Abstract
For achieving accurate and safe measurements of the force and power exerted on a load
during resistance exercise, the Smith machine has been used instead of free weights.
However, because some Smith machines possess counterweights, the equation for the
calculation of force and power in this system should be different from the one used
for free weights. The purpose of this investigation was to calculate force and power
using an equation derived from a dynamic equation for a Smith machine with counterweights
and to determine the differences in force and power calculated using 2 different equations.
One equation was established ignoring the effect of the counterweights (Method 1).
The other equation was derived from a dynamic equation for a barbell and counterweight
system (Method 2). 9 female collegiate judo athletes performed bench throws using
a Smith machine with a counterweight at 6 different loading conditions. Barbell displacement
was recorded using a linear position transducer. The force and power were subsequently
calculated by Methods 1 and 2. The results showed that the mean and peak power and
force in Method 1 were significantly lower relative to those of Method 2 under all
loading conditions. These results indicate that the mean and peak power and force
during bench throwing using a Smith machine with counterweights would be underestimated
when the calculations used to determine these parameters do not account for the effect
of counterweights.
Key words
upper body - weight training - linear position transducer
