Frequent low-load ischemic resistance exercise to failure enhances muscle oxygen delivery and endurance capacity

This study investigated the effects of frequent low-load ischemic resistance exercise performed to failure on quadriceps size and performance, muscle activation, oxygen kinetics and cardiovascular responses. Ten healthy males performed knee-extension exercise for 4 weeks (4 sessions/week) at 15% maximal voluntary muscle contraction (MVC). One leg was trained with free blood flow (C-leg) while in the other leg (I-leg) ischemia was induced by an inflatable cuff (≥230 mmHg). Quadriceps cross-sectional area (CSA) of the I-leg increased by 3.4% (P<0.05). A tendency for smaller increase in muscle CSAs at the cuff level was observed. MVC force did not change in either leg, whereas the number of repetitions during exercise test to failure increased (P<0.01) by 63% in I-leg and 36% in C-leg. The decrease in muscle oxygenated hemoglobin concentration acquired by NIRS was attenuated (P<0.01) by 56% in I-leg and 21% in C-leg. Electromyographic amplitude of rectus femoris in I-leg was ～45% lower (P<0.025) during the ischemic test. Also, ～9% increase (P<0.05) in pre-exercise diastolic pressure was observed. In conclusion, substantial gains in muscle endurance capacity were induced, which were associated with enhanced muscle oxygen delivery. The potential negative effects of ischemic exercise with high cuff pressure on muscle and nerve and on arterial pressure regulation need further investigation.     

Effects of strength and endurance training on antioxidant enzyme gene expression and activity in middle-aged men

This study was aimed at investigating the effects of a 21-week period of progressive strength or endurance training on peripheral blood mononuclear cells (PBMC) antioxidant enzyme gene expression and activity in healthy middle-aged untrained men. Strength ( n =11) and endurance ( n =12) training were performed twice a week, including resistance exercises to activate all the main muscle groups or cycle-ergometer pedaling, respectively. mRNA levels of catalase, glutathione peroxidase (GPx), mitochondrial superoxide dismutase (MnSOD) and cytosolic superoxide dismutase (CuZnSOD) were increased after 21 weeks of strength training, while endurance training induced significant changes only in MnSOD and GPx mRNA levels. CuZnSOD protein content was significantly increased only in strength-trained subjects. The program of strength or endurance exercise training had no significant effects on the activity of any of the antioxidant enzymes. In conclusion, in a middle-aged population, 21 weeks of strength or endurance training was a sufficient stimulus to up-regulate mRNA levels of PBMC antioxidant enzymes, the strength training being a more optimal stimulus. However, the discrepancies between enzyme protein and mRNA levels suggest that the present systematic strength or endurance training period had no beneficial effects on enzymatic antioxidant defense mechanisms in previously untrained middle-aged men.     

Prolonged constant load cycling exercise is associated with reduced gross efficiency and increased muscle oxygen uptake

This study investigated the effects of prolonged constant load cycling exercise on cycling efficiency and local muscle oxygen uptake responses. Fourteen well‐trained cyclists each completed a 2‐h steady‐state cycling bout at 60% of their maximal minute power output to assess changes in gross cycling efficiency (GE) and muscle oxygen uptake (mVO₂) at time points 5, 30, 60, 90, and 120 min. Near‐infrared spatially resolved spectroscopy (NIRS) was used to continually monitor tissue oxygenation of the Vastus Lateralis muscle, with arterial occlusions (OCC) applied to assess mVO₂. The half‐recovery time of oxygenated hemoglobin (HbO₂) was also assessed pre and post the 2‐h cycling exercise by measuring the hyperemic response following a 5‐min OCC. GE significantly declined during the 2‐h cycling bout (18.4 ± 1.6 to 17.4 ± 1.4%; P < 0.01). Conversely, mVO₂ increased, being significantly higher after 90 and 120 min than at min 5 (+0.04 mlO₂/min/100 g; P = 0.03). The half‐recovery time for HbO₂ was increased comparing pre and post the 2‐h cycling exercise (+7.1 ± 19s), albeit not significantly (d: 0.48; P = 0.27). This study demonstrates that GE decreases during prolonged constant load cycling exercise and provides evidence of an increased mVO₂, suggestive of progressive mitochondrial or contractile inefficiency.     

Effects of endurance and high intensity training on ICAM-1 and VCAM-1 levels and arterial pressure in obese and normal weight adolescents

Objectives: Obesity prevalence has increased in Iranian adolescents in recent years. However, few studies have examined the impact of intervention programs on this health issue. The main objective of this study was to evaluate the effects of 8-week endurance training (ET) and high intensity interval training (HIIT) on intercellular adhesion molecule-1(ICAM-1) and vascular adhesion molecule-1(VCAM-1) levels among obese and normal-weight male adolescents.

Methods: Thirty obese and 30 normal-weight subjects were assigned to the ET, HIIT, or control group for eight weeks. Before and after the intervention, ICAM-1, VCAM-1, body weight, BMI, VO_2max, and blood pressures were measured. SPSS (Version 21) was used for data analysis, and the significance level was set at p < 0.05.

Results: Mixed design ANOVAs indicated that the obese participants had significantly (p < 0.05) lower ICAM-1 levels in the ET (from 509 ± 61 ng/ml to 387 ± 43 ng/ml) and HIIT (from 517 ± 72 ng/ml to 374 ± 50 ng/ml), but their VCAM-1 level was significantly (p < 0.05) reduced only after the HIIT (from 1689 ± 119 ng/ml to 1282 ± 63 ng/ml). Similarly, normal weight participants significantly (p < 0.05) lowered their ICAM-1 levels in the ET (from 296 ± 18 ng/ml to 216 ± 14 ng/ml) and HIIT (from 289 ± 22 ng/ml to 202 ± 12 ng/ml), but their VCAM-1 level was significantly (p < 0.05) reduced only after the HIIT (from 895 ± 50 ng/ml to 673 ± 142 ng/ml). Systolic blood pressure and diastolic blood pressures of all the participants were significantly (p < 0.01) decreased at the conclusion of the ET and HIIT.

Conclusion: While both the ET and HIIT were useful in lowering the SBP and DBP of the participants, HIIT was more effective than ET in reducing ICAM-1 and VCAM-1 content in normal and obese adolescents.     

耐力训练对大鼠骨骼肌超微结构及IGF-1表达影响的研究

目的探讨大鼠骨骼肌对中等负荷耐力训练的适应性变化。方法40只雄性Wiser大鼠进行上坡跑中等负荷运动，观察不同训练阶段大鼠比目鱼肌的超微结构和IGF-1表达的变化。结果组织病理学观察示大鼠比目鱼肌发生了运动性肌肉损伤，且在第3周时损伤最重，出现骨骼肌结构相对“薄弱期”。同时，肌组织中IGF-1水平明显升高。肌组织在损伤后即开始自行修复，运动4周后，Z线异常率和IGF-1水平逐渐降低，病理改变逐渐减轻。结论肌肉损伤有一个逐渐加重后经修复逐渐减轻的过程，说明在损伤积累的同时，肌肉表现出良好的适应能力。     

Skeletal muscle fibre types in teenagers: relationship to physical performance and activity

Human skeletal muscle consists mainly of 2 types of fibres denoted type I (slow twitch) and type II (fast twitch). The aim of this investigation was to study skeletal muscle fibre characteristics together with physical performance, physical activity and interest in different physical activities, and the relationships between these variables among students in grade I in high school. Sixty-nine boys and 47 girls at the age of 16 were studied. The relative proportion of type I fibres (type 1%) in vastus lateralis was approximately 50% for both boys and girls and the interindividual variation was large, more so for boys than for girls. The muscle fibre areas for all fibre types were larger in boys than girls and the relationships between the sizes of the areas of type I, type IIA and type IIB differed between the sexes. The muscle enzymes succinate dehydrogenase, 3-hydroxyacyl-CoA-dehydrogenase and phosphofructokinase were all on average higher in boys than girls; the only significant difference was in succinate dehydrogenase. There was a positive correlation between performance in a 9-min run and type 1%. for boys but not for girls. Multiple correlation analysis indicated that factors determining the performance in the 9-min run were maximal oxygen uptake and type I% for boys, and maximal oxygen uptake but not fibre types for girls. The attitude to cross-country running was positively correlated with the type I% for boys but not for girls. There was a stronger positive correlation between degree of physical activity and type I% for boys than girls. In conclusion, stronger correlations between muscle fibre characteristics and physical performance, physical activity and interest in physical activity were found for boys than for girls.     

Effects of reduced‐volume of sprint interval training and the time course of physiological and performance adaptations

This study sought to determine the time course of training adaptations to two different sprint interval training programmes with the same sprint: rest ratio (1:8) but different sprint duration. Nine participants (M: 7; F: 2) were assigned to 15‐second training group (15TG) consisting of 4‐6 × 15‐second sprints interspersed with 2‐minute recovery, whereas eight participants (M: 5; F: 3) were assigned to 30‐second training group (30TG) consisting of 4‐6 × 30 second sprints interspersed with 4‐minute recovery. Both groups performed their respective training twice per week over 9 weeks and changes in peak oxygen uptake () and time to exhaustion (TTE) were assessed every 3 weeks. Additional eight healthy active adults (M: 6; F: 2) completed the performance assessments 9 weeks apart without performing training (control group, CON). Following 9 weeks of training, both groups improved (15TG: 12.1%; 30TG: 12.8%, P<.05) and TTE (15TG: 16.2%; 30TG: 12.8%, P<.01) to a similar extent. However, while both groups showed the greatest gains in at 3 weeks (15TG: 16.6%; 30TG: 17.0%, P<.001), those in TTE were greatest at 9 weeks. CON did not change any of performance variables following 9 weeks. This study demonstrated that while the changes in cardiorespiratory function plateau within several weeks with sprint interval training, endurance capacity (TTE) is more sensitive to such training over a longer time frame in moderately‐trained individuals. Furthermore, a 50% reduction in sprint duration does not diminish overall training adaptations over 9 weeks.     

Aerobic and anaerobic exercise capacities of elite middle-distance runners after two weeks of training at moderate altitude

The effect of short-term altitude training on sea-level physiological characteristics in elite runners was investigated. Seven middle-distance runners (6 men, 1 woman) belonging to the Swedish national team (mean age 23 years) spent 2 weeks of training at 2000 m above sea level in Kenya. Treadmill tests were performed before and 6 and 12 d after the altitude sojourn. Six other runners (4 men, 2 women) had a corresponding training sojourn at sea level in Portugal (control group). Ro of the runners (1 man, 1 woman) in the Kenya group were omitted from the study because of gastroenteritis. The maximal oxygen uptake (VO_{2 max}; pretravel: Kenya group 212 and control group 188 ml · kg^−0.75 - min⁻¹), maximal treadmill time and oxygen cost of running were unchanged in both groups. The maximal oxygen deficit increased in all subjects after the Kenya sojourn (mean 19±6%). Heart rates during running at specified submaximal running velocities were lower post-altitude (Kenya group), but tended to be higher after sea-level training (control group). Maximal heart rate was unchanged in both groups. Perceived exertion (Borg) during submaximal running was lower post-altitude. Submaximal and maximal blood lactate and plasma catecholamine concentrations were not altered in any of the groups. Post-exhaustive plasma ammonia levels were decreased 12 d after altitude descent in the Kenya group. The results suggest an unchanged aerobic capacity in elite middle-distance runners after short-term training at moderate altitude. However, a change in the circulatory regulation during submaximal exercise was observed. Furthermore, anaerobic capacity improved but this bore no clear relation to lactate or ammonia metabolism.