Effect of performance level on pacing strategy during a 10-km running race

The aim of this study was to examine the influence of the performance level of athletes on pacing strategy during a simulated 10-km running race, and the relationship between physiological variables and pacing strategy. Twenty-four male runners performed an incremental exercise test on a treadmill, three 6-min bouts of running at 9, 12 and 15 km h⁻¹, and a self-paced, 10-km running performance trial; at least 48 h separated each test. Based on 10-km running performance, subjects were divided into terziles, with the lower terzile designated the low-performing (LP) and the upper terzile designated the high-performing (HP) group. For the HP group, the velocity peaked at 18.8 ± 1.4 km h⁻¹ in the first 400 m and was higher than the average race velocity (P < 0.05). The velocity then decreased gradually until 2,000 m (P < 0.05), remaining constant until 9,600 m, when it increased again (P < 0.05). The LP group ran the first 400 m at a significantly lower velocity than the HP group (15.6 ± 1.6 km h⁻¹; P > 0.05) and this initial velocity was not different from LP average racing velocity (14.5 ± 0.7 km h⁻¹). The velocity then decreased non-significantly until 9,600 m (P > 0.05), followed by an increase at the end (P < 0.05). The peak treadmill running velocity (PV), running economy (RE), lactate threshold (LT) and net blood lactate accumulation at 15 km h⁻¹ were significantly correlated with the start, middle, last and average velocities during the 10-km race. These results demonstrate that high and low performance runners adopt different pacing strategies during a 10-km race. Furthermore, it appears that important determinants of the chosen pacing strategy include PV, LT and RE.     

The effect of a high carbohydrate diet on running performance during a 30-km treadmill time trial

Summary The purpose of the present study was to examine the influence of a high carbohydrate diet on running performances during a 30-km treadmill time trial. Eighteen runners (12 men and 6 women) took part in this study and completed a 30-km time trial on a level treadmill without modifying their food intake (trial 1). The runners were then randomly assigned to a control or a carbohydrate (CHO) group. The CHO group supplemented their normal diets with additional carbohydrate in the form of confectionery products during the 7 days before trial 2; the control group matched the increased energy intake of the CHO group by consuming additional fat and protein. The mean (SEM) carbohydrate intake of both groups was 334 (22) g before trial 1, after which the CHO group consumed 566 (29) g · day^–1 for the first 3 days and 452 (26) g · day^–1 for the remaining 4 days of recovery. Although there was no overall difference between the performance times for the two groups during trial 2, the CHO group ran faster during the last 5 km of trial 2 than during trial^–1 [3.64 (0.24) m · s^–1 vs 3.44 (0.26) m · s^–1 P < 0.05] . Furthermore, the 6 men in the CHO group ran the 30 km faster after carbohydrate loading [131.0 (5.4) min vs 127.4 (4.9) min;P < 0.05], whereas there was no such improvement in times of the men in the control group. Blood glucose concentrations of both groups decreased below pre-exercise values during trial^–1 (P < 0.001), but only the control group had a decrease in blood glucose concentrations during trial 2 (P < 0.001). There were no differences between the concentrations of plasma catecholamines of the control group during the two trials. However, the adrenaline concentrations of the CHO group were lower (P < 0.05) during trial 2 than during trial 1, even though they ran faster during trial 2. These results confirm that dietary carbohydrate loading improves endurance performance during prolonged running and that confectionery can be used as an effective means of supplementing the normal carbohydrate intake in preparation for endurance races.     

Energy system contribution in a maximal incremental test: correlations with pacing and overall performance in a 10-km running trial

This study aimed to verify the association between the contribution of energy systems during an incremental exercise test (IET), pacing, and performance during a 10-km running time trial. Thirteen male recreational runners completed an incremental exercise test on a treadmill to determine the respiratory compensation point (RCP), maximal oxygen uptake (V˙O2max), peak treadmill speed (PTS), and energy systems contribution; and a 10-km running time trial (T10-km) to determine endurance performance. The fractions of the aerobic (W_AER) and glycolytic (W_GLYCOL) contributions were calculated for each stage based on the oxygen uptake and the oxygen energy equivalents derived by blood lactate accumulation, respectively. Total metabolic demand (W_TOTAL) was the sum of these two energy systems. Endurance performance during the T10-km was moderately correlated with RCP, V˙O2maxand PTS (P<@0.05), and moderate-to-highly correlated with W_AER, W_GLYCOL, and W_TOTAL (P<0.05). In addition, W_AER, W_GLYCOL, and W_TOTAL were also significantly correlated with running speed in the middle (P<0.01) and final (P<0.01) sections of the T10-km. These findings suggest that the assessment of energy contribution during IET is potentially useful as an alternative variable in the evaluation of endurance runners, especially because of its relationship with specific parts of a long-distance race.     

本体感觉神经肌肉促进法对5 km越野后肌疲劳的作用及最佳干预时机

背景：5 km越野训练后会使人体出现肌疲劳,常导致各种程度的肌肉酸痛和肌无力等,而神经肌肉促进法可改善关节和肌肉柔韧性。 目的：观察感觉神经肌肉促进法对新入学军校学员5 km越野训练后肌疲劳的干预作用及最佳干预时机。 方法：选择新入学的健康军校男学员,均进5 km越野训练。分别在训练前、后针对双下肢、骨盆带肌肉采用本体感觉神经肌肉促进法干预,并设置正常训练组作对照。在训练前,训练后第1,3,5天分别评定其肌疲劳度,并检查相关血液生化指标。 结果与结论：训练后第1,3,5天全部对象肌疲劳度和相关血液生化指标肌红蛋白、谷丙转氨酶、谷草转氨酶、乳酸脱氢酶和肌酸磷酸激酶的平均增幅差异均为训练后神经肌肉促进干预组 < 训练前神经肌肉促进干预组 < 正常训练组(P < 0.05)。结果表明经本体感觉神经肌肉促进法干预可以降低5 km越野训练后相关血生化指标的增高,减轻肌损伤,降低肌疲劳。训练结束后当天行本体感觉神经肌肉促进法干预为最佳时机。     

Reproducibility of pacing strategy during simulated 20-km cycling time trials in well-trained cyclists

The aim of the study was to assess the reproducibility of pacing strategy, physiological and perceptual responses during simulated 20-km cycling time trials. Seventeen well-trained male cyclists ( [(V)\dot]\textO₂ max \dot{V}{\text{O}}_{2} \max  = 4.70 ± 0.33 L min⁻¹) completed three 20-km time trials on a Velotron Pro cycle ergometer within a maximum duration of 14 days. During all trials power output, cadence and respiratory exchange were recorded throughout, rating of perceived exertion and affective response were recorded every 2-km and capillary blood was sampled and assayed for the determination of lactate concentration every 4-km. Power output data was assigned to 1-km ‘bins’ and expressed relative to the mean to quantify pacing strategy. Reproducibility of the pacing strategy and the whole trial mean responses was subsequently quantified using typical error (TE) with 90% confidence intervals. The pacing strategy adopted was similar across repeat trials, though there was a higher degree of variability at the start and end of the trial (TE = 6.6 and 6.8% for the first and last 1-km), and a trend for a progressively blunted start on repeat trials. The reproducibility of performance, cardiorespiratory and perceptual measures was good (TE range 1.0–4.0%), but blood lactate exhibited higher variability (TE = 17.7%). The results demonstrate the performance, perceptual and physiological response to self-paced 20-km time trials is reproducible in well-trained cyclists. Future research should acknowledge that variability in pacing strategy at the start and end of a self-paced bout is likely regardless of any intervention employed.     

Effects of vibration and resistance training on neuromuscular and hormonal measures

The aim was to study whether whole body vibration (WBV) combined with conventional resistance training (CRT) induces a higher increase in neuromuscular and hormonal measures compared with CRT or WBV, respectively. Twenty-eight young men were randomized in three groups; squat only (S), combination of WBV and squat (S+V) and WBV only (V). S+V performed six sets with eight repetitions with corresponding eight repetition maximum (RM) loads on the vibrating platform, whereas S and V performed the same protocol without WBV and resistance, respectively. Maximal isometric voluntary contraction (MVC) with electromyography (EMG) measurements during leg press, counter movement jump (CMJ) measures (mechanical performance) including jump height, mean power (P _mean), peak power (P _peak) and velocity at P _peak (V _ppeak) and acute hormonal responses to training sessions were measured before and after a 9-week training period. ANOVA showed no significant changes between the three groups after training in any neuromuscular variable measured [except P _mean, S higher than V (P<0.05)]. However, applying t tests within each group revealed that MVC increased in S and S+V after training (P<0.05). Jump height, P _mean and P _peak increased only in S, concomitantly with increased V _ppeak in all groups (P<0.05). Testosterone increased during training sessions in S and S+V (P<0.05). Growth hormone (GH) increased in all groups but S+V showed higher responses than S and V (P<0.05). Cortisol increased only in S+V (P<0.05). We conclude that combined WBV and CRT did not additionally increase MVC and mechanical performance compared with CRT alone. Furthermore, WBV alone did not increase MVC and mechanical performance in spite of increased GH.     

The effect of skin temperature on performance during a 7.5-km cycling time trial

Aerobic exercise performance is seriously compromised in the heat. Possibly, a high skin temperature causes a rating of perceived exertion (RPE)-mediated decrease in exercise intensity. The purpose of this study was to determine the effect of skin temperature on power output during a 7.5-km cycling time trial. Thirteen well-trained male subjects performed a 7.5-km cycling time trial at 15°C and 50% relative humidity (CONTROL), with radiative heat stress during the time trial, and with (PRECOOL) or without (HEAT) precooling. Heat stress was applied by infrared heaters positioned in front of the cycle ergometer between 1.5 and 6.0 km. Skin, rectal, and pill temperature, power output, heart rate, and RPE were measured during the trial. Despite the lower mean skin temperature at the start of the time trial for PRECOOL compared to HEAT (-2.1 ± 0.7°C; P < 0.01) and CONTROL (-1.8 ± 0.6°C; P < 0.05), and a greater increase in mean skin temperature during the heat stress period for PRECOOL (4.5 ± 1.0°C) and HEAT (3.9 ± 0.8°C) than for CONTROL (-0.3 ± 0.6°C; P < 0.01), no differences in power output were found between HEAT (273 ± 45 W) and CONTROL (284 ± 43 W; P = 0.11) and between HEAT and PRECOOL (266 ± 50 W; P = 0.47). Power output during the time trial was greater for CONTROL than for PRECOOL (P < 0.05). Additionally, no differences were observed in core temperature measures, HR, and RPE. Skin temperature does not affect the selection and modulation of exercise intensity in a 7.5-km cycling time trial.     

Effects of isolated locomotor muscle fatigue on pacing and time trial performance

Purpose

Locomotor muscle fatigue impairs exercise performance during time to exhaustion tests. However, its effect on self-regulation of power output (pacing) is unknown. The primary aim of this study was to investigate the effects of locomotor muscle fatigue on pacing and time trial performance.

Methods

Ten healthy recreationally active men completed a 15-min time trial on a cycle ergometer 30 min after undergoing an eccentric fatiguing protocol designed to induce a substantial strength loss in the knee extensor muscles without inducing significant metabolic stress. This fatigue condition was compared with a control condition, using a randomly counterbalanced AB/BA crossover design.

Results

Total work completed during the 15-min cycling time trial was significantly reduced by 4.8 % in the fatigue condition compared with the control condition. This was caused by a significant reduction in power output. Rating of perceived exertion was significantly higher in the fatigue condition compared with the control condition only during the first 3 min of the time trial. Heart rate and vastus lateralis integrated electromyogram were not significantly different between the two conditions.

Conclusion

The results show that participants with fatigued locomotor muscles reduce their pace but do not change their pacing strategy. As a result, there was a significant reduction in time trial performance. As predicted by the psychobiological model of exercise performance, a slower pace may be a behavioral response to compensate for the significant increase in perception of effort induced by locomotor muscle fatigue.     

Vastus medialis muscle oxygenation trends during a simulated 20-km cycle time trial

In this study we examined the oxygenation trend of the vastus medialis muscle during sustained high-intensity exercise. Ten cyclists performed an incremental cycle ergometer test to voluntary exhaustion [mean (SD) maximum oxygen uptake 4.29 (0.63) l·min^–1; relative to body mass 60.8 (2.4) ml·kg^–1·min^–1] and a simulated 20-km time trial (20TT) on a wind-loaded roller system using their own bicycle (group time = 23–31 min) in two separate sessions. Cardiorespiratory responses were monitored using an automated metabolic cart and a wireless heart rate monitor. Tissue absorbency, which was used as an index of muscle oxygenation, was recorded simultaneously from the vastus medialis using near-infrared spectroscopy. Group mean values for oxygen uptake, ventilation, heart rate, respiratory exchange ratio, power output, and rating of perceived exhaustion were significantly (P≤0.05) higher during the incremental test compared to the 20TT [4.29 (0.63) l·min^–1 vs 4.01 (0.55) l·min^–1, 120.4 (26) l·min^–1 vs 97.6 (16.1) l·min^–1, 195 (8) beats·min^–1 vs 177 (9) beats·min^–1, 1.15 (0.06) vs 0.93 (0.06), 330.1 (31) W vs 307.2 (24.5) W, and 19 (1.5) vs 16 (1.7), respectively]. Oxygen uptake and heart rate during the 20TT corresponded to 93.5% and 90.7%, respectively, of the maximal values observed during the incremental test. Comparison of the muscle oxygenation trends between the two tests indicated a significantly greater degree of deoxygenation during the 20TT [–699 (250) mV vs –439 (273) mV; P≤0.05] and a significant delay in the recovery oxygenation from the 20TT. The mismatching of whole-body oxygen uptake and localised tissue oxygenation between the two tests could be due to differences in muscle temperature, pH, localised blood flow and motor unit recruitment patterns between the two tests. Electronic Publication     

Effects of resistance training combined with vascular occlusion or hypoxia on neuromuscular function in athletes

The aim was to investigate the effects of low-load resistant training combined with vascular occlusion or normobaric hypoxic exposure, on neuromuscular function. In a randomised controlled trial, well-trained athletes took part in a 5-week training of knee flexor/extensor muscles in which low-load resistant exercise (20 % of one repetition maximum, 1-RM) was combined with either (1) an occlusion pressure of approximately 230 mmHg (KT, n = 10), (2) hypoxic air to generate an arterial blood oxygen saturation of ~80 % (HT, n = 10), or (3) with no additional stimulus (CT, n = 10). Before and after training, participants completed the following tests: 3-s maximal voluntary contraction (MVC₃), 30-s MVC, and an endurance test (maximal number of repetitions at 20 % 1-RM, Reps₂₀). Electromyographic activity (root mean square, RMS) was measured during tests and the cross-sectional area (CSA) of the quadriceps and hamstrings was measured pre- and post-training. Relative to CT, KT, and HT showed likely increases in MVC₃ (11.0 ± 11.9 and 15.0 ± 13.1 %, mean ± 90 % confidence interval), MVC₃₀ (10.2 ± 9.0 and 18.3 ± 17.4 %), and Reps₂₀ (28.9 ± 23.7 and 23.3 ± 24.0 %). Compared to the CT group, CSA increased in the KT (7.6 ± 5.8) and HT groups (5.3 ± 3.0). KT had a large effect on RMS during MVC₃, compared to CT (effect size 0.8) and HT (effect size 0.8). We suspect hypoxic conditions created within the muscles during vascular occlusion and hypoxic training may play a key role in these performance enhancements.     

Effect of resistance training during hemodialysis on circulating cytokines: a randomized controlled trial

The purpose of this study was to evaluate the effect of a 12-week intradialytic progressive resistance training (PRT) regimen on circulating pro- and anti-inflammatory cytokines. Forty-nine patients (62.6 ± 14.2 years) were recruited from the outpatient hemodialysis unit of the St. George Public Hospital, Sydney, Australia. Patients were randomized to: PRT + usual care (n = 24) or usual care control (n = 25). The PRT group performed two sets of 10 exercises at high intensity using free-weights, 3 times per week for 12 weeks during dialysis, while the control group did not exercise. Tumor necrosis factor-alpha, interleukin-1b, interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10, and interleukin-12 were measured in serum before and after the intervention period. Muscle cross-sectional area (CSA), intramuscular lipid, intermuscular adipose tissue, and subcutaneous and total thigh fat, evaluated via computed tomography of the non-dominant mid-thigh, were also collected at both time points. All cytokines were significantly elevated in the total cohort at baseline compared with normative data. There were no cytokine changes over time or between groups (p > 0.05). In secondary analyses pooling the groups, changes in logIL-6 and IL-8 were inversely related to changes subcutaneous thigh fat (p < 0.05) while changes in logIL-6 were also inversely related to changes in thigh muscle CSA, and total thigh fat (p < 0.03). These data suggest that 12 weeks of intradialytic progressive resistance training does not improve circulating pro- and anti-inflammatory markers. Further research is required to elucidate the implications and mechanisms of the relationships between IL-6 and IL-8 and body composition in ESRD.     

Effects of running training on the blood glucose and lactate in rats during rest and swimming.

The purpose of this study was to examine the effect of physical training on the concentrations of glucose and lactate in the blood of rats during rest and after an acute bout of exercise. We used the following types and periods of training; (i) swimming for 4 weeks, (ii) running for 4 weeks, and (iii) running for 10 weeks. The results clearly show that the resting levels of blood glucose was significantly lower in groups trained by either swimming or running than untrained groups. In addition, after the acute exercise of swimming, animals trained by either running or swimming showed a lower increase in the blood lactate than untrained animals. Furthermore, the increases in the blood glucose after swimming were significantly lower in the group trained by swimming for 4 weeks and by running for 10 weeks than in untrained groups. These results suggest that after physical training by running, animals show an adaptation in the changes in the blood glucose and the blood lactate that are induced by a different type of physical stress, swimming.     

Serum hormones during prolonged training of neuromuscular performance

Summary The effects of a 24-weeks' progressive training of neuromuscular performance capacity on maximal strength and on hormone balance were investigated periodically in 21 male subjects during the course of the training and during a subsequent detraining period of 12 weeks. Great increases in maximal strength were noted during the first 20 weeks, followed by a plateau phase during the last 4 weeks of training. Testosterone/cortisol ratio increased during training. During the last 4 weeks of training changes in maximal strength correlated with the changes in testosterone/cortisol (P<0.01) and testosterone/SHBG (P<0.05) ratios. During detraining, correlative decreases were found between maximal strength and testosterone/cortisol ratio (P<0.05) as well as between the maximal strength and testosterone/SHBG ratio (P<0.05). No statistically significant changes were observed in the levels of serum estradiol, lutropin (LH), follitropin (FSH), prolactin, and somatotropin. The results suggest the importance of the balance between androgenic-anabolic activity and catabolizing effects of glucocorticoids during the course of vigorous strength training.     

Effects of acute ingestion of sodium citrate on metabolism and 5-km running performance: a field study.

The purpose of the study was to (a) assess the effects of sodium citrate ingestion on metabolism and performance capacity in a 5-km competitive outdoor stadium run in trained male runners, and (b) elucidate the potential relationship between citrate-induced changes in plasma volume, body mass, and performance. Ten subjects (age 22.1 +/- 2.5 yrs, body mass 74.1 +/- 6.1 kg, height 180.1 +/- 5.7 cm, (.)VO(2)max 60.8 +/- 5.5 ml x kg(-1) x min(-1)) participated in the study. There was no effect of treatment on 5-km running time: 1100.0 +/- 79.1 and 1082.7 +/- 62.0 s in citrate (CIT) and in placebo (PLC) trials, respectively, p = 0.09. Blood pH increased from 7.34 +/- 0.07 to 7.49 +/- 0.07 (p = 0.002) as a result of administering sodium citrate in the amount of 0.5 g x kg(-1) body mass in 1.5 litres of solution but remained stable while the equal volume of placebo drink was consumed: 7.40 +/- 0.04 and 7.44 +/- 0.09. The relative change in plasma volume after administering the drink was -1.99 +/- 3.49% in the PLC and 9.75 +/- 6.51% in the CIT trial (p = 0.001). Body mass did not differ before drinking; however, before the start the subjects were heavier in the CIT trial (74.2 +/- 6.1 kg) vs. the PLC trial (73.4 +/- 6.2 kg, p = 0.048). The shifts in plasma volume and body mass were not related to changes in performance. The results suggest that ingestion of sodium citrate induces an increase in water retention, plasma volume, and blood pH before exercise but does not improve performance in a 5-km competitive run in field conditions in trained male runners.     

Effects of high-intensity and blood flow-restricted low-intensity resistance training on carotid arterial compliance: role of blood pressure during training sessions

We examined the effects of high-intensity resistance training (HIT) and low-intensity blood flow-restricted (LI-BFR) resistance training on carotid arterial compliance. Nineteen young men were randomly divided into HIT (n = 9) or LI-BFR (n = 10) groups. The HIT and LI-BFR groups performed 75 and 30 %, respectively, of one-repetition maximum (1-RM) bench press exercise, 3 days per week for 6 weeks. During the training sessions, the LI-BFR group wore elastic cuffs around the most proximal region of both arms. Muscle cross-sectional area (CSA), 1-RM strength, and carotid arterial compliance were measured before and 3 days after the final training session. Acute changes in systolic arterial pressure (SAP), plasma endothelin-1 (ET-1), nitrite/nitrate (NOx), and noradrenalin concentrations were also measured during and after a bout of training session. The training led to significant increases (P < 0.01) in bench press 1-RM and arm and chest muscle CSA in the two training groups. Carotid arterial compliance decreased significantly (P < 0.05) in the HIT group, but not in the LI-BFR group. There was a significant correlation (r = ?0.533, P < 0.05) between the change in carotid arterial compliance and the acute change in SAP during training sessions; however, ET-1 and NOx did not correlate with carotid arterial compliance. Our results suggest that muscle CSA and strength increased following 6 weeks of both HIT and LI-BFR training. However, carotid arterial compliance decreased in only the HIT group, and the changes were correlated with SAP elevations during exercise sessions.     

Effects of marathon running on running economy and kinematics

The present study was designed to investigate interactions between running economy and mechanics before, during, and after an individually run marathon. Seven experienced triathletes performed a 5-min submaximal running test on a treadmill at an individual constant marathon speed. Heart rate was monitored and the expired respiratory gas was analyzed. Blood samples were drawn to analyze serum creatine kinase activity (S-CK), skeletal troponin I (sTnI), and blood lactate (B-La). A video analysis was performed (200 frames · s⁻¹) to investigate running mechanics. A kinematic arm was used to determine the external work of each subject. The results of the present study demonstrate that after the marathon, a standardized 5-min submaximal running test resulted in an increase in oxygen consumption, ventilation, and heart rate (P < 0.05), with a simultaneous decrease in the oxygen difference (%) between inspired and expired air, and respiratory exchange ratio (P < 0.05). B-La did not change during the marathon, while sTnI and S-CK values increased (P < 0.05), peaking 2 h and 2 days after the marathon, respectively. With regard to the running kinematics, a minor increase in stride frequency and a similar decrease in stride length were observed (P < 0.01). These results demonstrate clearly that weakened running economy cannot be explained by changes in running mechanics. Therefore, it is suggested that the increased physiological loading is due to several mechanisms: increased utilization of fat as an energy substrate, increased demands of body temperature regulation, and possible muscle damage. Accepted: 20 March 2000     

Effects of high-intensity resistance training and low-intensity resistance training with vascular restriction on bone markers in older men

The aim of this study was to examine and compare the effects of different resistance training protocols on bone marker concentrations in older men. Thirty-seven healthy older male subjects were assigned to one of three groups: high-intensity resistance training (HI-RT, age?=?57.5?±?0.8); low-intensity resistance training with vascular restriction (LI-VRT, age?=?59.9?±?1.0); and control (CON, age?=?57.0?±?1.1). Blood samples were collected before and after 6?weeks of resistance training to measure the changes in bone formation [bone alkaline phosphatase, (Bone ALP)] and resorption (C-terminal cross-linking telopeptide of Type-I collagen, CTX) marker concentrations. A significant main effect for time was detected in Bone ALP to CTX ratio for the exercise groups (p??LI-VRT, p?相似文献