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PubMed2000

Surface effects on ground reaction forces and lower extremity kinematics in running.

INTRODUCTION: Although running surface stiffness has been associated with overuse injuries, all evidence to support this suggestion has been circumstantial. In the present study, the biomechanical response of heel-toe runners to changes in running surface has been investigated. METHODS: Six heel-toe runners performed shod running trials over three surfaces: a conventional asphalt surface, a new rubber-modified asphalt surface, and an acrylic sports surface. The surfaces were categorised according to impact absorbing ability using standard impact test procedures (BS 7044). RESULTS: The rubber-modified asphalt was found to exhibit the greatest amount of mechanical impact absorption, and the conventional asphalt the least. The comparison of peak impact force values across surfaces for the group of subjects demonstrated no significant differences in magnitude of force. However, a significant reduction in loading rate of peak impact force was detected for the rubber-modified surface compared with conventional asphalt (P < 0.1). Although analysis of group data revealed no significant differences in kinematic variables when running on the different surfaces, a varied response to surface manipulation among runners was demonstrated, with marked differences in initial joint angles, peak joint angles, and peak joint angular velocities being observed. DISCUSSION: For some subjects, the maintenance of similar peak impact forces for different running surfaces was explained by observed kinematic adjustments. For example, when running on the surface providing the least impact absorption, an increased initial knee flexion was observed for some subjects, suggesting an increased lower extremity compliance. However, for some subjects, sagittal plane kinematic data were not sufficient for the explanation of peak impact force results. It appears that the mechanism of adaptation varies among runners, highlighting the requirement of individual subject analyses.

Biomechanical Phenomena↗

PubMed2001

Indices of lactate threshold and their relationship with 10-km running velocity.

PURPOSE: The object of this study was to determine the relationship of three measures of running velocity at lactate threshold (LT) with 10-km running velocity. The methods used to determine LT velocity (m.s(-1)) during submaximal treadmill running were: 1) LT(1), the velocity preceding two consecutive increases in blood lactate > or = 1 mmol.L(-1); 2) LT(D), the velocity associated with the maximum perpendicular distance between the nonlinear regression line and the straight line formed by the two end data points of the blood lactate profile; and 3) LT(4), the velocity corresponding to a blood lactate concentration of 4 mmol.L(-1). METHODS: Thirty competitive and recreational runners (11 female and 19 male) undertook two 10-km time trials (7 d apart), three treadmill familiarization sessions over the following 21 d, and then completed an incremental submaximal treadmill run. From blood lactate samples taken during the submaximal run, mean LT velocity (+/- SD) at LT(1) (3.76 +/- 0.57), LT(D) (3.79 +/- 0.58), and LT(4) (4.11 +/- 0.64) was determined. Pearson product moment correlation analysis revealed a strong relationship between all mean LT speeds and mean 10-km running velocity (3.77 +/- 0.57), with the strongest relationship observed for LT(D) (r = 0.86, P < 0.001). Correlations by gender between LT(D) and 10-km velocity were r = 0.84 (female) and r = 0.78 (male). Male subjects had significantly higher LT velocities than female subjects using all methods (P < 0.001), and velocity at LT(4) was significantly faster than 10-km velocity and velocity at LT(1) and LT(D) (P < 0.001). CONCLUSION: Of the methods measured, LT(D) appears to be the most sensitive and valid measure of LT velocity and may be of benefit in monitoring the training program of 10-km distance runners.

Adolescent↗

PubMed2001

Delta efficiencies of running and cycling.

PURPOSE: The purpose of the present study was to compare delta efficiencies of running with cycling, while several factors that can possibly influence delta efficiency were excluded. METHODS: Twelve subjects performed a submaximal running and cycling test on subsequent days. Delta efficiencies of running and cycling were compared at equal metabolic intensities. Furthermore, rest periods were included in the protocol to avoid fatigue. Pedaling and stride frequencies were held constant during the tests. Finally, the influence of two ways of applying extra external load (inclination of treadmill and horizontal impeding forces) on the delta efficiency of running and cycling was investigated. RESULTS: The results of the present study show that the mean delta efficiency of running (45.5%) is still significantly higher than the mean delta efficiency of cycling (25.7%). The way extra external load is applied does not influence delta efficiency. CONCLUSION: The way of loading and the difference in metabolic intensity can be excluded as causes for the observed difference in delta efficiency between running and cycling. It is suggested that a different contribution in the metabolic load attributable to muscular activity of the arms and/or trunk that does not directly contribute to the work needed to overcome the amount of applied external load may be a relevant factor.

Adult↗

PubMed2002

Effect of ingesting caffeine and ephedrine on 10-km run performance.

BACKGROUND: The ingestion of either caffeine (C) or ephedrine (E) has been shown to improve performance during high-intensity aerobic activity lasting 10-20 min, with an additive effect being found when the combination (C + E) was ingested. It was the purpose of this study to determine if the addition of E to C would improve performance in activity lasting longer than 20 min. METHODS: One and one half hours after ingesting a placebo (P), C (4 mg/kg), E (0.8 mg/kg), or C + E, 12 subjects performed a 10-km run while wearing a helmet and backpack weighing 11 kg. The trials were performed in a climatic suite at 12-13 degrees C, on a treadmill where the speed was regulated by the subject. VO(2), VCO(2), V(E), heart rate (HR), and rating of perceived exertion (RPE) were measured during the run at 15 and 30 min, and again when the individual reached 9 km. Blood was sampled at 15 and 30 min and again at the end of the run and assayed for lactate, glucose, and catecholamines. RESULTS: Run times (mean +/- SD), in minutes, were for C (46.0 +/- 2.8), E (45.5 +/- 2.9), C + E (45.7 +/- 3.3), and P (46.8 +/- 3.2). The run times for the E trials (E and C + E) were significantly reduced compared with the non-E trials (C and P). Pace was increased for the E trials compared with the non-E trials over the last 5 km of the run. VO(2) was not affected by drug ingestion. HR was elevated for the ephedrine trials (E and C + E). RPE remained similar for all trails. Caffeine increased the epinephrine and norepinephrine response associated with exercise and also increased blood lactate, glucose, and glycerol levels. Ephedrine reduced the epinephrine response but increased dopamine and FFA levels. CONCLUSION: The previously seen additive nature of E and C was not evident in this study, with the primary ergogenic effect being attributed to E.

Adult↗

PubMed2002

Changes in spring-mass characteristics during treadmill running to exhaustion.

PURPOSE: To determine whether the stiffness characteristics of the leg change during a treadmill run to voluntary exhaustion. METHODS: Fifteen runners performed a test run at a constant speed that elicited approximately 80% of their .VO(2peak). The run was performed on a treadmill instrumented to measure vertical ground reaction forces; vertical stiffness and leg stiffness were calculated from these forces. Force data were sampled for 15 s every 5 min and immediately before the end of the test. From the force data, average stiffness characteristics were determined for each sample period. An ANOVA with repeated measures (alpha = 0.01) was performed for the group on both vertical and leg stiffness. A single-subject, case-series analysis was also performed on each subject by using ANOVA (alpha = 0.01). RESULTS: Group analysis revealed significant decreases (P < 0.01) in both vertical (23.9 to 23.1 kN.m(-1)) and leg (9.3 to 9.0 kN.m(-1)) stiffness over the run. Based on single-subject ANOVA, 14 of the 15 runners experienced significant (P < or = 0.01) changes in k(vert) over the run. A significant correlation between changes in stride rate and vertical stiffness was found (r = 0.85). Changes in the stiffness properties of the leg, as determined via the spring-mass model, resulted in changes in vertical displacement of the center of mass and leg length (distance from ankle to hip) during stance, as opposed to changes in peak force during ground contact. CONCLUSIONS: Observed changes in stride rate possibly result from changes in the stiffness characteristics of the leg during a run to fatigue.

Adult↗

PubMed1987

Haematuria following a marathon run: source and significance.

Urine specimens were obtained from 98 runners before and immediately after running a half (21 km) or full (42 km) marathon. Specimens were examined for the presence of proteinuria, haematuria and whether the erythrocytes were normomorphic or dysmorphic as determined by phase contrast microscopy. Proteinuria occurred in 35% of those running the half and 69% running the full marathon. Haematuria with or without proteinuria occurred in 21% running the half and 22% running the full marathon. In runners with haematuria, dysmorphic erythrocytes were found in 30% of the half and 81% of the full marathon group. No urinary abnormalities were found on repeat examination 4 to 12 weeks after the run. These results suggest that non-glomerular bleeding, possibly from bladder contusions, predominates at shorter distances. With greater distances glomerular bleeding occurs. These abnormalities disappear with rest and do not appear to signify underlying urinary tract disease.

Erythrocytes↗

PubMed2001

Soleus H-reflex gain in humans walking and running under simulated reduced gravity.

The Hoffmann (H-) reflex is an electrical analogue of the monosynaptic stretch reflex, elicited by bypassing the muscle spindle and directly stimulating the afferent nerve. Studying H-reflex modulation provides insight into how the nervous system centrally modulates stretch reflex responses.A common measure of H-reflex gain is the slope of the relationship between H-reflex amplitude and EMG amplitude. To examine soleus H-reflex gain across a range of EMG levels during human locomotion, we used simulated reduced gravity to reduce muscle activity. We hypothesised that H-reflex gain would be independent of gravity level.We recorded EMG from eight subjects walking (1.25 m s-1) and running (3.0 m s-1) at four gravity levels (1.0, 0.75, 0.5 and 0.25 G (Earth gravity)). We normalised the stimulus M-wave and resulting H-reflex to the maximal M-wave amplitude (Mmax) elicited throughout the stride to correct for movement of stimulus and recording electrodes relative to nerve and muscle fibres. Peak soleus EMG amplitude decreased by ~30% for walking and for running over the fourfold change in gravity. As hypothesised, slopes of linear regressions fitted to H-reflex versus EMG data were independent of gravity for walking and running (ANOVA, P > 0.8). The slopes were also independent of gait (P > 0.6), contrary to previous studies. Walking had a greater y-intercept (19.9% Mmax) than running (-2.5% Mmax; P < 0.001). At all levels of EMG, walking H-reflex amplitudes were higher than running H-reflex amplitudes by a constant amount. We conclude that the nervous system adjusts H-reflex threshold but not H-reflex gain between walking and running. These findings provide insight into potential neural mechanisms responsible for spinal modulation of the stretch reflex during human locomotion.

Adult↗

PubMed1995

Salbutamol and high-intensity treadmill running in nonasthmatic highly conditioned athletes.

Salbutamol is a widely used drug among elite athletes. We wanted to provide more information on the effects of salbutamol in nonasthmatic athletes. Seventeen highly conditioned male athletes (VO2max > 70 ml.kg-1.min-1) participated in a randomized, double-blind and placebo-controlled cross-over study. Nebulized salbutamol (0.05 mg/kg) or placebo was inhaled prior to a high intensity (110% of VO2max) treadmill run to exhaustion. The measured variables included endurance time, oxygen uptake, ventilation, breathing rate, heart rate, and oxygen saturation. Lung function was measured as forced expiratory volume in the first second (FEV1) before and after medication, and during the recovery from the run. The high intensity runs led to total exhaustion after 4-10 min. A close-to-significant shortening in endurance time was found when salbutamol was given. During the running (0-4 min) the oxygen uptake was slightly lower and the heart rate was slightly higher when salbutamol was given. No differences were found in peak oxygen uptake, peak heart rate, ventilation, breathing rate or oxygen saturation. FEV1 reflected an increase in airway caliber after the inhalation of salbutamol. These changes were still present in the recovery from the test run with the exception of the measurement immediately after the exercise. Although evidence for beta-adrenergic stimulation was found, it was concluded that a therapeutic dose of nebulized salbutamol does not improve performance in highly trained athletes during a high-intensity run to exhaustion.

Administration, Inhalation↗

PubMed1998

Creatine supplementation delays onset of fatigue during repeated bouts of sprint running.

In this study we have investigated the effect of creatine supplementation on performance of repeated sprint runs in well-trained young male handball players. The subjects participated in a test before supplementation (T1) and then received creatine (15 g/d) or placebo for five days before a second test was carried out (T2). Following T2, a low dose of creatine (2 g/d) or placebo was maintained for an additional nine days before the third test was performed (T3). The tests consisted of eight 40 m maximal sprint runs with a 25-s rest period between each sprint. Run time was reduced on the last three sprint runs after five days with high doses of creatine supplementation compared to T1 (P < 0.05). Although the run time during the last three sprints was still significantly lower after supplementation of low doses of creatine compared to T1, analysis of variance showed only a tendency for an interaction between test day and random group (P = 0.14). No improvement was seen in the placebo group. Blood lactate was similar at T1 and T2 in the creatine and placebo groups. In conclusion, high doses of creatine supplementation improve performance during repeated sprint runs in well-trained handball players. Further studies are needed to clarify whether low doses of creatine supplementation, after a period with supplementation of high doses, are able to maintain improved performance.

Adult↗

PubMed2005

Exercise-induced arterial hypoxemia is not different during cycling and running in triathletes.

This study examined the effect of running and cycling on exercise-induced arterial hypoxemia (EIAH) in individuals well trained in each modality. Thirteen male triathletes (X+/-SD: age=36+/-5 years, mass=69+/-8 kg, body fat=12+/-1%) performed progressive exercise to exhaustion during cycle ergometry and treadmill running. Gas exchange was determined, while oxyhemoglobin saturation (SaO(2)) was measured with an ear oximeter. At maximal exercise, the respiratory exchange ratio (1.15+/-0.06 vs. 1.10+/-0.05) and the ventilatory equivalent for oxygen uptake (37.6+/-3.8 vs. 34.2+/-2.7) were greater during cycling vs. running (P<0.05). However, there were no differences at maximal exercise in oxygen uptake (64.4+/-3.2 vs. 67.0+/-4.6 mL kg(-1) min(-1)), SaO(2) (93.4+/-2.8% vs. 92.6+/-2.2%), or the ventilatory equivalent for carbon dioxide (V(E)/VCO(2); 33.1+/-3.1 vs. 31.0+/-3.1), during cycling vs. running, respectively. During submaximal exercise, the V(E)/VCO(2) was less for cycling (26.0+/-1.0) compared with running (29.1+/-0.4; P<0.05), but this had no apparent effect on the SaO(2) response. In conclusion, EIAH was not significantly different during cycling and running in athletes who were well trained in both exercise modalities.

Adult↗

PubMed1985

Seasonal changes in the relative importance of different avenues of heat loss in resting and running reindeer.

Exhaled air temperature (Te), respiratory frequency (f), and rectal temperature (Tb) were measured in two reindeer before, during and after running for 45 min at a constant speed of 9.2 km X hr-1 on a level treadmill at different ambient temperatures (Ta), in summer with fur insulation at a minimum and in winter with fur insulation at its prime. Before and immediately after the 45-min running period, skin temperature (Tsk) and radiative surface temperature (Tr) were also measured. Te, Tsk and Tr decreased at rest with decreasing Ta both summer and winter Tb was elevated during running except at low Ta in summer. During running Tsk, Te and f were higher in winter than in summer, while Tr was higher in summer than in winter. The changes in Tr and Tsk in response to running were more pronounced on the legs than on the trunk. It is suggested that in the running reindeer the body surface is an effective avenue of heat loss during summer, while heat dissipation by way of the respiratory tract attains increased importance in winter, when fur insulation is at its best.

Animals↗

PubMed1977

Mechanical work and efficiency in level walking and running.

1. The mechanical power spent to accelerate the limbs relative to the trunk in level walking and running, W(int), has been measured at various ;constant' speeds (3-33 km/hr) with the cinematographic procedure used by Fenn (1930a) at high speeds of running.2. W(int) increases approximately as the square of the speed of walking and running. For a given speed W(int) is greater in walking than in running.3. In walking above 3 km/hr, W(int) is greater than the power spent to accelerate and lift the centre of mass of the body at each step, W(ext) (measured by Cavagna, Thys & Zamboni, 1976b). In running W(int) < W(ext) up to about 20 km/hr, whereas at higher speeds W(int) > W(ext).4. The total work done by the muscles was calculated as W(tot) = W(int) + W(ext). Except that at the highest speeds of walking, the total work done per unit distance W(tot)/km is greater in running than in walking.5. The efficiency of positive work was measured from the ratio W(tot)/Net energy expenditure: this is greater than 0.25 indicating that both in walking and in running the muscles utilize, during shortening, some energy stored during a previous phase of negative work (stretching).6. In walking the efficiency reaches a maximum (0.35-0.40) at intermediate speeds, as may be expected from the properties of the contractile component of muscle. In running the efficiency increases steadily with speed (from 0.45 to 0.70-0.80) suggesting that positive work derives mainly from the passive recoil of muscle elastic elements and to a lesser extent from the active shortening of the contractile machinery. These findings are consistent with the different mechanics of the two exercises.

Adult↗

PubMed1987

Difference in the amplitude of the human soleus H reflex during walking and running.

1. The Hoffman reflex, or H reflex, was strongly modulated in the human soleus muscle during both walking (4 km/h) and running (8 km/h). It was relatively low at the time of heel contact, increased progressively during the stance phase, and reached its maximum amplitude late in the stance phase. During ankle dorsiflexion the H reflex was absent. 2. During running the peak e.m.g. level of the soleus was on average 2.4 times higher than during walking but the maximum amplitude of the H reflex was never larger than during walking. In fact, the H reflex was on average significantly (P less than 0.05 for one-tailed t test) smaller during running than during walking. Furthermore, the slope of the least-squares line fitted to the relation between the H reflex amplitude and the background e.m.g. was always steeper for the walking data than for the running data. 3. The difference in the H reflex in the two tasks is evidence that the size of the H reflex is not simply a passive consequence of the alpha-motoneurone excitation level, as indicated by the e.m.g., but is also influenced by other central neural mechanisms. We suggest that presynaptic inhibition is the most likely mechanism accounting for the change in the slope. 4. The modulation of the reflexes during walking and running can be interpreted in terms of the idea of automatic gain compensation. The decreased gain during running may be appropriate to reduce saturation of motor output and potential instability of the stretch reflex feed-back loop.

H-Reflex↗

PubMed2005

Sustained rise in triacylglycerol synthesis and increased epididymal fat mass when rats cease voluntary wheel running.

Four-week-old, Fischer-Brown Norway F1-generation male rats were given access to voluntary running wheels for 21 days, and then the wheels were locked for 5 (WL5), 10 (WL10), 29 (WL29), or 53 (WL53) hours. Two other groups (SED5 and SED10) had no access to voluntary running wheels and were killed at the same time as WL5 and WL10, respectively. Absolute and relative epididymal fat mass, mean cell volume, and amount of lipid per cell increased in WL53 relative to all other groups, with no change in cell number. C/EBPalpha protein levels in epididymal fat were 30% greater in SED5 than in WL5. The rate of triacylglycerol synthesis in epididymal fat was 4.2-fold greater in SED5 than in WL5, increased 14-fold between WLS and WL10, and was 79% lower in SED10 than in WL10. Triacylglycerol synthesis remained at this elevated level (at least 3.5-fold greater than SED5) through WL53. Thus, the rapid increase in epididymal fat mass with the cessation of voluntary wheel running is associated with a prolonged overshoot in epididymal fat triacylglycerol synthesis. Moreover, rats without running wheels had a 9.4% lower body mass after 21 days than those with running wheels. The individual mass of seven different muscles from the hindlimb, upper forelimb, and back were each lower in animals without running wheels, suggesting that physical activity in rapidly growing rats may be requisite for optimal muscle development.

Adipose Tissue↗

PubMed1977

Oxygen cost and energy expenditure of running in trained runners.

The oxygen cost and energy expenditure of submaximal treadmill running was evaluated in 9 male distance runners. The oxygen consumption--running speed relationship was highly significant (r = .917) and linear over the entire aerobic range. The caloric cost of 0.97 Kcal/kg/k was in close agreement with values found in the literature and was independent of running speed. The caloric cost per unit distance and time increased with acceleration in running speed. The slope of the regression line of oxygen consumption on running speed appear to measure a different component of efficiency than the fractional utilization coefficient of aerobic capacity. There is apparently a wide variation in the oxygen cost of running in trained runners.

Adult↗

PubMed2005

Cadence selection affects metabolic responses during cycling and subsequent running time to fatigue.

OBJECTIVES: To investigate the effect of cadence selection during the final minutes of cycling on metabolic responses, stride pattern, and subsequent running time to fatigue. METHODS: Eight triathletes performed, in a laboratory setting, two incremental tests (running and cycling) to determine peak oxygen uptake (VO2PEAK) and the lactate threshold (LT), and three cycle-run combinations. During the cycle-run sessions, subjects completed a 30 minute cycling bout (90% of LT) at (a) the freely chosen cadence (FCC, 94 (5) rpm), (b) the FCC during the first 20 minutes and FCC-20% during the last 10 minutes (FCC-20%, 74 (3) rpm), or (c) the FCC during the first 20 minutes and FCC+20% during the last 10 minutes (FCC+20%, 109 (5) rpm). After each cycling bout, running time to fatigue (Tmax) was determined at 85% of maximal velocity. RESULTS: A significant increase in Tmax was found after FCC-20% (894 (199) seconds) compared with FCC and FCC+20% (651 (212) and 624 (214) seconds respectively). VO2, ventilation, heart rate, and blood lactate concentrations were significantly reduced after 30 minutes of cycling at FCC-20% compared with FCC+20%. A significant increase in VO2 was reported between the 3rd and 10th minute of all Tmax sessions, without any significant differences between sessions. Stride pattern and metabolic variables were not significantly different between Tmax sessions. CONCLUSIONS: The increase in Tmax after FCC-20% may be associated with the lower metabolic load during the final minutes of cycling compared with the other sessions. However, the lack of significant differences in metabolic responses and stride pattern between the run sessions suggests that other mechanisms, such as changes in muscular activity, probably contribute to the effects of cadence variation on Tmax

Adult↗

PubMed2006

Muscle-specific creatine kinase gene polymorphism and running economy responses to an 18-week 5000-m training programme.

OBJECTIVE: To investigate the association between muscle-specific creatine kinase (CKMM) gene polymorphism and the effects of endurance training on running economy. METHODS: 102 biologically unrelated male volunteers from northern China performed a 5000-m running programme, with an intensity of 95-105% ventilatory threshold. The protocol was undertaken three times per week and lasted for 18 weeks. Running economy indexes were determined by making the participants run on a treadmill before and after the protocol, and the A/G polymorphism in the 3' untranslated region of CKMM was detected by polymerase chain reaction-restricted fragment length polymorphism (NcoI restriction enzyme). RESULTS: Three expected genotypes for CKMM-NcoI (AA, AG and GG) were observed in the participants. After training, all running economy indexes declined markedly. Change in steady-state consumption of oxygen, change in steady-state consumption of oxygen by mean body weight, change in steady-state consumption of oxygen by mean lean body weight and change in ventilatory volume in AG groups were larger than those in AA and GG groups. CONCLUSIONS: The findings indicate that the CKMM gene polymorphism may contribute to individual running economy responses to endurance training.

Adolescent↗

PubMed1987

Determinants of five kilometre running performance in active men and women.

Previous studies of elite endurance athletes have suggested that success in distance running is attributable to the possession of a high maximal oxygen uptake (VO2 max), the utilisation of a large fraction of the VO2 max and to running economy. The purpose of the present study was to examine the relationships between these physiological characteristics and running performance in active but not elite men and women. Maximal oxygen uptake values were 57.6 +/- 6.2 and 46.6 +/- 4.8 ml . kg.-1 min-1 for the men and women respectively (p less than 0.01). Running performance was assessed as a 5 km time trial and the men completed this distance in 19.77 +/- 2.27 min and the women in 24.44 +/- 3.19 min (p less than 0.01). Maximal oxygen uptake showed strong correlations (p less than 0.01) with running performance (men, r = -0.85; women, r = -0.80) but there was only a modest relationship between running economy and performance (men, r = 0.39; women, r = 0.34). The results of the present study suggest that the faster 5 km performance times recorded by the men were best explained by their higher VO2 max values.

Female↗