Muscular adaptations to fatiguing exercise with and without blood flow restriction.

The purpose of this study was to determine the muscular adaptations to low-load resistance training performed to fatigue with and without blood flow restriction (BFR). Middle-aged (42-62 years) men (n = 12) and women (n = 6) completed 18 sessions of unilateral knee extensor resistance training to volitional fatigue over 6 weeks. One limb trained under BFR, and the contralateral limb trained without BFR [free flow (FF)]. Before and after the training, measures of anterior and lateral quadriceps muscle thickness (MTh), strength, power and endurance were assessed on each limb. The total exercise training volume was significantly greater for the FF limb compared with the BFR limb (P<0·001). Anterior quadriceps thickness and muscle function increased following the training in each limb with no differences between limbs. Lateral quadriceps MTh increased significantly more (P<0·05) in the limb trained under BFR (BFR: 3·50 ± 0·61 to 3·67 ± 0·62 cm; FF: 3·49 ± 0·73 to 3·56 ± 0·70 cm). Low-load resistance training to volitional fatigue both with and without BFR is viable options for improving muscle function in middle-aged individuals. However, BFR enhanced the hypertrophic effect of low-load training and reduced the volume of exercise needed to elicit increases in muscle function.

Vascular adaptations to low-load resistance training with and without blood flow restriction.

PURPOSE: To examine the effects of low-load knee extensor training to fatigue with and without blood flow restriction (BFR) on calf vascular conductance, calf venous compliance, and peripheral arterial stiffness in middle-aged individuals. METHODS: Eleven men (55 ± 8 years) and five post-menopausal women (57 ± 5 years) completed 6 weeks of unilateral knee extensor training with one limb exercising with BFR (BFR limb) and the contralateral limb exercising without BFR (free flow, FF limb). Before and after the training, femoral pulse wave velocity (PWV), calf blood flow (normalized as conductance), and calf venous compliance were measured in each limb. RESULTS: PWV increased following training in both limbs (main effect of time, p = 0.036; BFR limb 8.9 ± 0.8 vs. 9.5 ± 0.9 m/s, FF limb 9.0 ± 1.2 vs. 9.0 ± 1.1; Pre vs. Post). Calf blood flow increased (p = 0.026) in the FF limb (25.0 ± 7.0 vs. 31.8 ± 12.0 flow/mmHg; Pre vs. Post) but did not change (p = 0.831) in the BFR limb (29.1 ± 11.3 vs. 28.7 ± 11.5 flow/mmHg; Pre vs. Post). Calf venous compliance did not change in either limb following training. CONCLUSIONS: These results suggest low-load BFR resistance training to fatigue elicits small increases in peripheral arterial stiffness without eliciting concomitant changes in venous compliance. In addition, unlike low-load knee extensor training without BFR, training with BFR did not enhance calf blood flow.

Ionizing radiation-induced bioeffects in space and strategies to reduce cellular injury and carcinogenesis.

BACKGROUND: The bioeffects of space radiation on organisms outside of the environment of Earth's magnetosphere are a concern for long-duration exploration spaceflights. Potential mutagenic effects from space radiation exposure result from direct DNA damage or indirectly from the production of reactive oxygen species (ROS). HYPOTHESES: 1) Transepithelial electrical resistance (TER) measurements in cell culture monolayers may be used as a model system for detecting cell damage produced by exposure to simulated space radiation and for testing potential chemoprotective agents; 2) biomarkers of exposure that quantitate indirect radiation effects may allow prediction of cellular DNA damage; and 3) a multiple agent, chemoprevention cocktail may reduce the bioeffects of simulated space radiation. METHODS: Normal human and canine lung, breast, and renal epithelial cells were assayed in vitro and exposed to escalating doses of gamma or heavy-ion carbon (290 MeV/u), ceon (400 MeV/u), or iron (600 MeV/u) irradiation. Post-exposure measurements of TER, lipid peroxidation (LP) via measurement of 4-hydroxy-nonenal (4-HNE), and malonaldehyde (MDA) and assessment of chromosome damage via fluorescence in situ hybridization with tandem labeling of chromosome 1 were performed. RESULTS: Cells exposed to intermediate or high doses of radiation (5, 10, and 25 Gy) showed characteristic diminution in TER, thought to be secondary to dysfunction of tight junctions, and associated with membrane LP and other mechanisms. The cells also showed increases in 4-HNE + MDA measurements and increased frequency of chromosomal aberrations. Preliminary studies of cells incubated with media containing a combination of chemoprotective agents at the time of radiation exposure showed a 15-50% reduction in the radiation-induced changes in membrane resistance, levels of LP, and chromosomal aberrations relative to their unprotected cellular counterparts. CONCLUSION: TER measurement, in conjunction with measures of LP, may provide a useful model for determination of physiological changes caused by radiation exposure and the efficacy of chemoprotective agents. A multi-agent mixture of chemoprotective agents may be more effective than previously evaluated single agents alone.

Mechanical stimulation of the plantar foot surface attenuates soleus muscle atrophy induced by hindlimb unloading in rats.

Unloading-induced muscle atrophy occurs in the aging population, bed-ridden patients, and astronauts. This study was designed to determine whether dynamic foot stimulation (DFS) applied to the plantar surface of the rat foot can serve as a countermeasure to soleus muscle atrophy normally observed in hindlimb unloaded (HU) rats. Forty-four mature (6 mo old), male Wistar rats were randomly assigned to ambulatory control, HU alone, HU with active DFS (i.e., plantar contact with active inflation), HU with passive DFS (i.e., plantar contact without active inflation), and HU while wearing a DFS boot with no plantar contact groups. Application of active DFS during HU significantly counteracted the atrophic response by preventing approximately 85% of the reduction in type I myofiber cross-sectional area (CSA) in the soleus while preventing approximately 57% of the reduction in type I myofiber CSA and 43% of the reduction in type IIA myofiber CSA of the medial gastrocnemius muscle. Wearing of a DFS boot without active inflation prevented myofiber atrophy in the soleus of HU animals in a fashion similar to that observed in HU animals that wore an actively inflated DFS boot. However, when a DFS boot without plantar surface contact was worn during HU, no significant protection from HU-induced myofiber atrophy was observed. These results illustrate that the application of mechanical foot stimulation to the plantar surface of the rat foot is an effective countermeasure to muscle atrophy induced by HU.

History of nutrition in space flight: overview.

Major accomplishments in nutritional sciences for support of human space travel have occurred over the past 40 y. This article reviews these accomplishments, beginning with the early Gemini program and continuing through the impressive results from the first space station Skylab program that focused on life sciences research, the Russian contributions through the Mir space station, the US Shuttle life sciences research, and the emerging International Space Station missions. Nutrition is affected by environmental conditions such as radiation, temperature, and atmospheric pressures, and these are reviewed. Nutrition with respect to space flight is closely interconnected with other life sciences research disciplines including the study of hematology, immunology, as well as neurosensory, cardiovascular, gastrointestinal, circadian rhythms, and musculoskeletal physiology. These relationships are reviewed in reference to the overall history of nutritional science in human space flight. Cumulative nutritional research over the past four decades has resulted in the current nutritional requirements for astronauts. Space-flight nutritional recommendations are presented along with the critical path road map that outlines the research needed for future development of nutritional requirements.

Water and energy dietary requirements and endocrinology of human space flight.

Fluid and energy metabolism and related endocrine changes have been studied nearly from the beginning of human space flight in association with short- and long-duration flights. Fluid and electrolyte nutrition status is affected by many factors including the microgravity environment, stress, changes in body composition, diet, exercise habits, sleep cycles, and ambient temperature and humidity conditions. Space flight exposes astronauts to all these factors and consequently poses significant challenges to establishing dietary water, sodium, potassium, and energy recommendations. The purpose of this article is to review the results of ground-based and space flight research studies that have led to current water, electrolyte, and energy dietary requirements for humans during space flight and to give an overview of related endocrinologic changes that have been observed in humans during short- and long-duration space flight.