The question that therefore arises concerns the degree
of importance of each of these weather variables and
measures in their effects on physiological responses. In
previous studies (Ingraham 1974; Lemerle and Goddard
1986), mean values mostly of the temperature-humidity
index (THI) have been investigated. However, as argued
by McDowell et al. (1976) averages for climatic conditions
are of little value in predicting performance, but
extremes in ambient temperature and perhaps humidity
are important in determining performance. It is also likely
that only temperature or humidity, but not in combination,
may have more influence on physiological responses
because of less variation in the combined values
(Igono and Johnson 1990). This is partly because, in
the tropics at maximum ambient air temperature, humidity
is at a minimum and vice versa.