Urinary excretion of electrolytes during prolonged physical activity in normal man

Nine normal young male students were studied during 2 days of relative rest, during 2 days of physical training and again during the succeeding 2 days of relative rest. Twenty-four hour urine collections showed that sodium and potassium excretion were lower during the exercise days, while urinary aldosterone excretion was increased. No differences in the 24-h urinary excretion of creatinine, calcium, and magnesium were found between the resting and exercise days. Hemoglobin concentration, hematocrit and red cell counts were decreased at 14 h and 42 h after exercise; these findings together with the increased serum bilirubin concentration could result from hemolysis. Plasma renin activity, angiotensin II and aldosterone concentration were increased 14 h after exercise but returned to baseline 42 h after exercise. Our data shows that one should take into account previous exercise when interpreting results of certain of these tests.     

Long-term bed rest-induced reductions in stroke volume during rest and exercise: cardiac dysfunction vs. volume depletion.

Long-term head-down-tilt bed rest (HDT) causes cardiovascular deconditioning, attributed to reflex dysfunctions, plasma volume reduction, or cardiac impairments. Our objective with the present study was to evaluate the functional importance and relative contribution of these during rest and exercise in supine and upright postures. We studied six subjects before (baseline), during [days 60 (D60) and 113 (D113)], and after [recovery days 0 (R0), 3 (R3), and 15 (R15)] 120 days of -6 degrees HDT. We determined cardiac output, stroke volume (SV), mean arterial pressure, and heart rate during rest and exercise in supine and upright postures. Cardiac output and SV decreased significantly in all four conditions, but the time courses differed for rest and exercise. Upright resting SV was decreased by 24 +/- 9% at D60 compared with baseline but had recovered already at R3. Supine exercise SV decreased more slowly (by 5 +/- 8% at D60 and by 18 +/- 4% at D113) and recovered more slowly after HDT termination. Steady-state mean arterial pressure showed no changes. Heart rate had increased by 18 +/- 4% at D60 and had recovered partially at R3. Our data indicate that long-term HDT causes both a rapid, preload-dependent reduction in SV, most evident during rest in the upright position, and a more slowly developing cardiac dysfunction, most evident during supine exercise. However, the ability to maintain blood pressure and to perform sustained low levels of dynamic exercise is not influenced by HDT.     

A comparison of 3 different rest intervals on the exercise volume completed during a workout

The purpose of this research was to compare differences between 3 different rest intervals on the squat and bench press volume completed during a workout. Fifteen college-aged men volunteered to participate in this study (age 20.73 +/- 2.60 years; body mass 80.73 +/- 10.80 kg). All subjects performed 3 testing sessions, during which 4 sets of the squat and bench press were performed with an 8 repetition maximum (8RM) load. During each testing session, the squat and bench press were performed with a 1, 2, or 5-minute rest interval between sets. Volume was defined as the total number of repetitions completed over 4 sets for each rest condition. Statistical analysis was conducted separately for the squat and bench press. One-way repeated analyses of variance with Bonferroni post hocs demonstrated significant differences between each rest condition for both exercises tested (p < 0.05). The 5-minute rest condition resulted in the highest volume completed, followed in descending order by the 2- and 1-minute rest conditions. The ability to perform a higher volume of training with a given load may stimulate greater strength adaptations.     

Metabolic response to green tea extract during rest and moderate-intensity exercise

BackgroundGreen tea catechins have been hypothesized to increase energy expenditure and fat oxidation by inhibiting catechol-O-methyltransferase (COMT) and thus promoting more sustained adrenergic stimulation. Metabolomics may help to clarify the mechanisms underlying their putative physiological effects.ObjectiveThe study investigated the effects of 7-day ingestion of green tea extract (GTE) on the plasma metabolite profile at rest and during exercise.MethodsIn a placebo-controlled, double-blind, randomized, parallel study, 27 healthy physically active males consumed either GTE (n=13, 1200 mg catechins, 240 mg caffeine/day) or placebo (n=14, PLA) drinks for 7 days. After consuming a final drink (day 8), they rested for 2 h and then completed 60 min of moderate-intensity cycling exercise (56%±4% VO₂max). Blood samples were collected before and during exercise. Plasma was analyzed using untargeted four-phase metabolite profiling and targeted profiling of catecholamines.ResultsUsing the metabolomic approach, we observed that GTE did not enhance adrenergic stimulation (adrenaline and noradrenaline) during rest or exercise. At rest, GTE led to changes in metabolite concentrations related to fat metabolism (3-β-hydroxybutyrate), lipolysis (glycerol) and tricarboxylic acid cycle (TCA) cycle intermediates (citrate) when compared to PLA. GTE during exercise caused reductions in 3-β-hydroxybutyrate concentrations as well as increases in pyruvate, lactate and alanine concentrations when compared to PLA.ConclusionsGTE supplementation resulted in marked metabolic differences during rest and exercise. Yet these metabolic differences were not related to the adrenergic system, which questions the in vivo relevance of the COMT inhibition mechanism of action for GTE.     

The impact of aging and habitual physical activity on static respiratory work at rest and during exercise

We investigated the effects of aging on the elastic properties of lung tissue and the chest wall, simultaneously quantifying the contribution of each component to static inspiratory muscle work in resting and exercising adults. We further evaluated the interaction of aging and habitual physical activity on respiratory mechanics. Static lung volumes and elastic properties of the lung and chest wall (pressure-volume relaxation maneuvers) in 29 chronically sedentary and 29 habitually active subjects, grouped by age, were investigated: young (Y, 20-30 years), middle-aged (M, 40-50 years), and older (O, >60 years). Using static pressure-volume data, we computed the elastic work of breathing (joules per liter, J.l(-1)), including inspiratory muscle work, over resting and exercising tidal volume excursions. Elastic work of the lung (Y = 0.79 +/- 0.05; M = 0.47 +/- 0.05; O = 0.43 +/- 0.05 J.l(-1)) and chest wall (Y = -0.49 +/- 0.06; M = -0.12 +/- 0.07; O = 0.04 +/- 0.05 J.l(-1) ) changed significantly with age (P < 0.05). With aging, a parallel displacement of the chest wall pressure-volume curve resulted in a shift from energy being stored primarily during expiration to energy storage during inspiration, and driving expiration, both at rest and during exercise. Although deviating significantly from young adults, this did not significantly elevate static inspiratory muscle work but resulted in a redistribution of the tissues on which this work was performed and the phase of the respiratory cycle in which it occurred. Nevertheless, static inspiratory muscle work remained similar across age groups, at rest and during exercise, and habitual physical activity failed to influence these changes.