Study connects low birth weight to reduced adult physical activity

Poorer gross motor skills, such as the ability to walk quickly, run, or jump, may explain some of the correlation between being born prematurely and the tendency to engage less in physical activity.

These are some of the findings of a recent Norwegian–Finnish study. Researchers have compared physical activity in adults who were born prematurely with a low birth weight (under 1500 grams), with adults who were born full-term with a normal birth weight. The aim was to investigate whether there were differences, and whether poorer motor function in adults affects how active they are.

This is the first study to show that reduced motor skills may explain some of the correlation between being born prematurely with very low birth weight and lower physical activity.

Poor gross motor skills

"We found a difference in how physically active adults born prematurely with very low birth weight are compared with adults born full-term with normal birth weight. We also saw that poor gross motor skills can account for approximately a third of the difference in physical activity between the two groups," said Silje Dahl Benum and Kristina Djupvik Aakvik. They are both PhD research fellows at the Norwegian University of Science and Technology (NTNU's) Department of Clinical and Molecular Medicine and lead authors of the study recently published in the Public Library of Science, PLoS one.

Run, cycle and walk less

A total of 87 prematurely born individuals with very low birth weight, i.e. under 1500 grams, participated in the study.

They were compared with a control group of 109 individuals born full-term. The study participants came from Finland and Norway and were between 31 and 42 years old.

The study shows that the prematurely born individuals spend less time running, cycling and walking at a fast and moderate pace compared with those born full-term.

Measured 1 week of physical activity

All the participants had activity trackers attached to their thighs and backs, and their activity levels were tracked around the clock for one whole week. The researchers used a (…) to identify the various daily activities. The same model has been developed for and is used in the world-renowned HUNT Study.

Based on intensity, the activities were divided into three categories:

• Moderate to high - running, cycling and walking at a fast and moderate pace
• Low - slow walking and standing
• Inactivity - sitting

Using recognized mobility assessment tools, the researchers investigated the correlation between low birth weight and how physically active the participants were on a daily basis. The analyses were adjusted for country, age and gender.

"The findings in our study provide important knowledge - prematurely born individuals have an increased risk of health problems that may be prevented by physical activity."

Nearly 50 minutes less per week

The prematurely born participants had 7.3 fewer minutes of moderate to high-intensity physical activity per day, which amounts to approximately 50 minutes less per week.

The time that the participants are active in these types of studies can also be converted into what is called MET minutes (Metabolic Equivalent of Task). This is a measurement of how much energy a person uses for all activities other than resting, and it indicates the intensity of the activity.

The researchers found that the prematurely born participants had 40.4 fewer MET minutes of moderate to high-intensity physical activity per day compared with the control group.

This is a significant difference, especially when seen over weeks and months."

Kristina Djupvik Aakvik, NTNU

Tested walking, jumping and running

The group with very low birth weight generally scored lower on the Revised High-level Mobility Assessment Tool (HiMAT). In this test, participants must perform exercises such as walking forwards and backwards quickly, walking on their toes, stepping over obstacles, running, hopping, and jumping forwards over a specified distance within a given time.

"We observed both a clear difference in activity levels between the two groups and that gross motor skills played a role in how much the prematurely born participants engaged in moderate to high-intensity physical activity," said Aakvik.

Collecting more and better data

These trends have been observed in previous scientific studies, some of which are based on self-reporting, others on activity tracker measurements. However, the Norwegian-Finnish study is based on more precise data, because the researchers used two trackers per person instead of one. They also measured physical activity over the course of a whole week rather than just a few days.

It is well known that physical activity is good for your health, and the World Health Organization recommends that adults engage in 150-300 minutes of moderate-intensity physical activity per week. Alternatively, they recommend 75 to 150 minutes of high-intensity activity, or a combination of both high and moderate intensity.

Heterogeneous group

Silje Dahl Benum and Kristina Djupvik Aakvik emphasize that prematurely born individuals with very low birth weight are a heterogeneous group.

On average, both groups in the study meet the WHO recommendations for weekly physical activity. The researchers also highlight that some of the participants feel they are more physically active than their peers. Despite this, they found a group difference in moderate to high-intensity physical activity.

"This highlights that people are different and that there can be large variations within this group. Nevertheless, the findings of our study provide important knowledge. Prematurely born individuals have an increased risk of experiencing health problems, and physical activity can help prevent them," said Silje Dahl Benum.

Measures and early stimulation

Gross motor skills develop in early childhood. The NTNU researchers believe that their findings support the idea that implementing systematic measures and stimulation of gross motor skills at an early life stage would be beneficial, and could have long-term effects.

Benum and Aakvik are affiliated with the NTNU Low Birth Weight Life research group. Their supervisor, professor and physiotherapist Kari Anne I. Evensen, heads the group that collaborates with Finnish researchers in the Helsinki Study of Very Low Birth Weight Adults, as well as other research groups in Europe, the USA, Canada, Australia and New Zealand.

Evensen says that the study is one of the longest follow-up studies in the world of children with low birth weight. The aim is to create a better understanding of how low birth weight affects physical and mental health, quality of life, cognitive and motor function, vision, and brain structure throughout life.