The rate of phosphocreatine hydrolysis and resynthesis in exercising muscle in humans using 31P-MRS

Time-resolved 31-phosphorus nuclear magnetic resonance spectroscopy (31P-MRS) of the biceps femoris muscles was performed during exercise and recovery in six healthy sedentary male subjects (maximal oxygen uptake; 46.6 +/- 1.7 (SEM) ml.kg-1.min-1), 5 male sprinters (56.2 +/- 2.5), and 5 male long-distance runners (73.6 +/- 2.2). Each performed 4 min of knee flexion exercises at absolute values of 1.63 W and 4.90 W, followed by 5 min of recovery in a prone position in a 2.1 T superconducting magnet with a 67 cm bore. 31P-MRS spectra were recorded every 12.8 s during the rest-exercise-recovery sequence. Computer-aided contour analysis and pixel imaging of phosphocreatine peaks (PCr) and inorganic phosphate (Pi) were performed. The work loads in the present study were selected as mild exercise (1.63 W) and heavy exercise (4.90 W), corresponding to 18-23% and 54-70% of maximal exercise intensity. Long-distance runners showed a significantly smaller decrement in PCr and less acidification at a given exercise intensity compared to those shown by sedentary subjects. The transient responses of PCr and Pi during recovery were characterized by first-order kinetics. After exercise, the recovery rates of PCr and Pi were significantly faster in long-distance runners than in sedentary subjects (P < 0.05). Since it is postulated that PCr resynthesis is controlled by aerobic metabolism and mitochondrial creatine kinase, it is suggested that the faster PCr and Pi recovery rates and decreased acidification seen in long-distance runners during and after exercise might be attributed to their greater capacity for aerobic metabolism.     

Morphological differences of elite Croatian track-and-field athletes

In this study we present the morphological characteristics of 54 Croatian national level track-and-field athletes. 21 anthropometric body measures were taken on a sample of 15 sprinters (S), 16 endurance sprinters (S4), 10 middle-distance runners (MD) and 13 long-distance runners (LD). Body fat percentage, body mass index and somatotype were also calculated. Canonical discriminative analysis showed significant difference between the athletes of various running events, in the measures of body volume and body fat, while no significant difference was found in the variables of longitudinal and transversal dimensions of the skeleton. ANOVA and Student t-test for independent samples showed statistically significantly higher thigh and lower leg circumference in sprinters, as well as greater upper arm skinfold in middle-distance runners. The mesomorphic component is a dominant characteristic of somatotype of the runners in all events, whereas the ectomorphic component is the least marked.     

The Role of Erythrocytic Acetylcholinesterase in Hormonal Regulation of Adaptation to Physical Exercise

Acetylcholinesterase (AchE) activity in erythrocytes and blood levels of cortisol and insulin were investigated in athletes training under different bioenergetic conditions (sprinters, middle-distance runners, and marathoners). The groups of sprinters and marathoners had a decreased enzyme activity compared to nonathletes (p < 0.05). In response to a standard exercise, load AchE activity increased in the groups of middle-distance runners and marathoners. A relationship was observed between the level of AchE activity and the cortisol-to-insulin ratio in the blood. This ratio is specific to the type of bioenergetic conditions and increases in the following order: controls, middle-distance runners, sprinters, and marathoners. In vitro experiments revealed an effect of insulin on AchE activity. This effect was significantly lower in sprinters than in the control group. A reduction in AchE activity and an increase in the cortisol-to-insulin ratio are considered as factors increasing metabolic turnover in athletes, mainly, lipid turnover. This mechanism ensures effective mobilization of substrates at the start of physical exercise and their recovery after. The observed relationship between the insulin level and the AchE activity may prove to be a mechanism of regulation of the insulin level. This relationship may change during adaptation to physical exercise, as in the case of sprinters, when the sensitivity of AchE to the inhibitory effect of insulin is decreased. A high blood level of cortisol and insulin is a distinctive feature of sprinters, which provides for a higher turnover of carbohydrates. In marathoners, low AchE activity leads to an increased effect of acetylcholine, which is manifested by an increased cortisol level and a decreased insulin level, thus providing for a higher lipid turnover.     

Sex differences in lactate and glycerol levels during maximal aerobic and anaerobic running

Lactate, glycerol, adrenaline, and noradrenaline in venous blood following 400 m and 3000 m runs were measured in 6 untrained male students, 5 female handball players, 6 female sprinters and 6 female long-distance runners. Physical performance in the two events by the untrained males was the same as for the female handball players, but was less than that by the female sprinters and female long-distance runners. Peak blood lactate levels obtained after 400 m sprinting, and glycerol concentration following the 3000 m run were not significantly different between the untrained males and the female handball players. On the other hand, both peak blood lactate concentrations after 400 m sprinting for female sprinters and peak blood glycerol levels following a 3000 m run for female long-distance runners were significantly higher than those in the untrained male subjects. In both runs there was no significant difference in adrenaline and noradrenaline between the untrained male group and the female handball players. These results suggest that blood lactate in a 400 m run, and glycerol in a 3000 m run might be a reflection of physical performance level but not of sex difference.     

Assessment of anaerobic capacity in runners

A new method for assessment of anaerobic capacity is presented. It consists of two treadmill runs at 22 km X h-1 and 7.5% slope, the first one being interrupted after 40 s (submax. test), the second continuing until volitional exhaustion (max. test). Measured variables are the increase in arterial lactate concentration over the pre-exercise value in the submax. test (delta L40), the maximal arterial lactate level in the max. test (Lmax), and time to exhaustion (tmax). Fifty-five male runners of high competitive level were examined with this procedure, including 400-m runners of differing performance capacity (400 m A and B/C), middle-distance (MD), long-distance (LD), and marathon runners (M). Eleven physical education students served as controls (C). tmax was 88.3 +/- 11.0, 85.2 +/- 11.4, 83.1 +/- 12.7, 63.1 +/- 11.4, 43.7 +/- 7.5, and 50.7 +/- 5.0 s for 400 m A, 400 m B/C, MD, LD, M, and C. The corresponding values for Lmax were 17.47 +/- 1.68, 17.52 +/- 2.03, 16.27 +/- 2.18, 13.44 +/- 2.13, 10.13 +/- 2.68, and 15.54 +/- 1.43 mmol X 1(-1) and for delta L40 5.93 +/- 1.10, 7.13 +/- 1.55, 6.39 +/- 0.89, 6.68 +/- 1.18, 8.19 +/- 1.37, and 10.76 +/- 1.62 mmol X 1(-1). The differences in delta L40, most likely reflecting differences in high energy phosphate utilization, suggest that excellent performance in any running event is associated with increased alactacid anaerobic capacity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peak blood ammonia and lactate after submaximal, maximal and supramaximal exercise in sprinters and long-distance runners

The purpose of this study was to elucidate the difference in peak blood ammonia concentration between sprinters and long-distance runners in submaximal, maximal and supramaximal exercise. Five sprinters and six long-distance runners performed cycle ergometer exercise at 50% maximal, 75% maximal, maximal and supramaximal heart rates. Blood ammonia and lactate were measured at 2.5, 5, 7.5, 10 and 12.5 min after each exercise. Peak blood ammonia concentration at an exercise intensity producing 50% maximal heart rate was found to be significantly higher compared to the basal level in sprinters (P less than 0.01) and in long-distance runners (P less than 0.01). The peak blood ammonia concentration of sprinters was greater in supra-maximal exercise than in maximal exercise (P less than 0.05), while there was no significant difference in long-distance runners. The peak blood ammonia content after supramaximal exercise was higher in sprinters compared with long-distance runners (P less than 0.01). There was a significant relationship between peak blood ammonia and lactate after exercise in sprinters and in long-distance runners. These results suggest that peak blood ammonia concentration after supramaximal exercise may be increased by the recruitment of fast-twitch muscle fibres and/or by anaerobic training, and that the processes of blood ammonia and lactate production during exercise may be strongly linked in sprinters and long-distance runners.     

Energetics of high-speed running: integrating classical theory and contemporary observations

We hypothesized that the anaerobic power and aerobic power outputs during all-out runs of any common duration between 10 and 150 s would be proportional to the maximum anaerobic (E(an-max)) and aerobic powers (E(aer-max)) available to the individual runner. Seventeen runners who differed in E(an-max) and E(aer-max) (5 sprinters, 5 middle-distance runners, and 7 long distance runners) were tested during treadmill running on a 4.6 degrees incline. E(an-max) was estimated from the fastest treadmill speed subjects could attain for eight steps. E(aer-max) was determined from a progressive, discontinuous, treadmill test to failure. Oxygen deficits and rates of uptake were measured to assess the respective anaerobic and aerobic power outputs during 11-16 all-out treadmill runs that elicited failure between 10 and 220 s. We found that, during all-out runs of any common duration, the relative anaerobic and aerobic powers utilized were largely the same for sprint, middle-distance, and long-distance subjects. The similar fractional utilization of the E(an-max) and E(aer-max) available during high-speed running 1) provides empirical values that modify and advance classic theory, 2) allows rates of anaerobic and aerobic energy release to be quantified from individual maxima and run durations, and 3) explains why the high-speed running performances of different event specialists can be accurately predicted (R(2) = 0.97; n = 254) from two direct measurements and the same exponential time constant.     

Force-velocity relationship and stretch-shortening cycle function in sprint and endurance athletes

This study examined the torque-velocity and power-velocity relationships of quadriceps muscle function, stretch shortening cycle function, and leg-spring stiffness in sprint and endurance athletes. Isokinetic maximal knee extension torque was obtained from 7 sprinters and 7 endurance athletes using a Con-trex isokinetic dynamometer. Torque and power measures were corrected for lean-thigh cross-sectional area and lean-thigh volume, respectively. Stretch-shortening cycle function and muscle stiffness measurements were obtained while subjects performed single-legged squat, countermovement, and drop-rebound jumps on an inclined sledge and force-plate apparatus. The results indicated that sprinters generated, on average, 0.15 +/- 0.05 N.m.cm(-2) more torque across all velocities compared with endurance athletes. Significant differences were also found in the power-velocity relationships between the 2 groups. The sprinters performed significantly better than the endurance athletes on all jumps, but there were no differences in prestretch augmentation between the groups. The average vertical leg stiffness during drop jumps was significantly higher for sprinters (5.86 N.m(-1)) compared with endurance runners (3.38 N.m(-1)). The findings reinforce the need for power training to be carried out at fast contraction speeds but also show that SSC function remains important in endurance running.     

Changes in spring-mass model parameters and energy cost during track running to exhaustion

The purpose of this study was to determine whether exhaustion modifies the stiffness characteristics, as defined in the spring-mass model, during track running. We also investigated whether stiffer runners are also the most economical. Nine well-trained runners performed an exhaustive exercise over 2000 meters on an indoor track. This exhaustive exercise was preceded by a warm-up and was followed by an active recovery. Throughout all the exercises, the energy cost of running (Cr) was measured. Vertical and leg stiffness was measured with a force plate (Kvert and Kleg, respectively) integrated into the track. The results show that Cr increases significantly after the 2000-meter run (0.192 +/- 0.006 to 0.217 +/- 0.013 mL x kg(-1) x m(-1)). However, Kvert and Kleg remained constant (32.52 +/- 6.42 to 32.59 +/- 5.48 and 11.12 +/- 2.76 to 11.14 +/- 2.48 kN.m, respectively). An inverse correlation was observed between Cr and Kleg, but only during the 2000-meter exercise (r = -0.67; P < or = 0.05). During the warm-up or the recovery, Cr and Kleg, were not correlated (r = 0.354; P = 0.82 and r = 0.21; P = 0.59, respectively). On track, exhaustion induced by a 2000-meter run has no effect on Kleg or Kvert. The inverse correlation was only observed between Cr and Kleg during the 2000-meter run and not before or after the exercise, suggesting that the stiffness of the runner may be not associated with the Cr.     

运动酸碱失衡恢复过程影响因素的研究

本研究对不同水平运动员在４００ｍ和１５００ｍ跑前及跑后恢复期中进行了摄氧量（ＶＯ２）、心输出量（ＣＯ）、血乳酸浓度（ＬＡ）和血气指标的测定,其目的是探讨影响运动酸碱失衡恢复快慢的主要因素。结果显示：１．不同水平运动员血液缓冲能力及运动后１５ｍｉｎ酸碱失衡恢复无显著差异（Ｐ＞０．０５）,但他们运动后ＬＡ和ｐＨ有显著差异（Ｐ＜０．０５）。这提示ＬＡ和ＰＨ变动的多少不是由血液缓冲能力的强弱所致,ＬＡ上升越少则酸碱失衡恢复过程越短。２．较高水平运动员心肺机能动员快,潜力大,与一般水平运动员有显著差异（Ｐ＜０．０５）。心肺机能的强弱一方面对运动中ＬＡ生成的多少有影响,另一方面与ＬＡ缓冲能否顺利进行有关。因此它对运动酸碱失衡恢复的快慢起着重要的作用。     

Iron status in runners of various running specialties.

The blood iron status of 44 male runners of various running specialties (18 sprinters, 13 middle- and 13 long-distance runners) is evaluated by measuring serum ferritin (SF), serum iron (Si), hemoglobin concentration (Hb), hematocrit (Ht), red blood cells content (RBC) and haptoglobin concentration (Hp). The results of these analyses (except Hp) are compared to those obtained in sedentary male subjects (control group) of the same mean age. Mean SF, SI, Hb and Ht measured in athletes are significantly lower than in control group. The remarkably low Hp values obtained in athletes suggests the occurrence of hemolysis. Using unpaired t test, it appears that the blood iron status of these runners does not depend on their running specialty.     

Breakdown of high-energy phosphate compounds and lactate accumulation during short supramaximal exercise

Muscle ATP, creatine phosphate and lactate, and blood pH and lactate were measured in 7 male sprinters before and after running 40, 60, 80 and 100 m at maximal speed. The sprinters were divided into two groups, group 1 being sprinters who achieved a higher maximal speed (10.07 +/- 0.13 m X s-1) than group 2 (9.75 +/- 0.10 m X s-1), and who also maintained the speed for a longer time. The breakdown of high-energy phosphate stores was significantly greater for group 1 than for group 2 for all distances other than 100 m; the breakdown of creatine phosphate for group 1 was almost the same for 40 m as for 100 m. Muscle and blood lactate began to accumulate during the 40 m exercise. The accumulation of blood lactate was linear (0.55 +/- 0.02 mmol X s-1 X l-1) for all distances, and there were no differences between the groups. With 100 m sprints the end-levels of blood and muscle lactate were not high enough and the change in blood pH was not great enough for one to accept that lactate accumulation is responsible for the decrease in running speed over this distance. We concluded that in short-term maximal exercise, performance depends on the capacity for using high-energy phosphates at the beginning of the exercise, and the decrease in running speed begins when the high-energy phosphate stores are depleted and most of the energy must then be produced by glycolysis.     

Study of the anaerobic metabolism during the preparation of runners

The anaerobic threshold of 37 male and 16 female athletes was studied under laboratory conditions and in the field (4.0 mmol.l-1 lactic acid accumulation was considered as anaerobic threshold). Elite sprinters, middle- and long-distance runners and walkers took part in the study. Sprinters reached the anaerobic threshold first and long-distance runners last, walkers performed it with almost the same speed as sprinters. A two-year follow up of the anaerobic threshold of a female long-distance and a male middle-distance runner was analized for the individual estimation of the physical fitness.     

Ventilatory and heart rate chemosensitivity in track-and-field athletes

Fifty-four male track-and-field athletes and 18 male non-athletes were examined by isocapnic progressive hypoxia and CO2 rebreathing tests. Ventilatory and heart rate (HR) responses to hypoxia were analysed by a hyperbolic relationship and the ventilatory response to hypercapnia by a linear regression. The results showed that ventilatory sensitivity during hypoxia was significantly attenuated in the long-distance runners and sprinters compared to the non-athletes. Although heart rate sensitivity during hypoxia in none of the athletes showed a significant difference compared to that of the non-athletes, baseline HR in the long-distance runners was significantly lower than that of the non-athletes. None of the athletes showed significant differences in ventilatory sensitivity during hypercapnia compared to the non-athletes.     

Post-competition blood lactate concentrations as indicators of anaerobic energy expenditure during 400-m and 800-m races

The relationships between anaerobic glycolysis and the average velocity (v) sustained during running were studied in 17 top level athletes (11 males and 6 females). A blood sample was obtained within 10 min of the completion of major competitions over 400 m, 800 m and 1500 m and the blood lactate concentration [la]b was measured. In both male and female athletes [la]b was related to the relative performance, as expressed as a percentage of the athlete's best v of the season. Over 400 m, r = 0.85 (P less than 0.01) and r = 0.80 (P less than 0.05) in males and females, respectively. Over 800 m, the corresponding values were r = 0.76 (P less than 0.01) and r = 0.91 (P less than 0.01). In male runners [la]b was correlated to v: r = 0.89 (P less than 0.01) and r = 0.71 (P less than 0.02) over 400 m and 800 m, respectively. No relationship to relative performance or v was obtained over 1500 m. Energy expenditure during competition running was estimated in male runners from the [la]b values. This estimate was based mainly on the assumption that a 1 mmol.1-1 increase in [la]b corresponded to the energy produced by the utilization of 3.30 ml.O kg-1. The energy cost of running was estimated, by dividing the estimated total energy expenditure by the race distance, at 0.211 ml.kg-1.min-1 over 800 m and 0.274 ml.kg-1.m-1 over 400 m.(ABSTRACT TRUNCATED AT 250 WORDS)     

Running-specific, periodized strength training attenuates loss of stride length during intense endurance running

The purpose of this study was to determine the effects of a running-specific, periodized strength training program (performed over the specific period [8 weeks] of a 16-week macrocycle) on endurance-trained runners' capacity to maintain stride length during running bouts at competitive speeds. Eighteen well-trained middle-distance runners completed the study (personal bests for 1500 and 5000 m of 3 minutes 57 seconds +/- 12 seconds and 15 minutes 24 seconds +/- 36 seconds). They were randomly assigned to each of the following groups (6 per group): periodized strength group, performing a periodized strength training program over the 8-week specific (intervention) period (2 sessions per week); nonperiodized strength group, performing the same strength training exercises as the periodized group over the specific period but with no week-to-week variations; and a control group, performing no strength training at all during the specific period. The percentage of loss in the stride length (cm)/speed (m.s) (SLS) ratio was measured by comparing the mean SLS during the first and third (last) group of the total repetitions, respectively, included in each of the interval training sessions performed at race speeds during the competition period that followed the specific period. Significant differences (p < 0.05) were found in mean percentage of SLS loss between the 3 study groups, with the periodized strength group showing no significant SLS change (0.36 +/- 0.95%) and the 2 other groups showing a moderate or high SLS loss (-1.22 +/- 1.5% and -3.05 +/- 1.2% for the nonperiodized strength and control groups, respectively). In conclusion, periodized, running-specific strength training minimizes the loss of stride length that typically occurs in endurance runners during fatiguing running bouts.     

Presynaptic inhibition of spinal α motoneurons in humans adapted to different types of motor activity

Changes in the presynaptic inhibition of spinal α motoneurons were studied in athletes during motor activities of different types. In the state where muscles were at relative rest, the presynaptic inhibition of spinal α motoneurons of the m. soleus was stronger in samboists (athletes specializing in the martial art of sambo) and sprinters than in long-distance runners. In samboists performing repeated static efforts, the presynaptic inhibition of spinal α motoneurons became stronger from one trial to the next. Both technique training and strength training enhanced the presynaptic inhibition of spinal α motoneurons, this enhancement being greater after strength training.     

Changes in the exercise-induced hormone response to branched chain amino acid administration.

It was the aim of the present experiment to detect possible effects of branched-chain amino acids (BCAA) on the endocrine response to 1 h of continuous running. Blood samples were collected from 14 long-distance runners (age 24-42 years) in two different trials performed at 1-week intervals. In both trials (E and P) blood samples were collected at the following times: 9 a.m. (basal values sample), 10.30 a.m. (sample 90), 11.30 a.m. (sample 150), 12.30 p.m. (sample 210); the athletes performed 1 h of running at a constant predetermined speed between samples 90 and 150. Following the basal sample a mixture containing BCAA (E trial), or not containing BCAA (P trial) was ingested. In both trials no hormone basal concentrations, except insulin, were changed before exercise. In P trial, following exercise (sample 150), human growth hormone (HGH), prolactin (PRL), adrenocorticotropic hormone (ACTH) and cortisol (C) increased, while testosterone (T) decreased. In sample 210, after 1 h of rest, while ACTH, PRL and HGH had recovered to basal concentrations, C remained elevated and T displayed a further decrease. In the E trial a similar pattern of change was observed in sample 150 for HGH, PRL, ACTH and C; in sample 210 HGH and PRL displayed significantly lower values than in the corresponding P trial samples. The T was not modified by the running exercise and increased during the recovery period. It is, therefore, suggested that BCAA administration before exercise affects the response of some anabolic hormones, mainly HGH and T.     

Optimization of Running Strategies According to the Physiological Parameters for a Two-Runners Model

In order to describe the velocity and the anaerobic energy of two runners competing against each other for middle-distance races, we present a mathematical model relying on an optimal control problem for a system of ordinary differential equations. The model is based on energy conservation and on Newton’s second law: resistive forces, propulsive forces and variations in the maximal oxygen uptake are taken into account. The interaction between the runners provides a minimum for staying 1 m behind one’s competitor. We perform numerical simulations and show how a runner can win a race against someone stronger by taking advantage of staying behind, or how they can improve their personal record by running behind someone else. Our simulations show when it is the best time to overtake, depending on the difference between the athletes. Finally, we compare our numerical results with real data from the men’s 1500 m finals of different competitions.     

ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery.

We used (31)P-magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of eight healthy men (25-45 yr), during brief (18-s) voluntary finger flexion exercise (0.67-Hz contraction at 10% maximum voluntary contraction; 50/50 duty cycle) and 180-s recovery. Phosphocreatine (PCr) concentration fell 19 +/- 2% during exercise and then recovered with half time = 0.24 +/- 0.01 min. Cell pH rose by 0.058 +/- 0.003 units during exercise as a result of H(+) consumption by PCr splitting, which (assuming no lactate production or H(+) efflux) implies a plausible non-P(i) buffer capacity of 20 +/- 3 mmol. l intracellular water(-1). pH unit(-1). There was thus no evidence of significant glycogenolysis to lactate during exercise. Analysis of PCr kinetics as a classic linear response suggests that oxidative ATP synthesis reached 48 +/- 2% of ATP demand by the end of exercise; the rest was met by PCr splitting. Postexercise pH recovery was faster than predicted, suggesting "excess proton" production, with a peak value of 0.6 +/- 0.2 mmol/l intracellular water at 0.45 min of recovery, which might be due to, e.g., proton influx driven by cellular alkalinization, or a small glycolytic contribution to PCr resynthesis in recovery.