Cardiac Structure and Function in Weight Trainers,Runners, and Runner/Weight Trainers

Abstract

The purpose of this study was to describe and compare cardiac structure and function in adult male weight trainers, runners, and those who do both activities. Subjects had actively participated in the various training programs for the previous five years. Age ranged from 28.4 to 31.3 years in the three groups. Echocardiography was used to assess selected heart diameters, volumes, indices of contractility, and thicknesses, while VO₂ max and percent body fat were measured using standard methods. Heart structure and function were expressed in absolute terms and relative to total body weight. An alpha level of .05 was used in all comparisons. Results indicated the runners demonstrated significantly greater relative LVID_d, LVID_s, and LVPW than the weight trainers. The runner/weight trainers possessed significantly greater relative LVID_d, LVID_s, LVPW, IVS, and LVEDV than the weight trainers. No significant differences, absolute or relative, existed between the runner and runner/weight trainer groups in any of the myocardial structure and function variables. It was concluded that men who run or run and weight train have similar structural and functional characteristics of the heart and possess greater relative internal diameter and left ventricular wall thickness than men who only weight train.     

Cardiac structure and function in women basketball athletes: seasonal variation and comparisons with nonathletic controls.

To characterize hypertrophy and quantify seasonal changes in cardiac structure and function of women collegiate basketball (BB) athletes (n = 15), echocardiographic (echo) measurements were made in the fall (FALL1), winter (WIN), and spring (SPR), then again during the subsequent fall (FALL2; n = 10). Comparisons were made to age-matched nonathletes (NA) measured during FALL1 (n = 22) and SPR (n = 5). Left ventricular (LV) internal dimension-diastole (LVIDd), LV end-diastolic volume (LVEDV), stroke volume (SV), LV mass (LVM), septal thickness (IVS), LV posterior wall thickness (LVPW), right ventricular (RV) internal dimension-diastole (RVIDd), and aortic root diameter (AOD) were significantly larger (12-70%) in the athletes; RVIDd-, LVEDV-, SV-, and LVM-index were also significantly greater (8-46%). From FALL1 to SPR measurement periods, LVIDd, RVIDd, LVEDV, SV, IVS, and LVM-index increased significantly (7-18%) in the athletes. Over the same period of time, LVIDd, LAD, AOD, LVEDV, and SV measured in the five NA subjects increased significantly. In the athletes, LVIDs, RVIDd, IVS, LVPW, and LVM decreased significantly (5-30%) from the SPR to FALL2 measurement period. These data characterize the general nature of the cardiac hypertrophy noted in women BB athletes compared to NA controls and show that distinct changes in heart structure corresponding to different periods of the competitive season can occur in these athletes.     

Isokinetic Leg Flexion and Extension Strength of Elite Adolescent Female Track and Field Athletes

Abstract

Sixty-two elite adolescent (age: 16.39 ± 1.62 yrs) female track and field athletes volunteered to be measured isokinetically for peak torque of the leg flexors and extensors. The sample included 16 throwers, 11 jumpers, 12 middle-distance runners (> 400 m), and 23 sprinters. A Cybex II isokinetic dynamometer was used to measure dominant leg strength at 180°/sec. One-way ANOVA revealed significant between group differences for absolute flexion and extension (Nm), extension/body weight (Nm/Kg), and extension/lean body weight (Nm/Kg). Scheffe post-hoc comparisons showed that, for absolute leg extension strength, throwers were stronger than middle-distance runners (by 54.4%), sprinters (35.6%), and jumpers (23.6%). For absolute leg flexion movements, throwers were stronger than middle distance runners (37.4%) and sprinters (32.1%). Jumpers had greater extension peak torque values than middle-distance runners relative to body weight (14.0%), and throwers were stronger than middle-distance runners for extension/lean body weight (14.9%)). No other comparisons were significant. However, when strength was expressed relative to body weight or lean body weight, there were few differences between events for flexion or extension. Given that absolute strength scores were correlated with body weight and lean body weight, peak torque/body weight or peak torque/lean body weight may be more sensitive than absolute values as indicators of underlying factors (such as training status or fiber type composition) responsible for the differences in muscular strength between groups.     

Cardiac Structure and Function in Women Basketball Athletes: Seasonal Variation and Comparisons with Nonathletic Controls

Abstract

To characterize hypertrophy and quantify seasonal changes in cardiac structure and function of women collegiate basketball (BB) athletes (n = 15), echocardiography (echo) measurements were made in the fall (FALL₁), winter (WIN), and spring (SPR), then again during the subsequent fall (FALL₂; n = 10). Comparisons were made to age-matched nonathletes (NA) measured during FALL₁ (n = 22) and SPR (n = 5). Left ventricular (LV) internal dimension–diastole (LVIDd), LV end-diastolic volume (LVEDV), stroke volume (SV), LV mass (LVM), septal thickness (IVS), LV posterior wall thickness (LVPW), right ventricular (RV) internal dimension-diastole (RVIDd), and aortic root diameter (AOD) were significantly larger (12–70%) in the athletes; RVIDd-, LVEDV-, SV-, and LVM-index were also significantly greater (8–46%). From FALL₁ to SPR measurement periods, LVWd, RVWd, LVEDV, SV, IVS, and LVM-index increased significantly (7–18%) in the athletes. Over the same period of time, LVIDd, LAD, AOD, LVEDV, and SV measured in the five NA subjects increased significantly. In the athletes, LVIDs, RVIDd, IVS, LVPW, and LVM decreased significantly (5–30%) from the SPR to FALL₂ measurement period. These data characterize the general nature of the cardiac hypertrophy noted in women BB athletes compared to NA controls and show that distinct changes in heart structure corresponding to different periods of the competitive season can occur in these athletes.     

Derivation of an Age and Weight Handicap for the 5K Run

The adverse effect of increasing age and/or body weight on distance run performance has been well documented. Accordingly, nearly all five kilometer (5K) road races employ age categories and, sometimes, a heavier body weight classification. Problems with such conventions include small numbers of runners within older age categories and the advantage given to the lightest runners within each weight category. We developed a 5K Handicap (5KH), a model that calculates an adjusted run time based on the inputs of actual 5K run time, age, and body weight for men and women. This adjusted time, then, can be compared between runners of different ages and body weights. The purpose of this paper was to explain, in detail, the derivation of the 5KH formula using published theoretical and empirical findings on age, body weight and distance run time relationships. To our knowledge, the 5KH is the first such model and overcomes the problems associated with being heavier within one weight class and having too few runners in certain age categories. We are currently undertaking large-scale validation studies and evaluation of its race day implementation.     

The effect of elevating the heels on spinal kinematics and kinetics during the back squat in trained and novice weight trainers

ABSTRACT

This research assessed the influence of various heel elevation conditions on spinal kinematic and kinetic data during loaded (25% and 50% of body weight) high-bar back squats. Ten novice (mass 67.6 ± 12.4 kg, height 1.73 ± 0.10 m) and ten regular weight trainers (mass 66.0 ± 10.7 kg, height 1.71 ± 0.09 m) completed eight repetitions at each load wearing conventional training shoes standing on the flat level floor (LF) and on an inclined board (EH). The regular weight training group performed an additional eight repetitions wearing weightlifting shoes (WS). Statistical parametric mapping (SPM1D) and repeated measures analysis of variance were used to assess differences in spinal curvature and kinetics across the shoe/floor conditions and loads. SPM1D analyses indicated that during the LF condition the novice weight trainers had greater moments around L4/L5 than the regular weight trainers during the last 20% of the lift (P < 0.05), with this difference becoming non-significant during the EH condition. This study indicates that from a perspective of spinal safety, it appears advantageous for novice weight trainers to perform back squats with their heels slightly elevated, while regular weight trainers appear to realize only limited benefits performing back squats with either EH or WS.     

女子拳击运动员心血管结构及功能的特征性变化

目的：探究优秀女子拳击运动员心血管结构及功能的超声心动图特征,为女子拳击项目的运动员选材提供依据。方法：采用超声技术检查22名女子拳击运动员及15名普通女大学生的心血管结构及功能。结果：女子拳击运动员心率、收缩压与舒张压均低于普通组（P＜0.05）;女子拳击运动员左室舒张末期内径（LVIDd）、左室收缩末期内径（LVIDs）、左心室舒张期后壁厚度（LVPWd）、左室舒张末期内径/体表面积（LVIDd/BSA）、左室收缩末期内径/体表面积（LVIDs/BSA）、左心室质量（LVM）、左心室质量指数（LVMI）、左室舒张末期容积（EDV）、左室收缩末期容积（ESV）、每搏量（SV）、心输出量（CO）及心指数（CI）均显著大于普通组（P＜0.05）,但射血分数（EF）、左室短轴缩短率（FS%）显著小于普通组（P＜0.05）;女子拳击运动员颈动脉、肱动脉、桡动脉、股动脉的横截面积以及肱动脉和股动脉的内径均显著大于普通组（P＜0.05）,股动脉内中膜厚度高于普通组（P＜0.05）;肱动脉内皮依赖性舒张功能（FMD）女子拳击运动员显著优于普通组（P＜0.05）。结论：优秀女子拳击运动员心血管的结构及功能在长期的训练后发生了适应性变化,表现在心室腔扩大、心室容量增加、动脉管腔的面积与内径增加,血管内皮舒张功能提高。     

Standardization indices of cardiac hypertrophy in weight lifters

In order to investigate further the use of standardization procedures to determine training effects on cardiac dimension and function, two groups of subjects were analysed noninvasively. A control group of sedentary men (n = 7) and an experimental group of weight lifters (n = 12) volunteered for a standard M-mode echocardiographic assessment. Indices of cardiac function as well as absolute left ventricular dimensions and left ventricular mass were similar between the groups. Standardizing for body surface area and body weight separated the groups. The weight lifters were shown to have a more muscular left ventricular posterior wall. The weight lifters also demonstrated a dilated left ventricle when indexing for body surface area. All other dimensional and volumetric indices were non-significant. The present investigation underlines the need for matching control and experimental groups to biometric variables in order to avoid misinterpreting cardiac enlargement. There is evidence for a true relative hypertrophy in weight lifters as indicated by similar absolute cardiac dimensions and similar biometric variables. Therefore, when evaluating athletes engaged in a chronic pressure overload, cardiac hypertrophy indices should consider body surface area (BSA), body weight and lean body weight (LBW). Future work in this field should incorporate rigorous controls on all biometric variables for better interpretation of hypertrophy in relative or absolute terms.     

The effect of shoe type on gait in forefoot strike runners during a 50-km run

PurposeTo observe the relative change in foot-strike pattern, pressure characteristics, surface electromyography (sEMG) recordings, and stride characteristics in forefoot strike runners wearing both minimalist and traditional shoes during a 50-km run.MethodsFour experienced minimalist runners were enrolled in this study. Each runner ran a 50-km simulated run in both minimalist shoes and traditional shoes. Pressure data, sEMG recordings, and limited 3D motion capture data were collected during the initial 0.8 km and final 0.8 km for each trial.ResultsThree runners in the traditional shoe type condition and one runner in the minimalist shoe type condition demonstrated a more posterior initial contact area (midfoot strike (MFS) pattern) after the 50-km run, which was supported by increased activity of the tibialis anterior in the pre-contact phase (as per root mean square (RMS) values). In addition, in both pre- and post-run conditions, there were increased peak pressures in the minimalist shoe type, specifically in the medial forefoot. Muscle fatigue as defined by a decreased median frequency observed in isometric, constant force contractions did not correspond with our hypothesis in relation to the observed foot strike change pattern. Finally, step rate increased and step length decreased after the 50-km run in both shoe type conditions.ConclusionMore runners adopted a more posterior initial contact area after the 50-km run in the traditional shoe type than in the minimalist shoe type. The runners who adopted a more posterior initial contact area were more closely associated with an increased median frequency of the medial gastrocnemius, which suggests there may be a change in motor unit recruitment pattern during long-distance, sustained velocity running. The increased peak pressures observed in the medial forefoot in the minimalist shoe type may predispose to metatarsal stress fractures in the setting of improper training.     

Anthropometric and training characteristics of female marathon runners as determinants of distance running performance

The purpose of this study was to determine how female marathon runners of varying standards differed in body composition and physique and in their training regimes, and secondly to develop predictors of distance running performance from the anthropometric and training variables. Female marathon runners (n = 36), all participants in a national 10 mile (16 km) road racing championship, were divided into three groups according to their best time for the 26.2 mile race. They were assessed for body composition and somatotype using anthropometric techniques and completed a questionnaire about their current training for the marathon. No difference was found between the groups of distance runners when measured for height, bone widths and circumferences. The three groups were found to have similar body weights of approximately 53 kg, a value which is much lower than the average for sedentary women, but which compares favourably with those from previous studies of female long distance runners. While all the runners had a lower per cent fat, as measured from skinfold thicknesses, than sedentary women, the elite runners were seen to have significantly lower values (P less than 0.05) than the other two groups. The difference in body fat was particularly reflected in the triceps skinfold value. There was also a tendency for the elite runners to be more ectomorphic and less endomorphic than the others. The better runners were seen, on the whole, to have been running longer, and to have more strenuous regimes, both in terms of intensity of training and distance run per week. Multiple regression and discriminant function analyses indicated that the number of training sessions per week and the number of years training were the best predictors of competitive performance at both 10 mile and marathon distances. They also indicated that a female long distance runner with a slim physique high in ectomorphy has the greatest potential for success.     

Training Content and Potential Impact on Performance

The purpose of the present investigation was to compare the content of 8 weeks of training in young endurance-trained male and female runners and study the potential impact of this training content on performance. Fourteen men and 11 women performed two criterion exercises until exhaustion on an outdoor track before and after the 8-week training period. The first test was a graded exercise to determine maximal aerobic velocity (Mav), the velocity at the lactate concentration threshold (v-Tlac), and the velocity at delta 50 (vΔ50: the velocity halfway between Mav and v-Tlac). The second test was a constant run at vΔ50 to determine the time to exhaustion at this velocity (tlimvΔ50). Training logs were used to monitor the self-directed training sessions. The results showed that the women had a lower training volume but trained at higher exercise velocities than the men. However, they presented similar values as the men for expected temporary performance capacity and did not improve their performance (Mav and tlimvΔ50) over the 8-week period. After the training period, only v-Tlac (absolute and relative values) was slightly but significantly increased by training. These results could be due to the fact that both men and women did not train more than 10% of the total distance run at exercise velocities equal to or higher than their Mav and did not increase their training load during the 8-week training period. We suggest that changes in training content during the season, such as severe (long-duration or high-intensity) training sessions, may have improved their performance capacity.     

Training content and potential impact on performance: a comparison of young male and female endurance-trained runners

The purpose of the present investigation was to compare the content of 8 weeks of training in young endurance-trained male and female runners and study the potential impact of this training content on performance. Fourteen men and 11 women performed two criterion exercises until exhaustion on an outdoor track before and after the 8-week training period. The first test was a graded exercise to determine maximal aerobic velocity (Mav), the velocity at the lactate concentration threshold (v-Tlac), and the velocity at delta 50 (v delta50: the velocity halfway between Mav and v-Tlac). The second test was a constant run at v delta50 to determine the time to exhaustion at this velocity (tlimv delta50). Training logs were used to monitor the self-directed training sessions. The results showed that the women had a lower training volume but trained at higher exercise velocities than the men. However they presented similar values as the men for expected temporary performance capacity and did not improve their performance (Mav and tlimv delta50) over the 8-week period. After the training period, only v-Tlac (absolute and relative values) was slightly but significantly increased by training. These results could be due to the fact that both men and women did not train more than 10% of the total distance run at exercise velocities equal to or higher than their Mav and did not increase their training load during the 8-week training period. We suggest that changes in training content during the season, such as severe (long-duration or high-intensity) training sessions, may have improved their performance capacity.     

Time Comparison between the Cross-Over and Jab-Step Starts

Abstract

The purpose of this investigation was to evaluate and quantify physiological differences among groups of distance runners. The subjects included 20 elite distance runners (8 marathon, 12 middle-long distance) and 8 good runners. Working capacity and cardiorespiratory function were determined by submaximal and maximal treadmill tests, and body composition by hydrostatic weighing. The variables studied were maximum oxygen uptake ([Vdot]O₂ max), [Vdot]O₂ submax, lactic acid submax, lean body weight, and fat weight. MANOVA showed that the good runners differed from the elite runners (p < 0.01) and the elite marathon runners differed from the elite middle-long distance runners (p < 0.05). Discriminant analysis showed that both functions were significant. The first was a general physiological efficiency factor that separated the good and elite runners. The second separated the elite marathon and middle-long distance groups. The second function showed that the marathon runners had lower lactic acid submax values. The middle-long distance runners had higher [Vdot]O₂ max values. Classification analysis was used to evaluate the accuracy of the discriminant analysis; 80% of the elite runners were correctly classified as marathon or middle-long distance runners. The discriminant functions were used to develop a multivariate scaling model for evaluating distance runners. Two premier runners, one marathoner (F. Shorter) and one middle-long distance runner (S. Prefontaine), were found to be at the extremes of the scale. The data showed that the discriminant functions provided a valid model for evaluating differences among elite distance runners.     

肥胖对大学生心肺功能和身体素质影响的实验比较研究

目的：探究肥胖对大学生心肺功能和身体素质的影响,为肥胖大学生制定科学的运动处方和体育教学提供参考依据。方法：将研究对象分为实验组和对照组。实验组为肥胖大学生,对照组为正常体重大学生,运用quarkb2型运动心肺功能测试仪测得受试者的最大摄氧量、氧脉搏、肺通气量等指标。在运动场测得受试者引体向上、立定跳远、50m跑和1 000m跑成绩,运用SPSS11.0统计软件对测试数据作差异统计学分析。结果：实验组的最大摄氧量绝对值大于对照组,而最大摄氧量相对值表现为对照组大于实验组。无氧阈表现为对照组大于实验组。氧脉搏绝对值表现为实验组大于对照组,相对值为对照组大于实验组。肺通气量绝对值表现为实验组大于对照组,而相对值表现为对照组大于实验组。对照组的四项身体素质测试成绩均明显好于实验组。结论：①由于多余体脂的影响,肥胖大学生的有氧耐力比较差。②肥胖者的最大摄氧量、最大氧脉搏绝对值高于正常体重者,是个体为克服过多体脂造成的过重负荷而表现出的生理性代偿。③肥胖大学生的骨骼肌对VO2max的利用率比较低。④肥胖是影响大学生心肺功能和身体素质的一个不良因素。     

Altered multi-muscle coordination patterns in habitual forefoot runners during a prolonged,exhaustive run

Abstract

Introduction: In response to fatigue during an exhaustive treadmill run, forefoot runner’s muscles must adapt to maintain their pace. From a neuromuscular control perspective, certain muscles may not be able to sustain the force to meet the run’s demands; thus, there may be alternative muscle coordination in the lower extremity that allows for continued running for an extended period of time. The aim of this study was to quantify the change in muscle coordination during a prolonged run in forefoot runners.

Methods: Thirteen forefoot runners performed exhaustive treadmill runs (mean duration: 15.4?±?2.2?min). The muscle coordination of seven lower extremity muscles was quantified using a high-resolution time–frequency analysis together with a pattern recognition algorithm.

Results: The mean EMG intensity for the lateral and medial gastrocnemius muscles decreased with the run (p?=?0.02; 0.06). The weight factors of the second principal pattern decrease by 128.01% by the end of run (p?=?0.05, Cohen’s d?=?0.42) representing a relatively greater biceps femoris activation in midstance but smaller midstance rectus femoris, vastus medialis, triceps surae, and tibialis anterior activation.

Discussion: These results suggest that forefoot runners cannot sustain plantar flexor activation throughout an exhaustive run and change their muscle coordination strategy as a compensation. Understanding the underlying compensation mechanisms humans use to cope with fatigue will help to inform training modalities to enhance these late stage muscle activation strategies for athletes with the goal of improving performance and reducing injury.     

Novice runners show greater changes in kinematics with fatigue compared with competitive runners

Fatigue, developed over the course of a run, may cause changes in running kinematics. Training status may influence the effect of fatigue on running kinematics, since well trained, competitive runners are used to running until exhaustion, whereas novice runners are not. This study aimed to determine changes in running kinematics during an exhaustive run in both novice (NOVICE) and competitive (COMP) long-distance runners. About 15 NOVICE and 15 COMP runners performed a treadmill run, until voluntary exhaustion at 3,200 m time trial pace. Joint angles and global trunk and pelvis angles were recorded at the beginning and at the end of the run. In both groups, peak pelvic anterior tilt, pelvic rotation range of motion (both during stance phase) and ankle plantar flexion during swing phase increased after the exhaustive run. There was a significant interaction effect between group and exhaustion for peak forward trunk lean, which increased only in the NOVICE group, and for hip abduction during mid-swing, which increased in NOVICE and decreased in COMP runners. In conclusion, NOVICE runners showed larger kinematic adjustments when exhausted than COMP runners. This may affect their running performance and should be taken into account when assessing a runner’s injury risk.     

Physiological Profiles of High School Female Cross Country Runners

Abstract

Percent body fat, ratings of perceived exertion and maximal oxygen consumption during a continuous running treadmill test were obtained on 127 high school female cross country runners. These young runners (x 15.6 yrs) were running approximately 25 miles per week at the time of testing. They had an average [Vdot]O₂ max of 50.8 ml · min^-1 and an HR max of 198.0 bpm. The mean percent body fat, as determined from hydrostatic weighing, was 15.4%. The onset of metabolic acidosis was estimated to occur at 78% of [Vdot]O₂ max. A stepwise multiple regression with the 3000 meter run as the dependent variable indicated that max treadmill run time, weight relative [Vdot]O₂ max and [Vdot] max entered the equation in that order, yielding an R of 0.67. Both HR and RPE increased with work intensity, but not at equal rates. These high school female runners had higher [Vdot]O₂ max's than previously reported for this age group; however, they were considerably below these values reported for national caliber distance runners.     

Heat production and storage are positively correlated with measures of body size/composition and heart rate drift during vigorous running

The purposes of this study were to determine the relationships between: (a) measures of body size/composition and heat production/storage, and (b) heat production/storage and heart rate (HR) drift during running at 95% of the velocity that elicited lactate threshold, which was determined for 20 healthy recreational male runners. Subsequently, changes in skin and tympanic temperatures associated with a vigorous 20-min run, HR, and VO2 data were recorded. It was found that heat production was significantly correlated with body mass (r = .687), lean mass (r = .749), and body surface area (BSA, r = .699). Heat storage was significantly correlated with body mass (r = .519), fat mass (r = .464), and BSA (r = .498). The percentage of produced heat stored was significantly correlated with body mass (r = .427), fat mass (r = .455), and BSA (r = .414). Regression analysis showed that the sum of body mass, percentage of body fat, BSA, lean mass, and fat mass accounted for 30% of the variability in heat storage. It was also found that HR drift was significantly correlated with heat storage (r = .383), percentage of produced heat stored (r = .433), and core temperature change (r = .450). It was concluded that heavier runners experienced greater heat production, heat storage, and core temperature increases than lighter runners during vigorous running.     

我国优秀男子800m运动员共同的技术特征

为了进一步提高我国优秀的男子中跑运动员的训练水平和运动成绩,缩小与亚洲乃至同世界先进水平的差距,同时也为我国广大中跑教练员科学的安排中跑技术训练提供理论依据,利用高速录像拍摄法、比较分析法、数理统计法等对参加2004年全国田径冠军赛暨大奖赛总决赛合肥站的我国优秀的男子800m运动员跑的运动学特征进行了研究.     

Erythrocyte Changes during Training in High School Women Cross-Country Runners

Abstract

Indices of red blood cell (RBC) status were assessed in eight high school women cross-country runners (experimental group) six times during a competitive season (Weeks 0, 1, 2, 4, 6, and 8) and three times (Weeks 0, 1, and 3) in 11 high school women who were not runners (comparison group). The only significant preseason hematological difference between the groups was a higher RBC fragility for the runners. All blood indices for both groups were within normal ranges throughout the study. During the competitive season (Weeks 0–8), the runners had a significant increase in [Vdot]O₂ max (ml/kg · min^?1) of 7.6% and a significant decrease in post step-test heart rate (13.4%) but showed no changes in body weight, height, or percent body fat. At Week 3, the comparison group showed an increase (0.9%) in body weight, but no changes were observed in the other anthropometric variables or post step-test heart rate. During the competitive season, the runners had significant changes in all blood variables except reticulocyte count; these changes were most marked during the first week of the season when there were significant decreases in hemoglobin (Hb) concentration (8.0%), hematocrit (Hct) (7.7%), RBC count (6.8%), and osmotic fragility (21.5% and 42.0% in 5.95 and 6.80 mM NaCl solutions, respectively) and a significant increase in mean RBC volume (1.8%). In contrast, the only significant change in blood indices of the comparison group was a decrease (1.9%) in mean RBC volume at the end of Week 1. Changes in blood variables of the runners appeared to be transient, in that values at Week 8 were comparable to those at preseason except for mean RBC volume. Although blood volume changes could be responsible for some of the blood variable changes in the runners, the results support increased RBC destruction rather than hemodilution as a cause of the RBC changes in the runners, and suggest a possible stress on body iron reserves for increased erythropoiesis during recovery from those changes.