Nongenomic effects of aldosterone on phosphocreatine levels in human calf muscle during recovery from exercise.

Nongenomic in vitro effects of aldosterone on the sodium-proton antiport and intracellular second messengers have been described in human mononuclear leukocytes, vascular smooth muscle cells, and endothelial cells. To test the potential physiological relevance of these effects, an in vivo 31P magnetic resonance spectroscopy study on the human calf at rest and during exercise was performed in 10 healthy volunteers receiving either 1 mg aldosterone or placebo iv in a double blind, randomized, cross-over trial. Spectra were analyzed for phosphocreatine, ATP, phosphomonoesters, inorganic intracellular phosphate, and intracellular pH. Resting values remained unchanged by aldosterone. After isometric contraction of the calf (50% body weight for 3 min), phosphocreatine recovered to significantly higher levels after application of aldosterone compared with placebo. Other parameters were not significantly changed by aldosterone. Effects appeared immediately after isometric contraction and, thus, occurred within 8 min of aldosterone administration. They are, therefore, likely to represent the first contemporary evidence of nongenomic in vivo effects of aldosterone in man. These findings also point to an involvement of aldosteron in the acute stress adaptation of cellular oxidative metabolism in human muscle physiology

A Comparison of Squatting Exercise on a Centrifuge and With Earth Gravity

Purpose: Long-duration space missions require countermeasures against the muscular wasting and cardiovascular deconditioning associated with microgravity. Replacing gravitational acceleration by means of centrifugation is a promising alternative as it challenges all physiological systems at once. The aim of this study is to examine the metabolic energy costs of squatting on a centrifuge in comparison with squatting in an upright standing posture under natural gravity.Methods: 24 subjects (11 male, 13 female) performed continuous squatting exercise for 9 min with increasing cadence (10, 12, and 15 squats min-1). This was done under three conditions: Upright under natural gravity and lying supine on a centrifuge at two radii (2.5 and 3.5 m) at 1 g of centrifugal acceleration at the subject’s average center of mass during the exercise.Results: Generally, subjects did not suffer from motion sickness. Exercise under natural gravity led to a higher Δ V’O2/body mass (7.1 ± 2.0, ml min-1 kg-1, mean ± SD) compared with exercise on the centrifuge (6.1 ± 1.6, ml min-1 kg-1, mean ± SD). Exercise efficiency was also reduced under natural 1 g at 28.2 ± 1.0% compared to 40.4 ± 1.5% on the centrifuge. As expected, oxygen consumption increased with increasing cadences. The Coriolis effect had a negligible impact as there was no significant difference in V’O2 between the two radii. However, during centrifugation and upward movement the right leg was more loaded than the leg left and vice versa during downward movement (centrifuge running clockwise looking down, so to the subjects’ right).Conclusion: The lower V’O2 on the centrifuge may be attributed to the unloading of trunk muscles while subjects were lying on the sled, which in the upright condition leaning against the sled were still working to stabilize the torso. Subjects tolerated high rotational rates combined with exercise very well

Effects of 21 days of bed rest and whey protein supplementation on plantar flexor muscle fatigue resistance during repeated shortening contractions.

PURPOSE:Space flight and bed rest (BR) lead to a rapid decline in exercise capacity. Whey protein plus potassium bicarbonate diet-supplementation (NUTR) could attenuate this effect by improving oxidative metabolism. We evaluated the impact of 21-day BR and NUTR on fatigue resistance of plantar flexor muscles (PF) during repeated shortening contractions, and whether any change was related to altered energy metabolism and muscle oxygenation. METHODS:Ten healthy men received a standardized isocaloric diet with (n = 5) or without (n = 5) NUTR. Eight bouts of 24 concentric plantar flexions (30 s each bout) with 20 s rest between bouts were employed. PF muscle size was assessed by means of peripheral quantitative computed tomography. PF muscle volume was assessed with magnetic resonance imaging. PF muscle force, contraction velocity, power and surface electromyogram signals were recorded during each contraction, as well as energy metabolism (31P nuclear magnetic resonance spectroscopy) and oxygenation (near-infrared spectroscopy). Cardiopulmonary parameters were measured during an incremental cycle exercise test. RESULTS:BR caused 10-15% loss of PF volume that was partly recovered 3 days after re-ambulation, as a consequence of fluid redistribution. Unexpectedly, PF fatigue resistance was not affected by BR or NUTR. BR induced a shift in muscle metabolism toward glycolysis and some signs of impaired muscle oxygen extraction. NUTR did not attenuate the BR-induced-shift in energy metabolism. CONCLUSIONS:Twenty-one days' BR did not impair PF fatigue resistance, but the shift to glycolytic metabolism and indications of impaired oxygen extraction may be early signs of developing reduced muscle fatigue resistance

Femoral anteversion (FNA) in individuals with X-linked hypophosphatemia (XLH)

Background/Introduction: XLH is a rare genetic condition which affects phosphate metabolism, resulting in osteomalacia. Individuals with XLH are also at risk of lower limb deformities and early onset of hip osteoarthritis. These two factors may be linked, as abnormal FNA (femoral torsion) is a risk factor for hip osteoarthritis. The contributions of regional femoral torsion e.g. intertrochanteric torsion (ITT), shaft torsion (ST) and condylar torsion(CT) to FNA differ between clinical groups and are important when planning femoral osteotomies to correct FNA. Purpose: This study aimed to compare FNA and regional femoral torsion of the femur between adults with XLH and controls. Methods: 13 individuals with XLH (5 male, age 49±9y) and 12 age, sex and weight-matched control participants (7 male, age 49±8y) were recruited following ethical approval and informed consent. Magnetic resonance imaging (MRI) scans of the femur were obtained, from which FNA, ITT, ST and CT were measured. Data were normally distributed, therefore group differences were assessed using t-tests. Results: FNA was 29° lower in individuals with XLH than controls (pb0.005). This resulted mainly from lower ITT (pb0.001) and in part CT (pb0.05) whereas ST was similar in the two groups (Fig. 1). Conclusion(s): We observed differences in FNA and regionspecific femoral torsion in individuals with XLH compared to controls. These differences may contribute to clinical problems such as hip osteoarthritis common in XLH. Information on region-specific differences may be useful in planning corrective surgeries. Future work should examine how pharmacological and other interventions in this group affect FNA

Resistive exercise with or without super-imposed whole-body vibration acutely effects bone turnover

[Background] Exercise is one of the well-known constituents to improve bone mass and to retain bone strength. Only few studies have reached the effects of resistive exercise on sclerostin levels, a protein that is thought to play a key role in orchestrating bone’s mechanical adaptation. Sclerostin is produced and released by osteocytes and acts as an inhibitor of bone formation through inhibition of the Wnt/β-catenin-signaling pathway. The objective of this study was to evaluate acute and long-term effects of exercise on bone biochemical marker expression. More specifically, we aimed to understand differences in the responses to resistance exercise with or without whole-body vibration. [Methods] A six week training intervention was performed including 26 healthy males (26 years, SD=4) in in a randomized parallel design. Performing either resistive exercise (RE, n=13) or resistive vibration exercise (RVE, n=13) training, with weekly increasing vibration frequencies 20-40 Hz. Serum samples were collected both at the initial and final exercise session. Changes in carboxy-terminal cross-linked telopeptide of type I collagen (sCTX-I), as a marker of bone resorption, and of procollagen type I amino terminal propeptide (P1NP) as a specific marker of bone formation as well as serum sclerostin concentrations were measured via ELISA (sCTX-I and sclerostin) or RIA (P1NP) measurements. [Results] Serum markers of sCTX-I decreased by 15% within the first minutes following either training intervention, both regarding the initial and final training session. Subsequently, levels of sCTX-I returned back to pre-bout baseline after RE (time effect: P<0.001), and they depicted an overshoot by 18% after 75min. Serum levels of P1NP depicted an acute increase by 15% to exercise (P<0.001). P1NP levels were non-substantially increased in RE at the end of the 6 week intervention (P<0.001), but decreased by 10% in RVE, as compared to baseline (P< 0.001). Pre-bout levels of sclerostin were marginally lowered at the end of the 6 week training phase. After the exercise bouts, sclerostin levels increased within the first minutes both RE and RVE (time effect: P<0.001). Notably, sclerostin responses to the initial exercise bouts differed significantly between RE and RVE P=0.029. [Conclusion] The present findings suggest that in young healthy adults both conditions RE and RVE elicited an acute exercise-induced bone resorption without any acute change in bone formation. Results are compatible with the idea that this response was mediated by sclerosti

Associations between long-term exercise participation and lower limb joint and whole-bone geometry in young and older adults

Introduction: Features of lower limb bone geometry are associated with movement kinematics and clinical outcomes including fractures and osteoarthritis. Therefore, it is important to identify their determinants. Lower limb geometry changes dramatically during development, partly due to adaptation to the forces experienced during physical activity. However, the effects of adulthood physical activity on lower limb geometry, and subsequent associations with muscle function are relatively unexplored. Methods: 43 adult males were recruited; 10 young (20–35 years) trained i.e., regional to world-class athletes, 12 young sedentary, 10 older (60–75 years) trained and 11 older sedentary. Skeletal hip and lower limb geometry including acetabular coverage and version angle, total and regional femoral torsion, femoral and tibial lateral and frontal bowing, and frontal plane lower limb alignment were assessed using magnetic resonance imaging. Muscle function was assessed recording peak power and force of jumping and hopping using mechanography. Associations between age, training status and geometry were assessed using multiple linear regression, whilst associations between geometry and muscle function were assessed by linear mixed effects models with adjustment for age and training. Results: Trained individuals had 2° (95% CI:0.6°–3.8°; p = 0.009) higher femoral frontal bowing and older individuals had 2.2° (95% CI:0.8°–3.7°; p = 0.005) greater lateral bowing. An age-by-training interaction indicated 4° (95% CI:1.4°–7.1°; p = 0.005) greater acetabular version angle in younger trained individuals only. Lower limb geometry was not associated with muscle function (p > 0.05). Discussion: The ability to alter skeletal geometry via exercise in adulthood appears limited, especially in epiphyseal regions. Furthermore, lower limb geometry does not appear to be associated with muscle function

ATHLETIC: Pseudo Anthropometric Exoskeleton with a Semi Passive Actuation System for Countermeasure

This paper presents the ongoing ESA project ATHLETIC (AstronauT HeaLtH EnhancemenT Integrated Countermeasure) which aims to develop a new approach of integrated countermeasure device in the shape of an exoskeleton. It focuses primarily on the training of the lower limbs, which are the most heavily affected body parts while astronauts are exposed to microgravity. The ATHLETIC system enables High Intense Resistive Training exercises (HIRT), as well as plyometric exercises such as hopping and jumping. Development and validation shall give an answer to the question if exoskeleton technology is suitable for countermeasure in zero gravity and how such a system performs compared to existing countermeasure devices for zero gravity applications

Effects of ageing and fitness on hopping biomechanics

Physical exercise promotes healthy aging and is associated with greater functionality and quality of life. Muscle strength and power are established factors in the ability to perform daily tasks and live independently. Stiffness, for mechanical reasons, is another important constituent of running performance and locomotion. This study aims to analyze the impact of age and training status on one-legged hopping biomechanics and to evaluate whether age-related power decline can be reduced with regular physical exercise. Forty-three male subjects were recruited according to their suitability for one of four groups (young athletes, senior athletes, young controls and senior controls) according to their age (young between 21 and 35, vs. older between 59 and 75) and training status (competing athletes vs. non-physically active). The impact of age and training status on one-legged hopping biomechanics were evaluated using the two-way analysis of variance (ANOVA) method. Significant differences among groups were found for hopping height (p &lt; 0.05), ground contact time (p &lt; 0.05), peak ground reaction force (p &lt; 0.05) and peak power (p &lt; 0.01). No differences among groups were found in ground-phase vertical displacement and vertical stiffness (p &gt; 0.05). Young athletes and older non-physically active people achieved the best and worst performance, respectively. Interestingly, there were not any differences found between young non-physically active people and senior athletes, suggesting that chronic training can contribute to partly offset effects that are normally associated with aging

Effect of Whole-body Vibration frequency on muscle tensile state during graded plantar flexor isometric contractions

Acute physiological and biomechanical alterations have been reported following whole-body vibration (WBV). Stiffening of muscles has only been anecdotally reported in response to WBV. Accordingly, this study investigated active plantar flexor muscle stiffness in response to a single WBV bout at four mechanical vibration frequencies

NEX4EX: Novel Exercise Hardware for Exploration

This paper presents the NEX4EX project Novel Exercise Hardware for Exploration, which aims to design, build and validate a full-body countermeasure platform that enables high intensive resistive and plyometric exercise as well as postural control training, and strength training. The NEX4EX exerciser herewith addresses neuromuscular and musculoskeletal deconditioning. The intended use is to improve crew health and fitness maintenance for long-duration space missions beyond ISS lifetime. This will require the system to be multi-purpose / versatile in terms of exercises added to a smaller footprint than systems currently used on ISS. NEX4EX is a novel concept for a novel utilization paradigm given future space exploration-class missions