pulse pressures (p < 0.001). These alterations in responses to the head-up tilt were associated with a fall by about 7% in plasma volume. CONCLUSIONS: These data demonstrate that Ramadan fasting leads to an impairment in muscular performances and to a decrease in orthostatic tolerance. Further studies are needed to verify the impact of these changes on +Gz tolerance.

Adult↗

PubMed1997

Quantitative assessment of degenerative changes in soleus muscle after hindlimb suspension and recovery.

The aim of this study was to quantify the degenerative and regenerative changes in rat soleus muscle resulting from 3-week hindlimb suspension at 45 degrees tilt (HS group, n = 8) and 4-week normal cage recovery (HS-R group, n = 7). Degenerative changes were quantified by microscope examination of muscle cross sections, and the myosin heavy chain (MHC) composition of soleus muscles was studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis. At the end of 3-week hindlimb suspension, histological signs of muscle degenerative changes were detected in soleus muscles. There was a significant variability in the percentage of fibres referred to as degenerating (%dg) in individual animals in the HS group [%dg = 8.41 (SEM 0.5)%, range 4.66%-14.08%]. Moreover, %dg varied significantly along the length of the soleus muscle. The percentage of fibres with internal nuclei was less than %dg in HS-soleus muscles [4.12 (SEM 0.3)%, range 1.24%-8.86%]. In 4-week recovery rats, the greater part of the fibres that were not referred to as normal, retained central nuclei [15.8 (SEM 2.2)%, range 6.2%-21.1%]. A significant increase in the slow isoform of MHG was recorded in the HS-R rats, compared to muscles from age-matched rats (P < 0.01). These results would suggest that a cycle of myofibre degeneration-regeneration occurred during HS and passive recovery, and that the increased accumulation of slow MHC observed in soleus muscles after recovery from HS could be related to the prevalence of newly formed fibres.

Animals↗

PubMed1997

Posture control after prolonged exercise.

The perturbations of equilibrium after prolonged exercise were investigated by dynamic posturography on nine well-trained subjects (four athletes and five triathletes). A sensory organization test, where the platform and visual surround were either stable or referenced to the subject's sway with eyes open or closed, was performed before and after a 25-km run (average time 1 h 44 min) by the nine subjects. In addition, the same test was performed on the five triathletes only, before and after ergocycle exercise of identical duration (i.e. ergocycle time = running time). The results showed that the ability to maintain postural stability during conflicting sensory conditions decreased after exercise, with some differences depending on the kind of exercise. Sensory analysis revealed that the subjects made less effective use of vestibular inputs after running than after cycling (P < 0.05). Adaptation to prolonged stimulation of proprioceptive, vestibular and visual inputs had probably occurred in the integrating centres during exercise. This adaptation was maintained during the recovery period and could explain the postexercise balance disorders. Other mechanisms such as impairment of motor efferents or haemodynamic changes should not be excluded.

Adult↗

PubMed1997

Muscle damage induced by running training during recovery from hindlimb suspension: the effect of dantrolene sodium.

We examined the extent of morphological alterations and the myosin heavy chain (MHC) distribution in the rat soleus muscle after a 4-week period of spontaneous recovery or retraining after hindlimb suspension (HS). Moreover, we tested the hypothesis that dantrolene sodium, which affects the flux of calcium over the sarcoplasmic reticulum membrane, was able to attenuate muscle damage. Three groups of rats were submitted to 3 weeks of HS, followed by either 4 weeks of unrestricted cage activity (HC, n = 7), or running training for the same period and were compared to age-matched animals (C, n = 8). Trained rats were treated with either placebo or dantrolene sodium (HTP, HTD, n = 8 each, respectively). Four weeks after HS recovery, the percentage of myofibres with internal nuclei (%in) was determined by histological staining with hematoxylin and eosin. %in was affected by the individual rat (P < 0.001), and was higher in the mid-belly region of the muscle (P < 0.05). Muscle damage, as estimated by %in, was more extensive in trained rats (i.e. HTP and HTD) than in HC animals (23% and 12%, respectively). Moreover, dantrolene sodium tended to exert a protective effect on training-induced muscle injury. A 12% increase in type I MHC was observed in both HTP and HTD rats, in comparison with group C animals (P < 0.001). The relative proportion of type-I MHC was inversely correlated with %in (r = -0.65, P < 0.001). Running recovery led to an increased citrate synthase activity in comparison with that of C or HC rats. In conclusion, the present findings demonstrate that running recovery from HS increases the incidence of muscle damage, and that dantrolene sodium administration has only limited protective effects against exercise-induced muscle injury.

Animals↗

PubMed1997

Myosin heavy chain composition of regenerated soleus muscles during hindlimb suspension.

The aim of this study was to determine the MHC profile of regenerated soleus muscles in control (C, n = 8) and hindlimb suspended rats (HS, n = 8). After muscle degeneration was induced by injection of snake venom containing notexin, male rats were either tail suspended for 21 days or submitted to normal weight-bearing activity. Separation and detection of MHCs by sodium dodecyl sulphate-polyarcylamide gel electrophoresis (SDS-PAGE) showed that regenerated soleus muscles from C rats contained only type I and type IIa MHCs. The relative amount of type I MHC was higher in regenerated (93.9 +/- 1.7%) than in untreated muscles (86.5 +/- 2.3%)(P < 0.01). In the HS group, the immunohistochemical analysis showed that the majority of regenerated myofibres reacted positively with the antibody against fast MHCs. SDS-PAGE analysis demonstrated that HS resulted in a shift toward faster MHCs in both intact and regenerated myofibres. Regenerated soleus muscle from HS rats contained approximately 34% type IIa MHC, approximately 37% type IIx/d MHC and approximately 18% type IIb MHC, when type I MHC contributed to only approximately 12% of total myosin. The proportions of fast MHC isoforms in regenerated muscles were higher than those recorded in untreated muscles. Collectively, these results suggest that the shift in the MHC profile associated with hindlimb unweighting in adult undamaged soleus muscles is also related to the heterogeneity of early myoblasts.

Animals↗

PubMed1997

Combined effects of caloric restriction and branched-chain amino acid supplementation on body composition and exercise performance in elite wrestlers.

Twenty-five competitive wrestlers restricted their caloric intake (28 kcal.kg-1.day-1) for 19 days, using a hypocaloric control (hC, n = 6), hypocaloric high-protein (hHP, n = 7), hypocaloric high-branched-chain amino acid (hBCAA, n = 6), hypocaloric low-protein (hLP, n = 6) diet to determine the effects of caloric restriction on body composition and performances versus control diet (C, n = 6). Anthropometric parameters (weight, percent body fat) and adipose tissue (AT) distribution measured by magnetic resonance imaging (MRI) obtained before and after diet, were compared. A significant highest body weight loss (-4 kg, p < 0.05) and decrease in the percent of body fat (-17.3%, p < 0.05) were observed for subjects of the hBCAA group. Subjects of the hBCAA group exhibited a significant reduction (-34.4%, p < 0.05) in abdominal visceral adipose tissue (VAT). There was no change in aerobic (VO2max) (p > 0.75) and anaerobic capacities (Wingate test) (p > 0.81), and in muscular strength (p > 0.82). We conclude that under our experimental conditions, the combination of moderate energy restriction and BCAA supplementation induced significant and preferential losses of VAT, and allowed maintainance of a high level of performance.

Amino Acids, Branched-Chain↗

PubMed1997

Administration of a GABAB agonist baclofen before running to exhaustion in the rat: effects on performance and on some indicators of fatigue.

The present study was designed to examine the effects of administration of a GABAergic agonist (Baclofen) on run-time to exhaustion in trained and untrained rats, and on some indicators of fatigue. Run-time to exhaustion on a treadmill set at a speed of 25 m.min-1 was significantly increased in both untrained (p < 0.01) and trained rats (p < 0.005) administered with baclofen one hour before the exercise. The animals who had run the longest time displayed the lowest concentrations of liver and muscle glycogen, and a decrease in plasma glucose concentrations (p < 0.05). The results of this investigation suggest that fatigue during prolonged exercise can be influenced by pharmacological administration of a GABAergic agonist. Indicators of fatigue such as glycemia, liver and muscular glycogen are not the limiting factors of performance and central mechanisms play a key role at exhaustion.

Analysis of Variance↗

PubMed1997

Relationships between running mechanics and energy cost of running at the end of a triathlon and a marathon.

The purpose of the present study was to check the increase in energy cost of running at the end of a triathlon and a marathon and to link the decrease in energy cost of running with running kinematic parameters. Seven well-trained triathletes performed 3 experimental trials: a 2 h 15 min triathlon (30 min swimming, 60 min cycling and 45 min treadmill running), a 2 h 15 min marathon where the last 45 min (MR) were run at the same speed as the triathlon run (TR) (i.e. 75% of maximal aerobic speed), and a 45 min isolated run (IR) done at the same speed. Oxygen uptake (VO2), minute ventilation (VE), heart rate (HR), respiratory exchange ratio (RER) and kinematic data were recorded during the 3 exercise runs. The results confirm a higher energy cost during MR compared with TR (+ 3.2%; p <0.05) and IR (+ 11.7%; p <0.01). The triathlon and the marathon were associated with greater weight loss (1.6 +/- 0.02 kg; p <0.01) than the isolated run (0.7 +/- 0.2 kg). After cycling, the mean stride length in TR1 was lower during IR1 and increased at the end of TR. The results show that MR led to decrease in stride length compared with IR. After cycling, the triathletes adopted a more forward leaning posture and the trunk gradient was less marked during the marathon. Moreover, the extension of the knee at foot-strike and the maximal knee angle in non-support phase both increased during MR compared with TR and IR. However, it appears that no single kinematic variable can fully explain the decrease in running efficiency: it seems that running economy during a triathlon and a marathon are linked to global alterations of many different parameters.

Adult↗