Hungry, unrestrained rats (N = 7) were rewarded for pressing a respons
e beam in excess of 11 different force requirements. Changes in peak f
orce production as a function of peak force requirement were examined
by analyses of the first four moments of distributions of peak respons
e forces: constant error, the within-subject standard deviation, skewn
ess, and kurtosis. Results were similar to those previously obtained w
ith human subjects: Constant error was positive at low and negative at
high force requirements, the within-subject standard deviation increa
sed as a negatively accelerating function of force requirement, and sk
ewness and kurtosis were positive at low force requirements and decrea
sed to negative values at the highest increments. Additional analyses
of response kinetics indicated that rats, like humans, meet increasing
force requirements by altering the rate of rise of force. The perform
ance similarities suggest that common processes are engaged by the hum
an and rat motor control systems to solve the problem of generating fo
rces that are appropriate to the prevailing environmental constraints.