The First Lactate Threshold Is a Limit for Heavy Occupational Work

Long-term heavy physical work often leads to early retirement and disability pension due to chronic overload, with a need to define upper limits. The aim of this study was to evaluate the value of the first lactate threshold (LTP₁) as a physiological marker for heavy occupational work. A total of 188 male and 52 female workers performed an incremental cycle ergometer test to determine maximal exercise performance and the first and second lactate (LTP₁; LTP₂) and ventilatory thresholds (VT₁; VT₂). Heart rate (HR) recordings were obtained during one eight-hour shift (HR_8h) and oxygen uptake was measured during 20 minutes of a representative work phase. Energy expenditure (EE) was calculated from gas-exchange measures. Maximal power output (P_max), maximal oxygen consumption (VO_{2 max}) and power output at LTP₁ and LTP₂ were significantly different between male and female workers. HR_8h was not significantly different between male and female workers. A significant relationship was found between P_max and power output at LTP₁. HR_8h as a percentage of maximum HR significantly declined with increasing performance (P_max:r = -0.56; p < 0.01; P_LTP1:r = -0.49; p < 0.01). Despite different cardio-respiratory fitness-levels; 95.4% of all workers performed their usual work below LTP₁. It is therefore suggested that LTP₁ represents the upper limit for sustained heavy occupational work; which supports its use to determine work capability and assessing the limits of heavy occupational work.