Showing papers in "Medicine and Science in Sports and Exercise in 1990"

Prediction of functional aerobic capacity without exercise testing.

Abstract: The purpose of this study was to develop functional aerobic capacity prediction models without using exercise tests (N-Ex) and to compare the accuracy with Astrand single-stage submaximal prediction methods. The data of 2,009 subjects (9.7% female) were randomly divided into validation (N = 1,543) and cross-validation (N = 466) samples. The validation sample was used to develop two N-Ex models to estimate VO2peak. Gender, age, body composition, and self-report activity were used to develop two N-Ex prediction models. One model estimated percent fat from skinfolds (N-Ex %fat) and the other used body mass index (N-Ex BMI) to represent body composition. The multiple correlations for the developed models were R = 0.81 (SE = 5.3 ml.kg-1.min-1) and R = 0.78 (SE = 5.6 ml.kg-1.min-1). This accuracy was confirmed when applied to the cross-validation sample. The N-Ex models were more accurate than what was obtained from VO2peak estimated from the Astrand prediction models. The SEs of the Astrand models ranged from 5.5-9.7 ml.kg-1.min-1. The N-Ex models were cross-validated on 59 men on hypertensive medication and 71 men who were found to have a positive exercise ECG. The SEs of the N-Ex models ranged from 4.6-5.4 ml.kg-1.min-1 with these subjects.(ABSTRACT TRUNCATED AT 250 WORDS).

Initial events in exercise-induced muscular injury.

Abstract: Immediately following unaccustomed exercise, particularly that with eccentric contractions, there is evidence of injury to skeletal muscle fibers: a) disruption of the normal myofilament structures in some sarcomeres, observable with both light and electron microscope and b) loss of intramuscular proteins (e.g., creatine kinase enzymes) into the plasma, indicating damage to sarcolemma. This pathology is probably responsible for the temporary reductions in muscle force and delayed-onset soreness that can occur following eccentric exercise. The mechanisms underlying this injury are not known, although loss of intracellular Ca2+ homeostasis could play a primary role. In other experimental muscle injury models, elevated [Ca2+]i appears to cause release of muscle enzymes through activation of phospholipase A2, which in turn could induce injury to sarcolemma through production of leukotrienes and prostaglandins, through free O2 radical formation (in the subsequent lipoxygenase and cyclooxygenase reactions), and/or through release of detergent lysophospholipids. On the other hand, the mechanism responsible for the rapid damage to myofibrils caused by increased [Ca2+]i is unknown. Regardless of the cause(s), the initial and early events in the injury process are autogenetic; i.e., they are indigenous to the muscle cells and occur before phagocytic cells enter the injury site.

Muscle strain injuries: clinical and basic aspects.

Abstract: Indirect or strain injury to muscle is a common cause of athletic disability. Strain injuries often occur during powerful muscle eccentric contractions. Clinical studies suggest that most injuries cause partial disruption of certain characteristic muscles. Diagnostic imaging studies can demonstrate the location of many injuries. Laboratory studies show that partial and complete injuries exhibit disruption of muscle fibers near the muscle-tendon junction. Healing of partial injuries is characterized by an initial inflammatory response followed by a healing phase marked by fibrosis. Biomechanical studies show that muscle failure occurs at forces much larger than maximal isometric force, and stretch is necessary to create injury. Compared to the passively stretched muscle, muscle activated by nerve contraction and stretched to failure attains a small increase in force at failure, no change in strain to failure, and a large increase in energy absorbed prior to failure. These studies emphasize the ability of muscles to function as energy absorbers in preventing injury to themselves and to bones and joints. Experimental muscle stretching protocols show significant stress relaxation and reduction of stiffness in muscle due to inherent viscoelastic properties of muscle rather than to reflex-mediated effects. These viscoelastic properties may be useful in understanding how muscle injury might be prevented.

The effects of arms and countermovement on vertical jumping.

Abstract: Countermovement and arm-swing characterize most jumping. For determination of their effects and interaction, 18 males jumped for maximal height from a force platform in all four combinations of arm-swing/no-arm-swing and countermovement/no-countermovement. For all jumps, vertical velocity peaked 0.03 s before and dropped 6-7% by takeoff. Peak positive power averaged over 3,000 W, and occurred about 0.07 s before takeoff, shortly after peak vertical ground reaction force (VGRF) and just before peak vertical velocity. Both countermovement and arm-swing significantly (P less than 0.05) improved jump height, but arm-swing's effect was greater, enhancing peak total body center of mass (TBCM) rise both pre and posttakeoff. Countermovement only affected the post-takeoff rise. The arm-swing resulted in higher peak VGRF and peak positive power. During countermovement, the use of arms resulted in less unweighting, slower and less extensive TBCM drop, and less negative power. Countermovement increased pretakeoff jump duration by 71-76%, increased average positive power, and yielded large positive and negative impulses. High test-retest reliability was shown for jump descriptive variables. Body weight together with peak posttakeoff TBCM rise effectively predicted peak power (multiple R2 = 0.89, standard error of estimate = 243 W). The results lend insight into which jumping techniques are most appropriate for given sports situations and indicate that a jump test can effectively be used to estimate peak power output.

Strength training effects in prepubescent boys

Abstract: Possible changes in muscle size and function due to resistance training were examined in prepubertal boys. Thirteen boys (9-11 yr) volunteered for each of the training and control groups. Progressive resistance training was performed three times weekly for 20 wk. Measurements consisted of the following: 1 repetition maximum (RM) bench press and leg press; maximal voluntary isometric and isokinetic elbow flexion and knee extension strength; evoked isometric contractile properties of the right elbow flexors and knee extensors; muscle cross-sectional area (CSA) by computerized tomography at the mid-right upper arm and thigh; and motor unit activation (MUA) by the interpolated twitch procedure. Training significantly increased 1 RM bench press (35%) and leg press (22%), isometric elbow flexion (37%) and knee extension strength (25% and 13% at 90 degrees and 120 degrees, respectively), isokinetic elbow flexion (26%) and knee extension (21%) strength, and evoked twitch torque of the elbow flexors (30%) and knee extensors (30%). There were no significant effects of training on the time-related contractile properties (time to peak torque, half-relaxation time), CSA, or %MUA of the elbow flexors or knee extensors. There was, however, a trend toward increased MUA for the elbow flexors and knee extensors in the trained group. Strength gains were independent of changes in muscle CSA, and the increases in twitch torque suggest possible adaptations in muscle excitation-contraction coupling. Improved motor skill coordination (especially during the early phase of training), a tendency toward increased MUA, and other undetermined neurological adaptations, including better coordination of the involved muscle groups, are likely the major determinants of the strength gains in this study.

Internal forces of chronic running injury sites.

Abstract: A model of the lower extremity was created and analyzed to estimate the magnitude of the loads at common injury sites during running and the proportions due to muscle and ground reaction forces. The range of peak loads, normalized to subject body weight (BW), estimated from five running trials were: (1) Achilles tendon force: 6.1-8.2 BW; (2) ankle bone-on-bone--compressive force: 10.3-14.1 BW; shear force: -0.4- -0.7 BW; (3) lower leg--compressive force: 10.3-14.1 BW; shear force: -0.4- -0.7 BW; bending moment: -85- -117 N.m; (4) patellar tendon force: 4.7-6.9 BW; (5) patello-femoral joint compressive force: 7.0-11.1 BW; (6) plantar fascia force: 1.3-2.9 BW. All peak loads were associated with mid-stance and push-off when muscle activity was maximal. The impact force at heel contact was estimated to have no effect on the peak force seen at the chronic injury sites. The plantarflexor muscles were shown to provide an anti-shear mechanism at the ankle and an anti-shear, anti-bending mechanism within the lower leg. Simple sensitivity analyses were performed on the models to display possible variability in the peak load estimates.

Endorphins and exercise: physiological mechanisms and clinical implications.

Abstract: In this paper we discuss recent experimental and clinical findings which lead us to propose that prolonged rhythmic exercise can activate central opioid systems by triggering increased discharge from mechanosensitive afferent nerve fibers (Group III or A-delta) arising from contracting skele

Etiologic factors associated with patellofemoral pain in runners

Abstract: The purpose of this study was to extend our knowledge of running related injuries by determining whether relationships exist between selected anthropometric, biomechanical, muscular strength and endurance, and training variables and runners afflicted with patellofemoral pain (PFP). Specifically, the objectives of this study were to examine differences in selected measures between a non-injured control group (C) of runners (N = 20) and a group of injured runners (INJ) diagnosed by an orthopedic surgeon as having PFP (N = 16). High speed photography, a force platform, and isokinetic dynamometry were used to determine rearfoot motion, ground reaction forces, and knee muscular strength and endurance. Stepwise discriminant function analyses were performed on the anthropometric, biomechanical, and muscular strength and endurance variables. Q angle was a significant discriminator (P less than 0.01) between the INJ and C groups. The muscular endurance data revealed several significant discriminators with the INJ subjects being weaker in knee extension endurance. Kinetic analysis revealed several significant discriminators whereas rearfoot movement variables were not good discriminators between the groups. The training data revealed that the INJ group ran significantly less (P less than 0.01) miles.wk-1 than the C group. Our results suggest that Q angle is a strong discriminator between runners afflicted with PFP and non-injured runners. In addition, several muscular endurance and kinetic variables may also be important components of the etiology of PFP.

The accuracy of self-reports of physical activity.

Abstract: This investigation determined the accuracy of self-reports of physical activity compared to observations obtained surreptitiously. Subjects were 44 adults engaged in 1 h of their preferred physical activity while actual activity levels were surreptitiously obtained and compared to immediate self-reported estimates of physical activity. Results indicated that subjects were moderately accurate in recalling their physical activity levels (R = 0.62) but underestimated sedentary activities and overestimated aerobic activities by over 300%. Males overestimated their activity relative to females, and obese subjects underestimated their activity levels compared to normal-weight subjects. Finally, a number of two-way interactions that moderated the accuracy of those subjects engaging in high chronic levels of physical activity were observed.

Current concepts in lactate exchange.

Abstract: There are several goals to this introductory paper in the symposium proceedings, "Current Concepts in Lactate Exchange." First, an attempt is made to set the historical context for the symposium and foreshadow how the paper of each participant contributes to our contemporary understanding of the field. As implied in the symposium title, an emphasis will be placed on the exchange of lactate for other metabolites and ions so that utilization can be temporally and spatially disassociated from formation. Thus, rather than a dead-end metabolite, which only accumulates during exercise, there appears to be great usefulness in the formation, exchange between cells, blood and organs, and utilization of lactic acid (lactate). Specific papers will deal with aspects of lactate release and uptake by skeletal muscle, hepatic lactate balance, the flux of dietary carbohydrate through various lactate pools in the synthesis of liver glycogen, lactate metabolism in the heart, properties of the sarcolemmal lactate transporter, and evolution of a model to predict lactate production from blood measurements. Second, in this review an attempt will be made to present and support a unifying hypothesis (the "lactate shuttle") in which the various aspects of lactate exchange may be integrated and understood. Emphasis will be placed on showing several corollaries between muscle and whole-body lactate metabolism. These are: temporal dependence on lactate uptake and release, the effects of beta-adrenergic stimulation on lactate formation and release, the effect of prior endurance training on lactate metabolism, the effect of lactate on glucose uptake and utilization, and the role of low oxygen tension (hypoxia) in loosening the control of glycolysis. The formation, exchange, and utilization of lactate represents a central means by which the coordination of intermediary metabolism in diverse tissues and different cells within tissues can be accomplished.

The evaluation and prediction of impact forces during landings

Abstract: The investigation of impact force attenuation during landings may help identify performance strategies. The purpose of the study was to evaluate the effects of height (three), distance (three), and technique (three) on impact forces during landings. Three male volunteer subjects were filmed while performing three right foot landings onto a force platform for each combination of height, distance, and technique for a total of 81 trials per subject. Between- and within-subject three-way ANOVAs and three regression models (mechanical, biomechanical, refined biomechanical) were computed on the dependent variables of first (F1) and second (F2) maximum vertical force. Results of the between-subject ANOVAs indicated significant (P less than 0.05) height, distance, and technique main effects for F1 and a height x technique interaction for F2. The within-subject ANOVA results identified unique models for each of the three subjects. The biomechanical regression model exhibited the best predictions of F1 and F2 for S1 (81.0 and 72.0% explained variance, respectively), while the refined biomechanical model accounted for 83.4, 81.3, 80.9, and 88.0% of the F1 and F2 variances for S2 and S3, respectively. In conclusion, the within-subject results identified unique individual landing strategies that were masked by the group analyses suggesting that caution be exercised in using between-subject analysis techniques.

Anthropometric estimation of muscle mass in men.

Abstract: Twelve male cadavers (aged 50-94 yr) were subjected to comprehensive anthropometry, dissection, and weighing of all skeletal muscle. Correlation coefficients of limb girths with total skeletal muscle mass (MM) were high: forearm r = 0.96, mid-thigh r = 0.94, calf r = 0.84, and midarm r = 0.82. These increased when limb girths were corrected (by subtracting pi times the skinfold thickness) to estimate muscle girth. For dimensional consistency, variables in the regression analyses included the product of stature and the square of each corrected girth. For the six unembalmed cadavers, this yielded a three-girth equation for MM (r2 = 0.93; SEE = 1.56 kg), which was then validated using data from the embalmed cadavers. It predicted MM with an SEE of 1.58 kg and r2 = 0.93. Because the values of these SEEs were similar, we pooled the subjects from the two groups to generate the final estimation equation: MM = STAT (0.0553CTG2 + 0.0987FG2 + 0.0331CCG2) - 2445 (SEE = 1.53 kg, r2 = 0.97), where STAT is stature (cm), CTG is thigh circumference corrected for the front thigh skinfold thickness (cm), FG is the uncorrected forearm circumference (cm), and CCG is the calf circumference corrected for the medial calf skinfold thickness (cm). Despite the limitations of the cadaver sample, the proposed equation appears to provide the best estimate of skeletal muscle mass to date, in that it is the only cadaver-validated equation and it gives values that are consistent with all known dissection data.

Patterns of weight loss and regain in wrestlers: has the tradition changed?

Abstract: To assess current weight loss practices in wrestlers, 63 college wrestlers and 368 high school wrestlers completed a questionnaire that examined the frequency and magnitude of weight loss, weight control methods, emotions associated with weight loss, dieting patterns, and preoccupation with

Accurate prediction of VO2max in cycle ergometry.

Abstract: Numerous equations exist for predicting VO2max from the duration (an analog of maximal work rate, Wmax) of a treadmill graded exercise test (GXT). Since a similar equation for cycle ergometry (CE) was not available, we saw the need to develop such an equation, hypothesizing that CE VO2max could be accurately predicted due to its more direct relationship with W. Thus, healthy, sedentary males (N = 115) and females (N = 116), aged 20-70 yr, were given a 15 W.min-1 CE GXT. The following multiple linear regression equations which predict VO2max (ml.min-1) from the independent variables of Wmax (W), body weight (kg), and age (yr) were derived from our subjects: Males: Y = 10.51 (W) + 6.35 (kg) - 10.49 (yr) + 519.3 ml.min-1; R = 0.939, SEE = 212 ml.min-1. Females: Y = 9.39 (W) + 7.7 (kg) - 5.88 (yr) + 136.7 ml.min-1; R = 0.932, SEE = 147 ml.min-1 Using the 95% confidence limits as examples of worst case errors, our equations predict VO2max to within 10% of its true value. Internal (double cross-validation) and external cross-validation analyses yielded r values ranging between 0.920 and 0.950 for the male and female regression equations. These results indicate that use of the equations generated in this study for a 15 W.min-1 CE GXT provides accurate estimates of VO2max.

The Caltrac accelerometer as a physical activity monitor for school-age children.

Abstract: The performance of the Caltrac accelerometer was studied in elementary school-age children under field and laboratory conditions. In Study 1, 35 children (20 boys, 15 girls, mean age = 10.8 yr) wore the accelerometer and a heart rate (HR) monitor for 2 d. Caltrac activity counts per hour were compared to the mean "activity HR", which was calculated by subtracting the mean of the five lowest HRs of the day from each recorded HR. Pearson r's between accelerometer and activity HR were 0.54 (P less than 0.001) on day 1 and 0.42 (P less than 0.02) on day 2. Inter-instrument reliability in the field was r = 0.96. Both accelerometer and HR data were significantly correlated with physical activity recalls of the same day. In Study 2, 15 children walked/ran for 10 min at 3, 4, and 5 mph on a horizontal treadmill while wearing two accelerometers. Oxygen uptake was directly measured each minute. Reliability of the Caltracs in the laboratory was 0.89. Activity count correlated r = 0.82 (SEE = 23%) with net calorie cost per kg of body weight. Net caloric expenditure per kg of weight was 0.101 kcal.kg-1.d-1 per Caltrac activity count. These data support the use of the Caltrac accelerometer as a physical activity measure for school-age children, and the objective data tended to corroborate the children's short-term activity recalls.

Physiological determinants of pulmonary gas exchange kinetics during exercise.

Abstract: We consider how the optimal selection of the profile of imposed work rate, coupled with rigorous, statistically justified analysis of the pattern of the pulmonary gas exchange response, makes it possible to assemble a control model incorporating the proportional role of the muscle, circulation, and gas stores. Gains, time constants, and delays may be assigned to the components of the response and its linearity assessed. These techniques also allow the investigator to examine the features of poorly understood and even unexpected response patterns. Recent interest in the analysis of the non-steady state of exercise-in normal subjects and in patients with gas exchange defects-has led to an improved understanding of the sub-threshold dynamics. At work rates above the lactate threshold, the more complex kinetics are to date poorly described, and hence poorly understood, remaining a fertile area for the application of control-systems techniques to exercise.

Time course of recovery and heat acclimation ability of prior exertional heatstroke patients.

Abstract: Our understanding of the time course of recovery from exertional heatstroke (EH) and the heat acclimation ability of prior EH patients is limited. This manuscript reviews previous findings regarding recovery from EH and presents original research involving the heat acclimation ability of 10 prior EH patients (PH) and 5 control subjects. Heat acclimation, by definition, distinguishes heat-intolerant from heat-tolerant prior heatstroke patients. Nine PH exhibited normal heat acclimation adaptations (40.1 degrees C, 7 d, 90 min.d-1), thermoregulation, sweat gland function, whole-body sodium and potassium balance, and blood values at 61 +/- 7 d after EH. One PH (subject A) did not adapt to exercise in the heat, was defined heat intolerant, but subsequently was declared heat tolerant (11.5 months post-EH). Three PH exhibited large, unexpected increases in serum CPK levels, which resolved upon subsequent testing, and were probably related to their detrained state and the exercise which they performed. It was concluded that: 1) sleep loss and generalized fatigue were the most common predisposing factors for PH; 2) recovery from EH was idiosyncratic and may require up to 1 year in severe cases; 3) PH were not hereditarily heat intolerant, prior to EH; 4) no measured variable predicted recovery from EH, or heat acclimation responses; 5) heat intolerance occurs in a small percentage of prior heatstroke patients, and may be transient or persistent.

Bicycle pedalling forces as a function of pedalling rate and power output.

Abstract: Eleven men with recreational bicycling experience rode a bicycle ergometer with instrumented force pedals to determine the effects of pedalling rate and power output on the total resultant pedal force, Fr, and the component of the force perpendicular to the crank arm. The force patterns were obtained at power outputs of 100 W and 200 W for pedalling rates of 40-120 rpm in intervals of 10 rpm. Data were not obtained at 40 rpm at the 200 W power output. The Fr averaged over a crank cycle (Far) was lowest at 90 rpm and 100 W, a value statically different (P less than 0.05) from those at 40, 50, and 120 rpm. At 200 W, the Fr was lowest at 100 rpm, a value statistically different (P less than 0.05) from those at 50, 60, and 70 rpm. The Far varied widely (range of 30% of mean for all subjects) for individuals at a given power output. The results suggest that pedalling at 90-100 rpm may minimize peripheral forces and therefore peripheral muscle fatigue even though this rate may result in higher oxygen uptake.

Field and clinical observations of exertional heat stroke patients

Abstract: Exertional heatstroke (EH) occurs when heat production, generated by muscular exercise, exceeds the body's heat dissipation capacities. This illness has been reported among young, active individuals, laborers, and religious pilgrims. Although EH includes a rectal temperature above 39.5 degrees C (depending on the timing of the measurement) and elevation of serum enzymes, altered mental status is the universally accepted sign which distinguishes EH from heat exhaustion. Once EH is suspected, cooling therapy should be initiated immediately and investigation of multiple-system involvement should be undertaken. Delay in diagnosis occurs more commonly in moderate environments, when suspicion of EH is low. Complications of EH include the central nervous, cardiovascular, pulmonary, and gastrointestinal systems, often with renal and hematologic involvement. Treatment at the point of collapse should focus on clearing the airway, measurement of rectal temperature, whole body cooling, intravenous therapy, and prompt evacuation. Hospital treatment should emphasize whole body cooling, control of convulsions, monitoring of acid-base status, cardiac function, and renal function. The incidence of EH has been reduced markedly in Israel, by using the following simple guidelines: rest periods during exercise in heat, medical monitoring of strenuous activities, use of meteorological indices, and evaluation of medical history.

Comparison of two regimens of concurrent strength and endurance training.

Abstract: To compare the responses to doing strength (S) training on alternate days with endurance (E) training vs doing both types of training on the same days per week, seven young men (group A-2 d) did S and E training together in single sessions 2 d.wk-1 for 20 wk. A second group (B-4 d, N = 8) did the S training on 2 d.wk-1 and E training on 2 other d.wk-1. S training was six to eight sets of 15-20 RM on a leg press weight machine. E training was six to eight 3-min bouts of cycle ergometer exercise at 90-100% VO2max. B-4 d (25%) increased leg press 1 RM more (P less than 0.05) than A-2 d (13%), but the groups increased similarly (A-2 d, B-4 d) in knee extensor (31%, 34%) and flexor (12%, 14%) cross-sectional area and vastus lateralis mean fiber area (33%, 25%). Increases in VO2max (7%, 6%), repetitions with 80% 1 RM (39%, 64%), repetitions with the pre-training 1 RM (33, 55), and PFK (19%, 10%) and LDH (15%, 23%) activity did not differ (P greater than 0.05) between groups. CS activity increased significantly only in A-2 d (26%; B-4 d, 6%). It is concluded that same day (vs different day) concurrent strength and endurance training may impede strength development without impeding hypertrophy. On the other hand, same day training may enhance increases in CS activity but not VO2max or weight lifting endurance.

Physiological effects of a weight loss regimen practiced by college wrestlers.

Abstract: The effects of weight loss (dehydration) techniques (which mimicked techniques used prior to actual competition) used by intercollegiate wrestlers on selected physiological parameters (strength, anaerobic power, anaerobic capacity, the lactate threshold (LT), and peak aerobic power) were examined in seven intercollegiate wrestlers. During the 36 h weight loss period, subjects lost 3.3 kg (4.9% body weight), all of which occurred during the 12 h prior to weigh-in, using exercise in a rubberized sweat suit. Weight loss resulted in a reduction in upper body but not lower body strength measures (peak torque and average work per repetition). Anaerobic power and anaerobic capacity were significantly reduced in a dehydrated state (81.4 kgm.s-1, normal weight; 63.9 kgm.s-1, weight loss; 1984.3 kgm.40 s-1, normal weight; 1791.4 kgm.40 s-1, weight loss). Analyses of treadmill data revealed the following: 1) velocity was decreased at LT (4.4%) and peak (6.5%) during weight loss (P less than 0.05); 2) VO2 peak was significantly reduced with weight loss (6.7%, P less than 0.05); 3) treadmill time to exhaustion was significantly reduced in the weight loss state (12.4%) (35.7 min, normal weight; 31.3 min, weight loss). It was concluded that typical wrestling weight loss techniques result in deleterious effects on strength, anaerobic power, anaerobic capacity, the lactate threshold, and aerobic power.

Control of body mass transfer as a function of speed of ascent in sit-to-stand.

Abstract: The purpose of this study was to test the hypothesis that a progressive variation in the speed of ascent would result in differences in the horizontal and vertical motions of the body center of mass (CM) and in the governing impulse-momentum relationship. A motion analysis system and two force platforms were used to examine the STS task among 10 healthy adults at each of three self-selected speeds. As the speed of ascent became faster, a progressively earlier time to the maximum vertical linear momentum and an increase in its magnitude occurred. In contrast, a relatively constant time to the maximum linear momentum, which was also the time when the propulsive impulse became the braking impulse, was found in the horizontal direction, and the propulsive impulse showed a disproportionately (1:3) smaller increase from slow to fast speeds than its vertical counterpart. The relative invariance in the horizontal motion suggested that different neuromuscular control strategies may have been employed in the horizontal and vertical directions to accomplish the different tasks of balance control in one direction and changing the gravitational potential energy in the other direction.

Effect of training on the anaerobic capacity.

Abstract: Intense exercise of short duration is heavily dependent on energy from anaerobic sources, and subjects successful in anaerobic types of sports may therefore have a larger anaerobic capacity and be able to release energy at a higher rate. Performances in these kinds of sports are improved by training, suggesting that the anaerobic capacity is trainable. The purpose of this investigation was to study the effect of training on anaerobic capacity. We therefore determined the anaerobic capacity, expressed as the maximal accumulated O2 deficit during treadmill running, of untrained, endurance-trained, and sprint-trained young men. In addition, seven women and five men trained for 6 wk, and their anaerobic capacity was compared before and after the training period. There was no difference in anaerobic capacity between the untrained and endurance-trained subjects, whereas the sprinters' anaerobic capacity was 30% larger (P less than 0.001). The women's anaerobic capacity was 17% less than the men's (P = 0.03). Six weeks of training increased the anaerobic capacity by 10%. We conclude that the anaerobic capacity varies significantly between subjects and that it can be improved within 6 wk. Moreover, there was a close relationship between a high anaerobic capacity and a high peak rate of anaerobic energy release.

The effects of moderate exercise training on immune response.

Abstract: The relationship between moderate exercise training (ET) (five 45-min sessions per week, brisk walking at 60 heart rate reserve for 15 wk) and changes in immune system variables and function was investigated in a group of 36 sedentary, mildly obese women. The study was conducted using a two (exercise (EX) and nonexercise (NEX) groups) by three (baseline, 6 wk, and 15 wk testing sessions) factorial design, with data analyzed using repeated measures ANOVA. The pattern of change over time between groups for number of peripheral blood lymphocytes (total), T cells (CD5), B cells (CD20), and serum IgG, IgA, and IgM levels was significantly different. This was not the case for spontaneous blastogenesis or number of T helper/inducer cells (CD4) or T cytotoxic/suppressor cells (CD8). Within-EX-group changes were characterized by significant decreases in percentage and number of total lymphocytes, and in T cell number after 6 wk, and significant increases in each of the serum immunoglobulins after both 6 and 15 wk of training. B cell number increased significantly in NEX subjects relative to baseline values at both 6 and 15 wk, with no significant changes experienced in EX subjects. In summary, these data suggest that moderate ET is not associated with an improvement in lymphocyte function but is associated with a 20% increase in serum immunoglobulins and several small changes in circulating numbers of immune system variables, highlighted by significant decreases in circulating numbers of lymphocytes, particularly the T cell subpopulation. These changes were especially apparent after 6 wk of training, with some attenuation by 15 wk.

The health belief model: predicting compliance and dropout in cardiac rehabilitation.

Abstract: We investigated the health belief model and the health locus of control constructs as predictors of group membership (compliers or dropouts) with cardiac rehabilitation and whether they added predictive utility to routinely assessed patient demographics and health behaviors Questionnaires were completed on entry into the study by 120 patients with coronary artery disease, and by the end of the 6 month program there were 58 compliers and 62 dropouts Discriminant function analyses were carried out to determine prediction of group membership The health belief model predicted group membership 646% of the time, explaining 52% of the variance Demographics, health behaviors, and health belief model factors accounted for 211% of the variance between compliers and total dropouts with group membership correctly predicted 744% of the time; avoidable and unavoidable dropout was correctly predicted 842% of the time with 569% of the variance explained Health locus of control did not distinguish between compliers and dropouts The addition of the health belief model provided additional information about compliance with cardiac rehabilitation beyond that explained by demographic and health behavior variables alone, particularly when predicting avoidable/unavoidable dropout

Effects of exercise training on the menstrual cycle: existence and mechanisms.

Abstract: This review evaluates the status of the evidence that exercise training affects the menstrual cycle beginning with evidence for the existence of delayed menarche, amenorrhea, and luteal suppression in athletes. A later age of menarche and a higher prevalence of amenorrhea and luteal suppression have been observed in athletes, but there is no experimental evidence that athletic training delays menarche, and alternative sociological and statistical explanations for delayed menarche have been offered. Cross-sectional studies of amenorrheic athletes have revealed abnormal reproductive hormone patterns, suggesting that the GnRH pulse generator in the hypothalamus is failing to initiate normal hypothalamic-pituitary-ovarian function. Longitudinal data show that the abrupt initiation of a high volume of aerobic training can disrupt the menstrual cycle in at least some women, but these women may be more susceptible to reproductive disruption than others, and some aspect of athletic training other than exercise (such as caloric deficiency) may be responsible for the observed disruption. Luteal suppression may be an intermediate condition between menstrual regularity and amenorrhea in athletes, or it may be the endpoint of a successful acclimation to exercise training. A potential endocrine mechanism of menstrual disruption in athletes involving the hypothalamic-pituitary-adrenal axis is discussed. Finally, promising future directions for research on this topic are described.

Effects of menstrual phase and amenorrhea on exercise performance in runners.

Abstract: DE SOUZA, M. J., M. S. MAGUIRE, K. RUBIN, and C. M. MARESH. Effects of menstrual phase and amenorrhea on exercise responses in runners. Med. Sci. Sports. Exerc., Vol. 22, No. 5, pp. 575–580, 1990. There are few well controlled studies in terms of subject selection, menstrual classification,

Bone mineral content of cyclically menstruating female resistance and endurance trained athletes.

Abstract: The bone mineral content (BMC) at four sites on the axial and appendicular skeleton was compared among four groups of young adult (age = 17-38 yr) cyclically menstruating athletes (N = 40) who regularly performed either weightlifting resistance exercise (body builders) or nonresistance endurance exercise (runners, swimmers) and an inactive group of females (N = 18) of about equal age. Forearm BMC was measured using single photon absorptiometry at proximal (shaft) and distal sites on the radius. Dual photon absorptiometry was used to measure BMC at the lumbar vertebrae (L2-4) and femur at the femoral neck, Ward's triangle, and greater trochanter. Fat-free body mass (FFBM) was estimated from densitometry. Body builders had greater BMC than swimmers, collegiate runners, recreational runners, and controls. Mean differences in BMC among runners, swimmers, and controls were not significant (P less than or equal to 0.05). FFBM was correlated significantly with BMC (r = 0.35-0.56) at each site in the combined group of athletes (N = 39), whereas total body weight and BMC were correlated significantly at the distal radius site (r = 0.38) only. The results suggest that weight training may provide a better stimulus for increasing BMC than run and swim training.

Effects of glycerol-induced hyperhydration prior to exercise in the heat on sweating and core temperature.

Abstract: Hypohydration reduces exercise performance and thermoregulatory capacity in the heat. Hyperhydration prior to exercise may decrease, delay, or eliminate the detrimental effects of hypohydration. The rapid clearance of excess fluid makes hyperhydration of subjects with common beverages difficult. Glycerol, a natural metabolite which is rapidly absorbed, has osmotic action, and is evenly distributed within the body fluid compartments, was tested as a possible hyperhydrating agent. In six subjects, the following fluid regimens at time 0 were randomly administered on three separate days: in trial 1, glycerol (1 g.kg−1 body weight) plus water (21.4 ml-kg−1 body weight); in trial 2, water (21.4 ml.kg−1); and in trial 3, water (3.3 ml-kg−1) was ingested at time 0. The subjects performed moderate exercise (equivalent to 60% JOURNAL/mespex/04.02/00005768-199008000-00017/ENTITY_OV0312/v/2017-07-20T222235Z/r/image-pngo2max in a comfortable environment) in a hot dry environment. The exercise started at 2.5 h after the fluids were ingested. The urine volume prior to exercise was decreased when glycerol was ingested, thus resulting in glycerol-induced hyperhydration. During the exercise following the glycerol-induced hyperhydration, there was elevated sweat rate and lower rectal temperature during the moderate exercise in the heat. There were no changes in hemoglobin, hematocrit, or serum electrolyte concentrations following glycerol intake. These data support the hypothesis that glycerol-induced hyperhydration reduces the thermal burden of moderate exercise in the heat.