Physical activity in the afternoon or evening is associated with reduced insulin resistance.

A new study published in Diabetologia, a journal of the European Association for the Study of Diabetes, found that physical activity in the afternoon or evening was associated
with reduced insulin resistance (and thus better control of blood sugar) compared to physical activity evenly distributed during the day.
Dr.
Jeroen van der Velde of the Department of Clinical Epidemiology at Leiden University Medical Center in the Netherlands and his colleagues concluded that there was no benefit
to doing physical activity in the morning.

The current global obesity epidemic is partly due to a lack of physical activity combined with sedentary (sedentary) behavior
during the day.
This behavior is associated with an increased risk of developing metabolic diseases, including type 2 diabetes (T2D), and earlier studies have found that short breaks in sedentary behaviors are associated
with improved cardiometabolic conditions.
This evidence is further supported by experimental studies showing that frequent interruptions of prolonged sitting with standing or light physical activity lead to lower triglyceride levels and lower blood sugar, indicating improved
blood glucose profiles.

High fasting serum triacylglycerol levels may be associated with elevated hepatic fat concentrations, which in turn are strongly associated
with insulin resistance.
Previous studies have shown that exercise is associated
with reduced liver fat and improved insulin sensitivity.
The authors hypothesize that taking a break from sedentary behavior may reduce liver fat, thereby reducing insulin resistance and ultimately preventing T2D
.

As important as sedentary time is, some argue that the time of day physically active may be a factor in
metabolic health.
In vitro and animal studies have revealed day-dependent changes in exercise capacity and associated metabolic risk markers, but such studies have been rare and inconsistent
in humans.
Therefore, the research team's goal was to investigate the relationship
between physical activity time and sedentary rest time in middle-aged adults and liver fat content and insulin resistance.

The researchers used data from the Dutch Obesity Epidemiology (NEO) study, a population-based prospective cohort study designed to investigate the development of
obesity-related diseases.
Participants were recruited between 2008 and 2012, aged between 45 and 65, with a self-reported body mass index (BMI) of 27 kg/m2 or higher, and men and women living in the Leiden Greater Region were invited to participate
.
At the same time, the researchers also sent out an invitation to all residents between the ages of 45 and 65 in a municipality in the region as a reference population for BMI representing the total population of the Netherlands, with a study population of 6,671 people
.

Study participants underwent a physical examination, during which blood samples were taken, fasting and postprandial (postprandial) blood glucose and insulin levels were measured, and demographic, lifestyle and clinical information
was obtained through questionnaires.
They were also screened for suitability for an MRI scan, and about 35 percent of them were randomly selected to measure their liver fat content
using this technique.

In addition, 955 random sub-sample participants were given a combination accelerometer and heart rate monitor worn for four days and nights to monitor exercise and activity
.
Measuring acceleration and heart rate was used to estimate physical activity energy expenditure (PAEE, in kJ/kg/day), which in turn allowed the team to determine the time
spent at different activity intensities.
These are expressed as metabolic equivalent tasks (METs) – the ratio of PAEE during activity to PAEE at rest (also the standard way to measure physical activity).

Sedentary time (excluding sleep) is defined as ≤1.
5 MET, while interruption in sedentary time is represented by a period of activity with an acceleration of >0.
75 m/s2 (as this acceleration has been identified by previous studies as an accurate indicator of breaking sedentary time).

Intensity above 1.
5 to 3 MET is defined as light physical activity (LPA), and higher intensity is defined as MVPA
.

The day is divided into three periods: morning (06:00-12:00); Afternoon (12:00-18:00); In the evening (18:00-24:00), the proportion of total daily MVPA for each period shows the most active period
.
If the share of MVPA in each region differs from the rest of the region by less than 5%, it is classified as an even distribution of
activities throughout the day.

The study is based on an analysis of results obtained from 775 participants who have a complete data set
.
Among them, 42% were males and 58% were females, with an average age of 56 years and an average BMI of 26.
2 kg/m2
.
After adjusting for variables such as age, sex, race, and total body fat, the researchers observed that higher total PAEE, particularly MVPA, was associated
with lower liver fat content and reduced insulin resistance.
Insulin resistance was also associated with the timing of MVPA during the day: MVPA in the afternoon or evening was associated with a decrease in insulin resistance, 18% and 25%, respectively, compared to the evenly distributed
activity throughout the day, even after adjusting for the total MVPA amount.
There was no significant difference
in insulin resistance between morning activity and average daytime activity.

The study found that neither the length of sedentary time nor the number of breaks taken during sedentary behavior were associated with liver fat content or insulin resistance
.
According to the authors: "In our study, it may be that the intensity of activity during rest is too light to cause a metabolic response
.
Most daily activities are low-intensity because we have not observed a link between LPA and insulin resistance, which may also explain the lack of link
between rest and insulin resistance.
”

Physical activity scheduling is a relatively unexplored area in human biology, and the mechanisms underlying the potential benefits of physical activity scheduling remain unclear
.
Early research has shown that metabolism responds differently to high-intensity exercise depending on the duration of exercise
.
In addition, muscle strength and metabolic function of skeletal muscle cells peaked in the late afternoon, suggesting that being most active during this time may lead to a more pronounced metabolic response
than earlier in the day.

The researchers concluded: "In addition to the total amount of MVPA per day, the timing of MVPA during the day was associated with reduced insulin resistance: most MVPA administered in the afternoon or evening reduced insulin resistance
by up to 25% compared to MVPA that was evenly distributed during the day.
" These results suggest that the time of day of physical activity is associated
with the beneficial effects of physical activity on inulin sensitivity.
Further research should assess whether time spent physically active is really important
for the development of type 2 diabetes.
”

Timing of physical activity in relation to liver fat content and insulin resistance