Differences in functional performance of the shoulder musculature with obesity and aging

• Obesity was associated with ∼25% higher shoulder strength.
• Endurance time was reduced with obesity and extended with older age.
• Rates of strength loss and discomfort increase were increased with obesity.
• Inconclusive results were found regarding obesity × age interactive effects.

The workforce includes an increasing number of workers who are obese and/or older, which may lead to higher rates of workplace injuries. We examined the main and interactive effects of obesity and age on strength and functional performance during sustained isometric exertions involving shoulder flexion in two postures. Four groups of eight participants each (non-obese (18.5 < BMI < 25 kg/m2) young (18–25 years), non-obese older (50–65 years), obese (30 < BMI < 40 kg/m2) young, and obese older) completed static endurance tasks in each posture, at fixed target levels of shoulder moment. Shoulder strength was ∼25% higher with obesity and equivalent between age groups. Both obesity and age affected endurance time, with the obese and younger groups both having shorter endurance. Obesity and age did not have an interactive effect on endurance time and the results were inconclusive regarding acute fatigue effects for individuals who are older and obese. Further work is needed under more realistic task conditions, to explore the likely complex effects of these individual differences.Relevance to industryShoulder strength was increased with obesity, though obesity was associated with substantially reduced endurance times. Such a difference may have implications for determining work-rest schedules based on task demand and predicted endurance times. It remains unclear whether obesity and age interact to cause substantial functional decrements.