Exhaustive Treadmill Running Research Articles

The Effect of Precooling on Exhaustive Performance in the Hot Environment.

BackgroundPre-cooling is known to enhance exercise performance in soccer players. However, little information currently exists regarding precooling effects in Iranian young soccer players.ObjectivesThe aim of this study was to assess the effect of precooling (water immersion) on exhaustive performance in the heat ( temperature = 32 - 34°C, humidity = 50%).Patients and MethodsSixteen young male soccer players from the provincial competitive teams were divided into two equal groups and were randomly assigned to precooling (age = 16.5 ± 1.1 year, height = 171.7 ± 6.4 cm, BMI = 21.5 ± 3.3, VO2max = 50.6 ± 6.9 mL/kg/min) and non-precooling (age = 16.1 ± 1.1 year, height = 170.0 ± 4.7 cm, BMI = 21.3 ± 3.6, VO2max = 50.6 ± 6.8 mL/kg/min) groups. An exhaustive treadmill run test was conducted after warm-up (non-precooling) or warm-up + water immersion (temperature = 22 - 24°C). Oral temperature, plasma lactate and plasma volume were measured at the baseline (fasting state), mid test (immediately after warm up or warm -up + water immersion) and post test (immediately after exhaustive test). Mixed repeated measures analysis of variance and independent t test were used for data analyzing. P < 0.05 was considered significant.ResultsThere were no significant differences between two groups at baseline, mid test and post test regarding oral temperature and plasma lactate. The time to exhaustion was considerably higher in the precooling group compared with the non-precooling group, but the difference was not statistically significant. No significant differences were found between the two groups on measures of the baseline and mid test plasma volume, but post test plasma volume was significantly higher in the precooling group compared to the non-precooling group (P < 0.05).ConclusionsThese results show that precooling effectively attenuates dehydration, but has no positive effect on exhaustion time in the hot environment.

β-glucan reduces exercise-induced stress through downregulation of c-Fos and c-Jun expression in the brains of exhausted rats

Immediate-early genes are involved in acute stress responses in the central nervous system. β-glucan stimulates innate immune defenses, exerts an anti-tumor response and increases resistance to a wide variety of types of infection. To date, the effect of β-glucan on the expression of immediate-early genes under stressful conditions has not been elucidated. In the present study, the effects of β-glucan on the expression of the oncogenes c-Fos and c-Jun in the hypothalamus, dentate gyrus and dorsal raphe in rats following exhaustive treadmill running were investigated. Male Sprague Dawley rats were randomly divided into five groups (n=10 in each group) as follows: Control, exercise, exercise and 50 mg/kg β-glucan treatment, exercise and 100 mg/kg β-glucan treatment, and exercise and 200 mg/kg β-glucan treatment. Rats in the β-glucan‑treated groups were administered β-glucan at the respective dose once per day for seven days. Rats in the exercise groups performed treadmill running once per day for six days. On the seventh day of the experiment, the time to exhaustion in response to treadmill running was determined for the exercise groups. The expression of c-Fos and c-Jun in the hypothalamus, dorsal raphe and hippocampus was enhanced by exhaustive treadmill running. Administration of β-glucan resulted in an increase in the time to exhaustion and the suppression of the exercise-induced increment in c-Fos and c-Jun expression. In conclusion, β-glucan may exert an alleviating effect on exercise-induced stress through the suppression of c-Fos and c-Jun expression in the brains of exhausted rats.

Cryotherapy suppresses tendon inflammation in an animal model

Cryotherapy (or cold treatment) has been a popular treatment to relieve pain caused by injuries to tissues such as tendons. However, the exact mechanisms behind the beneficial effects of cryotherapy in tendons remain largely unclear. As prostaglandin E2 (PGE2) is known to be a major mediator of acute inflammation in tissues, which is related to tissue pain, we hypothesized that the beneficial effects of cryotherapy in tendons are mediated by downregulation of PGE2 levels. To test this hypothesis, we applied cold treatment to mouse patellar and Achilles tendons using two animal models: exhaustive mouse treadmill running and acute mouse tendon injury by needle penetration. We then measured the levels of PGE2 and protein expression levels of COX-2, an enzyme responsible for PGE2 production in tissues, under both experimental conditions. We found that treadmill running increased PGE2 levels in both patellar and Achilles tendons compared to control mice without running. Cold treatment for 30 min after treadmill running was sufficient to reduce PGE2 levels to near baseline control levels in both tendons. An extension of cold treatment to 60 min resulted only in a marginal decrease in patellar tendons, but a marked decrease in Achilles tendons. Moreover, COX-2 protein levels in both tendons were also lowered by cold treatment, suggesting that the reduction of PGE2 levels in tendons by cold treatment is at least in part due to the decreased COX-2 expression. Similarly, in the acutely injured tendons, 30 min of cold treatment after needle penetration reduced PGE2 levels when compared to the controls at room temperature (22°C). This decrease was sustained up to at least 3 h after the administration of cryotherapy. Given that PGE2 is a known pain sensitiser, the results of this study suggest that the ability of cold treatment to reduce pain may be attributable to its ability to decrease PGE2 production in tendons.

Changes in leg spring behaviour, plantar loading and foot mobility magnitude induced by an exhaustive treadmill run in adolescent middle-distance runners

This study aimed to determine adjustments in spring-mass model characteristics, plantar loading and foot mobility induced by an exhaustive run. Within-participants repeated measures. Eleven highly-trained adolescent middle-distance runners ran to exhaustion on a treadmill at a constant velocity corresponding to 95% of velocity associated with VO₂max (17.8 ± 1.4 kmh(-1), time to exhaustion=8.8 ± 3.4 min). Contact time obtained from plantar pressure sensors was used to estimate spring-mass model characteristics, which were recorded (during 30 s) 1 min after the start and prior to exhaustion using pressure insoles. Foot mobility magnitude (a composite measure of vertical and medial-lateral mobility of the midfoot) was measured before and after the run. Mean contact area (foot to ground), contact time, peak vertical ground reaction force, centre of mass vertical displacement and leg compression increased significantly with fatigue, while flight time, leg stiffness and mean pressure decreased. Leg stiffness decreased because leg compression increased to a larger extent than peak vertical ground reaction forces. Step length, step frequency and foot mobility magnitude did not change at exhaustion. The stride pattern of adolescents when running on a treadmill at high constant velocity deteriorates near exhaustion, as evidenced by impaired leg-spring behaviour (leg stiffness) and altered plantar loading.

Protective Effect of Spirulina against Cell DNA Damage and Oxidative Stress Induced by Exhaustive Exercise

The aim of the present study was to observe the effect of Spirulina supplementation on DNA damage in mice blood cell and blood redox status after acute exercise. 40 male Kunming mice was randomly assigned into four groups: Control group (CG), exercise group without Spirulina supplementation (EG), Spirulina supplementation group without exercise (SG) and Spirulina supplementation group with exercise (SEG). The exercise fatigue model was built up for mice through the protocol of repeated exhaustive treadmill running for seven days and the single cell gel electrophoresis (SCGE) was used to detect the DNA damage of blood cells in different groups. Blood samples were drawn from different groups and the changes of SOD and GSH which stand for anti-oxidative level in plasma. Also, Malondialdehyde (MDA), a marker of lipid peroxidation, was measured in the plasma of mice.This studies showed that the DNA damage of blood cell in SEG group was significantly lower than that of EG group (P<0.01) and there was no statical difference between CG and SG groups. And the level of GSH in SEG group were significantly lower than that of EG group (P<0.01).This results showed that plasma concentrations of malondialdehyde (MDA) were significantly decreased after supplementation with spirulina (P < 0.001). Those results leaded to conclusion that acute exercise induced more free radical to change the level of SOD, GSH and MDA and also occurred more DNA damage. It was suggested that DNA breakage occurs in blood cell after exhaustive exercise as a consequence of oxidative stress and the Spirulina supplementation has obvious protective effect to prevent exercise-induced DNA damage.

IL-15 Is Required for Postexercise Induction of the Pro-Oxidative Mediators PPARδ and SIRT1 in Male Mice

Physical exercise induces transient upregulation of the pro-oxidative mediators peroxisome proliferator-activated receptor-δ (PPARδ), silent information regulator of transcription (sirtuin)-1 (SIRT1), PPARγ coactivator 1α (PGC-1α), and PGC-1β in skeletal muscle. To determine the role of the cytokine IL-15 in acute postexercise induction of these molecules, expression of these factors after a bout of exhaustive treadmill running was examined in the gastrocnemius muscle of untrained control and IL-15-knockout (KO) mice. Circulating IL-15 levels increased transiently in control mice after exercise. Control mice, but not IL-15-KO mice, upregulated muscle PPARδ and SIRT1 protein after exercise, accompanied by a complex pattern of mRNA expression for these factors. However, in exhaustive exercise, control mice ran significantly longer than IL-15-KO mice. Therefore, in a second experiment, mice were limited to a 20-minute run, after which a similar pattern of induction of muscle PPARδ and SIRT1 protein by control mice only was observed. In a separate experiment, IL-15-KO mice injected systemically with recombinant IL-15 upregulated muscle PPARδ and SIRT1 mRNA within 30 minutes and also exhibited increased muscle PPARδ protein levels by 3 hours. After exercise, both control and IL-15-KO mice downregulated IL-15 receptor-α (IL-15Rα) mRNA, whereas IL-15Rα-deficient mice exhibited constitutively elevated circulating IL-15 levels. These observations indicate IL-15 release after exercise is necessary for induction of PPARδ and SIRT1 at the protein level in muscle tissue and suggest that exercise releases IL-15 normally sequestered by the IL-15Rα in the resting state. These findings could be used to develop an IL-15-based strategy to induce many of the metabolic benefits of physical exercise.

ASIC1a opposes exercise induced hyperemia and maximal exercise capacity

Acid Sensing Ion Channel 1a (ASIC1a) is an extracellular proton‐gated, cation‐selective channel in neurons and vascular smooth muscle cells (VSMC). It is unknown if ASIC1a contributes to vascular tone under conditions associated with extracellular acidosis, such as strenuous exercise. During exercise, vessel recruitment and dilation, mediated by the accumulation of extracellular protons, contribute to increases in blood flow to the exercising muscles. To determine if ASIC1a contributes to vascular responses during exercise, we measured femoral vascular conductance (FVC) during a step‐wise electrical stimulation (0.5 – 5.0 Hz at 3V for 60 sec) of the left major hindlimb muscle groups in anesthetized ASIC1a+/+ and ASIC1a−/− mice. Baseline hemodynamic parameters were similar. FVC increased to a greater extent in ASIC1a−/− versus ASIC1a+/+ mice (0.44 ± 0.03 vs. 0.30 ± 0.04 ml×min−1×100g hindlimb mass−1, n=5 each, p=0.0009) with stimulation. The enhanced FVC was associated with a greater peak oxygen (O2) uptake in conscious ASIC1a−/− mice during exhaustive treadmill running (9563 ± 120 vs. 8836 ± 276 ml×kg−1×hr−1, n=6–7, p=0.0082). Differences in peak O2 uptake were not due to differences in absolute or relative lean body mass. Our findings suggest ASIC1a activity may oppose increases in vascular conductance during strenuous exercise thus limiting peak exercise capacity. Supported by NHLBI 51971.

Growth-Hormone Responses to Consecutive Exercise Bouts With Ingestion of Carbohydrate Plus Protein

Endocrine responses to repeated exercise have barely been investigated, and no data are available regarding the mediating influence of nutrition. On 3 occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6 ± 17.9 min). During the intervening 4-hr recovery, participants ingested either 0.8 g sucrose · kg-1 · hr-1 with 0.3 g · kg-1 · hr-1 whey-protein isolate (CHO-PRO), 0.8 g sucrose · kg-1 · hr-1 (CHO), or 1.1 g sucrose · kg-1 · hr-1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth-hormone concentrations increased from 2 ± 1 μg/L to 17 ± 8 μg/L during R1 considered across all treatments (M ± SD; p ≤ .01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19 ± 4 μg/L and 19 ± 5 μg/L, respectively), whereas ingestion of CHO-PRO produced an augmented response (31 ± 4 μg/L; p ≤ .05). Growth-hormone-binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (from 414 ± 202 pmol/L to 577 ± 167 pmol/L; p ≤ .01), as was the case for plasma total testosterone (from 9.3 ± 3.3 nmol/L to 14.7 ± 4.6 nmol/L; p ≤ .01). There was an overall treatment effect for serum cortisol (p ≤ .05), with no specific differences at any given time point but lower concentrations immediately after R2 with CHO-PRO (608 ± 133 nmol/L) than with CHO (796 ± 278 nmol/L) or CHO-CHO (838 ± 134 nmol/L). Ingesting carbohydrate with added whey-protein isolate during short-term recovery from 90 min of treadmill running increases the growth-hormone response to a second exhaustive exercise bout of similar duration.

Effects of synchronous music on treadmill running among elite triathletes

Objectives: Music can provide ergogenic, psychological, and psychophysical benefits during physical activity, especially when movements are performed synchronously with music. The present study developed the train of research on synchronous music and extended it to elite athletes. Design: Repeated-measures laboratory experiment. Method: Elite triathletes ( n = 11) ran in time to self-selected motivational music, a neutral equivalent and a no-music control during submaximal and exhaustive treadmill running. Measured variables were time-to-exhaustion, mood responses, feeling states, RPE, blood lactate concentration, oxygen consumption and running economy. Results: Time-to-exhaustion was 18.1% and 19.7% longer, respectively, when running in time to motivational and neutral music, compared to no music. Mood responses and feeling states were more positive with motivational music compared to either neutral music or no music. RPE was lowest for neutral music and highest for the no-music control. Blood lactate concentrations were lowest for motivational music. Oxygen consumption was lower with music by 1.0%–.7%. Both music conditions were associated with better running economy than the no-music control. Conclusions: Although neutral music did not produce the same level of psychological benefits as motivational music, it proved equally beneficial in terms of time-to-exhaustion and oxygen consumption. In functional terms, the motivational qualities of music may be less important than the prominence of its beat and the degree to which participants are able to synchronise their movements to its tempo. Music provided ergogenic, psychological and physiological benefits in a laboratory study and its judicious use during triathlon training should be considered.

Fatiguing Exercise Increases Complexity of Postural Control: Control Entropy of High-Resolution Accelerometry

We have previously used Control Entropy (CE) analysis of high-resolution accelerometer (HRA) signal to show complexity of gait decreases during exhaustive treadmill running. PURPOSE: To determine if complexity of postural control decreases following fatiguing Wingate exercise using CE of HRA. METHODS: Ten participants (5 M/5 F; 25±3 yr; 169.4±11.7 cm; 79.0±16.9 kg) consented to participation approved by Western Oregon University IRB and completed two trials separated by 2-7 days. Trials consisted of two single-legged balance tests separated by a Wingate anaerobic test (WAnT; PreWant/PostWant), or rest period (PreRest/PostRest). Balance tests consisted of a series of five single-legged stances, separated by 30 s rest, performed while standing on the dominant leg for 15-s with the participant crossing the arms over the chest and flexing the non-dominant knee to 90 degrees. HRA (MicroStrain, VT) were fixed superficial to L3/L4 at the approximate center of mass (COM). Triaxial signals from the HRA were streamed in real time to a base station at a frequency of 625 Hz and then exported to Matlab (Natick, MA) for analysis. COM accelerations were recorded in g's for vertical (VT), medial/lateral (ML), and anterior/posterior (AP). A newly developed statistic (R-test) was applied to group response shapes generated by Karhunen Loeve (KL) analysis modes resulting from Control Entropy (CE) analysis. RESULTS: R-tests showed a significant mean vector difference (p<.05) within conditions, between axes in all cases, except PostWant, indicating the shape of the complexity response was different in these cases. R-test between conditions, within axis, differences were only present in PostWant for AP (p<.05; 2.95 × 10-3) vs. PreWant (2.86× 10-3). T-tests showed a significantly higher overall CE PostWant in VT and ML compared to PreWant and PostRest (p<.0001). PostWant CE was also higher than PostRest in AP (p<.0001). CONCLUSIONS: These data indicate that fatiguing exercise eliminates the differential complexity response of postural control between axes, but increases complexity in all axes compared to the non-fatigued condition. This has implications with regard to the effects of fatigue on strategies of the control system to maintain postural control.

Association of SLC6A4 Gene 5-HTTLPR Polymorphism with Parameters of Simple and Complex Reaction Times and Critical Flicker Frequency Threshold in Athletes during Exhaustive Exercise

The incidence of SLC6A4 gene 5HTTLPR polymorphism alleles was evaluated in 223 male athletes engaged in endurance sports, the results were compared with those in 177 male nonathletes. Association between 5-HTTLPR genotypes and the effect of exhaustive treadmill running on simple and complex visual reactions and critical flicker frequency threshold was studied. We found that the incidence of LL genotype was significantly higher in athletes in comparison to nonathletes; after exercise, the velocity of visual reactions and critical flicker frequency increased; exercise did not change the velocity of complex visual reaction in LL-carriers, and increased it in SS-carriers. We conclude that exhausting treadmill running leads to facilitation sensory information processing in athletes and that SS-carriers are more susceptible to the effect of exhaustive treadmill running than LL-carriers.

The Effect of Training Status on the Metabolic Response of Bone to an Acute Bout of Exhaustive Treadmill Running

Strenuous exercise increases bone resorption but not formation. The effect of improved training status is unknown. Our objective was to examine the metabolic response of bone to strenuous running in recreationally active (RA) and endurance-trained (ET) men. Eleven RA, 10 ET, and 10 control (CON) subjects completed one 8-d trial. On d 4, RA and ET completed an exhaustive treadmill run. Blood was obtained at baseline (BASE), during exercise, during 2 h of recovery, and on four follow-up (FU) days (FU1-FU4). CON rested throughout, providing blood samples at BASE and on FU1-FU4. Markers of bone resorption [C-terminal telopeptide region of collagen type 1 (beta-CTX)] and bone formation [N-terminal propeptides of procollagen type 1 (P1NP) and bone alkaline phosphatase (ALP)], osteoprotegerin (OPG), PTH, albumin-adjusted calcium (ACa), and phosphate (PO4) were measured. There were no significant differences between ET and RA and no changes in CON for any variable. Exercise increased beta-CTX at FU1-FU4 (P<0.001) but had no effect on P1NP or bone ALP. OPG was increased after 20 min of exercise (P<0.001) and remained elevated at FU1 (P<0.001). PTH, ACa, and PO4 were increased throughout exercise (P<0.01). ACa and PO4 remained elevated in the 2 h after exercise (P<0.001), whereas PTH was lower than BASE from 1-2 h after exercise (P<0.001). After acute, exhaustive running, bone resorption but not formation was increased for 4 d in RA and ET men. The increased bone resorption might be related to the increase in PTH, whereas increased OPG might be a compensatory response to increased bone resorption. Training status did not significantly affect the metabolic response of bone to exhaustive running.

Ectopic Catalase Expression in Mitochondria by Adeno-Associated Virus Enhances Exercise Performance in Mice

Oxidative stress is thought to compromise muscle contractility. However, administration of generic antioxidants has failed to convincingly improve performance during exhaustive exercise. One possible explanation may relate to the inability of the supplemented antioxidants to effectively eliminate excessive free radicals at the site of generation. Here, we tested whether delivering catalase to the mitochondria, a site of free radical production in contracting muscle, could improve treadmill performance in C57Bl/6 mice. Recombinant adeno-associated virus serotype-9 (AV.RSV.MCAT) was generated to express a mitochondria-targeted catalase gene. AV.RSV.MCAT was delivered to newborn C57Bl/6 mouse circulation at the dose of 1012 vector genome particles per mouse. Three months later, we observed a ∼2 to 10-fold increase of catalase protein and activity in skeletal muscle and the heart. Subcellular fractionation western blot and double immunofluorescence staining confirmed ectopic catalase expression in the mitochondria. Compared with untreated control mice, absolute running distance and body weight normalized running distance were significantly improved in AV.RSV.MCAT infected mice during exhaustive treadmill running. Interestingly, ex vivo contractility of the extensor digitorum longus muscle was not altered. Taken together, we have demonstrated that forced catalase expression in the mitochondria enhances exercise performance. Our result provides a framework for further elucidating the underlying mechanism. It also raises the hope of applying similar strategies to remove excessive, pathogenic free radicals in certain muscle diseases (such as Duchenne muscular dystrophy) and ameliorate muscle disease.

Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development

This study examined the effect of two different intense exercise training regimens on skeletal muscle ion transport systems, performance, and metabolic response to exercise. Thirteen subjects performed either sprint training [ST; 6-s sprints (n = 6)], or speed endurance training [SET; 30-s runs approximately 130% Vo(2 max), n = 7]. Training in the SET group provoked higher (P < 0.05) plasma K(+) levels and muscle lactate/H(+) accumulation. Only in the SET group was the amount of the Na(+)/H(+) exchanger isoform 1 (31%) and Na(+)-K(+)-ATPase isoform alpha(2) (68%) elevated (P < 0.05) after training. Both groups had higher (P < 0.05) levels of Na(+)-K(+)-ATPase beta(1)-isoform and monocarboxylate transporter 1 (MCT1), but no change in MCT4 and Na(+)-K(+)-ATPase alpha(1)-isoform. Both groups had greater (P < 0.05) accumulation of lactate during exhaustive exercise and higher (P < 0.05) rates of muscle lactate decrease after exercise. The ST group improved (P < 0.05) sprint performance, whereas the SET group elevated (P < 0.05) performance during exhaustive continuous treadmill running. Improvement in the Yo-Yo intermittent recovery test was larger (P < 0.05) in the SET than ST group (29% vs. 10%). Only the SET group had a decrease (P < 0.05) in fatigue index during a repeated sprint test. In conclusion, turnover of lactate/H(+) and K(+) in muscle during exercise does affect the adaptations of some but not all related muscle ion transport proteins with training. Adaptations with training do have an effect on the metabolic response to exercise and specific improvement in work capacity.

Contraction‐induced interleukin‐6 transcription in rat slow‐type muscle is partly dependent on calcineurin activation

The present work aimed at determining whether interleukin-6 (IL-6) produced by skeletal muscle during exercise is related, at least partly, to calcineurin activity. Rats were treated with two specific calcineurin inhibitors, cyclosporin A (CsA) and FK506, or vehicle (Vhl); they were then subjected to exhaustive treadmill running. Modulatory Calcineurin-Interacting Protein-1 (MCIP-1) mRNA levels, a reliable indicator of calcineurin activity, and IL-6 mRNA levels were measured by real-time RT-PCR in soleus muscles, and IL-6 protein concentration was measured in the plasma. Because low carbohydrates availability enhances IL-6 transcription through p38 Mitogen Activated Protein Kinase (MAPK) pathway, muscle glycogen content and glycaemia were measured and p38 MAPK phosphorylation was determined in skeletal muscle by western blotting. As expected, exercise induced an increase in IL-6 (P < 0.01) and MCIP-1 mRNA (P < 0.01) in soleus muscle of Vhl rats, and enhanced p38 phosphorylation and plasmatic IL-6 protein (P < 0.05). Calcineurin inhibition did not affect running time, glycemia or soleus glycogen content. CsA administration totally inhibited the exercise-induced increase in MCIP-1 mRNA (P < 0.01), blunted the IL-6 gene transcription related to muscle activity, and suppressed the changes in IL-6 protein in plasma. In addition to its inhibition of calcineurin activity, FK506 administration totally suppressed the exercise-induced IL-6 gene transcription, likely by an inhibition of p38 activation. Taken together, these results demonstrate that in addition to p38 MAPK, increased calcineurin activity is one of the signalling events involved in IL-6 gene transcription.

Effects of Aging on the Renal Function after Physical Exercise

PURPOSE: The effects of aging on renal function (RF) following exhaustive exercise are unknown. This study was conducted to investigate these effects on 352 healthy subjects after an exhaustive treadmill run. METHODS: The subjects were of both sexes, and ranged in age from 8 to 76 years. Urinary excretion of protein (uTP), blood lactate (bLA), blood pressure(BP) and creatinine clearance (Ccr) were measured as an index of glomerular nitration rate (GFR). RESULTS: Ccr was found to decrease significantly directly after exercise and to recover to its pre-exercise level 30–60 min later. Ccr in males under 25 years of age decreased to 55.3% of the pre-exercise level directly after exercise, while in males 25 to 50 years old and those over 50, Ccr decreased to 68.8% and 86.9%, respectively, of the pre-exercise level. Similar levels of decrease in Ccr were observed in females directly after exercise. The net decrease in Ccr([[Unsupported Character - #8895;]] Ccr) directly after exercise was remarkable in younger subjects, and it was found to decrease with aging. Nevertheless, no difference in [[Unsupported Character - &#8895;]] Ccr was found in subjects from 8 to 40 years of age. NetuTP measured 30 min after exercise also decreased in relation to aging. A significant coefficient of correlation (r=−0.695, p <0.001) was found between [[Unsupported Character -#8895;]] Ccr and maximum heart rate (HRmax). CONCLUSIONS: The present results indicate that the younger the subject, the longer he or she is able to run before reaching exhaustion. A remarkable decrease in Ccr, and increases in BP, bLA and HRmax were induced after exhaustive exercise by younger subjects.

Kinetic Changes with Fatigue and Relationship to Injury in Female Runners

This research examined how ground reaction forces (GRF) changed with fatigue induced by an exhaustive treadmill run in female runners. A separate retrospective and prospective analysis correlated initial magnitude of GRF and fatigue-induced changes in GRF with lower-extremity injury. Ninety adult female runners had vertical GRF measured before and after an exhaustive treadmill run. Subjects initially were questioned about previous running injuries, and were contacted during the following year and asked to report any additional running injuries. Fatigue induced by the exhaustive treadmill run resulted in decreased impact peak and loading rates in all runners by an average of 6 and 11%, respectively. The changes in GRF were attributed to altered running cadence, step length, and lower-extremity joint kinematics. It is unclear whether these changes were attempts by the runners to minimize impact forces and protect against injury, or represented a fatigue-induced loss of optimal performance capabilities. An interaction between injury in the previous year and change in impact loading rate with fatigue was observed, suggesting previously injured runners are exposed to relatively higher impact forces over time. Habitual female runners appear to adapt their running style with fatigue, resulting in altered GRF. Changes in GRF with fatigue may be associated with lower-extremity running injuries.

American ginseng supplementation attenuates creatine kinase level induced by submaximal exercise in human beings

To investigate whether American ginseng (AG, Panax quinquefolium) supplementation was able to improve endurance exercise performance. Thirteen physically active male college students were divided into two groups (AG or placebo) and received supplementation for 4 wk, before the exhaustive running exercise. Treadmill speed was increased to a pace equivalent to 80% VO2max of the subject. A 4-wk washout period followed before the subjects crossed over and received the alternate supplement for the next 4 wk. They then completed a second exhaustive running exercise. The physiological variables that were examined included time to exhaustion and oxygen pulse. Moreover, the plasma creatine kinase (CK) and lactate were measured prior to the exercise, at 15 and 30 min during exercise, immediately after exercise, and 20, 40, 60, and 120 min after exercise. The major finding of this investigation was that the production plasma CK during the exercise significantly decreased for group AG than for group P. Secondary physiological finding was that 80% VO2max running was not improved over a 4-wk AG supplementation regimen. Supplementation with AG for 4 wk prior to an exhaustive aerobic treadmill running reduced the leakage of CK during exercise, but did not enhance aerobic work capacity. The reduction of plasma CK may be due to the fact that AG is effective for the decrease of skeletal muscle cell membrane damage, induced by exercise during the high-intensity treadmill run.

The V?O2 response for an exhaustive treadmill run at 800-m pace: a breath-by-breath analysis

Recent research in which data were averaged over 10 or 30 s suggests that the VO(2) response of aerobically fit individuals plateaus below VO(2 max) in an exhaustive square-wave run lasting approximately 2 min. To investigate this phenomenon we examined the breath-by-breath VO(2) response of trained runners to an exhaustive treadmill run at 800 m pace. Eight male competitive runners completed two treadmill tests on separate days: a ramp test to exhaustion and an exhaustive square-wave run at 800-m pace. For the ramp test, the breath-by-breath data were smoothed with a 15-s moving average and the highest of the smoothed values was taken as VO(2 peak) [mean (SD): 68.9 (5.6) ml kg(-1) min(-1)]. For the square-wave, the breath-by-breath data were interpolated to give one value per second and modelled using a monoexponential function. Following a delay of 11.2 (1.5) s, VO(2) increased quickly [phase-2 time constant of 10.7 (2.7) s] towards an asymptote that represented just 85 (6)% of VO(2 peak) from the ramp test. Expressed in ml kg(-1) min(-1), this asymptote was independent of VO(2 peak) (r=0.04, P=0.94). However, as a percentage of VO(2 peak) it was negatively correlated with VO(2 peak) itself (r=-0.96, P<0.001). It is concluded that in an exhaustive square-wave treadmill run lasting approximately 2 min the VO(2) of aerobically fit runners increases quickly to plateau at a level that is lower than, but independent of, VO(2max).

An Examination of the Relationship Among Three Indirect Tests of Anaerobic Threshold

0295 Presently, the most accurate method of determining anaerobic threshold is through direct measurement of blood lactate. This method can be both difficult and expensive. There have been several tests developed with the intention of estimating anaerobic threshold indirectly through analysis of an individual's power output as measured in watts. The Wingate cycle test has become the most widely used and accepted form of standardized indirect anaerobic testing. Yet, the cycling action of the Wingate test may not be conducive to best-effort results for those athletes whose main mode of movement is a running motion. It has been well established that muscles adapt to the specific patterns of movement that are employed during training. Therefore, an accurate noninvasive test of anaerobic threshold should utilize the same muscle recruitment patterns as the athlete's training regimen. PURPOSE: To determine the relationship among the Wingate 30-second cycle test (WAnT) and 2 running-based anaerobic tests: an exhaustive treadmill run (TR) of 8mph with an incline gradient of 20%, and a repeated sprint test (RST) consisting of six 35-meter non-continuous sprints. METHODS: Twenty-four male (78.6−± 8.1kg) and fourteen female (63.2 ± 4.9kg) anaerobically trained collegiate track and field athletes participated in this study. Correlation coefficients were calculated to distinguish relationships among anaerobic estimates. Statistical significance was set at p≤0.01. RESULTS: significant associations were established between the following: WAnT vs. TR (r = 0.705), WAnT vsFIRST (r = 0.760), and TR vsFIRST (r = 0.891). CONCLUSION: The TR or RST tests are feasible alternatives for coaches or athletes wishing to test anaerobic threshold in a manner consistent with the running specific motion utilized in training.