Much of the spotlight for coronavirus disease 2019 (COVID-19) is on the acute symptoms and recovery. However, many recovered patients face persistent physical, cognitive, and psychological symptoms well past the acute phase. Of these symptoms, fatigue is one of the most persistent and debilitating. In this “perspective article,” we define fatigue as the decrease in physical and/or mental performance that results from changes in central, psychological, and/or peripheral factors due to the COVID-19 disease and propose a model to explain potential factors contributing to post-COVID-19 fatigue. According to our model, fatigue is dependent on conditional and physiological factors. Conditional dependency comprises the task, environment, and physical and mental capacity of individuals, while physiological factors include central, psychological, and peripheral aspects. This model provides a framework for clinicians and researchers. However, future research is needed to validate our proposed model and elucidate all mechanisms of fatigue due to COVID-19.

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The marine copepod Calanus finmarchicus is known to overwinter at depth in a state analogous to diapause in terrestrial insects, but the cues which cause individuals to enter and leave this state are the subject of speculation. In this paper we use a simple demographic model, driven by environmental data from 4 distinct locations in the organism's eastern range, to test the plausibility of a number of candidate mechanisms. We start from Miller et al. 's (1991; Mar Ecol Prog Ser 72:79-91) hypothesis that diapause is controlled by photoperiod, and show that thls leads to unrealistic patterns of reproductive activity in northern waters. We extend the model to include the recently reported phenomenon (Hirche 1996a; Ophelia 44:lll-128) of delayed gonad maturation in females experiencing low food concentrations. This ylelds more plausible annual patterns, but falls to reproduce observed geographical variation in the timing of the yearly onset of reproductive activity. Our final model dispenses with photoperiodic control and assumes that diapause duration is controlled by the normal development processes operating at a reduced rate. This model reproduces all the qualitative features of the patterns of reproductive activity observed at our 4 test sites, thus demonstrating that photoperiod cueing is not a necessary prerequisite for the regular re-ascension of C. finmarchicus into surface waters.

Aim: To explore the link between breastfeeding duration and bed-sharing frequency among women reporting a prenatal intention to breastfeed.Methods: About 870 participants in a randomised breastfeeding trial, recruited at midpregnancy, provided weekly snapshots of breastfeeding and bed-sharing behaviour for 26 weeks following birth. Strength of prenatal breastfeeding intent was recorded at recruitment using Likert-type scales.Results: Outcomes were frequency of bed-sharing at home for at least one hour per week, and time to cessation of breastfeeding. There were insufficient data to classify bed-sharing pattern in 192/870 (22%) of mothers. Of the remainder, 44% (299/678) of participants 'rarely' or 'never' bed-shared, 28% (192/678) did so 'intermittently' and 28% (187/678) did so 'often'. These three groups did not differ significantly in marital status, income, infant gestational age, maternal age or delivery mode. Significantly, more participants who bedshared 'often' reported strong prenatal breastfeeding intent (70% vs. 57% and 56% for 'intermittent' and 'rare' bed-share groups) and attached high prenatal importance to breastfeeding (95% vs. 87% and 82%). Significantly, more women who bed-shared frequently were breastfeeding at 6 months (p < 0.0001) than those who intermittently or rarely/never bed-shared.

Previous North Sea food web studies are reviewed. These studies used estimates of primary production and fish energy requirements, then manipulated the energy flow pathway between the two to balance the budget. The resulting pathways largely ignored actual fish diets and consumption rates. In the present paper, North Sea biomass flow food webs are constructed for each quarter of the year from published estimates of fish abundance, diet and daily food consumption, and using long-term Continuous Plankton Recorder and North Sea benthos survey data. Estimates of daily production of each component of the web are derived from specific daily growth and gross growth efficiency measurements. The flow of biomass from secondary production to fish is sufficient to supply the food requirements of planktivorous pelagic fish and benthivorous demersal fish. Piscivorous pelagic fish obtain much of their food requirements from outside the North Sea. The food requirements of piscivorous demersal fish also do not appear to be adequately supplied from within the North Sea, but, in this case, immigration is not thought to provide the shortfall. The high predation pressure on demersal piscivores may explain why this group appears to be especially vulnerable to fishing. The supply of biomass from primary production to secondary producers appears to be sufficient without the need to postulate import into the North Sea. Indeed, the supply to the benthos is such that a detritivore trophic level can be inserted between organic settlement and production of macrobenthos