Effects of explosive type strength training on physical performance characteristics in cross-country skiers

Summary To investigate the effects of a combination of simultaneous strength and endurance training on selected neuromuscular and aerobic performance characteristics seven male cross-country skiers underwent training for a period of 6 weeks. The experimental group trained 6–9 times per week with a programme consisting of 34% explosive type strength training and 66% endurance training during the first 3 weeks of the experiment and 42% and 58% respectively during the last 3 weeks of the experiment. The total volume of training of the control group (eight skiers) was of the same magnitude but consisted of 85% pure endurance training and 15% endurance type strength training. The experimental training regime resulted in specific changes in neuromuscular performance. This was demonstrated by improvements (P<0.01) in the maximal heights of rise of the centre of gravity in the squat and countermovement jumps. A significant decrease (P<0.05) took place also in the time of rapid isometric force production during experimental training, while no changes occurred in the maximal force of the trained muscles. Aerobic performance characteristics of the experimental group did not change during the experimental training period. No significant changes occurred in neuromuscular or aerobic performance characteristics in the control group. These findings indicated that training-induced improvements in explosive force production may not be fully inhibited by this kind of aerobic training. They also suggested that endurance athletes could undertake explosive type strength training programmes without a concomitant reduction in aerobic capacity, if the overall loading of training were within predefined limits.     

Metabolic response of endurance athletes to training with added load

Summary Endurance athletes were divided into experimental (n=12) and control (n=12) groups to investigate the effects of extra-load training on energy metabolism during exercise. A vest weighing 9%–10% body weight was worn every day from morning to evening for 4 weeks including every (n=6) or every other (n=6) training session. After 4 weeks the control group had a lower blood lactate concentration during submaximal running, whereas the experimental group had significantly higher blood lactate and oxygen uptake (p<0.01–p<0.05), and a lower 2 mmol lactate threshold (p<0.05) and an increased blood lactate concentration after a short running test to exhaustion (p<0.05). Those experimental subjects (n=6) who used the added load during every training session had a lower 2 mmol lactate threshold, improved running time to exhaustion, improved vertical velocity when running up stairs and an increased during submaximal running after the added load period. It is concluded that the additional loading increased anaerobic metabolism in the leg muscles during submaximal and maximal exercise. An increased recruitment and adaptation of the fast twitch muscle fibres is suggested as the principal explanation for the observed changes.     

Muscle metabolism,blood lactate and oxygen uptake in steady state exercise at aerobic and anaerobic thresholds

Summary Muscle metabolites and blood lactate concentration were studied in five male subjects during five constant-load cycling exercises. The power outputs were below, equal to and above aerobic (AerT) and anaerobic (AnT) threshold as determined during an incremental leg cycling test. At AerT, muscle lactate had increased significantly (p<0.05) from the rest value of 2.31 to 5.56 mmol · kg^–1 wet wt. This was accompanied by a significant reduction in CP by 28% (p<0.05), whereas only a minor change (9%) was observed for ATP. At AnT muscle lactate had further increased and CP decreased although not significantly as compared with values at AerT. At the highest power outputs (> AnT) muscle lactate had increased (p<0.01) and CP decreased (p<0.01) significantly from the values observed at AnT. Furthermore, a significant reduction (p<0.05) in ATP over resting values was recorded. Blood lactate decreased significantly (p<0.01) during the last half of the lowest 5 min exercise, remained unchanged at AerT and increased significantly (p<0.05–0.01) at power outputs AnT. It is concluded that anaerobic muscle metabolism is increased above resting values at AerT: at low power outputs (AerT) this could be related to the transient oxygen deficit during the onset of exercise or the increase in power output. At high power outputs (> AnT) anaerobic energy production is accelerated and it is suggested that AnT represents the upper limit of power output where lactate production and removal may attain equilibrium during constant load exercise.     

Oxygen uptake response during maximal cycling in hyperoxia, normoxia and hypoxia

BACKGROUND: Oxygen uptake (VO2) on-kinetics is decelerated in acute hypoxia and accelerated in hyperoxia in comparison with normoxia during submaximal exercise. However, the effects of fraction of oxygen in inspired air (FIO2) on VO2 kinetics during maximal exercise are unknown. HYPOTHESIS: The effects of FIO2 on VO2 on-kinetics during maximal exercise are similar to submaximal exercise. METHODS: There were 11 endurance athletes who were studied during maximal 7-min cycle ergometer exercise in hyperoxia (FIO2 0.325), hypoxia (FIO2 0.166) and normoxia (FIO2 0.209). The individual VO2 data were fit to a curve by using a three exponential model. RESULTS: In hypoxia, VO2 on-response amplitude during Phase 2 (approximately 20-100 s from the beginning of exercise) was lower (p < 0.05) when compared with hyperoxia; time constant of VO2 Phase 3 (beyond approximately 100 s after beginning of exercise) was shorter (p < 0.05) when compared with hyperoxia; and mean response time (MRT, O-63%) for VO2peak was shorter (p < 0.05) when compared with normoxia and hyperoxia. VO2peak was higher in hyperoxia (4.80 +/- 0.48 L x min(-1), p < 0.05) and lower in hypoxia (4.03 +/- 0.46 L x min(-1), p < 0.05) than in normoxia (4.36 +/- 0.44 L x min(-1)). CONCLUSIONS: Moderate hypoxia or hyperoxia do not affect VO2 time constants at the onset of maximal exercise. However, MRT for VO2peak is shortened in hypoxia. It is suggested that the differences in VO2peak and power output during the latter half of the test and the point that FIO2 was modified only moderately might explain most of the discrepancy with the previous studies.     

Noninvasive Detection of Coronary Artery Stenosis Using 16-slice Spiral CT：a Comparison with Selective X-ray Coronary Angiography

Multislice spiral CT(MSCT)has recently e-volved as a modalityfor non-invasive coronaryi ma-ging.16-slice MSCT allows excellent distal coro-nary coverage with higer temporal and spatial reso-lution.It can be usedto detect stenosis of coronaryartery with a diameter≥1.5cm[1,2].We investi-gated a group of coronary MSCT angiography(MSCTA)results,with those of selective X-raycoronary angiography(SCA)serving as the refer-ence standard.1MATERIALS AND METHODS1.1PatientsBetween July20…     

空气喷磨对预防性树脂充填微渗漏的影响

目的 :体外评价空气喷磨、酸蚀和两者结合对预防性树脂充填微渗漏的影响。方法 :对照组 (I,n =12 )对人离体磨牙常规预防性树脂充填。其余组分别用 5 0 μ(Ⅱ,Ⅲ)和 27μ(Ⅳ ,Ⅴ)氧化铝喷磨 ,其中两组 (Ⅳ ,Ⅴ)酸蚀 30s。每组一半牙齿进行热循环处理 (5～ 5 5℃ ,2500周 )后 ,用亚甲基蓝溶液着色。结果 :不论结合酸蚀与否 ,用 5 0 μ氧化铝喷磨 ,均与对照组不存在显著性差异 (p >0.05)。但喷磨后酸蚀比单纯喷磨能显著地减少微渗漏 (p<0.05)。 5 0 μ较 27μ氧化铝微粒显著地减少微渗漏(p <0.05)。结论 :空气喷磨结合酸蚀能显著地减少预防性树脂充填的微渗漏。     

Headache induced by a nitric oxide donor (nitroglycerin) responds to sumatriptan. A human model for development of migraine drugs

Experimental "vascular" headache in humans may be used in characterizing new migraine drugs. The effects of sumatriptan on nitroglycerin-(NTG)-induced headache and arterial responses were therefore studied. Following a double-blind randomized crossover design, 10 healthy volunteers received sumatriptan 6 mg s.c. or placebo succeeded by 20 min NTG (0.12 mg/kg/min) infusion. Headache was rated on a 10 points scale. Temporal and radial artery diameters and velocity in the middle cerebral artery (MCA) were measured with ultrasound. Sumatriptan reduced the NTG-induced headache, median score 1.5 versus 4 after placebo ( p <0.01) and decreased temporal and radial artery diameters 75±3 and 86±3% of baseline respectively ( p <0.05), Blood velocity in the MCA was unaffected. The NTG model may prove to be a valuable tool in the development of future migraine drugs. The results suggest that NTG headache in non-migraineurs may share mechanisms with migraine headache.