The intricate relationship between aerobic capacity and manual lifting tasks is a multifaceted topic. The text elaborates on how the aerobic capacity necessary to safely perform a job without incurring undue fatigue is contingent upon the average energy expenditure rate and the duration of the activity. Research highlights that individuals can sustain only a fraction of their full aerobic capacity over prolonged periods to avoid excessive fatigue—a state from which recovery by the next day is not feasible.

The threshold for the percentage of aerobic capacity that can be sustained is influenced primarily by the nature of the activity (e.g., lifting versus walking), the intensity of the activity, and its duration. Numerous studies have explored the correlation between maximum acceptable workload and specific work activities, intensities, and durations.

The “Work Practices Guide for Manual Lifting” (NIOSH, 1981) recommends that workers limit their energy expenditure to 33% of their aerobic capacity (AC) for tasks performed over an eight-hour period. This recommended AC threshold diminishes to 21% for lifts above 30 inches from ground level and further reduces for manual material handling tasks conducted below 30 inches from ground height. Given that approximately half of the lifting performed by employees occurs below 30 inches and half above, a threshold intermediary between the limits for lifting above and below 30 inches is deemed appropriate for this study. The average of the two thresholds is calculated to be 25.2%.

The Basics… 

Metabolism is a direct indicator at how physically intense a job (or tasks) is on the employee.

There are many different work intensity indicators that impact metabolic rates. Research has pointed to: oxygen consumption, galvanic responses, heart rate, accelerometry and other biometric responses that can be used as component metrics to predict overall energy expenditure.

Generally, this is conducted in a laboratory VO2 Max test. However, we have been able to take the biometric responses (mentioned above) and calculate over all energy expenditure through non-invasive, on-site methods.

Why is understanding work intensity important?

Jobs that require employees to exert themselves beyond their physical limitation can lead to soft tissue injury and heat stress. Exhaustion has also been closely linked with poor decision making and careless mistakes, some that can be very severe.

Work intensity measures can be used for:

• Pre-hire: Physical Ability Testing – Knowing the cardiovascular requirements of the job allows you to ensure those you hire have the capacity to handle the workload. This protects future employees from entering into a hazardous situation. It also protects the company from excess Workers Compensation costs.
• Justifying Headcount: If work intensity levels are higher than the average population can withstand (in a shift), adding employees into the space off-sets the amount of energy required by smaller group of employees. We will assist in calculating how many employees are needed to keep work at a safe work intensity (under the exhaustion threshold).