Spawning sources of King George whiting
Sillaginodes punctatus
populations in the states of South Australia and Victoria (south-eastern Australia) were analysed using otolith chemistry and ...microstructure from post-larvae sampled from 3 nursery areas in each state in the spring of 2011 and 2012. Univariate and multivariate analysis of the chemistry of the core region of otoliths showed differences between states, particularly for the 2011 cohort, primarily related to higher Mg in South Australian samples, while differences in Sr and Zn also made a contribution. Even though spawning times overlapped, early larval growth rates were higher for post-larvae from South Australia than Victoria. Differences in microchemistry were most evident for elements influenced by physiological processes and were potentially influenced by the different larval growth rates. Overall, otolith chemical and microstructure analyses for post-larvae in Victoria and South Australia indicated that spawning sources for the 2 states were different, qualified by results from otolith microchemistry that were less clear for the 2012 cohort. Even though genetic analyses do not indicate genetic differentiation across the 2 states, and therefore would support cross-jurisdictional management, the results of this study give qualified support to the current arrangement wherein the
S. punctatus
fishery is managed separately by the individual jurisdictions, subject to further information on stock structure coming to light in the future.
Aim
High‐intensity interval training (HIT) results in potent metabolic adaptations in skeletal muscle; however, little is known about the influence of these adaptations on energetics in vivo. We used ...magnetic resonance spectroscopy to examine the effects of HIT on ATP synthesis from net PCr breakdown (ATPCK), oxidative phosphorylation (ATPOX) and non‐oxidative glycolysis (ATPGLY) in vivo in vastus lateralis during a 24‐s maximal voluntary contraction (MVC).
Methods
Eight young men performed 6 sessions of repeated, 30‐s ‘all‐out’ sprints on a cycle ergometer; measures of muscle energetics were obtained at baseline and after the first and sixth sessions.
Results
Training increased peak oxygen consumption (35.8 ± 1.4 to 39.3 ± 1.6 mL min−1 kg−1, P = 0.01) and exercise capacity (217.0 ± 11.0 to 230.5 ± 11.7 W, P = 0.04) on the ergometer, with no effects on total ATP production or force–time integral during the MVC. While ATP production by each pathway was unchanged after the first session, 6 sessions increased the relative contribution of ATPOX (from 31 ± 2 to 39 ± 2% of total ATP turnover, P < 0.001) and lowered the relative contribution from both ATPCK (49 ± 2 to 44 ± 1%, P = 0.004) and ATPGLY (20 ± 2 to 17 ± 1%, P = 0.03).
Conclusion
These alterations to muscle ATP production in vivo indicate that brief, maximal contractions are performed with increased support of oxidative ATP synthesis and relatively less contribution from anaerobic ATP production following training. These results extend previous reports of molecular and cellular adaptations to HIT and show that 6 training sessions are sufficient to alter in vivo muscle energetics, which likely contributes to increased exercise capacity after short‐term HIT.
The results of recent studies indicate that in healthy men and women aged beyond approximately 65 years, the energy-producing pathways in skeletal muscle may combine with changes in motor unit ...behavior and muscle contractile properties to provide a unique environment for resisting muscle fatigue under some conditions.
Abstract People with multiple sclerosis (MS) often report problems with balance, which may be most apparent during challenging postural tasks such as leaning or reaching, and when relying on ...non-visual sensory systems. An additional obstacle facing people with MS is a high incidence of symptomatic fatigue (>70%). The purpose of this study was to investigate the changes in balance during upright stance in individuals with mild-to-moderate disability due to MS under normal and restricted vision and different levels of self-reported fatigue. Limb loading asymmetry, sway and magnitude of postural shift in center of pressure, and time-to-contact the stability boundary of the center of mass and center of pressure were assessed during quiet standing and maximal lean and reach tasks. Compared to controls, people with MS displayed greater postural sway, greater loading asymmetry, and shorter time-to-contact during quiet standing. In the postural perturbation tasks the MS group had smaller postural shifts and reduced stability compared to controls in the direction perpendicular to the lean and reach. Limiting vision increased loading asymmetry during quiet standing and postural instability during backward lean in the MS group. Inducing additional fatigue in the MS group did affect postural control in the more challenging balance conditions but had no impact during quiet upright standing. The results of this study indicate subtle changes in postural control during standing in people with mild-to-moderate impairments due to MS.
Muscle atrophy in patients receiving hemodialysis: Effects on muscle strength, muscle quality, and physical function.
Dialysis patients are less active and have reduced functional capacity compared ...to individuals with normal renal function. Muscle atrophy and weakness may contribute to these problems. This investigation was undertaken to quantify the extent of atrophy in the lower extremity muscles, to determine whether defects in muscle specific strength (force per unit mass) or central nervous system (CNS) activation are present, and to assess the relationship between muscle size and physical performance in a group of patients on hemodialysis.
Thirty-eight dialysis subjects (aged 55 ± 15 years) and nineteen healthy sedentary controls (aged 55 ± 13 years) were enrolled. Magnetic resonance imaging of the lower leg was used to determine the total cross-sectional area (CSA) and the area of contractile and non-contractile tissue of the ankle dorsiflexor muscles. Isometric dorsiflexor strength was measured during a maximal voluntary contraction with and without superimposed tetanic stimulation (N = 22 for dialysis subjects, N = 12 for controls). Physical activity was measured by accelerometry, and gait speed was recorded as a measure of physical performance.
Dialysis subjects were weaker, less active, and walked more slowly than controls. Total muscle compartment CSA was not significantly different between dialysis subjects and controls, but the contractile CSA was smaller in the dialysis patients even after adjustment for age, gender, and physical activity. Central activation and specific strength were normal. Gait speed was correlated with contractile CSA.
Significant atrophy and increased non-contractile tissue are present in the muscle of patients on hemodialysis. The relationship between contractile area and strength is intact in this population. Muscle atrophy is associated with poor physical performance. Thus, interventions to increase physical activity or otherwise address atrophy may improve performance and quality of life.
1 Department of Exercise Science, University of Massachusetts, Amherst, Massachusetts; and 2 Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, New Haven, ...Connecticut
Submitted 13 May 2005
; accepted in final form 4 July 2005
Energy for muscle contractions is supplied by ATP generated from 1 ) the net hydrolysis of phosphocreatine (PCr) through the creatine kinase reaction, 2 ) oxidative phosphorylation, and 3 ) anaerobic glycolysis. The effect of old age on these pathways is unclear. The purpose of this study was to examine whether age may affect ATP synthesis rates from these pathways during maximal voluntary isometric contractions (MVIC). Phosphorus magnetic resonance spectroscopy was used to assess high-energy phosphate metabolite concentrations in skeletal muscle of eight young (2035 yr) and eight older (6580 yr) men. Oxidative capacity was assessed from PCr recovery after a 16-s MVIC. We determined the contribution of each pathway to total ATP synthesis during a 60-s MVIC. Oxidative capacity was similar across age groups. Similar rates of ATP synthesis from PCr hydrolysis and oxidative phosphorylation were observed in young and older men during the 60-s MVIC. Glycolytic flux was higher in young than older men during the 60-s contraction ( P < 0.001). When expressed relative to the overall ATP synthesis rate, older men relied on oxidative phosphorylation more than young men ( P = 0.014) and derived a smaller proportion of ATP from anaerobic glycolysis ( P < 0.001). These data demonstrate that although oxidative capacity was unaltered with age, peak glycolytic flux and overall ATP production from anaerobic glycolysis were lower in older men during a high-intensity contraction. Whether this represents an age-related limitation in glycolytic metabolism or a preferential reliance on oxidative ATP production remains to be determined.
acidosis; creatine kinase; glycolysis; oxidative phosphorylation; fatigue
Address for reprint requests and other correspondence: J. A. Kent-Braun, Dept. of Exercise Science, Totman 108, Univ. of Massachusetts, Amherst, MA 01003 (e-mail: janekb{at}excsci.umass.edu )
Department of Exercise Science, University of
Massachusetts, Amherst, Massachusetts 01003
Several studies have suggested
that women may be more resistant to muscle fatigue than men (Fulco CS,
Rock ...PB, Muza SA, Lammi E, Cymerman A, Butterfield G, Moore, LG, Braun
B, and Lewis SF. Acta Physiol Scand 167: 233-239, 1999)
possibly because of differences in muscle oxidative metabolism.
We evaluated muscle fatigue produced by intermittent, maximal
volitional isometric contractions of the dorsiflexor muscles of healthy
young (21-34 yr) men ( n = 8) and women
( n = 8) under two conditions: free-flow (FF)
circulation and ischemia. Measures of voluntary and stimulated
(10- and 50-Hz) force, central activation ratio (CAR), and compound
muscle action potential (CMAP) were collected in each session. The
ischemic protocol induced greater fatigue than the FF protocol,
in both sexes, and was associated with greater reductions in CAR, CMAP, stimulated force, and the ratio of 10- to 50-Hz force compared with the
FF condition. Women fatigued less than men in FF but not during
ischemia, and this difference was roughly paralleled by a
difference in CAR. No sex effects on the CMAP, tetanic force, and
measures of excitation-contraction coupling function were found in the
FF condition, suggesting that the primary mechanism behind the
difference in fatigue was a relatively greater impairment of central
activation in men. The observation that ischemia eliminated the
sex differences in fatigue is consistent with a number of studies
(Kent-Braun JA, Ng AV, Doyle JW, and Towse TF. J Appl Physiol
93: 1813-1823, 2002) relating fatigue to muscle metabolism and might be the result of sex-based differences in metabolic pathway
utilization during muscle contraction.
blood flow; central fatigue; muscle activation
1 Department of Exercise Science,
University of Massachusetts, Amherst, Massachusetts 01003;
2 Exercise Science Program, Marquette
University, Milwaukee, Wisconsin 53201; and
3 Magnetic Resonance ...Unit, Department of
Radiology, University of California, San Francisco, California
94121
The purpose of this study
was to compare the magnitude and mechanisms of ankle dorsiflexor muscle
fatigue in 20 young (33 ± 6 yr, mean ± SD) and 21 older
(75 ± 6 yr) healthy men and women of similar physical activity
status. Noninvasive measures of central and peripheral (neuromuscular
junction, sarcolemma) muscle activation, muscle contractile function,
and intramuscular energy metabolism were made before, during, and after
incremental isometric exercise. Older subjects fatigued less than young
( P < 0.01); there was no effect of gender on fatigue
( P = 0.24). For all subjects combined, fatigue was
modestly related to preexercise strength ( r = 0.49, P < 0.01). Neither central (central activation ratio)
nor peripheral (compound muscle action potential) activation played a
significant role in fatigue in any group. During exercise,
intracellular concentrations of P i and
H 2 PO increased more and pH fell more in
young compared with older subjects ( P < 0.01) and in
men compared with women ( P < 0.01). These varied
metabolic responses to exercise suggest a greater reliance on
nonoxidative sources of ATP in young compared with older subjects and
in men compared with women. These results suggest that the mechanisms of fatigue vary with age and gender, regardless of whether differences in the magnitude of fatigue are observed.
physical activity; magnetic resonance spectroscopy; central
fatigue; activation; excitation-contraction coupling; metabolism
The functional implications of central motor impairment and peripheral muscle alterations in multiple sclerosis are unclear. Muscle strength, central and peripheral activation, and symptomatic ...fatigue were investigated in 16 patients with multiple sclerosis (MS) and 18 control subjects. Voluntary and electrically stimulated isometric contractions were obtained from the ankle dorsiflexor muscles. Maximal voluntary contraction (MVC) was 27% lower in MS patients than controls, although electrically stimulated force was similar. Muscle fat‐free cross‐sectional area (CSA) was similar in both groups. These data indicate central activation impairment in MS. Such impairment in MS was further demonstrated by decreased foot‐tap speed, rate of voluntary force development, and central activation ratio. Peripheral activation changes in MS patients were modest. Although stimulated tetanic force was similar, force relaxation was slower in MS patients compared to controls, resulting in a left‐shifted force–frequency relationship in MS. Motor function changes were not associated with fatigue but were associated with impaired ambulation. Thus, weakness and walking impairment, but not fatigue, were related to impaired central activation in MS. These findings may help optimize rehabilitation strategies designed to improve function in persons with MS. Muscle Nerve 29: 843–852, 2004
Physical activity levels in patients on hemodialysis and healthy sedentary controls.
Patients on dialysis have reduced exercise tolerance compared with age-matched sedentary controls. The reasons for ...this debility have not been fully elucidated, but physical inactivity could be a contributing factor. The purpose of the current study was to determine whether patients on hemodialysis are less active than healthy sedentary controls and to explore clinical correlates of physical activity level in a group of hemodialysis patients.
Thirty-four hemodialysis patients and 80 healthy sedentary individuals participated in the study. Physical activity was measured for seven days with a three-dimensional accelerometer and with an activity questionnaire.
Vector magnitude values from the accelerometer for the dialysis and control subjects were 104,718 ± 9631 and 161,255 ± 6792 arbitrary units per day, respectively (P < 0.0001, mean ± SEM). The estimated energy expenditure values derived from the questionnaire were 33.6 ± 0.5 kcal/kg/day and 36.2 ± 0.5 kcal/kg/day (P = 0.002). The difference between patients on dialysis and controls increased with advancing age. Among the dialysis subjects, some measures of nutritional status correlated with physical activity level, including serum albumin concentration (r = 0.58, P = 0.003), serum creatinine concentration (r = 0.37, P = 0.03), and phase angle derived from bioelectrical impedance analysis (r = 0.40, P = 0.02).
Patients on hemodialysis are less active than healthy sedentary controls, and this difference is more pronounced among older individuals. There is an association between the level of physical activity and nutritional status among patients on dialysis. These findings are of great concern, given the trend toward increasing age in incident dialysis patients and the well-known association between inactivity and increased mortality in the general population.
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