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Biomedical subjects

G S Krahenbuhl

Publications and source records attributed to G S Krahenbuhl.

At least 19 recordsLinked to original sources
PubMed1997

Menstrual cycle phase and running economy.

To further elucidate the relationship between RE and menstrual cycle phase, eight eumenorrheic moderately-trained female runners were studied throughout their menstrual cycles, which were divided into five phases: early follicular (EF), late follicular (LF), early luteal (EL), mid-luteal (ML), and late luteal (LL). Subjects were studied at rest and while running at speeds initially corresponding to 55% and 80% maximal oxygen consumption (VO2max). Ventilation (L x min-1) was significantly (P < 0.05) higher in ML compared with EF during all three conditions (mean +/- SE) (rest: 12.4 +/- 0.7 vs 10.3 +/- 0.8; 55% VO2max: 46.2 +/- 0.9 vs 42.2 +/- 1.4; and 80% VO2max: 68.8 +/- 3.0 vs 63.3 +/- 2.0 L x min-1, respectively). Resting VO2 (mL x kg-1 x min-1) was significantly (P < 0.05) hi gher in ML (4.8 +/- 0.1) compared with EF (3.9 +/- 0.2). Profile of Mood States (POMS) total mood disturbance (TMD) and three subscale (depression, fatigue, and confusion) scores were also significantly higher during ML compared with EF; TMD: 127 +/- 6.0 vs 104 +/- 6.0; depression: 6 +/- 1.4 vs 3 +/- 1.4; fatigue: 9 +/- 1.0 vs 4 +/- 0.9; and confusion: 7 +/- 0.9 vs 5 +/- 1.2, respectively. The POMS vigor subscale score was significantly lower during ML (11 +/- 1.5) when compared with EF (19 +/- 0.7). RE at speeds corresponding to 55% VO2max was not significantly different between phases of the menstrual cycle. RE at speeds corresponding to 80% VO2max was, however, significantly less (higher VO2) during ML (41.4 +/- 0.8 mL x kg-1 x min-1) than EF (40.2 +/- 0.5 mL x kg-1 x min-1). It was concluded that RE at speeds corresponding to 80% VO2max in moderately-trained female runners covaries independently with ventilatory drive changes and with fluctuations in mood state which occur throughout the menstrual cycle.

Affect↗
PubMed1995

Variation in the aerobic demand of running among trained and untrained subjects.

Variation in the aerobic demand (VO2) of submaximal running was quantified among trained and untrained subjects stratified by performance capability. Based on a retrospective analysis of seven published studies, maximal aerobic power (VO2max), and submaximal VO2 values were analyzed in three groups of trained distance runners (Category 1 (C1) (elite runners; N = 22), Category 2 (C2) (sub-elite runners; N = 41), and Category 3 (C3) (good runners; N = 16), and one group (N = 10) of untrained subjects (Category 4; C4). Results indicated that VO2max differed significantly (P < 0.05) across groups, such that C1 > C2 > C3 > C4. Analysis of submaximal VO2 data also revealed that C4 was more uneconomical than C1, C2, and C3 and that C2 and C3 were less economical than C1. Average within-group variability in submaximal VO2 was similar across categories and a marked overlap of minimum, mean and maximal economy values existed across categories. These data suggest that 1) trained subjects are more economical than untrained subjects, 2) elite runners display better economy compared to less-talented counterparts, and 3) economical and uneconomical runners can be found in all performance categories.

Adult↗
PubMed1994

Daily variability in exercise ventilation.

The purpose of this study was to quantify daily variability in ventilation (VE) during submaximal exercise and establish the number of testing sessions required to produce stable exercise ventilation measures. Following 60 min of treadmill accommodation, four male (M) and four female (F) distance runners completed 5 weeks of daily treadmill testing at the same time of day while engaged in a normal routine of training and racing. During each test session, subjects completed three 6-min level treadmill runs at either 3.13, 3.57, and 4.02 m.sec-1 for F or 3.57, 4.02, and 4.47 m.sec-1 for M. Measures of VE were obtained during the last 2 min of each 6-min run. Results indicated that the mean coefficient of variation (CV) for VE across speeds was 4.33%. Reliability analyses examining all possible combinations of testing days over the 5-week period revealed that 97% of the variation in mean VE was accounted for in either 2 consecutive or non-consecutive days, while 98% of the variation in mean VE was accounted for in 5 consecutive days. These data suggest that when treadmill exposure and circadian variation are controlled, intraindividual differences in exercise VE are relatively small in male and female subjects following an unrestricted program of training and competitive racing. Additionally, acceptably stable VE values in this cohort can be derived by averaging duplicate measures obtained from consecutive or non-consecutive testing sessions.

Adult↗
PubMed1992

Running economy: changes with age during childhood and adolescence.

The purpose of this study was to synthesize work directed at describing and understanding changes in running economy (the steady-state demand for oxygen at a set running speed) that occur with increased age during childhood and adolescence. Although the data are limited, a number of tentative conclusions were drawn. Children are less economical than adults. Running economy improves steadily with age in normally active children and adolescents, even in the absence of formal running training. Running economy in later childhood fails to respond to either short-term instruction on the techniques of running or short-term participation in running training. Long-term participation in running training may augment improvements in running economy that occur naturally with age. In a group of heterogeneous subjects of the same age, running economy is not strongly related to performance. Within a subject over a period of years, running economy is strongly related to performance. Children are less economical than adults because when compared with adults, children exhibit (a) higher resting metabolic rates, (b) greater ventilatory equivalents for oxygen, and (c) disadvantageous stride rates and stride lengths.

Adolescent↗
PubMed1991

Mood state and running economy in moderately trained male runners.

The purpose of this study was to determine the relationship between psychological states as measured by the Profile of Mood States (POMS) inventory and within-subject variation in running economy (RE) in moderately trained male runners (N = 10). Subjects (ages 20-34 yr) were monitored during treadmill running, five times a week (Monday through Friday) for 4 wk, at 2.68, 3.13, and 3.58 m, s-1. Tension, depression, anger, vigor, fatigue, confusion, and a total mood disturbance (TMD) score were assessed every Friday prior to the treadmill running sessions. Oxygen consumption (VO2) was determined via the open-circuit method during each of the three running paces. VO2 values were averaged over 5 d and three speeds for each week (RE) and were correlated with the weekly TMD scores, resulting in a nonsignificant group correlation of r = -0.28. The within-subject group correlation between TMD scores and RE was r = 0.88. This positive correlation indicates that, when the focus of attention was on within-subject variation, weeks featuring more economical values were associated with more positive mental health profiles. Correlations between average VO2 and the six POMS subscales were tension. r = 0.81; depression, r = 0.73; anger, r = 0.58; vigor, r = -0.60: fatigue, r = 0.18; and confusion, r = 0.60. All correlation coefficients except for fatigue were significantly (P less than 0.01) related to average VO2. In conclusion, it appears that short-term fluctuations in RE of moderately trained male runners are closely tied to their mood state.

Adult↗
PubMed1991

Daily variation in running economy of moderately trained male runners.

The purpose of this study was to quantify total within-subject variation in running economy (RE) in moderately trained male runners (N = 10). Subjects (ages 20-34 yr) were monitored during treadmill running, five times a week (Mon-Fri) for 4 wk, at 2.68, 3.13, and 3.58 m.s-1. Oxygen consumption (VO2) was determined via the open-circuit method during each of the three running paces. Coefficients of variation among the three paces were not significantly (P greater than 0.05) different. An analysis of variance with repeated measures and a three-factor (3 x 4 x 5) design indicated that speed was the only significant (P less than 0.05) effect. Reliability tests performed on the data indicated that although there is an improvement in the percentage of variation accounted for as the number of tests conducted is increased, the benefit obtained by testing 5 d is very small when compared with testing 2 d. When effect sizes are used in the determination of subject numbers needed to detect significant effects, it is apparent that smaller anticipated effect sizes necessitate large sample sizes. In conclusion, RE appears to be a stable physiological measure in moderately trained male runners, and a criterion value based on the average of two measures per subject is recommended to obtain an acceptably stable RE value.

Adult↗
PubMed1991

Variability in running economy and mechanics among trained male runners.

Data from two studies were analyzed to quantify intraindividual variability and reliability in running economy (RE) and mechanics. Following 30-60 min of treadmill accommodation, stride-to-stride and day-to-day biomechanical stability were assessed in 31 male runners (studies 1 and 2) who performed two level treadmill runs (3.33 m.s-1) at the same time of day, in the same footwear, and in a nonfatigued state. Under the same testing conditions, daily stability in RE was determined in 17 of the 31 subjects (study 2). RE demonstrated high day-to-day reliability (r = 0.95), and the mean coefficient of variation in RE was 1.32% (range = 0.30-4.40%). Stride-to-stride reliability for temporal (T), kinematic (KNM), and kinetic (KIN) measures was very high (mean r = 0.96; range = 0.91-0.99), but day-to-day reliability was lower for KIN (mean r = 0.67; range = 0.28-0.88) compared with T and KNM (mean r = 0.91; range = 0.68-0.98). Further analyses revealed no significant (P less than or equal to 0.05) mean stride-to-stride differences for any biomechanical variable, and only three of 22 variables (peak resultant velocity of the ankle joint, step length, and swing time) demonstrated statistically significant day-to-day differences. Viewed in concert, these results suggest that, if the testing environment is controlled, multiple trials are not required to obtain stable measures of running economy and basic mechanical characteristics in trained male runners if group data from adequate sample sizes are considered. However, if individual records are scrutinized or if small sample sizes cannot be avoided, at least two measures of individual performances should be secured.

Adult↗
PubMed1990

Effects of a prolonged maximal run on running economy and running mechanics.

The purpose of this study was to document the effects of a prolonged (30 min) maximal run (PMR) on running economy (RE) and running mechanics in 16 male runners (mean VO2max = 59.0 +/- 4.5 ml.kg-1.min-1). After completing 60 min of treadmill accommodation, each subject performed two 10 min economy runs at 200 m.min-1. Subjects were also filmed at 100 fps during the last 30 s of each run in order to quantify 20 temporal, kinematic, and kinetic gait descriptors previously associated with RE variation. Following the second run, each subject completed the PMR at 85% of his predicted velocity at VO2max (89% VO2max). One, two, and four days after the PMR, subjects repeated the 10 min economy run. No significant difference (P greater than or equal to 0.05) in RE (range = 42.3-42.6 ml.kg-1.min-1) was observed following the PMR. Biomechanical analyses also indicated that, with the exception of one variable (plantar flexion angle at toe-off), gait characteristics remained unaltered after the PMR. When considered from a cross-disciplinary perspective, these data suggest that a 30 min maximal run does not increase the aerobic demand of running or disrupt the running mechanics of moderately trained male subjects who perform subsequent submaximal runs over the short term.

Adult↗
PubMed1989

Longitudinal changes in distance-running performance of young males.

Longitudinal studies of adolescent males have shown that absolute maximal aerobic power (VO2max) and distance-running performance improve with age, while VO2max expressed relative to body mass remains stable. These earlier studies used subjects that were engaged in distance-run training; therefore, it was not possible to assess the relative importance of growth and/or run training to improved performance. The purpose of this study, therefore, was to quantify longitudinal changes in VO2max, running economy (RE), and distance-running performance in non-run-trained young males. Six subjects were tested at mean ages of 9.9 (T1) and 16.8 years (T2). Statistical tests of mean values revealed that over the 7-year period, relative VO2max remained unchanged (T1, 48.9 ml.kg-1.min-1; T2, 47.8 ml.kg-1.min-1) and RE improved (T1, 234.2; T2, 202.8 ml.kg-1.km-1), 9-min run distance increased (T1, 1637 m; T2, 2115 m), and the estimated percent of VO2max incurred during the 9-min run increased from 85.8% (T1) to 99.5% (T2). It was concluded that the improvement in distance-running performance observed in adolescent boys was not dependent upon run training. In view of the fact that maximal aerobic power remained stable, this change appears to be attributable to better running economy and an ability in runs of a fixed duration to perform at a higher relative work load.

Adolescent↗
PubMed1989

Factors affecting running economy.

Running economy, defined as the steady-state VO2 for a given running velocity, has been shown to account for a large and significant proportion of variation in distance-running performance among runners roughly comparable in VO2 max. Despite this recognition, relatively little is known regarding the potpourri of physiological, environmental, structural and mechanical factors potentially associated with a lower aerobic demand of running. Early attempts at quantifying the energy expenditure of exhaustive runs incorporated measurements of oxygen consumption before, during, and after exercise. The validity of this approach has been questioned, however, since recent evidence has demonstrated that only a moderate relationship exists between postexercise VO2 and anaerobic metabolism. The energy demands for submaximal running (i.e. running economy) can be quantified by calculating the steady-state VO2, expressed with respect to body mass and time, for a standardised, submaximal running speed. Since this variable represents the aerobic demand of running, the generation of energy must derive wholly from cell respiration and not from substantial protein catabolism. Research has indicated that at low to moderate work rates, the steady-state energy condition is attained in about 3 minutes. Trained individuals reach steady-state sooner than unfit subjects. While limited by methodological constraints, the existence of a steady-state has also been verified by the lack of blood lactate accumulation and the presence of a respiratory exchange ratio of less than 1.00. The ability of economy, either singly or in combination with VO2 max, to account for a substantial portion of performance variation among trained distance runners and untrained subjects of comparable ability and fitness level has been demonstrated in recent cross-sectional studies. Limited data from short and long term longitudinal research also suggests that endurance running success is linked to training and growth-related improvements in economy. Intraindividual variation in economy has been shown to vary between 2% and 11% for a given speed. Most of this variation can probably be attributed to biological error. While the majority of evidence does not support a gender difference in running economy, data from some studies suggest that males may be more economical than women. Prepubescent children are less economical than older children and adults, whereas older adults exhibit the same trend when compared to younger counterparts. Because of air and wind resistance, the aerobic demands of indoor treadmill running significantly underestimate the cost of overground running, especially at higher speeds.(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical Phenomena↗
PubMed1985

Biogenic amine/metabolite response during in-flight emergencies.

Urine excretion of epinephrine (E), norepinephrine (NE), dopamine (DA), serotonin (5HT) and the metabolites vanillylmandelic acid (VMA), 4-hydroxy-3 methoxyphenylglycol (MHPG), homovanillic acid (HVA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) was determined for students (n = 19) and instructors (n = 21) involved in flying training in-flight emergencies. Timed urine samples were analyzed using high-performance liquid chromatography with electrochemical detection. Basal excretion rates were determined at a later date. Four indices showed significant alteration during the emergencies. Epinephrine and the sum of epinephrine plus norepinephrine increased, the ratio dopamine/norepinephrine decreased and the ratio norepinephrine/serotonin increased. Instructors and students differed only in that VMA and the sum VMA plus MHPG were higher in students. Among the emergencies monitored, smoke and fumes in the cockpit and mechanical problems caused the greatest stress responses.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1985

Physiological responses to a 20-mile run under three fluid replacement treatments.

Ten experienced male marathon runners ran 20 miles (32.18 km) on an outdoor course in a warm climate to measure responses in selected physiological variables as a result of drinking water, an electrolyte-glucose solution (ERG), or a caffeine solution (5 mg X kg-1 body weight) before and during the run. The caffeine solution and water were colored and flavored to resemble the electrolyte-glucose solution so that a double-blind condition could be maintained. Subjects ingested a different fluid in each of the three trials in a counterbalanced design. Parameters studied were: heart rate; rectal temperature; body weight; hemoglobin and hematocrit; serum glucose, sodium, potassium, chloride, and free fatty acids; perceived exertion; respiratory exchange ratio (R); and fractional utilization of VO2max (percentage of VO2max). Both R and percentage of VO2max were higher in subjects who drank the caffeine solution compared to those who drank water. Although post-run free fatty acid mean values were significantly higher than pre-run levels, there were no statistically significant differences among the fluid treatments. Since no other differences were observed, we concluded that, under the outdoor road-running conditions encountered here, these fluid replacement treatments did not differ in their effects on the parameters studied.

Adult↗
PubMed1983

Characteristics associated with running performance in young boys.

The purpose of the study was to replicate and extend the investigation of characteristics associated with running performance in young boys. Two groups of 10-year-old males were studied. One group (A runners) consisted of subjects who placed above the 55th percentile on a 1.6-km run; a second group (B runners) included children who placed below the 45th percentile. No significant (P greater than 0.05) between-group mean differences were noted for leg length, skeletal age, body coordination, or running economy (the aerobic demands at steady-state submaximal speeds). Significant (P less than 0.05) between-group mean differences were found for maximal aerobic power (A, 55.1; B, 48.6 ml X min-1 X kg-1), two-site skinfold sum (A, 15.2; B, 22.7 mm), and maximal sprinting speed (A, 359.7; B, 341.1 m X min-1). When compared with A runners, B runners performed 9-min runs at a higher percentage of their maximal speed (A, 58.0; B, 51.6%), required a higher VO2 to maintain this pace (A, 48.5; B, 40.8 ml X min-1 X kg-1), and exhibited higher 4.5-min post-run blood lactate levels (A, 9.1; B, 6.7 mM X 1(-1). It was concluded that post-exercise blood lactate levels are associated, and maturity and body composition are not associated with differences in distance-running performance in boys of this age.

Age Determination by Skeleton↗