Carbohydrate supplementation stabilises plasma sodium during training with high intensity.

BACKGROUND: Investigations of the effect of beverages containing carbohydrates, only, on the sodium and fluid balance during intermittent exercise of high intensity are rare. Therefore, we compared the effects of water and carbohydrate supplementation on plasma, blood volume, and electrolyte shifts during intermittent exercise. METHODS: Ten male subjects performed an intermittent exercise test twice. In one trial, tap water (4 ml/kg/15 min) was consumed (Plac trial). In the other trial, the same amount of water supplemented with maltodextrin to achieve a 9.1 % carbohydrate solution (CHO trial) was ingested. Training schedule: warm-up at 50 % for 15 min. Afterwards, power changed between 100 % of the maximum power from a previous incremental test minus 10 and 10 W for each 30 s. Venous blood was sampled to measure electrolytes, osmolality, [protein], hct, [Lactate], [glucose], [Hb] and catecholamines. Hydration status was evaluated by BIA before and after exercise. RESULTS: After beverage ingestion [glucose] was significantly higher in CHO until the end of the trial. Starting with similar resting values, osmolality increased significantly more during CHO (p = 0.002). PV decreased by 5 % under both conditions, but recovered partly during exercise under Plac (p = 0.002). [Na+] and [Cl(-)] decreased with Plac during exercise (both p < 0.001) but remained constant during exercise with CHO. CONCLUSIONS: Sole carbohydrate supplementation seems to stabilise plasma [Na+]. This cannot be explained simply by a cotransport of glucose and [Na+], because that should lead to a recovery of the blood and plasma volume under CHO. In contrast, this was found during exercise with Plac.

Musculoskeletal effects of 5 days of bed rest with and without locomotion replacement training.

OBJECTIVES: The present study evaluated the effectiveness of a short and versatile daily exercise regime, named locomotion replacement training (LRT), to maintain muscle size, isometric strength, power, and endurance capacity of the leg muscles following 5 days of head-down tilt (HDT) bed rest. METHODS: 10 male subjects (age 29.4 ± 5.9 years; height 178.8 ± 3.7 cm; body mass 77.7 ± 4.1 kg) performed, in random order, 5 days of 6° head-down tilt bed rest (BR) with no exercise (CON), or BR with daily 25 min of upright standing (STA) or LRT. RESULTS: Knee extensor and plantar flexor cross-sectional area (CSA) were reduced by 2-3 % following bed rest (P < 0.01) for CON and STA, yet maintained for LRT. Knee extensor isometric strength (MVC) decreased by 8 % for CON (P < 0.05), was maintained for STA, and increased with 12 % for LRT (P < 0.05). Plantar flexor MVC remained unaltered during the study. Maximum jump height declined (~1.5 cm) for all conditions (P < 0.001). Neural activation and knee extensor fatigability did not change with bed rest. Bone resorption increased during BR and neither LRT nor STA was able to prevent or attenuate this increase. CONCLUSION: LRT was adequate to maintain muscle size and to even increase knee extensor MVC, but not muscle power and bone integrity, which likely requires more intense and/or longer exercise regimes. However, with only some variables showing significant changes, we conclude that 5 days of BR is an inadequate approach for countermeasure assessments.

The influence of respiratory acid-base changes on muscle performance and excitability of the sarcolemma during strenuous intermittent hand grip exercise.

Acidification has been reported to provide protective effects on force production in vitro. Thus, in this study, we tested if respiratory acid-base changes influence muscle function and excitability in vivo. Nine subjects performed strenuous, intermittent hand grip exercises (10 cycles of 15 s of work/45 s of rest) under respiratory acidosis by CO(2) rebreathing, alkalosis by hyperventilation, or control. The Pco(2), pH, K(+) concentration ([K(+)]), and Na(+) concentration were measured in venous and arterialized blood. Compound action potentials (M-wave) were elicited to examine the excitability of the sarcolemma. The surface electromyogram (EMG) was recorded to estimate the central drive to the muscle. The lowest venous pH during the exercise period was 7.24 ± 0.03 in controls, 7.31 ± 0.05 with alkalosis, and 7.17 ± 0.04 with acidosis (P < 0.001). The venous [K(+)] rose to similar maximum values in all conditions (6.2 ± 0.8 mmol/l). The acidification reduced the decline in contraction speed (P < 0.001) but decreased the M-wave area to 73.4 ± 19.8% (P < 0.001) of the initial value. After the first exercise cycle, the M-wave area was smaller with acidosis than with alkalosis, and, after the second cycle, it was smaller with acidosis than with the control condition (P < 0.001). The duration of the M-wave was not affected. Acidification diminished the reduction in performance, although the M-wave area during exercise was decreased. Respiratory alkalosis stabilized the M-wave area without influencing performance. Thus, we did not find a direct link between performance and alteration of excitability of the sarcolemma due to changes in pH in vivo.

Dynamics of ion currents in the membrane of the isolated mollusc neuron under high pressure.

The action of helium (up to 101 abs. atm.) under high pressure on ionic currents through the cellular membrane was studied in experiments on isolated neurons of a gastropod. A method of intracellular dialysis which is new for physiological investigations under hyperbaric conditions was used. A substantial decrease in the inward (sodium) current with increased pressure was found. Its amplitude was decreased by 10-15% at 25 abs. atm. and by 64% at 101 abs. atm. as compared with the control. At the same time, a shift in the currentvoltage characteristics along the abscissa was not observed. Significant changes in the outward (potassium) current were not appreciable. The inhibition of the sodium current observed in these experiments with increased pressure is associated with a possible change in the structure of the cell membrane under the influence of pressure; this leads in its turn to shifts in the functioning of the membrane components participating in the generation of the nerve impulse.

[The dynamics of the ion currents in the membrane of an isolated mollusk neuron under the action of high pressure]. / Dinamika ionnykh tokov v membrane izolirovannogo neirona molliuska pri deistvii vysokogo davleniia.

The effect of high ambient pressure on the inward and outward currents in the membrane of the snail isolated neuron was studied. A significant inhibition of the inward (sodium) current occurred at 101 ata. No significant modification of the outward (potassium) current was found. The data obtained corroborates the hypothesis of inhibitory effect of high pressure on some membrane structures involved in generation of neuronal activity.

[Effect of amiloride and strophanthin K on sodium transport through isolated frog skin under increased pressure]. / Vliianie amilorida i strofantina K na transport natriia cherez izolirovannuiu kozhu liagushki pri uvelichenii davleniia.

A pressure increase up to 101 ata led to 17.8% and 50% increase of the electrical potential difference and short-circuited current, resp., as well as to a 22% decrease of electrical resistance in the isolated frog skin. The changes were due to a high hydrostatic pressure and the increase of the solution temperature by 2.8 +/- 0.14 degrees C. At 100 ata, the ability of amiloride to block Na-channels in the cell membranes of the frog skin was preserved, and inspite of the intense increase in the work of the sodium active transport system, the kinetics of inhibition of the Na-pump by strophanthin K remained the same as in case of normal pressure.

[Epileptic studies in the Baikal-Amur Main Line zone]. / Epilepticheskie issledovaniia v zone BAMa.

A comprehensive examination has covered 75 epileptic patients. It has been established that there are no specific epileptogenic conditions in the studied region and that the development of cases of epilepsy in the region of the Baikal-Amur railway is due to the migration of patients. The development of epilepsy in children is largely related to perinatal factors.