The study, by researchers from Virginia Tech in Blacksburg and colleagues, examined the endurance of 32 individuals in four categories (non-obese young, obese young, non-obese older, and obese older).

The participants completed three distinct tasks that involved a range of upper extremity demands - hand grip, intermittent shoulder elevation, and a simulated assembly operation.

Each task involved periods of work and rest, and included pacing demands similar to those experienced by workers in manufacturing settings.

"Our findings indicated that on average, approximately 40 percent shorter endurance times were found in the obese group, with the largest differences in the hand grip and simulated assembly tasks," said Lora A Cavuoto, an assistant professor in the department of industrial and systems engineering at the University at Buffalo, SUNY, in Buffalo, New York.

"During those tasks, individuals in the obese group also exhibited greater declines in task performance, though this difference was only evident among females," Cavuoto said.

In addition to examining how obesity affected physical demands and capacity, Cavuoto and her colleagues looked at the interactive effect of obesity and age on endurance times.

"Previous studies have indicated that both age and obesity lead to decreased mobility, particularly when it comes to walking and performing lower extremity tasks," said Maury A Nussbaum, a professor in the department of industrial and systems engineering at Virginia Tech, who also worked on the study.

"However, we found no evidence of an interactive effect of obesity and age on endurance times, which is contrary to previous findings," said Nussbaum.

Obesity is associated with physiological changes at the muscular level, including a decrease in blood flow, thereby limiting the supply of oxygen and energy sources.

When performing sustained contractions, these physiological changes may lead to a faster onset of muscle fatigue.

"Workers who are obese may need longer rest breaks to return to their initial state of muscle function," said Cavuoto.

"Based on the increased fatigue found among workers who are obese, workplace designers may need to consider adding fixtures and supports to minimise the amount of time that body mass segments need to be supported," said Cavuoto.

The study is published in the Journal of Occupational and Environmental Hygiene.

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