Essential Science: Why the time of day for exercising matters

Posted Jun 17, 2019 by Tim Sandle
If you exercise regularly, do you prefer to get up early and go for a jog or head to gym after a long day at work? The time of the day which you choose to exercise can be important, according to new research.
In this file photo  a man is seen jogging on a beach in Saint George's  Grenada  one of two Car...
In this file photo, a man is seen jogging on a beach in Saint George's, Grenada, one of two Caribbean island states set to vote on whether to keep the Britain-based court
Jewel SAMAD, AFP/File
Looking at the differences between morning or evening effects on the body in terms of exercise regimes, scientists from the University of Copenhagen have discovered that the impact of exercise appears to differ according to times of day. They have conducted their research using rodents, but are of the view that the results, based on physiological similarities, are applicable to humans.
By studying mice, the researchers have shown that morning exercise leads to a greater metabolic response in skeletal muscle. In contrast, electing to exercise in the evening leads to increased energy expenditure for a longer period of time.
The inner timekeeper dubbed the "circadian clock"  governs the day-night cycle that guides...
The inner timekeeper dubbed the "circadian clock", governs the day-night cycle that guides sleep and eating patterns, hormones and even body temperature
This means the research points to new evidence that body's circadian clock affects our health. A circadian clock refers to the biochemical oscillator that cycles in synchronicity with solar time. This ‘internal body clock’ is to the tune of almost 24 hours (that is, a solar day). The function of circadian clocks is to enable organisms to anticipate the environmental changes that follow the day–night cycle. Importantly the body will attempt to adjust its biology according to the clock. Disruptions to the clock can lead to metabolic changes (which is one of the reasons, over the longer-term, why night-shift has been linked to metabolic diseases).
Drawing on the evidence from the mouse model, Professor Jonas Thue Treebak says about the research: “There appears to be rather significant differences between the effect of exercise performed in the morning and evening, and these differences are probably controlled by the body's circadian clock.”
Treebak's research group are setting out to define the molecular and physiological mechanisms through which dietary compounds, weight loss, and physical activity can improve insulin sensitivity. This is orientated towards mechanisms to prevent and treat type 2 diabetes.
He adds that: “Morning exercise initiates gene programs in the muscle cells, making them more effective and better capable of metabolizing sugar and fat. Evening exercise, on the other hand, increases whole body energy expenditure for an extended period of time.”
Screen Capture
To gain this insight, the scientists took readings in the muscle cells, and this included assessing transcriptional response and effects on the metabolites. Here effects were far stronger in the morning compared with the evening. A metabolite is the intermediate end product of metabolism (digestion or other bodily chemical processes), and metabolites have different functions, such as providing energy, structure, signaling, stimulatory and inhibitory effects on enzymes.
So, in other words, different things are gained from the time of exercising and this may help people to tailor their exercise regimes accordingly, should the results be supported through further scientific inquiry (and the researchers plan follow-up studies).
Here exercising early in the day seems to raise the ability of muscle cells to metabolize sugar and fat. This time of the day would be of more benefit to those who are severely overweight or obese and who have type 2 diabetes.
In contrast, when exercise is undertaken later on in the day, this has the effect of increasing energy expenditure. This effect of energy depletion continues for several hours after the exercise session has been completed. This may lead to greater weight loss.
Research paper
The research has been published in the journal Cell Metabolism, with the research paper titled “Time of Exercise Specifies the Impact on Muscle Metabolic Pathways and Systemic Energy Homeostasis.”
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This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week our topic was about the best time drink coffee? And how can you avoid drinking too much? An algorithm has the answers.
The week before we looked at how a genetically modified fungus rapidly kills 99 percent of malaria mosquitoes; a new study reveals. The introduction of the transgenic fungus has been successful in a pilot study.