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At least 973 records · Page 54Linked to original sources

PubMed1999

High-speed running performance is largely unaffected by hypoxic reductions in aerobic power.

We tested the importance of aerobic metabolism to human running speed directly by altering inspired oxygen concentrations and comparing the maximal speeds attained at different rates of oxygen uptake. Under both normoxic (20.93% O2) and hypoxic (13.00% O2) conditions, four fit adult men completed 15 all-out sprints lasting from 15 to 180 s as well as progressive, discontinuous treadmill tests to determine maximal oxygen uptake and the metabolic cost of steady-state running. Maximal aerobic power was lower by 30% (1.00 +/- 0.15 vs. 0.77 +/- 0.12 ml O2. kg-1. s-1) and sprinting rates of oxygen uptake by 12-25% under hypoxic vs. normoxic conditions while the metabolic cost of submaximal running was the same. Despite reductions in the aerobic energy available for sprinting under hypoxic conditions, our subjects were able to run just as fast for sprints of up to 60 s and nearly as fast for sprints of up to 120 s. This was possible because rates of anaerobic energy release, estimated from oxygen deficits, increased by as much as 18%, and thus compensated for the reductions in aerobic power. We conclude that maximal metabolic power outputs during sprinting are not limited by rates of anaerobic metabolism and that human speed is largely independent of aerobic power during all-out runs of 60 s or less.

Adult↗

PubMed2000

Oxygen uptake kinetics in treadmill running and cycle ergometry: a comparison.

The purpose of the present study was to comprehensively examine oxygen consumption (VO(2)) kinetics during running and cycling through mathematical modeling of the breath-by-breath gas exchange responses to moderate and heavy exercise. After determination of the lactate threshold (LT) and maximal oxygen consumption (VO(2 max)) in both cycling and running exercise, seven subjects (age 26.6 +/- 5.1 yr) completed a series of "square-wave" rest-to-exercise transitions at running speeds and cycling power outputs that corresponded to 80% LT and 25, 50, and 75%Delta (Delta being the difference between LT and VO(2 max)). VO(2) responses were fit with either a two- ( LT) exponential model. The parameters of the VO(2) kinetic response were similar between exercise modes, except for the VO(2) slow component, which was significantly (P < 0.05) greater for cycling than for running at 50 and 75%Delta (334 +/- 183 and 430 +/- 159 ml/min vs. 205 +/- 84 and 302 +/- 154 ml/min, respectively). We speculate that the differences between the modes are related to the higher intramuscular tension development in heavy cycle exercise and the higher eccentric exercise component in running. This may cause a relatively greater recruitment of the less efficient type II muscle fibers in cycling.

Adult↗

PubMed2000

Effect of endurance training on oxygen uptake kinetics during treadmill running.

The purpose of this study was to examine the effect of endurance training on oxygen uptake (VO(2)) kinetics during moderate [below the lactate threshold (LT)] and heavy (above LT) treadmill running. Twenty-three healthy physical education students undertook 6 wk of endurance training that involved continuous and interval running training 3-5 days per week for 20-30 min per session. Before and after the training program, the subjects performed an incremental treadmill test to exhaustion for determination of the LT and the VO(2 max) and a series of 6-min square-wave transitions from rest to running speeds calculated to require 80% of the LT and 50% of the difference between LT and maximal VO(2). The training program caused small (3-4%) but significant increases in LT and maximal VO(2) (P<0.05). The VO(2) kinetics for moderate exercise were not significantly affected by training. For heavy exercise, the time constant and amplitude of the fast component were not significantly affected by training, but the amplitude of the VO(2) slow component was significantly reduced from 321+/-32 to 217+/-23 ml/min (P<0.05). The reduction in the slow component was not significantly correlated to the reduction in blood lactate concentration (r = 0. 39). Although the reduction in the slow component was significantly related to the reduction in minute ventilation (r = 0.46; P<0.05), it was calculated that only 9-14% of the slow component could be attributed to the change in minute ventilation. We conclude that the VO(2) slow component during treadmill running can be attenuated with a short-term program of endurance running training.

Adult↗

PubMed2001

Ambulatory estimates of maximal aerobic power from foot -ground contact times and heart rates in running humans.

Seeking to develop a simple ambulatory test of maximal aerobic power (VO(2 max)), we hypothesized that the ratio of inverse foot-ground contact time (1/t(c)) to heart rate (HR) during steady-speed running would accurately predict VO(2 max). Given the direct relationship between 1/t(c) and mass-specific O(2) uptake during running, the ratio 1/t(c). HR should reflect mass-specific O(2) pulse and, in turn, aerobic power. We divided 36 volunteers into matched experimental and validation groups. VO(2 max) was determined by a treadmill test to volitional fatigue. Ambulatory monitors on the shoe and chest recorded foot-ground contact time (t(c)) and steady-state HR, respectively, at a series of submaximal running speeds. In the experimental group, aerobic fitness index (1/t(c). HR) was nearly constant across running speed and correlated with VO(2 max) (r = 0.90). The regression equation derived from data from the experimental group predicted VO(2 max) from the 1/t(c). HR values in the validation group within 8.3% and 4.7 ml O(2) x kg(-1) x min(-1) (r = 0.84) of measured values. We conclude that simultaneous measurements of foot-ground constant times and heart rates during level running at a freely chosen constant speed can provide accurate estimates of maximal aerobic power.

Acceleration↗

PubMed2001

Effect of carbohydrate ingestion on metabolism during running and cycling.

The effects of carbohydrate or water ingestion on metabolism were investigated in seven male subjects during two running and two cycling trials lasting 60 min at individual lactate threshold using indirect calorimetry, U-14C-labeled tracer-derived measures of the rates of oxidation of plasma glucose, and direct determination of mixed muscle glycogen content from the vastus lateralis before and after exercise. Subjects ingested 8 ml/kg body mass of either a 6.4% carbohydrate-electrolyte solution (CHO) or water 10 min before exercise and an additional 2 ml/kg body mass of the same fluid after 20 and 40 min of exercise. Plasma glucose oxidation was greater with CHO than with water during both running (65 +/- 20 vs. 42 +/- 16 g/h; P < 0.01) and cycling (57 +/- 16 vs. 35 +/- 12 g/h; P < 0.01). Accordingly, the contribution from plasma glucose oxidation to total carbohydrate oxidation was greater during both running (33 +/- 4 vs. 23 +/- 3%; P < 0.01) and cycling (36 +/- 5 vs. 22 +/- 3%; P < 0.01) with CHO ingestion. However, muscle glycogen utilization was not reduced by the ingestion of CHO compared with water during either running (112 +/- 32 vs. 141 +/- 34 mmol/kg dry mass) or cycling (227 +/- 36 vs. 216 +/- 39 mmol/kg dry mass). We conclude that, compared with water, 1) the ingestion of carbohydrate during running and cycling enhanced the contribution of plasma glucose oxidation to total carbohydrate oxidation but 2) did not attenuate mixed muscle glycogen utilization during 1 h of continuous submaximal exercise at individual lactate threshold.

Adult↗

PubMed2004

Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle.

To utilize the rat spinotrapezius muscle as a model to investigate the microcirculatory consequences of exercise training, it is necessary to design an exercise protocol that recruits this muscle. There is evidence that the spinotrapezius is derecruited during standard treadmill exercise protocols performed on the uphill treadmill (i.e., 6 degrees incline). This investigation tested the hypothesis that downhill running would effectively recruit the spinotrapezius muscle as assessed by the presence of an exercise hyperemia response. We used radioactive 15-microm microspheres to determine blood flows in the spinotrapezius and selected hindlimb muscles of female Sprague-Dawley rats at rest and during downhill (i.e., -14 degrees incline; 331 +/- 5 g body wt, n = 7) and level (i.e., 0 degrees incline; 320 +/- 11 g body wt, n = 5) running at 30 m/min. Both level and downhill exercise increased blood flow to all hindlimb muscles (P < 0.01). However, in marked contrast to the absence of a hyperemic response to level running, blood flow to the spinotrapezius muscle increased from 26 +/- 6 ml.min(-1).100 g(-1) at rest to 69 +/- 8 ml.min(-1).100 g(-1) during downhill running (P < 0.01). These findings indicate that downhill running represents an exercise paradigm that recruits the spinotrapezius muscle and thereby constitutes a tenable physiological model for investigating the adaptations induced by exercise training (i.e., the mechanisms of altered microcirculatory control by transmission light microscopy).

Adaptation, Physiological↗

PubMed2005

Transcriptional profiling in mouse skeletal muscle following a single bout of voluntary running: evidence of increased cell proliferation.

Skeletal muscle undergoes adaptation following repetitive bouts of exercise. We hypothesize that transcriptional reprogramming and cellular remodeling start in the early phase of long-term training and play an important role in skeletal muscle adaptation. The aim of this study was to define the global mRNA expression in mouse plantaris muscle during (run for 3 and 12 h) and after (3, 6, 12, and 24 h postexercise) a single bout of voluntary running and compare it with that after long-term training (4 wk of running). Among 15,832 gene elements surveyed in a high-density cDNA microarray analysis, 900 showed more than twofold changes at one or more time points. K-means clustering and cumulative hypergeometric probability distribution analyses revealed a significant enrichment of genes involved in defense, cell cycle, cell adhesion and motility, signal transduction, and apoptosis, with induced expression patterns sharing similar patterns with that of peroxisome proliferator activator receptor-gamma coactivator-1alpha and vascular endothelial growth factor A. We focused on the finding of a delayed (at 24 h postexercise) induction of mRNA expression of cell cycle genes origin recognition complex 1, cyclin A2, and cell division 2 homolog A (Schizoccharomyces pombe) and confirmed increased cell proliferation by in vivo 5-bromo-2'-deoxyuridine labeling following voluntary running. X-ray irradiation of the hindlimb significantly diminished exercise-induced 5-bromo-2'-deoxyuridine incorporation. These findings suggest that a single bout of voluntary running activates the transcriptional network and promotes adaptive processes in skeletal muscle, including cell proliferation.

Animals↗

PubMed2003

Improved running economy in elite runners after 20 days of simulated moderate-altitude exposure.

To investigate the effect of altitude exposure on running economy (RE), 22 elite distance runners [maximal O(2) consumption (Vo(2)) 72.8 +/- 4.4 ml x kg(-1) x min(-1); training volume 128 +/- 27 km/wk], who were homogenous for maximal Vo(2) and training, were assigned to one of three groups: live high (simulated altitude of 2,000-3,100 m)-train low (LHTL; natural altitude of 600 m), live moderate-train moderate (LMTM; natural altitude of 1,500-2,000 m), or live low-train low (LLTL; natural altitude of 600 m) for a period of 20 days. RE was assessed during three submaximal treadmill runs at 14, 16, and 18 km/h before and at the completion of each intervention. Vo(2), minute ventilation (Ve), respiratory exchange ratio, heart rate, and blood lactate concentration were determined during the final 60 s of each run, whereas hemoglobin mass (Hb(mass)) was measured on a separate occasion. All testing was performed under normoxic conditions at approximately 600 m. Vo(2) (l/min) averaged across the three submaximal running speeds was 3.3% lower (P = 0.005) after LHTL compared with either LMTM or LLTL. Ve, respiratory exchange ratio, heart rate, and Hb(mass) were not significantly different after the three interventions. There was no evidence of an increase in lactate concentration after the LHTL intervention, suggesting that the lower aerobic cost of running was not attributable to an increased anaerobic energy contribution. Furthermore, the improved RE could not be explained by a decrease in Ve or by preferential use of carbohydrate as a metabolic substrate, nor was it related to any change in Hb(mass). We conclude that 20 days of LHTL at simulated altitude improved the RE of elite distance runners.

Acclimatization↗

PubMed2001

Artificial selection for intrinsic aerobic endurance running capacity in rats.

Artificial selection for intrinsic aerobic endurance running capacity was started using genetically heterogeneous N:NIH stock of rats as a founder population (n = 168). Selection for low and high capacity was based upon distance run to exhaustion on a motorized treadmill using a velocity-ramped running protocol. The starting velocity was 10 m/min and was increased by 1 m/min every 2 min (slope was constant at 15 degrees ). At each generation, within-family selection was practiced using 13 families for both the low and high lines. A rotational breeding paradigm maintained the coefficient of inbreeding at less than 1% per generation. On average the founder population ran to exhaustion in 355 +/- 11 m. Six generations of selection produced lines that differed in running capacity by 171%, with most of the change occurring in the high line. At generation 6 the low line ran 310 +/- 8 m and the high line 839 +/- 21 m at exhaustion. Selection for running capacity produced changes in body weight as a correlated trait. By generation 6, the low-line females were 20% heavier than the high-line females, and the low-line males were 16% heavier than the high-line males.

Animals↗

PubMed2006

[Running and its influence on smoking habits].

OBJECTIVE: To investigate whether running influences smoking habits. DESIGN: Study of cases and controls, with 1:1 pairing. Retrospective longitudinal observational study. SETTING: Primary care. City of Toledo, Spain. PARTICIPANTS CASES: 48 healthy volunteer runners of 47+/-7.8 years of age. CONTROLS: 48 healthy subjects, paired by gender and year of birth, chosen at random from the medical list assigned to the medical researcher. PRINCIPAL MEASUREMENTS: Smoking habits and alcohol consumption in grams per week using a questionnaire, weight, height, blood pressure, and heart rate at rest. The odds ratio (OR) was obtained on the proportion of subjects who smoked or smoked at some time, those who continued smoking and the probabilities of giving up tobacco in each group. RESULTS: The OR of the proportion of subjects who smoked or had smoked between the groups of runners (54.2%) and controls (70.9%) was 0.486 (95% confidence interval [CI], 0.205-1.149; chi(2)=2.8; P=.093). The OR for continuing the habit between groups of runners (8.4%) and controls (41.7%) was 0.127 (95% CI, 0.035-0.456; chi(2)=14.0; P=.0002). In the group of runners, 45.8% had stopped smoking, as well as 31.2% of the controls (OR=7.85; 95% CI, 1.89-32.52; chi(2)=11.8; P=.0007); 50% of the runners who smoked had given it up since starting to run and 76.9% of these had given it up just at the time of starting to run. CONCLUSIONS: There is a negative association between running and tobacco. If a smoker decides to run regularly he/she has high probabilities of giving up smoking and continue to do so.

Adult↗

PubMedDate not supplied

MR imaging of the hip and knee before and after marathon running.

BACKGROUND: Despite its obvious benefits regarding aerobic fitness, the possible deleterious effects of long-distance running remain controversial. The repetitive loading associated with this activity could potentially predispose to the subsequent development of osteoarthritis. Lower extremity malalignment can also result in abnormal joint loading and is another possible contributing factor for premature articular cartilage degeneration. The purpose of this study is to investigate whether external impact loading in marathon runners creates internal stresses on bone and cartilage that are demonstrable on MR images. Participants were separately assessed for static lower extremity alignment, using standard radiographs. METHODS: Six recreational and two semi-professional runners underwent magnetic resonance (MR) imaging of the hip and knee before and after a marathon run using coronal T1-weighted and coronal STIR sequences. RESULTS: The pre-run and post-run scans failed to demonstrate marrow oedema, periosteal stress reactions, or joint effusions in seven runners. One patient who underwent a reconstruction of his anterior cruciate ligament 18 months ago demonstrated a small effusion in the reconstructed knee before and after the race. CONCLUSIONS: Our results suggest that the high impact forces in long-distance running are well tolerated and subsequently do not demonstrate changes on MR images.

Biomechanical Phenomena↗

PubMedDate not supplied

Herniated lumbar disk associated with running. A review of 10 cases.

This paper studies the courses of treatment and recovery in 10 runners with acute back and leg pain. All ran at least 20 miles/week, had pain during or shortly after running, and were diagnosed for herniated lumbar disk for myelogram, electromyogram (EMG), or objective motor weakness and reflex changes. Two or more high-risk factors contributed to the disk syndrome in each runner. These included being 30 to 50 years old (9 runners), being under 72 inches tall (6 runners), having tight joints (6 runners), changing running style (5 runners), and having a previous herniated lumbar disk (3 runners). Early diagnostic problems led to incorrect initial diagnosis in three runners. The conservative treatment program consisted of controlled rest, anti-inflammatory medication, alternative exercises, and a gradual return to running in 6 to 12 weeks. All runners were treated with Williams' exercises. Eight were put in traction as inpatients, and seven were given injections of epidural steroids. Three required laminectomies; two of these resumed active running. The return to sports participation was excellent in this group. Eight returned to active running and one became a marathon bicyclists. Only one runner was unable to return actively to sports.

Adult↗

PubMedDate not supplied

Effect of viscoelastic shoe insoles on vertical impact forces in heel-toe running.

The purposes of this study were: 1) to compare the impact forces in running using running shoes with conventional insoles to the impact forces using running shoes with four different viscoelastic insoles, 2) to discuss possible effects of the viscoelastic insoles on lower leg kinematics, and 3) to explain the force and kinematic results using a mechanical model. Kinetic and kinematic data were collected for 14 subjects running heel-toe at an average speed of 4 m/s. The results showed that the four tested viscoelastic insoles did not differ in variables describing the vertical impact forces (vertical force peak, time of occurrence of vertical force peak, maximum vertical loading rate) compared to the conventional insoles furnished in running shoes. Furthermore, the viscoelastic insoles did not influence kinematic variables of the lower extremities in a systematic way.

Computer Simulation↗

PubMedDate not supplied

The effects of knee brace wear on perceptual and metabolic variables during horizontal treadmill running.

Past research has indicated that runners who wear a Lenox Hill Derotation Brace during treadmill running at 6 mph have an approximate 5% increase in oxygen consumption compared to those who run without the brace. The present study expanded those findings by determining the metabolic and perceptual effects of wearing four commercially available braces while treadmill running at speeds of 6, 7, and 8 mph. The four braces used in this study were the Generation II Poli-Axial Knee Cage, the Orthotech Performer, the CTi Brace, and the Lenox Hill Derotation Brace. Results indicated that the braces caused increases (P less than 0.008) in oxygen consumption, heart rate, and ventilation in the 3% to 8% range compared to running without the brace. Peripheral ratings of perceived exertion were also elevated (P less than 0.001) between 9% and 13%. However, no significant differences were found between the braces. Analysis of covariance indicated the weight of the brace accounted for the increased oxygen consumption during the treadmill runs. We concluded that the braces examined in this study will cause a consistent increase in metabolic cost, which is related to the weight of the braces.

Adolescent↗

PubMed1987

The biomechanics of lower extremity action in distance running.

The role of quantitative biomechanical measurements in the evaluation of the running patient is discussed. Many techniques are now available to provide insight into the external mechanics of lower extremity action during running, and results from such measurements are presented for symptom-free subjects at distance running speeds. Details of stride length, stride time, and foot placement are first presented followed by a discussion of kinematic data, including stick figures, angle-time graphs, and angle-angle diagrams for the sagittal plane motion of the hip, knee, and ankle joints. The measurement of rearfoot motion, as an approximation of coronal plane subtalar joint movements, is also discussed. Results from acceleration, force, and pressure measurements are considered, and the assertion is made that bilateral asymmetry in many of these measures is a fairly common finding. There are, at present, few reports in the literature of the application of biomechanical techniques to the evaluation of patients with running injuries. It is anticipated that there will be rapid developments in this area in the future and that this will provide considerable insight into the etiology, diagnosis, and treatment of running injuries.

Acceleration↗

PubMed2004

Rigorous running increases growth hormone and insulin-like growth factor-I without altering ghrelin.

It has been suggested that ghrelin may play a role in growth hormone (GH) responses to exercise. The present study was designed to determine whether ghrelin, GH, insulin-like growth factor-I (IGF-I), and IGF-binding protein-3 (IGFBP-3) were altered by a progressively intense running protocol. Six well-trained male volunteers completed a progressively intense intermittent exercise trial on a treadmill that included four exercise intensities: 60%, 75%, 90%, and 100% of Vo2max. Blood samples were collected before exercise, after each exercise intensity, and at 15 and 30 mins following the exercise protocol. Subjects also completed a separate control trial at the same time of day that excluded exercise. GH changed significantly over time, and GH area under the curve (AUC) was significantly higher in the exercise trial than the control trial. Area under the curve IGF-I levels for the exercise trial were significantly higher than the control trial. There was no difference in the ghrelin and IGFBP-3 responses to the exercise and control trials. Pearson correlation coefficients revealed significant relationships between ghrelin and both IGF-I and IGFBP-3; however, no relationship between ghrelin and GH was found. In conclusion, intense running produces increases in total IGF-I concentrations, which differs from findings in previous studies using less rigorous running protocols and less frequent blood sampling regimens. Moreover, running exercise that produces substantial increases in GH does not affect peripheral ghrelin levels; however, significant relationships between ghrelin and both IGF-I and IGFBP-3 exist during intense intermittent running and recovery, which warrants further investigation.

Adolescent↗

PubMed1998

Serum leptin levels in male marathon athletes before and after the marathon run.

Leptin is a hormone produced by the adipocytes to regulate food intake and energy expenditure at the hypothalamic level. It is commonly accepted that the main determinants of leptin secretion are the net amount of body fat and the mean size of adipocytes. On the contrary, important vectors of energy flux in the organism, such as food intake and energy expended on exercise, are not thought to be regulators of that secretion. To understand whether leptin is regulated by an acute energy expenditure such as strenuous exercise, 29 male athletes who had trained for marathon running were studied before and after a marathon run and compared with 22 nonobese, age-, sex-, and body mass index (BMI)-matched sedentary controls. Controls and marathon athletes showed no differences in BMI or fat-free mass. Marathon runners showed a strong reduction in total fat mass (6.2 +/- 0.4 kg; 9.1 +/- 0.5% of body fat) compared with controls (12.3 +/- 0.5 kg; 16.1 +/- 0.5% of body fat; P < 0.05). This difference in body composition was paralleled by a mean serum leptin level that in marathonians (2.9 +/- 0.2 micrograms/L) was significantly (P < 0.05) reduced compared with that in controls (5.1 +/- 0.6 micrograms/L). It is remarkable that the ratio of leptin per kg body fat, showed a very good agreement between the two groups, 0.40 +/- 0.04 microgram/L.kg for controls and 0.46 +/- 0.03 microgram/L.kg for marathonians. In the two groups, leptin was correlated with both body weight, BMI, and fat mass (P < 0.001). The marathon trajectory was the standard 42.195 km accomplished in an average time of 3 h, 17 min, 7 s, with a calculated energy expenditure of over 2800 Cal. After the marathon run, a water imbalance occurred, with a significant decrease in body weight and an increase in serum albumin. A significant (P < 0.05) reduction in leptin values was observed after the run (2.6 +/- 0.2 micrograms/L) compared with before (2.9 +/- 0.2 micrograms/L), which was more relevant considering the relative hemoconcentration. In conclusion, 1) compared with sedentary subjects, leptin levels are reduced in male marathon runners in parallel with the relevant reduction in total body fat; 2) expressed as a ratio of leptin per kg body fat, no differences were observed between marathonians and controls; and 3) after an energy expenditure of 2800 Cal in the marathon run, a reduction in leptin levels occurred. Strong changes in energy expenditure may regulate serum leptin levels in man.

Adult↗

PubMed1982

Endorphins and mood changes in long-distance running.

Acute and chronic positive mood changes have been said to occur with running and jogging. It has been suggested that endogenous substances with opioid activity (endorphins) may serve as modulators of mood. The authors report experiments in which mood changes associated with long-distance running were measured by pre- and post-run difference--scores on a mood adjective checklist, the Profile of Mood States (POMS). Following this, the narcotic antagonist, naloxone, was given subcutaneously in double-blind fashion. The dose was 0.8 mg. The POMS was again presented 15 min later, and post-run/post-injection difference scores were obtained. No naloxone effect was found. The failure of naloxone to reverse the running-associated mood shift indicates that endorphins are not involved. The authors discuss the possible physiologic role of endorphins in light of these and other findings.

Adult↗