Reaction time and electromyographic activity during a sprint start

Summary Eight male sprinters were filmed running three maximal starts over 3 m on a long force platform. The subjects were divided into two groups (n=4) according to the leg on which the electromyograph (EMG) electrodes were fixed. When in the set position one group had electrodes on the front leg (FLG) and the other group on the rear leg (RLG). The EMG activities of the gastrocnemius caput laterale muscle (GA), vastus lateralis muscle (VL), biceps femoris caput longum muscle (BF), rectus femoris muscle (RF) and gluteus maximus muscle (GM) were recorded telemetrically using surface electrodes. Total reaction time (TRT) was defined as the time from the gun signal until a horizontal force was produced with a value 10% above the base line. Pre-motor time was defined as the time from the gun signal until the onset of EMG activity and motor time (MT) as the time between the onset of EMG activity and that of force production. Reproducibility of the reaction time variables was satisfactory (r=0.792–0.89; coefficient of variation= 8.8%–11.6%). The TRT was 0.121 s, SD 0.014 in FLG and 0.119 s, SD 0.011 in RLG. The MT ranged from 0.008 s, SD 0.009 (GM) to 0.057 s, SD 0.050 (GA) in FLG and from 0.018 s, SD 0.029 (GA) to 0.045 s, SD 0.009 (GM) in RLG. In some individual cases there were no MT values before horizontal force production. Significant positive correlations were observed between MT and maximal horizontal force and the velocity of the centre of gravity during the last observable contact on the blocks (P<0.05–0.01). The EMG activities of the muscles analysed demonstrated large individual variations until the end of the first contact after the blocks. This resulted in non-observable MT in some individual cases. In general, however, despite the complex multijoint character of TRT, its fractions could be analysed during the early phases on the blocks. To optimize starting action it is desirable that all the important muscles should be activated before any force can be detected against the blocks.     

Lactate and catecholamine responses in male and female sprinters during a Wingate test

A total of six male and six female sprinters at the same national competition level and aged 18–20 years performed a force/velocity test and a 30-s supramaximal exercise test (Wingate test) on 2 different days, separated by a maximal interval of 15 days. The maximal anaerobic power (W _max) was determined from the force/velocity test, and the mean anaerobic power (W) from the Wingate test. Immediately after the Wingate test, a 5-ml venous blood sample was drawn via a heparinized catheter in an antebrachial vein for subsequent catecholamine (adrenaline and noradrenaline) analysis. After 5 min recovery a few microlitres of capillary blood were also taken for an immediate lactate determination. Even expressed per kilogram lean body mass,W _max andW were significantly lower in women. The lactate and adrenaline responses induced by the Wingate test were also less pronounced in this group whereas the noradrenaline levels were not significantly different in men and women. Above all, very different relationships appeared between lactate, adrenaline, noradenaline and W according to sex. Thus, as reported by other authors, the adrenergic response to a supramaximal exercise seemed to be lower in women than in men. Nevertheless a different training status between the two groups, even at same national competition level, could not be excluded and might contribute, at least in part, to the gender differences observed in the present study.     

高原训练对人体生理机能的影响研究

目的：研究高原短跑运动员不同负荷训练前后白细胞、血红蛋白的变化。方法：分析不同运动负荷状态（安静时、定量负荷后、极量负荷后）下高原短跑运动员心率、血红蛋白及白细胞的变化,并进行比较。结果：安静状态时运动员白细胞处于正常值范围内,随着负荷的增加,白细胞数明显增加（P〈0．01）,定量负荷和极量负荷后接近和超过其正常范围值。3种不同负荷状态下血红蛋白水平有明显差别。随着运动负荷的增加,血红蛋白水平增加,差异有统计学意义（P〈0．01）。结论：高原短跑运动员不同负荷训练前后白细胞、血红蛋白明显增加,呈现一定的规律,可为高原短跑训练中负荷控制和医务监督提供实验依据,并为高原短跑训练提供生理学参考。     

A comparison of respiratory compensation thresholds of anaerobic competitors,aerobic competitors and untrained subjects

This study compared respiratory compensation thresholds (RCT) (CO₂ inflection point) of competitors in highly aerobic events (aerobic competitors, ARC) (n=16), competitors in highly anaerobic events (anaerobic competitors, ANC) (n=15), and untrained subjects (UT) (n=25). Maximal oxygen consumption (O_2max), respiratory compensation threshold as a percentage of O_2max (RCT), and O₂ at RCT (O_2RCT) were determined during a maximal Bruce treadmill protocol. O_2max (ml kg^–1 min^–1) was significantly greater (P<0.05) for ARC [67.2 (8.5)] than for ANC [50.0 (7.8)] and UT [43.8 (5.4)]. However, the difference between ANC and UT only approached significance (P=0.07). RCT was not significantly different between ARC [76.3 (8.7)] and ANC [80.7 (6.8)] but was significantly lower (P<0.05) for UT [62.5 (8.8)]. O_2RCT (ml kg^–1 min^–1) was significantly greater (P<0.05) for ARC [51.6 (11.0)] and ANC [40.2 (6.6)] than for UT [27.4 (5.4)], with a significant difference also between ARC and ANC. While used as a criterion for group assignment, greater O_2max, as well as RCT values in ARC (vs UT), reflect chronic aerobic training adaptations. ANC demonstrated O_2max values intermediate to ARC and UT, with RCT very comparable to those found in ARC. The results suggest subjects competitive in highly anaerobic events do not possess excessively high O_2max values. These individuals, however, demonstrate a high RCT when values are expressed relative to O_2max. Oxygen consumption at the RCT in this group is superior to that in UT but inferior to that in ARC, which likely has important implications regarding performance.     

Case report 319

Three cases of bilateral pelvic avulsion fractures in adolescent sprinters are reviewed. Anacute avulsion fracture of the anterior superior iliac spine (ASIS) occurred during active running in three teenaged sprinters. Radiography confirmed a healed fracture of the contralateral ASIS. The clinical features and radiologic appearances are characteristic. The pathophysiology of this type of unique pediatric fracture is discussed. Conservative treatment is successful.