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At least 937 records · Page 52Linked to original sources

PubMed2001

Leg power and hopping stiffness: relationship with sprint running performance.

PURPOSE: Although sprint performance undoubtedly involves muscle power, the stiffness of the leg also determines sprint performance while running at maximal velocity. Results that include both of these characteristics have not been directly obtained in previous studies on human runners. We have therefore studied the link between leg power, leg stiffness, and sprint performance. METHODS: The acceleration and maximal running velocity developed by 11 subjects (age 16 +/- 1) during a 40-m sprint were measured by radar. Their leg muscle volumes were estimated anthropometrically. Leg power was measured by an ergometric treadmill test and by a hopping test. Each subject executed a maximal sprint acceleration on the treadmill equipped with force and speed transducers, from which forward power was calculated. A hopping jump test was executed at 2 Hz on a force platform. Leg stiffness was calculated using the flight and contact times of the hopping test. RESULTS: The treadmill forward leg power was correlated with both the initial acceleration (r = 0.80, P < 0.01) and the maximal running velocity (r = 0.73, P < 0.05) during track sprinting. The leg stiffness calculated from hopping was significantly correlated with the maximal velocity but not with acceleration. CONCLUSION: Although muscle power is needed for acceleration and maintaining a maximal velocity in sprint performance, high leg stiffness may be needed for high running speed. The ability to produce a stiff rebound during the maximal running velocity could be explored by measuring the stiffness of a rebound during a vertical jump.

Adolescent↗

PubMed2002

Impacts and kinematic adjustments during an exhaustive run.

PURPOSE: To examine the kinematic adjustments that runners make during an exhaustive run and to look at the effects these adjustments have on shock and shock attenuation. METHODS: Ten recreational runners ran to volitional exhaustion on a treadmill at a velocity equal to their average 3200-m running velocity at maximal effort (average time: 15.7 +/- 1.7 min). Head and leg accelerometers, a knee electrogoniometer, and a rearfoot electrogoniometer were attached to each subject. The data were sampled at 1000 Hz at the start, middle, and end of the run. RESULTS: The knee became significantly more flexed at heel impact (start: 164.9 +/- 2.3 degrees; end: 160.5 +/- 2.9 degrees; P < 0.05). The rearfoot angle became more inverted at impact (start: 12.2 +/- 1.6 degrees; end: 13.6 +/- 1.9 degrees; P < 0.05). These kinematic changes resulted in a lower extremity that that had a lower effective mass during the impact. This decreased effective mass allowed the leg to accelerate more easily; thus, peak leg impact accelerations (start: 6.11 +/- 0.96 g; end: 7.38 +/- 1.05 g; P < 0.05) and impact attenuation (start: 74.5 +/- 5.4%; end: 77.5 +/- 4.1%; P < 0.05) increased during the progression of the run. CONCLUSIONS: The increase in peak impact accelerations at the leg was not considered an increased injury risk because of the decreased effective mass. The altered kinematics may have resulted in increased metabolic costs during the latter stages of the exhaustive run.

Adaptation, Physiological↗

PubMed2002

The acute effects of prior cycling cadence on running performance and kinematics.

PURPOSE: To determine if cycling cadence affects subsequent running speed through changes in stride frequency. METHODS: Thirteen male triathletes completed three sessions of testing on separate days. During the first session (control condition), the participants completed a 30-min cycling bout of high intensity at their preferred cadence, immediately followed by a 3200-m run at race effort. During the second and third sessions (fast condition and slow condition), the participants repeated the protocol but with a cycling cadence 20% faster or 20% slower than the control condition. RESULTS: After cycling at a fast cadence, the 3200-m run time averaged nearly a min faster than after cycling at a slow cadence. Running stride frequency after cycling at a fast cadence was significantly greater than after cycling at a normal or slow cadence. Stride length did not differ between conditions. Joint kinematics at foot strike, mid-stance, toe-off, and mid-swing were not different between conditions. CONCLUSION: Increased cycling cadence immediately before running increased stride frequency and, as a result, increased speed.

Adult↗

PubMed2003

Interrelationships between muscle structure, muscle strength, and running economy.

PURPOSE: The present study was designed to investigate possible differences in running economy (RE) among elite middle-distance runners by examining muscle structure and maximal isometric force (MVC). METHODS: Ten young male runners ran at six different running speeds. During the running bouts, respiratory gases, and blood lactate were measured. Muscle biopsies were obtained from the vastus lateralis muscle for analyzing fiber type distribution, muscle fiber area, myosin heavy chain (MHC) composition, activities of a number of metabolic enzymes (citrate synthase, lactate dehydrogenase, phosphofruktokinase, and 3-hydroxyacyl-CoA-dehydrogenase), and titin isoforms. RESULTS: Energy expenditure (EE) increased linearly up to the speed of 6.0 m.s. The relative distribution of the MHC isoforms was MHC I: 67.0%, MHC IIA: 31.5%, and MHC IIX: 1.5%. The present results demonstrated that higher the area of Type II fibers, higher the MVC (r = 0.59, P< 0.05). The amount of MHC II correlated inversely with EE when running close to the competition speed (r = -0.61, P< 0.05). Enzyme activities did not correlate significantly with either RE or EE. Titin analysis revealed that a faster-mobility titin band was observed in all subjects, whereas a lower-mobility titin band was observed only in the most economical runner. CONCLUSION: Differences in RE among homogeneous group of middle-distance runners were observed at various running speeds. This may partly be explained by differences in muscle fiber distribution, MHC composition, and titin isoforms.

Adult↗

PubMed2006

Management of lower extremity malalignment during running with neuromuscular retraining of the proximal stabilizers.

This case report presents a high-level female runner with a history of more than 25 years of recurrent lower extremity (LE) injuries and LE malalignment problems during running. Due to her LE malalignment, she has been unable to run for the past 3 years. A definitive diagnosis was not found for her inability to run so by exclusion we diagnosed dysfunction of the hip, spine, and pelvic stabilizers that resulted in her in LE malalignment. To treat this muscle weakness, we designed a Pilates-evolved functional movement intervention to improve the control and strength of the proximal stabilizers and regain normal LE alignment. The Pilates-evolved treatment approach involved a series of functional and progressive resistance exercises designed to dynamically stabilize the spine, pelvis, and hip through all planes of motion. After 1 year of Pilates-evolved training, the athlete's disabling movement pattern resolved and she has returned to a regular running program. The purpose of this case report is to describe a Pilates-evolved functional movement intervention that resolved this runner's LE malalignment and returned her to running when other traditional treatment approaches were not effective in doing so.

Athletic Injuries↗

PubMed2005

Running exercise of different duration and intensity: effect on endothelial progenitor cells in healthy subjects.

BACKGROUND: Increased numbers of circulating endothelial progenitor cells (EPC) are associated with improved vascular function. Exercise is a central component of the primary prevention of vascular diseases. The effect of physical activity on circulating EPC in healthy individuals is not known. DESIGN: A prospective crossover study. METHODS AND RESULTS: In order to study a potential link between the extent of physical exercise and progenitor cells in humans, EPC were quantified by flow cytometry and cell culture in 25 healthy volunteers undergoing three protocols of running exercise. Intensive running, defined as 30 min at 100% of the velocity of the individual anaerobic threshold (IAT; approximately 82% maximal oxygen consumption; VO2max), as well as moderate running with 30 min at 80% of the velocity of the IAT ( approximately 68% VO2max), increased circulating EPC numbers to 235+/-93% and 263+/-106% of control levels, respectively. However, moderate short-term running for 10 min did not upregulate EPC counts. The maximum increase in circulating EPC numbers was observed 10-30 min after intensive running. Exercise increased EPC migratory and colony-forming capacity. CONCLUSIONS: Intensive and moderate exercising for 30 min, but not for 10 min, increased circulating levels of EPC, which may represent an important beneficial outcome of physical exercise. The data support the notion that increased numbers of EPC correlate with cardiovascular health and suggest EPC quantification as a novel surrogate parameter of the vascular effects of exercising.

Adult↗

PubMed2004

Gait selection in the ostrich: mechanical and metabolic characteristics of walking and running with and without an aerial phase.

It has been argued that minimization of metabolic-energy costs is a primary determinant of gait selection in terrestrial animals. This view is based predominantly on data from humans and horses, which have been shown to choose the most economical gait (walking, running, galloping) for any given speed. It is not certain whether a minimization of metabolic costs is associated with the selection of other prevalent forms of terrestrial gaits, such as grounded running (a widespread gait in birds). Using biomechanical and metabolic measurements of four ostriches moving on a treadmill over a range of speeds from 0.8 to 6.7 m s(-1), we reveal here that the selection of walking or grounded running at intermediate speeds also favours a reduction in the metabolic cost of locomotion. This gait transition is characterized by a shift in locomotor kinetics from an inverted-pendulum gait to a bouncing gait that lacks an aerial phase. By contrast, when the ostrich adopts an aerial-running gait at faster speeds, there are no abrupt transitions in mechanical parameters or in the metabolic cost of locomotion. These data suggest a continuum between grounded and aerial running, indicating that they belong to the same locomotor paradigm.

Animals↗

PubMed2006

Tuataras and salamanders show that walking and running mechanics are ancient features of tetrapod locomotion.

The lumbering locomotor behaviours of tuataras and salamanders are the best examples of quadrupedal locomotion of early terrestrial vertebrates. We show they use the same walking (out-of-phase) and running (in-phase) patterns of external mechanical energy fluctuations of the centre-of-mass known in fast moving (cursorial) animals. Thus, walking and running centre-of-mass mechanics have been a feature of tetrapods since quadrupedal locomotion emerged over 400 million years ago. When walking, these sprawling animals save external mechanical energy with the same pendular effectiveness observed in cursorial animals. However, unlike cursorial animals (that change footfall patterns and mechanics with speed), tuataras and salamanders use only diagonal couplet gaits and indifferently change from walking to running mechanics with no significant change in total mechanical energy. Thus, the change from walking to running is not related to speed and the advantage of walking versus running is unclear. Furthermore, lumbering mechanics in primitive tetrapods is reflected in having total mechanical energy driven by potential energy (rather than kinetic energy as in cursorial animals) and relative centre-of-mass displacements an order of magnitude greater than cursorial animals. Thus, large vertical displacements associated with lumbering locomotion in primitive tetrapods may preclude their ability to increase speed.

Animals↗

PubMed2003

Ontogenies in mice selected for high voluntary wheel-running activity. I. Mean ontogenies.

The evolutionary importance of postnatal ontogenies has long been recognized, but most studies of ontogenetic trajectories have focused exclusively on morphological traits. For animals, this represents a major omission because behavioral traits and their ontogenies often have relatively direct relationships to fitness. Here four replicate lines of house mice artificially selected for high early-age wheel running and their four replicate control lines were used to evaluate the effects of early-age directional selection, genetic drift, and activity environment (presence or absence of a running wheel) on variation in the ontogenies of three traits known to be genetically correlated: voluntary wheel running, body mass, and food consumption. Early-age selection significantly changed both the shape and position of the wheel-running and food-consumption ontogenies while influencing the position, but not the shape, of the body mass ontogeny. Genetic drift (as indicated by variation among replicate lines) produced significant changes in both the position and shape of all three ontogenies; however, its effect differed between the selection and control groups. For wheel running and food consumption, genetic drift only influenced the control ontogenies, whereas for body mass, genetic drift had a significant effect in both selection groups. Both body-mass and food-consumption ontogenies were significantly altered by activity environment, with the environment causing significant changes in the shape and position of both ontogenies. Overall the results demonstrate strong effects of early-age selection, genetic drift, and environmental variation on the evolution and expression of behavioral and morphological ontogenies, with selection changing only the position of the morphological ontogeny but both the position and shape of the behavioral ontogenies.

Analysis of Variance↗

PubMed1992

Effect of forced-running stress on beta-adrenergic receptors in rat brain regions and liver.

Rats were exposed to forced-running stress for 1 day, 3 days or a long term (approximately 2 weeks), and beta-adrenergic receptor binding was then assayed using [3H]dihydroalprenolol (DHA) in six brain regions and the liver. In the pons + med.obl., hypothalamus and midbrain, a reduction in beta-adrenergic receptor density was first evident on day 1. In contrast, a decrease in beta-adrenergic receptor density in the cerebral cortex and hippocampus was first evident on day 3. Decreased [3H]DHA binding in the pons + med.obl., cerebral cortex and hippocampus subsequently plateaued for the duration of the forced-running stress. In the midbrain and hypothalamus, however, decreased [3H]DHA binding subsequently returned to control levels despite the exposure to the forced-running stress. In the cerebellum and the liver, [3H]DHA binding did not change significantly throughout the stress. These results indicate that the forced-running stress induces both the time- and region-specific changes in beta-adrenergic receptors. Moreover, the rats showed either a behavioral depression or a spontaneous recovery of running activity during the 2 weeks following the end of the long-term stress. Thus, we also examined the relationship of beta-adrenergic receptors to these behavioral differences. [3H]DHA binding for the behavioral depression group was lower in the hippocampus and higher in the liver than for the spontaneous recovery group.

Animals↗

PubMed1998

A trauma-like elevation of plasma cytokines in humans in response to treadmill running.

1. Elevated levels of cytokines, especially interleukin (IL)-6 and IL-1ra, can be measured in the plasma of athletes after exhaustive long term exercise. 2. The present study investigates the kinetics of several cytokines and chemokines in ten male athletes before, during and after 2.5 h of treadmill running at 75 % of maximal oxygen consumption (VO2,max). Blood was sampled before, every half-hour during running and every hour in the following 6 h recovery period. 3. The plasma concentration of IL-6 increased after 30 min of running, and peaked at the end of running with a 25-fold increase compared with the pre-exercise value. IL-1ra increased only after running, and peaked after 2 h of rest with an 18-fold increase compared with the pre-exercise value. No changes were found in the concentrations of IL-1beta, tumour necrosis factor (TNF)alpha, IL-15 and macrophage inflammatory protein (MIP)-1beta, and the concentrations of IL-8 and MIP-1alpha were below detection limits. 4. The results suggest that very early events in exercise trigger the release of IL-6, and that the cytokine response to exercise has similarities to that observed after trauma.

Adult↗

PubMed1998

Kinematic and kinetic analysis of running in children with cerebral palsy.

Computer-based analysis of gait was used to study walking and running in 19 children with spastic-diplegic cerebral palsy (CP) and 15 healthy control children. Temporospatial parameters, kinematic and kinetic data were compared and contrasted between groups for both types of gait. The majority of children with diplegic CP, who are independent ambulators, are able to run. These children increase their velocity by increasing their cadence, a mechanism that is distinct (and presumably less energy efficient) from that used by healthy children. Sagittal-plane kinematic and kinetic profiles at the ankle in children with CP were more similar to normal profiles in running than in walking, suggesting that the primary deviations at the ankle associated with CP are better tolerated at greater velocities. Relative power analysis showed that, like healthy children, those with CP depend more upon the proximal musculature about the hip for power generation as the velocity of gait increases. Children with CP achieve energy transfer between adjacent joints during walking and running in a manner comparable to unaffected children. Running is an important activity for children and should be considered in the functional assessment of those with CP.

Cerebral Palsy↗

PubMed1994

The transition between walking and running in humans: metabolic and mechanical aspects at different gradients.

Five subjects walked and ran at overlapping speeds and different gradients on a motorized treadmill. At each gradient the speed was obtained at which walking and running have the same metabolic cost (Sm) and the speed of spontaneous (Ss) transition between the two gaits was measured. Ss was found to be statistically lower than Sm at all gradients, the difference being in the range of 0.5-0.9 km h-1. The motion analysis of walking reveals that at all gradients and at increasing speed: (1) the percentage of recovery, an index of mechanical energy saving related to the pendulum-like characteristic of walking, decreases; (2) the lower limb spread reaches a limit in walking; and consequently (3) both the stride frequency and the internal mechanical work, due to limb acceleration in relation to the body centre of mass, increase much more in walking than in running. Switching to a run, although implying a higher frequency, makes the internal work decrease as a result of the lower limb spread. In this paper several influences, such as the 'ratings of perceived exertion' (RPE), on the choice of beginning to run when it is more economical to walk, are discussed. A tentative hypothesis on the determinants of Ss, which is emphasized to be a speed which has to be studied in detail but is generally avoided in locomotion, is based on a comfort criterion from peripheric afferences and is reflected by the fact that at Ss a running stride costs as much as a walking stride.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2000

Fatigue-related loading imbalance on the shank in running: a possible factor in stress fractures.

In previous reports we have shown that in long distance running the impact acceleration on the shank increases with progressing fatigue. The aim of the present study was to test whether, in parallel to this increase, an imbalance in the activities between the ankle plantar and dorsi flexor muscles develops. The tests were made on fourteen subjects during 30 min treadmill running above their anaerobic thresholds. Respiratory data were collected to determine the anaerobic threshold speed and to indicate the progressively developing metabolic fatigue. Surface electromyogram (EMG) was monitored to indicate the changing activity of the shank muscles. In the tibialis anterior the average integrated EMG (iEMG) and the mean power frequency (MPF) significantly decreased from the beginning to the end of running. In the gastrocnemius iEMG did not change, while MPF increased during the course of running. The impact acceleration, measured by means of an accelerometer attached to the tibial tuberosity, significantly increased during the course of running. It was concluded that, with developing fatigue, an imbalance in the contraction of the shank muscles develops in parallel to an increase in shank shock acceleration. The combination of these two changes may hamper the loading balance on the tibia since the bone becomes exposed to excessive bending stresses and to higher risk of stress injury.

Acceleration↗

PubMed1992

Effects of downhill running on the responses to an oral glucose challenge.

Because muscle damage from eccentric exercise has been associated with alterations in muscle glycogen metabolism, this study determined the effects of exercise on the insulin and glucose responses to an oral glucose tolerance test (OGTT). In a repeated-measures design, 11 subjects undertook either no exercise, 2 min of isokinetic leg exercise, or 50 min of level or downhill running. No exercise was performed and diet was controlled during the 48 hrs after the treatments and before the OGTT. Ratings of muscle soreness and CK activity were significantly elevated 48 hrs after downhill running. Level running also increased CK activity but did not induce muscle soreness. Isokinetic exercise did not affect either one. Blood glucose responses to the OGTT were similar among the treatments. In contrast, the insulin responses to the OGTT following downhill running were significantly increased. These results suggest that eccentric exercise associated with downhill running that results in delayed muscle soreness is associated with the development of a mild insulin-resistant condition.

Adult↗

PubMed1997

Water versus carbohydrate-electrolyte ingestion before and during a 15-km run in the heat.

Twelve highly trained male runners ran 15 km at self-selected pace on a treadmill in warm conditions to demonstrate differences in physiological responses, fluid preferences, and performance when ingesting sports drinks or plain water before and during exercise. One hour prior to the start of running, an equal volume (1,000 ml) of either water or a 6% or an 8% carbohydrate-electrolyte (CE) drink was ingested. Blood glucose was significantly higher 30 min following ingestion of 6% and 8% CE compared to water, significantly lower at 60 min postingestion with both sports drinks than with water, but similar after 7.5 km of the run for all beverages. During the first 13.4 km, oxygen uptake and run times were not different between trials; however, the final 1.6-km performance run was faster with both CE drinks compared to water. Despite a lower preexercise blood glucose, CE consumption prior to and during exercise significantly improved performance in last 1.6 km of a 15-km run compared to water.

Adult↗

PubMed1997

Carbohydrate intake and recovery of intermittent running capacity.

The purpose of the present study was to examine the influence of an increased carbohydrate intake on the recovery of endurance running capacity after exhaustive intermittent running. Six male subjects were randomly assigned to two dietary recovery conditions, each involving two running tests separated by 22 hr. The protocol comprised a prolonged, intermittent, high-intensity shuttle run test (I-HI). One week later subjects repeated the I-HI on consecutive days under different dietary conditions. During the 22-hr recovery, either the carbohydrate intake of the subjects was increased (CHO) or they ate an isocaloric diet by supplementing their normal diet with extra protein and fat (CON). Intermittent running capacity was improved when subjects increased their carbohydrate intake to 10 g.kg-1 bm during the 22-hr recovery between trials, but an isocaloric diet without additional carbohydrate did not bring about the same improvements.

Adult↗

PubMed2004

Inadequate carbohydrate intake following prolonged exercise does not increase muscle soreness after 15 minutes of downhill running.

In Delayed Onset Muscle Soreness (DOMS), muscles become sore 24 to 48 hours after eccentric and unaccustomed activity. Fiber stiffness, due to decreased muscle glycogen, may predispose muscle to greater damage during eccentric exercise. This study sought to determine if inadequate carbohydrate intake following a protocol to decrease muscle glycogen would increase DOMS after 15 min of downhill running. Thirty-three male subjects (age, 18-35 years) were randomized into 3 groups for testing over a 7-day period. The depletion (DEP) group (n= 12) underwent a glycogen depletion protocol prior to a 15-min downhill run designed to induce DOMS. The repletion (FED) group (n = 10) underwent a glycogen depletion protocol followed by a carbohydrate repletion protocol (>80% CHO) prior to downhill running. The third (ECC) group (n = 11) performed only the downhill running protocol. Subjective muscle soreness, isometric force production, relaxed knee angle, and thigh circumference were measured pretreatment and on days 1, 2, 3, 4, and 6 post treatment. Subjective muscle soreness for all groups increased from 0 cm pretreatment to 3.05 +/- 0.72 cm (on a 10-cm scale) on day 1 post treatment (p<.05). All groups were significantly different from baseline measurements until day 4 post treatment. Each group experienced a decline in isometric force from 281 +/- 45 N pre- to 253 +/- 13 N on day 1 post treatment (p <.05). The decrease in isometric force persisted in all groups for 4 days post treatment. Increases in thigh circumference and relaxed knee angle elevations in all 3 groups were statistically different (p <.05) from pretreatment until day 4. No differences were noted between groups for any of the parameters examined. In the current study, 15 min of downhill running is sufficient to cause DOMS with the associated functional and morphological changes; however, inadequate carbohydrate intake after a glycogen depleting exercise does not appear to exacerbate DOMS and the associated symptoms.

Adolescent↗