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Biomedical subjects

D L Costill

Publications and source records attributed to D L Costill.

At least 19 recordsLinked to original sources
PubMed2002

Unilateral lower limb suspension does not mimic bed rest or spaceflight effects on human muscle fiber function.

We used Ca2+-activated skinned muscle fibers to test the hypothesis that unilateral lower leg suspension (ULLS) alters cross-bridge mechanisms of muscle contraction. Soleus and gastrocnemius biopsies were obtained from eight subjects before ULLS, immediately after 12 days of ULLS (post-0 h), and after 6 h of reambulation (post-6 h). Post-0 h soleus fibers expressing type I myosin heavy chain (MHC) showed significant reductions in diameter, absolute and specific peak Ca2+-activated force, unloaded shortening velocity, and absolute and normalized peak power. Fibers obtained from the gastrocnemius were less affected by ULLS, particularly fibers expressing fast MHC isoforms. Post-6 h soleus fibers produced less absolute and specific peak force than did post-0 h fibers, suggesting that reambulation after ULLS induced cell damage. Like bed rest and spaceflight, ULLS primarily affects soleus over gastrocnemius fibers. However, in contrast to these other models, slow soleus fibers obtained after ULLS showed a decrease in unloaded shortening velocity and a greater reduction in specific force.

Adult↗
PubMed2001

Calf muscle strength in humans.

In an effort to measure strength characteristics of the calf muscles, 18 subjects (14 male, 4 female, age =34.3+/-2.4yrs) were tested using a specially designed torque velocity device (TVD). This TVD is a hardware interface with the subject's lower leg which stabilizes the leg for calf muscle strength measurements. Calf muscle strength measurements consisted of 1) isometric force production at ankle angles of 80, 90, and 100 degrees of plantar flexion, 2) peak torque at six isokinetic angular velocities 0.52, 1.05, 2.09, 3.14, 4.19, and 5.24 rad x s(-1), and 3) a fatigue test consisting of 30 maximal contractions at 3.14 rad x s(-1). The greatest force production occurred at 80 degrees of ankle plantar flexion (148.5 +/- 40.2 Nm). Isokinetic force production ranged from 114.1 +/- 24.7 Nm at 0.52 rad x s(-1) to 16.8 +/- 6.5 Nm at 5.24 rad x s(-1). A fatigue test consisting of 30 maximal repetitions at 3.14 rad x s(-1) resulted in a 61 +/- 15% decline in force production. To assess reproducibility and day to day variation, measurements at 1.05 and 2.09 rad x s(-1) were made during five different trials in a single day and one trial per day for three days, respectively. The within subject coefficient of variation was 2.6 to 6.5% for reproducibility and 1.9 to 7.4% for day to day variation. Magnetic resonance imaging (MRI) of the lower limb and muscle biopsy specimens from the gastrocnemius (lateral head) and soleus muscles were obtained to examine the relationship between strength and morphological characteristics of the calf muscles. Cross-sectional area of the primary plantar flexors (gastrocnemius and soleus) was 47.9 +/- 1.3 cm2 while muscle volume was 642 +/- 16 cm3. Muscle fiber composition of the gastrocnemius and soleus averaged 57 +/- 2 and 85 +/- 3% type I fibers, respectively. A poor correlation was found between fiber type and maximal isometric force production (r =0.38; p>0.05). However, calf muscle strength and muscle size was positively correlated (r = 0.76; p < 0.05). These data indicate that using the TVD interface to stabilize the lower leg is a reliable and reproducible procedure for the measurement of calf muscle strength.

Adult↗
PubMed2001

Functional properties of slow and fast gastrocnemius muscle fibers after a 17-day spaceflight.

The purpose of this investigation was to study the effects of a 17-day spaceflight on the contractile properties of individual fast- and slow-twitch fibers isolated from biopsies of the fast-twitch gastrocnemius muscle of four male astronauts. Single chemically skinned fibers were studied during maximal Ca2+-activated contractions with fiber myosin heavy chain (MHC) isoform expression subsequently determined by SDS gel electrophoresis. Spaceflight had no significant effect on the mean diameter or specific force of single fibers expressing type I, IIa, or IIa/IIx MHC, although a small reduction in average absolute force (P(o)) was observed for the type I fibers (0.68 +/- 0.02 vs. 0.64 +/- 0.02 mN, P < 0.05). Subject-by-flight interactions indicated significant intersubject variation in response to the flight, as postflight fiber diameter and P(o) where significantly reduced for the type I and IIa fibers obtained from one astronaut and for the type IIa fibers from another astronaut. Average unloaded shortening velocity [V(o), in fiber lengths (FL)/s] was greater after the flight for both type I (0.60 +/- 0.03 vs. 0.76 +/- 0.02 FL/s) and IIa fibers (2.33 +/- 0.25 vs. 3.10 +/- 0.16 FL/s). Postflight peak power of the type I and IIa fibers was significantly reduced only for the astronaut experiencing the greatest fiber atrophy and loss of P(o). These results demonstrate that 1) slow and fast gastrocnemius fibers show little atrophy and loss of P(o) but increased V(o) after a typical 17-day spaceflight, 2) there is, however, considerable intersubject variation in these responses, possibly due to intersubject differences in in-flight physical activity, and 3) in these four astronauts, fiber atrophy and reductions in P(o) were less for slow and fast fibers obtained from the phasic fast-twitch gastrocnemius muscle compared with slow and fast fibers obtained from the slow antigravity soleus [J. J. Widrick, S. K. Knuth, K. M. Norenberg, J. G. Romatowski, J. L. W. Bain, D. A. Riley, M. Karhanek, S. W. Trappe, T. A. Trappe, D. L. Costill, and R. H. Fitts. J Physiol (Lond) 516: 915-930, 1999].

Atrophy↗
PubMed2001

Comparison of a space shuttle flight (STS-78) and bed rest on human muscle function.

The purpose of this investigation was to assess muscle fiber size, composition, and in vivo contractile characteristics of the calf muscle of four male crew members during a 17-day spaceflight (SF; Life and Microgravity Sciences Spacelab Shuttle Transport System-78 mission) and eight men during a 17-day bed rest (BR). The protocols and timelines of these two investigations were identical, therefore allowing for direct comparisons between SF and the BR. The subjects' age, height, and weight were 43 +/- 2 yr, 183 +/- 4 cm, and 86 +/- 3 kg for SF and 43 +/- 2 yr, 182 +/- 3 cm, and 82 +/- 4 kg for BR, respectively. Calf muscle strength was examined before SF and BR; on days 2, 8, and 12 during SF and BR; and on days 2 and 8 of recovery. Muscle biopsies were obtained before and within 3 h after SF (gastrocnemius and soleus) and BR (soleus) before reloading. Maximal isometric calf strength and the force-velocity characteristics were unchanged with SF or BR. Additionally, neither SF nor BR had any effect on fiber composition or fiber size of the calf muscles studied. In summary, no changes in calf muscle strength and morphology were observed after the 17-day SF and BR. Because muscle strength is lost during unloading, both during spaceflight and on the ground, these data suggest that the testing sequence employed during the SF and BR may have served as a resistance training countermeasure to attenuate whole muscle strength loss.

Adult↗
PubMed2000

An upper arm model for simulated weightlessness.

This investigation examined the effects of 4 weeks of non-dominant arm unloading on the functional and structural characteristics of the triceps brachii muscle of six normo-active college-age males (age: 23 +/- 1 years, height: 176 +/- 4 cm, weight: 76 +/- 6 kg). The primary intention of this study was to determine if arm unloading is an effective analogue for simulating the effects of weightlessness on human skeletal muscle. Subjects were tested 2-3 days preceding unloading in a standard arm sling and following removal of the sling. The sling was worn during waking hours to unload the arm. Subjects were allowed to remove the sling during sleep and bathing. Torque production (Nm) during maximal isometric extension at 90 degrees significantly declined (P < 0.05) in response to unloading (53.93 +/- 5.07 to 47.90 +/- 5.92; 12%). There was no significant change (P > 0.05) in the force-velocity attributes of the triceps over the other measured velocities (1.05, 1.57, 2.09, 3.14, 4.19, 5.24 rad.s-1). Cross-sectional muscle area (CSA) of the upper arm was smaller (44.3 +/- 2.7 to 42.4 +/- 2.5 cm2; 4%) following 4 weeks of unloading (P < 0.05). Histochemical analysis of individual muscle fibres demonstrated reductions in fibre CSA of 27 and 18% for type I and type II fibres, respectively. However, these changes were not statistically significant. Electrophoretic analysis of muscle samples revealed a significant increase (40 +/- 7 to 58 +/- 4%, pre- and post-, respectively) in myosin heavy chain (MHC) type II isoforms following unloading. Reductions in type I MHC isoform composition failed to reach statistical significance (P < 0.08). Amplitude of the integrated electromyographic (IEMG) signal during maximal isometric contraction of the long head of the triceps decreased by 21% in response to the 4-week unloading period (P < 0.05). The changes in triceps, muscle structure and function found with arm unloading are similar in magnitude and direction to data obtained from humans following exposure to real and simulated weightlessness. These findings demonstrate that arm unloading produces some of the effects seen in response to weightlessness in muscles of the upper arm and provides potential for an additional model to simulate the effects of microgravity on human skeletal muscle.

Adult↗
PubMed2000

Decreased thin filament density and length in human atrophic soleus muscle fibers after spaceflight.

Soleus muscle fibers were examined electron microscopically from pre- and postflight biopsies of four astronauts orbited for 17 days during the Life and Microgravity Sciences Spacelab Mission (June 1996). Myofilament density and spacing were normalized to a 2. 4-microm sarcomere length. Thick filament density ( approximately 1, 062 filaments/microm(2)) and spacing ( approximately 32.5 nm) were unchanged by spaceflight. Preflight thin filament density (2, 976/microm(2)) decreased significantly (P < 0.01) to 2,215/microm(2) in the overlap A band region as a result of a 17% filament loss and a 9% increase in short filaments. Normal fibers had 13% short thin filaments. The 26% decrease in thin filaments is consistent with preliminary findings of a 14% increase in the myosin-to-actin ratio. Lower thin filament density was calculated to increase thick-to-thin filament spacing in vivo from 17 to 23 nm. Decreased density is postulated to promote earlier cross-bridge detachment and faster contraction velocity. Atrophic fibers may be more susceptible to sarcomere reloading damage, because force per thin filament is estimated to increase by 23%.

Actin Cytoskeleton↗
PubMed2000

Progressive resistance training reduces myosin heavy chain coexpression in single muscle fibers from older men.

The purpose of this study was to examine myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following 12 wk of progressive resistance training (PRT). A needle biopsy was taken from the vastus lateralis to determine fiber-type expression [ATPase (pH 4.54) and MHC/MLC] in seven healthy men (age = 74.0 +/- 1.8 yr). Subjects were also tested for 1-repetition maximum (1-RM), pre- and posttraining. The progressive knee extensor protocol consisted of three sets at 80% of 1-RM 3 days/wk for 12 wk. Freeze-dried, single muscle fibers were dissected for MHC and MLC analysis and then subjected to SDS-PAGE and silver staining, pre- and posttraining. MHC expression increased in the I (10.4%; P < 0.05) and decreased in I/IIa (9.0%; P < 0.05), I/IIa/x (0.9%; P < 0.05), and IIa/x (8.9%; P < 0.05) isoforms, with no change in the IIa and IIx isoforms, pre- vs. posttraining (total fibers = 3,059). The MLC(3f)-to-MLC(2) ratio did not change with the PRT in either the MHC I or MHC IIa isoforms (total fibers = 902), pre- to posttraining. ATPase fiber distribution did not significantly differ following training (I: 50. 4 +/- 6.7 vs. 51.9 +/- 7.9, IIa: 36.8 +/- 5.3 vs. 41.1 +/- 7.0, IIb: 12.8 +/- 5.6 vs. 7.0 +/- 4.0%; pre- vs. posttraining, respectively). 1-RM increased (51.9%; P < 0.05) from pre- to posttraining. The PRT provide a stimulus for alterations in MHC isoforms, which demonstrated a decrease in all hybrid isoforms and an increase in MHC I expression (not found in the ATPase results), unlike the MLC ratio (3:2), which was not altered with training.

Adenosine Triphosphatases↗
PubMed1999

Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres.

1. Soleus biopsies were obtained from four male astronauts 45 days before and within 2 h after a 17 day spaceflight. 2. For all astronauts, single chemically skinned post-flight fibres expressing only type I myosin heavy chain (MHC) developed less average peak Ca2+ activated force (Po) during fixed-end contractions (0.78 +/- 0. 02 vs. 0.99 +/- 0.03 mN) and shortened at a greater mean velocity during unloaded contractions (Vo) (0.83 +/- 0.02 vs. 0.64 +/- 0.02 fibre lengths s-1) than pre-flight type I fibres. 3. The flight-induced decline in absolute Po was attributed to reductions in fibre diameter and/or Po per fibre cross-sectional area. Fibres from the astronaut who experienced the greatest relative loss of peak force also displayed a reduction in Ca2+ sensitivity. 4. The elevated Vo of the post-flight slow type I fibres could not be explained by alterations in myosin heavy or light chain composition. One alternative possibility is that the elevated Vo resulted from an increased myofilament lattice spacing. This hypothesis was supported by electron micrographic analysis demonstrating a reduction in thin filament density post-flight. 5. Post-flight fibres shortened at 30 % higher velocities than pre-flight fibres at external loads associated with peak power output. This increase in shortening velocity either reduced (2 astronauts) or prevented (2 astronauts) a post-flight loss in fibre absolute peak power (microN (fibre length) s-1). 6. The changes in soleus fibre diameter and function following spaceflight were similar to those observed after 17 days of bed rest. Although in-flight exercise countermeasures probably reduced the effects of microgravity, the results support the idea that ground-based bed rest can serve as a model of human spaceflight. 7. In conclusion, 17 days of spaceflight decreased force and increased shortening velocity of single Ca2+-activated muscle cells expressing type I MHC. The increase in shortening velocity greatly reduced the impact that impaired force production had on absolute peak power.

Adult↗
PubMed1999

Effects of precooling on thermoregulation during subsequent exercise.

PURPOSE: The purpose of this study was to examine the effect of a decreased body core temperature before a simulated portion of a triathlon (swim,15 min; bike, 45 min) and examine whether precooling could attenuate thermal strain and increase subjective exercise tolerance in a warm environment (26.6 degrees C/60% relative humidity (rh)). METHODS: Six endurance trained triathletes (28+/-2 yr, 8.2+/-1.7% body fat) completed two randomly assigned trials 1 wk apart. The precooling trial (PC) involved lowering body core temperature (-0.5 degrees C rectal temperature, Tre) in water before swimming. The control trial (CON) was identical except no precooling was performed. Water temperature and environmental conditions were maintained at 25.6 degrees C and 26.6 degrees C/60% rh, respectively, throughout all testing. RESULTS: Mean time to precool was 31+/-8 min and average time to reach baseline Tre during cycling was 9+/-7 min. Oxygen uptake (VO2), HR, skin temperature (Tsk), Tre, RPE, and thermal sensation (TS) were recorded following the swim segment and throughout cycling. No significant differences in mean body (Tb) or Tsk were noted between PC and CON, but a significant difference (P < 0.05) in Tre between treatments was noted through the early phases of cycling. No significant differences were reported in HR, VO2, RPE, TS, or sweat rate (SR) between treatments. Body heat storage (S) was negative following swimming in both PC (-92+/-6 W x m2) and CON (-66+/-9 W x m2). A greater S occurred in PC (109+/-6 W x m2) vs CON (79+/-4 W x m2) during cycling (P < 0.05). CONCLUSIONS: Precooling attenuated the rise in Tre, but this effect was transient. Therefore, precooling is not recommended before a triathlon under similar environmental conditions.

Adult↗
PubMed1998

Disproportionate loss of thin filaments in human soleus muscle after 17-day bed rest.

Previously we reported that, after 17-day bed rest unloading of 8 humans, soleus slow fibers atrophied and exhibited increased velocity of shortening without fast myosin expression. The present ultrastructural study examined fibers from the same muscle biopsies to determine whether decreased myofilament packing density accounted for the observed speeding. Quantitation was by computer-assisted morphometry of electron micrographs. Filament densities were normalized for sarcomere length, because density depends directly on length. Thick filament density was unchanged by bed rest. Thin filaments/microm2 decreased 16-23%. Glycogen filled the I band sites vacated by filaments. The percentage decrease in thin filaments (Y) correlated significantly (P < 0.05) with the percentage increase in velocity (X), (Y = 0.1X + 20%, R2 = 0.62). An interpretation is that fewer filaments increases thick to thin filament spacing and causes earlier cross-bridge detachment and faster cycling. Increased velocity helps maintain power (force x velocity) as atrophy lowers force. Atrophic muscles may be prone to sarcomere reloading damage because force/microm2 was near normal, and force per thin filament increased an estimated 30%.

Actin Cytoskeleton↗
PubMed1998

Force-velocity-power and force-pCa relationships of human soleus fibers after 17 days of bed rest.

Soleus muscle fibers from the rat display a reduction in peak power and Ca2+ sensitivity after hindlimb suspension. To examine human responses to non-weight bearing, we obtained soleus biopsies from eight adult men before and immediately after 17 days of bed rest (BR). Single chemically skinned fibers were mounted between a force transducer and a servo-controlled position motor and activated with maximal (isotonic properties) and/or submaximal (Ca2+ sensitivity) levels of free Ca2+. Gel electrophoresis indicated that all pre- and post-BR fibers expressed type I myosin heavy chain. Post-BR fibers obtained from one subject displayed increases in peak power and Ca2+ sensitivity. In contrast, post-BR fibers obtained from the seven remaining subjects showed an average 11% reduction in peak power (P < 0.05), with each individual displaying a 7-27% reduction in this variable. Post-BR fibers from these subjects were smaller in diameter and produced 21% less force at the shortening velocity associated with peak power. However, the shortening velocity at peak power output was elevated 13% in the post-BR fibers, which partially compensated for their lower force. Post-BR fibers from these same seven subjects also displayed a reduced sensitivity to free Ca2+ (P < 0.05). These results indicate that the reduced functional capacity of human lower limb extensor muscles after BR may be in part caused by alterations in the cross-bridge mechanisms of contraction.

Adult↗
PubMed1997

Thermoregulatory responses to cycling with and without a helmet.

This study examined the effects of wearing a helmet on selected body temperatures and perceived heat sensation of the head and body while cycling in a hot-dry (D) (35 degrees C, 20% relative humidity (RH) and hot-humid (H) (35 degrees C, 70% RH) environment. Ten male and four female cyclists (mean +/- SD: males = age 27 +/- 7 yr, peak O2 uptake (VO2) 4.10 +/- 0.54 L.min-1; females = age 26 +/- 3 yr, peak O2 uptake (VO2) 3.08 +/- 0.49 L.min-1) performed four randomized 90-min cycling trials at 60% of peak VO2 both with (HE) and without (NH) a commercially available cycling helmet in both D and H environments. VO2, core (Te), skin (Tsk), and head skin temperatures, heart rate (HR), rating of perceived exertion (RPE), and perceived thermal sensation of head (TSH) and body (TSB) were measured throughout exercise. For all measured variables, no significant difference was evident between HE and NH. However, Tc, Tsk, and mean head skin temperatures were higher (P < 0.001) in H than D. Likewise, RPE, TSH, TSB (P < 0.001), and sweat rates (H = 1.33 +/- 0.32, D = 1.14 +/- 0.23 L.h-1) (P < 0.01) were higher in H versus D. Results indicate that use of a commercially available cycling helmet while riding in a hot-dry or hot-humid environment does not cause the subjects to become more hyperthermic or increase perceived heat sensation of the head or body.

Adult↗
PubMed1997

Glycemic and insulinemic responses to multiple preexercise carbohydrate feedings.

This investigation was undertaken to determine whether consuming several small feedings of preexercise carbohydrate (CHO), rather than a single bolus, would affect blood glucose and insulin responses during rest and exercise. Eight trained cyclists ingested 22.5, 45, or 75 total g maltodextrin and dextrose dissolved in 473 ml of water or an equal volume of placebo (PL). Drinks were divided into four portions and consumed at 15-min intervals in the hour before a 120-min ride at 66% VO2max. Serum glucose values were elevated by the CHO feedings at rest and fell significantly below baseline and PL at 15 min of exercise. However, glucose concentrations were similar in each of the CHO trials. Insulin concentrations also increased rapidly during rest, then fell sharply at the onset of exercise. The findings demonstrate that CHO consumed within an hour before exercise, even when taken in several small feedings, can produce transient hypoglycemia near the onset of exercise. Additionally, the magnitude of the response appears to be unrelated to either the amount of CHO ingested or the insulin response.

Adult↗
PubMed1997

Effect of 17 days of bed rest on peak isometric force and unloaded shortening velocity of human soleus fibers.

The purpose of this study was to examine the effect of prolonged bed rest (BR) on the peak isometric force (P0) and unloaded shortening velocity (V0) of single Ca(2+)-activated muscle fibers. Soleus muscle biopsies were obtained from eight adult males before and after 17 days of 6 degrees head-down BR. Chemically permeabilized single fiber segments were mounted between a force transducer and position motor, activated with saturating levels of Ca2+, and subjected to slack length steps. V0 was determined by plotting the time for force redevelopment vs. the slack step distance. Gel electrophoresis revealed that 96% of the pre- and 87% of the post-BR fibers studied expressed only the slow type I myosin heavy chain isoform. Fibers with diameter > 100 microns made up only 14% of this post-BR type I population compared with 33% of the pre-BR type I population. Consequently, the post-BR type I fibers (n = 147) were, on average, 5% smaller in diameter than the pre-BR type I fibers (n = 218) and produced 13% less absolute P0. BR had no overall effect on P0 per fiber cross-sectional area (P0/CSA), even though half of the subjects displayed a decline of 9-12% in P0/CSA after BR. Type I fiber V0 increased by an average of 34% with BR. Although the ratio of myosin light chain 3 to myosin light chain 2 also rose with BR, there was no correlation between this ratio and V0 for either the pre- or post-BR fibers. In separate fibers obtained from the original biopsies, quantitative electron microscopy revealed a 20-24% decrease in thin filament density, with no change in thick filament density. These results raise the possibility that alterations in the geometric relationships between thin and thick filaments may be at least partially responsible for the elevated V0 of the post-BR type I fibers.

Actin Cytoskeleton↗
PubMed1997

Effects of diet on muscle triglyceride and endurance performance.

The purpose of this investigation was to examine the effects of diet on muscle triglyceride and endurance performance. Seven endurance-trained men completed a 120-min cycling bout at 65% of maximal oxygen uptake. Each subject then ingested an isocaloric high-carbohydrate (Hi-CHO; 83% of energy) or a high-fat (Hi-Fat; 68% of energy) diet for the ensuing 12 h. After a 12-h overnight fast, a 1,600-kJ self-paced cycling bout was completed. Muscle triglyceride measured before (33.0 +/- 2.3 vs. 37.0 +/- 2.1 mmol/kg dry wt) and after (30.9 +/- 2.4 vs. 32.8 +/- 1.6 mmol/kg dry wt) the 120-min cycling bout was not different between the Hi-CHO and Hi-Fat trials, respectively. After the 24-h dietary-fasting period, muscle triglyceride was significantly higher for the Hi-Fat (44.7 +/- 2.4 mmol/kg dry wt) vs. the Hi-CHO (27.5 +/- 2.1 mmol/kg dry wt) trial. Furthermore, self-paced cycling time was significantly greater for the Hi-Fat (139.3 +/- 7.1 min) compared with the Hi-CHO (117.1 +/- 3.2 min) trial. These data demonstrate that there was not a significant difference in muscle triglyceride concentration before and after a prolonged moderate-intensity cycling bout. Nevertheless, a high-fat diet increased muscle triglyceride concentration and reduced self-paced cycling performance 24 h after the exercise compared with a high-carbohydrate diet.

Adult↗
PubMed1996

Selected psychological characteristics and health behaviors of aging marathon runners: a longitudinal study.

This report summarizes the health behaviors and psychological characteristics of fifteen male marathon runners who were first tested in 1969 (N = 8) and 1976 (N = 7). The participants in this study averaged 29 years of age at the outset, and the mean age at the time of follow-up was 50 years. These subjects were found to score in the normal range on all of the psychological variables, and they were characterized by the "iceberg" profile described earlier for elite athletes in various sports. This profile includes scores that fall below the population average on mood states such as tension, depression, anger, fatigue and confusion along with above average scores on vigor. Also, the psychological traits of these former runners have been remarkably stable across the past two decades, with the exception that a uniform decline has been observed for the neuroticism measure. Earlier research by Eysenck has shown that neuroticism decreases with age. These former marathon runners continue to be moderately active, and it is noteworthy that they first became involved as runners while in high school. All but one of the participants had attended college, and each had participated in competitive running while in college. Training for marathon competition took place following the college years. It is likely that much of the early success enjoyed by this group was governed to a substantial degree by heredity. This sample possessed an average aerobic power of 70 ml.kg-1.min-1 along with a unique somatotype when first tested, and these factors are known to have a substantial heritability component. The health behaviors studied in this group were uniformly positive. They were found to be physically active, and their physical self-esteem fell above that of other men in their age group. The subjects reported moderate use of alcohol, no insomnia, few physical problems and good overall mood. The sample of former marathon runners described in this report is unique in a number of respects, and caution is urged in making generalizations. With this qualification in mind, it is concluded that a lifetime of regular physical activity is associated with desirable physical and mental health.

Adult↗
PubMed1996

The effects of pre-exercise starch ingestion on endurance performance.

This study compared the physiological responses and performance following the ingestion of a waxy starch (WS), resistant starch (RS), glucose (GL) and an artificially-sweetened placebo (PL) ingested prior to exercise. Ten college-age, male competitive cyclists completed four experimental protocols consisting of a 30 min isokinetic, self-paced performance ride preceded by 90 min of constant load cycling at 66% VO2max. Thirty min prior to exercise, they ingested 1 g.kg-1 body weight of GL, WS, RS, or PL At rest, GL elicited greater (p < 0.05) serum glucose and insulin responses than all other trials. During exercise, however, serum glucose, insulin, blood C-peptide and glucagon responses were similar among trials. The mean total carbohydrate oxidation rates (CHOox) were higher (p < 0.05) during the GL, WS, and RS trials (2.59 +/- 0.13, 2.49 +/- 0.10, and 2.71 +/- 0.15 g.min-1, respectively) compared to PL (2.35 +/- 0.12 g.min-1). Subjects were able to complete more work (p < 0.05) during the performance ride when they ingested GL (434 +/- 25.2 kj) or WS (428 +/- 22.5 kj) compared to PL (403 +/- 35.1 kj). They also tended to produce more work with RS ingestion (418 +/- 31.4 kj), although this did not reach statistical significance (p < 0.09). These results indicate that preexercise CHO ingestion in the form of starch or glucose maintained higher rates of total carbohydrate oxidation during exercise and provided an ergogenic benefit during self-paced cycling.

Adult↗