Glycogen supercompensation is due to increased number, not size, of glycogen particles in human skeletal muscle.

NEW FINDINGS: What is the central question of this study? Glycogen supercompensation after glycogen-depleting exercise can be achieved by consuming a carbohydrate-enriched diet, but the associated effects on the size, number and localization of intramuscular glycogen particles are unknown. What is the main finding and its importance? Using transmission electron microscopy to inspect individual glycogen particles visually, we show that glycogen supercompensation is achieved by increasing the number of particles while keeping them at submaximal sizes. This might be a strategy to ensure that glycogen particles can be used fast, because particles that are too large might impair utilization rate. ABSTRACT: Glycogen supercompensation after glycogen-depleting exercise can be achieved by consuming a carbohydrate-enriched diet, but the associated effects on the size, number and localization of intramuscular glycogen particles are unknown. We investigated how a glycogen-loading protocol affects fibre type-specific glycogen volume density, particle diameter and numerical density in three subcellular pools: between (intermyofibrillar) or within (intramyofibrillar) the myofibrils or beneath the sarcolemma (subsarcolemmal). Resting muscle biopsies from 11 physically active men were analysed using transmission electron microscopy after mixed (MIX), LOW or HIGH carbohydrate consumption separated by glycogen-lowering cycling at 75% of maximal oxygen consumption until exhaustion. After HIGH, the total volumetric glycogen content was 40% [95% confidence interval 16, 68] higher than after MIX in type I fibres (P < 0.001), with little to no difference in type II fibres (9% [95% confidence interval -9, 27]). Median particle diameter was 22.5 (interquartile range 20.8-24.7) nm across glycogen pools and fibre types, and the numerical density was 61% [25, 107] and 40% [9, 80] higher in the subsarcolemmal (P < 0.001) and intermyofibrillar (P < 0.01) pools of type I fibres, respectively, with little to no difference in the intramyofibrillar pool (3% [-20, 32]). In LOW, total glycogen was in the range of 21-23% lower, relative to MIX, in both fibre types, reflected in a 21-46% lower numerical density across pools. In comparison to MIX, particle diameter was unaffected by other diets ([-1.4, 1.3] nm). In conclusion, glycogen supercompensation after prolonged cycling is exclusive to type I fibres, predominantly in the subsarcolemmal pool, and involves an increase in the numerical density rather than the size of existing glycogen particles.

Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men.

KEY POINTS: When muscle biopsies first began to be used routinely in research on exercise physiology five decades ago, it soon become clear that the muscle content of glycogen is an important determinant of exercise performance. Glycogen particles are stored in distinct pools within the muscles, but the role of each pool during exercise and how this is affected by diet is unknown. Here, the effects of diet and exercise on these pools, as well as their relation to endurance during prolonged cycling were examined. We demonstrate here that an improved endurance capacity with high carbohydrate loading is associated with a temporal shift in the utilisation of the distinct stores of glycogen pools and is closely linked to the content of the glycogen pool closest to actin and myosin (intramyofibrillar glycogen). These findings highlight the functional importance of distinguishing between different subcellular microcompartments of glycogen in individual muscle fibres. ABSTRACT: In muscle cells, glycogen is stored in three distinct subcellular pools: between or within myofibrils (inter- and intramyofibrillar glycogen, respectively) or beneath the sarcolemma (subsarcolemmal glycogen) and these pools may well have different functions. Here, we investigated the effect of diet and exercise on the content of these distinct pools and their relation to endurance capacity in type 1 and 2 muscle fibres. Following consumption of three different diets (normal, mixed diet = MIX, high in carbohydrate = HIGH, or low in carbohydrate = LOW) for 72 h, 11 men cycled at 75% of V̇O2 max until exhaustion. The volumetric content of the glycogen pools in muscle biopsies obtained before, during, and after exercise were quantified by transmission electron micrographs. The mean (SD) time to exhaustion was 150 (30), 112 (22), and 69 (18) minutes in the HIGH, MIX and LOW trials, respectively (P < 0.001). As shown by multiple regression analyses, the intramyofibrillar glycogen content in type 1 fibres, particularly after 60 min of exercise, correlated most strongly with time to exhaustion. In the HIGH trial, intramyofibrillar glycogen was spared during the initial 60 min of exercise, which was associated with levels and utilisation of subsarcolemmal glycogen above normal. In all trials, utilisation of subsarcolemmal and intramyofibrillar glycogen was more pronounced than that of intermyofibrillar glycogen in relative terms. In conclusion, the muscle pool of intramyofibrillar glycogen appears to be the most important for endurance capacity in humans. In addition, a local abundance of subsarcolemmal glycogen reduces the utilisation of intramyofibrillar glycogen during exercise.

The Danish High Risk and Resilience Study--VIA 7--a cohort study of 520 7-year-old children born of parents diagnosed with either schizophrenia, bipolar disorder or neither of these two mental disorders.

BACKGROUND: Severe mental illnesses like schizophrenia and bipolar disorder are known to be diseases that to some extent, but not entirely can be understood genetically. The dominating hypothesis is that these disorders should be understood in a neurodevelopmental perspective where genes and environment as well as gene-environment-interactions contribute to the risk of developing the disease. We aim to analyse the influences of genetic risk and environmental factors in a population of 520 7-year-old children with either 0, 1 or 2 parents diagnosed with schizophrenia spectrum psychosis or bipolar disorder on mental health and level of functioning. We hypothesize that a larger proportion of children growing up with an ill parent will display abnormal or delayed development, behavioural problems or psychiatric symptoms compared to the healthy controls. METHODS/DESIGN: We are establishing a cohort of 5207 year old children and both their parents for a comprehensive investigation with main outcome measures being neurocognition, behaviour, psychopathology and neuromotor development of the child. Parents and children are examined with a comprehensive battery of instruments and are asked for genetic material (saliva or blood) for genetic analyses. The participants are recruited via Danish registers to ensure representativity. Data from registers concerning social status, birth complications, somatic illnesses and hospitalization are included in the database. Psychological and relational factors like emotional climate in the family, degree of stimulation and support in the home and attachment style are also investigated. DISCUSSION: Data collection started January 1, 2013, and is successfully ongoing. By Aug 2015 424 families are included. About 20% of the invited families decline to participate, equal for all groups.

Good radiological and functional results after intramedullary nailing of distal radius fractures.

To evaluate the results after fixation of distal radius fractures using Micronail internal fixation, a prospective cohort study was performed, including displaced fractures of the distal radius (AO type A 2.2, A3.1, and A3.2). In total, 60 patients were included and 44 patients were available for 1-year follow-up (radiological and clinical examination) and 39 for 5-year follow-up (telephone interview). It was found that all fractures healed, with an average radial volar tilt of 2°, radial length of 11 mm, and a radial inclination of 22°. The functional result was excellent-to-good in 93% of the patients. Thirteen patients (30%) reported paraesthesia of the superficial branch of the radial nerve at the 1-year follow-up. In four patients the paraesthesia of the radial nerve was persistent. No other complications or reoperations were reported by the patients at the 5-year follow-up and only one implant had been removed. The study confirms that the Micronail is a minimal invasive method that can provide a stable fixation of selected distal radius fractures and provide a good functional outcome with a very low need of implant removal after fracture healing with few complications related to the operation, the main complication being permanent damage to the radial nerve.