Demographic data
Of the 502 randomly selected rubber tappers, 427 participated
in the study. The mean age was 38 years and two-thirds of them
were male. Most participants had a BMI in the normal range and
had no underlying disease. However, nearly half of them smoked
and one-third had experience using kratom (Mitragynine speciosa),
which is a mildly narcotic plant that is locally grown. Two-thirds of
the participants had low levels of education and long-term experience
in rubber tapping (Table 1).
Due to a high physical load of performing the tapping task, half
of the participants had a high level of perceived fatigue with an