Concurrent endurance and explosive type strength training improves neuromuscular and anaerobic characteristics in young distance runners

To study effects of concurrent explosive strength and endurance training on aerobic and anaerobic performance and neuromuscular characteristics, 13 experimental (E) and 12 control (C) young (16 - 18 years) distance runners trained for eight weeks with the same total training volume but 19% of the endurance training in E was replaced by explosive training. Maximal speed of maximal anaerobic running test and 30-m speed improved in E by 3.0 +/- 2.0% (p < 0.01) and by 1.1 +/- 1.3% (p < 0.05), respectively. Maximal speed of aerobic running test, maximal oxygen uptake and running economy remained unchanged in both groups. Concentric and isometric leg extension forces increased in E but not in C. E also improved (p < 0.05) force-time characteristics accompanied by increased (p < 0.05) rapid neural activation of the muscles. The thickness of quadriceps femoris increased in E by 3.9 +/- 4.7% (p < 0.01) and in C by 1.9 +/- 2.0% (p < 0.05). The concurrent explosive strength and endurance training improved anaerobic and selective neuromuscular performance characteristics in young distance runners without decreases in aerobic capacity, although almost 20% of the total training volume was replaced by explosive strength training for eight weeks. The neuromuscular improvements could be explained primarily by neural adaptations.     

The profile and distribution of myosin heavy chain isoforms in middle-aged sedentary persons

AIM: Human lifestyle has drastically changed during the past century as the share of physical work in daily life has decreased. The purpose of the present study was to examine the distribution of myosin heavy chain (MHC) isoforms in middle-aged sedentary persons, to compare the proportion of MHC isoforms of middle-aged and young sedentary persons and to demonstrate the effect of physical activity of MHC isoforms in middle-aged sedentary persons. METHODS: Eighty-nine middle-aged sedentary and 13 young sedentary persons volunteered for the study. Thirty middle-aged sedentary subjects participated in strength-conditional exercise program during 9 months. Vertical jumping height and maximal anaerobic work capacity were measured. Muscle samples were taken from vastus lateralis muscle. MHC isoform composition was determined by SDS-PAGE. RESULTS: Variation of MHC I and MHC IIa isoforms in middle-age sedentary persons demonstrated normal distribution. Significant differences of MHC isoform proportions between middle-aged and young sedentary participants were not observed. The proportion of MHC IIx decreased significantly after the exercise period that significantly improved the maximal anaerobic power and jumping height of participants. CONCLUSIONS: Normal distribution illustrated the proportion of MHC I and MHC IIa isoforms in 89 middle-aged sedentary persons while significant differences of MHC isoforms proportion between young and middle-aged sedentary persons were not observed. Even small increase of physical activity improved physical performance and decrease the MHC IIx proportion of middle-aged sedentary persons. Physically active lifestyle in middle age, when age-related changes have not started yet, may delay age-related changes in skeletal muscle.     

The role of the Child Health Services in the identification of children with possible Attention Deficit Hyperactivity Disorder/Deficits in Attention, Motor Control and Perception (ADHD/DAMP)

Literature concerning the role of the Child Health Services in the identification of children with possible Attention Deficit Hyperactivity Disorder/Deficits in Attention, Motor Control and Perception (ADHD/DAMP) is summarized in order to establish a background for evaluation, discussion and conclusion.     

Nutritional and genetic contributions to serum cholesterol concentration in a children's follow-up study

In the Finnish multicentre study of cardiovascular risk in young Finns in 1980, 1983 and 1986, 2429, 2052 and 1841 9 to 18-year-old children and adolescents participated. In 1980, subjects of eastern origin living in the west had, despite their western diet, higher serum cholesterol concentrations than subjects both residing in and originating from the west. In males, eastern origin increased the eastlwest difference in serum cholesterol concentrations. Between 1980 and 1986 the mean serum total cholesterol of the study cohorts decreased by 5.5% and simultaneously the east/west differences in serum cholesterol concentrations disappeared in boys. The study suggests that genetic background is a separate factor determining serum total cholesterol level, but with declining serum cholesterol concentrations the effect of the genetic factor does not become manifest.     

Neuromuscular characteristics and fatigue during 10 km running

This study investigated neuromuscular characteristics and fatigue during 10 km running (10 K) performance in well-trained endurance athletes with different distance running capability. Nine high (HC) and ten low (LC) caliber endurance athletes performed the 10 K on a 200 m indoor track, constant velocity lap (CVL, 4.5 m x s(-1)) 5 times during the course of the 10 K and maximal 20 m speed test before (20 m(b)) and after (20 m(a)) the 10 K. Running velocity (V), ground contact times (CT), ground reaction forces (F) and electromyographic activity (EMG) of the leg muscles (vastus lateralis; VL, biceps femoris; BF, gastrocnemius; GA) were measured during 20 m(b), 20 m(a), and CVLs. The 10 K times differed (p<0.001) between HC and LC (36.3+/-1.2 and 39.2+/-2.0 min, respectively) but no differences were observed in 20 m(b) velocity. The 10 K led to significant (p<0.05) decreases in V, F and integrated EMG (IEMG) and increases in CTs of 20 m(a) in both groups. No changes were observed in HC or LC in F and IEMG during the CVLs but HC showed shorter (p<0.05) mean CT of CVLs than LC. A significant correlation (r = -0.56, p<0.05) was observed between the mean CT of CVLs and velocity of 10 K (V10K). Pre-activity of GA in relation to the IEMG of the total contact phase during the CVLs was higher (p<0.05) in HC than LC. The relative IEMGs of VL and GA in the propulsion phase compared to the IEMG of the 20 m(b) were lower (p<0.05) in HC than LC. In conclusion, marked fatigue took place in both HC and LC during the 10 K but the fatigue-induced changes in maximal 20 m run did not differentiate endurance athletes with different V10K. However, a capability to produce force rapidly throughout the 10 K accompanied with optimal preactivation and contact phase activation seem to be important for 10 km running performance in well trained endurance athletes.     

EPO, red cells, and serum transferrin receptor in continuous and intermittent hypoxia

PURPOSE: Erythropoietic response in 10 healthy nonsmoking volunteers exposed to normobaric hypoxia continuously or intermittently 12 h daily for 7 d was evaluated in a randomized cross-over study. METHODS: An oxygen content of 15.4% corresponding to an altitude of 2500 m was created by adding nitrogen into room air in a flat. Venous blood samples for hemoglobin (Hb), hematocrit (Hct), reticulocytes, serum erythropoietin (S-EPO), red cell 2,3-diphosphoglycerate (2,3-DPG), serum ferritin (S-Ferrit), and serum soluble transferrin receptor (S-TransfR) were drawn at 8:00 a.m. RESULTS: S-EPO was increased from baseline values of 22.9+/-9.6 and 20.5+/-10.1 U x L(-1) to 40.7+/-12.9 (P < 0.05) and 35+/-14.3 U x L(-1) (P < 0.05) after the first night in continuous and intermittent hypoxia, respectively, and remained elevated throughout both exposures. Hb and Hct values did not show any significant changes. Red cell 2,3-DPG rose from baseline a value of 5.0+/-0.8 to 5.9+/-0.7 mmol x L(-1) (P < 0.05) after the first day in continuous hypoxia and from 5.2+/-0.7 mmol x L(-1) to 6.1+/-0.5 mmol x L(-1) on day 3 (P < 0.05) during intermittent hypoxia. The reticulocyte count rose significantly (P < 0.05) after 5 d in both experiments. S-transferrin receptor level rose significantly from 2.2+/-0.4 and 2.1+/-0.5 mg x L(-1) to 2.6+/-0.5 mg x L(-1) and 2.3+/-0.6 mg x L(-1) on day 5 (P < 0.05), to 2.7+/-0.5 mg x L(-1) and 2.5+/-0.6 mg x L(-1) on day 7 (P < 0.05) under continuous and intermittent hypoxia, respectively. CONCLUSIONS: We suggest that intermittent exposure to moderate normobaric hypoxia 12 h daily for 1 wk induces a similar stimulation of erythropoiesis as continuous exposure.     

中国和英国精神科医生对儿童多动行为症状的评估比较

目的 :比较不同文化背景的精神专科医生在评估多动症儿童各种症状表现时的一致程度 ,探讨文化对儿童多动症诊断可能产生的影响。方法 :使用单独或集体行为观察清单 ,让两地的精神科医生对儿童多动症的各种表现进行症状评估 ;所有的评估者均观察同一录像带上患儿的行为表现 ;对其评定结果进行统计和比较。结果 :儿童独自活动观察量表的 12项中有 11项症状条目评定结果类似 ,有 3项英国医生的评分高于中国医生 ,有 9项中国医生评分高于英国医生 ,其中 1项具有显著性差异。结论 :对行为表现和症状认知的文化差异可能使流行病学的研究出现不同的结果 ,即使使用统一的诊断标准和症状评分量表作为诊断工具 ,不同文化背景的国家 ,儿童多动症的患病率仍然可不一致     

Mechanical work and efficiency in ergometer bicycling at aerobic and anaerobic thresholds

Internal and external mechanical work, energy consumption and mechanical efficiency were studied in constant-load ergometer bicycling at five different power outputs below, equal to, and above the aerobic (AerT) and anaerobic (AnT) thresholds. The gross, net and true efficiencies of the whole body in five male subjects were calculated. The work against the external load was defined as the external mechanical work. The internal mechanical work was calculated as the sum of the increments of kinetic and potential energy in all body segments by using methods of film analysis. Total energy consumption was measured by combining aerobic and anaerobic energy production. When the power output of the bicycle ergometer was increased from 146 +/- 15 to 283 +/- 17 W, oxygen consumption increased from 2.20 +/- 0.98 to 4.22 +/- 0.20 l min-1 (P less than 0.001), while the oxygen consumption at rest was 0.30 +/- 0.03 l min-1. The concentration of blood lactate increased from 2.2 +/- 0.4 at the lowest work load to 8.6 +/- 1.2 mmol l-1 at the highest work load (P less than 0.001). The amount of external work done per revolution increased from 139 +/- 20 to 277 +/- 29 J (P less than 0.001), while the amount of internal work per revolution remained almost constant (56 +/- 12 J). The gross efficiency in the present study was 17-20%, net efficiency 18-22% and true efficiency 21-30%, respectively. The highest gross and net efficiencies were reached at the AerT. The lowest efficiencies were obtained at highest work load.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of prolonged skeletal muscle stretch-shortening cycle on recoil of elastic energy and on energy expenditure

The enhancement of performance in stretch-shortening exercises has been attributed to the recoil of elastic energy stored during the stretching phase. If the time between stretching and shortening (coupling time) is too long the stored elastic energy can be wasted. In the present study, coupling time was increased by asking ten male subjects to run on a treadmill at different speeds (2.2-5.2 m X s-1) using special soft shoes in addition to normal shoes. The results indicated that running with soft shoes required greater energy consumption than running with normal shoes except at slow speed (2.2 m X s-1). When the running speed was increased the extra energy consumed using soft shoes was parallelly enhanced (0.4 J X kg-1/step at 5.2 m X s-1). It was suggested that the effect of coupling time as limiting factor for recoil of elastic energy was relevant in fast twitch (FT) fibers, which were progressively recruited when the running speed was increased. This is consistent to the fact that cross-bridge life time in FT fibers is very short, and therefore more sensitive to coupling time. At slow running speed (2.2 m X s-1) only slow twitch (ST) fibers were recruited and the enhancement of coupling time was not long enough to provocate detachment of cross-bridges of ST fibers, which possess a long cross-bridge life time. It was concluded that the different recruitment of ST and FT fibers influenced the pattern of recoil of elastic energy which was dependent on the running speed.     

Serum hormone and myocellular protein recovery after intermittent runs at the velocity associated with V˙O2max

The responses of serum myocellular proteins and hormones to exercise were studied in ten well-trained middle-distance runners [maximal oxygen consumption (V˙O_2max)?=?69.4?(5.1)?ml?·?kg^?1?·?min^?1] during 3 recovery days and compared to various measures of physical performance. The purpose was to establish the duration of recovery from typical intermittent middle-distance running exercises. The subjects performed, in random, order two 28-min treadmill running exercises at a velocity associated with V˙O_2max: 14 bouts of 60-s runs with 60?s of rest between each run (IR₆₀) and 7 bouts of 120-s runs with 120?s of rest between each run (IR₁₂₀). Before the exercises (pre- exercise), 2?h after, and 1, 2 and 3 days after the exercises, the same series of measurements were performed, including those for serum levels of the myocellular proteins creatine kinase, myoglobin and carbonic anhydrase III (S-CK, S-Mb and S-CA III, respectively), serum hormones testosterone, Luteinizing hormone, follicle-stimulating hormone and cortisol (S-testosterone, S-LH, S-FSH and S-cortisol, respectively) and various performance parameters: maximal vertical jump height (CMJ) and stride length, heart rate and ratings of perceived exertion during an 8-min run at 15?km?·?h^?1 (SL_15?km·h?1, HR_15?km?·?h?1 and RPE_15?km?·?h?1, respectively). Two hours after the end of both exercise bouts the concentration of each measured serum protein had increased significantly (P?15?km?·?h?1 or CMJ. During the recovery days only S-CK was significantly raised (P?P?15?km?·?h?1 (P?120 the post-exercise responses returned to their pre-exercise levels within the 3 days of recovery. The present findings suggest that a single 28-min intermittent middle-distance running exercise does not induce changes in serum hormones of well-trained runners during recovery over 3 days, while changes in S-CK, CMJ and RPE_15?km?·?h?1 indicate that 2–3 days of light training may be needed before the recovery at muscle level is complete.