Non-trained Subjects Research Articles

Activación de la coagulación y fibrinólisis inducida por un ejercicio de larga duración (carrera de maratón)

Introduction and objectives During physical exercise coagulation and fibrinolytic activities are increased. Moderate and regular exercise is associated with a decrease on thrombotic episodes. On the other hand exhausting physical exercise seems to be a trigger of thrombotic events, especially on non-trained subjects. The objective of this study is to investigate the effect of a marathon race on coagulation and fibrinolytic parameters on trained subjects. Material and methods We studied 31 amateur athletes who had followed a training program for 4 months. Blood samples were collected before and after exercise and at 24 hours and 72 hours to test the effects of a marathon race on prothrombin time, prothrombin activity, activated partial thromboplastin time, fibrinogen, antithrombin III (AT3) and D dimer. Results There was an increase in coagulation activity and a marked increase in D dimmer (marker of fibrinolytic activity) in post-exercise samples. There was also a decrease in fibrinogen levels, probably due to it has been used up during the exercise period. The 24 hour hours samples showed a decrease in AT3 levels, also as a result of AT3 consumption during the physical exercise. Conclusions These data, suggests that in trained subjects, a general balance in haemostatic mechanisms is achieved (coagulation and fibrinolysis activation) with continued physical exercise.

Comparação da performance funcional do membro inferior entre jovens futebolistas e jovens não treinados

INTRODUÇÃO: Em atletas, a utilização de testes de performance funcional permite avaliar com maior validade ecológica possíveis alterações do membro inferior observadas na prática desportiva. OBJETIVO: O objetivo do presente estudo consistiu na comparação da performance funcional do membro inferior entre jovens futebolistas e jovens não treinados. METODOLOGIA: A amostra foi constituída por 39 jovens do sexo masculino, divididos em dois grupos: um grupo composto por 19 futebolistas (idade = 16,8 ± 0,83 anos; peso = 69,8 ± 6,2 kg; altura = 176,6 ± 0,5 cm) e outro composto por 20 sujeitos não treinados (idade = 16,6 ± 0,8 anos; peso = 66,3 ± 11,0 kg; altura = 172,0 ± 0,8 cm). Para avaliação da performance funcional do membro inferior foram utilizados três testes: o Single-Leg Hop Test, o Quadrant Jump Test e o Hexagon Test. RESULTADOS: Os jovens futebolistas obtiveram melhor performance do que os jovens não treinados em ambos os membros inferiores no Single-Leg Hop Test (membro inferior direito: 124 ± 62 cm, membro inferior esquerdo: 127 ± 68 cm versus membro inferior direito: 99 ± 10 cm, membro inferior esquerdo: 97 ± 12 cm; p < 0.001), em ambas as direções, na execução do Hexagon Test (sentido dos ponteiros do relógio: 5,1 ± 0,6 s, sentido inverso: 4,9 ± 0,5 s versus sentido dos ponteiros do relógio: 6,0 ± 0,4 s, sentido inverso: 5,7 ± 0,4 s; p < 0.001) e no Quadrant Jump Test (32,4 ± 2,5 pontos versus 28,2 ± 2,5 pontos, p < 0.001). Dentro de cada grupo não foi encontrada diferença entre os dois membros inferiores no Single-Leg Hop Test, nem entre as duas direções do Hexagon Test. CONCLUSÕES: Os resultados do presente estudo indicam que jovens futebolistas apresentam melhor performance funcional do membro inferior do que jovens não treinados.

Influence of Supervision Ratio on Muscle Adaptations to Resistance Training in Nontrained Subjects

The purpose of the present study was to compare the changes in muscle strength in nontrained young males performing resistance training under different supervision ratios. One hundred twenty-four young men were randomly assigned to groups trained under a high (HS, 1:5 coach to athlete ratio) or low (LS, 1:25) supervision ratio. Both groups performed identical resistance training programs. Subjects were tested for maximum bench press 1 repetition maximum (1RM) and knee extensor torque before and after 11 weeks of training. According to the results, only HS lead to a significant increase (11.8%) in knee extensor torque. Both groups significantly increased bench press 1RM load; the increases were 10.22% for LS and 15.9% for HS. The results revealed significant differences between groups for changes in knee extensor torque and 1RM bench press, with higher values for the HS group. There were no differences between groups for the increases in bench press and leg press work volume or training attendance. The proportion of subjects training with maximum intensity was higher in HS for both bench press and leg press exercises. In addition, the distribution of subjects training with maximal intensity was higher for the bench press than for the leg press exercise in both groups. The primary findings of the present study are that the strength gains for both lower- and upper-body muscles are greater in subjects training under higher supervision ratios, and this is probably because of higher exercise intensity. These results confirm the importance of direct supervision during resistance training.

Visual stimuli for the P300 brain–computer interface: A comparison of white/gray and green/blue flicker matrices

The white/gray flicker matrix has been used as a visual stimulus for the so-called P300 brain-computer interface (BCI), but the white/gray flash stimuli might induce discomfort. In this study, we investigated the effectiveness of green/blue flicker matrices as visual stimuli. Ten able-bodied, non-trained subjects performed Alphabet Spelling (Japanese Alphabet: Hiragana) using an 8 x 10 matrix with three types of intensification/rest flicker combinations (L, luminance; C, chromatic; LC, luminance and chromatic); both online and offline performances were evaluated. The accuracy rate under the online LC condition was 80.6%. Offline analysis showed that the LC condition was associated with significantly higher accuracy than was the L or C condition (Tukey-Kramer, p < 0.05). No significant difference was observed between L and C conditions. The LC condition, which used the green/blue flicker matrix was associated with better performances in the P300 BCI. The green/blue chromatic flicker matrix can be an efficient tool for practical BCI application.

Perceptual thresholds for detecting modifications applied to the acoustical properties of a violin

This study is the first step in the psychoacoustic exploration of perceptual differences between the sounds of different violins. A method was used which enabled the same performance to be replayed on different "virtual violins," so that the relationships between acoustical characteristics of violins and perceived qualities could be explored. Recordings of real performances were made using a bridge-mounted force transducer, giving an accurate representation of the signal from the violin string. These were then played through filters corresponding to the admittance curves of different violins. Initially, limits of listener performance in detecting changes in acoustical characteristics were characterized. These consisted of shifts in frequency or increases in amplitude of single modes or frequency bands that have been proposed previously to be significant in the perception of violin sound quality. Thresholds were significantly lower for musically trained than for nontrained subjects but were not significantly affected by the violin used as a baseline. Thresholds for the musicians typically ranged from 3 to 6 dB for amplitude changes and 1.5%-20% for frequency changes. Interpretation of the results using excitation patterns showed that thresholds for the best subjects were quite well predicted by a multichannel model based on optimal processing.

Agonist and antagonist EMG activity of neck muscles during maximal isometric flexion and extension at different positions in young healthy men and women

The aim of this study was to compare maximal isometric torque and EMG activity of neck flexors and extensors in flexed and extended positions between men and women. Twenty four non-trained young healthy subjects (12 men vs. 12 women) performed maximal isometric neck flexion and extension within 30° around the neutral position in a sitting posture using a modified isokinetic dynamometer. Surface EMG activity of sternocleidomastoid, scalenus, paraspinal and upper trapezius muscles was recorded bilaterally. Men exhibited higher normalized-to-lean body weight torque than women mainly during neck flexion (44%, P < 0.001) compared to extension (18%, P < 0.05). In addition, torque increased from extended to flexed positions in women only (+17%, P < 0.001). This was associated with a decrease in EMG of neck extensors and upper trapezius muscles (from 35% to 20% and from 18% to 7%, P < 0.001, respectively) without changes in agonistic activity of neck flexors with neck position. In contrast, men displayed similar torque and muscle activation level within 30° of range of motion around the neutral position for both directions. These findings demonstrate gender-specific differences in neck function that was probably linked to higher coactivation level in antagonist muscles (neck extensors) and stabilizers (upper trapezius muscles).

A Simplified Strategy for the Estimation of the Exercise Ventilatory Thresholds

To analyze the limits of agreement between exercise ventilatory threshold values (VT1 and VT2) estimated from a combination of pulmonary gas exchange and ventilatory variables (cardiopulmonary exercise testing) and those derived from an alternative approach based on the ventilatory response only (V(E), ventilometry). Forty-two nontrained subjects (24 males, aged 18-48, peak VO(2) = 33.1 +/- 8.6 mL.min(-1).kg(-1)) performed a maximum incremental cardiopulmonary exercise testing on an electromagnetically braked cycle ergometer. The participants breathed through a Pitot tube (Cardio2 System, MGC) and a fixed-resistance ventilometer (Micromed, Brazil), which were connected in series. HR values at the estimated VT (VTHR1 and VTHR2) were obtained by the conventional method (ventilatory equivalents, end-expiratory pressures for O(2) and CO(2), and the V-slope procedure) and an experimental approach (V(E) vs time, V(E)/time vs time, and breathing frequency vs time). There were no significant between-method differences on VT(HR1), VT(HR2), VT(VE1), VT(VE2), and peak V(E) (P > 0.05). After certification of data normality, a Bland-Altman analysis revealed that the mean bias +/- 95% confidence interval of the between-method differences were lower for VT(HR2) than VT(HR1) (2 +/- 9 and 0 +/- 17 bpm, respectively). VT(HR2) according to ventilometry differed more than 10 bpm from the standard procedure in 3 out of 42 subjects (9%). Between-method differences were independent of the level of fitness, as estimated from peak VO(2) (P > 0.05). : A simplified approach, based on the ventilatory response as a function of time, can provide acceptable estimates of the exercise ventilatory thresholds--especially VT2--during ramp-incremental cycle ergometry. This new strategy might prove to be useful for exercise training prescription in nontrained adults.

Lipid-binding proteins and lipoprotein lipase activity in human skeletal muscle: influence of physical activity and gender

The protein and mRNA levels of several muscle lipid-binding proteins and the activity and mRNA level of muscle lipoprotein lipase (mLPL) were investigated in healthy, nonobese, nontrained (NT), moderately trained, and endurance-trained (ET) women and men. FAT/CD36 protein level was 49% higher (P < 0.05) in women than in men, irrespective of training status, whereas FAT/CD36 mRNA was only higher (P < 0.05) in women than in men in NT subjects (85%). Plasma membrane-bound fatty acid binding protein (FABPpm) content was higher in ET men compared with all other groups, whereas training status did not affect FABPpm content in women. FABPpm mRNA was higher (P < 0.05) in NT women than in ET women and NT men. mLPL activity was not different between gender, but mLPL mRNA was 160% higher (P < 0.001) in women than in men. mLPL activity was 48% higher (P < 0.05) in ET than in NT subjects, irrespective of gender, in accordance with 49% higher (P < 0.05) mLPL mRNA in ET than in NT subjects. A 90-min exercise bout induced an increase (P < 0.05) in FAT/CD36 mRNA (approximately 25%) and FABPpm mRNA (approximately 15%) levels in all groups. The present study demonstrated that, in the NT state, women had higher muscle mRNA levels of several proteins related to muscle lipid metabolism compared with men. In the ET state, only the gender difference in mLPL mRNA persisted. FAT/CD36 protein in muscle was higher in women than in men, irrespective of training status. These findings may help explain gender differences in lipid metabolism and, furthermore, suggest that the balance between gene transcription, translation, and possibly breakdown of several proteins in muscle lipid metabolism depend on gender.

Exercise training improves insulin-stimulated myocardial glucose uptake in patients with dilated cardiomyopathy

Background The effects of exercise training on myocardial substrate utilization have not previously been studied in patients with idiopathic dilated cardiomyopathy and mild heart failure. Methods and results Myocardial glucose uptake was studied in 15 clinically stable patients with dilated cardiomyopathy (New York Heart Association class I-II, ejection fraction 34% ± 8%) with the use of 2-[fluorine 18]fluoro-2-deoxy- d-glucose ([F-18]FDG) and positron emission tomography under euglycemic hyperinsulinemia. Eight of these patients participated in a 5-month endurance and strength training program, whereas seven patients served as nontrained subjects. Left ventricular function was assessed by 2-dimensional echocardiography before and after the intervention. After the training period, insulin-stimulated myocardial fractional [F-18]FDG uptake and glucose uptake rates were significantly increased in the anterior, lateral, and septal walls ( P < .01) in the trained subjects but remained unchanged in the nontrained subjects. In the trained patients, whole-body insulin-stimulated glucose uptake was enhanced and serum free fatty acid levels were suppressed during hyperinsulinemia compared with the baseline study ( P < .05). No changes were observed in the nontrained group. Conclusions These results indicate that exercise training in patients with dilated cardiomyopathy improves insulin-stimulated myocardial glucose uptake. This improvement in glucose uptake may be indicative of a switch in myocardial preference to a more energy-efficient substrate.

Effects of athletic training on heart rate variability triangular index.

The purpose of this study was to assess the heart rate variability triangular index (HRVI) in elite track and field athletes. Sixty healthy males (mean aged 22.1 +/- 3.5 years) -15 long distance runners (group A), 15 speed runners (Group B), 15 throwers (Group C) and 15 non-trained subjects (Group D) were submitted to spiroergometric test, m-mode echocardiography and 24-h ambulatory ECG monitoring. The HRVI, mean heart rate, mean interval between two consecutive R waves of the QRS complexes (R-R interval) and standard deviation of the R-R (SDRR) were assessed through time domain method on computed 24-h Holter recordings. The HRVI and the SDRR were 62.2 +/- 9.6 and 220 +/- 40 ms correspondingly in group A, 52.7 +/- 6.0 and 210 +/- 40 ms in B, 44.5 +/- 5.3 and 180 +/- 40 ms in C, 39.3 +/- 6.4 and 180 +/- 30 ms in D. The HRVI and the mean R-R were found to differ statistically between groups A, B and C versus D (P < 0.05). However, the higher value in HRVI was found in group A. Maximal oxygen consumption (VO2max) was 62.0 +/- 4.4 ml kg-1 min-1 in group A, 52.7 +/- 6.0 in group B, 44.6 +/- 5.3 in C and 41.6 +/- 6.0 in D. The higher value in VO2max was also found in group A. The left ventricular mass index (LVMI) and end-diastolic volume index (EDVI) were 136 g m-2 and 83 ml m-2 correspondingly in group A, 136 and 79 in B, 124 and 56 in C and 88 and 55 in group D. The HRVI was found to have a significant relationship with VO2max and EDVI only in group A. On the other hand, no significant relationships were found between HRVI and LVMI in all groups. It is concluded, that the enhanced HRVI in athletes is affected by exercise training pattern. Moreover, HRVI depends on the level of VO2max in endurance-trained, but is independent from the extent of myocardial hypertrophy in all types of training.

The H and T-reflex response parameters of long and short-distance athletes

It is well known that the training level of a muscle belongs to the parameters that affect the H-reflex response amplitude. The aim of this study was to investigate the effects of training type on H- and T-reflex response parameters. For this purpose, 20 long-distance athletes (group I, test group), 18 short-distance athletes (group II, test group) and 20 non-trained subjects (group III, control group) were involved in this study in which the H- and T-reflex amplitude and latency values were measured. The H-reflex amplitude and latency values found in groups I, II and III were 3.64±0.28 mV and 26.88±1.45 ms, 3.17±0.26 mV and 26.19±1.89 ms, and 6.07±0.34 mV and 26.77±1.32 ms, respectively. The T-reflex amplitude and latency values of the groups I, II and III were 3.30±0.18 mV and 32.01±1.02 ms, 3.11±0.20 mV and 31.47±1.16 ms, 4.24±0.21 mV and 31.47±1.16 ms, respectively. There was no statistically significant difference between the groups with respect to latencies of H- and T-reflexes (p&gt;0.05). In both test groups, the amplitudes of the H-reflex and T-reflex were significantly smaller than the control group (p&lt;0.05). The results of this study suggest that training of muscles affect the H- and T-reflex response parameters.

Physical exercise and/or enriched foods for functional improvement in frail, independently living elderly: A randomized controlled trial

Chin A Paw MJM, de Jong N, Schouten EG, Hiddink GJ, Kok FJ. Physical exercise and/or enriched foods for functional improvement in frail, independently living elderly: a randomized controlled trial. Arch Phys Med Rehabil 2001;82:811-7. Objective: To examine the effects of an exercise program and an enriched food regimen on physical functioning of frail elderly persons. Design: A 17-week randomized, placebo-controlled trial. Setting: Community. Participants: One hundred fifty-seven independently living frail elderly (mean age, 78.7 ± 5.6yr). Intervention: Thirty-nine subjects participated in a twice weekly group exercise designed to improve daily functioning; 39 subjects daily ate foods enriched with vitamins and minerals (at 25%-100% of the recommended daily allowances); 42 subjects exercised and ate enriched foods; and 37 subjects served as controls. Nonexercising groups followed a social program; nonsupplement groups received the same food products without the micronutrients. Main Outcome Measures: Functional performance based on 6 performance tests, physical fitness based on 7 fitness tests, and disabilities based on the self-reported ability to perform 16 daily activities. Results: Performance sum scores were significantly enhanced in trained (+8%) compared with nontrained subjects (−8%) (difference in change: 1.9 points, p <.001, adjusted for baseline scores). Fitness sum scores were significantly enhanced as well (+3% in trained vs −2% in nontrained) (difference in change: 0.9 points, p =.05, adjusted for baseline scores). No exercise effects on the disability score were observed. Consumption of enriched products did not affect performance, fitness, or disability scores. Conclusion: Our comprehensive exercise program, designed for widespread applicability, enhanced physical performance and fitness in a population of frail elderly. Daily consumption of micronutrient enriched foods showed no functional benefits within 17 weeks.

EXPRESSION OF HEAT SHOCK PROTEIN HSP72 IN HUMAN LEUKOCYTES - INFLUENCE OF DIFFERENT TYPES OF EXERCISE

HSP72 is a cell protective stress protein, that is mainly induced by hyperthermia, reactive oxygen species and inflammatory cytokines. By using flow cytometry and RT-PCR we investigated the influence of different types of running exercise on HSP72 expression in leukocytes of the peripheral blood. An intensive endurance run (half marathon, HM, ca. 105% of the individual anaerobic threshold, IAT), a short exhaustive run (SER), and a long continuous run (LCR) were compared. Methods: HM: 12 male athletes achieved an intensive endurance run like a competing half marathon (21.1 km, 90.34ñ12.8 min). SER: Another 7 male non-trained subjects performed a graded treadmill test which was followed by a continuous run until exhaustion 15 min later at 110% IAT (10.8ñ0.7 min, max. lactate 8.9ñ0.6 mmolxl−1). LCR: 6 endurance trained subjects performed a continuous run of one hour at 90% IAT on the treadmill. Blood samples were drawn at rest, directly, 3, 24 and 48 h after exercise for determination of differential counts, plasma CK and HSP72 expression in leukocytes. Results: Lactate values after exercise were 5.1ñ2.2 (HM), 9.0ñ2.1 (SER), 2.16ñ0.07 (LCR) mmolxl−1. Plasma CK reached highest values 24 h after exercise, 289.4ñ221 (HM), 133.4ñ91 (SER), 82.0ñ20 (LCR) Uxl−1. The maximal increase of leukocyte counts after exercise was 14.7ñ2.1 (HM), 11.5ñ19.2 (SER), 9.6ñ2.9 (LCR). HM significantly stimulated HSP72 expression in leukocytes at protein- and mRNA-level (p < 0.005) whereas SER revealed only significant effects on RNA-level (p < 0.05). LCR induced significant, but minor increases, which were down-regulated after 48 h. Conclusion: Short time heavy exercise is not very efficient in stimulating HSP72 in peripheral leukocytes. Duration of exercise seems to be of causal importance for the rise of HSP72 expression in leukocytes. Supported by the Bundesinstitut für Sportwissenschaften, Germany.

Experience-dependent changes in cerebral activation during human REM sleep.

The function of rapid-eye-movement (REM) sleep is still unknown. One prevailing hypothesis suggests that REM sleep is important in processing memory traces. Here, using positron emission tomography (PET) and regional cerebral blood flow measurements, we show that waking experience influences regional brain activity during subsequent sleep. Several brain areas activated during the execution of a serial reaction time task during wakefulness were significantly more active during REM sleep in subjects previously trained on the task than in non-trained subjects. These results support the hypothesis that memory traces are processed during REM sleep in humans.

Training and fatty acid metabolism.

Older studies in humans seem to suggest a correlation between plasma long chain fatty acid (LCFA) turnover and oxidation on the one hand and plasma LCFA concentration on the other hand during submaximal exercise. However, recent studies in man, in which higher concentrations of plasma LCFA have been reached during prolonged submaximal exercise, have revealed a levelling off in net uptake in spite of increasing plasma LCFA concentrations. Furthermore, this relationship between plasma LCFA concentration and plasma LCFA uptake and oxidation was altered by endurance training such that levelling off was not apparent in the trained state. These recent findings in man give support to the notion from other cell types that transport of fatty acids from the vascular compartment to the cytosolic space in the muscle cell is not only due to simple diffusion, but is predominantly carrier-mediated. During prolonged submaximal knee-extension exercise it has been demonstrated that the total oxidation of LCFA was approximately 60% higher in trained compared to nontrained subjects. The training-induced adaptations responsible for this increased utilization of plasma fatty acids by the muscle could be located at several steps from the mobilization of fatty acids to skeletal muscle metabolism in the mitochondria. To what extent triacylglycerol located in the muscle cell contribute to the overall lipid utilisation during exercise is still not clear. However, due to underestimation of the contribution of plasma LCFA and fatty acids liberated from the circulating VLDL-triacylglycerols to the overall fatty acid oxidation during exercise there is increasing understanding that muscle triacylglycerol contributes to a lesser extent as fuel during exercise in man than mostly stated.

Current issues in exercise metabolism: the crossover concept.

1. Since ancient times, athletes have consumed proteins because of the belief they were the necessary substrate for optimal performance. Even though this concept was proven to be incorrect before the beginning of the 19th century, the practice continued until several decades ago. 2. By 1939, careful metabolic investigations on the changes in the respiratory exchange ratio had demonstrated that the metabolic transformations of lipids and carbohydrates were the primary sources of energy for muscular exercise. 3. Metabolic investigations on the profile of energy transformations during exercise have indicated that aspects related to exercise intensity, state of training, the availability of circulating free fatty acids, the activity of the sympathetic nervous system, resting levels of muscle and liver glycogen and muscle triglyceride concentrations have to be considered to explain a specific response. 4. In 1994, Brooks and Mercier introduced the concept of 'crossover' in their review manuscript to explain the shift in substrate utilization from lipids to carbohydrates by trained subjects when the power output was increased. In addition, the concept was advanced to reconcile divergent results by different investigators. 5. In 1995, Coggan and associates investigated the glucose kinetics of non-trained and trained subjects performing power outputs equal to 80% VO2max and concluded that the crossover concept was unable to explain their metabolic results from trained subjects. 6. Because of the importance of the topic to exercise physiologists and the uncertainties the controversy has created for teachers and researchers, the American Physiological Society Section on Environmental and Exercise Physiology scheduled a Point-Counterpoint forum at the 1997 Experimental Biology Meeting. The subsequent manuscripts of Brooks and Coggan are a result of that forum.

Effect of endurance training on fatty acid metabolism: local adaptations

Older studies of humans seem to suggest a correlation between free fatty acid (FFA) turnover and oxidation on the one hand and plasma FFA concentration on the other hand during submaximal exercise. However, recent studies, in which higher concentrations of plasma FFA have been reached during prolonged submaximal exercise, have revealed a levelling off in net uptake in spite of increasing plasma FFA concentrations. Furthermore, this relationship between FFA concentration and FFA uptake and oxidation is altered by endurance training. These recent findings in humans support the notion from other cell types that transmembrane fatty acid transport is not only by simple diffusion, but predominantly carrier-mediated. During prolonged submaximal knee-extension exercise it has been demonstrated that the total oxidation of fatty acids was approximately 60% higher in trained subjects than in nontrained subjects. The training-induced adaptations responsible for this increased utilization of plasma fatty acids by the muscle could be located at several steps from the mobilization of fatty acids to skeletal muscle metabolism in the mitochondria. In this paper regulation at the transport steps and also at various metabolic steps is discussed.

Kinetics of plasma potassium concentrations during exhausting exercise in trained and untrained men

The purpose of this study was to examine the time course of changes in plasma potassium concentration during high intensity exercise and recovery in trained and untrained men. The subjects performed two exercise protocols, an incremental test and a sprint, on a cycle ergometer. A polyethylene catheter was inserted into the antecubital vein to obtain blood samples for the analysis of plasma electrolyte concentrations and acid-base parameters, during and after exercise. During both tests, venous plasma sodium, potassium and chloride concentrations increased in all the subjects, although the largest relative increase was detected in potassium concentration--35% and 31% over rest in the progressive test and 61% and 37.7% in the sprint test, for cyclists and controls, respectively. After exercise plasma potassium concentration decreased exponentially to below resting values. There was a linear correlation between the amount of potassium accumulated in plasma during exercise and the amount eliminated from plasma when the exercise ceased. We found that, although plasma potassium accumulation occurred in both forms of exercise in the trained and nontrained subjects, the time constant of potassium decrease following exercise was shorter in the trained subjects. Thus, the trained subjects exhibited a better capacity to recover to resting concentrations of plasma potassium. We propose that the extracellular potassium accumulation acts as a negative feedback signal for sarcolemma excitability depending on the muscle metabolic rate.

Skeletal muscle adaptations during early phase of heavy-resistance training in men and women.

An 8-wk progressive resistance training program for the lower extremity was performed twice a week to investigate the time course for skeletal muscle adaptations in men and women. Maximal dynamic strength was tested biweekly. Muscle biopsies were extracted at the beginning and every 2 wk of the study from resistance-trained and from nontrained (control) subjects. The muscle samples were analyzed for fiber type composition, cross-sectional area, and myosin heavy chain content. In addition, fasting blood samples were measured for resting serum levels of testosterone, cortisol, and growth hormone. With the exception of the leg press for women (after 2 wk of training) and leg extension for men (after 6 wk of training), absolute and relative maximal dynamic strength was significantly increased after 4 wk of training for all three exercises (squat, leg press, and leg extension) in both sexes. Resistance training also caused a significant decrease in the percentage of type IIb fibers after 2 wk in women and 4 wk in men, an increase in the resting levels of serum testosterone after 4 wk in men, and a decrease in cortisol after 6 wk in men. No significant changes occurred over time for any of the other measured parameters for either sex. These data suggest that skeletal muscle adaptations that may contribute to strength gains of the lower extremity are similar for men and women during the early phase of resistance training and, with the exception of changes in the fast fiber type composition, that they occur gradually.

Effect of graded exercise on esophageal motility and gastroesophageal reflux in nontrained subjects

The effects of graded exercise on esophageal motility and gastroesophageal reflux were evaluated in nine nontrained subjects, using a catheter with three strain-gauge transducers connected to a solid-state datalogger and an ambulatory intraesophageal pH monitor. Subjects exercised on a stationary bike at 45%, 60%, 75%, and 90% of peak O2 uptake (VO2 max). Durations of exercise sessions and rest periods varied among subjects. Studies were performed after an overnight fast and subjects received only intravenous infusion of 5% glucose solution during the study. Plasma concentrations of gastrin, motilin, glucagon, pancreatic polypeptide (PP), and vasoactive intestinal peptide (VIP) were determined at rest and before and after each exercise session. The duration, amplitude, and frequency of esophageal contractions declined with increasing exercise intensity, and the differences were significant (P < or = 0.05) for all three variables at 90% VO2 max. The number of gastroesophageal reflux episodes and the duration of esophageal acid exposure were significantly (P < or = 0.05) increased during exercise at 90% VO2 max. Plasma regulatory peptide concentrations showed no significant changes between rest and the various exercise sessions. Thus, exercise has profound effects on esophageal contractions and gastroesophageal reflux, which are intensity dependent. These effects were not mediated by the hormones measured. The results were similar to those observed in highly trained athletes, suggesting that the effects of exercise on esophageal function are similar in trained and nontrained subjects performing at similar percentages of VO2 max, even though the absolute levels of exercise achieved in each group are different.